Investigation of room scattered neutrons and their importance for the calibration of albedo dosemeters

In routine monitoring the energy response of personnel dosemeters is such that there is a need for a more or less sophisticated field calibration of dosemeters in each stray neutron field. Survey meters used as a reference for the actual dose equivalent as well as albedo dosemeters are highly energy dependent and therefore sensitive to room scattered neutrons. In contrast to the standard calibration technique with the aim of scatter free calibration conditions, the field calibration has to take into account the total dosemeter reading and the actual dose equivalent without subtracting the contribution of room return neutrons. For the purpose of field calibrations the scattered neutron component has been investigated in the environment of a Cf-252 neutron source as a function of source distance and at different heights above floor using the Anderson-Braun counter, the 30 cm polyethylene sphere and albedo neutron dosemeters. Differences in estimating the source detector constant using the shadow-cone method and the semi-empirical method recommended by Eisenhauer and Schwartz are explained by detector characteristic effects. On the basis of experimental results the paper discusses the room scattered component of the detector reading, the differences in calibration factors derived from standard, routine and field calibrations as well as the general aspects of field calibration in personnel monitoring