Long-lived Isotopes Research Articles

Long Term Neutron Activation in JET DD Operation

In the 2019 C38 Deuterium-Deuterium campaign at JET several different ITER-relevant materials and dosimetry foils were irradiated in a specially designed long-term irradiation station located inside the vacuum vessel with the purpose of testing the activation of ITER materials by fusion neutrons. The samples were exposed to a neutron fluence of 1.9E14 n/cm2 during JET discharges performed in the experimental campaign over a period of 5 months. Gamma ray spectroscopy measurements were performed on irradiated samples to determine the activation of different long-lived isotopes in the samples. Monte Carlo computational analysis was performed to support the experiment by using the measured neutron yield and irradiation time. In this paper we focus on the computational analysis of the dosimetry foils that are used in order to measure the local neutron energy spectrum and flux. The foils were chosen to cover different neutron energies: thus Yttrium and some of the Nickel and Cobalt reactions were used to determine the Deuterium-Tritium fusion fraction, while Scandium and Iron and some of the Nickel and Cobalt reactions were used for comparison of the computed activity with the experimental measurements. The obtained C/E values show a reasonably good agreement between calculated and measured activity, thus validating the computational methodology and providing the basis for the analysis of the ITER-relevant materials and future experiments performed at JET in the Deuterium-Tritium campaign.

Underground production of 81Kr detected in subsurface fluids

Radiokrypton dating using the long-lived natural isotope 81Kr has been developed for determining the age of ancient groundwater. 81Kr is attractive for this purpose because it is generally thought to be produced solely in the upper atmosphere. Its 229,000-year half-life, a spatially homogeneous distribution in the atmosphere, and the absence of anthropogenic sources makes it an ideal tracer to determine ages up to ∼1.3 million years. As a noble gas, it is inert and thus not subject to interfering geochemical reactions that may alter the age information. We sought to date groundwater samples collected from deep (0.6–1.9 km) rock fractures in the Kaapvaal Craton, South Africa. Previous studies using other dating methods have estimated groundwater ages at these sites in the 1–100 million year range. Surprisingly, three of the four samples collected from flowing boreholes in gold and diamond mines showed 81Kr isotopic abundances at 2–5 times the atmospheric value. This is the first time that underground production of 81Kr has been detected, indicating that 81Kr can be generated underground in measurable quantities in contrast to the long-held paradigm that such production is insignificant in natural rocks. A radionuclide production and release model is proposed in order to quantify the importance of different factors that affect the concentrations of 81Kr in the groundwater. It is not only the high effective uranium content of the rock but also a higher 81Kr fission yield than previously anticipated that are likely causing the elevated 81Kr values in this case. In less extreme environments with average crustal composition (i.e. moderate U concentration), however, we anticipate that the underground production minimally affects groundwater 81Kr dating as demonstrated.

A Review of the Occurrence of Alpha-Emitting Radionuclides in Wild Mushrooms.

Alpha-emitting radioisotopes are the most toxic among all radionuclides. In particular, medium to long-lived isotopes of the heavier metals are of the greatest concern to human health and radiological safety. This review focuses on the most common alpha-emitting radionuclides of natural and anthropogenic origin in wild mushrooms from around the world. Mushrooms bio-accumulate a range of mineral ionic constituents and radioactive elements to different extents, and are therefore considered as suitable bio-indicators of environmental pollution. The available literature indicates that the natural radionuclide 210Po is accumulated at the highest levels (up to 22 kBq/kg dry weight (dw) in wild mushrooms from Finland), while among synthetic nuclides, the highest levels of up to 53.8 Bq/kg dw of 239+240Pu were reported in Ukrainian mushrooms. The capacity to retain the activity of individual nuclides varies between mushrooms, which is of particular interest for edible species that are consumed either locally or, in some cases, also traded on an international scale. The effective radiation dose from the ingestion of this food can reportedly range from 0.033 µSv/kg dw to 26.8 mSv/kg and varies depending on the country. Following pollution events, such consumption may expose consumers to highly radiotoxic decay particles produced by alpha emitters.

