Anomalously high237Np in intertidal sediments from the Ribble Estuary in the Irish Sea

Depth profiles and inventories of²³⁷Np in sediment cores from the Ribble Estuary in the Irish Sea have been studied along with those of Pu isotopes,²⁴¹Am and¹³⁷Cs, to allow a more detailed look of anomalously high²³⁷Np content observed in this estuary previously. The comprehensive data obtained showed that the depth profiles of both²³⁷Np contents and²³⁷Np/^239,240Pu activity ratios were clearly different from those of^239,240Pu,²⁴¹Am, and¹³⁷Cs and their activity ratios. As much as 80–90% of²³⁷Np inventories (0.32–1.06 kBq/m²), found in three cores, were estimated to be derived from a source other than Sellafield, on the basis of comparison of the²³⁷Np/^239,240Pu inventory ratio (0.65–1.74%) found in the Ribble Estuary cores with those (0.10–0.16%) in the Ravenglass Estuary cores.     

Distribution and behaviour of99Tc,237Np,239,240Pu,and241Am in the coastal and estuarine sediments of the Irish Sea

Intertidal coastal and estuarine sediments from 24 sites in the Irish Sea have been analyzed for⁹⁹Tc,²³⁷Np,²³⁸Pu,^239,240Pu and²⁴¹Am. The²³⁷Np activity and²³⁹Pu/²⁴⁰Pu ratio were measured simultaneously by ICP-MS, and⁹⁹Tc was determined by HR-ICP-MS which is ten times more sensitive than Q-ICP-MS.The activities of⁹⁹Tc,²³⁷Np,^239,240Pu and²⁴¹Am were distributed over a wide range of 1.5–70.5, 0.01–13.3, 2.3–1589, 2.6–1894 Bq/kg, respectively. Activities of these radionuclides decreased exponentially with distance from the Sellafield source. The²⁴¹Am/^239,240Pu and²³⁷Np/^239,240Pu ratios were almost constant with distance from the Sellafield. This result suggests that the distribution and behavior of Np and Pu are controlled by complicated factors such as the influence of transport, the variation with time of Np/Pu ratio in the Sellafield discharges and sedimentary mixing processes in the Irish Sea.     

Determination of237Np and241Pu in environmental samples: In soil and sediment

This paper describes the analytical methods for the determination of²³⁷Np, Pu isotopes, and²⁴¹Am, with particular emphasis on²³⁷Np by alpha-ray spectrometry and²⁴¹Pu by liquid scintillation technique. Results are also presented for the sediment cores collected from Mikata Five Lakes in Fukui Prefecture, Japan.     

Distribution of global fallout237Np,Pu isotopes,and241Am in lake and sea sediments

In order to investigate the sedimentary behaviour of neptunium,²³⁷Np together with Pu isotopes and²⁴¹Am have been measured for the sediment cores collected from Lake Mikata (freshwater) and from Lake Kugushi (brakish water) both belonging to the Mikata Five Lakes, and from Nyu Bay (sea water). In all sediment core samples²³⁷Np was detected, and its concentrations were far below those of^239,240Pu and²⁴¹Am measured for the same samples. Inventories of²³⁷Np in Lake Mikata, Lake Kugushi and Nyu Bay were estimated to be 0.53, 0.29 and 0.34 MBq/km², respectively. The activity ratio of²³⁷Np/^239,240Pu calculted from the inventories in each sediment core was 0.29% for Lake Mikata, 0.15% for Lake Kugushi and 0.10% for Nyu Bay. These values except for the value for Lake Mikata are two or three times lower than the value of 0.3–0.4% observed for surface soils of 0–20 cm depth, suggesting that Np is more soluble compared with Pu.     

3He induced nuclear reactions on237Np targets

The cross sections for the³He induced nuclear reactions on²³⁷Np leading to the formation of^236sNp,²³⁸Np,²³⁶Pu,²³⁷Pu,²³⁸Pu,²³⁷Am and²³⁹Am were studied by the irradiation of thin and thick targets of²³⁷Np. The cross sections were determined in the energy range of 20–26 MeV using the stacked-foil technique with thin targets. The cross sections were used for the calculation of the thick-target yields for the production of²³⁶Pu,²³⁷Pu and²³⁸Pu from²³⁷Np irradiated with³He²⁺ ions in the energy range of 20–26 MeV.     

