Logarithmic-diode count-rate and period meter

THE DESIRE to achieve safe automatic start-up of nuclear power reactors — especially where rapid starting of marine or airborne reactors is required — has led to attempts to measure transients in neutron flux at power levels that correspond to 10⁻¹⁰, or less, of full operating power. At these levels, one uses instruments such as counters and count-rate meters, that operate on individual neutron detections. Logarithmic count-rate meters are frequently used for convenience in monitoring wide ranges of neutron flux. Furthermore, the variable most commonly used for control during reactor start-up is the time derivative of the logarithm of the neutron flux, which is by definition proportional to the reciprocal of the period.