Sm Isotopes Research Articles

Cooper pairs in atomic nuclei

We consider the development of Cooper pairs in a self-consistent Hartree-Fock mean field for the even Sm isotopes. Results are presented at the level of a BCS treatment, a number-projected BCS treatment and an exact treatment using the Richardson ansatz. For a fixed value of the pairing strength, projected BCS captures much of the pairing correlation energy that is absent from BCS, but still misses a sizable component, typically of order 1 MeV. Furthermore, because it does not average over the properties of the fermion pairs, the exact Richardson solution permits a more meaningful definition of the Cooper wave function and of the fraction of pairs that are collective.

NMR study of Sm 2Co 17H x hydrides

An NMR study of Sm 2Co 17H x ( x = 0, 1.5, 4.6) hydrides is reported. The 147Sm and 149Sm spin echo spectra were measured on powder samples at 4.2 K with no applied magnetic field. The quadrupole septets (nuclear spin I of both Sm isotopes is 7/2) observed in the spectra are attributed to Sm sites with different numbers of hydrogen nearest neighbours located at the 9(e) and 18(g) sites in the crystal structure. Hydrogen neighbours at 9(e) sites cause a decrease of Sm hyperfine field, whereas hydrogen at 18(g) sites causes its increase, which is attributed to the changes of an anisotropic contribution of spin dipolar origin. The 9(e) neighbours cause a decrease of the quadrupole splitting, which corresponds to an increase of the lattice contribution to the electric field gradient. Hydrogen at 18(g) sites causes a slight decrease of the lattice electric field gradient. The results are analysed in terms of electron transfer between hydrogen and samarium sites and the difference between the effect of hydrogen at the 9(e) and 18(g) sites on the magnetocrystalline anisotropy is discussed.

Heterogeneous distribution of p-process Sm and Nd isotopes in the solar nebula

Heterogeneous distribution of p-process Sm and Nd isotopes in the solar nebula

Precise measurement of Sm isotopes by TIMS using double spike technique

Precise measurement of Sm isotopes by TIMS using double spike technique

Europium isotopic variations in Allende CAIs and the nature of mass-dependent fractionation in the solar nebula

We measured the 153Eu/ 151Eu ratio by MC-ICP-MS for a terrestrial basalt, two terrestrial soils, and four meteorites (whole rocks and/or chondrules of Bjurböle, Forest City, Murchison, and Allende) and found no isotopic variations. By contrast, two CAI separates from two different pieces of Allende show a 153Eu deficit of up to one per mil. Such a shortage in the heavy isotopes, which had also been identified in Allende CAIs for Sr [Patchett, P.J. 1980b. Sr isotopic fractionation in Allende chondrules: a reflection of solar nebular processes. Earth Planet. Sci. Lett. 50, 181–188], cannot reflect evaporative fractionation. The lack of Sm isotope fractionation in the same samples further makes fractionation by purely kinetic processes an unlikely cause of the anomalous Eu isotopic composition. An alternative interpretation is condensation from a vapor already significantly depleted in Eu, but in such a scenario the fate of the missing material is unclear. We therefore prefer yet another interpretation, based on the low ionization potential of Eu (and Sr), in which electromagnetic separation of the ionized gas preferentially depletes the nebular gas in heavy isotopes.

Regolith history of the aubritic meteorite parent body revealed by neutron capture effects on Sm and Gd isotopes

Enstatite achondrites (aubrites) when compared to other stone meteorites have unusually long cosmic-ray exposure (CRE) ages. We report here the 150Sm/ 149Sm and 158Gd/ 157Gd ratios in six different structural phases, i.e., light and dark (shocked) grains and in matrix materials of Pesyanoe, in three different fragments from Pena Blanca Spring, and in one from Norton County, Shallowater, and Khor Temiki, to investigate the regolith history on the aubrite parent body. The results from phases components of Pesyanoe confirm earlier reported evidence for regolith irradiation of several aubrites. The inferred neutron fluences for six Pesyanoe separates vary between (2.13 and 2.82) × 10 16 n cm −2. The fluences also significantly exceed those expected from cosmic-ray irradiation during transit to Earth and approach those observed in the lunar regolith. These observations confirm that the brecciated Pesyanoe meteorite, which contains solar wind (SW) gases only in dark phases, was processed in a regolith and that structural phases were differentially irradiated before compaction. On the other hand, in some aubrites (Mt. Egerton, Shallowater, Pena Blanca Spring, Norton County) neutron capture effects may entirely be due to space irradiation.

