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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Behaviour of cadmium isotopes in sulfidic waters and sediments of the Black Sea: Implications for global cadmium cycling and the application of cadmium isotopes as a paleo-oceanographic proxy

The cadmium isotope system has found use as a tracer for biological productivity, redox and organic carbon burial in the oceans. There are, however, very few observational constraints on Cd isotopic behaviour in modern sulfidic marine conditions, limiting our understanding of the modern Cd cycle, and our ability to use Cd isotope measurements of ancient sedimentary deposits as a paleoceanographic proxy. Here we study the behaviour of dissolved Cd in the water column of the Black Sea and its incorporation into sediments on the basin floor. The isotopic composition of dissolved Cd in the upper ∼50 m of the Black Sea water column is controlled by a combination of biological uptake and regeneration along with mixing of river water and Mediterranean seawater. Cadmium declines to <2 % of its peak subsurface concentration within the zone of nitrate-reduction but above the sulfide chemocline. The isotopic composition of dissolved Cd below the sulfide chemocline evolves in a manner that is consistent with experimental Cd sulfide fractionation factors, providing field-based support for these earlier studies. In contrast, the stability of the dissolved Cd isotopic signature above the chemocline, despite a large reduction in dissolved Cd concentrations, is explained by diffusion towards the Cd-sulfide sink below the chemocline. Sediments accumulating in the deep Black Sea below the sulfide chemocline have isotopic compositions that are similar to dissolved Cd in its near-surface aqueous concentration maximum. Sediments accumulating at shallower depths have lighter isotopic compositions that are likely affected by non-sulfidic burial pathways mediated by macrofaunal mixing and diagenesis of shallow burial phases. Our study shows that the isotopic composition of bulk sediments accumulating under sulfidic conditions is similar to dissolved Cd in the upper water column, supporting its use as a paleo-chemical proxy for ancient seawater as long as basin-scale controls on open ocean seawater sources are considered. We show that Cd burial in the deep Black Sea, predominantly as CdS, accounts for ∼0.5–15 % of total annual Cd burial in the global ocean.

Biogeochemical cycles↗
DOE OSTI2022

Cadmium isotope systematics in sedimentary carbonate: Extending the utility of the cadmium isotope palaeo-productivity proxy

The cadmium (Cd) isotope compositions of seven Holocene (<11.7 ka) carbonate sediments, including the bulk carbonate, as well as the > 140 μm (zooplankton), <63 μm and < 20 μm (phytoplankton) fractions, and individual species of foraminifera isolated from the bulk carbonate were obtained for sub-samples processed using the Cd-cleaning and Mg/Ca cleaning methods. The respective Cd isotope systematics of each carbonate archive were then compared with the Cd isotope signature within the ocean using modern seawater data. We show that a constant Cd isotope fractionation factor of -0.25 ± 0.03 ‰ (2SE, n = 4) describes the partitioning of Cd from seawater into the carbonate phase ($Δ^{114}Cd_{CdC O_3 - seawater}$), allowing for accurate reconstructions of the past seawater nutrient regime. The Cd isotope signature of the < 63 µm and < 20 µm (phytoplankton) fractions can display comparable values to those recorded in the modern surface ocean, and can be used to model the magnitude of Cd uptake and utilisation in the past ocean. Individual species of planktic and benthic foraminifera, which inhabit different depths of the water column, can provide a full surface to deep water column reconstruction of the Cd nutrient regime, while infaunal benthic foraminifera can be used to interrogate the Cd isotope systematics of sediment porewaters. Bulk sediment and the > 140 µm (zooplankton) fraction also retain important information relating to the overlying water column Cd isotope systematics and can serve as essential archives for palaeo-productivity reconstructions where the separation of individual components from the bulk sediment is not possible. This new Cd isotope palaeo-productivity toolkit can considerably aid reconstruction efforts and vastly improves the ability to quantify the role of phytoplankton in modulating carbon sequestration through transitions in Earth’s climate evolution.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Examining the effects of chemical cleaning, leaching, and partial dissolution on zinc and cadmium isotope fractionation in marine carbonates

