[en] The plutonium and americium components in the authorised discharges from BNFL Sellafield are rapidly removed from Irish Sea seawater onto the particulate phase. These actinides tend to be concentrated in fine sediment deposits on the Irish Sea bed and in estuaries where fine sediment accumulates. This paper focuses on these estuarine areas and brings together the available data on the levels and distributions of Pu and Am within the estuarine sediments. The results from field and laboratory experiments which have been undertaken in order to determine the degree of Pu and Am remobilisation, and the mechanism responsible, are also reviewed. These sediment-associated actinides may undergo both chemical and physical remobilisation, leading to increased dissolved concentrations in low-salinity waters and to apparent losses from the estuary on the sediment phase under certain conditions. Saltmarsh sediments are demonstrated to be the most important reservoirs for Pu and Am. The radiological significance of the levels of Pu and Am found in these and in other sediments is summarised, by comparison with GDLs. The appropriateness of GDLs for assessing the radiological significance of Pu and Am in these saltmarsh sediments is discussed. A more site-specific assessment methodology is recommended. (author)

[en] Several recent measurements of the absolute emission probability of the 1001 keV gamma ray of Pa-234m have resulted in doubts concerning the recommended decay for this radionuclide. A value of 0.00590(10) has been adopted in previous evaluations on the basis of a single datum generated by Bjornholm and Nielsen (1963). However, more recent gamma-ray studies by Moss (1986), Scott and Marlow (1990), Siemon et al (1992), and Lin and Harbottle (1992) are in good agreement to give a newly recommended value of 0.00835 ± 0.00011. Some of these recent measurements also include new gamma-ray data for Pa-234g decay. Thus, comprehensive re-evaluations have been undertaken of the decay schemes for both radionuclides, and the resulting data have been included in the UK Heavy Element and Actinide Decay Data library (UKHEDD-2). The new value for the 1001 keV gamma-ray emission of Pa-344m should provide a consistent basis for measurement and reporting of this radionuclide in environmental monitoring programmes. (author)

[en] Recent gamma-ray spectroscopy measurements have highlighted problems in determining the Pa-234m and Th-234 content of environmental samples. These radionuclides are daughters of U-238 and should rapidly reach secular equilibrium, and maintain this balance between their measured activities. A detailed evaluation of the relevant nuclear decay data by Nichols and Toole (1) has resulted in a significant revision of the recommended emission probability of the 1001 keV gamma ray of Pa-234m from 0.00590 ± 0.00010 to 0.00835 ± 0.00011. However, intercomparison exercises between laboratories have continued to indicate a discrepancy between the measured activities of Th-234 and Pa-234m, and hence a detailed study of the decay data for Th-234 has been undertaken. This re-evaluation had generated a recommended value for the emission probability of the 63.3 keV gamma ray of Th-234 of 0.037 ± 0.002, compared with values between 0.040 and 0.048 from previous evaluations. A detailed examination has been made of the gamma-ray spectroscopic methods adopted for low-energy gamma-ray measurements as applied to Th-234. Such quantitative studies are relatively difficult, and therefore a recommended procedure is given in this paper, together with experimental and computer-modelling validations. Measurements were undertaken on four silt samples from the Ribble Estuary using this procedure and the recommended emission probability data: such a combination of improvements resulted in good agreement between the Th-234 and Pa-234m activities in secular equilibrium. (author)

[en] Samples of atmospheric particulate material and rainwater from sampling stations in the United Kingdom have been collected and analysed for selected radionuclides. Results of the analyses of these samples are presented for 1994 and 1995. Average concentrations of Cs-137 in air during 1995 are similar to those observed in 1994. The measured concentrations remain less than 0.1% of those in 1986, the year of the Chernobyl nuclear power reactor accident, and are of negligible radiological significance. Pu-(239+240) concentrations in air and rainwater were a very small fraction of the National Radiological Protection Board's Generalised Derived Limit for members of the public. Estimates are given of the world-wide deposit of Cs-137 and Sr-90 to the end of 1995. There has been no significant input of these radionuclides into the global environment since 1986 and the estimated deposits continue to decline through radioactive decay. (UK)

