Correlated uncertainties in Monte Carlo reaction rate calculations

被引:7
|
作者
Longland, Richard [1 ,2 ]
机构
[1] North Carolina State Univ, Raleigh, NC 27695 USA
[2] Triangle Univ Nucl Lab, Durham, NC 27708 USA
来源
ASTRONOMY & ASTROPHYSICS | 2017年 / 604卷
关键词
methods: numerical; methods: statistical; nuclear reactions; nucleosynthesis; abundances; THERMONUCLEAR REACTION-RATES; GALACTIC GLOBULAR-CLUSTERS; SELF-POLLUTION; RESONANCE STRENGTHS; PROTON-CAPTURE; MASSIVE STARS; NUCLEOSYNTHESIS; NUCLEI; COMPUTATION; EVOLUTION;
D O I
10.1051/0004-6361/201730911
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
Context. Monte Carlo methods have enabled nuclear reaction rates from uncertain inputs to be presented in a statistically meaningful manner. However, these uncertainties are currently computed assuming no correlations between the physical quantities that enter those calculations. This is not always an appropriate assumption. Astrophysically important reactions are often dominated by resonances, whose properties are normalized to a well-known reference resonance. This insight provides a basis from which to develop a flexible framework for including correlations in Monte Carlo reaction rate calculations. Aims. The aim of this work is to develop and test a method for including correlations in Monte Carlo reaction rate calculations when the input has been normalized to a common reference. Methods. A mathematical framework is developed for including correlations between input parameters in Monte Carlo reaction rate calculations. The magnitude of those correlations is calculated from the uncertainties typically reported in experimental papers, where full correlation information is not available. The method is applied to four illustrative examples: a fictional 3-resonance reaction, Al-27(p, gamma)Si-28, Na-23(p, alpha)Ne-20, and Na-23(alpha, p)Mg-26. Results. Reaction rates at low temperatures that are dominated by a few isolated resonances are found to minimally impacted by correlation effects. However, reaction rates determined from many overlapping resonances can be significantly affected. Uncertainties in the Na-23(alpha, p)Mg-26 reaction, for example, increase by up to a factor of 5. This highlights the need to take correlation effects into account in reaction rate calculations, and provides insight into which cases are expected to be most affected by them. The impact of correlation effects on nucleosynthesis is also investigated.
引用
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页数:9
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