A gamma-spectrometric method for the determination of plutonium isotope ratios

A gamma-spectrometric method using an intrinsic high resolution germanium detector has been developed for the determination of isotope ratios of plutonium from samples in solution form. The method is based on the assay of low energy gamma-rays of²³⁸Pu,²³⁹Pu,²⁴⁰Pu and²⁴¹Pu and does not require the use of branching intensities or the knowledge of detection efficiencies for different gamma rays. Since low energy gamma-rays are used, the effect of²⁴¹Am has also been studied. It is found that results are not affected up to 0.5 wt% of²⁴¹Am in plutonium samples. An accuracy of 3% is achievable in the determination of²⁴⁰Pu/²³⁹Pu and²⁴¹Pu/²³⁹Pu atom ratios as demonstrated by carrying out measurements on isotopic standards of plutonium.     

Dosage du237Np en trances dans l'uranium et le plutonium

The²³⁷Np content of²³⁸Pu or²³⁹Pu samples were determined by the gammaspectrometry of²³⁸Np formed by thermal neutron activation. The measurements were carried out on irradiated²³⁸Pu samples directly, and after the chemical separation of²³⁹Pu samples. The²³⁷Np content of natural uranium was determined from the ratio of the alpha-activities of²³⁸Pu and²³⁹Pu isotopes formed from the decay of neptunium isotopes produced by the activation of²³⁷Np and²³⁸U isotopes, respectively.      

Simultaneous determination of plutonium and americium in soils by extraction chromatography

A radiochemical method is described for the determination of²³⁸Pu,^239(240)Pu and²⁴¹Am in a single soil sample. Plutonium is separated from a HNO₃ leaching solution by a Microthene-TNOA column; amcricium is coprecipitated by oxalic acid, decontaminated from polonium by a TNOA-column in HCl medium, separated from the rare earth elements by a Microthene-HDEHP column, eluted with a 0.07M DTPA+1M lactic acid solution and finally purified by a PMBP-TOPO extraction. The method supplies a good decontamination of Am and Pu from natural alpha emitters; starting from 50 g soil, the average yields were 75.1±13.4% for plutonium and 57.7±10.8% for Am.^239(240)Pu,²³⁸Pu and²⁴¹Am concentrations (mBq/kg) in three different kinds of soil were the following: 255, 10.4, 81.3 (uncultivated soils); 236, 11.6, 76.7 (cultivated soils); 46, 1.9, 19.8 (river sediment). The average ratios²³⁸Pu to^239(240)Pu and²⁴¹Am to^239(240)Pu were 0.044 and 0.350, respectively.     

Application of instrumental radioanalytical techniques to nuclear waste testing and characterization

This paper describes the validation of a multi-technique analytical methodology that uses inductively coupled plasma-mass spectrometry, α-spectrometry, and γ-spectrometry for the routine analysis of samples containing transuranic radionuclides. This methodology is capable of the determination of concentrations of both²³⁸Pu and²⁴¹Pu in the presence of²³⁸U and²⁴¹Am without the need for chemical separations. The relative merits of these three techniques were evaluated as they are applied in a nuclear waste material and spent nuclear fuel testing program by analytical (1) standards and (2) solutions prepared from the dissolution of glasses doped with²³⁷Np,²³⁹Pu, and²⁴¹Am. The uncertainty associated with technique was within ±4% for standards and ±10% for doped nuclear waste glasses. The methodology was then used to analyze three fully radioactive waste glasses.     

Sorption characteristics of237Np,238Pu and241Am in sedimentary materials

Adsorption experiments were performed to measure distribution coefficients of²³⁷Np(V),²³⁸Pu(IV) and²⁴¹Am(III) for sedimentary sequential chemical extraction of the adsorbed radionuclides was carried out with water, CaCl₂, KCl, NH₂OH−HCl, K-oxalate and H₂O₂ solutions, to elucidate their dominant sorption mechanisms. The distribution coefficient of²³⁷Np was two orders of magnitude smaller than that of²³⁸Pu and²⁴¹Am. Most of²³⁷Np adsorbed was extracted with CaCl₂ solution and its sorption was controlled by a reversible ion exchange reaction. The adsorbed²³⁸Pu was mainly extracted with NH₂OH−HCl+K-oxalate solution and its sorption was possibly controlled by irreversible reactions.     

