Charge state distribution of 16O from the 4He(12C,16O)γ reaction of astrophysical interest studied both experimentally and theoretically

• DOI: 10.1016/j.nimb.2014.02.115
• Publication Date: 2014-03-20T11:30:37Z
• Authors: Shengjin Liu; Makoto Sakurai; Kenshi Sagara; Takashi Teranishi; Kunihiro Fujita; Hiroyuki Yamaguchi; Sayaka Matsuda; Tatsuki Mitsuzumi; Makoto Iwazaki; Mariya T. Rosary; Daiji Kato; I.Yu. Tolstikhina
• Keywords: Charge density; Momentum (technical analysis)

In astrophysics, He-4(C-12,O-16)gamma reaction places an important role. At Kyushu University Tandem accelerator Laboratory (KUTL), the measurement of He-4(C-12,O-16)gamma cross section is in progress in the energy range of astrophysical nuclear reaction. Since the charge state of product O-16 ions after passing through the gas target is spread and only one charge state can be measured at terminal detector, it is necessary to know the charge state distribution of O-16 ions passing through the He gas target precisely. Here, we report the charge state distribution of the O-16 recoils both experimentally and theoretically. Experimentally, we measured the equilibrium charge state distribution of O-16 ions in the windowless helium gas target with the beam energy of primary O-16 ions at 7.2, 4.5, and 3.45 MeV at KUTL. The measured results showed a Gaussian distribution for the charge state fraction. Theoretically, we proposed a framework for the charge state distribution study. Charge state distribution was computed by solving a set of differential equations including a series of charge exchange cross sections. For the ionization cross section, plane-wave Born approximation was applied and modified by taking target atomic screening as a function of momentum transfer into account. For the capture cross section, continuum distorted wave approximation was applied and the influence of the gas target density was taken into account in the process of electron capture. Using above charge exchange cross sections, the charge state evolution was simulated. According to the equilibrium distribution, we compared the theoretical calculation to the experimental data. After taking into account the density effects in the charge exchange process, the theoretical charge state distributions shows a good agreement with the experimental data. Both experimental and theoretical results are useful to understand the charge fraction of recoil oxygen created via He-4(C-12,O-16)gamma reaction, especially in the energy range of astrophysical nuclear reaction. (C) 2014 Elsevier B.V. All rights reserved.