作者：王维达

机构：上海博物馆文物保护与考古科学实验室 上海 200231

中文关键词：热释光测定年代;;α效率;;α值系统;;K值系统

英文关键词：Thermoluminescence dating, Alpha effectiveness, System of a- value, System of K- value

中文摘要：研究了a值系统和K值系统中α相对于β的热释光效率α和K_(3.7)的意义和作用。对α值系统进行了评价。肯定了用总径迹长度密度来标定α源辐照场强度S和计算α效率的重要性,否定了α值的必要性。研究了不需要经过α值而直接从α源的辐照场强度S求得K_(3.7)的方法。

英文摘要：In the fine - grain thermoluminescence (TL) dating the full alpha dose must be converted into equivalent beta dose. The conversion is accomplished by alpha effectiveness K3.7-value. The definition for K3.7- value given by Zimmerman: K3.7 is the effectiveness in inducing TL of alpha particles of energy 3.7 MeV relative to that of beta ray i.e. In fact, the K3. 7 is an alpha effectiveness of external irradiation for the alpha energy of 3.7MeV. If the alpha energy is not 3 . 7MeV the effectiveness will be another value .To obtain K3 7 a collimated alpha beam from source must be used, of which the energy should be just 3.7MeV while it arrive at the irradiated sample. It is very difficult for general laboratory of TL dating. Therefore Aitken proposed the "α - value system . This system has a great advantage that the difficulty of alpha source calibration surmounted by " S " . The " S " is alpha source strength , it is the total trace length of alpha particles per unit volume of quartz sample per unit time, expressed in (μm/μm3)/ min or μm-2/min .The alpha effectiveness K3.7 can be obtained directly from the strength 5 of an alpha source. According to the function relation of the energy to the mass stopping power of the alpha particles in three materials, for a 3. 7MeV alpha particle the stopping power in quartz is 0.85 MeV ·cm ·mg . The density of quartz p = 2. 6g/cm3 . So for a 3 . 7MeV alpha the rate of energy loss in quartz is(2 . 6g/cm3 ) × (0 . 85MeV· cm2 · mg-1 ) = 0 . 221MeV/μm (2)When a quartz sample is irradiated by an alpha source of the strength 5 , the absorbed energy of quartz is equal to track length per min per cubic micrometer in quartz times the rate of energy loss in quartz. According to Expiation (2) , the relation of the track length per unit volume to the absorbed dose rate is obtained byBecause 1 Gy = 1J/kg, IMeV = 1 . 6 × 10-13 J, therefore 1 MeV = 1 . 6 ×10-10Gy · g. Substitute 1 MeV = 1 .6 × 10-10Gyg into Equation(3) .Then the absorbed dose rate in quartz for a 3.7MeV alpha particle isThe K3.7 for quartz is obtained by K3.7( quartz) = Qβ/13.6S . Where Qβ is an equivalent beta dose for the alpha absorbed dose of 13 . 6S .If irradiated sample is CaSO4 and the alpha energy is also 3 . 7MeV , the absorbed dose rate for Ca-SO4 isThe K3.7 for CaS04 can be also obtained by K3.7(CaSO4) =Qβ/12.8S.Where Qβ is an equivalent beta dose for the alpha absorbed dose of 12.8S .The same , if irradiated sample is CaF2 and the alpha energy is also 3 . 7MeV , the absorbed dose rate for CaF2 is The K3.7 for CaF2 can be also obtained by K3 7(CaF2) = Qp/11.55. Where Qβ is an equivalent beta dose for the alpha absorbed dose of 11.58. The rest may be deduced by analogy. The α - value system is reviewed as follows;(1) The "S" is very useful to alpha source calibration and alpha effectiveness calculation in a -value system, In this system the problem of alpha source calibration is solved by the "S".(2) The alpha effectiveness K3.7 can be obtained directly from the strength S of the alpha source, and it is not convert from the aaaaaaaaa - value. Therefore a ~ value is unnecessary in TL dating.(3) The relation of a to K3.7 should be aaaaaaaa - r1r2K3.7. Where r1 and r2 are respectively the mass stopping power ratio and the density ratio between other material and quartz.

[中文刊名]：文物保护与考古科学 [出版日期]：2002-12-30 [CN]：31-1652/K [ISSN]：1005-1538

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