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Title: Detailed photonuclear cross-section calculations and astrophysical applications

Abstract

We have investigated the role of an isomeric state and its coupling to the ground state (g.s.) via photons and neutron inelastic scattering in a stellar environment by making detailed photonuclear and neutron cross-section calculations for /sup 176/Lu and /sup 210/Bi. In the case of /sup 176/Lu, the g.s. would function as an excellent galactic slow- (s-) process chronometer were it not for the 3.7-h isomer at 123 keV. Our calculations predicted much larger photon cross sections for production of the isomer, as well as a lower threshold, than had been assumed based on earlier measurements. These two factors combine to indicate that an enormous correction, a factor of 10/sup 7/, must be applied to shorten the current estimate of the half-life against photoexcitation of /sup 176/Lu as a function of temperature. This severely limits the use of /sup 176/Lu as a stellar chronometer and indicates a significantly lower temperature at which the two states reach thermal equilibrium. For /sup 210/Bi, our preliminary calculations of the production and destruction of the 3 /times/ 10/sup 6/ y isomeric state by neutrons and photons suggest that the /sup 210/Bi isomer may not be destroyed by photons as rapidly as assumed in certainmore » stellar environments. This leads to an alternate production path of /sup 207/Pb and significantly affects presently interpreted lead isotopic abundances. We have been able to make such detailed nuclear cross-section calculations using: modern statistical-model codes of the Hauser-Feshbach type, with complete conservation of angular momentum and parity; reliable systematics of the input parameters required by these codes, including knowledge of the absolute gamma-ray strength-functions for E1, M1, and E2 transitions; and codes developed to compute large, discrete, nuclear level sets, their associated gamma-ray branchings, and the presence and location of isomeric states. 7 refs., 2 figs.« less

Authors:
; ;
Publication Date:
Research Org.:
Lawrence Livermore National Lab., CA (USA)
OSTI Identifier:
5591330
Report Number(s):
UCRL-100547; CONF-8905187-3
ON: DE89017531
DOE Contract Number:  
W-7405-ENG-48
Resource Type:
Conference
Resource Relation:
Conference: WEIN '89: international symposium on weak and electromagnetic interactions in nuclei, Montreal, Canada, 15-19 May 1989; Other Information: Portions of this document are illegible in microfiche products
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; BISMUTH 210; PHOTONUCLEAR REACTIONS; LUTETIUM 176; ASTROPHYSICS; CALCULATION METHODS; CROSS SECTIONS; GROUND STATES; INELASTIC SCATTERING; ISOMERIC NUCLEI; PHOTOPRODUCTION; S PROCESS; STATISTICAL MODELS; TEMPERATURE DEPENDENCE; ALPHA DECAY RADIOISOTOPES; BASIC INTERACTIONS; BETA DECAY RADIOISOTOPES; BETA-MINUS DECAY RADIOISOTOPES; BISMUTH ISOTOPES; DAYS LIVING RADIOISOTOPES; ELECTROMAGNETIC INTERACTIONS; ENERGY LEVELS; HEAVY NUCLEI; HOURS LIVING RADIOISOTOPES; INTERACTIONS; INTERMEDIATE MASS NUCLEI; INTERNAL CONVERSION RADIOISOTOPES; ISOTOPES; LUTETIUM ISOTOPES; MATHEMATICAL MODELS; NUCLEAR REACTIONS; NUCLEI; ODD-ODD NUCLEI; PARTICLE PRODUCTION; RADIOISOTOPES; RARE EARTH ISOTOPES; RARE EARTH NUCLEI; SCATTERING; STAR EVOLUTION; YEARS LIVING; YEARS LIVING RADIOISOTOPES; 653003* - Nuclear Theory- Nuclear Reactions & Scattering

Citation Formats

Gardner, D G, Gardner, M A, and Hoff, R W. Detailed photonuclear cross-section calculations and astrophysical applications. United States: N. p., 1989. Web.
Gardner, D G, Gardner, M A, & Hoff, R W. Detailed photonuclear cross-section calculations and astrophysical applications. United States.
Gardner, D G, Gardner, M A, and Hoff, R W. 1989. "Detailed photonuclear cross-section calculations and astrophysical applications". United States. https://www.osti.gov/servlets/purl/5591330.
@article{osti_5591330,
title = {Detailed photonuclear cross-section calculations and astrophysical applications},
author = {Gardner, D G and Gardner, M A and Hoff, R W},
abstractNote = {We have investigated the role of an isomeric state and its coupling to the ground state (g.s.) via photons and neutron inelastic scattering in a stellar environment by making detailed photonuclear and neutron cross-section calculations for /sup 176/Lu and /sup 210/Bi. In the case of /sup 176/Lu, the g.s. would function as an excellent galactic slow- (s-) process chronometer were it not for the 3.7-h isomer at 123 keV. Our calculations predicted much larger photon cross sections for production of the isomer, as well as a lower threshold, than had been assumed based on earlier measurements. These two factors combine to indicate that an enormous correction, a factor of 10/sup 7/, must be applied to shorten the current estimate of the half-life against photoexcitation of /sup 176/Lu as a function of temperature. This severely limits the use of /sup 176/Lu as a stellar chronometer and indicates a significantly lower temperature at which the two states reach thermal equilibrium. For /sup 210/Bi, our preliminary calculations of the production and destruction of the 3 /times/ 10/sup 6/ y isomeric state by neutrons and photons suggest that the /sup 210/Bi isomer may not be destroyed by photons as rapidly as assumed in certain stellar environments. This leads to an alternate production path of /sup 207/Pb and significantly affects presently interpreted lead isotopic abundances. We have been able to make such detailed nuclear cross-section calculations using: modern statistical-model codes of the Hauser-Feshbach type, with complete conservation of angular momentum and parity; reliable systematics of the input parameters required by these codes, including knowledge of the absolute gamma-ray strength-functions for E1, M1, and E2 transitions; and codes developed to compute large, discrete, nuclear level sets, their associated gamma-ray branchings, and the presence and location of isomeric states. 7 refs., 2 figs.},
doi = {},
url = {https://www.osti.gov/biblio/5591330}, journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu Jun 15 00:00:00 EDT 1989},
month = {Thu Jun 15 00:00:00 EDT 1989}
}

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