E1 and E2 S factors of 12C(α,γ0)16O from γ-ray angular distributions with a 4 π-detector array
E1 and E2 S factors of 12C(α,γ0)16O from γ-ray angular distributions with a 4 π-detector array
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DOI：
10.1103/physrevc.73.055801
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发表时间：
2006-05-01
影响因子：
3.1
通讯作者：
Weil, J. L.
中科院分区：
文献类型：
--
作者：
Assuncao, M.;Fey, M.;Weil, J. L.
用斯图加特DYNAMITRON提供的高达340微安的强α粒子束，在常规运动学下进行了一项新的实验，以确定C-12(α，伽马)O-16反应的热核截面。首次使用4pi-Ge探测器装置同时测量所有角度的伽马射线角分布。它由九个EUROGAM高纯Ge探测器组成的阵列，在紧密的几何结构中，分别用锗酸铋晶体进行主动屏蔽。在注入过程中，通过磁分离对C-12靶进行同位素富集化。用卢瑟福背散射法测定了C-12靶中注入碳的深度分布，用于截面归一化和E_1和E_2 S因子的绝对测定。在E-Cm=1.30-2.78 MeV的能量范围内和在30度-130度的角度范围内测量了O-16基态的伽马衰变的角分布。根据这些分布，计算了天体物理的E_1和E_2 S因子与能量的函数，这两个函数对于该反应的模拟和向低能量的外推都是不可或缺的。通过将相位值Phi(12)作为自由参数，并利用相同能量范围内C-12的弹性α粒子散射结果来固定它，从而实现了E1和E2俘获通道的分离。
A new experiment to determine the thermonuclear cross section of the C-12(alpha,gamma)O-16 reaction has been performed in regular kinematics using an intense alpha-particle beam of up to 340 mu A from the Stuttgart DYNAMITRON. For the first time, a 4 pi-germanium-detector setup has been used to measure the angular distribution of the gamma rays at all angles simultaneously. It consisted of an array of nine EUROGAM high-purity Ge detectors in close geometry, actively shielded individually with bismuth germanate crystals. The C-12 targets were isotopically enriched by magnetic separation during implantation. The depth profiles of the implanted carbon in the C-12 targets were determined by Rutherford backscattering for purposes of cross-section normalization and absolute determination of the E1 and E2 S factors. Angular distributions of the gamma decay to the O-16 ground state were measured in the energy range E-c.m.=1.30-2.78 MeV and in the angular range (lab.) 30 degrees-130 degrees. From these distributions, astrophysical E1 and E2 S-factor functions vs energy were calculated, both of which are indispensable to the modeling of this reaction and the extrapolation toward lower energies. The separation of the E1 and E2 capture channels was done both by taking the phase value phi(12) as a free parameter and by fixing it using the results of elastic alpha-particle scattering on C-12 in the same energy range.