skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Stellar neutron capture cross sections of the Lu isotopes

Abstract

The neutron capture cross sections of {sup 175}Lu and {sup 176}Lu have been measured in the energy range 3-225 keV at the Karlsruhe 3.7 MV Van de Graaff accelerator. Neutrons were produced via the {sup 7}Li(p,n){sup 7}Be reaction by bombarding metallic Li targets with a pulsed proton beam, and capture events were registered with the Karlsruhe 4{pi} barium fluoride detector. The cross sections were determined relative to the gold standard using isotopically enriched as well as natural lutetium oxide samples. Overall uncertainties of {approx}1% could be achieved in the final cross section ratios to the gold standard, about a factor of 5 smaller than in previous works. Maxwellian averaged neutron capture cross sections were calculated for thermal energies between kT = 8 and 100 keV. These values are systematically larger by {approx}7% than those reported in recent evaluations. These results are of crucial importance for the assessment of the s-process branchings at A 175/176.

Authors:
; ; ;  [1];  [2]
  1. Forschungszentrum Karlsruhe, Institut fuer Kernphysik, Postfach 3640, D-76021 Karlsruhe (Germany)
  2. (Russian Federation)
Publication Date:
OSTI Identifier:
20771236
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. C, Nuclear Physics; Journal Volume: 73; Journal Issue: 1; Other Information: DOI: 10.1103/PhysRevC.73.015807; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; BARIUM FLUORIDES; BERYLLIUM 7; BRANCHING RATIO; CAPTURE; CROSS SECTIONS; KEV RANGE; LITHIUM 7 TARGET; LUTETIUM 175; LUTETIUM 176; LUTETIUM OXIDES; NEUTRON REACTIONS; NEUTRONS; PROTON BEAMS; PROTON REACTIONS; S PROCESS