Evolution of the early to late Archean mantle from Hf-Nd-Ce isotope systematics in basalts and komatiites from the Pilbara Craton

Inferences on the early evolution of the Earth's mantle can be deduced from long-lived radiogenic isotope systems such as 176Lu-176Hf and 147Sm-143Nd, for which both parent and daughter elements largely remain immobile at low metamorphic grades. However, it remains ambiguous when and to what extent mantle-crust differentiation processes had started in the Archean. For a better understanding of Archean mantle-crust evolution, we determined the initial 176Lu-176Hf, 147Sm-143Nd, and, in a new approach, the 138La-138Ce isotope compositions of a suite of Archean mafic-ultramafic rock samples from the 3.53-2.83 Ga old Pilbara Craton and 2.78-2.63 Ga old Fortescue Group in NW Australia. These rocks represent one of the best-preserved Archean successions worldwide and contain mafic-ultramafic rocks that were erupted during repeated and long-lived pulses of volcanism throughout much of the Archean. Mantle-derived mafic-ultramafic rock samples were collected from six major stratigraphic groups of the Pilbara Craton and the overlying Fortescue Group in order to characterize the parental mantle source regions of the lavas and to reconstruct the temporal evolution of the ambient mantle beneath this piece of cratonic lithosphere. In addition, we analyzed contemporaneous TTG-like igneous suites and interbedded sediments in order to reconstruct the lithospheric evolution of the Pilbara Craton.The Hf-Nd-Ce isotope data imply the onset of mantle-crust differentiation in the Pilbara Craton as early as ∼4.2 Ga, well prior to any of the preserved stratigraphy. Within error, coupled Ce-Nd-Hf isotope arrays all intersect chondritic values, implying that the Earth is of broadly chondritic composition, also for the 138La-138Ce isotope system. Mafic rocks usually yield strongly coupled εHf(i), εNd(i) and εCe(i) values that form a mixing line between an evolving depleted upper mantle composition and the primitive mantle value (εHf(i) ca. 0.0 to + 3.2, εNd(i) ca. +0.2 to +1.7 and εCe(i) ca. +0.3 to -0.1). As all Paleoarchean samples lack co-variations between Nb/Th with εHf(i) or εNd(i), contamination with an enriched crust is unlikely to explain this mixing trend. The most primitive mantle-like mafic samples show elevated GdN/YbN ratios (2.2-1.4), implying the involvement of a deep-rooted, near-primitive, upwelling mantle that was progressively mixed into the depleted upper mantle. In contrast to the mafic rocks, most, but not all komatiites are decoupled in their initial Hf-Nd-Ce isotope compositions, by having extremely radiogenic εHf(i) values at only moderately high εNd(i) and low εCe(i) values. This decoupling is best explained by the assimilation of mantle domains that underwent early melt depletion in the garnet stability field and evolved at high 176Lu/176Hf ratios but at moderate 147Sm/143Nd and 138La/138Ce ratios over time. The disappearance of rocks with decoupled Hf-Nd isotope compositions after ∼3.2 Ga is likely linked to decreasing mantle temperatures that were no longer able to melt such refractory mantle domains. Collectively, our new data for mafic rocks from the Pilbara Craton confirm the presence of long-term depleted mantle domains in the early Archean that are not sampled by the zircon Hf isotope record in the Pilbara Craton.

Using <sup>226</sup>Ra and <sup>228</sup>Ra isotopes to distinguish water mass distribution in the Canadian Arctic Archipelago

