title: The evaluation of nylon and polyethylene as build-up material in a neutron therapy beam.
abstract: In high-energy neutron beams a substantial amount of build-up material is required to irradiate biological samples under conditions of charged particle equilibrium. Ideally A-150 tissue-equivalent plastic is used for this purpose. This material is however not always readily available and hence the need for a substitute compound. The selected hydrocarbon should satisfy two requirements: the quality of the radiation on the distal side needs to be the same as that measured for A-150 plastic and the absorbed dose should remain consistent. A tissue-equivalent proportional counter operating at reduced pressure not only measures the absorbed dose accurately but provides a means for assessing the nature of a radiation field in terms of a secondary charged particle spectrum. Using build-up caps manufactured from nylon (type 6) and polyethylene, it is shown that the former is an acceptable substitute for A-150 plastic. The data further demonstrate that both the absorbed dose and the spectral character of the measured single-event distribution are altered when polyethylene is used and that these discrepancies are attributable to the higher hydrogen content of polyethylene.
authors.affiliation: National Accelerator Centre, Faure, South Africa.
authors.forename: J H
authors.initials: JH
authors.lastname: Hough
authors.forename: P J
authors.initials: PJ
authors.lastname: Binns
mesh_terms: D006801:Humans; D008961:Models, Structural; D017247:Neutron Capture Therapy / Q000295:instrumentation; D009757:Nylons; D011095:Polyethylenes; D011879:Radiotherapy Dosage
chemical_list: D009757:Nylons; D011095:Polyethylenes