Neutron dosimetry and fission-track age calibration: insights from intercalibration of uranium and thorium glass dosimeters
Neutron dosimetry and fission-track age calibration: insights from intercalibration of uranium and thorium glass dosimeters
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中子剂量测定和裂变径迹年龄校准：铀和钍玻璃剂量计相互校准的见解
DOI：
10.1016/0009-2541(92)90162-x
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发表时间：
1992
期刊：
影响因子：
3.9
通讯作者：
S. Nishimura
中科院分区：
文献类型：
--
作者：
T. Tagami;S. Nishimura
在KUR-TCPn、KUR-Pn 2和MITR-IP三个不同中子热化的反应堆设施上，对具有不同U同位素和Th/U比值的三种玻璃剂量计NBS-SRM 612（612）、Corning® 1（CN 1）和Corning® 3（CN 3）进行了互校，以评价快中子诱发238 U和232 Th裂变对裂变径迹（FT）年龄刻度的影响。两对玻璃偶，<$CN 3 <$CN 1和<$612 <$CN 1的诱导径迹密度比显示出与增加的热中子与快中子通量比Φ th Φ f的系统负相关。这些事实表明，238 U和232 Th裂变对在较少热化的设施（其中Φ th Φ f为10）中观测到的感生径迹密度有重要贡献。为了定量评价238 U和232 Th裂变，从数学上考察了互校概念，从而建立了它们的一般描述。根据在高热化装置上测得的理想232 Th/CN 3/CN 1比值，由每个装置上测得的232 Th/CN 3/CN 1比值和未知样品的Th/U比值（或238 U/235 U比值）给出了232 Th裂变（或238 U裂变）的影响程度。这些结果阐明，在FT年龄校准的背景下，“以及热化”的中子通量的标准是由所使用的注量监测器，Th/U比的样品被日期和分析允许的最小误差控制。各种限制，影响和建议的中子剂量学和FT年龄校准进行了讨论。
Three glass dosimeters possessing various U isotopic and Th/U ratios, ie NBS-SRM612 (612), Corning® 1 (CN1) and Corning® 3 (CN3), were intercalibrated at three reactor facilities of different neutron thermalisation, ie KUR-TCPn, KUR-Pn2 and MITR-IP facilities, to assess the influence of fast neutron-induced fissions of 238 U and 232 Th on fission-track (FT) age calibration. The induced track density ratios for two glass couples, ϱ CN 3 ϱ CN 1 and ϱ 612 ϱ CN 1, show systematic, negative correlation with increasing thermal to fast neutron flux ratios, Φ th Φ f. These facts demonstrate the significant contribution of 238 U and 232 Th fissions to observed induced track density at less thermalised facilities wherein Φ th Φ f is∼ 10. For the quantitative assessment of 238 U and 232 Th fissions, the intercalibration concept was examined mathematically and thus their generalised descriptions were established. On the basis of the ideal ϱ CN 3 ϱ CN 1 ratio determined at a highly thermalised facility, the magnitude of influence of 232 Th fission (or that of 238 U fission) is accordingly given by the measured ϱ CN 3 ϱ CN 1 at each facility and Th/U (or 238 U 235 U) ratio of an unknown sample. These results elucidate that in the context of FT age calibration, the criterion of “well-thermalised” neutron flux is controlled by the fluence monitor used, Th/U ratio of a sample to be dated and the minimum error allowed for analysis. Various constraints, implications and recommendations on neutron dosimetry and FT age calibration are discussed.