Detection of uranium fission tracks in minerals using tandem accelerator and its application to paleo-geothermal history analysis

1.在古地热区进行了野外调查和取样。调查区域为（1）后藤江岛古地热田，（2）大分县山国翁田地区热液蚀变带，(3)大分县的国崎八条金矿田（4）鹿儿岛县的南佐都和北佐津金矿田（5）长崎县的桥见金矿田和佐贺县的有田瓷土存款（6）长崎县的云仙地热田（7）福冈县的星野金矿田（8）大分县的大雄金矿田。XRD研究澄清了每个研究区的热液蚀变分带。对岩石样品进行了锆石、磷灰石裂变径迹年龄、黑云母、角闪石K-Ar年龄和石英热释光年龄测定。这些地区的容矿岩或蚀变岩的时代为中新世中期至更新世晚期。在九州大学的串列加速器上，将锆石和磷灰石安装在聚四氟乙烯盘上，并进行重离子辐照。射束能量为80-95 MeV，并且离子通量用具有Au箔的卢瑟福散射来控制。辐照后，对样品进行化学腐蚀，成功地探测到了与重离子径迹相交的铀裂变径迹。Ni便于产生重离子。硅半导体探测器可用于控制离子束注量。

1. Field survey and sampling were performed in the paleo-geothermal area. Investigated areas are (1) paleo-geothermal field in Goto-Fukue island, (2) hydrothermal alteration zone in Yamaguni-Onta area in Oita Pref., (3) Kunisaki-Bajyo gold field in Oita Pref. (4) Nansastu and Hokusatsu gold fields in Kagoshima Pref. (5) Hasami gold field in Nagasaki Pref.and Arita porcelain clay deposit in Saga Pref. (6) Unzen geothermal field in Nagasaki Pref. (7) Hoshino gold field in Fukuoka Pref. (8) Taio gold field in Oita Pref.XRD study clarified hydrothermal alteration zoning in each study field. Then fission track age of zircon and apatite, K-Ar age of biotite and hornblende and thermoluminescence age of quartz were determined for rock samples. Host rocKs or altered rocks in such areas indicated ages of middle Miocene to late Pleistocene.2. Zircon and apatite were mounted in tefron disk and irradiated with heavy ion at a tandem accelerator in Kyushu University. Beam energy was 80-95 MeV,and ion flux was controlled with Rutherford scattering with Au foil. After irradiation, sample was chemically etched, and then confined fission tracks of uranium intersecting heavy ion tracks were detected successfully. Ni is convenient to generate heavy ions. Silicon semi-conductor detector is useful to control fluence of ion beam.