A dual-compensated cryogenic microcalorimeter for radioactivity standardizations.
Efforts are underway by our laboratory to develop a microcalorimeter that can be routinely used for radioactivity standardizations of nuclides that decay by pure beta-emission or by low-Z electron capture. The prototype calorimeter consists of a cryostat with two temperature-controlled stages and a base stage that are operated at nominal temperatures of 8 K. A unique aspect of the calorimeter's design is the ability to repeatedly engage and disengage the radioactive source from the second stage heat path using a magnetically activated elevator. The measurement of the total power from a radioactive sample is obtained from the difference in the second stage power with and without the source in place. As a result of extensive performance evaluations using 90Sr-90Y and 32P brachytherapy seeds as well as with an internal calibration heater, many initial design flaws have been identified and are being addressed.
Collé
R
R
Physics Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899-8462, USA. rcolle@nist.gov
Zimmerman
B E
BE