Abstract. As a shelf-dominated basin, the Arctic Ocean and its biogeochemistry are heavily influenced by continental and riverine sources. Radium isotopes (226Ra, 228Ra, 224Ra, and 223Ra), are transferred from the sediments to seawater, making them ideal tracers of sediment–water exchange processes and ocean mixing. As the two long-lived isotopes of the radium quartet, 226Ra and 228Ra (226Ra with a t1∕2 of 1600 years and 228Ra with a t1∕2 of 5.8 years) can provide insight into the water mass compositions, distribution patterns, as well as mixing processes and their associated timescales throughout the Canadian Arctic Archipelago (CAA). The wide range of 226Ra and 228Ra activities, as well as of the 228Ra∕226Ra, measured in water samples collected during the 2015 GEOTRACES cruise, complemented by additional chemical tracers – dissolved inorganic carbon (DIC), total alkalinity (AT), barium (Ba), and the stable oxygen isotope composition of water (δ18O) – highlight the dominant biogeochemical, hydrographic, and bathymetric features of the CAA. Bathymetric features, such as the continental shelf and shallow coastal sills, are critical in modulating circulation patterns within the CAA, including the bulk flow of Pacific waters and the inhibited eastward flow of denser Atlantic waters through the CAA. Using a principal component analysis, we unravel the dominant mechanisms and apparent water mass end-members that shape the tracer distributions. We identify two distinct water masses located above and below the upper halocline layer throughout the CAA and distinctly differentiate surface waters in the eastern and western CAA. Furthermore, we highlight water exchange across 80∘ W, inferring a draw of Atlantic water (originating from Baffin Bay) into the CAA. This underscores the presence of an Atlantic water “U-turn” located at Barrow Strait, where the same water mass is seen along the northernmost edge at 80∘ W as well as along the southeasternmost confines of Lancaster Sound. Overall, this study provides a stepping stone for future research initiatives within the Canadian Arctic Archipelago, revealing how quantifying disparities in the distributions of radioactive tracers can provide valuable information on water mass distributions, flow patterns, and mixing within vulnerable areas such as the CAA.

STRENGTHENING OF THE WORKING EDGES OF THE BLADES OF STEAM TURBINES

Abstract. The working conditions of the blades of steam turbines require increased hardness of the input edges and resistance to impact erosion, high corrosion resistance. In order to increase the service life of the blades, the inlet edges are quenched by high-frequency currents. The hardened layer was formed by electrospark alloying with T15K6 alloy and 15X11MFSh steel. The use of the widely used T15K6 alloy as a hardened electrode is limited due to the presence of cobalt, as an element forming, as a result of activation, long-lived isotopes that reduce the erosion resistance of the blades. Ultra high speed heating and cooling, pulsed effects of temperatures and pressures result lead to the fact that the composition of the alloyed layer can significantly differ from the composition of the starting materials. The microstructure, microhardness, and thickness of the deposited layer were investigated. The hardened surface was monitored by external inspection, bending tests, microhardness measurements, and microstructure studies. The advantages of 15X11MFSh steel for hardening the input edges of the working blades of steam turbines are substantiated.

Stellar 78,80,84,86Kr(n,γ) Reactions Studied by Activation at SARAF-LiLiT, Atom Trap Trace Analysis and Decay Counting

We report on (n,γ) neutron capture experiments performed with the Liquid-Lithium Target (LiLiT) and the mA-proton beam at 1.92 MeV (2-3 kW) from the Soreq Applied Research Accelerator Facility (SARAF). The setup yields high-intensity 30-keV quasi-Maxwellian neutrons (3-5 × 1010 n/s) closely reproducing the conditions of s-process stellar nucleosynthesis. The 78,80,8486Kr(n,γ) reactions at the border between weak- and strong- s-process were studied. A Ti sphere filled with 107.7 mg of natural Kr gas was placed in an irradiation chamber downstream of LiLiT with a gold foil used as a neutron fluence monitor during the activation. The activities of the short-lived Kr isotopes (7985m87Kr) were measured by γ decay counting with a HPGe detector. The long-lived Kr isotopes (81,85gKr) were measured by atom counting via Atom Trap Trace Analysis (ATTA) at Argonne and Low-Level Counting (LLC) at Bern.

Hyperfine structure study of Tc97,98,99 in a new laser ion source for high-resolution laser spectroscopy

Using a novel concept for efficient laser spectroscopy, we investigated the hyperfine splittings of three different atomic transitions in the long-lived isotopes $^{97\ensuremath{-}99}\mathrm{Tc}$. Despite the refractory character of the element technetium, sample sizes as low as ${10}^{11}$ atoms were sufficient to achieve excellent signal-to-noise ratios at a spectroscopic linewidth of less than 100 MHz. The obtained spectra were analyzed in detail, which results in a very good consistency for the extracted hyperfine parameters from the different transitions. The presented measurements provide the first hyperfine structure data for the isotopes $^{97,98}\mathrm{Tc}$ from which, in combination with the known nuclear moments of $^{99}\mathrm{Tc}$, their nuclear magnetic dipole and electric quadrupole moments were extracted. In addition, the experimental data confirm the predicted nuclear spin of $^{98}\mathrm{Tc}$ to $I=6$. In combination with atomic Multiconfiguration Dirac-Hartree-Fock calculations, the observed isotope shifts were investigated and the changes in mean-square charge radii were determined.

