Thermoluminescent dosimetry for fast neutron beams using CaF2: Mn

A comparison of two methods of in vivo dosimetry for a high energy neutron beam

Two methods of in vivo dosimetry have been compared in a high energy neutron beam. These were activation dosimetry and thermoluminescence dosimetry (TLD). Their suitability was determined by comparison with estimates of total dose, obtained using a tissue equivalent ionization chamber. Measurements were made on the central axis and a profile of a 10 x 10 cm square field and also behind a shielding block in order to simulate conditions of clinical use. The TLD system was found to provide the best estimate of total dose.

The response of thermoluminescence dosemeters to fast (14-7 MeV) and thermal neutrons

The response of common TLD materials has been measured in a 14-7 MeV neutron field with a small and well known gamma component. Values for the thermal neutron response of some TLD materials with low thermal neutron sensitivity have been determined in the NPL standard thermal flux facility.

Transfer dosemeters for fast neutron sources

The increasing use of fast neutron sources in radiobiology, radiotherapy, etc. makes dosimetry intercomparisons (intercalibrations) by mail desirable. After comparing the relative advantages and disadvantages of the various available integrating fast neutron detectors, fission fragment track etching was chosen because such detectors can be made sufficiently small, rugged, fading resistant, inexpensive and accurate. Using several combinations of 232Th or 237Np as fissile materials, and organic and inorganic track detectors, it was established that both automatic spark counting and visual track counting techniques can be developed to cover the desirable dose range (approximately 50-500 rad) with sufficient accuracy (sigma less than or equal to 5%). One possible source of errors is the overlapping size distributions of fission fragment and recoil particle tracks in organic foils exposed at high neutron energies. Several approaches to reduce this problem are discussed.