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$$E1$$ and $$E2$$ cross sections of the $$^{12}$$C($$alpha$$,$$gamma$$)$$^{16}$$O reaction at $$E_{rm{eff}}$$ $$sim$$ 1.2 MeV using pulsed $$alpha$$ beams

重心系エネルギー1.2MeV付近におけるパルス化$$alpha$$ビームを用いた$$^{12}$$C($$alpha$$,$$gamma$$)$$^{16}$$O反応断面積測定

牧井 宏之; 上田 仁*; 天満 康之*; 永井 泰樹*; 嶋 達志*; 藤本 臣哉*; 瀬川 麻里子; 三島 賢二*; 西山 潤*; 井頭 政之*

Makii, Hiroyuki; Ueda, Hitoshi*; Temma, Yasuyuki*; Nagai, Yasuki*; Shima, Tatsushi*; Fujimoto, Shinya*; Segawa, Mariko; Mishima, Kenji*; Nishiyama, Jun*; Igashira, Masayuki*

$$^{12}$$C($$alpha$$,$$gamma$$)$$^{16}$$O反応はHe燃焼期における恒星の進化を理解するうえで非常に重要な反応である。しかしながら、低エネルギー領域での断面積の測定結果には大きな不確定性がある。われわれは大立体角・高効率NaI(Tl)検出器,パルス化$$alpha$$ビーム,標的膜厚モニターからなる新しいシステムの構築を行った。この測定システムを用いて$$^{12}$$C($$alpha$$,$$gamma$$)$$^{16}$$O反応により発生した$$gamma$$の角度分布を行い、重心系エネルギー1.2MeV付近で$$E1$$及び$$E2$$断面積の絶対値を導出した。

The $$^{12}$$C($$alpha$$,$$gamma$$)$$^{16}$$O reaction cross section plays an important role in stellar evolution at the stage of helium-burning. However, the cross section at low energy still has a large uncertainty mainly due to the poor determination of the ratio of $$E2$$ cross section to $$E1$$ one. Hence, we have installed new system to make a precise measurement of the cross section. In this experiment, we used the high efficiency anti-Compton NaI(Tl) spectrometers with a large S/N ratio, an intense pulsed $$alpha$$ beams, and the monitoring system of target thickness. With use of the system we succeeded in removing a background due to neutron and could clearly detect the $$gamma$$-ray from the $$^{12}$$C($$alpha$$,$$gamma$$)$$^{16}$$O reaction with high statistics. We determined the $$E1$$ and $$E2$$ cross section down to $$E_{rm{eff}} sim $$ 1.2 MeV, and thus obtained results are compared to recent theoretical calculations.

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