D.P. Child

Sample processing for earth science studies at ANTARES

Abstract AMS studies in earth sciences at ANTARES, ANSTO created a need for the processing of mineral and ice samples for 10Be, 26Al and 36Cl target preparation. Published procedures have been adapted to our requirements and improved upon where necessary. In particular, new methods to isolate Be with reproducible, high recoveries in the presence of excess Al and Ti were achieved. An existing elution scheme for a cation exchange column procedure was modified to incorporate the use of a 0.25 M H 2 SO 4 +0.015% H 2 O 2 washing step to elute the Ti peroxide complex formed. Problems with dust contamination in ice contributing to measured 10Be signals are also addressed and a procedure developed for its removal.

Measurement of 236U in environmental media

The long-lived uranium isotope 236U (T1/2=23.4 Ma) is produced by 235U neutron capture and builds up to high levels in nuclear fuel. It has been distributed in the environment as a result of nuclear activities including nuclear explosions, accidents at nuclear plants, dumping of nuclear waste and releases from nuclear facilities. 236U is a potentially useful tracer of irradiated uranium for nuclear safeguards or other applications, due to its virtual absence in natural samples (236U:238U ratio ∼10−10 in uranium ore). We have measured 236U in soil and sediment reference materials (IAEA 375, 135 and 300) by accelerator mass spectrometry (AMS). The AMS system on the ANTARES accelerator has been upgraded to make such measurements possible. The system, including sample preparation procedures, is described and the results discussed.

7Be and 10Be concentrations in recent firn and ice at Law Dome, Antarctica

Abstract Over the past three years, the Australian National Tandem for Applied Research (ANTARES) AMS facility at ANSTO has been expanding its sample preparation and measurement capability, particularly for 10 Be, 26 Al and 36 Cl. During this time, ANSTO has continued its collaboration with the AAD and CSIRO Atmospheric Research on the measurement of cosmogenic isotopes from Law Dome, Antarctica. This research program has been supported by the construction of a dedicated geochemistry laboratory for the processing of ice and rock samples for the preparation of AMS targets. Here we present our first results for 10 Be concentrations measured in ice cores from three sites at Law Dome and describe the sample processing protocol and aspects of the AMS measurement procedure. These sites are characterised by an eightfold difference in accumulation rate with a common precipitation source. In combination with an established ice chronology, this has enabled some preliminary findings concerning the relationship between the snow accumulation rate and the measured 10 Be concentration for Law Dome during recent times. Additionally, we present 7 Be and 10 Be/ 7 Be measurements made for a few surface snow samples from Law Dome and Australia.

High sensitivity analysis of plutonium isotopes in environmental samples using accelerator mass spectrometry (AMS)

This article presents a methodology for the determination of the concentration and isotopic ratio of plutonium occurring at femtogram levels in environmental matrices such as soils and sediments by accelerator mass spectrometry (AMS). Results on analyses of a number of reference materials (IAEA-375, IAEA-135, IAEA-300, IAEA-327, NIST 4350, NIST 4353b) are presented as validation of the method in reproducibly measuring the plutonium isotopic ratio 240Pu : 239Pu in a variety of environmental sample matrices.

AMS measurement of 129I, 36Cl and 14C in underground waters from Mururoa and Fangataufa atolls

AMS analyses of 36Cl, 129I and 14C in underground water have been performed as part of IAEA’s assessment of the radiological situation at Mururoa and Fangataufa atolls. The samples consisted of waters from monitoring wells, and from two cavity-chimneys created by underground nuclear tests. The water samples from the monitoring wells contained varying concentrations of radionuclides, with the highest concentrations of radionuclides found in the two test cavity-chimneys. A comparison of the concentrations of radionuclides determined by AMS, 36Cl and 129I, and with radionuclides determined using conventional methods, 3H, 90Sr and 137Cs, shows a reasonable correlation. However, some differences in behaviour, mainly attributed to differences in the sorption characteristics of the elements, are discernible. The concentrations of radionuclides in the underground environment were used to validate geosphere transport models.

Measurement of fallout radionuclides, (239)(,240)Pu and (137)Cs, in soil and creek sediment: Sydney Basin, Australia.

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.

