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Lal R, Fifield LK, Tims SG, Wasson RJ. 239Pu fallout across continental Australia: Implications on 239Pu use as a soil tracer. JOURNAL OF ENVIRONMENTAL RADIOACTIVITY 2017; 178-179:394-403. [PMID: 28939090 DOI: 10.1016/j.jenvrad.2017.08.009] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/05/2016] [Revised: 07/21/2017] [Accepted: 08/14/2017] [Indexed: 06/07/2023]
Abstract
At present there is a need for the development of new radioisotopes for soil erosion and sediment tracing especially as fallout 137Cs levels become depleted. Recent studies have shown that 239Pu can be a useful new soil erosion and sediment radioisotope tracer. 239Pu was released in the major atmospheric nuclear weapons tests of 1950's and 1960's. However 239Pu has a half-life of 24110 years and more than 99% of this isotope is still present in the environment today. In contrast 137Cs with a half-life of 30.07 year has decayed to <35% of initially deposited activities and this isotope will become increasingly difficult to measure in the coming decades especially in the southern hemisphere, which received only about a third of the total global fallout from the atmospheric tests (UNSCEAR, 2000). In this study an assessment of the 239Pu fallout in Australia was carried out from comparison of measured 239Pu inventories with expected 239Pu inventories from fallout models. 239Pu inventories were also compared with rainfall and measured 240Pu/239Pu ratios across Australia. 239Pu fallout inventories ranged from 430 to 1461 μB/cm2. Central Australia, with fallout 107% in excess of expected values, seems to be strongly impacted by local fallout deposition. In comparison other sites typically show 5-40% variation between expected and measured fallout values. The fallout inventories were found to weakly correlate (using power functions, y = axb) with rainfall with r2 = 0.50 across the southern catchments (25-40°S latitude band). Across the northern catchments (10-25°S latitude band) fallout showed greater variability with rainfall with r2 = 0.24. Central Australia and Alice Springs which seem to be strongly impacted by local fallout are excluded from the rainfall correlation data (with these sites included r2 = 0.08 and r2 < 0.01 respectively). 240Pu/239Pu atom ratios range from 0.045 to 0.197, with averages of 0.139(0.017), 0.111(0.052) and 0.160(0.027) in the 10-20°S, 20-30°S and 30-40°S latitude bands respectively. The 240Pu/239Pu atom ratios in Central Australia (0.069) likely represent fallout from the Australian tests which also have low 240Pu/239Pu atom ratios i.e., Maralinga (0.113) and Montebello (0.045). The average ratios in the 20-30°S and 30-40° bands are closer to the global average (0.139 and 0.177 respectively when not including the close-in fallout data from the nuclear test sites) if the Australian test sites and Central Australian sites are neglected as they clearly represent the effects of close in fallout.
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Affiliation(s)
- R Lal
- Department of Nuclear Physics, The Australian National University, ACT 0200, Australia; Department of Physics, College of Engineering, Science and Technology, Fiji National University, Fiji.