Characterization of an Irish Sea radioactively contaminated marine sediment core by radiometric and mass spectrometric techniques

Summary A radioactively contaminated marine sediment core stemming from Irish Sea has been characterized by radiometric and mass spectrometric techniques as for ²³⁷Np, ²⁴¹Am, ²³⁹Pu, ²⁴⁰Pu, ²⁴¹Pu, ¹³⁷Cs and ¹⁵⁴Eu. The data obtained with independent methods in the framework of a QA/QC program as compared with the source term discharges, as well as with those reported in literature, are in good agreement.     

Refinement of Pu parent–daughter isotopic and concentration analysis for forensic (dating) purposes

Plutonium (Pu) metal samples from an interlaboratory exchange exercise and simulated swipe samples were dated using plutonium–uranium (Pu–U) and plutonium–americium (Pu–Am). Metal data were evaluated for consistency and the swipe data against its source material. Metal ages based on ²³⁹Pu versus ²³⁵U and ²⁴⁰Pu versus ²³⁶U agreed to within a few percent, while the ²³⁸Pu–²³⁴U and ²⁴¹Pu–²⁴¹Am measurements had larger uncertainties. Swipe ages compared favorably with the material’s known history. Neptunium (²³⁷Np) analyses were examined in the context of the ²⁴¹Pu–²⁴¹Am–²³⁷Np system to estimate whether Np can provide insights on material from which Am, Np, and U were removed.     

<Superscript>237</Superscript>Np in peat and lichen in Finland

Activity concentrations of ²³⁷Np in peat and lichen samples in Finland were determined and contributions from nuclear weapons testing in 1950–1960s and the Chernobyl accident were estimated. ²³⁷Np was determined with ICP-MS using ²³⁵Np as a tracer. Activity concentrations of ²³⁷Np in peat samples varied between 1.98 ± 0.05 and 14.1 ± 0.3 mBq/m². The contribution from the Chernobyl accident to the total ²³⁷Np deposition in peat was 0.1–13%, the Chernobyl-derived fraction of total ²³⁷Np in peat being much lower than the previously determined corresponding Chernobyl-derived fractions of ^239+240Pu, ²⁴¹Pu, ²⁴¹Am and ²⁴⁴Cm.     

Recent developments in the analysis of transuranics (Np,Pu, Am) in seawater

Summary A procedure is described to extend the current radiochemical method of seawater analysis for Pu and Am including Np. Short-lived ²³⁹Np tracer was prepared by separation from its ²⁴³Am parent. Irish Sea Water reference material (IAEA-381) containing known concentrations of ²³⁷Np, Pu isotopes and ²⁴¹Am was used to test the procedure for small water volumes. Inductively-coupled plasma mass spectrometry (ICP-MS) was used in addition to alpha spectrometry for measurement of ²³⁷Np in the purified final Np fractions.     

Measurements of99Tc,137Cs,237Np, Pu isotopes and241Am in sediment cores from intertidal coastal and estuarine regions in the Irish Sea

Long-lived radionuclides,⁹⁹Tc,¹³⁷Cs,²³⁷Np, Pu isotopes and²⁴¹Am were determined in the long sediment cores collected from nine intertidal sites around the west Cumbria of the Irish Sea, UK. The inventories of all nuclides measured varied considerably among the sampling sites, but generally their inventories decreased with increasing distance from Sellafield. Furthermore, the inventory ratios with respect to relationship with distance from Sellafield enabled comparison of transport behavior of⁹⁹Tc,¹³⁷Cs,²³⁷Np and²⁴¹Am compared with^239,240Pu. As a consequence, the apparent fractional rate of solution transport to the intertidal sediment was found to increase as follows:⁹⁹Tc>¹³⁷Cs>²³⁷Np>^239,240Pu≥²⁴¹Am.     

A separation procedure for the analysis of90Sr,154Eu, and the actinides237Np,239Pu,241Am and244Cm

A procedure for the analysis of⁹⁰Sr,¹⁵⁴Eu,²³⁷Np,²³⁹Pu,²⁴¹Am and^242−244Cm was developed. Separation was done with the separating agent, di-2(ethyl hexyl)-phosphoric acid (HDEHP), and results in fractions containing the different elements to be analysed.⁹⁰Sr analysis was done by analysing its daughter nuclide⁹⁰Y, detected through the Cherenkov radiation emitted by this high energy β⁻-emitter.¹⁵⁴Eu was detected using γ-spectrometry with a lower Compton background as a result of the removal of other fission products.²⁴¹Am could also be detected with γ-spectrometry or together with^242−244Cm with α-spectrometry. The long-lived radionuclides²³⁷Np and²³⁹Pu were detected using inductively coupled plasma mass spectrometry (ICP-MS).     

