Development of Air Sampling Technology by the Atomic Energy Research Establishment, Harwell

For many years the Health Physics and Medical Division of the Atomic Energy Research Establishment, Harwell, has pursued a vigorous programme of investigation and development in the field of air-sampling technology. The programme has made important contributions to the development of sampling media, the design of sampling equipment, the characterization of environmental airborne contamination and the interpretation of air-sampling data in terms of personal exposure. These developments form the basis for the present operational and research programmes in this field in the United Kingdom Atomic Energy Authority (U.K.A.E.A). . This paper, which summarizes the advances made in the Harwell laboratories in the above fields, is divided into three sections: 1. Sampling techniques. The development and characterization of glass-fibre filter papers (Stevens and Hounam) with improved surface collection properties has simplified counting procedures and has made ' possible detailed autoradiographic examination of the dust collected. The problem of energy degradation of alpha radiation by absorption in particles and paper has been studied (Stevens and Toureau). Development of charcoal-impregnated papers (Stevens and Hounam) has facilitated the detection and measurement of airborne contamination by iodine vapour. The combination of these papers with granular characoal in the May Pack (May) has given a sampling device which is now in common use for the determination and characterization of atmospheric iodine contamination. The concept and development of the personal air sampler (Sherwood and Greenhalgh) led to a better appreciation of the uncertainties of conventional air sampling and to the first quantitative demonstration of the problems of interpreting air samples in terms of personal inhalation exposure. Work on the design of a size selective head for the personal air sampler has not yet resolved the difficulties. The drawbacks of the cascade impactor as a continuous size selective operational sampler (e.g. its low permissible flow rate and short sampling time) have been overcome by the application of 9 principle not hitherto used in air sampling in which the coarse fraction of the dust is concentrated in the centre of an air stream converging through an orifice (Hounam and Sherwood). This device (the cascade centripeter) and the personal air sampler are being used in the current air-sampling investigation programmes in a number, of U.K.A.E.A. establishments. 2. Sample examination, characterization and interpretation. Autoradiographic techniques developed for examining filter-paper air samples (Stevens) have illustrated the diverse nature of airborne radioactive particles found in active areas. The variability of the concentration of airborne particulate radioactivity has been demonstrated during simulated incidents and during resuspension experiments with a multihead air sampler, with personal air samplers and by measuring the activity collected on a sample paper in the air inlet of a respirator (Jones et al.). Although the development of new instruments and techniques are continuing to emphasize the difficulties of interpreting environmental air samples in terms of personal exposure, their use in careful environmental investigation programmes is leading to a better assessment of hazards in particular operations. 3. Sampling for specific radionuclides. The Electronics and Applied Physics Division at Harwell has developed equipment for continuous air monitoring in plutonium (SM-95/29). One of the most difficult airborne contaminants to monitor is plutonium-241; for this radionuclide the counting of ashed samples in a gas-flow proportional counter has been shown to be an efficient control procedure (Gale and Peaple). A programme of tritium monitoring has culminated in the development of a continuous monitor for tritiated water vapour which can be operated in a high gamma-ray background and is insensitive to radioactive gases (Gibson and Burt). (author)