Application of Accelerator Mass Spectrometry for 236U analysis

The long-lived radioisotope 236-uranium (T1/2=23.4Ma) is produced predominantly by neutron capture on 235U, building up to high levels in nuclear fuel. It is a potentially useful tracer of irradiated uranium for a variety of applications, due to its virtual absence in natural samples (236U:238U ratio ~10-10 in uranium ore). 236U has been distributed in the environment as a result of nuclear activities including nuclear explosions, accidents at nuclear plants, dumping of nuclear waste and releases from nuclear facilities. It is also present in depleted uranium, due to the recycling of uranium fuel in enrichment plants, and has been dispersed in areas where DU munitions have been used. We have measured 236U in a variety of environmental media by Accelerator Mass Spectrometry (AMS). AMS has the advantage of very high abundance sensitivity. Such measurements are possible using only a few grams of environmental materials, yielding a few micrograms of uranium for analysis by AMS. The resulting 236:238 isotopic ratios are typically in the range 10-6 to 10-9.

Challenges associated with the behaviour of radioactive particles in the environment

A series of different nuclear sources associated with the nuclear weapon and fuel cycles have contributed to the release of radioactive particles to the environment. Following nuclear weapon tests, safety tests, conventional destruction of weapons, reactor explosions and fires, a major fraction of released refractory radionuclides such as uranium (U) and plutonium (Pu) were present as entities ranging from sub microns to fragments. Furthermore, radioactive particles and colloids have been released from reprocessing facilities and civil reactors, from radioactive waste dumped at sea, and from NORM sites. Thus, whenever refractory radionuclides are released to the environment following nuclear events, radioactive particles should be expected. Results from many years of research have shown that particle characteristics such as elemental composition depend on the source, while characteristics such as particle size distribution, structure, and oxidation state influencing ecosystem transfer depend also on the release scenarios. When radioactive particles are deposited in the environment, weathering processes occur and associated radionuclides are subsequently mobilized, changing the apparent Kd. Thus, particles retained in soils or sediments are unevenly distributed, and dissolution of radionuclides from particles may be partial. For areas affected by particle contamination, the inventories can therefore be underestimated, and impact and risk assessments may suffer from unacceptable large uncertainties if radioactive particles are ignored. To integrate radioactive particles into environmental impact assessments, key challenges include the linking of particle characteristics to specific sources, to ecosystem transfer, and to uptake and retention in biological systems. To elucidate these issues, the EC-funded COMET and RATE projects and the IAEA Coordinated Research Program on particles have revisited selected contaminated sites and archive samples. This COMET position paper summarizes new knowledge on key sources that have contributed to particle releases, including particle characteristics based on advanced techniques, with emphasis on particle weathering processes as well as on heterogeneities in biological samples to evaluate potential uptake and retention of radioactive particles.

Measurement of 233U/234U ratios in contaminated groundwater using alpha spectrometry

The uranium isotope (233)U is not usually observed in alpha spectra from environmental samples due to its low natural and fallout abundance. It may be present in samples from sites in the vicinity of nuclear operations such as reactors or fuel reprocessing facilities, radioactive waste disposal sites or sites affected by clandestine nuclear operations. On an alpha spectrum, the two most abundant alpha emissions of (233)U (4.784 MeV, 13.2%; and 4.824 MeV, 84.3%) will overlap with the (234)U doublet peak (4.722 MeV, 28.4%; and 4.775 MeV, 71.4%), if present, resulting in a combined (233+234)U multiplet. A technique for quantifying both (233)U and (234)U from alpha spectra was investigated. A series of groundwater samples were measured both by accelerator mass spectrometry (AMS) to determine (233)U/(234)U atom and activity ratios and by alpha spectrometry in order to establish a reliable (233)U estimation technique using alpha spectra. The Genie™ 2000 Alpha Analysis and Interactive Peak Fitting (IPF) software packages were used and it was found that IPF with identification of three peaks ((234)U minor, combined (234)U major and (233)U minor, and (233)U major) followed by interference correction on the combined peak and a weighted average activity calculation gave satisfactory agreement with the AMS data across the (233)U/(234)U activity ratio range (0.1-20) and (233)U activity range (2-300 mBq) investigated. Correlation between the AMS (233)U and alpha spectrometry (233)U was r(2) = 0.996 (n = 10).

The Use of 236U as a Tracer of Irradiated Uranium

A brief review of the use of 236U as a tracer of irradiated uranium is given. Data on vertical migration of irradiated uranium in various types of soils, the destruction degree of fuel particles determined by carbonate leaching of 236U (VI), the nuclear fuel burn-up fraction in Chernobyl originated fallout and the total contamination of territory of Belarus by irradiated uranium are presented.