Determination of actinide nuclides in water samples from the primary circuit of a research reactor

Primary coolant samples from a research have been analyzed for^239,240Pu,²³⁸Pu,²³⁸U,²³⁷Np and²³⁹Np. The determination of²³⁷Np and²³⁸U was carried out with the help of isotope dilution neutron activation analysis with²³⁹Np or²³⁸Np as tracer. For determination of^239,240Pu and²³⁸Pu alpha spectroscopic isotope dilution analysis with²³⁸Pu as tracer was used.²³⁹Np was determined with the help of isotope dilution analysis using²³⁸Np as tracer. Nuclides were isolated by chemical separation on anionite resin. Before measurement, Pu isotopes were electrolytically deposited on stainless steel plates. Activity ratios referred to²³⁸U were reported. They are helpful for identification of the sources of actinide activity in reactor effluents.     

Electrodeposition on copper powder as a means of separation for trace analysis of noble metals in activation analysis: A tracer study

Studies are reported to illustrate surface adsorption of¹⁴⁴Ce,⁵⁹Fe,²³⁴Th,²³³U,²³⁷Np,²³⁹Pu and²⁴¹Am on a dextran gel made by crosslinkage of the polysaccharide dextran (Sephadex). Fixation of such elements was studied from aqueous solution and was found to depend on pH, age of the tracer solution, hydrolytic behaviour of the adsorbed species, concentration and the valency of the adsorbed element.     

Radiochemical determination of the yields of transuranium nuclides produced from natural uranium irradiated in a reactor

Transuranium nuclides were produced by irradiating a pellet of natural uranium sulfide in the Japan Material Testing Reactor (JMTR). After irradiation, a successive separation of uranium, plutonium, americium and curium was carried out. The fractional concentrations of the nuclides²³⁸Pu,²³⁹Pu,²⁴⁰Pu,²⁴¹Am,²⁴³Am,²⁴²Cm and²⁴⁴Cm were determined by α-ray spectrometry, and those of²⁴¹Pu and^242mAm were estimated from the build-up of α-emitting daughters,²⁴¹Am and²⁴²Cm, respectively. As the yield of²⁴²Pu was too slight to be detected by α-counting, the neutron activation analysis of the plutonium fraction based on the²⁴²Pu(n, γ)²⁴³Pu reaction was carried out by γ-ray spectrometry, and it was shown that a few pg of²⁴²Pu could be determined. A burn-up of²³⁵U was also estimated by neutron activation analysis. The experimental results are compared with the calculated ones.     

A gamma monitoring technique for estimating plutonium contamination around nuclear weapons facilities

The objectives of this study were to establish a ratio for²⁴¹Am to²³⁹Pu in soil at the Rocky Flats Plant and to compare²⁴¹Am concentrations obtained using in-situ and laboratory gamma spectroscopy measurements to concentrations determined with radiochemical analysis and alpha spectroscopy. Soil samples were collected for radiochemical and laboratory gamma spectroscopy analysis from vertical profiles in 3 cm layers to a depth of 21 cm at predetermined locations along transects oriented in the direction of prevailing winds. The origin for the transects was the center of the 903 Pad at the Rocky Flats Plant, which is believed to be the source for most of the²⁴¹Am and²³⁹Pu contamination. A 100 minute in-situ gamma spectroscopy measurement was made at each soil sample location with a portable HPGe detector. Soil samples were dried, passed through a 2 mm sieve, mixed, and split in two fractions. One fraction was analyzed radiochemically for²⁴¹Am and²³⁹Pu and the second was analyzed using laboratory gamma spectroscopy. The median ratio of²⁴¹Am to²³⁹Pu activities, which appears to be independent of soil depth and distance from suspected sources, was 0.17. There is a strong correlation between²⁴¹Am and²³⁹Pu concentrations determined using radiochemical analysis with alpha spectroscopy and concentrations determined with laboratory gamma spectroscopy. Results from in-situ gamma spectroscopy measurements were also correlated with the radiochemical analyses but exhibited greater variability than laboratory measurements. This on-going investigation has demonstrated that it is possible to indirectly measure²³⁹Pu concentrations in soil if the ratio of²⁴¹Am to²³⁹Pu can be established. The results indicate that judicious use of a combination of radiochemical analyses with laboratory and in-situ gamma spectroscopy measurements may provide a cost-effective approach for characterization of large sites where²⁴¹Am and²³⁹Pu contamination occur.