The application of zinc (Zn) and cadmium (Cd) isotopes as palaeo-proxies in carbonate sediment is rapidly expanding due to their potential for tracing changes in biological productivity in the modern and past oceans. However, there are limited investigations into the chemical cleaning methods required to produce the most consistent and accurate data for these novel isotope systems. This could impact their use as palaeo-proxies to reconstruct ocean-atmosphere-climate interactions throughout Earth's history. To address this concern and expand the utility of the Zn and Cd stable isotope systems as palaeo-productivity tracers, the performance of two standard chemical cleaning protocols for acquiring robust and reliable Zn and Cd isotope datasets were assessed. These include (i) the Cd-cleaning method that uses a reductive step to selectively leach contaminating secondary iron (Fe)-manganese (Mn) (oxyhydr)oxide coatings from the carbonate surface, and an oxidative step that is used to remove post-depositional organic matter and sulphide precipitates; and (ii) the magnesium/calcium cleaning protocol that includes an oxidative step only, leaving secondary Fesingle bondMn (oxyhydr)oxide coatings largely intact. Well-preserved Holocene-, and Mesozoic-aged carbonate sediments were used to test the reliability of these two chemical cleaning methods. The Holocene samples comprised not only aliquots of bulk sediment, but also individual species of planktic and benthic foraminifera. Our results show that the best practice chemical cleaning method for retrieving consistent and accurate Zn and Cd isotope, and Zn/Ca and Cd/Ca datasets for carbonate sediments, requires both reductive and oxidative cleaning following the Cd-cleaning method. This differs from most methodological approaches applied to date that remove the reductive step from the chemical cleaning protocol and apply an oxidative step only, or no chemical cleaning at all. Inclusion of the reductive step in the chemical cleaning method typically shifts δ 66 Zn by ~0.1‰ lower and δ 114 Cd by 0.3‰ higher in the solid phase, while Zn/Ca and Cd/Ca typically decrease 2-fold. The benthic foraminifera, C. wuellerstorfi, that live in ocean bottom waters where the seawater Zn and Cd isotope composition is homogeneous display evidence of Zn and Cd isotope fractionation between seawater and carbonate on the order of 0.08 ± 0.08‰ (2SE, n = 4) and -0.25 ± 0.13‰ (2SE, n = 4), respectively, in agreement with experimental constraints. Furthermore, evidence of Zn isotope fractionation effects are recorded in a naturally-dissolved carbonate sediment, together with laboratory-controlled carbonate dissolution experiments. Based on these results, we recommend the Cd-cleaning method and the application of Zn and Cd isotope fractionation factors to accurately reconstruct past seawater Zn and Cd isotope compositions from carbonate sediments.

58 GEOSCIENCES↗
DOE OSTI2016

Photonuclear reactions on the cadmium isotopes {sup 106,108}Cd at the bremsstrahlung endpoint energy of 55.5 MeV

The gamma-activation technique was used to measure the absolute yields of photonuclear reactions on the cadmium isotopes {sup 106,108}Cd. The results obtained in this way were compared with the results of the calculations based on the statistical model. For reactions on the isotope {sup 108}Cd, agreement between these theoretical and experimental results is good, but the experimental ratio of the yields of photoproton and photoneutron reactions on the isotope {sup 106}Cd differs substantially from its theoretical counterpart. The results of our present study are discussed from the point of view of the production of bypassed nuclei in the p-process of nucleosynthesis.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Cadmium mass measurements between the neutron shell closures at N = 50 and 82

The mass values of the neutron-deficient cadmium isotopes {sup 99-109}Cd and of the neutron-rich isotopes {sup 114,120,122-124,126,128}Cd have been measured using ISOLTRAP. The behavior of the separation energies of the cadmium isotopes from N = 50 to 82 is discussed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