Branchings in the γ process path revisited

The location of the (gamma,p)/(gamma,n) and (gamma,alpha)/(gamma,n) line at gamma-process temperatures is discussed, using updated reaction rates based on global Hauser-Feshbach calculations. The results can directly be compared to classic gamma-process discussions. The nuclei exhibiting the largest sensitivity to uncertainties in nuclear structure and reaction parameters are specified and suggestions for experiments are made. Additionally, the impact of employing two recent global alpha+nucleus potentials is discussed. It is found that branchings at higher mass depend more sensitively on these potentials. The case of 146Sm/144Sm production is addressed separately. Also in this case, the more recent alpha+nucleus potentials seem to improve the issues concerning the production of these Sm isotopes in massive stars. In conclusion it is found that it is unlikely that the calculated underproduction of p nuclides in the Mo-Ru region is due to nuclear physics deficiencies but that problems at higher mass number may still be cured by improved nuclear input.

Postorogenic shoshonitic rocks and their origin by melting underplated basalts: The Miocene of Limnos, Greece

Research Article| January 01, 2009 Postorogenic shoshonitic rocks and their origin by melting underplated basalts: The Miocene of Limnos, Greece Georgia Pe-Piper; Georgia Pe-Piper * 1Department of Geology, Saint Mary's University, Halifax, Nova Scotia B3H 3C3, Canada †E-mail: gpiper@smu.ca. Search for other works by this author on: GSW Google Scholar David J.W. Piper; David J.W. Piper 2Geological Survey of Canada (Atlantic), Bedford Institute of Oceanography, P.O. Box 1006, Dartmouth, Nova Scotia B2Y 4A2, Canada Search for other works by this author on: GSW Google Scholar Ioannis Koukouvelas; Ioannis Koukouvelas 3Department of Geology, University of Patras, Patras 26110, Greece Search for other works by this author on: GSW Google Scholar Lila M. Dolansky; Lila M. Dolansky 4Department of Geology, Saint Mary's University, Halifax, Nova Scotia B3H 3C3, Canada Search for other works by this author on: GSW Google Scholar Sotiris Kokkalas Sotiris Kokkalas 5Department of Geology, University of Patras, Patras 26110, Greece Search for other works by this author on: GSW Google Scholar GSA Bulletin (2009) 121 (1-2): 39–54. https://doi.org/10.1130/B26317.1 Article history received: 23 Aug 2007 rev-recd: 06 Apr 2008 accepted: 22 Apr 2008 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Georgia Pe-Piper, David J.W. Piper, Ioannis Koukouvelas, Lila M. Dolansky, Sotiris Kokkalas; Postorogenic shoshonitic rocks and their origin by melting underplated basalts: The Miocene of Limnos, Greece. GSA Bulletin 2009;; 121 (1-2): 39–54. doi: https://doi.org/10.1130/B26317.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Potassium-rich volcanic rocks of the shoshonite suite are common features of postorogenic extensional settings inboard from subduction zones. Various petrogenetic processes and tectonic settings have been proposed for their origin. Early Miocene volcanic rocks of Limnos, part of the northeast Aegean shoshonite belt, show distinctive geochemical features that allow their petrogenesis to be well constrained. The rocks are principally trachyandesites and dacites. Very strong fractionation of light and middle rare earth elements (REEs), similar to that found in adakites, is inconsistent with a mantle source, but it can be modeled by melting of meta-basalt enriched in incompatible elements. A comparison with experimental melting of metabasaltic amphibolite requires small degrees of dehydration melting of amphibole, plagioclase, clinopyroxene, and minor garnet at a temperature >950 °C. Melting was triggered by mantle-derived magma, evidenced by repetitive zoning in clinopyroxene with Cr-rich cores. Nd and Sm isotopes suggest that some of this magma was similar to lamproite found elsewhere in this shoshonite belt and some was of asthenospheric origin. The amphibolite source is inferred to be subduction-enriched metabasalt that underplated the crust during pre-Mesozoic subduction. The regional trigger for dehydration melting was upwelling of asthenosphere as a result of slab detachment. The geochemistry and radiogenic isotopes of other shoshonitic rocks in the northeastern Aegean suggest a similar origin, but with higher degrees of partial melting of base-of-crust metabasaltic amphibolite. Similar processes appear likely for shoshonitic magmatism in some postcollisional settings elsewhere. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Octupole collectivity in the Sm isotopes

