Precise measurement of stellar reaction rate of ^<12>C(α, γ)^<16>O with new experimental methods

利用新实验方法精确测量^<12>C(α, γ)^<16>O恒星反应速率

• 批准号: 11440077
• 负责人: SHIMA Tatsushi
• 金额: $ 4.99万
• 依托单位: Osaka University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (B).
• 财政年份: 1999
• 资助国家: 日本
• 起止时间: 1999 至 2000
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-11440077/
• 关键词: Nuclear astrophysics; Star; Nucleosynthesis; Helium-burning; ^<12>C(α, γ)^<16>O

The ^<12>C(α, γ)^<16>O reaction plays crucial roles in stellar He-burning, because it governs ^<12>C/^<16>O ratio after core He-burning, abundances of intermediate-mass nuclei produced in He-burning, and the iron core mass just before the type-II supernova explosion. Therefore it is quite important to determine the reaction rate at the center-of-mass energy Ecm<1 MeV, which corresponds to the temperature of stellar interior.In order to determine the reaction rate accurately, we developed a new experimental method using a pulsed α beam and the prompt γ-ray detection technique.In 1999 we developed a measurement system, consisting of a high-sensitivity and low-background γ-ray spectrometer and a 2ns pulsed α beam. We carried out a test experiment to check the performance of the system, and found major background is caused by the fast neutrons, which are produced by the (α, n) reactions on boron isotopes contained in the carbon target.Therefore, in 2000, we made efforts to reduce the backgrounds due to those neutrons. We changed the material of the target chamber from stainless steel to aluminum, which has a small (n, γ) cross section. Here the λ rays from the (n, γ) reactions occurring near the target is quite dangerous, because the area around the target is directly viewed by the γ-ray detectors. With the above improvement, we could obtain the S/N ratios better than 18 and 360 with a natural carbon target and an enriched ^<12>C target, respectively. With the present result, it is expected that the ^<12>C(α, γ)^<16>O cross section can be measured accurately down to Ecm 〜900keV.In addition, we designed another new method, which measures the inverse reaction, i.e. the ^<16>O(γ, α)^<12>C reaction. In this method, we will use a laser-Compton backscattered γ-ray beam and a time projection chamber filled with CO_2 gas. We made an experimental plan, and proposed it to U.S.DOE.

^<12>C（α，γ）^<16>O反应在恒星氦燃烧中起着至关重要的作用，因为它决定了核心氦燃烧后的^<12>C/^<16>O比，氦燃烧中产生的中等质量核的丰度，以及II型超新星爆炸前的铁核质量。因此，在质心能量Ecm&lt;1 MeV的范围内（对应于恒星内部的温度）测量反应速率是非常重要的。为了准确地测量反应速率，我们发展了一种新的实验方法，利用脉冲α束和瞬发γ射线探测技术，于1999年建立了一套测量系统，并在此基础上，对实验结果进行了分析。由高灵敏度、低背景的γ射线谱仪和2ns脉冲α束组成。我们进行了一次测试实验来检查系统的性能，发现主要的本底是由碳靶中硼同位素的（α，n）反应产生的快中子引起的，因此，我们在2000年努力减少这些中子引起的本底。我们将靶室的材料从不锈钢改为铝，铝具有小的（n，γ）截面。在这里，在目标附近发生的（n，γ）反应产生的λ射线是非常危险的，因为目标周围的区域直接被γ射线探测器观察到。通过上述改进，我们可以分别用天然碳靶和富集的N2 C靶获得优于18和360的S/N比<12>。在此基础上，<12><16>我们设计了一种新的方法来测量^O（γ，α）^C反应的逆反应，即^<16>O（γ，α）^<12>C反应。在这种方法中，我们将使用激光康普顿背散射γ射线束和充满CO_2气体的时间投影室。我们制定了一个实验计划，并提交给美国能源部。

项目成果

H.Makii, K.Mishima, T.Shima, Y.Nagai, E.Sano, M.Igashira, T.Ohsaki and K.Tosaka: "A new experimental system for the ^<12>C(α, γ)^<16>O reaction in the MeV region"Nuclear Instruments and Methods in Physics Research A. (in press). (2001)

H.Makii、K.Mishima、T.Shima、Y.Nagai、E.Sano、M.Igashira、T.Ohsaki 和 K.Tosaka：“^<12>C(α, γ)^ 的新实验系统<16>MeV区域中的O反应”《核仪器和物理研究方法A.》(出版中)。(2001)

T.Kii, T.Baba, T.Takahashi, T.Shima and Y.Nagai: "^<16>O(γ, α)^<12>C reaction using monochromatic gamma ray"Proceedings of Int.Symp.on Origin of Matter and Evolution of Galaxies 97, Ed.S.Kubono et al., World Scientific. 374-377 (1998)

T.Kii、T.Baba、T.Takahashi、T.Shima 和 Y.Nagai：“使用单色伽马射线的 ^<16>O(γ, α)^<12>C 反应”Int.Symp.on Origin 论文集物质与星系演化 97，Ed.S.Kubono 等人，世界科学 374-377 (1998)。

T.Shima,H.Makii,K.Mishima et al.: "New project of the ^<12>C(α,γ)^<16>O experiment"Proceedings of Int.Symp.on Origin of Matter and Evolution of Galaxies. 176-181 (1998)

T.Shima、H.Makii、K.Mishima 等人：“^<12>C(α,γ)^<16>O 实验的新项目”Int.Symp.on 物质起源和演化论文集星系。176-181（1998）

T.Kii,T.Baba,T.Takahashi et al.: "^<16>O(γ,α)^<12>C reaction using monochromatic gamma ray"Proceedings of Int.Symp.on Origin of Matter and Evolution of Galaxies. 374-377 (1998)

T.Kii、T.Baba、T.Takahashi 等人：“使用单色伽马射线的^<16>O(γ,α)^<12>C 反应”Proceedings of Int.Symp.on Origin of Matter and Evolution of Matter星系。374-377（1998）

H.Makii,K.Mishima,T.Shima et al.: "A new experimental system for the ^<12>C(α,γ)^<16>O reaction in the MeV region"Nuclear Instruments and Methods in Physics Research A. (in press). (2001)

H.Makii、K.Mishima、T.Shima 等人：“MeV 区域中 ^<12>C(α,γ)^<16>O 反应的新实验系统”物理研究中的核仪器和方法A.（正在出版）（2001）。