到$s$ -过程分支点$^{79}$的全部和部分恒星横截面的首次测量
First measurements of the total and partial stellar cross section to the $s$-process branching-point $^{79}$Se
摘要：
虽然$^{79}$ Se代表了弱s过程中的一个重要分支，但这种同位素的恒星中子俘获截面还没有被实验测量。在这种情况下，实验数据是必不可少的，以评估在$^{79}$硒的s-过程反应路径中的重要分支。总截面的$^{78}$硒在恒星能量为kT = 25千电子伏的活化技术和加速器质谱（AMS）的组合进行了研究，因为离线衰变计数是禁止的，由于地球上的半衰期长的$^{79}$硒（2.80 $\pm$ 0.36 $\times10^5$ y），以及没有合适的$γ$ -射线转换。总麦克斯韦平均截面的初步结果为$<σ>_{30 keV}$ = 60.1 $\pm$ 9.6 mbarn，显著低于先前的推荐值。在第二次测量中，还通过$γ$ -光谱测定3.92 min-异构体的部分截面，并得到$<σ>_{30 keV}$（部分）= 42.0 $\pm$ 2.0 mbarn.
英文摘要：
Although $^{79}$Se represents an important branching in the weak s process, the stellar neutron capture cross sections to this isotope have not yet been measured experimentally. In this case, experimental data is essential for evaluating the important branching in the s-process reaction path at $^{79}$Se. The total cross section of $^{78}$Se at a stellar energy of kT = 25 keV has been investigated with a combination of the activation technique and accelerator mass spectrometry (AMS), since offline decay counting is prohibitive due to the long terrestrial half life of $^{79}$Se (2.80$\pm$0.36 $\times10^5$ y) as well as the absence of suitable $γ$-ray transitions. The preliminary result for the total Maxwellian averaged cross section is $<σ>_{30 keV}$= 60.1$\pm$9.6 mbarn, significantly lower than the previous recommended value. In a second measurement, also the partial cross section to the 3.92 min-isomer was determined via $γ$-spectroscopy and yielded $<σ>_{30 keV}$(part.)= 42.0$\pm$2.0 mbarn.
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