Peak detector circuitry for use in nuclear logging apparatus

In the nuclear logging apparatus radiation detectors output signals via a multiplexer (176, Fig 24, not shown) to a programmable gain amplifier (178) which improves signal to noise ratio and quantifies pulse amplitudes within predetermined spectral limits. The output signal from the PGA is received by peak detection means 180 which converts the signal to a stable DC pulse for digitising by an A/D converter (184). The peak detection circuit includes a first unitary gain follower U9 through which a memory capacitor C57 is charged to the same voltage as the input pulses, a second unitary gain follower U12 to isolate the capacitor from the output, and a digital comparator U10 which opens a switch SW1 when the input pulse reaches its peak to isolate the memory capacitor.