Neutron capture effects and pre-atmospheric sizes of meteoroids  

作　　者：WANG Daode & LIN Yangting Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China Correspondence should be addressed to Wang Daode (e-mail: gzwangdd @public.guangzhou.gd.cn) 

出　　处：《Chinese Science Bulletin》2003年第20期2236-2240,共5页

基　　金：supported by the National Natural Science Foundation of China(Grant No.40232026).

摘　　要：Excesses of 80Kr and 82Kr, produced by secondary neutron capture effects of 79Br and 81Br, were observed in meteorites. Epithermal neutron flux, Jn (30—300 eV), and fast neutron flux, Jn( > 5 MeV), were determined according to reactions of 79Br(n, gb)80Kr, 81Br(n, gb)82Kr, and 24Mg(n, a)21Ne, respectively. Cosmogenic noble gases of several ordinary chondrites fell in China indicate a positive relationship between Jn (30—300 eV)/Jn ( > 5 MeV) ratio and Jn (30—300 eV). This suggests large pre-atmospheric sizes of the meteorites, and a considerable fraction of the secondary neutrons were slowed down to epithermal energy. According to its relationship with Jn (30—300 eV)/Jn ( > 5 MeV) ratio, the pre-atmospheric minimum radii and masses of several Chinese chondrites were estimated as below: Zhaodong: 60 cm, 3200 kg; Laochengzhen: 23 cm, 490 kg; Suizhou: 31 cm, 450 kg; Xi Ujimgin: 22 cm, 160 kg; Dongtai: 21 cm, 140 kg.Excesses of 80Kr and 82Kr, produced by secondary neutron capture effects of 79Br and 81Br, were observed in meteorites. Epithermal neutron flux, Jn (30—300 eV), and fast neutron flux, Jn( > 5 MeV), were determined according to reactions of 79Br(n, gb)80Kr, 81Br(n, gb)82Kr, and 24Mg(n, a)21Ne, respectively. Cosmogenic noble gases of several ordinary chondrites fell in China indicate a positive relationship between Jn (30—300 eV)/Jn ( > 5 MeV) ratio and Jn (30—300 eV). This suggests large pre-atmospheric sizes of the meteorites, and a considerable fraction of the secondary neutrons were slowed down to epithermal energy. According to its relationship with Jn (30—300 eV)/Jn ( > 5 MeV) ratio, the pre-atmospheric minimum radii and masses of several Chinese chondrites were estimated as below: Zhaodong: 60 cm, 3200 kg; Laochengzhen: 23 cm, 490 kg; Suizhou: 31 cm, 450 kg; Xi Ujimgin: 22 cm, 160 kg; Dongtai: 21 cm, 140 kg.

关 键 词：流星体 陨星 中子俘获 大气层前尺寸 宇宙成因核素 

分 类 号：P185[天文地球—天文学]