E2 rotational invariants of 0$^{+}_{1}$ and 2$^{+}_{1}$ states for 106 Cd: The emergence of collective rotation

The collective structure of 106 Cd is elucidated by multi-step Coulomb excitation of a 3.849 MeV/A beam of 106 Cd on a 1.1 mg/cm 2 208 Pb target using GRETINA-CHICO2 at ATLAS. Fourteen E2 matrix elements were obtained. The nucleus 106 Cd is a prime example of emergent collectivity that possesses a simple structure: it is free of complexity caused by shape coexistence and has a small, but collectively active number of valence nucleons. This work follows in a long and currently active quest to answer the fundamental question of the origin of nuclear collectivity and deformation, notably in the cadmium isotopes. The results are discussed in terms of phenomenological models, the shell model, and Kumar-Cline sums of E2 matrix elements. The < 0$^{+}_{2}$ ||E2||2$^{+}_{1}$ > matrix element is determined for the first time, providing a total, converged measure of the electric quadrupole strength, < Q 2 >, of the first-excited 2$^{+}_{1}$ level relative to the 0$^{+}_{1}$ ground state, which does not show an increase as expected of harmonic and anharmonic vibrations. Strong evidence for triaxial shapes in weakly collective nuclei is indicated; collective vibrations are excluded. This is contrary to the only other cadmium result of this kind in 114 Cd by C. Fahlander et al., Nucl. Phys. A485, 327 (1988), which is complicated by low-lying shape coexistence near midshell.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Measurement of Mass-Independent Perturbations of Cadmium in Nuclear Debris Samples

The isotopic composition of cadmium in nuclear debris was measured by multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS). Mass-independent perturbations due to fission product decay on the isotopes of Cd were observed. Relative fission yields for masses 111, 112, 114 and 116 were determined in each sample of nuclear debris and compared with reported values found in irradiated plutonium and uranium fuels. Mass spectrometry measurements of the valley fission product endpoints are extremely challenging due to the low cumulative fission yields and small amounts of each isotope that are produced. To overcome these challenges, a new purification method for Cd was developed and validated by examination of a number of geological reference materials.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2011

Nuclear Data Sheets for A = 127

The 1996 evaluation for the A=127 mass chain (1996Ki01) has been revised. The experimental results from various decays and reactions for the A=127 mass chain have been compiled and evaluated. The nuclides covered in this evaluation are from {sup 127}Ag to {sup 127}Nd. The data are summarized and presented, together with adopted level schemes.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Measurements of ISGMR in Sn, Cd and Pb isotopes and the asymmetry of nuclear matter incompressibility

The compression-mode isoscalar giant monopole resonance (ISGMR) has been studied in the Sn, Cd and Pb isotopes using inelastic scattering of 400 MeV {alpha}-particles at extreme forward angles, including 0 deg. We have obtained completely 'background-free' inelastic-scattering spectra for the Sn, Cd, and Pb isotopes for a wide angular and excitation-energy range. The various giant resonances excited with different transferred angular momenta were extracted by a multipole-decomposition analysis (MDA). It was found that the centroid energies of the ISGMR in Sn isotopes are significantly lower than the theoretical predictions. The K{sub {tau}} in the empirical expression for the nuclear incompressibility has been determined to be K{sub {tau}} = -550{+-}100 MeV for the Sn isotopes. The extracted value for the Cd isotopes is K{sub {tau}} = -480{+-}100 MeV. These numbers are consistent with values of K{sub {tau}} = -370{+-}120 MeV obtained from an analysis of the isotopic transport ratios in medium-energy heavy-ion reactions, K{sub {tau}} -500{sub -100}{sup +120} MeV obtained from constraints placed by neutron-skin data from anti-protonic atoms across the mass table, and K{sub {tau}} = -500{+-}50 MeV obtained from theoretical calculations using different Skyrme interactions and relativistic mean field (RMF) Lagrangians. Stringent constraints on interactions employed in nuclear structure calculations are obtained on the basis of the experimentally determined values for K{sub {infinity}} and K{sub {tau}}. These parameters constrain as well the equation of state (EOS) of nuclear matter. However, a significant discrepancy still remains. The ISGMR positions in Sn and Cd isotopes are systematically lower than the predictions obtained on basis of determined from the ISGMR in {sup 208}Pb. This raises the question ''Why are Sn and Cd nuclei so soft?''. For a clue to solve the problem, we discuss the preliminary results on the exact positions of the ISGMR in {sup 204,206,208}Pb.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

