Determination of zeta values for fission-track age calibration using thermal neutron irradiation at the JRR-3 reactor of JAEA, Japan

抄録

We recently determined new zeta values of zircon and apatite for fission-track dating using diallyl phthalate (DAP) detectors. Thermal neutron irradiation was performed using the pneumatic tube No.2 at the JRR-3 reactor of Japan Atomic Energy Agency (JAEA), for which the cadmium ratio for Au is 24. The resulting zeta values are 416 ± 3 (ED1) and 371 ± 3 (ED2) for zircon with Q-DAP detectors by an observer (TD), 414 ± 3 (ED1) and 391 ± 4 (ED2) for zircon with Q-DAP detectors, and 337 ± 4 (ED1) for apatite with S-DAP detectors by a second observer (HI). These values are 6-11 % higher than those obtained for the pneumatic tube at the JRR-4 reactor of JAEA, with a cadmium ratio of 3.6. The significant difference in zeta values between the two irradiation sites can be partly attributed to the effect of the fast neutron-induced fissions of ²³²Th and ²³⁸U in SRM612 glass at JRR-4, with its relatively poor thermalisation.