Evaluation of the activation of brass apertures in proton therapy using gamma-ray spectrometry and Monte Carlo simulations

Collimating apertures are used in proton therapy to laterally conform treatment fields to the target volume. While this is a standard technique in passive spreading treatment heads, patient-specific apertures can supplement pencil-beam scanning (PBS) techniques to sharpen the lateral dose fall-off. A radiation protection issue is that proton-induced nuclear reactions can lead to the formation of radionuclides in the apertures. In the experiments of the current study, cylindrical, thick brass targets were irradiated with quasi-monoenergetic proton fields of 100.0 MeV and of 226.7 MeV in PBS mode. The radioactivation of these two brass samples was characterised with a low-level gamma-ray spectrometer. The activation products were scored in a Monte Carlo simulation, too, and compared with the experimental activities. For the high-energy field, 63Zn, 60Cu, and 61Cu were the most important short-lived isotopes regarding the measured specific activity. After irradiation with the 100.0 MeV field, 62Cu, 63Zn, and 60Cu had the highest activity. Regarding long-lived isotopes, which determine the storage time of the used apertures, the isotopes 57Co, 65Zn, 54Mn, 56Co had the largest contribution to the activity. The relative difference of activities between simulation and experiment was typically between 10%–20% for short-lived nuclides and were up to a factor of five larger for long-lived nuclides. Summarising experiments and simulations for both incident proton energies, 62Cu was the most important detected residual nucleus regardless if specific activity or equivalent dose is considered.

Radium Mass Balance Sensitivity Analysis for Submarine Groundwater Discharge Estimation in Semi-Enclosed Basins: The Case Study of Long Island Sound

Estimation of submarine groundwater discharge (SGD) to semi-enclosed basins by Ra isotope mass balance is herein assessed. We evaluate 224Ra, 226Ra and 228Ra distributions in surface and bottom waters of Long Island Sound (CT-NY, USA) collected during spring 2009 and summer 2010. Surface water and bottom water Ra activities display an apparent seasonality, with greater activities during the summer. Long-lived Ra isotope mass balances are highly sensitive to boundary fluxes (water flux and Ra activity). Variation (50%) in the 224Ra, 226Ra and 228Ra offshore seawater activity results in a 63 – 74% change in the basin-wide 226Ra SGD flux and a 58 – 60% change in the 228Ra SGD flux, but only a 4 – 9% change in the 224Ra SGD flux. This highlights the need to accurately constrain long-lived Ra activities in the inflowing and outflowing water, as well as water fluxes across boundaries. Short-lived Ra isotope mass balances are sensitive to internal Ra fluxes, including desorption from resuspended particles and inputs from sediment diffusion and bioturbation. A 50% increase in the sediment diffusive flux of 224Ra, 226Ra and 228Ra results in a ~30% decrease in the 224Ra SGD flux, but only a ~6 – 10% decrease in the 226Ra and 228Ra SGD flux. When boundary mixing is uncertain, 224Ra is the preferred tracer of SGD if sediment contributions are adequately constrained. When boundary mixing is well-constrained, 226Ra and 228Ra are the preferred tracers of SGD, as sediment contributions become less important. A three-dimensional numerical model is used to constrain boundary mixing in Long Island Sound, with mean SGD fluxes of 1.2 ± 0.9 *1013 L y-1 during spring 2009 and 3.3 ± 0.7 *1013 L y-1 during summer 2010. The SGD flux to Long Island Sound during summer 2010 was one order of magnitude greater than the freshwater inflow from the Connecticut River. The maximum marine SGD-driven N flux is 14 ± 11 *108 mol N y-1 and rivals the N load of the Connecticut River.