Microscopic models suggest the occurrence of strong octupole correlations in nuclei with $N\ensuremath{\approx}88$. To examine the signatures of octupole correlations in this region, the spdf interacting boson approximation model is applied to Sm isotopes with $N=86\text{\ensuremath{-}}92$. The effects of including multiple negative-parity bosons in this basis are compared with more standard one negative-parity boson calculations and are analyzed in terms of signatures for strong octupole correlations. It is found that multiple negative-parity bosons are needed to describe properties at medium spin. Bands with strong octupole correlations (multiple negative-parity bosons) become yrast at medium spin in $^{148,150}\mathrm{Sm}$. This region shares some similarities with the light actinides, where strong octupole correlations were also found at medium spin.

Anomalously Large Deformation in Some Medium and HeavyNuclei**The project supported by National Natural ScienceFoundation of China under Grant No. 10125521, the 973National Major State Basic Research and Development of Chinaunder Grant No. G2000077400, the CAS Knowledge InnovationProject No. KJCX2-SW-N02, and the Research Fund for theDoctoral Program of Higher Education of China under Grant No. 20010284036

We investigate the properties of theCe isotopes with neutron number N = 60–90 and the propertiesof the heavy nuclei near 242Am within the framework of deformedrelativistic mean-field (RMF) theory. A systematic comparison betweentheoretical results and experimental data is made. The calculatedbinding energies, two-neutron separation energies, and two-protonseparation energies are in good agreement with experimental ones.The variation trend of experimental quadrupole deformationparameters on the Ce isotopes can be approximately reproduced bythe RMF model. It is found that there exists an abnormally largedeformation in the ground state of proton-rich Ce isotopes. Thisphenomenon can be the general behavior of proton-rich nuclei on theneighboring isotopic chains such as Nd and Sm isotopes. For theheavy nuclei near 242Am the properties of the ground stateand superdeformed isomeric state can be approximatelyreproduced by the RMF model. The mechanism of the appearance ofanomalously large deformation or superdeformation is analyzed andits influence on nuclear properties is discussed. Furtherexperiments to study the anomalously largedeformation in some proton-rich nuclei are suggested.

Shape evolution for Sm isotopes in relativistic mean-field theory

The critical point nuclei in Sm isotopes, which marks the first order phase transition between spherical U(5) and axially deformed shapes SU(3), have been investigated in the microscopic quadrupole constrained relativistic mean field (RMF) model plus BCS method with all the most used interactions, i.e., NL1, NL3, NLSH and TM1. The calculated potential energy surfaces show a clear shape transition for the even-even Sm isotopes with $N = 82\sim 96$ and the critical point nuclei are found to be $^{148}$Sm, $^{150}$Sm and $^{152}$Sm. Similar conclusions can also be drawn from the microscopic neutron and proton single particle spectra.

Chemical characterization of earth’s most ancient clastic metasediments from the Isua Greenstone Belt, southern West Greenland

