Abstract
Heavy ion accelerators presently serve not only for solving scientific problems. A large portion of the operating time of accelerators is allotted for applied purposes. Moreover, heavy ion accelerators intended only for commercial use are being created. An acceler ator complex is already a production tool and should be optimized with respect to its parameters for solving a specific problem. A very important parameter of such a complex is its cost. The problem of creating optimal biological protection of an accelerator is becoming urgent since it comprises a considerable share of the cost.
Abstract
A distinctive feature of the creation of commercial accelerators is the rejection of universality. For exam ple, accelerators for the production of track mem branes are being built for accelerating a particular set of ions from argon and heavier. The energy of the ions is fixed, without the possibility of changing it, and as a rule is selected in the range from 1 to 5 MeV/nucleon. Radiation injuries during passage of ions through a substance are maximum in the indicated range.
Abstract
Biological protection of the accelerator and devices should correspond to the range of energies and set of ions. Unfortunately, in the indicated range there are few investigations related to radiation accompanying the process of acceleration of ions and their use. We can indicate only works [1][2][3][4], in which the yield, angular distribution, energy spectrum or dose rate from neutrons produced in reactions of ions not heavier than neon with targets made from structural metals in the energy range higher than 2-3 MeV/nucleons were studied. But these data are clearly insufficient for calculating optimal protection and there are no data for heavier ions. , and Xe +20 ions with a fixed 2.5 MeV/nucleon energy were obtained on this cyclotron. Preliminary data for calculating biological protection were obtained as a result of investigations conducted on the Alfa irradia tion complex [6] constructed in Dubna. The complex includes the CYTRACK cyclotron accelerating Ar +8 ions with 2.4 MeV/nucleon energy and intensity up to 0.2 μA. After startup of the DC 110 cyclotron, new data were obtained and previous data were refined thanks to substantially better statistical reliability.
Abstract
The irradiation complex is composed of an isoch ronous cyclotron, extracted beam transport system, and device for irradiating polymer film.
Abstract
When designing biological protection and organiz ing safe servicing of the device, it is most important to know such parameters as:
Abstract
1. Neutron yields during interaction of ions with various materials; 2. angular distributions of neutrons relative to beam axis.
Abstract
It was known after the Alfa complex comissioned that the neutron flux in the room of the device was not very great, and therefore a detector with maximum sensitivity was selected for measuring neutron yields. The SNM 18 neutron detector in a polyethylene moderator was selected for measuring neutron yields. The dependence of the function of detector sensitivity on neutron energy with the use of moderators of dif ferent sizes was studied in [7, 8]. On the basis of the data given in [1, 2] on neutron energy spectra upon interaction of the investigated ions with a substance, a detector with an 8 inch diameter moderator was Abstract-Neutron yields during irradiation of structural metals and polymer film by argon, krypton, and xenon ions with 2.4 and 2.5 MeV/nucleon energies are measured on the CYTRACK and DC 110 cyclotrons. The angular distributions of neutrons from the target are measured. The LISE ++ is used for extrapolating the data obtained to other ions, their energy, and to other targets. The program was tested on experimental data found in the literature. As a result of comparison, it is established that the calculation results coincide with the experimental data within a coefficient of two.

Heavy ion accelerators presently serve not only for solving scientific problems. A large portion of the operating time of accelerators is allotted for applied purposes. Moreover, heavy ion accelerators intended only for commercial use are being created. An acceler ator complex is already a production tool and should be optimized with respect to its parameters for solving a specific problem. A very important parameter of such a complex is its cost. The problem of creating optimal biological protection of an accelerator is becoming urgent since it comprises a considerable share of the cost.

A distinctive feature of the creation of commercial accelerators is the rejection of universality. For exam ple, accelerators for the production of track mem branes are being built for accelerating a particular set of ions from argon and heavier. The energy of the ions is fixed, without the possibility of changing it, and as a rule is selected in the range from 1 to 5 MeV/nucleon. Radiation injuries during passage of ions through a substance are maximum in the indicated range.

Biological protection of the accelerator and devices should correspond to the range of energies and set of ions. Unfortunately, in the indicated range there are few investigations related to radiation accompanying the process of acceleration of ions and their use. We can indicate only works [1] [2] [3] [4] , in which the yield, angular distribution, energy spectrum or dose rate from neutrons produced in reactions of ions not heavier than neon with targets made from structural metals in the energy range higher than 2-3 MeV/nucleons were studied. But these data are clearly insufficient for calculating optimal protection and there are no data for heavier ions. ions with 2.4 MeV/nucleon energy and intensity up to 0.2 μA. After startup of the DC 110 cyclotron, new data were obtained and previous data were refined thanks to substantially better statistical reliability.

The irradiation complex is composed of an isoch ronous cyclotron, extracted beam transport system, and device for irradiating polymer film.

