锦屏深地核天体物理实验(JUNA)的首个结果:^(25)Mg(p,γ)^(26)Al反应92 keV共振的精确测量

First result from the Jinping Underground Nuclear Astrophysics experiment JUNA:precise measurement of the 92 keV ^(25)Mg(p,γ)^(26)Al resonance

银河系星际介质中的^(26)Al衰变发射的1.809 MeVγ射线是γ天文学的主要观测对象之一,是银河系中正在进行核合成的关键证据,也为核合成理论与天文观测进行比较提供一个重要基准.在大质量恒星氢燃烧中,^(26)Al主要通过^(25)Mg(p,γ)^(26)Al反应产生,因此该反应在1.809 MeVγ射线研究中起着重要的作用.在天体环境温度为0.1 GK左右时,^(25)Mg(p,γ)^(26)Al天体物理反应率主要由92 keV共振俘获过程决定.作为在中国锦屏地下实验室(CJPL)中锦屏核天体物理实验(JUNA)装置上进行的首个实验,本工作对^(25)Mg(p,γ)^(26)Al反应的92 keV共振进行了精确的实验测量,得到了该共振的共振强度为ωγ=(3.80.3)10^(-10) eV,基态分支比为f0=0.660.04.与之前的工作相比,本工作大大提高了92 keV共振数据的精度.基于测量的92 keV共振参数和以前的间接测量结果,得到了精度最高的^(25)Mg(p,γ)^(26)Al天体物理反应率.结果表明,在0.1 GK左右时,新的反应率比REACLIB数据库中采用的反应率大2.4倍,这将导致^(26)Al和宇宙1.809 MeVγ射线的产额提高.同时,新反应率也将对理解太阳系的形成、球状星团的元素丰度反相关等问题提供重要的数据支撑.

The ^(25)Mg(p,γ)^(26)Al reaction plays an important role in the study of cosmic 1.809 MeV γ-ray as a signature of ongoing nucleosynthesis in the Galaxy.At astrophysical temperature around 0.1 GK,the ^(25)Mg(p,γ)^(26)Al reaction rates are dominated by the 92 keV resonance capture process.We report a precise measurement of the 92 keV ^(25)Mg(p,γ)^(26)Al resonance in the day-one experiment at Jinping Underground Nuclear Astrophysics experiment(JUNA)facility in the China Jinping Underground Laboratory(CJPL).The resonance strength and ground state feeding factor are determined to be 3.8±0.3×10^(-10) eV and 0:660:04,respectively.The results are in agreement with those reported in the previous direct underground measurement within uncertainty,but with significantly reduced uncertainties.Consequently,we recommend new ^(25)Mg(p,γ)^(26)Al reaction rates which are by a factor of 2.4 larger than those adopted in REACLIB database at the temperature around 0.1 GK.The new results indicate higher production rates of ^(26g)Al and the cosmic 1.809 MeV γ-ray.The implication of the new rates for the understanding of other astrophysical situations is also discussed.