Representation of water absorbed dose in collimated mixed neutron-photon field of the PTB

An irradiation facility and the characteristics of the measurement devices are described that are capable to determine the absorbed dose to water in an intense mixed neutronphoton field. The collimated irradiation field of the PTB has a diameter of approximately 40 mm and is generated with the cyclotron beam via the d(Ed = 13.3 MeV)+Be reaction. A water absorbed dose rate of up to 15 mGy/s at a distance of 585 mm from the neutron source can be achieved. The absolute absorbed dose to water is determined with a calorimeter with an uncertainty of less than 2.5%. The water calorimeter is transportable and can be used at the customer's site. A tissue-equivalent ionisation chamber is applied as a secondary standard instrument. The photon dose of the mixed field is determined with a Geiger-Mueller counter. An open-to-air ionisation chamber with an active volume of 0.125 cm3 and made from polymethyl methacrylate is connected to a flexible hose and is operated in a water phantom. It serves as a relative dose transfer device. (orig.)