A device for jettisoning a payload from a spacecraft, the device comprising: connection means between the payload and the spacecraft; an energy storage device for jettisoning the payload; and a releasable latching device for latching the payload to the spacecraft. In the device for jettisoning a payload: the connection means comprises a single rod in alignment with the axis of symmetry of the jettisoning device and having a first end fixed to the payload; the energy storage device acts on the first end of the connection rod; and the releasable latching device acts on the second end of the connection rod, said device being fixed to the spacecraft. Application to the aerospace industry.

There are various reasons why a payload may need to be jettisoned from a satellite. Typically, it is a safety technique used in last resort when the payload cannot be recovered on returning to Earth, or when the payload has failed and cannot be repaired, or when the payload constitutes a danger for satellite integrity.
The ideal jettisoning device is one that makes it possible, on actuation, to cut all physical ties between the payload and the satellite instantaneously while being capable of imparting a velocity to the payload such as to enable it to cover a predetermined safety distance in the shortest time. Jettisoning should take place in controlled manner with minimum transfer of energy to the spacecraft so as to reduce perturbations induced by rapid separation of the payload, i.e. by the reaction forces due to the fact that releasing the stored ejection energy requires devices to be activated that cause transient impacts to be exchanged between the various components of a jettisoning device. Such reduction in perturbations is a condition that is very difficult to satisfy in practice and it corresponds to one of the priority needs in the art in question that has yet to find a satisfactory solution.
In this respect, two elements are critical for satisfying this condition: the device that stores the energy for ejecting the payload; and the device that provides controlled release of the energy stored in this way.
Essentially two types of solution are used for the device that stores jettisoning energy:
preloaded springs in which the jettisoning energy is stored in the form of elastic energy; or
devices containing a gas or a liquid under pressure for providing the thrust required for jettisoning.
The solution using fluid under pressure is of complex design and is used particularly for jettisoning large-sized items, such as launcher fairings, rather than payloads having the dimensions under consideration in the present invention.
Devices based on the use of springs are very common: to this end a variety of designs exist with different spring dispositions. It is common to use one or more helical springs that are preloaded in compression. Devices using a plurality of springs appear to satisfy the requirements of the designers of this type of device, particularly because they increase operating safety given that failure or jamming are the most probable types of breakdown for a spring.
Naturally, the disposition of a spring is closely tied to the retaining device adopted for holding the spring under tension, i.e. the latching device, and also to the guide device which is normally provided for controlling the motion of the payload while it is being subjected to the action of a spring.
Pyrotechnical devices have been very widely used for actuating jettisoning devices and for unlatching the retaining devices.
In particular, explosive nuts and bolt-cutters can constitute a satisfactory solution, particularly since they are now standard tools. However, they cannot be used on their own because of the limit on the size of the part to be cut (the part is typically 12.7 mm (0.5 inches) in diameter, which in turn puts a limit on the load-carrying capability of the system). To overcome these limitations, a dedicated latching device could be used for activation by firing a pyrotechnical device; alternatively, it would be possible merely to use a set of pyrotechnical devices.
However, the increasing complexity of the project makes the use of pyrotechnical devices not very attractive. In addition, a synchronization problem may arise in a distributed system of pyrotechnical devices. Solutions to this problem exist, but they involve further penalties in terms of design complexity.
In any event, the operating safety of pyrotechnical devices may be questioned if their performance is considered in terms of lifetime and the principle on which they operate. No matter what the success rate of samples tested, it nevertheless remains possible that a pyrotechnical device may be defective and fail.
Pyrotechnical bolt-cutters are often used for separating a Marman clamp. This type of clamp is doubtless the device that is most commonly in use, probably because of the simplicity of its operating principle.
Nevertheless, it suffers from a certain number of drawbacks which, in the opinion of the Applicant, are usually overlooked by persons skilled in the art. These drawbacks are as follows:
a. The activation dynamics for releasing a pretensioned clamp constitute a stochastic event. The vibrations of the clamp and its interactions with the surrounding items can be predicted only with the help of dedicated computer models, and only to a certain extent. Real dynamic behavior may differ significantly because of strong dependence on certain parameters, such as prestress, interface geometry, and manufacturing tolerances, and it may exhibit peculiarities. This is normally taken into account by adding devices for catching the clamp after it has been released and for damping vibrations. Also, confidence in the repeatability of clamp behavior is based on testing which can be very expensive, in particular for items of large size, and is sensitive to variations in the parameters mentioned above.
b. To ensure that the jettison device opens properly, the clamp must be released extremely quickly. This may be difficult to achieve in practice, and jamming may take place because of asymmetrical spring action, particularly when a plurality of springs are used.
c. To prevent jamming with bolt-cutters, the clamp must be free to rotate without limit. This means that it may also be necessary to have specially designed bolt-clamping devices.
Naturally that increases the complexity of a project that was initially simple. An interesting solution is that adopted for the Cassini spin and jettison device. A Marman clamp is made up of a certain number of individual clamps uniformly spaced apart around a separation ring. Each individual clamp is activated by a preloaded spring and is held in place by a prestressed cable. The cable is cut with pyrotechnical devices. This solution can allow some mass saving, in particular for clamps of large size. A container is naturally also provided for the cable.
Three publications are mentioned below illustrating the state of the art relating to the field of the present invention.
The article "The design and analysis of a double swivel toggle release mechanism for the Orbiter stabilized payload deployment system" by G. King and T. Sai, 23rd Aerospace Mechanisms Symposium, 3-5 May, 1989, pp. 39-57, NASA-CP-3032 describes a release mechanism which uses a swivel screw hinge and three retraction means acting radially for release purposes.
Nevertheless, in that solution, the release device is activated by pyrotechnical means.
The article "A clamp mechanism for deployable three-ton payloads" by R. Birner and H. Ral. 15th Aerospace Mechanisms Symposium, May 14-15 1981, pp. 375-390, NASA-CP-2181 describes, inter alia, a latching or clamping device in which the latching means is withdrawn by means of a system including a hinge and a slide.
Also, the article "A spring-actuated spin and ejection device for interplanetary missions" by V. Comparetto and P. Coste, 4th European Space Mechanism and Tribology Symposium, 20-22 Sep., 1989, pp. 207-214, ESA-SP-299 describes the use of a Marman clamp which includes a plurality of individual clamps held in place by a cable.
An object of the present invention is thus to provide a device for jettisoning a payload which satisfies practical requirements better than prior art devices of the same type and for the same purpose, in particular with respect to:
the energy interchanged between the payload and the satellite is minimized, while nevertheless enabling payload separation to take place in a predefined sequence; this has the consequence of reducing the vibration and perturbations induced on the satellite by jettisoning the payload (which may be a problem in some applications), i.e. on the experiments or operations that are taking place when jettisoning from the satellite occurs, with this being for the purpose of avoiding significant data loss or damage to on-board instruments or even the interruption of all on-going experiments or operations; in this respect, i.e. jettisoning while inducing only small disturbances on the satellite and thus having only a small impact on the orientation thereof, it was decided during development of the jettisoning device of the present invention to eliminate the use of Marman clamps and also the use of pyrotechnical devices as mentioned above;
the initial velocity of the jettisoned payload ensures that given clearance from the satellite is obtained after a predetermined length of time, with said clearance being specified as an allowable safety "envelope" for the payload, so that after separation from the satellite the payload is free to move without interfering therewith;
it has adequate stiffness to enable the payload to operate in orbit and for transmitting launch or re-entry loads, which may be a decisive factor in the design of a jettisoning device, depending on the characteristics of the payload;
there is no risk of failure or jamming in the spring that stores the minimum energy required for imparting the ejection velocity to the payload; and
no guidance is required for the payload.
The objects mentioned above make it possible to associate simple structure with increased lifetime, thereby making the jettisoning device of the invention highly effective, i.e. behaving very similarly to the ideal device mentioned above.

Device for jettisoning a payload from a spacecraft


The first synchronous FF is disposed at the starting point of the clock tree of the frequency-divided clock of each lower hierarchical block, and the first maximum delay time of the reference clock from the branch point of the reference clock and the frequency-divided clock to the first synchronous FF is acquired. The second maximum delay time of the reference clock between adjacent two of second synchronous FFs is determined so as to be less than half the period of the reference clock. The number of stages of the second synchronous FFs is determined according to the first and second maximum delay times. The target delay time from the branch point is determined so as to be not more than the second maximum delay time, and the second synchronous FF and a latch are disposed so as to achieve the target delay time.