[en] An assessment has been carried out of the radiological impact of artificial radionuclides in the Esk estuary in Cumbria, UK. Measurements were made of the distributions of ¹³⁷Cs, ^239+240Pu, and ²⁴¹Am in water, surface bed sediments and core profiles. The highest measured concentrations in surface sediments were 2.8 Bq g^-1 of ¹³⁷Cs, 3.1 Bq g^-1 of ^239+240Pu and 4.7 Bq g^-1 of ²⁴¹Am. These values represent significant decreases from similar measurements made in 1970-1980. The measured behaviour of the actinides in low salinity water at the head of the estuary supports previous observations of actinide remobilisation from the bed. A model has been developed which simulates the long-term behaviour of radioactivity in the estuary. The model incorporates representations of tidal mixing, sediment transport, seasonal and long-term sediment accretion. The model also represents long-term build-up in salt marsh regions. The model gives good agreement with measured distributions of ¹³⁷Cs, but tends to underestimate actinide concentrations by factors of 2-3. Dose calculations show the importance of radionuclide uptake through livestock grazing sea-washed pasture alongside the estuary. ¹³⁷Cs and ²⁴¹Am are identified as the most important radionuclides considered in the assessment. (Author)

[en] The particle track analysis and α-spectrometric techniques have been applied to a comparative study of excess ²³⁰Th dating of three deep-sea cores from the Eastern Atlantic. Both methods yield similar sediment accumulation rates. Limitations of the α-track phase of the particle track detection process, arising from the non-specific determination of ²³⁰Th and from the mobility of some alpha-emitting daughters, suggest that details of the sedimentation record may fail to be identified. The conventional radiochemical technique, on the other hand, specifically isolates all the radionuclides of interest but at the expense of a more complex experimental procedure and a longer sample processing time. The combined particle track technique (i.e. α and fission track analyses) therefore seems excellently suited to a complementary role in tandem with the α-spectrometric method of ²³⁰Th dating. Uranium determination by the fission track technique is accurate and rapid, showing good agreement with the α-spectrometric method. (author)

[en] Samples of atmospheric particulate and rainwater have been collected from the United Kingdom and elsewhere. Results are presented of analyses of these samples for various fission products and certain other radionuclides. Average concentrations of Cs-137 in air in the United Kingdom in 1992 were about 60% of those measured in 1991 and less than 0.1% of those in 1986, the year of the Chernobyl nuclear power reactor accident. Pu-(239+240) concentrations in air and rainwater were a very small fraction of the National Radiological Protection Board's Generalised Derived Limit for members of the public. Estimates are given of the worldwide deposit of Cs-137 and Sr-90 to the end of 1992. (author)

[en] Samples of atmospheric particulate and rainwater were collected from the United Kingdom and elsewhere. Results are presented of analyses of these samples for various fission products and certain other radionuclides. Average concentrations of Cs-137 in air in the U.K. in 1991 were similar to those measured in 1990 and less than 0.1% of those in 1986. Pu-(239+240) concentrations in air and rainwater were a very small fraction of the National Radiological Protection Board's Generalised Derived Limit for members of the public. Estimates are given of the worldwide deposit of Cs-137 and Sr-90 to the end of 1991. Gamma and beta-ray dose rates from fallout at Chilton are estimated. (author)

[en] Samples of atmospheric particulate and rainwater have been collected at sampling stations in the United Kingdom. Results are presented of analyses of these samples for various fission products and certain other radionuclides. Average concentrations of Cs-137 in air in the United Kingdom in 1993 indicate a slight increase compared with those measured in 1992. However, the measured concentrations remain much less than 0.1% of those in 1986, the year of the Chernobyl nuclear power reactor accident. Pu-(239+240) concentrations in air and rainwater, including those observed following an accidental release from BNFL Sellafield, were a very small fraction of the National Radiological Protection Board's Generalised Derived Limit for members of the public. Estimates are given of the worldwide deposits of Cs-137 and Sr-90 to the end of 1993. (author)

[en] This communication reports the development of an analytical method for the measurement of low-levels of lead-210 in natural waters via measurement of the beta activity of its in-grown bismuth-210 daughter. The analysis essentially consists of three stages: (a) Pre-concentration of the lead-210 in a known volume of water by co-precipitation with a mixed barium/lead sulphate, where the efficiency of the step is determined by gamma measurement of a barium-133 internal tracer; (b) Separation of the in-grown bismuth-210 from its lead-210 parent by solvent extraction of a bismuth carrier into a solution of diethylammonium diethyldithiocarbamate (DDTC) in chloroform; and (c) Preparation of a bismuth oxychloride source for gross beta counting to determine the bismuth-210 activity. The reported method is capable of achieving a detection limit (4σb) of <10 mBq/l