An absorbed dose to water calorimeter for collimated radiation fields

A transportable calorimeter of compact design has been developed as a devic e for the absolute determination of the absorbed dose to water. The ease of operation of the calorimeter allows the application in clinical therapy be ams of various energies, specifically for neutron, proton and heavy ion bea ms. The calorimeter requires collimated radiation fields with diameters les ser than 40 mm. The temperature rise caused by radiation is measured with a thermistor probe which is located in the centre of the calorimeter core. T he calorimeter core consists of a cylindrical water-filled gilded aluminium can suspended by three thin nylon threads in a vacuum block in order to re duce the heat transfer by conduction. In addition, it operates at a tempera ture of 4 degreesC, preventing heat transfer in water by convection. Heat t ransfer from the core to the surrounding by radiation is minimised by the u se of two concentric temperature-controlled jackets, the inner jacket being operated at core temperature. A description of the mechanical and electric al design, of the construction and operation of the water calorimeter is gi ven. In addition, calculations with a finite-element program code performed to determine correction factors for various radiation conditions are inclu ded. (C) 2000 Elsevier Science B.V. All rights reserved.