This invention relates to a clock synchronization method for synchronizing the phases of a reference clock and a frequency-divided clock which are supplied from a clock generation circuit provided in a top hierarchical block to terminal flip-flops (FFs) provided in each of a plurality of lower hierarchical blocks.
In a layout design of a large-scale semiconductor integrated circuit, a hierarchical layout design technique is used. In the hierarchical layout design technique, a large part of a circuit in a semiconductor integrated circuit is divided into a plurality of lower hierarchical blocks, and the layout design of each of the lower hierarchical blocks is carried out. Subsequently or concurrently, a layout design of a top hierarchical block excluding the lower hierarchical blocks is carried out, and a clock signal is connected to each of the lower hierarchical blocks while wirings interconnecting between the lower hierarchical blocks are connected.
In the layout design of the lower hierarchical blocks and the top hierarchical block, in order to supply a clock signal to a group of a very large number of FFs in each of the lower hierarchical blocks, a technique called clock tree synthesis is used. The clock tree synthesis is a function for making uniform the delay times (synchronizing the phases) of the clock signal which reaches, through associated paths, all of the FFs in each of the lower hierarchical blocks from a starting point in the top hierarchical block.
In the hierarchical layout design technique, since clock wiring extends across the top hierarchical block and each of the lower hierarchical blocks, a clock tree of a downstream portion is generated in each of the lower hierarchical blocks. Then, on the basis of the result, a clock tree of an upstream portion is generated in the top hierarchical block, and the delay time of a clock signal in the top hierarchical block is adjusted such that the delay times of the clock signal from the clock signal starting point to all of the FFs in each of the lower hierarchical blocks are made uniform.
In a semiconductor integrated circuit, fluctuation in the delay times of signals occurs due to process variation in manufacturing, voltage/temperature variation during operation, or the like. When the layout design is made, timing closure is carried out such that the circuit operates normally even if delay time variation among signals occurs. Specifically, the variation in delay time of each signal is called "On Chip Variation (OCV)," and the timing closure is carried out such that the semiconductor integrated circuit operates normally even if a margin for OCV is taken into account.
Further, in a large-scale integrated circuit, in many cases, a frequency-divided clock group is generated from a reference clock by a clock generation circuit in a top hierarchical block, and is distributed to each of lower hierarchical blocks. Thus, the reference clock and the frequency-divided clock are branched off on an upstream side of a clock tree, and the paths of the reference clock and the frequency-divided clock after the branch point tend to be longer. Since the long clock paths for each of the lower hierarchical blocks after the branch point vary individually, a timing margin to be considered is to be a large value, which leads to difficulty in timing closure.
FIG. 6 is a conceptual diagram of an example showing the configuration of a conventional semiconductor integrated circuit. A semiconductor integrated circuit 70 shown in the drawing is designed by a hierarchical layout design technique, and is provided with three lower hierarchical blocks A, B, and C, and a top hierarchical block excluding the lower hierarchical blocks A, B, and C. The top hierarchical block includes a clock generation circuit 12, and the clock generation circuit 12 includes a PLL circuit 14 and a frequency divider circuit 16.
In the case of the semiconductor integrated circuit 70, in the clock generation circuit 12, a reference clock 15 is generated by the PLL circuit 14, and the reference clock 15 output from the PLL circuit 14 is frequency-divided by the frequency divider circuit 16 to generate a frequency-divided clock 17. Each of the lower hierarchical blocks A, B, and C is provided with first terminal FFs 18 operating in synchronization with the reference clock 15 and second terminal FFs 20 operating in synchronization with the frequency-divided clock 17. The reference clock 15 and the frequency-divided clock 17 are supplied from the clock generation circuit 12 to all of the first terminal FFs 18 and all of the second terminal FFs 20 in each of the lower hierarchical blocks A, B, and C, respectively.
When layout design of the semiconductor integrated circuit 70 is carried out, in the hierarchical layout design technique, first, clock trees (in FIG. 6, indicated by triangular frames) 19 and 21 of the reference clock and the frequency-divided clock are generated for each of the lower hierarchical blocks A, B, and C. Since the lower hierarchical blocks A, B, and C are different in size or the number of the first terminal FFs 18 and the number of the second terminal FFs 20, the delay times of the clock trees are different. In the example shown in the drawing, the delay times of the clock trees 19 and 21 of the reference clock and the frequency-divided clock in the lower hierarchical blocks A, B, and C are 2 ns, 7 ns, and 5 ns, respectively.
Subsequently, clock trees of the reference clock 15 and the frequency-divided clock 17 are generated in the top hierarchical block. In this case, the delay times of the clock trees of the reference clock 15 and the frequency-divided clock 17 in the top hierarchical block are adjusted so as to eliminate skews, that is, the delay times of the clock trees 19 and 21 of the reference clock and the frequency-divided clock in the lower hierarchical blocks A, B, and C. In the example shown in the drawing, the delay times of the clock trees of the reference clock 15 and the frequency-divided clock 17 from the clock generation circuit 12 to the lower hierarchical blocks A, B, and C are 10 ns, 5 ns, and 7 ns, respectively.
From this, the delay times from a branch point 13 of the reference clock 15 and the frequency-divided clock 17 to the first terminal FFs 18 and the second terminal FFs 20 of each of the lower hierarchical blocks A, B, and C are adjusted to 12 ns, and consequently, all of the first terminal FFs 18 and second terminal FFs 20 of the lower hierarchical blocks A, B, and C can be synchronously operated.
However, in this case, there is a problem in that the timing margins of the reference clock 15 and the frequency-divided clock 17 are excessively large, and therefore, the design is difficult. Since the frequency-divided clock 17 branched off from the reference clock 15 in the clock generation circuit 12 is supplied to each of the lower hierarchical blocks A, B, and C, the clock path corresponding to 12 ns downstream of the branch point 13 of the reference clock 15 and the frequency-divided clock 17 is a portion to have OCV variation.
As shown in FIG. 7, when a period of the reference clock 15 is 5 ns, that is, when a period of the frequency-divided clock 17 obtained by dividing the frequency of the reference clock 15 by two is 10 ns, for example, there is needed a large timing margin exceeding one period of the reference clock 15, that is, in this example, the timing margin of 12 ns in total including 6 ns before the rising timing of the reference clock 15 and the frequency-divided clock 17 and 6 ns after the same, and thus, the layout design becomes extremely difficult.
In order to solve this problem, as shown in FIG. 8, a synchronous FF 41 which receives the frequency-divided clock 17 as a data signal in synchronization with the reference clock 15 and newly outputs the frequency-divided clock 17 in synchronization with the reference clock 15 is disposed on the path of the frequency-divided clock 17 at a position near each of the lower hierarchical blocks A, B, and C.
With this, the branch point is moved from the branch point 13 of the reference clock 15 and the frequency-divided clock 17 to a branch point 37 near each of the lower hierarchical blocks A, B, and C, and as shown in FIG. 9, the timing margin can be made small to a certain degree. In this example, the timing margin can be reduced to 8 ns in total.
Further, as shown in FIG. 10, the synchronous FF 41 is moved to a position near the second terminal FFs 20 inside each of the lower hierarchical blocks A, B, and C, whereby the branch point can be moved from the branch point 13 of the reference clock 15 and the frequency-divided clock 17 to a branch point 39 near the second terminal FFs 20 inside each of the lower hierarchical blocks A, B, and C, and as shown in FIG. 11, the timing margin can be made still smaller. In this example, the timing margin can be reduced to 4 ns in total.
However, in this case, there is a problem in that the timing closure of the synchronous FF 41 disposed on the clock path is difficult.
As shown in FIG. 12, in many cases, the delay time of the reference clock 15 supplied to the synchronous FF 41 is greater than one period of the reference clock 15. In this example, the delay times of the reference clock 15 from the branch point 13 of the reference clock 15 and the frequency-divided clock 17 inside the clock generation circuit 12 to the synchronous FFs 41 inside the lower hierarchical blocks A, B, and C are 11 ns, 7 ns, and 9 ns, respectively.
When the delay exceeding a period of the reference clock 15 occurs in the reference clock 15 flowing through the clock path of the synchronous FF 41, in many cases, the same degree of delay also occurs in the frequency-divided clock 17 flowing through the data path running parallel to the clock path of the synchronous FF 41. If the delay time of the data path exceeds the period, a set-up restriction of synchronous design may not be satisfied. For this reason, as shown in FIG. 13, it is necessary to add plural stages of synchronous FFs 41 to the data path such that the delay time of the data path falls within one period of the reference clock 15.
However, even if the plurality of synchronous FFs 41 are added such that the delay time of the data path falls within one period, it is difficult to satisfy a hold restriction.
Hereinafter, difficulty in satisfying the hold restriction will be described.
First, as shown in FIG. 14, timing closure of a group of synchronous FFs 41 with respect to one lower hierarchical block is considered.
If only the group of synchronous FFs 41 is in question, as shown in FIG. 15, buffers 45 are inserted in the paths of the reference clock from the branch point of the reference clock and the frequency-divided clock to all of the synchronous FFs 41 to make the delay times uniform (to eliminate a clock skew), whereby the set-up/hold restriction can be satisfied.
Meanwhile, as in the above-described example, when there are three lower hierarchical blocks A, B, and C, and the delay times associated with the lower hierarchical blocks A, B, and C are 11 ns, 7 ns, and 9 ns, respectively, and thus different, in general, the clock delays are adjusted to 11 ns which is the maximum value among the three values so as to prevent punch-through of data.
However, in this case, there is a problem in that by adjusting the delay times of the FFs constituting the frequency divider circuit and all groups of synchronous FFs 41 to the maximum delay time, the number of buffers 45 added on the path of the reference clock becomes very large, and accordingly, the layout area and power consumption increase. Furthermore, if the difference between the maximum value and the minimum value of the delay time of the reference clock exceeds one period of the reference clock, this exceeds a time width which can be dealt with by synchronous design, and thus, timing closure is not possible.
In this case, the above-described method of adjusting the delay times of the reference clock to the maximum delay time does not work well. Therefore, as shown in FIG. 16, the set-up/hold restriction needs to be satisfied while partially or wholly shifting the delay times of the reference clock.
Next, difficulty in satisfying the set-up/hold restriction while shifting the delay times of the reference clock will be described.
Since a semiconductor integrated circuit needs to be operated under various temperature, voltage, and process conditions within an operation guaranteed range, it is necessary to consider delay fluctuation caused by various operation environments. In order to prevent punch-through of data, as shown in FIGS. 17A and 17B, data Q output from a preceding-stage FFA needs to be delayed by buffers 47 so that data D of a subsequent-stage FFB changes after the rise of a clock CLK of the subsequent-stage FFB. For this reason, in this configuration, the delay time of the buffers 47 in the data path should be larger than the delay time of buffers 49 in the clock path.
Although the delay time of each of the cells fluctuates due to the operation environment, since the delay times of the buffers 47 and 49 are large, the magnitude of delay fluctuation of the data path is large. Since the clock path also has delay variation, it is difficult to carry out timing closure to satisfy the set-up/hold restriction while considering the delay variations of both paths. In actual layout design of a semiconductor integrated circuit, usually, it is necessary to readjust timing closure many times.
Here, prior art literatures relevant to the invention include JP 2002-76127 A relating to a distribution system of a clock signal for synchronization on a semiconductor integrated circuit and a semiconductor chip, JP 2002-158286 A relating to a semiconductor integrated circuit or the like which controls clock distribution, JP 2001-320022 A relating to a clock distribution system in an integrated circuit in which a multi-phase clock is distributed to internal circuits, and JP 9-51255 A relating to a clock generation circuit which generates a plurality of delayed clocks by dividing the frequency of a reference clock to delay the reference clock.


