[A twin type heat flow microcalorimeter for radioactivity measurement]

A microcalorimeter is described which was developed and tested for measuring the activity of pure beta particle emitters. Two identically made calorimeter cells are used, each 46.5 mm i.d. and 54.0 mm deep and each fitted with thermomodules generating an emf of about 29 mV degrees C-1. The thermal energy from the cells flows into a surrounding mass of aluminium (15 kg) embedded in 30 mm thick styrofoam. The entire assembly is then immersed into an open thermostat bath controlled by electric heaters an arrangement which facilitates access for sample changing. The outputs of the modules (sensors) are connected in opposing polarities, the net output being amplified and this voltage signal is used to estimate the radioactivity in the samples. In order to demonstrate usefulness of this calorimeter, approximately 3.7 GBq(100 mCi) of tritiated water was measured. The result was compared with that of liquid scintilation counting method and found to be agreed within 5%.