Current-Sensitive Nuclear Instrument

Abstract

The radiation detector is by nature a current generator of high output impedance. A current sensitive amplifier of low input and high output impedance can be devised for incorporation in a nuclear electronic system, providing a matched impedance at the terminal of the detector cable. The amplifier output is given by i×Ai (i: detector current output pulse, Ai: current amp. gain), when the amplifier rise time (t r ) is faster than the current pulse rise time. Meanwhile, when t r , is longer than the current pulse width, the output should be defined by Q/t r ×Ai (Q: detector output charge) in amp/coulomb units. The rise time of fission counters, BF3 counters, PR gas-flow proportional counters and inorganic scintillators with conventional photomultipliers is short and is even shorter in the case of fast photomultipliers combined with organic scintillators and semi-conductor detectors. Thus marked improvement in signal-to-noise ratio can be expected from a current-sensitive system, and this has been proved even with a slow amplifier (t r =200 ns), not to mention what can be expected with a faster amplifier (t r <20 ns). G-M tubes are inherently, slow, and combination with slow amplifiers does not distort the current pulse shape. Current pulse transmission via. cable is more rational and easier than the conventional voltage pulse transmission. In the present study, G-M tube current pulses were successfully sent over a distance of 1 km without any preamplifier or pulse transformer.