液闪法绝对测量α放射性活度及元素物质的量

Absolute Measurement of Alpha Radioactivity and Elemental Amount of Substance Using Liquid Scintillation Method

  • 摘要: 液闪法是一种简单的绝对测量α射线的方法,但实际使用频率不如预期。本文从文献资料、标准溶液验证实验、3种液闪仪测量多种α核素的对比实验等方面证实了该方法的可靠性。研究结果表明:用液闪法测量α射线,计数效率通常都为100%,这也通过TDCR(三双符合比)=1得到了证实。验证实验的结果与标准样品标称值的相对误差小于1%,对比实验结果的相对标准偏差小于1%。确定α/β甄别最优参数是准确测定α射线的关键,用A类液闪仪测量且有β和γ射线干扰时推荐使用拐点法,用B类液闪仪测量时则利用更简单的二维谱图法。通常情况下液闪法测得的是样品中总α放射性活度。对于U、Np、Pu、Am,当满足有限干扰条件时,结合液闪法、α能谱法和γ能谱法,可通过总α放射性活度计算元素物质的量。

     

    Abstract: The liquid scintillation counting method is a simple technique for the absolute activity measurement of α particles. However, it is less common in analytical applications than might be expected. Following a literature analysis, verification experiments using a 241Am standard solution were performed and comparative experiments using three liquid scintillation counters were conducted to measure α-nuclides, including 237Np, 238-240Pu, 242Pu, 241Am, 244Cm, and 252Cf. Generally, the counting efficiency of α-nuclides measured by this method is essentially 100%, as confirmed by the triple-to-double coincidence ratio (TDCR) method. TDCR values for all α-nuclides were consistently determined to be 1, indicating 100% counting efficiency. Therefore, this method enables the absolute activity measurement of α-nuclides. For the verification experiments using the 241Am standard solution, the relative error between the measured results and the nominal value is less than 1%, and for the comparative experiments across the three counters, the relative standard deviation of the results is also less than 1%. Determining the optimal parameters for α/β discrimination is crucial for accurately measuring α-nuclides. For liquid scintillation counters incapable of providing a two-dimensional spectrum, such as the PerkinElmer 1220 Quantulus and TriCarb 2910, the crossover plot method can be used in the absence of β- and γ-ray interference. Conversely, the inflection point method is recommended when such interference is present. The use of liquid scintillation counters capable of providing a two-dimensional spectrum, such as the Hidex 300 SL, is particularly recommended, as it facilitates the acquisition of the optimal discrimination parameters from the spectrum. The liquid scintillation counting method has poor energy resolution for α-nuclides, limiting its application to the measurement of the total alpha activity in the sample. For U, Np, Pu, and Am, when limited interference conditions are met, the amount of substance can be calculated from the total alpha activity by integrating liquid scintillation, alpha spectroscopy, and gamma spectroscopy. These limited interference conditions are follows. 1) The activity originates exclusively from nuclides of the same element and their daughters, where the element has no stable nuclide. 2) The sample has been aged sufficiently, so that only nuclides with half-lives exceeding 1 year and their daughters need to be considered. 3) The half-life of the primary radioactive nuclide is sufficiently long, and isotopes with longer half-lives are absent or negligible in the sample. 4) All radioactive isotopes are identified; if they cannot be identified, the uncertainties introduced are sufficiently small to be negligible.

     

/

返回文章
返回