高通量试验堆(HFETR)辐照<sup>40</sup>Ar-<sup>39</sup>Ar定年样品条件初探

李军杰; 刘汉彬; 张佳; 金贵善; 张建锋; 韩娟; 石晓

doi:10.3799/dqkx.2019.006

高通量试验堆(HFETR)辐照⁴⁰Ar-³⁹Ar定年样品条件初探

doi: 10.3799/dqkx.2019.006

核工业北京地质研究院, 北京 100029

基金项目:

国家重点研发计划项目 2017YFC0602600

详细信息

作者简介:
李军杰(1986-), 男, 工程师, 博士研究生, 主要从事⁴⁰Ar-³⁹Ar同位素定年技术方法研究

通讯作者:
刘汉彬

中图分类号: P597
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出版历程
- 收稿日期: 2019-01-16
- 刊出日期: 2019-03-15

Primary Research of High Flux Engineering Test Reactor(HFETR) for Irradiation of ⁴⁰Ar-³⁹Ar Dating Samples

Beijing Research Institute of Uranium Geology, Beijing 100029, China

摘要

摘要: 国内目前用于⁴⁰Ar-³⁹Ar定年样品辐照的反应堆较少且开堆频率低，样品辐照周期长，且不同类型样品辐照条件缺乏系统研究.首次对高通量试验堆（HFETR）用于⁴⁰Ar-³⁹Ar定年样品的辐照工作进行了研究.通过辐照一定质量的黑云母标准物质ZBH-25，确定了辐照孔道³⁹Ar_K产率，为不同年龄和不同含钾量样品的辐照时间提供了参考依据.辐照孔道轴向中子通量梯度仅为3.3%/cm，且均呈二次曲线特征分布（R²>0.99），中子通量在径向上存在差异，最大差异达到7.1%/cm；通过辐照纯的钾盐和钙盐，得出辐照孔道内校正因子（³⁶Ar/³⁷Ar）_Ca的值为（3.52±0.11）×10^-4，且在样品辐照罐内不同位置基本一致，而校正因子（⁴⁰Ar/³⁹Ar）_K和（³⁹Ar/³⁷Ar）_Ca的值在辐照样品罐内存在明显的差异；Cd皮对于降低校正因子（⁴⁰Ar/³⁹Ar）_K的影响在样品罐底部更加明显，而在样品罐顶部几乎没有影响，这可能是由辐照孔道内中子能谱的差异造成的；以FCs透长石为中子通量监测物质，对标准物质ZBH-25黑云母和BSP-1角闪石进行了年龄测定，ZBH-25黑云母获得了理想的坪年龄，证明此反应堆满足⁴⁰Ar-³⁹Ar定年样品辐照的要求；BSP-1角闪石的坪年龄准确度和精度较差，与样品本身异常老的年龄和较低的K/Ca比有关，对于此类样品，准确确定干扰校正因子并合理延长照射时间对获得高精度⁴⁰Ar-³⁹Ar定年结果非常重要.
- 高通量试验堆 /
- ⁴⁰Ar-³⁹Ar定年 /
- 样品辐照 /
- 中子通量梯度 /
- 干扰校正因子 /
- 地质年代学
Abstract: The domestic reactors which could be utilized for the irradiation of ⁴⁰Ar-³⁹Ar dating samples are not only rare but the operation frequency is very low, which makes the period of the irradiation for samples extremely long.Besides, the optimized parameters of irradiation for different kinds of samples are short of systematic research.To solve the above-mentioned problems, primary research was done on the HFETR in the application of the irradiation of ⁴⁰Ar-³⁹Ar dating samples for the first time.Through the irradiation of certain amount of biotite standard ZBH-25, the production efficiency of ³⁹Ar_K is determined, which could provide the basis for the irradiation time for samples with different ages or potassium contents.The axial neutron flux gradient of the irradiation channel, which shows approximative conic function (R²>0.99), is only 3.3%/cm.However, the radial flux gradient is much more obvious, which is as high as 7.1%/cm.The interference factors are determined through the irradiation of pure potassium salt and calcium salt.It is found that the (³⁶Ar/³⁷Ar)_Ca factor is uniform with the value (3.52±0.11)×10^-4, but the interference factors (⁴⁰Ar/³⁹Ar)_K and (³⁶Ar/³⁷Ar)_Ca are scattered at different positions of the irradiation channel.The shielding effect of cadmium for the decrease of the interference factor of (⁴⁰Ar/³⁹Ar)_K is prominent at the bottom of the sample vessel but negligible at the top of the sample vessel, which may result from the difference of the neutron spectrum along the axial direction of the irradiation channel.Taking the international standard sanidine FCs as neutron flux monitor, the domestic standards biotite ZBH-25 and hornblende BSP-1 are dated.Excellent plateau age is obtained for the ZBH-25 biotite standard, indicating that the HFETR could satisfy the requirement of the sample irradiation.However, the precision and accuracy of the plateau age of the BSP-1 hornblende is somewhat worse, which maybe has something to do with the relatively old age and low ratio of the K/Ca.Precise determination of the interference factors and proloning of the irradiation time are necessary for the improvement of the age quality for such kind of sample.
- HFETR /
- ⁴⁰Ar-³⁹Ar dating /
- sample irradiation /
- neutron flux gradient /
- interference factor /
- geochronology

