Phase-sensitive Microcalorimetry for Study of Low-level Radioactive SourcesH. Chen-Mayer, R. E. Tosh
NIST, Gaithersburg, MD, USA
Microcalorimetry for standardizing activities of radionuclide samples entails measurements of input power heat flow from the sample cell, with the radioactive sample compared to the reference cell under balanced conditions. The measurement is susceptible to noise due to drift and 1/f effects; thus, a better result might be expected with periodic insertion of the source into the sample chamber and analysis using phase-sensitive methods. The heat source used to simulate the radioactive source heating uses a function generator and high-precision resistors attached to the lid of the sample holder to provide a periodic, square-wave Joule-heating input. Preliminary modeling of the system was carried out in a simplified 2D model to assess the system time and frequency domain response to the heat source.