‘Detectivity’: the Reciprocal of Noise Equivalent Input of Radiation

THERE is a perfectly sound and well-known way of stating the ability of a radiation detector to detect weak signals. One simply states the amount of input radiation that produces a steady electrical output equal to the root-mean-square noise voltage, under conditions of measurement that are stated adequately. But unfortunately the noise equivalent input suffers from a crippling psychological defect: it is upside down—the better detector has a lower noise equivalent input.