Assessment of occupational exposure in New Zealand from personal monitoring records

This paper assesses recent occupational exposures in New Zealand based on doses reported by the National Radiation Laboratory (NRL) monitoring film service. Beginning in 1996, doses reported to monitored groups by NRL have been entered in a data base which records for each measured film details such as wearing position, wearing period and assessed dose. Although all details have not been systematically provided, the data base offers the potential for assessing cumulated doses to monitored personnel. In such an assessment matters to be taken into account are the handling of incomplete data, the derivation of effective doses from reported doses, particularly when protective clothing is being worn, and the treatment of doses below reporting levels. Algorithms for relating reported doses for badges worn with or without protective aprons and for different badge wearing positions (collar, under apron, over apron) have been developed based on published effective dose to Hp(10) ratios. For a sample of 2844 persons continuously monitored for more than one year only 52 (1.8 %) received doses exceeding 1 mSv/y, and 77 % received no detectable exposure at all. No individual approached the dose limit of 20 mSv/y recommended by the ICRP, and only one individual accumulated more than 5 mSv/y. As observed in a review of occupational exposures 15 years ago the highest mean annual dose was recorded by industrial radiographers, although the current mean dose at 0.8 mSv is well below the 2.3 mSv (effective dose equivalent) found over 1984/85 when a greater volume of industrial work was being carried out within the country. Nuclear medicine workers were again in second position with 0.65 mSv/y, but this was also less than the 1.4 mSv mean annual dose found over 1984/85. With the growth in interventional radiology, cardiologists emerge as a group with significant collar exposures, and also nurses and medical radiation technologists working in theatres where such work is carried out may receive comparable exposures. Apart from these small groups or sub-groups, most persons monitored for occupational exposure receive doses which are either zero or well within the variations of natural radiation exposure from place to place within New Zealand. Copyright (2000) Australasian Radiation Protection Society Inc