Calorimeters Dosimetry

Burns, D.T. and Morris, W.T., Recent developments in graphite and water calorimeters for electron beam dosimetry at NPL, Proc. Int. workshop on Water Calorimetry, Report NRC-29637, National Research Council of Canada, Ottawa, Canada (1988) 25-30. 

In case (1) in gamma facilities the dose vs. irradiation time (in plants with no product transport system) or the dwell time (in plants with product transport system) can be measured by using different reference standard, transfer standard, or routine dosimeters. In EB facilities, the dose vs. conveyor speed relationship can be measured mainly with process calorimeters, but other dosimetry systems with quick dose evaluation capabilities after irradiation can also be used for this purpose. 

Calorimetry is an absolute method of dosimetry, since almost all absorbed radiation energy is converted into heat that can be readily measured as a temperature rise of the calorimetric body. Calorimeters that are used as primary dosimeters do not require calibration and, ideally, their response is independent of dose rate, radiation characteristics, and environmental factors (Domen 1987). The calorimeters that are used in radiation processing for the measurement of absorbed dose are relatively simple and need calibration (ISO/ASTM 2003b). The use of calorimeters as primary standard dosimeters for electron beam irradiation is described by McEwen and Dusatuoy (2009) and for gamma irradiation by Seuntjens and Duane (2009). 

Two types of calorimeters are used in radiation dosimetry, i.e., the total energy absorption calorimeters (e.g., to determine the energy or power of a particle beam) and thin calorimeters that are partially absorbing and used to measure absorbed dose. The temperature of the calorimeter can be measured either during irradiation (online) or before and after irradiation (ofif-line). 

Semi-adiabatic calorimeters have been designed for dosimetry at high-energy electron accelerators (1-10 MeV) both for calibration and for routine process control (Humphreys and McLaughlin 1989 Miller and Kovacs 1985 Burns and Morris 1988) and also for low energies between 100 keV and 500 keV (Janovsky and Miller 1987). The disc-shape absorber is either water or graphite containing thermistors for temperature measurement placed in the center of the absorber. The absorber is placed in polystyrene foam insulation. 

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