In-beam fast-timing measurements in {sup 103,105,107}Cd

Fast-timing measurements were performed in the region of the medium-mass {sup 103,105,107}Cd isotopes, produced in fusion evaporation reactions. Results on new and reevaluated half-lives are analyzed within a systematic study of transition rates. The 7/2{sub 1}{sup +} states in {sup 103,105,107}Cd are interpreted as arising from a single-particle excitation. The 9/2{sup +} states configuration assignment is based on the observed decay branches.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Mapping quadrupole collectivity in the Cd isotopes: The breakdown of harmonic vibrational motion

The stable Cd isotopes have long been used as paradigms for spherical vibrational motion. Extensive investigations with in-beam {gamma} spectroscopy have resulted in very-well-established level schemes, including many lifetimes or lifetime limits. A programme has been initiated to complement these studies with very-high-statistics {beta} decay using the 8{pi} spectrometer at the TRIUMF radioactive beam facility. The decays of {sup 112}In and {sup 112}Ag have been studied with an emphasis on the observation of, or the placement of stringent limits on, low-energy branches between potential multi-phonon levels. A lack of suitable 0{sup +} or 2{sup +} three-phonon candidates has been revealed. Further, the sum of the B(E2) strength from spin 0{sup +} and 2{sup +} states up to 3 MeV in excitation energy to the assigned two-phonon levels falls far short of the harmonic-vibrational expectations. This lack of strength points to the failing of collective models based on vibrational phonon structures.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

The ferroelectric phase of CdTiO{sub 3}: A powder neutron diffraction study

The synthesis of bulk samples of polycrystalline CdTiO{sub 3} in both the rhombohedral ilmenite and orthorhombic perovskite forms is described and the structures of these have been refined using powder neutron diffraction data. This involved the preparation of samples enriched in {sup 114}Cd. Cooling perovskite-type CdTiO{sub 3} to 4 K induces a ferroelectric phase transition, with the neutron data suggesting the low temperature structure is in Pna2{sub 1}. Mode analysis shows the polar mode to be dominant at low temperatures. The ilmenite-structure of CdTiO{sub 3} is compared with that of ZnTiO{sub 3}. The refined scattering length of the {sup 114}Cd is estimated to be 5.56 fm. Attempts to dope CdTiO{sub 3} with Ca and Sr are described. - Graphical abstract: The structure of three phases of CdTiO{sub 3} have been refined using high resolution powder neutron diffraction data. This involved the preparation of samples enriched in {sup 114}Cd. Cooling perovskite-type CdTiO{sub 3} to 4 K results in a ferroelectric phase in Pna2{sub 1}. Highlights: > Both the ilmenite and perovskite forms of CdTiO{sub 3} have been prepared using {sup 114}Cd. > Cooling the perovskite form results in a ferroelectric phase. > The structures of these are refined from powder neutron diffraction data. > Attempts to dope CdTiO{sub 3} are described.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Nuclear Structure Research at Richmond

The goals for the final year were; (1) to continue ongoing efforts to develop and enhance GRETINA and work towards GRETA; (2) to investigate the structure of non-yrast states in shape transitional Sm and Gd nuclei; (3) to investigate the structure of selected light Cd nuclei; (4) to exploit the surrogate reaction technique to extract (n,f) cross sections for actinide nuclei, particularly the first measurement of the 236 Pu and 237 Pu(n,f) cross sections.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