Thermoluminescent dosimetry for fast neutron beams using CaF₂:Mn

Abstract

Calcium fluoride (Mn) Teflon thermoluminescent dosimetry (TLD) has been used for dosimetric studies of the fast neutron beam from the MRC Cyclotron. The very small intrinsic sensitivity of this phosphor to fast neutrons makes it suitable for investigating the gamma contribution in the field. The percentage of dose due to y-rays was found to be 5yo, in reasonable agreement with a measurement of 3% using photographic film. Exposures in pairs, one in a hydrogenous surround (polythene), the other in lead, enable the gamma and neutron components to be memured separately. This method has been applied to depth dose studies in tissue-equivalent phantoms.The dosemeters were discs 0.13 x 6.0 mm and the read-out instrument used was Conrad Type 5100. Reproducibility of 376 has been obtained using a controlled calibration and annealing technique. The angular response severely limits its application in clinical use.

The response of thermoluminescence dosimeters to fast (14.7 MeV) and thermal neutrons

“…The higher values of some of the earlier work may to some extent be explained by the use of containers of different materials, for example, aluminium in which sensitization is enhanced through ( n , p ) and (n, a ) reactions and the induced radioactivity. The cross-sections of the corresponding reactions in 19F are about 20% of those in 27Al and hence a PTFE container would contribute less to the response, as has been found by Blum, Bewley and Heather (1973) and Greene and Miles (1976).…”