Erich Hrnecek

Neptunium determination by dc glow discharge mass spectrometry (dc-GDMS) in Irish Sea sediment samples

Direct current glow discharge mass spectrometry (dc-GDMS) has been applied for the direct analysis of 237Np in marine sediment samples from the Irish Sea. The secondary cathode technique was exploited to promote the sputtering of the sediment samples once compacted into a pellet. A certified marine sediment doped with a certified 237Np solution was used for obtaining matrix-matching samples for calibration purposes. Acquiring 100 points over an integration time of 300 ms a detection limit down to 80 pg g−1 was obtained. Results on 237Np were in agreement with those obtained by the determination of 233Pa by γ-spectrometry.

Sample preparation methods for the determination of plutonium and strontium in environmental samples by low level liquid scintillation counting and α-spectrometry

Summary Two different methods – leaching and microwave assisted total dissolution – have been exploited for the treatment of environmental samples for the determination of plutonium and strontium. Leaching applied to reference materials demonstrated the procedure to be applicable for the recovery of technogenic Pu and Sr from environmental samples. For the measurement of the alpha emitters of plutonium, co-precipitation with calcium oxalate and ferric hydroxide and separation with anion exchange has been used. For preparation of α-spectrometry sources, co-precipitation with NdF3 on a membrane filter or electro-deposition using the (NH4)2C2O4/HCl method have been tested. The beta emitter 241Pu was measured by liquid scintillation counting. Pu isotope concentrations determined in the reference materials agreed well with the certified concentrations. 90Sr was measured in the leachate solutions from environmental samples collected close to a nuclear facility and from reference materials, after separation from the other leached elements, by liquid scintillation counting and Cherenkov counting. The 90Sr-concentrations determined in the reference materials agreed well with the certified concentrations. In the samples collected close a nuclear facility (soil, grass and sheep faeces), 90Sr was found at higher levels, which could also be correlated with the location of the sampling.

Application of microprecipitation on membrane filters for Alpha Spectrometry, liquid scintillation counting and Mass Spectrometric determination of plutonium isotopes

Summary For the determination of plutonium isotopes in environmental samples, chemical separation of plutonium together with a suitable sample preparation method for measurement is necessary. In this work, a combined method for the determination of 238Pu, 239Pu, 240Pu and 241Pu based on alpha spectrometry, Liquid Scintillation Counting (LSC) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) is presented. For the alpha spectrometric determination of 238Pu and 239(40)Pu, sample preparation by coprecipitation of Pu with NdF3 on a membrane filter after separation by anion exchange, using 242Pu as tracer, is widely used. This sample preparation method was also applied as a preconcentration step for the determination of 240Pu/239Pu ICP-MS after wet ashing of a part of the membrane filter. 241Pu was measured with LSC after dissolving a part of the same membrane filter in a suitable cocktail and using the total alpha activity of the filter for determination of the chemical yield. The use of this approach gives the advantage of combining the strengths of both radiometric and mass spectrometric methods for plutonium determination after chemical separation from environmental samples. Results from the measurement of reference materials and from sediment samples from the Irish Sea are presented and the applied methods are compared with respect to their detection limits for the investigated nuclides.

Determination of U, Pu and Am isotopes in Irish Sea sediment by a combination of AMS and radiometric methods

Samples from a marine sediment core from the Irish Sea (54.416 N, 3.563 W) were analyzed for the isotopic composition of uranium, plutonium and americium by a combination of radiometric methods and AMS. The radiochemical procedure consisted of a Pu separation step by anion exchange, subsequent U separation by extraction chromatography using UTEVA® and finally Am separation with TRU® Resin. Additionally to radiometric determination of these isotopes by alpha spectrometry, the separated samples were also used for the determination of (236)U/(238)U and plutonium isotope ratios by Accelerator Mass Spectrometry (AMS) at the VERA facility.

Assessment of a Compton-event suppression γ-spectrometer for the detection of fission products at trace levels

Abstract The improvement in detection limits for low and high activity samples measured with the Compton-suppression γ-spectrometer installed at the Institute for Transuranium Elements (ITU) for environmental monitoring of radioactivity, as well as nuclear safeguards, is discussed. The advantage of using two parallel acquisition lines for simultaneous measurement with and without Compton-event suppression is outlined with respect to cascade and non-cascade γ-emitters. The background reduction by Compton-event suppression made it possible to detect small peaks, which otherwise would not have been found in a conventional spectrum. In Compton-event suppression mode, the detection limit for 137Cs was improved by a factor of about 3, for 241Am we found a factor of 1.2 both in high and low active samples. The measurements of environmental reference samples showed good agreement with certified values in both acquisition modes. The application of this instrument for the determination of fission products in smear samples is described. In particular, for nuclides like 54Mn, 125Sb and 144Ce, an improvement in the detection limits by a factor of 1.6–2.4 was obtained.

Vertical distribution of 238Pu, 239(40)Pu, 241Am, 90Sr and 137Cs in Austrian soil profiles

Abstract The occurrence of 238Pu, 239(40)Pu, 241Am, 90Sr and 137Cs in the region of Nassfeld (Salzburg, Austria) is discussed at four different locations by evaluating a depth profile for each radionuclide. Furthermore, the plutonium separated from the soil samples was measured by Accelerator Mass Spectrometry (AMS) to get information on the isotope ratio 240Pu/ 239Pu. The radiochemical procedure consisted of a Pu separation step from Am and Sr by anion exchange in 8 M HNO3 after oxidation state adjustment to Pu(IV). Am and Sr were coprecipitated with calcium oxalate. Am was separated from Sr by extraction chromatography using TRU-resin. The Sr separation was performed also by extraction chromatography using Sr-resin; after coprecipitation as oxalate, 90Sr was measured in a gas proportional counter. For the determination of 239(40)Pu and 241Am by α-spectrometry thin sources were prepared by microprecipitation with NdF3. With the respective Pu isotope ratios, it was possible to identify the global fallout as source of the contamination. This was confirmed by the ratio 241Am/239(40)Pu. From the activity ratio 90Sr/ 137Cs, it could be shown that most of these radionuclides stem from the reactor accident in Chernobyl.

