Spectroscopy of Be-11 via B-11(d,He-2)Be-11 reaction at E(sub d) = 270 MeV

Abstract

In this study, the excited state of the neutron halo nucleus Be-11 was investigated by using the B-11(d,He-2)Be-11 reaction at Ed = 270 MeV. He-2 indicates proton-proton system coupled to the singlet S-state. The (d,He-2) reaction excites exclusively spin-isospin-flip excitation such as Gamow-Teller (GT) transitions ((Delta)L = 0) and Spin-flip Dipole (SD) transitions ((Delta)L = 1). The measurement was performed by means of the polarized deuteron. The thickness of the Be-11 self supporting target was 18.9 mg/sq cm. The scattered two protons were momentum analyzed by the spectrograph, SMART, and were detected by a multi wire chamber and a scintillator hodoscope located at the first focal plane. The angular distributions of the differential cross section and the analyzing powers, Ay, Ayy, and Axx were measured in the range theta(sub L) = 0 deg - 16 deg. The typical spectra of the differential cross section and the tensor analyzing power Axx showed several GT transitions at low excited energy region, a new peak at E(sub x) = 8.4 MeV and a broad bump at around E(sub x) = 10 MeV. The new peak is considered to be GT transition and the broad bump is seemed to be consisted of the spin-dipole transitions and higher (Delta)L transitions.

本研究では、中性子ハロー原子核Be-11の励起状態をEd=270MeVにおけるB-11(d,He-2)Be-11反応を用いて調べた。He-2は1重項S-状態に連結した陽子-陽子系を示す。(d,He-2)反応は、ガモフ-テラー(GT)遷移(ΔL=0)、スピン-フリップ双極子(SD)遷移(ΔL=1)の様なスピン-アイソスピン-フリップ励起を独占的に引き起こす。測定は偏極重陽子を使用して行った。Be-11単味標的の厚さは18.9 mg/平方センチメートルである。散乱した2個の陽子は分光写真器SMARTで運動量を分析し、多線式チェンバおよび第1の焦平面におけるシンチレータホドスコープにより検出した。微分断面積および偏極解析能Ay、Ayy、Axxの角分布をθ(sub L)=0度?16度の範囲で測定した。微分断面積およびテンソル偏極解析能Axxの典型的なスペクトルには、低い励起エネルギー領域で幾つかのGT遷移が、E(sub x)=8.4MeVに新しいピークが、またE(sub x)=10MeV付近に広い山が示された。この新しいピークはGT遷移と考えられ、また広い山はスピン-双極子遷移と高いΔL遷移から成っていると思われる。