The new NMi orthovolt x-rays absorbed dose to water primary standard based on water calorimetry

Phys. Med. Biol. 53 (2008) 3531–3542. doi:10.1088/0031-9155/53/13/009.
L.A. de Prez and J.A. de Pooter

Abstract
A new water calorimeter for orthovolt x-rays has been developed at NMi. The purpose of this calorimeter is to provide calibrations in terms of absorbed dose to water. Four internationally accepted CCRI qualities (100–250 kV) have been characterized. Correction factors have been determined with measurements, Monte Carlo calculations and heat transport models. The results of the calculations have been validated against measurements. The absorbed dose to water calibration coefficient, NDw,WCM, with the new calorimeter has been compared to the NDw,NCS based on an air-kerma calibration coefficient, using the current NCS-10 dosimetry protocol. A good agreement is found for all beam qualities where the total uncertainty (1 SD) has decreased from 2.5% for NDw,NCSto better than 1.5% for NDw,WCM, using the new water calorimeter.

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