Aspects of the present disclosure provide techniques that determine whether each configuration item in a plurality of configuration items is associated with every other configuration item therein. If each configuration item in the plurality of configuration items is associated with every other configuration item therein, the plurality of configuration items are merged such that each attribute associated therewith is associated with one configuration item. If each configuration item in the plurality of configuration items is not associated with every other configuration item therein, it is determined whether at least one configuration item may be ignored.

A configuration management database ("CMDB") is a repository of information related to a system, such as an information technology ("IT") system. A CMDB includes details of configuration items ("CIs"), which are structural units thereof. A CI may be an abstract data object that represents an entity belonging to the system. The entity may be an IT resource, such as a server, a database, or other hardware and software elements.
An entity of a computer system may have various attributes associated therewith. For example, if an entity represents server hardware, an attribute may be an operating system attribute of UNIX, an IP address attribute of 188.8.131.52, and a MAC address attribute of 35938a48-a6f5-4865-b996-b68c2ffd01bb. These attributes may be reflected in the CI representing the entity. Some attributes may be suitable for identifying an instance of a computer system in the short term. Over the long term, however, computer systems may change. Components of a computer system may be upgraded, replaced, removed, added or otherwise altered, until the computer system has few or no original components left. As components are replaced or upgraded, attributes of the computer system also change, which may be referred to as "system drift."

Merging and ignoring configuration items

Hewlett-Packard Development Company, L.P.


A remotely operable drive coupling for selectively engaging and disengaging a driving shaft and a driven shaft operable in accordance with the direction of shaft rotation. The coupling comprises a splined axially movable member connected to the driven shaft and having a screw-threaded bore, and a screw-threaded terminal part on the driving shaft adapted to be threadably received in the threaded bore when the driving shaft is rotated in one direction and the axially movable member is urged toward and in engagement with the terminal part of the driving shaft coupling the two members. Upon rotation of the driving shaft in the opposite direction, the parts become unscrewed and the axially movable part is resiliently urged away from the driving shaft uncoupling the members.. The device can be controlled hydraulically, pneumatically or electrically.

A submersible pump especially for use in deep wells, either water or oil and combinations thereof, comprises an electric motor and a plurality of pump stages, the motor being lowermost and separated from the pump stages by a seal section to substantially prevent well fluid leakage into the motor housing. At times, there are a hundred or more pump stages and the electric motor may be some thirty feet in length with a diameter of approximately six inches. In order to optimize and/or change the pumping performance, pump stages are added or subtracted from the assembly, which requires pulling the assembly from the well. This is not only time consuming and costly, but is also inconvenient and unnecessary.
This invention provides a means of adding or subtracting pump stages by remotely controlling one or more couplings strategically located in the assembly.
The coupling of this invention is not limited to underground applications but can be used in other applications where similar problems of coupling and uncoupling members occur.


The disclosed invention is a panel-like computer with physical and electrical connections enabling it to be connected to the interior front wall of a matching bag. The resulting bag computer may further includes: a bag with means to attach matching computer equipment components; a pivoting display panel located near the exterior top front of the bag front with its display facing away from the bag; a pivoting cover for the display panel; an optional input device, such as a keyboard, located near the exterior center of the bag front. The computing unit panel is mounted to the interior of the bag's front wall using a support structure which physically and electrically holds and aligns the bag and other computing equipment while forming a rigid front to assist storage of the exterior front mounted equipment.

There are many panel-like devices containing computing units. There are also many examples of computing unit panels being mounted to support structures on bags, vests, shirts or other wearable structures for mobile use. Electrical connections between computing unit panels mounted to the inside a bag and input/output devices mounted to the outside the bag are also common.
The computing unit panel described in this application is specialized to fit, align and support the component arrangement of the bag computer. These components may include, in addition to the computing unit panel, the bag, display panel and manual character input device (MCID) and these match each other physically and electrically. The components, themselves, have special features distinguishing them from other inventions. These features may include, for example, the position of the display panel on the bag, the edge attachment means of the display panel to the bag, the positioning of the MCID on the bag, the use of the cover flap for MCID mounting, etc. The computing unit panel must fit these other components as well as provide a rigid panel of appropriate size so the bag front can accept the display panel for storage.
The computing unit panel is a component of the bag computer described in application Ser. No. 11/796,920. Other applications dealing with the bag computer and its components include: Ser. Nos. 12/454,327, 12/387,594, 12/384,952, 11/799,011, 12/004,637, 12/216,650 and 12/216,651.

This patent is subject to a terminal disclaimer.


The disclosed device winds film in a continuous rapid-sequence mode or a non-continuous single-frame mode. A disengagement arrangement responds to a winding completion signal after each frame is wound in the continuous mode and disengages the transmission during the subsequent shutter release, but allows the transmission to remain engaged in the non-continuous mode and at the end of a winding sequence in the continuous mode. According to one embodiment, the disengagement arrangement contains an electromagnet that also actuates the camera's shutter release in the continuous mode.

1. Field of the Invention
This invention relates to cameras, and particularly, to a camera motor drive which performs film winding and shutter energizing operations.
2. Description of Prior Art
In one type of conventional automatic camera film winder, the winder is started upon completion of the shutter closing process and then stopped upon having completed the winding of a frame of film; the shutter is then released immediately after completion of the film winding process. However, immediately after completion of a film winding action, each part of the film winding mechanism still remains loaded or stressed, i.e., in motion, because of the inertia of the motor and the winding mechanism. Hence, if the shutter release starts immediately after a film winding action, the film is likely to be exposed to light before it actually stops. Such a conventional arrangement thus introduces the possibility of blurred pictures.
In addition to this problem, with the coupled parts of a shutter release mechanism and the film winding mechanism being in a stressed condition, each mechanism might be prevented from operating smoothly or might even be rendered inoperative. To eliminate these difficulties, it is desirable to remove the stressed or loaded condition. During non-continuous operation, one frame of film at a time is used, thus obviating the stressed condition because a sufficiently long period of time elapses between completion of film winding and shutter release. The condition is also absent after the last frame of film has been wound in a continuous photographic operation.
A conventional automatic film winding device is provided with a sliding clutch in its transmission gear mechanism and is arranged to absorb any excessive load or stress developed after completion of a film winding action because of the sliding action thereof removing the strain resulting from the film winding action. However, this method involves detecting the excessive stress after it has occurred. This response to detecting the completion of a film winding action results in delays. Besides, the provision of the sliding clutch in the film winding gear complicates the film winding mechanism and hinders efforts to reduce the size of the device. Furthermore, an excessive load is imposed on the motor by initiation of the sliding action of the sliding clutch and this overload on the motor makes adjustment thereof difficult. Also, the use of such a sliding clutch during a continuous picture taking sequence with an electromagnetic release type camera tends to expose the film to light during operation of the sliding clutch because shutter release begins immediately after a film winding action. In order to prevent this, the shutter release is arranged to begin in response to a signal representing completion of operation of the sliding clutch. A delay in the completion of a film winding action would occur after the film is actually wound and the film feed speed would then be decreased.
An attempt to solve these problems appears in Japanese Laid Open Patent Application, Publication No. 53-39123 which discloses an electric film winding device. In this device, an electromagnetic clutch, disposed in a film winding gear driving mechanism, is arranged to be turned off, upon completion of a film winding action, to disconnect the winding gear of the motor and prevent it from being overloaded. In this prior art device, the electromagnetic clutch is off when non-energized and is turned on when energized. The power supply to the clutch is cut off every time a winding action is completed. In carrying out a continuous photographic operation, the overloading which otherwise takes place every time a film winding action is completed, is effectively prevented by the electromagnetic clutch before the next exposure is initiated so that transition to the next exposure can be effected in a short period of time.
However, in a non-continuous picture taking operation, or before starting a continuous picture taking operation following a non-continuous operation, an ample length of time exists between a photographic operating cycle on one film frame and the next cycle on another, ie., before the next exposure action and the next film winding action. In such a case, the arrangement for operating an electromagnetic clutch to prevent overload is unnecessary. Even if an overloaded condition arises, upon completion of a film winding action, which is performed after completion of a non-continuous, single-frame, photographic operation, the overload can be eliminated during this amply long time interval before the next operation and the overloaded condition thus disappears in time. Hence, the electromagnetic clutch which turns off every time a film winding action is completed, wastes electric power as it operates even when its operation is not required. Moreover, in this example of the prior art, the electromagnetic clutch is disposed directly within the film winding gear driving mechanism. This arrangement necessitates having the electromagnetic clutch intermittently turning the transmission torque on and off, making the size of the clutch relatively large. The relatively large size of the electromagnetic clutch introduces the problem of placing it in the limited space of a compact electric motor drive film winder.

Camera and electric motor drive therefor


A method for fabricating a thin-film magnetic read/write head that eliminates contrast effects producing notching in a thin-film magnetic head coil caused by subsurface reflectivity at a reflective layer step during a photolithography step in the fabrication of the coil is provided. The method comprises the steps of forming a first permalloy yoke on a substrate, wherein the edges of the first yoke create steps from the top of the first yoke down to the substrate, forming a partial conformal layer of an electric insulation material over the first permalloy yoke and the substrate, forming a conformal copper seed layer over the electric insulation layer, forming a conductive coil on the electric insulation layer, wherein the copper coil is fabricated using a lithography process including placing a phase-shifting mask, formed in the image of the coil and containing non-printable openings covered by transparent material of a thickness that creates a 180.degree. phase-shift in illumination, over a photoresist layer, the phase-shifting mask creating illumination destructive interference in regions of the photoresist that are covered by the mask layer and immediately adjacent to regions of the photoresist not covered by the mask, forming a second electric insulation layer over the conductive coil, wherein the second electric insulation layer planarizes the coil topography, and forming a second permalloy yoke over the second electric insulation layer, wherein the second yoke is joined to the first yoke at a back gap but separated from the first yoke by a thin insulating layer at a recording gap.