| | - L K Fifield
- Department of Nuclear Physics, The Australian National University, ACT 0200, Australia
| | - S G Tims
- Department of Nuclear Physics, The Australian National University, ACT 0200, Australia
| | - R J Wasson
- Institute of Water Policy, National University of Singapore AS2, #04-321 Arts Link, 117570, Singapore
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Smith BS, Child DP, Fierro D, Harrison JJ, Heijnis H, Hotchkis MAC, Johansen MP, Marx S, Payne TE, Zawadzki A. Measurement of fallout radionuclides, (239)(,240)Pu and (137)Cs, in soil and creek sediment: Sydney Basin, Australia. JOURNAL OF ENVIRONMENTAL RADIOACTIVITY 2016; 151 Pt 3:579-586. [PMID: 26344369 DOI: 10.1016/j.jenvrad.2015.06.015] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/21/2015] [Revised: 06/12/2015] [Accepted: 06/19/2015] [Indexed: 06/05/2023]
Abstract
Soil and sediment samples from the Sydney basin were measured to ascertain fallout radionuclide activity concentrations and atom ratios. Caesium-137 ((137)Cs) was measured using gamma spectroscopy, and plutonium isotopes ((239)Pu and (240)Pu) were quantified using accelerator mass spectrometry (AMS). Fallout radionuclide activity concentrations were variable ranging from 0.6 to 26.1 Bq/kg for (137)Cs and 0.02-0.52 Bq/kg for (239+240)Pu. Radionuclides in creek sediment samples were an order of magnitude lower than in soils. (137)Cs and (239+240)Pu activity concentration in soils were well correlated (r(2) = 0.80) although some deviation was observed in samples collected at higher elevations. Soil ratios of (137)Cs/(239+240)Pu (decay corrected to 1/1/2014) ranged from 11.5 to 52.1 (average = 37.0 ± 12.4) and showed more variability than previous studies. (240)Pu/(239)Pu atom ratios ranged from 0.117 to 0.165 with an average of 0.146 (±0.013) and an error weighted mean of 0.138 (±0.001). These ratios are lower than a previously reported ratio for Sydney, and lower than the global average. However, these ratios are similar to those reported for other sites within Australia that are located away from former weapons testing sites and indicate that atom ratio measurements from other parts of the world are unlikely to be applicable to the Australian context.
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Affiliation(s)
- B S Smith
- GeoQuEST, School of Earth and Environmental Sciences, University of Wollongong, Wollongong, NSW, 2522, Australia
| | - D P Child
- Institute for Environmental Research, Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW, 2234, Australia
| | - D Fierro
- Institute for Environmental Research, Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW, 2234, Australia
| | - J J Harrison
- Institute for Environmental Research, Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW, 2234, Australia
| | - H Heijnis
- Institute for Environmental Research, Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW, 2234, Australia
| | - M A C Hotchkis
- Institute for Environmental Research, Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW, 2234, Australia
| | - M P Johansen
- Institute for Environmental Research, Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW, 2234, Australia
| | - S Marx
- GeoQuEST, School of Earth and Environmental Sciences, University of Wollongong, Wollongong, NSW, 2522, Australia
| | - T E Payne
- Institute for Environmental Research, Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW, 2234, Australia
| | - A Zawadzki
- Institute for Environmental Research, Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW, 2234, Australia
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Tims SG, Froehlich MB, Fifield LK, Wallner A, De Cesare M. (236)U and (239,)(240)Pu ratios from soils around an Australian nuclear weapons test site. JOURNAL OF ENVIRONMENTAL RADIOACTIVITY 2016; 151 Pt 3:563-567. [PMID: 26141189 DOI: 10.1016/j.jenvrad.2015.06.020] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/12/2015] [Revised: 06/17/2015] [Accepted: 06/24/2015] [Indexed: 06/04/2023]
Abstract
The isotopes (236)U, (239)Pu and (240)Pu are present in surface soils as a result of global fallout from nuclear weapons tests carried out in the 1950's and 1960's. These isotopes potentially constitute artificial tracers of recent soil erosion and sediment movement. Only Accelerator Mass Spectrometry has the requisite sensitivity to measure all three isotopes at these environmental levels. Coupled with its relatively high throughput capabilities, this makes it feasible to conduct studies of erosion across the geographical extent of the Australian continent. In the Australian context, however, global fallout is not the only source of these isotopes. As part of its weapons development program the United Kingdom carried out a series of atmospheric and surface nuclear weapons tests at Maralinga, South Australia in 1956 and 1957. The tests have made a significant contribution to the Pu isotopic abundances present in the region around Maralinga and out to distances ∼1000 km, and impact on the assessment techniques used in the soil and sediment tracer studies. Quantification of the relative fallout contribution derived from detonations at Maralinga is complicated owing to significant contamination around the test site from numerous nuclear weapons safety trials that were also carried out around the site. We show that (236)U can provide new information on the component of the fallout that is derived from the local nuclear weapons tests, and highlight the potential of (236)U as a new fallout tracer.
