Plan for lifetime measurements of excited states using the recoil decay tagging technique with gas-filled recoil separator

Abstract

An In-beam gamma ray spectroscopy experiment using the recoil decay tagging and a lifetime measurement of excited states with Gas filled Recoil Isotope Separator (GARIS) are proposed. The recoiling nuclei are separated from the primary beam by the GARIS, and then are implanted into a two-dimensional Position Sensitive Detector (PSD). The implantation of the Evaporation Residues (ER) and their alpha decays are detected by the PSD. The time of flight measurement is additionally performed between a Micro Channel Plate (MCP) assembly, set before the PSD and the PSD. By using the gamma ray detectors placed around the target, both the fully Doppler shifted and the reduced Doppler shifted gamma rays are measured. In order to determine the fully Doppler shifted peak, a retardation foil is placed between the target and the GARIS. The effect of the thickness of retardation foil on the gamma ray spectra of fully Doppler shifted peak and the reduced Doppler shifted peak of transition from 2(sub 1)(+) to 0(sub 1)(+) in Pt-174, produced by the reaction In-115(Cu-63,4n), was simulated under appropriate assumptions in this study. When the gold foil of the thickness of 2 mg/sq cm was used as the retardation foil, the gamma ray spectrum could not be divided into two peaks, however when a 4 mg/sq cm thick gold foil was used, the spectrum could be divided into two peaks. The decay curve, R(D), can be determined simply from the peak intensity of fully Doppler shifted component, I(sub fs)(D), by considering the following relation: R(D) = 1 - I(sub fs)(D)/I(sub fs)(infinity), where D is the distance between the target and the retardation foil. The component I(sub fs)(D) at every distance can be normalized by using the total number of the recoiling nuclei, which can be deduced from the alpha decay spectrum detected by the PSD. The value of I(sub fs)(infinity) can be measured by setting the apparatus without a retardation foil.

反跳崩壊タギングを用いたインビームγ線分光実験と、ガス充填反跳同位体分離器(GARIS)による励起状態の寿命測定を提案した。この方法では、反跳原子核をGARISにより1次ビームから分離後、2次元的な位置敏感検出器(PSD)に注入し、注入した蒸発残留物(ER)とそのα崩壊をPSDで検出する。PSDの前にマイクロチャネルプレート(MCP)を置き、PSDまで飛行時間を補足的に測定する。ターゲット周囲に配置したγ線検出器により、完全にドップラーシフトしたγ線とドップラーシフトが低減されたγ線の両者を測定する。完全なドップラーシフトを測定するため、ターゲットとGARIS間に遅延箔を設ける。本研究では、γ線スペクトルの完全なドップラーシフトピークと、In-115(Cu-63,4n)反応で生成したPt-174における2(sub 1)(+)から0(sub 1)(+)への遷移に対応する低減されたドップラーシフトピークに対する遅延箔の厚さの影響を、適切な仮定のもとにシミュレートした。その結果は、2mg/平方センチメートルのAu箔では両ピークを分離できないが、4mg/平方センチメートルのAu箔では両ピークを分離できることを示した。崩壊曲線R(D)は完全にドップラーシフトしたピーク強度、I(sub fs)(D)と、R(D)=1-I(sub fs)(D)/I(sub fs)(∞)の関係から簡単に同定できる。ここでDはターゲットと遅延箔間の距離であり、すべての距離におけるI(sub fs)(D)に対する正規化は、PSDで検出したα崩壊スペクトルから求めた反跳原子核の全数を用いて行うことが可能であり、I(sub fs)(∞)の値は、遅延箔を除いた装置構成で測定できる。