High detectivity microcalorimeters

Abstract

The minimum power or energy detectable by calorimeters is considered from the point of view of thermal fluctuations. Essential noise, detectivity and figure of merit are defined for power- or energy-measuring calorimeters. The figures of merit of some microcalorimeters are compared. Design considerations for thermophile instruments are analysed. A calorimeter with a single container built on these lines is described and its performance discussed. Its essential features are: heat capacity 10 J degc-1; time constant 180 sec: noise-equivalent power 10-7 w; accuracy to within 0-2%; range 10-1-10-7w.