フィッション・トラック年代測定における熱中性子フルエンスの絶対測定とその応用

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The absolute measurements of thermal neuron fluence for fission track dating have been developed after the proceeding results of Honda et al. (1987). The 2,200 m/sec activation cross section of ^<197>Au (98.8 barn) is corrected to 87.4 barn (<σ_a>^^^-) by the three factors of the neutron temperature, Maxwellian distribution of thermal neutrons and non Ijv correction factor for the above absolute measurement. The calibrated factor (B_<th>) of standard glasses (SRM613, SRM962a, CN-1 and CN-2) and zeta-a (ζ_a) values for fission track dating are determined on the basis of these experimental results. The values of B_<th>, (7.47±0.29)×10^9 for SRM613, (7.43±0.34)×10^9 for SRM962a, (2.50±0.06)×10^9 for CN-1 and (2.74±0.06)×10^9 for CN-2 closely agree with those reported previously by Honda et al. (1987). Further, the Co. values of 392.3±16.5 for SRM962a and SRM613,131.4±3.1 for CN-1 and 144.1±3.3 for CN-2 calculated from B_<th>, effective thermal neutron fission cross-section <σ_f>^^^- (497.4 barn), isotopic abundance ratio ^<235>U/^<239>U, I (7.2527×10^<-3>) and spontaneous fission decay constant of ^<238>U, λ_f (6.85×10^<-17>^a^<-1>) show close agreement with C& values (392.5±10.0, 131.6±3.3, 140.1±3.5) derived from the absolute age of Fish Canyon Tuff (27.9±0.7Ma) respectively. The fission track dating of zircons separated from Oligocene-Miocene tuff distributed in Eastern Hokkaido have been carried out by the external detector method using ζ_a. The_obtained ages are 28.6±0.7 Ma (1-2) and 23.3±0.7 Ma (3-2). These results agree well with the geologic age supported from Ashoro Fossil Fauna, K-Ar ages of volcanic rocks and stratigraphy in this area.
地学団体研究会の論文
1988-05-25

フィッション・トラック年代測定における熱中性子フルエンスの絶対測定とその応用

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