Direct measurements of low-energy resonance strengths of the 23Na(p,?)24Mg reaction for astrophysics
Direct measurements of low-energy resonance strengths of the 23Na(p,?)24Mg reaction for astrophysics
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天体物理学中 23Na(p,?)24Mg 反应低能共振强度的直接测量
DOI：
10.1016/j.physletb.2019.05.044
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发表时间：
2019
影响因子：
4.4
通讯作者：
Boeltzig A
中科院分区：
文献类型：
--
作者：
Boeltzig A
摘要NeNa和MgAl循环在经历热底部燃烧的渐近巨星分支星的核合成中起着重要作用。Na 23（p，γ）24 Mg反应将这两个循环联系起来，需要精确测定其速率，以正确估计这些恒星对Na，Mg和Al各种同位素化学演化的贡献。在50 μ T ~ 110 MK的温度下，Ep = 140和251 keV的窄共振是反应速率的主要贡献者，除了在温度范围的较低部分占主导地位的直接捕获之外。我们提出了新的测量这些共振的强度在地下核天体物理实验室（LUNA）。我们使用了两种互补的检测方法：高效率的4π BGO探测器为140 keV的共振，和高分辨率的HPGe探测器为251 keV的共振。由于LUNA宇宙线背景的降低，我们能够确定251 keV共振的共振强度为ω γ= 482（82）μ eV，并在ex = 11931 keV处观察到Mg 24相应态衰变的新的γ射线跃迁。利用高效的BGO探测器，我们首次在直接测量中观察到了140 keV共振的信号，其强度为ω γ 140= 1.46− 0.53+ 0.58 neV（68% CL）。我们的测量将Na 23（p，γ）24 Mg反应速率在0.05 ~ 0.1 GK温度范围内的不确定度降低到0.07 GK时最多− 35%+ 50%。因此，我们的结果意味着显着减少的不确定性的核合成计算。
Abstract The NeNa and the MgAl cycles play a fundamental role in the nucleosynthesis of asymptotic giant branch stars undergoing hot bottom burning. The Na 23 (p, γ) 24 Mg reaction links these two cycles and a precise determination of its rate is required to correctly estimate the contribution of these stars to the chemical evolution of various isotopes of Na, Mg and Al. At temperatures of 50≲ T≲ 110 MK, narrow resonances at E p= 140 and 251 keV are the main contributors to the reaction rate, in addition to the direct capture that dominates in the lower part of the temperature range. We present new measurements of the strengths of these resonances at the Laboratory for Underground Nuclear Astrophysics (LUNA). We have used two complementary detection approaches: high efficiency with a 4π BGO detector for the 140 keV resonance, and high resolution with a HPGe detector for the 251 keV resonance. Thanks to the reduced cosmic ray background of LUNA, we were able to determine the resonance strength of the 251 keV resonance as ω γ= 482 (82) μ eV and observed new gamma ray transitions for the decay of the corresponding state in Mg 24 at E x= 11931 keV. With the highly efficient BGO detector, we observed a signal for the 140 keV resonance for the first time in a direct measurement, resulting in a strength of ω γ 140= 1.46− 0.53+ 0.58 neV (68% CL). Our measurement reduces the uncertainty of the Na 23 (p, γ) 24 Mg reaction rate in the temperature range from 0.05 to 0.1 GK to at most− 35%+ 50% at 0.07 GK. Accordingly, our results imply a significant reduction of the uncertainties in the nucleosynthesis calculations.