Coulomb excitation of both Z and N approximately equal to 28

Abstract

Coulomb excitation of the N and Z approximately equal to 28 nucleus such as Ni-56 and Fe-56 was studied by the use of an unstable beam provided by the RIPS (RIKEN (Institute of Physical and Chemical Research) Projectile fragment Separator) at RIKEN ring cyclotron facility. A Pb-208 target was bombarded by a Ni-56 beam, and scattered Ni-56 nuclei were detected by a capital delta-E-E silicon detector telescope. The detected charged particle was identified by the capital delta-E-E method. The excitation to the 2(sup +) state of Ni-56 was identified by measuring the gamma-ray deexcitation of the 2(sup +) state in coincidence with the scattered Ni-56 particles. Fifty-six NaI(Tl) scintillators were placed around the target to detect the gamma rays. A 0.5 mm thick plastic scintillator was placed in front of the silicon detector telescope to obtain a timing signal providing the coincidence condition with the gamma-ray detector. A single photopeak at the 2.7 MeV corresponding to the 2(sup +) to 0(sup +) transition has been observed in the gamma-ray spectrum. The excitation cross section was obtained to be 212+/-13 mb. An experimental deformation parameter was extracted by comparing the predicted cross section, which was calculated by a coupled channel code ECIS88, with the experimental one. Electric quadrupole transition probability B(E2: 0(sup +) excited to 2(sup +)) was obtained from this deformation parameter to be 580+/-70 e(exp 2) fm(exp 4), which agreed with the value deduced from an analysis of the (Ni-56)+p inelastic scattering within experimental errors.

理化学研究所のリングサイクロトロン施設にあるRIPS(理化学研究所入射核破片分離器)の不安定核ビームを使って、Ni-56やFe-56のようなN?Z?28の核種のクーロン励起を研究した。標的核Pb-208にNi-56ビームを衝突させ、散乱したNi-56核をΔE-E型シリコン検出器望遠鏡で検出した。検出した荷電粒子はΔE-E法で同定した。Ni-56の2(sup +)状態への励起は、散乱されたNi-56粒子と同時に2(sup +)状態のγ-線脱励起を測定して同定した。標的の周囲にNaI(Tl)シンチレータを56個配置して、γ線を検出した。厚さ0.5mmのプラスチックシンチレータをシリコン検出器望遠鏡の前に置き、γ線検出器と同時条件となるタイミング信号を得た。γ線スペクトルのデータには、2(sup +)→0(sup +)遷移に対応して2.7MeVに単独のフォトピークが観測された。励起断面積は212±13mbであった。結合チャネルコードECIS88で計算した断面積の予測値を実験値と比較し、実験的な変形パラメータを求めた。この変形パラメータから求めた4重極遷移確率B(E2:0(sup +)→2(sup +))は580±70e(exp 2)fm(exp 4)であり、非弾性散乱(Ni-56)+pの解析から求めた値と実験誤差内で一致していた。