1. Technical Field
The present invention relates in general to coil fabrication in thin-film magnetic recording heads, and particularly to producing high resolution coils in thin-film magnetic recording heads using phase-shifting masks.
2. Description of the Related Art
Thin-film magnetic read/write heads are used for magnetically reading and writing information upon a magnetic storage medium such as a magnetic disk or magnetic tape. It is highly desirable to provide a high density of information storage on the magnetic storage medium.
Increased storage density in a recording system may be achieved by providing an area density as high as possible for a given recording surface. In the case of rotating disk drives (both floppy and hard disk), the area density is found by multiplying the number of flux reversals per unit length along the track (linear density in units of flux reversals per inch) by the number of tracks available per unit length in the radial direction (track density in units of tracks per inch).
The demand for increased storage density in magnetic storage media has led to reduced magnetic head dimensions. Magnetic heads are now fabricated in a manner similar to that used for semiconductor integrated circuits in the electronic industry.
During fabrication, many thin-film magnetic heads are deposited across the entire surface of the wafer (or substrate). After the layers are deposited, the wafer is "diced" or sliced into many individual thin-film heads, each carried by a portion of the wafer so that an upper pole tip, a lower pole tip, and a gap are exposed. Pole tips and gap (and the portion of the substrate which underlies them) are then lapped in a direction generally inward, toward the center of the thin-film head, to achieve the desired dimensions. This lapping process is a grinding process in which the exposed portion of top and bottom pole tips and gap are applied to an abrasive, such as a diamond slurry. Electrical contacts are connected to conductive coils. The completed head is next attached to a carrying fixture for use in reading and writing data on a magnetic storage medium such as a computer disk.
FIG. 1 is a diagram of a thin-film head. The thin-film magnetic head 5 consists of a bottom yoke 2 of Permalloy, some insulating layers, a spiral conductor 4 (coil), and a top yoke I of Permalloy, which is joined to the bottom yoke at the back gap but separated from it by a thin insulator at the recording gap. The Permalloy pole tips 6 and 3 at the recording gap are often called pole tip 1 (P1) and pole tip 2 (P2), respectively.
In operation, a magnetic storage medium is placed near the exposed upper and lower pole tips (P1 and P2). During the read operation, the changing magnetic flux of the moving storage medium impresses a changing magnetic flux upon upper and lower pole tips. This magnetic flux is carried through the pole tips and yoke core around the conductor coil 4. The changing magnetic flux induces an electrical voltage across the conductor coil 4 which may be detected using electrical detection circuitry. The electrical voltage is representative of the changing magnetic flux produced by the moving magnetic storage medium.
During a write operation, an electrical current is caused to flow in the conductor coil 4. This electric current induces a magnetic field in top yoke 1 and bottom yoke 2 and causes a magnetic field across the gap between the upper and lower pole tips 3 and 6. A fringe field extends in the vicinity beyond the boundary of the pole tips and into the nearby magnetic storage medium. This fringe field may be used to impress magnetic fields upon the storage medium and write information.
In the manufacture of thin-film magnetic read/write heads, photolithographic printing is employed to fabricate circuit pattern images onto rigid substrates. In this process, photosensitive films called photoresist are coated onto the substrate, exposed to light, and then developed in an alkaline developer solution. Upon development, a pattern configuration forms in the photoresist corresponding to a change in solubility of those regions of the photoresist material exposed to the irradiating light. The clarity or resolution of the lines which define these patterns at microns or even sub-micron geometries to a great extent serves as a limitation to the photolithographic process. Today, photolithographic technology is approaching its ultimate limit, the point beyond which resolution cannot be improved because of diffraction effects, incompatibility of materials, and complexity of processing.
One of the major resolution problems which exists in processes of this type is called reflectivity. This is caused by the fact that some of the light striking a thin layer of photoresist material will usually pass through the layer and be reflected upward from a lower reflective layer during the radiation exposure. The reflectivity problem as it relates to thin-film magnetic heads is illustrated in FIG. 2.
During fabrication, a ferromagnetic Permalloy is deposited on a substrate to create the P1 yoke. Overlaying the P1 yoke is a thin layer of dielectricnonmagnetic material which controls the magnetic gap between pole tips. Overlaying said magnetic gap (usually alumina sputtered material) is a layer I1 of electrically insulating material (usually a high temperature polymerized organic material such as photoresist). The insulation layer I1 cannot fully planarize the step created by the edges of the P1 yoke down to the substrate surface. Prior to the coil photostep, a CrCu seed layer is sputter deposited on top of the insulation layer I1. Overlaying the seed layer is placed a positive photoresist and the coil mask. During the expose cycle of the coil process, the actinic illumination is obliquely reflected from the highly reflective copper seed layer at the step, creating severe notching illumination. Also, the incident light is generally not perfectly normal to the surface of the photoresist layer, and as it may be diffracted upon passage through the photoresist, the incident light will be reflected angularly from the surface of the substrate rather than normally therefrom. Such light will impinge upon the unexposed portions of the photoresist and some may again pass through the photoresist to strike the opaque portions of, for example, a photo mask, and this light will be reflected back into some portions of the photoresist which are not intended to be exposed. This is called "flare" and results in a loss of contrast.
As a result of light being reflected at the seed layer step and other angular light from the reflective surface, there may be a pronounced detrimental effect upon the ultimate resolution which can be obtained upon photo development. This reflective notching phenomenon, experienced when patterning or photo developing the material, could cause inter-Cu coil shorts.
Previous attempts to correct the reflectivity problems, as disclosed in, for example, U.S. Pat. No. 4,102,683, call for interposing a light absorbing layer between the surface of the substrate and the photoresist material. These so-called anti-reflective layers have the property of absorbing light which passes through the photoresist and not reflecting it back upward. They may be comprised of, for example, a quarter-wave plate having an odd multiple thickness of one-quarter of the wavelength of light to which the photoresist layer is sensitive. This plate is comprised of silicon dioxide thermally grown or deposited in any manner, such as by the decomposition of silane. Alternatively, such a light absorbing layer may be manufactured by mixing a fluorescent dye such as an organic phosphor with an organic binder such as Fluorel made by the 3-M Company or Viton made by DuPont, which is a rubber.
However, such prior art anti-reflective layers have exhibited a number of problems not the least of which is the fact that, in general, when the surface of the substrate is irregular, there is required an additional planarization material or layer. Other disadvantages are, for example, that when prior art organic binders have been patterned by a wet etch development, such layers develop isotropically resulting in undercutting during development which results in a narrow processing latitude or even complete lift-off of sub-micron geometries. Also, certain organic binders such as polymethylmethacrylate (PMMA) and polybutene-sulfone when employed as an anti-reflective sublayer have poor stability as vehicles for etching patterns onto the substrate. Moreover, the prior art organic binders cannot be coated in a fully conformable layer at or near a step region. The lack of thickness control will create larger undercuts and variable light reflected from the seed layer at or near the steps region. In addition, another prior art technique is to coat the resist with a top layer of polymer material which acts as an internal anti-reflection coating and minimizes internal (resist) reflections. In all the stated techniques, the actinic radiation that finally acts upon the resist must continue to be of the same intensity to provide for the proper contrast. These techniques only slightly modify the way the radiation is coupled into the resist and in many applications they have to be tailored to each individual situation. Moreover, anti-reflective layers and actinic dyes in the photoresist only reduce the reflective notching problem. They do not eliminate the problem of coil shorts, thus, resulting in a lower thin-film magnetic head yield.
Therefore, it would be desirable to provide a method of fabrication for thin-film magnetic heads which provides a simple and effective method of eliminating notching at the P1 yoke step and improving coil resolution in the photoresist processing step.

Magnetic storage system using thin film magnetic recording heads using phase-shifting mask

International Business Machines Corporation


A resistor assembly is disclosed and comprises a surface mounted layer comprising a first conductive trace, a second conductive trace, and a plurality of trimming bridges that electrically couple the first conductive trace to the second conductive trace. The resistor assembly also comprises a second layer disposed underneath the surface mounted layer. The second layer comprises an embedded thin film resistor electrically coupled to the surface mounted layer. The plurality of trimming bridges are each removable to increase a resistance of the embedded thin film resistor. The resistor assembly also comprises a plurality of vias that electrically couple the first conductive trace of the surface mounted layer to the embedded thin film resistor.

Thin film resistors are typically created by depositing a thin film constructed of a metal alloy upon a substrate. Specifically, the thin film is deposited upon a substrate using a sputtering deposition process. Thin film resistors are found in laminate substrates used for electronic applications such as, for example, printed circuit boards.
A thin film resistor may be attached to a top surface of the electronic substrate or, alternatively, embedded within the laminate substrate. When embedded in a substrate, the thin film resistor is referred to as an embedded thin film resistor. Embedded thin film resistors are typically composed of nickel-chromium alloys such as, for example, nickel chromium aluminum silicon (NiCrAlSi). The nickel-chromium alloy is deposited upon a copper foil. The nickel-chromium alloy and the copper foil are then bonded to a dielectric layer using a lamination process, where the copper foil acts as a conductive layer and the nickel-chromium alloy acts as a resistive layer. The resistive layer is then etched to define discrete embedded thin film resistors. Any number of etching process may be used to define the embedded thin film resistors, however, the specific etching process is selected based on the specific metals included in the nickel-chromium alloy.
The resistance variation of a thin film resistor depends upon several factors. Specifically, physical properties such as, for example, film thickness, residual stress, uniformity, and surface roughness of the conductive layer may affect the resistance variation of the thin film resistor. Moreover, the sheet resistance of the nickel-chromium alloy before etching is inversely proportional to thickness. The thickness of the nickel-chromium layer is determined based on sputtering parameters such as linear speed and power, however, the sputtering parameters may be difficult to control. Additionally, the resolution and specific type of etching used to create the discrete resistor elements also affects the resistance variations. Finally, the temperature and cycle time of the lamination process also affects the resistance of the nickel-chromium alloy. Thus, it is challenging to control the resistance variation of a thin film resistor.

