Photofission of Bi at intermediate energies

Biの中高エネルギー光核分裂反応

羽場 宏光; 笠岡 誠*; 五十嵐 学*; 鷲山 幸信*; 松村 宏*; 大浦 泰嗣*; 柴田 誠一*; 坂本 浩*; 古川 路明*; 藤原 一郎*

Haba, Hiromitsu; Kasaoka, Makoto*; Igarashi, Manabu*; Washiyama, Koshin*; Matsumura, Hiroshi*; Oura, Yasuji*; Shibata, Seiichi*; Sakamoto, Ko*; Furukawa, Michiaki*; Fujiwara, Ichiro*

最大エネルギー(E)=450-1100MeVの制動放射線をBi標的に照射し、生成核質量数領域56A135において総計63核種の光核分裂収率を測定した。これらの収率値に、most probable charge(Z)をAの一次関数Z=RA+S,分布の半値幅FWHMをAによらず一定と仮定したガウス関数を最小二乗フィットさせ荷電分布を求めた。Z並びにFWHM値は、E600MeVで変化せず一定でR=0.4210.001, S=0.60.1, FWHM=2.10.1c.d.であった。これらの荷電分布パラメータを基に収率データがある質量数で質量収率を求めた。得られた対称的質量収率分布はガウス関数で再現でき、その半値幅(FWHM)とmost probable mass(A)はそれぞれFWHM=331m.u.,A=961m.u.であった。本研究で得られたBiの荷電分布,質量収率分布は、Auの同様の実験結果並びに光子誘起核内カスケード理論計算PICA3/GEM(Photon-induced Intranuclear Cascade Analysis code combined with the Generalized Evaporation Model)と比較しながら議論する。

The reaction yields of 63 radionuclides with the mass number A = 56-135 produced in the photofission of Bi by bremsstrahlung of end-point energies (E) from 450 to 1100 MeV have been measured using a catcher foil technique. The charge distribution was well reproduced by a Gaussian function with the most probable charge (Z) expressed by Z = RA + S, and with the A-independent FWHME. The charge distribution parameters R, S and FWHM were independent of E above 600 MeV. The weighted mean values at E 600 MeV were R = 0.421 0.001, S = 0.6 0.1 and FWHM = 2.1 0.1 charge unit (c.u.). Based on the charge distribution parameters, the symmetric mass yield distributions with the most probable mass A of 96 1 mass unit (m.u.) and the width FWHM of 33 1 m.u. were also obtained. The characteristics of the charge and mass yield distributions are discussed by referring to those for Au based on the results of calculations using PICA3/GEM.