Using a water calorimeter, the absorbed dose to water from low LET (linear energy transfer) ionizing radiation such as high energy x rays and by [gamma] rays is obtained by measuring the temperature rise produced in the water by the absorbed dose and correcting for the effect of other materials (walls, etc.) on the temperature rise.
Recently, the decision was made to operate the NRC "sealed" water calorimeter at 4 [degrees]C in order to avoid the convective heat transfer that occurs at 21 [degrees]C (6).
Shortt, The NRC Sealed Water Calorimeter: Correction Factors and Performance, A.
Domen, An absorbed dose water calorimeter: theory, design, and performance, J.
Many water calorimeters are operated at 4 [degrees]C.
We have published two reaction models for calculating the heat defect for aqueous solutions used in water calorimeters. Model II was published in 1991 (2) and an "improved" model, model III, in 1997 (1).
suggest the fault lies with the NIST water calorimeter being operated at 22 [degrees]C and the method with which the measurements were made.
Key words: absorbed dose; calorimeter; convection; excess heat; finite element analysis; thermistor; water calorimeter.
The first part of this paper presents results of a detailed analysis of the dissipation of the excess heat in the temperature probes used to measure absorbed dose in a water calorimeter. Earlier papers (2,3) presented only a rough estimate of the upper limit of this effect as afunction of time after radiation.
Sensitive measurements showed that there was no internal convection within the cylinder when the water calorimeter was radiated with a collimated [[blank].sup.60]Co beam directed vertically downward.
Domen, A sealed water calorimeter for measuring absorbed dose, J.