Production of Cf-252 and other transplutonium isotopes at Oak Ridge National Laboratory

Abstract In 1957 Glenn T. Seaborg conceived and advocated for the construction of the High Flux Isotope Reactor (HFIR) and the Transuranium Processing Plant (since then renamed the Radiochemical Engineering Development Center, or REDC) at Oak Ridge National Laboratory. Heavily shielded hot cells, glove boxes, and laboratories allow recovery of transuranium elements produced in substantial quantities. Seaborg’s vision of HFIR and REDC producing milligram quantities of berkelium, californium, and einsteinium has been fulfilled beginning in 1966 through May 2019 with 78 production campaigns yielding a cumulative totals of 1.2 g of 249Bk, 10.2 g of 252Cf, 39 mg of 253Es, and 15 pg of 257Fm. Notably, 252Cf is a neutron source used in many industrial applications including oil exploration; process control systems for the cement industry, coal analysis, and power production; sources to start nuclear reactors and perform nondestructive materials analyses; homeland security and national defense detection devices; and medical research. Isotopes made available through transplutonium production at HFIR/REDC have enabled scientists to study the nuclear properties and reactions, chemical properties, optical properties, and solid-state properties of transplutonium elements. Long-lived isotopes have served as targets in heavy ion accelerators to produce heavier elements leading to the discovery of 104Rf, 105Db, 106Sg, 113Nh, 114Fl, 115Mc, 116Lv, 117Ts, and 118Og. This paper reviews the evolution of the processing flowsheets to produce, separate, and purify transplutonium isotopes, which have evolved over 50 years of operation at HFIR and REDC, and summarizes directions of future work to improve the efficiency of the production operations.

Determination of uranium and thorium isotopes in kaolinitic samples by ICP-MS/MS

The use of natural uranium and thorium long-lived isotopes was applied to study the evolution of kaolinitic materials. To do that, a radiochemical method for separation of Th and U in phyllosilicate samples was developed with the main aim of their analysis by ICP-MS/MS. Given the lack of certified phyllosilicate reference materials with certified isotope abundances, the method was tested using a stepwise approach. First, a preliminary setup was done using a sediment reference sample. Then, the extrapolation of this method to the samples of interest has been tested using a phyllosilicate sample certified for U and Th concentrations. The results showed that an extension of the plateau time of digestion in the used microwave system was peremptory as to get full digestion of the sample. The use of the isotope dilution technique allowed both the quantification of major isotopes (238U and 232Th) simultaneous to the determination of isotope ratios (234U/238U, 235U/238U for quality control and 230Th/232Th). The established method was applied to six kaolinitic samples from the Iberian Range (NE Spain), showing the potential of this isotope approach for the characterization of their time evolution.

Early diagenesis of radium 226 and radium 228 in lacustrine sediments influenced by former mining sites

Radium is a naturally occurring radioactive element commonly found at low levels in natural systems such as lacustrine or marine sediments. Anthropogenic activities including former uranium mining activities can lead to the dissemination of radium isotopes having high radiological toxicities, which potentially threaten the safety of nearby environments. Although radium mobility in oxidized environments is known to be largely governed by sorption/desorption onto Fe and Mn oxyhydroxides and coprecipitation with sulfate minerals (e.g. barite), little is known regarding its behavior under reducing conditions, which are the conditions typically encountered in organic-rich systems such as wetlands and lake sediments.The present study aims at understanding the behavior of long-lived radium isotopes (226Ra and 228Ra), during early diagenesis of lake sediments contaminated by former uranium mining activities. Solid and pore water concentrations of 226Ra and 228Ra were determined using ultra low background gamma spectrometry, which allowed improvement of detection limits and measurement accuracy.This study shows that the downcore distribution of radium isotopes is closely related to the reductive dissolution of iron and manganese oxyhydroxides below the sediment-water interface. The resulting diffusive fluxes of 226Ra and 228Ra (4.1 10−25 and 4.7 10−28 mol cm−2.s−1) are however significantly lower than other radium-impacted environments, such as uranium mill tailings pond and phosphate industry-impacted sediments, and are similar to those reported for natural marine environments. Hence, in the reduced lake sediments of Saint-Clement, the major fraction of radium is trapped by the solid phase, while early diagenesis only induces a slight mobility of this radioelement.