Citation Formats

Wisshak, K., Voss, F., Kaeppeler, F., Kazakov, L., and Institute for Physics and Power Engineering, Obninsk, Kaluga-Region. Stellar neutron capture cross sections of the Lu isotopes. United States: N. p., 2006. Web. doi:10.1103/PhysRevC.73.015807.
Wisshak, K., Voss, F., Kaeppeler, F., Kazakov, L., & Institute for Physics and Power Engineering, Obninsk, Kaluga-Region. Stellar neutron capture cross sections of the Lu isotopes. United States. doi:10.1103/PhysRevC.73.015807.
Wisshak, K., Voss, F., Kaeppeler, F., Kazakov, L., and Institute for Physics and Power Engineering, Obninsk, Kaluga-Region. Sun . "Stellar neutron capture cross sections of the Lu isotopes". United States. doi:10.1103/PhysRevC.73.015807.
@article{osti_20771236,
title = {Stellar neutron capture cross sections of the Lu isotopes},
author = {Wisshak, K. and Voss, F. and Kaeppeler, F. and Kazakov, L. and Institute for Physics and Power Engineering, Obninsk, Kaluga-Region},
abstractNote = {The neutron capture cross sections of {sup 175}Lu and {sup 176}Lu have been measured in the energy range 3-225 keV at the Karlsruhe 3.7 MV Van de Graaff accelerator. Neutrons were produced via the {sup 7}Li(p,n){sup 7}Be reaction by bombarding metallic Li targets with a pulsed proton beam, and capture events were registered with the Karlsruhe 4{pi} barium fluoride detector. The cross sections were determined relative to the gold standard using isotopically enriched as well as natural lutetium oxide samples. Overall uncertainties of {approx}1% could be achieved in the final cross section ratios to the gold standard, about a factor of 5 smaller than in previous works. Maxwellian averaged neutron capture cross sections were calculated for thermal energies between kT = 8 and 100 keV. These values are systematically larger by {approx}7% than those reported in recent evaluations. These results are of crucial importance for the assessment of the s-process branchings at A 175/176.},
doi = {10.1103/PhysRevC.73.015807},
journal = {Physical Review. C, Nuclear Physics},
number = 1,
volume = 73,
place = {United States},
year = {Sun Jan 15 00:00:00 EST 2006},
month = {Sun Jan 15 00:00:00 EST 2006}
}
  • The neutron capture cross sections of 175,176Lu and 176,177,178,179,180Hf have been measured in the energy range from 3 to 225 keV at the Karlsruhe 3.7 MV Van de Graaff accelerator relative to the gold standard. Neutrons were produced by the 7Li(p,n)7Be reaction and capture events were detected by the Karlsruhe 4{pi}BaF2 detector. The cross section ratios could be determined with uncertainties between 0.9 and 1.8% about a factor of five more accurate than previous data. A strong population of isomeric states was found in neutron capture of the Hf isotopes, which are only partially explained by CASINO/GEANT simulations based onmore » the known level schemes.Maxwellian averaged neutron capture cross sections were calculated for thermal energies between kT = 8 keV and 100 keV. Severe differences up to40% were found to the data of a recent evaluation based on existing experimental results. The new data allow for a much more reliable analysis of the important branching in the s-process synthesis path at 176Lu which can be interpreted as an s-process thermometer.« less
  • The neutron capture cross sections of [sup 146,148,150]Nd have been determined relative to that of gold by means of the activation method. The samples were irradiated in a quasistellar neutron spectrum for [ital kT]=25 keV using the [sup 7]Li([ital p],[ital n])[sup 7]Be reaction near threshold. Variation of the experimental conditions in different activations and the use of different samples allowed for the reliable determination of corrections and the evaluation of systematic uncertainties. The resulting stellar cross sections can be given with uncertainties around 6%, which represents a considerable improvement compared to previous measurements. These data are complemented by a newmore » set of calculated cross sections for the unstable isotopes [sup 147]Nd, [sup 147,148,149]Pm, and [sup 151]Sm, which act as branching points in the [ital s]-process path. Based on these results, the [ital s]-process flow in the Nd-Pm-Sm region is discussed with respect to the neutron density during stellar helium burning and to isotopic anomalies in meteorites. The updated [ital s]-abundances are also used for a discussion of [ital r]- and [ital p]-process residuals.« less
  • The neutron capture cross sections of [sup 134]Ba, [sup 135]Ba, [sup 136]Ba, and [sup 137]Ba were measured in the energy range from 5 to 225 keV. Neutrons were produced via the [sup 7]Li ([ital p],[ital n])[sup 7] Be reaction by bombarding metallic Li targets with a pulsed proton beam. Capture events were registered with the Karlsruhe 4[pi] barium fluoride detector. The cross section ratios were determined with an overall uncertainty of [similar to]3%, an improvement by factors of 5 to 8 compared to existing data. Severe discrepancies were found with respect to previous results. As a new possibility in timemore » of flight experiments, isomeric cross section ratios could be determined for [sup 135]Ba, [sup 136]Ba, and [sup 137]Ba. Maxwellian averaged neutron capture cross sections were calculated for thermal energies between [ital kT]=10 keV and 100 keV. These stellar cross sections were used in an [ital s]-process analysis. For the [ital s]-only isotopes [sup 134]Ba and [sup 136]Ba the [ital N][sub [ital s]][l angle][sigma][r angle] ratio was determined to 0.875[plus minus]0.025. Hence, a significant branching of the [ital s]-process path at [sup 134]Cs can be claimed for the first time, in contrast to predictions from the classical approach. This branching yields information on the [ital s]-process temperature, indicating values around [ital T][sub 8]=2. The new cross sections are also important for the interpretation of barium isotopic anomalies, which were recently discovered in SiC grains of carbonaceous chondrite meteorites. Together with the results from previous experiments on tellurium and samarium, a general improvement of the [ital N][sub [ital s]][l angle][sigma][r angle] systematics in the mass range [ital A]=120--150 is achieved. This yields a more reliable separation of [ital s]- and [ital r]-process contributions for comparison with stellar observations, but reveals a 20% discrepancy with respect to the solar barium abundance.« less
  • The neutron capture cross sections of {sup 114}Sn, {sup 115}Sn, {sup 116}Sn, {sup 117}Sn, {sup 118}Sn, and {sup 120}Sn were measured in the energy range from 3 to 225 keV at the Karlsruhe 3.75 MV Van de Graaff accelerator. Neutrons were produced via the {sup 7}Li({ital p},{ital n}){sup 7}Be reaction using a pulsed proton beam. Capture events were registered with the Karlsruhe 4{pi} barium fluoride detector. The experiment was complicated by the small ({ital n},{gamma}) cross sections of the proton magic tin isotopes and by the comparably low enrichment of the rare isotopes {sup 114}Sn and {sup 115}Sn. Despite significantmore » corrections for capture of scattered neutrons and for isotopic impurities, the high efficiency and the spectroscopic quality of the BaF{sub 2} detector allowed the determination of the cross-section ratios with overall uncertainties of 1{endash}2{percent}, five times smaller compared to existing data. Based on these results, Maxwellian averaged ({ital n},{gamma}) cross sections were calculated for thermal energies between {ital kT}=10 and 100 keV. These data are used for a discussion of the solar tin abundance and for an improved determination of the isotopic {ital s}- and {ital r}-process components. {copyright} {ital 1996 The American Physical Society.}« less
  • The neutron capture cross sections of {sup 142}Nd, {sup 143}Nd, {sup 144}Nd, {sup 145}Nd, {sup 146}Nd, and {sup 148}Nd have been measured in the energy range from 3 to 225 keV at the Karlsruhe 3.75 MV Van de Graaff accelerator. Neutrons were produced via the {sup 7}Li(p,n){sup 7}Be reaction by bombarding metallic Li targets with a pulsed proton beam. Capture events were registered with the Karlsruhe 4{pi} Barium Fluoride Detector. The cross sections were determined relative to the gold standard. The experiment was difficult due to the small cross sections of the even isotopes at or near the magic neutronmore » number N=82, and also since the isotopic enrichment of some samples was comparably low. The necessary corrections for capture of scattered neutrons and for isotopic impurities could be determined reliably thanks to the high efficiency and the spectroscopic quality of the BaF{sub 2} detector, resulting in a consistent set of (n,{gamma}) cross sections for the six stable neodymium isotopes involved in the s process with typical uncertainties of 1.5{endash}2{percent}. From these data, Maxwellian averaged cross sections were calculated between kT=10 and 100 keV. The astrophysical implications of these results were investigated in an s-process analysis, which deals with the role of the s-only isotope {sup 142}Nd for the N{sub s}{l_angle}{sigma}{r_angle} systematics near the magic neutron number N=82, the decomposition of the Nd abundances into the respective r-, s-, and p-process components, and the interpretation of isotopic anomalies in meteoritic material. {copyright} {ital 1998} {ital The American Physical Society}« less