Measurement of fusion cross section of neutron-skin nucleus He-6

Abstract

The fusion cross section between a neutron skin nucleus He-6 and Ar-40 was measured in the vicinity of the Coulomb barrier with RIPS (RI Projectile-fragment Separator) at the Institute of Physical and Chemical Research cyclotron facility. A Be-9 production target was bombarded with a B-11 beam. The He-6 beam was separated by RIPS from other reaction fragments. The energy of He-6 was determined event by event by measuring a time of flight between two plastic scintillators placed at intervals of 5.3 m. The He-6 beam was led into a Multiple-Sampling and Tracking Proportional Chamber (MSTPC) to detect a three dimensional image of several tracks of charged particles and to detect the energy loss of those particles along their tracks. The MSTPC was filled with a mixed gas of 98 percent argon and 2 percent methane at 100 Torr pressure, where the gas acted as a target as well as a detection gas. In this paper, the energy losses for a fusion event and an elastic scattering event as well as the tracks of the projectile and target nuclei in an elastic scattering event are shown as examples.

中性子表面原子核He-6とAr-40の間の融合断面積を理化学研究所サイクロトロンのRIPS(RIビーム発生装置)においてクーロン障壁の近傍で測定した。Be-9製標的にB-11ビームを衝撃させた。He-6ビームはRIPSによって他の反応分裂片から分離した。He-6のエネルギーは、実験毎に、5.3mの間隔に置かれた2つのプラスチック製シンチレータの間の飛行時間を測定して決めた。He-6ビームは多重サンプリングおよびトラッキング比例チェンバ(MSTPC)に導入され、荷電粒子の飛跡数本を3次元画像で検出し、また各々の飛跡に沿ったこれら粒子のエネルギー損失を求めた。MSTPCは100Torr圧でアルゴン98%およびメタン2%の混合気体で満たされており、この気体は標的および検出気体としての役目を果たす。本報では、融合実験および弾性散乱実験でのネルギー損失、ならびに弾性散乱実験での発射体と標的原子核の飛跡を例として示してある。