Thin film resistor having surface mounted trimming bridges for incrementally tuning resistance


A circuit and method for controlling a current level in a switched reluctance motor phase coil are provided. The circuit includes a current sensor for generating a current indicative signal indicative of a level of current in the phase coil and first and second comparators for comparing the current indicative signal to upper and lower hysteresis band limit signals. The circuit further includes a drive circuit, such as a flip-flop, for generating a drive signal responsive to the first and second comparators and first and second switches disposed on either side of the phase coil for providing current to the phase coil. The first switch is responsive to the drive signal and a phase control signal to maintain the current in the coil within the hysteresis band defined by the upper and lower hysteresis band limit signals.

1. Field of the Invention
This invention relates to switched reluctance motors, and, more particularly, to a method and a circuit for controlling the current in each motor phase of a switched reluctance motor between two predetermined current levels.
2. Disclosure of Related Art
A conventional switched reluctance motor (SRM) includes a stator having a plurality of pairs of diametrically opposed stator poles and a rotor having a plurality of pairs of diametrically opposed rotor poles. Windings or coils are typically disposed about the stator poles and the windings around any two diametrically opposed stator poles may be connected in series or in parallel to define one motor phase of the multiphase SRM. The windings associated with a motor phase may be referred to as a phase coil. By generating current through the phase coil, magnetic fields are established about the stator poles and a torque is produced that attracts a pair of rotor poles into alignment with the stator poles. The current in the phase coils is generated in a predetermined sequence in order to produce a constant torque on the rotor. The period during which current is provided to the phase coil--and the rotor poles are brought into alignment with the stator poles--is known as the "active stage" of the motor phase. At a certain point--either as the rotor poles become aligned with the stator poles or at some point prior thereto--it becomes desirable to commutate the current in the phase coil to prevent a negative or braking torque from acting on the rotor poles. Once this "commutation point" is reached, current is no longer generated in the phase coil and the current is allowed to dissipate from the phase coil. The period during which current is allowed to dissipate from the phase coil is known as the "inactive stage" of the motor phase.
SRMs typically employ pulse width modulation (PWM) or current chopping to control the current level in each phase coil during the active stage of the motor phase. Conventional circuits and methods for performing PWM or current chopping have often incorporated microprocessors. The use of microprocessors is disadvantageous, however, because it increases the cost of the motor and limits the bandwidth of electrical signals within the control system for the motor.
There is thus a need for an apparatus and method for controlling a switched reluctance motor that will minimize or eliminate one or more of the above-mentioned deficiencies.

Hysteresis control in switched reluctance motors


A recumbent tricycle which includes a propulsion system which includes a combination of foot and arm power for propulsion. Pedals are operated with the rider""s legs. Handles are also connected to the drive mechanism, with the handles pulled back and pushed forward to add to propulsive power. The handles are also connected through a tie rod arrangement to the front wheels such that the wheels may be turned so that the vehicle can be steered by moving the handles toward one side or the other. Preferably, two large front wheels similar to conventional bicycle wheels are provided in front, with a single smaller diameter but wider driven rear wheel. The rear wheel is mounted on a sub-frame pivotally secured to the vehicle frame and supported on a shock absorber. Brake and gear change mechanism controllers are mounted on the handles.

This invention relates in general to three wheel tricycles powered both by leg powered peddles and arm powered movable handlebars.
A wide variety of propulsion systems have been developed for bicycles, tricycles, etc. Commonly, such cycles have a rotating sprocket connected to pedals that revolve around the sprocket axis, with the sprocket carrying a chain driving a sprocket connected to the rear wheel. The front wheel is mounted on a stem and is turned by a pair of outwardly extending handlebars. Whether the rider is positioned in an upright or recumbent position, the cycle is relatively easy to steer and propel. The arms are used solely for steering and are not involved in propelling the cycle.
A number of different drive systems have been devised to gain additional propelling energy from the arms. Typical of these are the xe2x80x9crowingxe2x80x9d type systems described by Young in U.S. Pat. No. 5,272,928, McCahon in U.S. Pat. No. 5,653,663 and Keskitalo in U.S. Pat. No. 5,690,346. Each of these recumbent cycles uses a xe2x80x9crowingxe2x80x9d motion in which handles and pedals are alternately pushed back in forth in a generally straight line. Handles or a handle assembly must be rotated or pivoted while being moved back and forth. With these complex mechanisms and straight line motion, maintaining balance and smoothly steering while providing maximum power is quite difficult.
Braun in U.S. Pat. No. 4,541,647 combines pedals on a sprocket for rotation by the legs and two closely spaced handles alternately pushed and pulled forward and back. One handle is pushed forward while the other is pulled back, creating unbalanced forces which will make steering the cycle by tilting the handle assembly very difficult.
Sommer et al. in U.S. Pat. No. 5,328,195 describe a basically conventional bicycle having a pedal sprocket connected to a drive sprocket at the rear wheel with handlebars that can be lifted and lowered as a unit. The handlebar motion pulls a cable wrapped around a pulley secured to the drive sprocket to provide added rotational force during the lifting phase of handlebar movement. Lifting handlebars generate considerably less force that will a pulling motion back toward the rider and a cable and pulley arrangement is much less positive than a chain and sprocket.
Thus, there is a continuing need for a cycle, particularly for off-road riding, that is simple is structure and avoids unreliable complexity, is low to the ground for increased stability and lower wind resistance, provides for increase power generation by both a rider""s arms and legs and avoids unbalanced forces on the steering mechanism to provide easy and accurate steering while providing maximum arm propulsive forces.
The above-noted problems, and others, are overcome by the dual power tricycle of this invention, which basically comprises a frame, a rider""s seat mounted on the frame, three wheels mounted on the frame, with two wheels forward and one aft of the seat or, alternatively, one forward and two aft of the seat, a foot power assembly connected between foot pedals operable by a rider""s feet and at least one of the wheels for rotating the wheels in response to foot pedal rotation, two hand levers operable by a rider""s hands for moving forward and aft, a hand power assembly connected between said hand levers and at least one of the wheels for further rotating said wheels in response to forward and aft movement of said hand levers, steering means for steering forward wheel(s) in response to sideways movement of said hand levers and brake operating means mounted on said hand levers and connected to wheel rotation braking means at least some of said wheels.
While the frame may be constructed of any suitable material and components, a welded tubular metal frame and/or a tubular fiber reinforced resin frame is preferred. Any suitable seat may be used. Preferably, since the rider sits in a semi-recumbent position with his or her legs extending forward, the seat has a back.
The foot poser assembly comprised a pair of conventional foot pedals forward of the seat, directly driving a first sprocket connected via a chain and conventional gearbox(es) to the rear wheel(s). Preferably, a first conventional gear changing mechanism is provided adjacent to the pedals with a gear changing lever for the first gear changer on one hand lever. A second conventional gear box is positioned generally below the seat, with a second gear changing lever for the rear gear box mounted on the second hand lever. Regular bicycle chains run from the first gear box to the second gear box and then to the wheel. Idler gears are provided as desired to direct the chain between these components and to adjust chain tension.
The hand power assembly comprises the two hand levers mounted so as to pivot forward and aft about a pivot point at the lower ends of the levers. A standard bicycle chain is secured to a crosspiece connecting the two hand levers, wraps around a ratchet sprocket attached coaxially with the first sprocket and pedals, then to a stiff spring fastened to the frame. When the handles are not moved forward and aft (or are moved slowly) the ratchet sprocket free wheels. When the handles are moved sufficiently rapidly to cause the rim speed of the ratchet sprocket to exceed the rim of the first sprocket, the ratchet will lock and the force rotating the ratchet sprocket is transmitted to the drive chain assembly, increasing vehicle speed. Generally, the ratchet sprocket will have a considerably smaller diameter than the first sprocket, since the foot pedaling speed is likely to be greater than the hand lever motion.
The lower ends of the hand levers are mounted on the crosspiece so as to be pivotable to either side. A bracket on the crosspiece pivots sideways with the hand levers. A cable connected to sides of the bracket is connected to a tie rod adjacent to the front wheel(s) axis, so that sideways pivoting of the hand levers will cause rotation of the front wheel(s) about a generally vertical axis, steering the vehicle.
Each of the three wheels is preferably mounted on a shock absorbing assembly, to reduce bumps and vibration when the vehicle is ridden along a rough surface.
Conventional caliper brakes are mounted to engage the front wheel(s) via conventional handlebar mounted levers and cables. A disk brake is mounted along a side of the rear wheel(s) and is actuated by levers.


A method for the immobilization of a radioactive anion on the surface of a metal substrate, said method comprising treating the substrate with an oxidizing agent in the presence of a solution of a radioactive anion which forms an insoluble salt with ions of said metal. Preferably, a binding agent will also be present. Preferably, the metal is silver, the radioactive anion is 125Ixe2x88x92 and the binding agent comprises bromide ions.

