Constraints on the 22Ne(a,n)25Mg s-Process Neutron Source from Analysis of natMg+n Total and 25Mg(n,
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.
- Research Organization:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-00OR22725
- OSTI ID:
- 829108
- Report Number(s):
- P03-117761; PRVCAN; TRN: US0602160
- Journal Information:
- Physical Review, C (Nuclear Physics), Vol. 66, Issue 5; ISSN 0556-2813
- Country of Publication:
- United States
- Language:
- English
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