A preclinical PET dual-tracer imaging protocol for ER and HER2 phenotyping in breast cancer xenografts

BackgroundNuclear medicine is on the constant search of precision radiopharmaceutical approaches to improve patient management. Although discordant expression of the estrogen receptor (ER) and the human epidermal growth factor receptor 2 (HER2) in breast cancer is a known dilemma for appropriate patient management, traditional tumor sampling is often difficult or impractical. While 2-deoxy-2[18F]fluoro-D-glucose (18F-FDG)-positron emission tomography (PET) is an option to detect subclinical metastases, it does not provide phenotype information. Radiolabeled antibodies are able to specifically target expressed cell surface receptors. However, their long circulating half-lives (days) require labeling with long-lived isotopes, such as 89Zr, in order to allow sufficient time for tracer clearance from the blood compartment and to accumulate adequately in target tumors and, thus, generate high-quality PET images. The aim of this study was to develop a dual-tracer PET imaging approach consisting of a fast-clearing small molecule and a slow-clearing antibody. This approach was evaluated in a model consisting of mice harboring separate breast cancer xenografts with either an ER+/HER2− or ER−/HER2+ phenotype, comparable to human metastatic disease with intertumor heterogeneity. Lastly, the aim of our study was to determine the feasibility of specifically identifying these two important phenotypes in an acceptable time window.MethodsFemale nude mice were subcutaneously implanted on opposite shoulders with the ER+/HER2− and ER−/HER2+ MCF-7 and JIMT-1 tumor cell lines, respectively. A second model was developed consisting of mice implanted orthotopically with either MCF-7 or JIMT-1 cells. Pharmacokinetic analysis, serial PET imaging, and biodistribution were first performed for [89Zr]Zr-DFO-trastuzumab (89Zr-T) up to 8 days post-injection (p.i.) in JIMT-1 bearing mice. Region-of-interest (ROI) and biodistribution-derived uptake (% injected-activity/gram of tissue [%IA/g]) values and tumor-to-background ratios were obtained. Results were compared in order to validate ROI and identify early time points that provided high contrast tumor images. For the dual-tracer approach, cohorts of tumor-bearing mice were then subjected to sequential tracer PET imaging. On day 1, mice were administered 4-fluoro-11β-methoxy-16α-[18F]-fluoroestradiol (4FMFES) which targets ER and imaged 45 min p.i. This was immediately followed by the injection of 89Zr-T. Mice were then imaged on day 3 or day 7. ROI analysis was performed, and uptake was calculated in tumors and selected healthy organs for all radiotracers. Quality of tumor targeting for all tracers was evaluated by tumor contrast visualization, tumor and normal tissue uptake, and tumor-to-background ratios.Results89Zr-T provided sufficiently high tumor and low background uptake values that furnished high contrast tumor images by 48 h p.i. For the dual-tracer approach, 4FMFES provided tumor uptake values that were significantly increased in MCF-7 tumors. When 89Zr-T-PET was combined with 18F-4FMFES-PET, the entire dual-tracer sequential-imaging procedure provided specific high-quality contrast images of ER+/HER2− MCF-7 and ER−/HER2+ JIMT-1 tumors for 4FMFES and 89Zr-T, respectively, as short as 72 h from start to finish.ConclusionsThis protocol can provide high contrast images of tumors expressing ER or HER2 within 3 days from injection of 4FMFES to final scan of 89Zr-T and, hence, provides a basis for future dual-tracer combinations that include antibodies.

A systematic study of α-decay in superheavy nuclei using a Hartree-Fock-Bogoliubov model

Predictions on the alpha decay and spontaneous fission of the superheavy nuclei in the range of Z = 106–118 have been systematically done within the Hartree-Fock-Bogoliubov model and different Skyrme type interactions. A comparison of the results of the current study with experimental values showed good agreement. This study was extended to unknown isotopes in the range of Z = 116–118. The calculated alpha decay half-lives are in the range of 10−5 to 102 s which lie within measurable values. To identify the long-lived isotopes in the mass region, spontaneous fission half-lives were performed using a semi-empirical formula. The results revealed that the isotopes 276,275,274,272,268110, 276,275,273111, 282,280,279112, 281,280,279113, 284,283114, 286115, 289116, 296,295,292,291117, 297,296118, and 295,293,292118 survived fission and had alpha decay mode as the predominant mode of decay which could be synthesized in the laboratory.