Brachytherapy is a general term covering medical treatment which involves placement of a radioactive source near a diseased tissue and may involve the temporary or permanent implantation or insertion of a radioactive source into the body of a patient. The radioactive source is thereby located in proximity to the area of the body which is being treated. This has the advantage that a high dose of radiation may be delivered to the treatment site with relatively low dosages of radiation to surrounding or intervening healthy tissue.
Brachytherapy has been proposed for use in the treatment of a variety of conditions, including arthritis and cancer, for example breast, brain, liver and ovarian cancer and especially prostate cancer in men (see for example J. C. Blasko et al., The Urological Clinics of North America, 23, 633-650 (1996), and H. Ragde et al., Cancer, 80, 442-453 (1997)). Prostate cancer is the most common form of malignancy in men in the USA, with more than 44,000 deaths in 1995 alone. Treatment may involve the temporary implantation of a radioactive source for a calculated period, followed by its removal. Alternatively, the radioactive source may be permanently implanted in the patient and left to decay to an inert state over a predictable time. The use of temporary or permanent implantation depends on the isotope selected and the duration and intensity of treatment required.
Permanent implants for prostate treatment comprise radioisotopes with relatively short half-lives and lower energies relative to temporary sources. Examples of permanently implantable sources include iodine-125 or palladium-103 as the radioisotope. The radioisotope is generally encapsulated in a titanium casing to form a xe2x80x9cseedxe2x80x9d which is then implanted. Temporary implants for the treatment of prostate cancer may involve iridium-192 as the radioisotope.
Recently, brachytherapy has also been proposed for the treatment of restenosis (for reviews see R. Waksman, Vascular Radiotherapy Monitor, 1998, 1, 10-18, and MedPro Month, January 1998, pages 26-32). Restenosis is a re-narrowing of the blood vessels after initial treatment of coronary artery disease.
Coronary artery disease is a condition resulting from the narrowing or blockage of the coronary arteries, known as stenosis, which can be due to many factors including the formation of atherosclerotic plaques within the arteries. Such blockages or narrowing may be treated by mechanical removal of the plaque or by insertion of stents to hold the artery open. One of the most common forms of treatment is percutaneous transluminal coronary angioplasty (PTCA)xe2x80x94also known as balloon angioplasty. At present, over half a million PTCA procedures are performed annually in the USA alone. In PTCA, a catheter having an inflatable balloon at its distal end is inserted into the coronary artery and positioned at the site of the blockage or narrowing. The balloon is then inflated which leads to flattening of the plaque against the artery wall and stretching of the artery wall, resulting in enlargement of the intraluminal passage way and hence increased blood flow.
PTCA has a high initial success rate but 30-50% of patients present themselves with stenotic recurrence of the disease, i.e. restenosis, within 6 months. One treatment for restenosis which has been proposed is the use of intraluminal radiation therapy. Various isotopes including iridium-192, strontium-90, yttrium-90, phosphorus-32, rhenium-186 and rhenium-188 have been proposed for use in treating restenosis.
Conventional radioactive sources for use in brachytherapy include so-called seeds, which are sealed containers, for example of titanium or stainless steel, containing a radioisotope within a sealed chamber but permitting radiation to exit through the container/chamber walls (U.S. Pat. Nos. 4,323,055 and 3,351,049). Such seeds are only suitable for use with radioisotopes which emit radiation which can penetrate the chamber/container walls. Therefore, such seeds are generally used with radioisotopes which emit xcex3-radiation or low-energy X-rays, rather than with xcex2-emitting radioisotopes.
Brachytherapy seeds comprising a coating of radioactive silver iodide on a silver wire encapsulated inside a titanium container are known in the art (U.S. Pat. No. 4,323,055). Such seeds are formed by first chloriding or bromiding the silver to form a layer of silver chloride or bromide, and then replacing the chloride or bromide ions with radioactive iodide ions (I-125) by ion exchange. Such seeds are available commercially from Medi-Physics, Inc., under the Trade Name I-125 Seed(copyright) Model No. 6711 or OncoSeed(trademark) Iodine-125 seeds (Nycomed Amersham).
Other conventional brachytherapy seeds comprise titanium containers encapsulating ion exchange resin beads onto which a radioactive ion, for example I-125, has been absorbed (U.S. Pat. No. 3,351,049). The immobilisation of a radioactive powder within a polymeric matrix has also been proposed (WO97/19706).
The processes disclosed in U.S. Pat. No. 4,323,055 for the production of I-125 containing seeds involve a number of separate steps. We believe a more efficient and rapid method for the production of radioactive sources comprising insoluble salts, especially silver salts, is desirable from a manufacturing viewpoint.
According to one aspect of the invention there is therefore provided a method for the immobilisation of one or more radioisotopes on the surface of a metal substrate, said method comprising treating the substrate with an oxidising agent to produce metal cations, in the presence of a source of a radioactive anion containing one or more radioisotopes, which anion forms an insoluble salt with said metal cations. Preferably, the radioactive anion will be present in solution or in a dispersion. Preferably, a binding agent will also be present. The products of the method of the invention are radioactive substrates.
Any metal which can form an insoluble salt with a radioactive anion on oxidation may be used as the metal substrate in the method of the invention. Suitable metals include silver, copper, lead, zinc, palladium, thallium, cadmium, lanthanum and gold. Preferably, the metal substrate is silver. The substrate may be made of solid metal or a suitable material plated with a layer of metal, for example silver, zinc, palladium or thallium. Suitable materials for plating include other metals, for example gold, copper or iron, and plastics, for example polypropylene, polystyrene, nylon, delrin, Kevlar(trademark), and any other plastic or composite which can form a solid rod for plating with the metal of interest. Suitable plating methods are known in the art and include chemical deposition, sputtering and ion plating techniques.
The substrate should be of a suitable size and dimensions for incorporation into a source, for example a seed, for use in brachytherapy. Conventional seeds for use in the treatment of prostate cancer, for example, are typically substantially cylindrical in shape and approximately 4.5 mm long with a diameter of approximately 0.8 mm, such that they may be delivered to the treatment site using a hypodermic needle. For use in the treatment of restenosis, a source should be of suitable dimensions to be inserted inside a coronary artery, for example with a length of about 10 mm and a diameter of about 1 mm, preferably a length of about 5 mm and a diameter of about 0.8 mm, and most preferably with a length of about 3 mm and a diameter of about 0.6 mm. Sources for use in the treatment of restenosis are typically delivered to the treatment site using conventional catheter methodology.
Preferably, the substrate is of a suitable size and dimensions to fit inside a conventional seed container, such as those disclosed in U.S. Pat. No. 4,323,055 which is hereby incorporated by reference. Preferred seed containers are those made of titanium, titanium alloy or stainless steel. Preferably, the substrate will be substantially cylindrical in shape, for example in the form of a rod or wire. Suitable dimensions are about 3 mm long and about 0.10 mm to 0.70 mm in diameter, preferably about 0.5 mm in diameter.
Alternatively, the radioactive substrates may be incorporated into a polymer or ceramic matrix. Suitable polymer matrices include those disclosed in WO97/19706 which is hereby incorporated by reference. If the radioactive anion comprises a xcex2-emitter, the radioactive substrate should not be encapsulated in a metal container as such containers would absorb the xcex2-particles emitted and prevent them from reaching the treatment site.
If the metal substrate comprises silver or another X-ray opaque metal such as gold, copper or iron, there is the added advantage that sources comprising the radioactive substrate will be detectable by X-ray when inserted or implanted into a patient. Preferably, the substrate is shaped such that its orientation can also be determined by X-ray imaging. If the substrate comprises an X-ray transparent material plated with a metal such as silver, the radiopaque metal thickness is preferably greater than about 0.050 mm to ensure X-ray visualisation.
The radioactive anions for use in the method of the invention may be simple anions such as 125Ixe2x88x92 or 35S2xe2x88x92, or complex anions such as 32PO43xe2x88x92, 35SO42xe2x88x92 or 51CrO42xe2x88x92. If the anion is a complex anion, it may comprise one or more radioisotopes, preferably one, two or three radioisotopes. More than one type of radioactive anion may be used together in the method of the invention, for example 125Ixe2x88x92 together with 35SO42xe2x88x92. The choice of anion(s) and radioisotopes will depend in part on the intended use of the resulting brachytherapy source and the type of radiation which the sources should emit. For example, the radioactive anion may emit xcex3-radiation or low-energy X-rays, or it may be a xcex2-emitter.
A radioactive anion which forms an insoluble salt with the metal of the metal surface of the substrate should be used. Preferred radioactive anions include those comprising 125Ixe2x88x92, 35S, 32P or 33P. Possible anions include 125Ixe2x88x92, 131Ixe2x88x92, 123Ixe2x88x92, 35S2xe2x88x92, 35SO42xe2x88x92, 35SO32xe2x88x92, 125IO3xe2x88x92, 131Ixe2x88x92, 123IO3xe2x88x92, 51CrO42xe2x88x92, 32PO43xe2x88x92, H32PO42xe2x88x92 and H232PO4xe2x88x92. For the purposes of the invention, a salt is considered to be insoluble if its solubility product constant is lower than about 1xc3x9710xe2x88x925, preferably less than about 1xc3x9710xe2x88x922 and most preferably less than 1xc3x9710xe2x88x9216. For a sparingly soluble salt MxAy in contact with its saturated solution, the solubility product is given by Ksp=[My+]x[Axxe2x88x92]y.
Concentrations are normally given in moles/liter at 298xc2x0 K. For example, if the metal is silver, suitable anions include those shown in the Table 1 below. Values are taken from the Handbook of Chemistry and Physics, 74th Edition, 1993-4, Section 8, page 49.
Other possible anions include complex anions derived from pyrophosphoric acid, such as H3P2O7xe2x88x92, wherein one or more of H, P or O comprise a radioisotope. Suitable anions derived from pyrophosphoric acid are disclosed in WO97/49335 which is hereby incorporated by reference. When the metal surface is silver, a preferred anion is 125I-iodide.
