Gain stabiliser in radioactive well logging tool - with light emitting diode supplying reference pulses to photomultiplier tube to compensate gain-variations

摘要

Radioactive well-logging appts. includes a neutron source and a scintillation detector responsive to gamma radiation. A photomultiplier tube forms voltage pulses from light flashes produced by the detector. A gain stabilising arrangement includes a light emitting diode mounted between the scintillation and the photomultiplier. An oscillator drives the diode to emit light pulses which are coupled through a transparent mounting disc to the photomultiplier. The device is mounted in a sonde which is lowered down a borehole into an earth formation to be scanned. The diode produces reference pulses for use in compensating gain variations in the system. The gain stabilising appts. can be easily removed and replaced in the sonde.