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图 1 石英管内辐照样品位置示意图

Fig. 1. The position of the irradiated sample in the quartz tube

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图 2 铝板平面图(a)和辐照样品罐结构(b)

Fig. 2. Ichnography of the aluminum plate (a) and structure of the irradiated sample vessel (b)

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图 3 ³⁹Ar_K产率曲线(a)和不同年龄样品的辐照时间与⁴⁰Ar^*/³⁹Ar_K值关系(b)

Fig. 3. The ³⁹Ar_K production efficiency (a) and relationship of the ⁴⁰Ar^*/³⁹Ar_K value and irradiation time to the samples with different age (b)

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图 4 不同径向位置的轴向方向中子通量梯度变化曲线

Fig. 4. Curves about the neutron flux gradient along with the axial direction at different radial positions

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图 5 中子通量径向平面分布

Fig. 5. The position of the irradiated sample in the quartz tube

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图 6 辐照孔道不同位置校正因子变化

Fig. 6. The interference factor changes at different position of the irradiation channel

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图 7 ZBH-25黑云母和BSP-1角闪石坪年龄谱图

Fig. 7. Plateau age of biotite ZBH-25 and hornblende BSP-1

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表 1 不同类型辐照样品测试的接收器配置

Table 1. The detector configuration for the different kinds of irradiated samples

接收器	H2	H1	AX	L1	L2	CDD
钙盐	⁴⁰Ar	³⁹Ar	³⁸Ar	³⁷Ar	³⁶Ar	-
	-	⁴⁰Ar	³⁹Ar	³⁸Ar	³⁷Ar	³⁶Ar
	-	-	-	-	-	³⁹Ar
钾盐	⁴⁰Ar	³⁹Ar	³⁸Ar	³⁷Ar	³⁶Ar	-
钾盐	-	⁴⁰Ar	³⁹Ar	³⁸Ar	³⁷Ar	³⁶Ar
监测物质	⁴⁰Ar	³⁹Ar	³⁸Ar	³⁷Ar	³⁶Ar	-
	-	⁴⁰Ar	³⁹Ar	³⁸Ar	³⁷Ar	³⁶Ar
	-	-	-	-	-	³⁷Ar
注：H2、H1、AX、L1和L2为法拉第杯, 其中H2放大器高阻为10¹¹ Ω，其余4个法拉第杯的放大器高阻为10¹² Ω；CDD为二次电子倍增器.采用表中加粗的接收杯强度值.

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表 2 BSP-1角闪石⁴⁰Ar-³⁹Ar年龄测试数据

Table 2. The ⁴⁰Ar-³⁹Ar dating data of hornblende BSP-1

温度(℃)	$ {{\left(\frac{^{40}\text{Ar}}{^{39}\text{Ar}} \right)}_{\text{m}}}$	$ {{\left(\frac{^{36}\text{Ar}}{^{39}\text{Ar}} \right)}_{\text{m}}}$	${{\left(\frac{^{37}\text{Ar}}{^{39}\text{Ar}} \right)}_{\text{m}}} $	³⁹Ar_K×10_mol^-14	$ \frac{^{40}\text{A}{{\text{r}}^{*}}}{^{39}\text{Ar}}$	³⁹Ar_K(%)	$ \frac{\text{K}}{\text{Ca}}\pm 1\sigma $	视年龄(Ma, 1σ)
900	577.126	0.152	0.484	0.085	532.370	0.43	0.20±0.03	2 176.83±10.48
1 000	1 795.387	0.070	0.374	0.083	1 775.423	0.45	0.22±0.04	3 936.52±10.58
1 100	613.571	0.063	1.121	0.152	595.495	0.81	0.08±0.01	2 321.51±7.05
1 200	474.078	0.009	0.954	6.360	471.955	34.69	0.10±0.01	2 026.69±6.15
1 300	453.681	0.004	0.961	1.050	452.899	57.68	0.09±0.01	1 976.65±6.05
1 400	427.166	0.105	0.937	0.109	424.479	5.95	0.09±0.01	1 899.36±5.94
注：表中下标m表示测试值，下标mol表示摩尔值.样品质量为0.02 g，辐照参数J=0.004 33±0.000 02.

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