Ge telescope for gamma-ray Doppler correction

Abstract

A germanium (Ge) counter telescope was developed for in-beam gamma ray spectroscopy utilizing High Spin Isomer Beam (HSIB). This system consists of a portion of Ge divided into 10 x 10 mm squares (hereafter Segge) for use as a DeltaE counter and a large-volume clover shaped portion of Ge (hereafter Clge) for use as an E counter. A gamma-ray Compton scattered by Segge is detected by Clge. Using a 50 percent Ge as an E counter, the gamma-ray spectrum of Eu-152 was obtained. Compared with those taken in a single mode only with Segge or Clge, the dependence of detection efficiency on energy level in a telescopic mode was relatively constant, which was similar to a simulated calculation. The recoil velocity of the reaction products of Al-27 bombarded by S-32 at E = 90 MeV was about 2 percent the velocity of light (beta was approximately 0.02), and when Doppler correction is applied to the gamma-ray spectrum, an energy resolution of below 10 KeV was obtained. The recoil velocity beta of Gd-148 formed by the irradiation of 7-MeV/u Ce-140 beam to C-12 was approximately 0.01. A small projection when no correction was made became a detectable peak as a result of Doppler correction.

高スピン異性核ビーム(HSIB)を用いたインビームγ線分光用のGeカウンタ望遠鏡を開発した。このシステムは、10×10mmの正方形に分割したGe(Segge)部のΔEカウンタと、大きな体積のクローバ形Ge(Clge)部のEカウンタからなる。Segge部でコンプトン散乱されたγ線をClge部で検出する。50%GeをEカウンタとして用い、Eu-152のガンマ線スペクトルを得た。Segge部やClge部などだけの単一モードと比べ、望遠モードにおける検出効率のエネルギー依存性は比較的一定で、シミュレーション計算により再現できた。90MeVのS-32を照射したAl-27の反応生成物の反跳速度は光速の約2%(β?0.02)で、γ線スペクトルにドップラー補正すると10KeV以下のエネルギー分解能が得られた。7MeV/uのCe-140ビームをC-12に照射して生成したGd-148の反跳速度はβ?0.10で、補正しないときの小さな突起がドップラー補正によりピークとして検出できた。