40Ar/39Ar dating method is widely applied to measure geologic time, from the formation of the Earth, which is 4.6 Ga, to the eruption of Vesuvius in 79 AD（Renne et al., 1997）.39 K（n, p） 39Ar is an important reaction for 40Ar/39Ar geochronology,which is usually carried on in 235U fission reactor.However, the neutron energy of a 235U fission reactor ranges widely from less than 0.1 MeV to higher than 10 MeV.Besides 39Ar is produced via 39 K（n, p） 39Arreaction, other Argon isotopes can also be produced by reaction between lower energy neutrons and K, Ca, Cl isotopes such as 40K（n,p）40Ar and 40Ca（n,nα）36Ar. These unwanted interfering reactionsare the main factor controlling the precision of dating results（McDougal and Harrison 1999）, especially for the young samples with high Ca/K ratio.In addition,39Ar produced by high energy neutrons can recoil from their original crystal chemical site. Mean recoil distance for silicates is 0.08 μm for neutrons in a fission spectrum（Villa et al., 1997, Renne et al., 2005）. Therefore, 39Ar maybe lost during irradiation if grain size is small, and recoiling of produced 39Ar may cause fractionation between 39Ar and 40Ar which will influence apparent ages. Thus, based on the neutron energy, recoiling of 39Ar, and corrections for data processing, the ideal neutron energy for 40Ar/39Ar geochronology is 2-3 Me V（Renne et al., 2005）. Renne et al.（2005） proposed to apply a Deuteron-Deuteron neutron generator to 40Ar/39Ar geochronology. Neutron flux of Deuteron-Deuteron neutron generator is much lower than that of 235U fission reactor, thus low production of 39Ar after irradiation by Deuteron-Deuteron neutron generator cause the Ar isotope measurement difficult. Either developing high flux neutron generator or optimizing low amount Ar measurement can overcome this difficulty. In our study, we make 40Ar/39Ar dating with DeuteronDeuteron neutron generator come true by improving mass spectrometric 40Ar/39Ar measurements.
类型: 国际会议
作者: SU Fei,HE Huaiyu,LI Youjuan,LAN Changlin,CHEN Wen
来源: 第九届世界华人地质科学研讨会 2019-06-01
年度: 2019
分类: 基础科学
专业: 地质学,地质学
单位: Institute of Geology and Geophysics, Chinese Academy of SciencesUniversity of Chinese Academy of SciencesInstitute of Geology,China Earthquake AdministrationLanzhou UniversityInstitute of Geology, Chinese Academy of Geosciences
分类号: P597.3
DOI: 10.26914/c.cnkihy.2019.028513
页码: 417
总页数: 1
文件大小: 127k
下载量: 1
本文来源: https://www.lunwen90.cn/article/ec68dc2e11dce377a27d8037.html