Geiger tube dosimeter These use a conventional Geiger-Muller tube, typically a ZP1301 or similar energy-compensated tube, requiring between 600 and 700V and pulse detection components. The display on most is a bubble or miniature LCD type with 4 digits and a discrete counter integrated chip such as 74C925/6. LED units usually have a button to turn the display on and off for longer battery life, and an infrared emitter for count verification and calibration. The voltage is derived from a separate pinned or wire-ended module that often uses a unijunction transistor driving a small step-up coil and multiplier stage. While expensive, it is reliable over time and especially in high-radiation environments, sharing this trait with tunnel diodes, though the encapsulants, inductors and capacitors have been known to break down internally over time. These have the disadvantage that the stored dose in becquerels or microsieverts is volatile and vanishes if the power supply is disconnected, though there can be a low-leakage capacitor to preserve the memory for short periods without a battery. Because of this, most units use long-life batteries and high-quality contacts. Recently-designed units log dose over time to non-volatile memory, such as a 24C256 chip so it may be read out via a serial port.
Geiger tube dosimeter These use a conventional Geiger-Muller tube, typically a ZP1301 or similar energy-compensated tube, requiring between 600 and 700V and pulse detection components. The display on most is a bubble or miniature LCD type with 4 digits and a discrete counter integrated chip such as 74C925/6. LED units usually have a button to turn the display on and off for l,onger battery life, and an infrared emitter for count verification and calibration. The voltage is derived from a separate pinned or wire-ended module that often uses ?a unijunction transistor driving a small step-up coil and multiplier stage. While expensive, it is reliable over time and especially in high-radiation environments, sharing this trait with tunnel diodes, though the encapsulants, inductors and capacitors have been known to break down internally over time. These have the disadvantage that the stored dose in becquerels or microsieverts is volatile and vanishes if the power supply is disconnected, though there can be a low-leakage capacitor to preserve the memory for short periods without a battery. Because of this, most units use long-life batteries and high-quality contacts. Recently-designed units log dose over time to non-volatile memory, such as a 24C256 chip so it may be read out via a serial port.