A water calorimeter for neutron dosimetry

A water calorimeter has been used for the direct measurement of absorbed dose to water in a d(15)+Be neutron beam. The absorbed dose measured with the calorimeter was compared with that measured with an Exradin ionisation chamber, constructed of A-150 plastic. The doses measured by the ionisation chamber were calculated according to the European (ECNEU) protocol. Absorbed dose to tissue measured with the calorimeter was 4.3% lower than that measured with the ionisation chamber. Relative to ionisation chamber dosimetry, dose measurements with the calorimeter in the neutron beam were 9% lower than similar measurements in 4 and 9 MV photon beams. The significance of the results is discussed in terms of the heat defect in water. (author)