Design of Active-Type Personal Dosemeter for High-Energy Neutrons
*In order to design an active-type personal dosemeter having sufficient sensitivity to high-energy neutrons up to 100 MeV, the characteristic response of several types of silicon (Si) semiconductor detectors has been investigated experimentally and theoretically. At first, the response of each detector has been checked to protons accelerated by a Van de Graff accelerator installed at Kobe University. A fully-depleted Si detector was selected as a promising detector element owing to a simple structure and comprehensive characteristics. In the next step, neutron irradiation experiments were carried out in a monoenergetic reference field in JAEA. On the other hand, theoretical distributions of the deposited energy were estimated in a simplified geometry consisting of Si and PE layers. An agreement in the relative shape was confirmed between the theoretical and experimental results. Applying this calculation procedure to other neutron energies and various thickness of sensitive layer, it was found that the energy dependence could be improved by the two-window technique by setting different discrimination levels on the pulse height. Another important characteristic of the angular dependence was also discussed for practical application of a personal dosemeter for high energy neutrons.
The determination of the neutron component of cosmic radiation fields in spacecraft
Abstract Poly allyl diglycol carbonate (PADC or CR-39®) etched track detectors may be used to estimate the neutron component of the cosmic radiation in spacecraft using simple techniques developed for neutron personal dosimetry. Electrochemically etched pits are identified and counted using fully automated read-out procedures. The neutron component of the radiation field at the location of the dosimeter will produce electrochemically etchable tracks, as will the proton and energetic heavy charged particle components, depending on particle type, energy and angle of incidence. The response to incident charged particles which produce tracks and are counted as if produced by a neutron, will lead to an over-estimate of the neutron component. A correction can be applied to take account of this, or an additional chemical etch carried out which allows discrimination. Recent results for exposures in low-Earth orbit are reported.
Ten years on : The NRPB PADC neutron personal monitoring service
Development of the NRPB PADC neutron dosimetry system was carried out during the years 1982 to 1985. In 1985 the monitoring service was set up, and following 9 months of operational trials, was given approval by the UK Health and Safety Executive in April 1986. This paper traces the developments, and outlines the present situation. At an early stage it was judged that the most critical component of the system was likely to be the reliable supply of plastic of suitable quality. However, the 'quality' of plastic is very dependent on the processing and read procedures chosen. A commercial manufacturer of PADC was selected, and a two stage etch (chemical, electrochemical) plus a chemical post-etch, was developed which gave adequate dosemeter response characteristics, combined with a low background track density. Rigorous quality control procedures needed to be applied to the sheets of PADC in order to satisfy an operational criterion of a minimum detectable dose of 200 μSv. The choice of reader was made largely on the basis of known reliability. Procedures were kept as simple as possible with the further aim of maximising commonality with other NRPB monitoring systems. The intention was to optimise the system from an operational point of view. This meant, for example, the choice of etch parameters which did not necessarily give the greatest values of sensitivity, but gave values which were less dependent on small changes in plastic properties or etch parameters.