When designing biological protection and organiz ing safe servicing of the device, it is most important to know such parameters as:

1. Neutron yields during interaction of ions with various materials; 2. angular distributions of neutrons relative to beam axis.
MEASUREMENT INSTRUMENTS
It was known after the Alfa complex comissioned that the neutron flux in the room of the device was not very great, and therefore a detector with maximum sensitivity was selected for measuring neutron yields. The SNM 18 neutron detector in a polyethylene moderator was selected for measuring neutron yields. The dependence of the function of detector sensitivity on neutron energy with the use of moderators of dif ferent sizes was studied in [7, 8] . On the basis of the data given in [1, 2] on neutron energy spectra upon interaction of the investigated ions with a substance, a detector with an 8 inch diameter moderator was selected for both CYTRACK and DC 110 accelera tors. This detector has maximum sensitivity precisely in the neutron energy region of interest to us.
MEASUREMENT INSTRUMENTS
The ambient neutron dose rate measurements were less sensitive, but checked by a DKS 96n dosimeter. The moderator of the dosimeter has a 10 inch diameter.
MEASUREMENT INSTRUMENTS
The neutron detectors were located in the median plane of the beam at a height of 130 mm above the concrete floor level.
METHOD OF TAKING MEASUREMENTS
For taking measurements on operating commercial accelerators, it is necessary to adapt to actual condi tions; there is no possibility here to construct any kind of additional apparatus or devices. Measurements were taken in the very same room where the accelera tor is located.
METHOD OF TAKING MEASUREMENTS
Diagnostic box located at a distance of about 6 m from the accelerator in the beam transport channel was used; when measuring of neutron and their angu lar distributions are carry out. The box is equipped with beam profilometer and Faraday cup.
METHOD OF TAKING MEASUREMENTS
The ion beam size and shape were preliminarily measured by a profilometer. Then the investigated tar get was attached on it. With the use of a transporting and focusing system, a 2 × 3 cm beam was formed and aimed at the target to avoid an increased local heat load. The target size was 5 × 10 cm. The ion beam cur rent was preliminarily measured by a Faraday cylinder when the target was extracted. The stability of the beam current was monitored. It was established that fluctuations of the beam current didn't exceed 5%.
METHOD OF TAKING MEASUREMENTS
As follows from the description of the experimental conditions, they weren't ideal. When measuring the yields, it wasn't possible to install any additional pro tection in order to distinguish a specific source of neu trons. Owing to this, in addition to neutrons from the target, neutrons from other sources, e.g., from the accelerator of the beam transport system, could have contributed to the results of measurements by means of a detector installed at some point.
METHOD OF TAKING MEASUREMENTS
So that the contribution of neutrons from the investigated target is determining, it is desirable to take measurements as close as possible to it. But in that case, the size of the detector with a moderator 8 inches in diameter and 40 cm long becomes comparable to the distance to the radiation source (R), which leads to a difference of the dependence of the detector readings from the 1/R 2 law. In that case, to obtain data in abso lute units, it's necessary to calibrate the detector read ings at each measurement point.
METHOD OF TAKING MEASUREMENTS
Calibration was done by installing a Pu-Be source with a yield of 1 ± 0.1 × 10 5 neutrons/s at the target site with the accelerator disconnected. Measurements of the count of detectors at points at distances of 1 m, 2 m, and 3 m from the target at an angle of 90° to the beam axis and at a distance of 2 m at other angles were taken. In so doing, consideration of the effect on the measurement results of neutron attenuation and scat tering by all matter surrounding the source was achieved automatically.
METHOD OF TAKING MEASUREMENTS
The contribution of neutrons from other sources exclusive of the target, was measured on the DC 110 cyclotron at these same points during irradiation by Ar, Kr, and Xe ions, for which a tantalum plate was installed at the site of the target. The threshold energy for a nuclear reaction on tantalum is about 5 MeV/nucleon, and the neutron yield from such tar get at an energy of 2.5 MeV/nucleon is negligibly small. As a result, it was established that, when mea suring neutron yields from the investigated targets, the contribution of neutrons from other sources in the worst case didn't exceed 10%; nevertheless, this con tribution was always subtracted from the measurement results. It can be pointed out that the regularity of the dependence of the results on target distance matches well the dependence of the measurement results with the Pu-Be neutron source. The fact that the contri bution of neutrons from other sources is measured with sufficient accuracy is demonstrated by this.
METHOD OF TAKING MEASUREMENTS
Measurements with Be, C, Al, and Cu targets were taken on Ar, Kr, and Xe ion beams with 2.5 MeV/nucleon energy. The neutron yield from a stainless steel 12Kh18N10T target was additionally investigated on an argon beam since this is the most widespread structural material on accelerators. Mea surements of the neutron flux were taken at angles of 30°, 45°, 60°, 90°, 135°, and 150° to the beam axis.
METHOD OF TAKING MEASUREMENTS
The neutron yield during irradiation of a polymer film by argon ions was measured on the Alfa irradia tion complex. Such investigations weren't conducted on the DC 110 cyclotron.
MEASUREMENT RESULTS
The total neutron yield was calculated by integra tion of the angular distribution measured in accessible regions of the angles. As shown in [2, 3] , the angular distribution of neutrons during bombardment by heavy ions is described satisfactorily by the semiem pirical formula: f(Θ) = (4πln(1 + 1/γ)(γ + sin 2 Θ/2)) -1 ,
MEASUREMENT RESULTS
where Θ is the angle to the beam axis and γ is a param eter which must be determined experimentally for each specific ion, its energy, and target material. For describing the measured angular distributions by means of formula (1), the parameter γ is selected according to the measurement results at angles 30°, 45°, 60°, and 90°. In the case of irradiating Al and Cu targets, the description of distributions by formula (1) is satisfactory in the region of all angles. In the case of Be and C targets, the measurement results are described satisfactorily by formula (1) in the region of front angles, but an isotropic distribution not corre

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