Measurements of 236U in Ancient and Modern Peat Samples and Implications for Postdepositional Migration of Fallout Radionuclides

(236)U was analyzed in an ombrotrophic peat core representing the last 80 years of atmospheric deposition and a minerotrophic peat sample from the last interglacial period. The determination of (236)U at levels of 10(7) atoms/g was possible by using ultraclean laboratory procedures and accelerator mass spectrometry. The vertical profile of the (236)U/(238)U isotopic ratio along the ombrotrophic peat core represents the first observation of the (236)U bomb peak in a terrestrial environment. A constant level of anthropogenic (236)U with an average (236)U/(238)U isotopic ratio of (1.24 ± 0.08) × 10(-6) in the top layers of the core was observed. Comparing the abundances of the global fallout derived (236)U and (239)Pu along the peat core, the post depositional migration of plutonium clearly exceeds that of uranium. However, the cumulative (236)U/(239)Pu ratio of 0.62 ± 0.31 is in agreement with previous studies on the global fallout uranium and plutonium. In the interglacial peat samples a (236)U/(238)U isotopic ratio of (3.3 ± 0.7) × 10(-12) was detected; although this measurement is an upper limit, it constitutes a significant step forward in the experimental determination of the natural (236)U abundance and represents a true background sample for the ombrotrophic peat core.

Determination of 239Pu, 240Pu, 241Pu and 242Pu at femtogram and attogram levels – evidence for the migration of fallout plutonium in an ombrotrophic peat bog profile

The isotopic composition of plutonium ((239)Pu, (240)Pu, (241)Pu and (242)Pu) was investigated in a ∼0.5 m long peat core from an ombrotrophic bog (Black Forest, Germany) using clean room procedures and accelerator mass spectrometry (AMS). This sophisticated analytical approach was ultimately needed to detect reliably the Pu concentrations present in the peat samples at femtogram (fg) and attogram (ag) levels. The mean (240)Pu/(239)Pu isotopic ratio of 0.19 ± 0.02 (N = 32) in the peat layers, representing approximately the last 80 years, was in good agreement with the accepted value of 0.18 for the global fallout in the Northern Hemisphere. This finding is largely supported by the corresponding and rather constant (241)Pu/(239)Pu (0.0012 ± 0.0005) and (242)Pu/(239)Pu (0.004 ± 0.001) ratios. Since the Pu isotopic composition characteristic of the global fallout was also identified in peat samples pre-dating the period of atmospheric atom bomb testing (AD 1956-AD 1980), migration of Pu within the peat profile is clearly indicated. These results highlight, for the first time, the mobility of Pu in a peat bog with implications for the migration of Pu in other acidic, organic rich environments such as forest soils and other wetland types. These findings constitute a direct observation of the behaviour of Pu at fg and ag levels in the environment. The AMS measurements of Pu concentrations (referring to a corresponding activity of (240+239)Pu from 0.07 mBq g(-1) to 5 mBq g(-1)) essentially confirm our a priori estimates based on existing (241)Am and (137)Cs data in the investigated peat core and agree well with the global fallout levels from the literature. Exclusively employing the Pu isotope ratios established for the peat samples, the date of the Pu irradiation (AD 1956, correctable to AD 1964) was calculated and subsequently compared to the (210)Pb age of the peat layers; this comparison provided an additional hint that global fallout derived Pu is not fixed in the peat column, but has migrated downwards along the peat profile to layers preceding the nuclear age.

Investigation of the 236U/238U Isotope Abundance Ratio in Uranium Ores and Yellow Cake Samples

Abstract Uranium ores and yellow cake samples of known geographic origin were investigated for their n(236U)/n(238U) isotope abundance ratio. Samples from four different uranium mines in Australia, Brazil and Canada were selected. Uranium was separated by UTEVA® Resin and was measured by Accelerator Mass Spectrometry (AMS) at the Vienna Environmental Research Accelerator (VERA). The measurement of the isotope abundance ratio n(236U)/n(238U) will be used to investigate possible correlations between the original mineral (uranium ore) and the intermediate product (yellow cake). Such correlations are useful indicators for nuclear forensic or for non-proliferation purposes.

Stand-Off Radioluminescence Mapping of Alpha Emitters Under Bright Lighting

Remote detection of alpha emitters is achieved by measuring the secondary radioluminescence light (air fluorescence) that is induced by alpha particles when absorbed in air. A telescope was used to collect the radioluminescence photons to a photomultiplier tube, which is operated in the photon counting mode. Careful matching of photocathode response and filter pass-band allows the sensing of a faint radioluminescence emission in a brightly illuminated environment, which is essential for operative use. A minimum detectable alpha activity of 4 kBq was reached at 1 m distance in 10 s time, when ultraviolet-free lighting is present, and 800 kBq under bright fluorescent lighting. These sensitivities are realized using an ultra-bialkali and cesium-telluride photocathodes in the aforementioned environments respectively. The presented approach is a robust and affordable solution to remotely detect and localize moderate alpha activities in a field environment, providing a means for automated alpha contamination mapping. Moreover, it is shown that a signal increase of more than two orders of magnitude (150–420) can be achieved in deep ultraviolet (close to 260 nm), if nitrogen or argon purge are used to enhance the detection.