Accelerator mass spectrometry: a remarkable week in May 1977

During a week in May 1977, solutions were found to the forty-year old problem of radiocarbon dating using mass spectrometry, as well as for the generalized mass spectrometry of measuring the abundances of extremely rare radioactive isotopes, such as long lived 236U. These solutions will be described together with a historical introduction, which points out the inherent advantages of some of the equipment developed for nuclear physics research that led towards the new mass spectrometry. In addition, the further developments, in what later came to be called accelerator mass spectrometry or AMS, can now be seen to have been the need to develop a better understanding of the following problems. (1) The appropriate atomic and molecular ion properties in order to expedite the separation of isobars. (2) The properties of the newer versions of the caesium sputter negative ion source that was hoped would almost eliminate the ion source memory effect. (3) The use of an improved accuracy tandem accelerator high voltage control for analysing very low final ion fluxes. Finally, (4) there was the need to assess the possible low level radiocarbon and other backgrounds of the accelerators or devices used to assist the isobar separation, after the accelerators had been used previously for many years of nuclear reaction studies. These developments were needed in order to add atomic and molecular isobar separation to the mass spectrometry for the further development of accelerator mass spectrometry (AMS) with tandem accelerators. When the basic problems had been solved, the detection and the accurate measurement of important natural very rare long-lived radio-active isotopes, such as for the sub parts per trillion (14C/C < 10−12) of natural 14C, was facilitated after further research. It was shown that there are very low levels of the atomic isobar anion 14N− from the caesium solid sample sputter ion source and that the 14C could be detected in the presence of over 1010 times as many mass 14 molecular anion hydrides 13CH−. The first and second excited states of the N anion, N(1S)− & N(1D)–, were shown later to exist but with short enough lifetimes for them not to interfere with the detection of 14C− at well below the level of 10−15 of 12C. The residual 14C background for an MP tandem accelerator, previously used for nuclear reaction studies, as well as the ion source memory effect were also found to be smaller than about 14C/C ~ 10−15 after the accelerator voltage control problem had been solved. These aims were all achieved during a week in May 1977 at the University of Rochester, leading also to the promise of the further successful development of radiocarbon dating by ion counting and the natural abundance measurements of other rare long lived radioactive isotopes by mass spectroscopy with anions or cations. In addition, the ability to date much smaller quantities of carbon, by a factor near 1000, was a huge advantage of the new method, as expected. However, it took almost a further decade of research and development to equal the accuracy of the mature beta counting radiocarbon dating method. The elimination of molecular ions from the mass spectrometry was later shown to be the key to detecting very low levels of actinides where atomic isobars are usually absent. The development of AMS for many other long lived radioactive isotopes is still continuing, as is the gradually increasing understanding of the need for an accelerator in some but not in all cases.

Production of quasi-stellar neutron field at explosive stellar temperatures

Neutron-induced reactions on unstable isotopes play a key role in the nucleosynthesis $i$--, $r$--, $p$--, $rp$-- and $\nu p$--processes occurring in astrophysical scenarios. While direct cross section measurements are possible for long-living unstable isotopes using the neutron Time-of-Flight method, the currently available neutron intensities ($\approx10^{6}$ n/s) require large samples which are not feasible for shorter lifetime isotopes. For the last four decades, the $^{7}$Li$(p,n)$ reaction has been used to provide a neutron field at a stellar temperature of $\approx$ 0.3 GK with significantly higher intensity, allowing the successful measurement of many cross sections along the $s$-process path. In this paper we describe a novel method to use this reaction to produce neutron fields at temperatures of $\approx$ 1.5-3.5 GK, relevant to scenarios such as convective shell C/Ne burning, explosive Ne/C burning, and core-collapse supernovae. This method will allow direct cross section measurements of many important reactions at explosive temperatures, such as $^{26}$Al$(n,p)$, $^{75}$Se$(n,p)$ and $^{56}$Ni$(n,p)$.

