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Title: Constraints on the 22Ne(a,n) 25Mg s-Process Neutron Source from Analysis of natMg+n Total and 25Mg(n,

Abstract

The {sup 22}Ne(a,n){sup 25}Mg reaction is thought to be the neutron source during the s process in massive and intermediate mass stars as well as a secondary neutron source during the s process in low-mass stars. Therefore, an accurate determination of this rate is important for a better understanding of the origin of nuclides heavier than iron as well as for improving s-process models. Also, the s process produces seed nuclides for a later p process in massive stars, so an accurate value for this rate is important for a better understanding of the p process. Because the lowest observed resonance in direct {sup 22}Ne(a,n){sup 25}Mg measurements is considerably above the most important energy range for s-process temperatures, the uncertainty in this rate is dominated by the poorly known properties of states in {sup 26}Mg between this resonance and threshold. Neutron measurements can observe these states with much better sensitivity and determine their parameters (except {Lambda}{sub a}) much more accurately than direct {sup 22}Ne(a,n){sup 25}Mg measurements. I have analyzed previously reported {sup nat}Mg+n total and {sup 25}Mg(n,y) cross sections to obtain a much improved set of resonance parameters for states in {sup 26}Mg between threshold and the lowest observed {supmore » 22}Ne(a,n){sup 25}Mg resonance, and an improved estimate of the uncertainty in the {sup 22}Ne(a,n){sup 25}Mg reaction rate. For example, definitely two, and very likely at least four, of the states in this region have natural parity and hence can contribute to the {sup 22}Ne(a,n){sup 25}Mg reaction, but two others definitely have non-natural parity and so can be eliminated from consideration. As a result, a recent evaluation in which it was assumed that only one of these states has natural parity has underestimated the reaction rate uncertainty by at least a factor of 10, whereas evaluations that assumed all these states could contribute probably have overestimated the uncertainty.« less

Authors:
Publication Date:
Research Org.:
ORNL Oak Ridge National Laboratory
Sponsoring Org.:
USDOE
OSTI Identifier:
829108
Report Number(s):
P03-117761
Journal ID: ISSN 0556-2813; PRVCAN; TRN: US0602160
DOE Contract Number:  
AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review, C (Nuclear Physics); Journal Volume: 66; Journal Issue: 5
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; 73 NUCLEAR PHYSICS AND RADIATION PHYSICS; CROSS SECTIONS; ENERGY RANGE; IRON; ISOTOPES; NEUTRON SOURCES; NEUTRONS; NUCLEAR PHYSICS; ORIGIN; PARITY; REACTION KINETICS; RESONANCE; S PROCESS; SENSITIVITY; STARS

Citation Formats

Koehler, P.E.. Constraints on the 22Ne(a,n)25Mg s-Process Neutron Source from Analysis of natMg+n Total and 25Mg(n,. United States: N. p., 2002. Web. doi:10.1103/PhysRevC.66.055805.
Koehler, P.E.. Constraints on the 22Ne(a,n)25Mg s-Process Neutron Source from Analysis of natMg+n Total and 25Mg(n,. United States. doi:10.1103/PhysRevC.66.055805.
Koehler, P.E.. Wed . "Constraints on the 22Ne(a,n)25Mg s-Process Neutron Source from Analysis of natMg+n Total and 25Mg(n,". United States. doi:10.1103/PhysRevC.66.055805.
@article{osti_829108,
title = {Constraints on the 22Ne(a,n)25Mg s-Process Neutron Source from Analysis of natMg+n Total and 25Mg(n,},
author = {Koehler, P.E.},
abstractNote = {The {sup 22}Ne(a,n){sup 25}Mg reaction is thought to be the neutron source during the s process in massive and intermediate mass stars as well as a secondary neutron source during the s process in low-mass stars. Therefore, an accurate determination of this rate is important for a better understanding of the origin of nuclides heavier than iron as well as for improving s-process models. Also, the s process produces seed nuclides for a later p process in massive stars, so an accurate value for this rate is important for a better understanding of the p process. Because the lowest observed resonance in direct {sup 22}Ne(a,n){sup 25}Mg measurements is considerably above the most important energy range for s-process temperatures, the uncertainty in this rate is dominated by the poorly known properties of states in {sup 26}Mg between this resonance and threshold. Neutron measurements can observe these states with much better sensitivity and determine their parameters (except {Lambda}{sub a}) much more accurately than direct {sup 22}Ne(a,n){sup 25}Mg measurements. I have analyzed previously reported {sup nat}Mg+n total and {sup 25}Mg(n,y) cross sections to obtain a much improved set of resonance parameters for states in {sup 26}Mg between threshold and the lowest observed {sup 22}Ne(a,n){sup 25}Mg resonance, and an improved estimate of the uncertainty in the {sup 22}Ne(a,n){sup 25}Mg reaction rate. For example, definitely two, and very likely at least four, of the states in this region have natural parity and hence can contribute to the {sup 22}Ne(a,n){sup 25}Mg reaction, but two others definitely have non-natural parity and so can be eliminated from consideration. As a result, a recent evaluation in which it was assumed that only one of these states has natural parity has underestimated the reaction rate uncertainty by at least a factor of 10, whereas evaluations that assumed all these states could contribute probably have overestimated the uncertainty.},
doi = {10.1103/PhysRevC.66.055805},
journal = {Physical Review, C (Nuclear Physics)},
number = 5,
volume = 66,
place = {United States},
year = {Wed May 01 00:00:00 EDT 2002},
month = {Wed May 01 00:00:00 EDT 2002}
}