One advantage of the method of the invention is that it is a xe2x80x9cone-stepxe2x80x9d chemical reaction. The prior art chemical processes comprise two or more steps, which lead to longer preparation times, greater variability of iodide distribution and greater costs. The method of the invention is also readily applicable to substrates of a variety of different geometric shapes, for example spheres or rods. The method can be applied to a single substrate or to a plurality of substrates wherein the number of substrates can range from 2 to about 100,000 or more, for example in a batchwise process. Treatment of a metal substrate with an oxidizing agent in the presence of a radioactive anion in a one-pot reaction leads to immobilization of the anion on the substrate in situ. Preferably, both the oxidizing agent and the radioactive anion are used as solutions in the same solvent, for example in aqueous solution. Alternatively, a solid oxidising agent may be added to a reaction mixture comprising the metal substrate and a solution or dispersion of a radioactive anion.
The source of the radioactive anion may be present in solution in a suitable solvent. Alternatively, it may be present in the form of a dispersion or precipitate in a suitable liquid phase. For example, if the radioactive anion is iodide, it may be present as a dispersion of silver iodide, or a dispersion of any insoluble metal iodide salt which displays greater solubility than that of the insoluble radioactive salt to be formed using the method. For example, if the substrate is silver and the radioactive anion is iodide, the iodide source may be a dispersion of an iodide salt of copper, lead, palladium or thallium. Table 2 below shows the solubility of some iodide salts. Copper, lead, palladium and thallium iodide are all more soluble than silver iodide, and so could be used as an iodide source in the immobilisation of iodide ions on a silver substrate using the method of the invention. Gold iodide is less soluble than silver iodide and hence would not be a suitable iodide source in such a method using a silver substrate.
On oxidation of a silver substrate, the iodide should transfer from the dispersion to the surface of the substrate.
Alternatively, the source of radioactive iodide ions may be present in the form of an organic iodide-containing compound, for example an alkyl iodide such as 2-iodoethanol, ethyl iodide, iodobutylacetate, iodobutyric acid, 3-iodopropanol, epiiodohydrin, glyceryl iodide, an activated iodomethylcarbonyl compound such as iodoacetamide or iodoacetic acid, an iodinated lachrymator such as iodinated acetone or 1-iodo-2-(trimethylsilyl)acetylene, or an iodosilicon compound such as iodotrimethyl silane, each of which may degrade over the course of the immobilisation reaction to generate iodide ions in the solution phase.
Radioactive iodide ions may also be present in the form of a complex with a suitable complexing agent, for example starch, amylose, amylopectin, or another complex carbohydrate, which will gradually release iodine, and thence iodide ions, in the presence of hydroxide ions, into the solution phase over the course of the immobilisation reaction. Complexes of other radioactive anions may also be used in the method of the invention.
Alternatively, the radioactive anion source may be a suitable ion exchange resin bead with radioactive anions adsorbed thereon. Any ion exchange resin which can act as a reservoir for the radioactive anions may be used (for example, Pbxe2x88x922exe2x88x92xe2x86x92Pb2+, Resin-SO42xe2x88x92xe2x86x92Resin+SO42xe2x88x92, Pb2+xe2x86x92SO42xe2x88x92xe2x86x92PbSO4).
Suitable oxidizing agents are known in the art, including those disclosed in U.S. Pat. No. 4,323,055 which is herein incorporated by reference. They include sodium chlorite (NaClO2), sodium chlorate (NaClO3), sodium chromate (Na2CrO4), hydrogen peroxide (H2O2), potassium dichromate (K2Cr2O7), potassium permanganate (KMnO4), and potassium ferricyanide (K3Fe(CN)6). For the immobilisation of iodide ions on silver metal, a preferred oxidizing agent is potassium ferricyanide.
The oxidizing agent and the metal should be chosen such that the oxidizing agent can oxidize the metal surface of the substrate under the reaction conditions. The metal cations thus formed at the surface of the substrate should combine with the radioactive anions in solution to form a layer of an insoluble salt on the surface of the substrate, thus immobilizing the anions on the surface of the substrate. Immobilization of a radioactive anion on the metal surface of a substrate provides a radioactive metal substrate.
Whether or not a particular oxidising agent is suitable for use in the method of the invention with a particular metal and a particular radioactive anion can be predicted by reference to the standard electrode potentials of the relevant half-reactions. If the sum of the standard electrode potentials for the oxidation half-reaction and the reduction half-reaction is positive, then in the absence of inhibiting kinetic effects, reaction should occur spontaneously. Tables of standard electrode potentials are readily available, for example in D. A. Skoog and D. M. West, Principles of Instrumental Analysis, Holt, Rinehart, and Winston, Inc., New York, 1971, pp 678-680, and W. M. Latimer, The Oxidation States of the Elements and Their Potentials in Aqueous Solution, Prentice Hall, Englewood Cliffs, N.J., 1952. A selection of standard electrode potentials (Excex8) is shown in Table 2 below. Values are taken from Skoog and West.
If the radioactive anion to be immobilised is iodide, then preferably an oxidising agent is chosen which will not oxidise iodide ions to molecular iodine under the reaction conditions. Molecular iodine is volatile and generation of a volatile radionuclide such as 125I2 involves increased risk of exposure to radiation for the manufacturing personnel or, at least, rapid saturation of the carbon filters. However, if an oxidising agent is used which is strong enough to oxidise silver and to oxidise iodide to molecular iodine, the oxidation of the silver should occur preferentially as this is the more favourable reaction.
In one embodiment of the invention, ferricyanide is used as the oxidising agent. Under standard conditions, it is postulated that the reaction between ferricyanide and silver/silver iodide is very energetically favourable, i.e.,
Ecell=Ecathodexe2x88x92Eanode
Ecell=0.36xe2x88x92(xe2x88x920.152)
Ecell=0.512
while the possible reaction between ferricyanide and iodide would not be a spontaneous reaction under standard conditions, i.e.,
Ecell=0.36xe2x88x92(0.54)
Ecell=xe2x88x920.18
Standard conditions are given as reagent activities of 1. For example, the concentration of both ferricyanide and the reduced form, ferrocyanide, would be equal to 1 molar.
However, the impact of concentration is predicted by the Nernst equation:
Exc2xdxe2x80x2=Exc2xdxc2x0xe2x88x92(0.059/n)log(reduced form/oxidised form)xe2x80x83xe2x80x83(i)
For the oxidising half cell, this becomes:
Exc2xdxe2x80x2=Exc2xdxc2x0xe2x88x92(0.059)log([Agxc2x0]/[Ag+])xe2x80x83xe2x80x83(ii)
while the reduction half cell becomes:
E{fraction (1/2)}xe2x80x2=E{fraction (1/2)}xc2x0xe2x88x92(0.059)log([Fe(CN)64xe2x88x92]/[Fe(CN)63xe2x88x92])xe2x80x83xe2x80x83(iii)
However, in the presence of iodide, the silver oxidation is coupled to the follow-up reaction as shown here:
Oxidation: Agxc2x0xe2x86x92Ag++exe2x88x92 125Ixe2x88x92+Ag+xe2x86x92Ag125Ixe2x80x83xe2x80x83(iv)
The thermodynamics of equation (iv) are governed by the equilibrium constant, which for insoluble species is also known as the solubility product or Ksp as shown here:
Ksp=[Ag+][125Ixe2x88x92]xe2x80x83xe2x80x83(v)
Substituting equation (v) into equation (ii), the operative Nernst equation for the net reaction can be written as:
Exc2xdxe2x80x2=Exc2xdxc2x0xe2x88x92(0.059)log([Ag+]/(Ksp/[125Ixe2x88x92])
By rearranging the log term and grouping all the constants including the Ksp term into a new Exc2xdxc2x0xe2x80x2, the impact of [125Ixe2x88x92] on the overall reaction can be seen:
Exc2xdxe2x80x2={Exc2xdxc2x0+(0.059)log(Ksp)}xe2x88x920.059log[125Ixe2x88x92]xe2x80x83xe2x80x83(vi)
where {Exc2xdxc2x0+(0.059)log(Ksp)}=Exc2xdxc2x0xe2x80x2 for reaction (iv) above
Accordingly, it is postulated that in the oxidation of silver by ferricyanide, the initial conditions and those throughout the process are as follows:
This suggests that this reaction remains energetically favourable throughout the deposition of silver iodide.
The same type of process can be carried out for the possible side reaction of the oxidation of iodide to iodine. The operative Nernst equation for this half-cell is given by:
Exc2xdxc2x0=Exc2xdxe2x88x92(0.059/2)log([Ixe2x88x92]2/[I2])
These calculations suggest that in the earliest part of the reaction, there is the chance to produce 125I2 via oxidation by ferricyanide.
In a preferred embodiment of the invention, both ferricyanide and ferrocyanide are added to start the reaction to minimize the production of 125I2. Preferably, ferricyanide and ferrocyanide are added at an initial molar ratio of 10=[Fe(CN)63xe2x88x92]/[Fe(CN)64xe2x88x92]. In particular, an aqueous solution prepared from potassium ferricyanide and potassium ferrocyanide trihydrate can be made and added to the reaction vial. It is postulated that the presence of the ferrocyanide reduces the propensity for the side reaction to occur while the energetics behind the oxidation of silver to silver iodide remain very good. Those skilled in the art will recognize that similar reactions can occur in the presence of other redox couples.
The more resistant the metal is to oxidation, the stronger the oxidising agent should be. For example if the metal substrate is gold, a more powerful oxidizing agent such as permanganate may be used in the method of the invention.
The amount of oxidising agent required may be readily calculated by a skilled person depending on the amount of radioactive anion it is desired to immobilize on the metal substrate.
The amount of the radioactive anion, for example the concentration of a solution of the radioactive anion, can be chosen depending on the activity level desired in the resultant brachytherapy source. For example, substantially all of the anions present may be radioactive (i.e. xe2x80x9chotxe2x80x9d) or the radioactive anions may be diluted with non-radioactive (i.e. xe2x80x9ccoldxe2x80x9d or carrier) anions. For example, radioactive 125I-iodide may be diluted with non-radioactive 127I-iodide. Conventional brachytherapy sources for use in the treatment of prostate cancer normally have activities in the region of 0.2 to 1.5 mCi. Using the method of the invention, coated substrates with an activity of up to as high as about a Curie may be prepared. Such substrates, and radioactive sources comprising such substrates, form further features of the invention.
In order for the insoluble salt to form a stable layer which is strongly bound to the metal substrate and which does not flake or fail to adhere to the substrate, it may be necessary to also use a binding agent in the method of the invention. The binding agent preferably comprises a non-radioactive anion which also forms an insoluble salt with cations of the metal and which is different to the radioactive anion. Preferably, the salt formed by cations of the metal with the binding agent will be less insoluble, i.e. more soluble than that formed by the radioactive anion with cations of the metal or with the binding agent counter-ion. For example, if the radioactive anion is 125I-iodide, suitable binding agents include chloride or bromide ions, preferably bromide ions.
