加速器质谱法测定~（40）Ca的恒星（n，γ）截面
Determination of the stellar (n,gamma) cross section of 40Ca with accelerator mass spectrometry
摘要：
用活化技术和加速器质谱（AMS）相结合的方法测量了kT=25 keV的~（40）Ca的（n，γ）截面。当产生的活性的直接离线计数由于长半衰期和/或缺失的伽马射线跃迁而受到损害时，需要这种组合。中子活化是在卡尔斯鲁厄Van de Graaff加速器上用7 Li（p，n）7 Be反应产生的kT=25 keV的准星中子谱进行的。随后的AMS测量是在维也纳环境研究加速器（VERA）用3 MV串列加速器进行的。双魔40 Ca是硅不完全燃烧的瓶颈同位素，其中子俘获截面决定了泄漏量，从而影响铁族元素的最终生成。由于其高丰度，40 Ca也可以作为s-过程的“中子毒物”发挥次要作用。以前在恒星能量下对这个值的测定是基于飞行时间测量的。我们的方法使用一个独立的方法，并产生麦克斯韦平均截面在kT=30 keV的值为30 <sigma>keV= 5.73+/-0.34 mb。
英文摘要：
The stellar (n,gamma) cross section of 40Ca at kT=25 keV has been measured with a combination of the activation technique and accelerator mass spectrometry (AMS). This combination is required when direct off-line counting of the produced activity is compromised by the long half-life and/or missing gamma-ray transitions. The neutron activations were performed at the Karlsruhe Van de Graaff accelerator using the quasistellar neutron spectrum of kT=25 keV produced by the 7Li(p,n)7Be reaction. The subsequent AMS measurements were carried out at the Vienna Environmental Research Accelerator (VERA) with a 3 MV tandem accelerator. The doubly magic 40Ca is a bottle-neck isotope in incomplete silicon burning, and its neutron capture cross section determines the amount of leakage, thus impacting on the eventual production of iron group elements. Because of its high abundance, 40Ca can also play a secondary role as "neutron poison" for the s-process. Previous determinations of this value at stellar energies were based on time-of-flight measurements. Our method uses an independent approach, and yields for the Maxwellian-averaged cross section at kT=30 keV a value of <sigma>30 keV= 5.73+/-0.34 mb.
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