摘要
含钾岩石矿物中的39K经反应堆快中子福照后产生^(39)Ar是^(39)Ar-^(40)Ar法定年的前提,国内可应用于样品辐照的反应堆资源紧缺、不同类型样品辐照参数缺乏,制约我国高精度^(39)Ar-^(40)Ar定年技术的发展。本次工作首次针对高通量试验堆具有高中子通量的G10中心孔道辐照参数进行探讨。通过辐照ZBH-25黑云母标准、CaF_(2)晶体和K2SO4晶体,探讨中子通量轴向梯度变化特征、反应堆辐照孔道^(39)ArK产率以及副反应校正因子。结果表明,辐照14 h和35 h的J值均呈现二次线性关系分布(R^(2)≥0.979),与中子通量余弦函数分布特征相符,中子通量梯度变化小,分别为0.88和0.45%·cm^(-1),表明石英管处于中子活性区轴向稳定区域,有利于准确计算待测样品辐照参数J值;孔道内^(39)ArK产率介于2.32×10^(-12)~2.99×10^(-12)(mol·h^(-1)·%K2O)之间,高于同反应堆的外围孔道以及其他反应堆报道值;辐照K2SO4晶体得到(^(40)Ar/^(39)Ar)K校正因子平均值为2.96×10^(-3),诱发产生^(40)Ar占总^(40)Ar比例为(29±6)%;辐照CaF_(2)晶体获得(^(36)Ar/^(37)Ar)Ca校正因子平均值为2.54×10^(-4)、(^(39)Ar/^(37)Ar)Ca校正因子平均值为7.31×10^(-4),诱发产生^(36)Ar占总^(36)Ar比例为(97±1)%,中子通量升高可以减小副反应校正因子计算时大气氩的干扰;ZBH-25黑云母标准物质测得的坪年龄为132.89±0.93 Ma(2σ,MSWD=0.56),与前人报道的132.7±0.6 Ma(2σ)年龄值基本一致,证明高通量试验堆G10中心孔道可以满足^(39)Ar-^(40)Ar定年样品辐照要求,此孔道尤其适用于年龄老,低K/Ca比的样品辐照。
^(39)Ar produced from 39K in potassium-containing rocks and minerals that is irradiated by fast neutrons in nuclear reactor is the basic of^(39)Ar-^(40)Ar dating.There are few reactor resources for sample irradiation in China and lacked of irradiation parameters for different types of samples,which limits the development of high-precision^(39)Ar-^(40)Ar dating.In this work,the irradiation parameters of G10 center channel with high neutron flux in High Flux Engineering Test Reactor(HFETR)were discussed for the first time.By irradiating biotite standard ZBH-25,calcium salt and potassium salt,the axial gradient of neutron flux,the production of^(39)ArK and the correction factor of interfering reaction were investigated.The results show that the J values of biotite standard ZBH-25 for 14 h and 35 h irradiation present a quadratic linear distribution(R^(2)≥0.979),which is corresponding to the cosine function distribution of neutron flux,the neutron flux gradients are 0.88%·cm^(-1)and 0.45%·cm^(-1)which the variation is small,respectively indicating that the quartz tube is in the axially stable region of neutron flux and it is helpful to accurately calculate the J value of the sample.The production of^(39)ArK is 2.32×10^(-12)to 2.99×10^(-12)(mol·h^(-1)·%K2O),which is higher than the values of the outer channel of HFETR and other reactors.The average value of correction factor(^(40)Ar/^(39)Ar)K obtained by the irradiation of K2SO4 crystal is 2.96×10^(-3),and the proportion of induced^(40)Ar to the total^(40)Ar is(29±6)%,the average value of correction factor(^(36)Ar/^(37)Ar)Ca obtained by irradiation of CaF_(2)crystal is 2.54×10^(-4),the average value of correction factor(^(39)Ar/^(37)Ar)Ca is 7.31×10^(-4),and the proportion of induced^(36)Ar to the total^(36)Ar is(97±1)%.The correction factor results show that the increase of neutron flux can reduce the interference of atmospheric argon when calculating.The plateau age of biotite standard ZBH-25 is 132.89±0.93 Ma(2σ,MSWD=0.56),which is the same with the 132.7±0.6 Ma(2σ)age issued by previous studies.In summary,the G10 center channel in HFETR can satisfy the irradiation requirements of^(39)Ar-^(40)Ar dating samples,especially is suitable for samples with old age and low K/Ca ratio.
作者
石晓
刘汉彬
张佳
张建锋
韩娟
石雅静
石健
SHI Xiao;LIU Hanbin;ZHANG Jia;ZHANG Jianfeng;HAN Juan;SHI Yajing;SHI Jian(Beijing Research Institute of Uranium Geology,Beijing 100029,China;Wuchang Shipbuilding Industry Group CO.,Ltd,Wuhan 430416,China)
出处
《世界核地质科学》
CAS
2024年第5期1023-1031,共9页
World Nuclear Geoscience
基金
核工业北京地质研究院自主研发项目(编号:测ZY2401)资助。