Whether or not a binding agent is required in any particular case will depend, at, least in part, on the nature of the metal of the substrate and the radioactive anion to be immobilized. Whether or not a binding agent improves the stability of the coated substrate in a particular case may be determined by routine trial and error experiments.
The applicants do not wish to be bound by any particular theory regarding the rxc3x4le played by the binding agent in the method of the invention, but it is postulated that the binding anion is preferably physically smaller than the radioactive anion such that it can fit into gaps or cracks in the coating layer to help hold the layer together. It is also possible that the binding ions take part in establishing a template on the metal surface that affords a more adhesive layer of the insoluble salt of interest.
A layer comprising both the binding agent and the radioactive anion will form on the metal surface of the substrate. Provided the reaction is carried out with sufficient mixing e.g. stirring or agitation, the radioactive anion can be homogeneously distributed throughout this layer. Silver substrates coated using the prior art two-step process of U.S. Pat. No. 4,323,055 comprise the radioactive anion in a layer of silver iodide on the surface of a silver bromide-coated silver substrate.
If the metal is silver and the radioactive ion is 125I-iodide, carrying out the method of the invention in the presence of an excess of bromide ions leads to formation of a more physically stable layer than if the bromide ions are not present. The binding agent thus enhances adherence of the Ag125I salt to the surface of the substrate. In addition, the use of bromide ions as a binding agent leads to formation of AgBr on the surface of the substrate in addition to Ag125I. The AgBr may form a coating over some or all of the Ag125I, which may help to minimize loss of radioactivity from the source due to physical handling of the coated substrate. It is postulated that the small amount of bromide ion present may serve to help establish the crystal form of the resulting AgI such that it is a more cohesive layer, and adhesive to the metal substrate. In one embodiment, the molar ratio of bromide to iodide present in the surface layer of the substrate is preferably in the range of 2.25 to 2.75 and, more preferably 2.5.
In one embodiment of the invention, I-125 may be immobilised on a silver substrate by treating the substrate with a solution or dispersion comprising I-125 ions and bromide ions and a solution of an oxidising agent, for example an aqueous solution of potassium ferricyanide. The I-125 and bromide ions may, for example, be present as an aqueous solution of Na125I and NaBr. Alternatively, the source of I-125 ions may be a dispersion of Ag125I in a suitable solution phase, for example an aqueous solution.
It is postulated that in this embodiment the following reactions occur:
Ag+Fe(CN)63xe2x88x92xe2x86x92Ag++Fe(CN)64xe2x88x92
Ag++Brxe2x88x92xe2x86x92AgBr
Ag++125Ixe2x88x92xe2x86x92Ag125I
AgBr+125Ixe2x88x92xe2x86x92Ag125I+Brxe2x88x92
If the I-125 ions are present as a dispersion of Ag125I, some of the Ag125I will gradually dissolve as the immobilisation reaction progresses thus generating I-125 iodide ions in solution. I-125 ions in solution may react directly with the oxidised silver (i.e. the Ag+ cation) to form Ag125I. Alternatively, the oxidised silver may react first with bromide ions to form AgBr, followed by ion-exchange of I-125 iodide for bromide to give Ag125I. Thus both oxidation of the silver and formation of AgBr will result in removal of I-125 from the solution phase. Substantially all of the I-125 from the solution phase is therefore immobilised on the substrate using the method of the invention. The radioactivity of the product is therefore highly dependent on the effective concentration of 125I or on the amount of 125I effectively available in the initial solution phase.
When a plurality of substrates, for example metal wires or metal coated substrates such as metal coated organic compositions including metal coated plastics or polymers, or metal coated inorganic compositions such as metal coated ceramics or glasses are treated together, the nominal amount of radioactive ion that is immobilized on the metal surface of each substrate can vary from substrate to substrate giving rise to a statistically normal distribution of an average amount of radioactivity per substrate. In a kinetically rapid reaction, the width of the statistical distribution may be controlled to some extent by increasing the volume of the reacting solution without increasing the amount of reagents, thereby effectively diluting the reagents and slowing the reaction. In addition, applicants have unexpectedly observed that the presence of a salt additive to the reaction mixture at elevated concentrations can narrow the statistical distribution of the amount of radioactivity per substrate. One possible explanation is that the increased concentration of ions in the solution decreases the solution activity coefficient of the ions of interest (i.e. the radioactive anions and/or the binding agent) and hence slows the reaction.
The concentration of salt additive can range from about 0.01 molar up to saturation levels of the salt in solution, the latter varying as a function of the salt and temperature of the solution. For example, useful salts include NaCl which has a saturation level of about 357 grams per liter in water at 0xc2x0 C. and about 391.2 grams per liter in water at 100xc2x0 C.; KCl which has a saturation level of about 347 grams per liter in water at 30xc2x0 C. and about 567 grams per liter in water at 100xc2x0 C.; CsCl which has a saturation level of about 745 grams per liter in water at 20xc2x0 C. and about 1590 grams per liter in water at 100xc2x0 C.; LiCl which has a saturation level of about 637 grams per liter in water at 0xc2x0 C. and about 1300 grams per liter in water at 95xc2x0 C.; and MgCl2 which has a saturation level of about 542.5 grams per liter in water at 20xc2x0 C. and about 727 grams per liter in water at 100xc2x0 C.; and NaNO3 which has a saturation level of about 921 grams per liter in water at 20xc2x0 C. and about 1800 grams per liter in water at 100xc2x0 C. A number of these chloride and nitrate salts have been evaluated and shown to be effective at narrowing the statistical distribution of the amount of radioactive anion, for example iodide, present from substrate to substrate.
The saturation levels of other useful highly soluble salts can be found in the Handbook of Chemistry and Physics, CRC Press, 55th Edition. Saturated solutions of added salts can be achieved when an excess of undissolved salt is present in the reaction mixture in equilibrium with dissolved salt. The optimum level of ionic strength per added salt or mixtures of added salts which promotes the narrowest distribution of radioactivity uptake per substrate can be readily found by one skilled in the art using routine experimentation. At the end of the immobilisation reaction leading to uptake of radioisotope onto the metal substrate to form a radioactive substrate, excess salts can be removed by washing the substrate with aliquots of water.
Without the added volume or the added salt, the statistical distribution of radioactivity on the individual substrates is critically dependant upon the rate of mixing. Distributions ranging from 5 to 15% (relative standard deviation) are often observed. With the addition of increased volumes, these values drop to  less than 6% (relative standard deviation). Addition of 2 M NaCl unexpectedly results in distributions  less than 3% (relative standard deviation). The additional chloride ions may not take part in the reaction, but may simply decrease the activity coefficient of the reacting ions (e.g., bromide and iodide) thereby decreasing the critical dependence on the rates of mixing of the reagents themselves. It is, however, known that silver chloride is appreciably soluble in concentrated alkali chlorides where chloro complexes are formed (see Cotton, F. A. and Wilkinson, G. in Advanced Inorganic Chemistry, Interscience Publishers, John Wiley and Sons, page 863, 1962).
If the radioactive anion is present as a dispersion or in the form of a complex or a degradable compound, there may be the advantage that thorough mixing of the substrate(s), the oxidizing agent and the source of the radioactive anion occurs before the immobilisation reaction begins, leading to a more even distribution of the radioactive anions over the substrate(s)
The use of organic salts of the radioactive anions might also be useful at slowing the reaction of iodide with the silver wires, for example pyridinium iodides may be useful as an iodide source using this approach. Adding the radioactive anion to the reaction mixture as a solid salt may also be useful as the kinetics of dissolution may slow down the exposure of the wires to solution phase anion until mixing is completed. While the solid salt is not insoluble, the change from the solid phase to the solution phase could accomplish the desired alterations in the speed of the reaction.
In the specific case of the immobilisation of radioactive iodide ions on a plurality of silver substrates using potassium ferricyanide as the oxidising agent and bromide ions as a binding agent, the addition of  greater than 1 M NaCl to the reaction mixture gives rise to a yellow green precipitate shortly after the addition of the potassium ferricyanide. This green precipitate clears as the substrates coat with a mixed silver bromide/silver iodide salt. Chemical analysis of the precipitate shows high levels of silver and trace levels of iron suggesting the nature of the precipitate to comprise silver halide. This precipitation may allow mixing to occur before the bulk of the oxidation takes place, thereby ensuring a better distribution of iodide amongst the individual substrates.
Some metal halides, for example silver halides, are light-sensitive. Among the silver halides, silver bromide is most light-sensitive, followed by silver chloride and silver iodide respectively. One disadvantage of the prior art process of U.S. Pat. No. 4,323,055 for forming silver iodide-coated silver wires was that the light-sensitivity of the silver iodide meant that the process could not be carried out under natural light, but had to be carried out under red light.
A further significant advantage of the method of the present invention is that it need not be carried out under safe lights but can be carried out under normal room (fluorescent) lights. While a colour change is observed during the washing and drying steps from lime green of the initial coated wires to a darker, olive green for dried coated wires, analyses for iodide content either by radiochemical analysis or by the spectrophotometric method described in Example 1 below do not reveal any change in amount or loss of iodide from the coated wires. Better than 99% uptake is consistently achieved under normal, fluorescent lighting. It is possible that since the iodide is distributed throughout the deposited layer using the method of the invention, the light sensitivity is not critical, whereas the previous process resulted in Iodide deposited onto the surface of an existing AgBr coating, thereby exposing the AgI directly to any light incident upon the wires. This significantly improves the ease of manufacture and handling and avoids the need for expensive dark room facilities. It also significantly improves working conditions for those personnel involved in the manufacturing process and improves the morale of the manufacturing team.

Method of coating a metal substrate with a radioactive layer