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Affiliation(s)
- S G Tims
- Department of Nuclear Physics, Research School of Physics and Engineering, Australian National University, Canberra, ACT 2601, Australia.
| | - M B Froehlich
- Department of Nuclear Physics, Research School of Physics and Engineering, Australian National University, Canberra, ACT 2601, Australia
| | - L K Fifield
- Department of Nuclear Physics, Research School of Physics and Engineering, Australian National University, Canberra, ACT 2601, Australia
| | - A Wallner
- Department of Nuclear Physics, Research School of Physics and Engineering, Australian National University, Canberra, ACT 2601, Australia
| | - M De Cesare
- Department of Nuclear Physics, Research School of Physics and Engineering, Australian National University, Canberra, ACT 2601, Australia
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Tims SG, Tsifakis D, Srncik M, Keith Fifield L, Hancock GJ, De Cesare M. Measurements of low-level anthropogenic radionuclides from soils around Maralinga. EPJ WEB OF CONFERENCES 2013. [DOI: 10.1051/epjconf/20136303010] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Cresswell AJ, Sanderson DCW. Evaluating airborne and ground based gamma spectrometry methods for detecting particulate radioactivity in the environment: a case study of Irish Sea beaches. THE SCIENCE OF THE TOTAL ENVIRONMENT 2012; 437:285-296. [PMID: 22947616 DOI: 10.1016/j.scitotenv.2012.08.064] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/06/2012] [Revised: 06/15/2012] [Accepted: 08/17/2012] [Indexed: 06/01/2023]
Abstract
In several places, programmes are in place to locate and recover radioactive particles that have the potential to cause detrimental health effects in any member of the public who may encounter them. A model has been developed to evaluate the use of mobile gamma spectrometry systems within such programmes, with particular emphasis on large volume (16l) NaI(Tl) detectors mounted in low flying helicopters. This model uses a validated Monte Carlo code with assessment of local geochemistry and natural and anthropogenic background radiation concentrations and distributions. The results of the model, applied to the example of particles recovered from beaches in the vicinity of Sellafield, clearly show the ability of rapid airborne surveys conducted at 75 m ground clearance and 120 kph speeds to demonstrate the absence of sources greater than 5 MBq (137)Cs within large areas (10-20 km(2)h(-1)), and identify areas requiring further ground based investigation. Lowering ground clearance for airborne surveys to 15m whilst maintaining speeds covering 1-2 km(2) h(-1) can detect buried (137)Cs sources of 0.5MBq or greater activity. A survey design to detect 100 kBq (137)Cs sources at 10 cm depth has also been defined, requiring surveys at <15m ground clearance and <2 ms(-1) ground speed. The response of airborne systems to the Sellafield particles recovered to date has also been simulated, and the proportion of the existing radiocaesium background in the vicinity of the nuclear site has been established. Finally the rates of area coverage and sensitivities of both airborne and ground based approaches are compared, demonstrating the ability of airborne systems to increase the rate of particle recovery in a cost effective manner. The potential for equipment and methodological developments to improve performance are discussed.
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Affiliation(s)
- A J Cresswell
- Scottish Universities Environmental Research Centre, Scottish Enterprise Technology Park, East Kilbride, G75 0QF, UK.
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Long S, Martin L. Optimisation of systems to locate discrete gamma-ray sources within a large search area. JOURNAL OF ENVIRONMENTAL RADIOACTIVITY 2007; 94:41-53. [PMID: 17289229 DOI: 10.1016/j.jenvrad.2006.12.012] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/13/2006] [Revised: 12/12/2006] [Accepted: 12/13/2006] [Indexed: 05/13/2023]
Abstract
Most systems used to locate discrete gamma-ray sources involve systematically passing a detector over the search area while seeking a significant increase in the observed count-rate. This paper discusses the ways in which such systems may be designed to maximise the probability of locating a source. It is shown that optimised systems use a collimated, energy-discriminating detector and overlapping counting intervals determined by the scanning geometry and speed.
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Affiliation(s)
- S Long
- Australian Radiation Protection and Nuclear Safety Agency, 619 Lower Plenty Road, Yallambie 3085, Australia.
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