New and published major and trace element abundances of clastic metasediments (mainly garnet-biotite-plagioclase schists) from the ∼3.8 Ga Isua Greenstone Belt (IGB), southern West Greenland, are used in an attempt to identify the compositional characteristics of the protoliths of these sediments. Compositionally, the metasediments are heterogeneous with enrichment of LREE (La/Sm chond = 1.1–3.9) and variable enrichment and depletion of HREE (Gd/Yb chond = 0.8–4.3). Chondrite-normalized Eu is also variable, spanning a range from relative Eu depletion to enrichment (Eu/Eu* = 0.6–1.3). A series of geochemical and geological criteria provides conclusive evidence for a sedimentary origin, in disagreement with some previous studies that questioned the presence of genuine clastic metasediments. In particular, trace element systematics of IGB metasediments show strong resemblance to other well-documented Archaean clastic sediments, and are consistent with a provenance consisting of ultramafic, mafic and felsic igneous rocks. Two schists, identified as metasomatized mafic igneous rocks from petrographic and field evidence, show distinct compositional differences to the metasediments. Major element systematics document incipient-to-moderate source weathering in the majority of metasediments, while signs of secondary K-addition are rare. Detailed inspection of Eu/Eu*, Fe 2O 3 and CIW (chemical index of weathering) relationships reveals that elevated iron contents (when compared to averages for continental crust) and strong relative enrichment in Eu may be due to precipitation of marine Fe-oxyhydroxides during deposition or diagenesis on the seafloor. Some of the IGB metasediments have yielded anomalous 142Nd and 182W isotopic compositions that were respectively interpreted in terms of early mantle differentiation processes and the presence of a meteorite component. Alternatively, W and possibly Nd isotopes could have been affected by thermal neutron capture on the Hadean surface. The latter process was tested in this study by analysis of Sm isotope compositions, which serve as an effective monitor for neutron capture effects. As no anomalous variation from terrestrial values was detected, we infer that isotope systematics (including 182W and 142Nd) of IGB metasediments were not affected by neutron capture, but reflect decay of radioactive parent isotopes.

Systematic study ofL⩽3giant resonances in Sm isotopes via multipole decomposition analysis

Background-free inelastic scattering spectra have been obtained for five Sm isotopes with $386\text{\ensuremath{-}}\text{MeV}$ $\ensuremath{\alpha}$ particles at forward angles (including $0\ifmmode^\circ\else\textdegree\fi{}$) to investigate the effect of deformation on the compressional-mode giant resonances. The strength distributions for the $L\ensuremath{\leqslant}3$ isoscalar giant resonances have been extracted via a multipole decomposition analysis using angular distributions calculated in the framework of the density-dependent single-folding model. We observed a splitting of the giant monopole resonance because of its mixing with the giant quadrupole resonance. For the isoscalar giant dipole resonance, the observed effects of deformation are different for the low- and high-excitation-energy components. Evidence has been obtained for the theoretically predicted mixing between the isoscalar giant dipole resonance and the high energy octupole resonance.

Specific heat capacity and phase transition on 148—158Sm nucleiin microscopic core plus two-quasiparticle model

Using microscopic core plus two-quasiparticle model, the ground-band, β-band, γ-band and partial high spins states at zero temperature in even 148—158 Sm isotopes are successfully reproduced, these values are coincident with recent experimental one. Under canonical ensemble theory, their finite temperature specific heat capacity is calculated. Seeing that the peak of specific heat capacity is the signal of phase transition, it is by means of this approach that the phase transition of model thermo-excited, one from the superfluid nuclear phase to the normal phase, and one from the deformed shape to the spherical shape taken place in nuclei may be described untidily. The aligned energy and the identity of two-quasiparticle are discussed, and then the thermal stability of nuclear shape is investigated.

Caracterização isotópica de metabasitos e anfibolitos dos Grupos Açungui e Setuva na Porção Sul da Faixa Ribeira

Pb, Rb, Sr, Sm and Nd isotope analyses were carried out on amphibolitic rocks from Campo Largo (PR), Rio Branco do Sul (PR) and Adrianópolis (PR) and for the metabasite from Adrianópolis and Apiaí (SP), all belonging to the Açungui and Setuva Groups, southern portion of the Ribeira Belt. These occurrences were chosen because each exhibits geochemical data indicative of a mantle source, having different signatures. Geochronologic determinations are available only for the Apiaí metagabbro with Neoproterozoic ages of 617 ± 4 Ma (U/Pb in zircon) and 839 ± 85 Ma (Rb/Sr, whole rock). Age determinations by Sm/Nd mineral isochron using whole rock, plagioclase and pyroxene yield values of 885 ± 53 Ma for the Apiaí metagabbro and 820 ± 84 Ma for the Adrianópolis metabasite. These results agree within error with the Rb/Sr isochron of 839 ± 85 Ma may possibly be interpreted as the time of extraction of the magma from the mantle, as suggested by positive µNd(850) values (+2,76) from an Adrianópolis sample. An µNd values versus 87Sr/86Sr diagram shows that each studied occurrence plots in a different position, following approximately the mantle array trend, the most primitive being the metabasite of Adrianópolis, near the MORB field, and the most enriched being the amphibolite from the same region, near the enriched mantle and or crustal contamination field. The distinct difference in isotopic signatures between the amphibolite and metabasite suggests derivation from different mantle sources, as supported by available geochemical data. Nevertheless, some of the samples show isotopic evidence of the action of metamorphism, crustal contamination and weathering.