Quantifying Lithogenic Inputs to the Southern Ocean Using Long-Lived Thorium Isotopes

Thorium (Th) isotopes were applied to quantify the supply of lithogenic inputs from the Kerguelen Plateau to the Southern Ocean. The dissolved concentrations of 232Th and 230Th were measured following a novel pre-concentration method using the Nobias resin from 10 stations above and on the slopes of the plateau. Elevated 232Th/230Th ratios in the upper 500 m of the water column confirm the input of lithogenic material from islands, glaciers and the resuspension of shelf-deposited sediments. 230Th concentrations were used to calculate a scavenging residence time for Th, which was then applied to calculate the flux of dissolved 232Th required to match the observed concentrations of dissolved 232Th. The 232Th content of the lithogenic material from the Kerguelen Plateau was used with the solubility of Th reported in the literature, to estimate a lithogenic particle flux of 7 to 810 mg m–2 day–1. This flux is comparable to fluxes obtained using sediment traps (8–777 mg m–2 day–1) in other continental-margin zones of the Southern Ocean. The flux of dissolved iron, generated by the dissolution of particles, was also calculated (4,189–6,800 nmol m–2 day–1) based on the iron/thorium ratio in the material from the Kerguelen Plateau. This is higher than previous estimates (1,342 nmol m–2 day–1), suggesting the dissolution of particles as the missing source of iron, thus closing the iron budget of the region. This study confirms the utility of long-lived Th isotopes to quantify lithogenic inputs from continental margin settings.

EFFICIENCY OF VARIOUS MATERIALS APPLICATION FOR RADIATION SHIELDING AT TRANSPORTATION AND STORAGE OF SPENT NUCLEAR FUEL BY DRY METHOD

A model of the transport container intended for transportation of spent nuclear fuel (SFN) is studied. The passage of γ-quanta from the major long-lived isotopes is examined. The radiation shields made of iron, lead and depleted uranium, which are equivalent in mass to the thickness of iron of 15 to 35 cm is considered. The calculations are carried out using the Monte Carlo method (in MCNP and PHITS packages). The change in the characteristics of γ-radiation beyond the shields, made of different materials and with different thicknesses, is determined. For SNF from WWER-1000 with the thicknesses up to ~ 21 cm, the shield made of lead and uranium is shown to be more effective. If the thickness of the shield exceeds ~ 21 cm, then the shield made of iron is more effective. Increasing the thickness of the shields above 25 cm is shown to be inefficient, since the shields mass increases but the dose rate decreases slightly in this case.

ОЦЕНКА СКОРОСТИ НАРАБОТКИ ИЗОТОПОВ ЭЙНШТЕЙНИЯ И БЕРКЛИЯ В РЕАКТОРЕ ПИК

The production of einsteinium and berklium isotopes at reactor PIK is considered. Presently the design of the reactor core for reactor operation after full power startup is under consideration. The additional places for isotopes production in the reactor core can be organized besides the central experimental channel. The irradiation conditions in the central water trap and in the core are comparing. For this purpose we are comparing calculated here the neutron spectrums, neutron fluxes and cross sections of the main reactions which are influence on the isotope production. We maid the approximation of the averaged over reactor spectrums neutron reaction cross sections using thermal cross sections, resonance integral and Westcott factors. For the realistic isotope targets we have calculated the amound of produced einsteinium and berclium. Also we compare the accumulation speed of these two elements in the central water trap and in the reactor core. We have made the verification of the MCNP code calculations of the isotope production using analitic calculations and code SCALE. We have demonstrated that for targets with initial isotopes placed in the core the amount of produced einsteinium and berclium can be 4-5 times greater then for targets placed in the central experimental channel. However the time for isotope production in the core can be about two times longer. We are discussing also the main ambiguities in the reaction cross section which influences on the amount of the produced einsteinium in the target. The main ambiguity in the calculations of the produced amount of rather long-lived isotope Es-254 is introduced the neutron reaction cross sections of Es-253 nuclei espessially the isomeric ratio of the reaction of the neutron radiation capture.