10 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 b y the UK Health and Safety Executive in April 1986. This paper traces the developments, and outlines the present situation. At an early stag e it was judged that the most critical component of the system was lik ely 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, an d a two stage etch (chemical, electrochemical) plus a chemical post-et ch, was developed which gave adequate dosemeter response characteristi cs, combined with a low background track density. Rigorous quality con trol procedures needed to be applied to the sheets of PADC in order to satisfy an operational criterion of a minimum detectable dose of 200 mu Sv. The choice of reader was made largely on the basis of known rel iability. 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 et ch parameters.