Compressional-mode giant resonances in deformed nuclei

Background-free inelastic scattering spectra have been obtained for the Sm isotopes with 400 MeV α particles at forward angles (including 0°) to investigate the effect of deformation on the compressional-mode giant resonances. The strength distributions for the isoscalar giant resonances (L⩽3) have been extracted for the spherical nucleus 144Sm and the deformed nucleus 154Sm. We have observed that the effects of deformation are different for the low- and high-excitation-energy components of the isoscalar giant dipole resonance in 154Sm. Evidence for the theoretically predicted coupling between the isoscalar dipole resonance and the high-energy octupole resonance is reported.

Collective Degrees of Freedom in Nuclear Level Densities

A finite temperature extension of the interacting boson model is developed and applied to the calculation of the collective partition function of transitional even-even Sm isotopes. The effective boson number decreases with increasing temperature, leading to a natural damping of collectivity. Positive and negative parity contributions to the boson partition function are computed and compared to rotational and vibrational enhancement factors commonly used in the generalized superfluid model.

Quadrupole moments of highly deformed structures in the A approximately 135 region: probing the single-particle motion in a rotating potential.

The latest generation gamma-ray detection system, GAMMASPHERE, coupled with the Microball charged-particle detector, has made possible a new class of nuclear lifetime measurement. For the first time differential lifetime measurements free from common systematic errors for over 15 different nuclei ( >30 rotational bands in various isotopes of Ce, Pr, Nd, Pm, and Sm) have been extracted at high spin within a single experiment. This comprehensive study establishes the effective single-particle transition quadrupole moments in the A approximately 135 light rare-earth region. Detailed comparisons are made with theoretical calculations using the self-consistent cranked mean-field theory which convincingly demonstrates the validity of the additivity of single-particle quadrupole moments in this mass region.

The dependence of the scissors mode on the deformation in the 140–150Ce isotopes

In this study, using a rotational invariant microscopic model which is free from any adjustable parameter in the random phase approximation, the total M1 transition intensities of the 1+ levels arising from the scissors mode for the Ce isotopes up to 4 MeV have been calculated and their dependence on the square of the deformation parameter δ2 has been investigated. In the Ce isotopes, the dependence of the total B(M1) transition on δ2 is linear as in the case of Nd and Sm isotopes. The separation of the rotational branch from the 1+ states causes the fragmentation of the scissors mode and the collectivization of low-lying states.

Radioelement transport in the Bangombé nuclear reactor zone (Gabon) – Evidence from U and Sm isotopes

ABSTRACTAs a natural analogue study of relevance to the safety margin of radioactive waste repository conditions, mineralogical and isotopic studies were carried out to assess the effects of the alteration of the Bangombé natural nuclear reaction zone. Mobilization and retention of reactor products were identified around the reactor. The high temperature alteration associated with the heat released during nuclear reactions lead to the partial dissolution of uraninite and the sorption of released U mostly by Al-chlorite. This was followed by the precipitation of secondary U-phases such as Zr-bearing uraninite and U-Ti oxides. The recent (<1 Ma) low temperature alteration lead to further dissolution of reactor core uraninite and mobilization of U and fissiogenic REE. Migrations took place laterally through hydraulically conductive fractures within sandstones and vertically through compacted shales, likely by diffusion-type process. Adsorption onto clays and Fe-oxides is the dominant mechanism of retention as inferred by the results of selective extraction experiments. The amounts released appear to be low compared with the quantities initially produced in the core and the transfers may have been limited within several meters around the reactor.