【摘要】 本文从试样盘具反散射以及試样本身具自吸收、自散射和反散射本領的观点出发,提出一綜合性半經驗自吸收公式:I=m/(am+be^cm)其中I——试样厚度为m时測得的放射性強度;m——試样厚度;a,b,c——常数。利用同一碘-14标記乙醛制出的不同厚度的标記碳酸鋇和标記2,4-二硝基苯腙試样証明上式在外推至厚度为无限薄时仍然适用。这就能利用任意厚度的試样进行放射性強度的絕对测量。将上式与現有的負指数型和双曲綫型自吸收公式比較,可明确后两經驗公式的缺点以及其适用范围。更多还原

【Abstract】 A semi-empirical formula is proposed which may well describe the complex pheno mena of the absorption and scattering of weak beta rays emitted by the radioactive samples of different thicknesses mounted on planchets. The formula obtained as a result of a theoretical consideration of the back-scattering of the sample mount and the back scattering, the self-scattering as well as the self-absorption of the sample itself isI=am/(am+be^-cm,where I is the observed counting rate in counts per minute, m is the weight of the sample over a fixed area, and a, b and c are constants. Two series of planchets carrying labeled barium carbonate and labeled 2,4-dinitrophenylhydrazone of varying weights prepared from the same purified carbon-14 labeled acetaldehyde were counted by an endwindow counter in identical conditions. The ratio of the experimental specific activities of the two compounds at zero absorption consistent with the theoretical requirement shows that the above formula still holds even when the sample thickness approaches zero. Thus, it will be possible to carry out absolute counting with thick samples. A comparison between the formula and those of the exponential type and the hyperbolic type presented in the literature reveals the disadvantages of the latter two and the limited conditions under which they may be applied. A correction formula recommended for selfabsorption correction for carbon-14 samples is given in the following form:s⁰/s=a/bm+e^-cmwhere s is the observed specific activity per minute per milligram sample, s⁰ is the specific activity of the sample at zero absorption, and a, b and c are constants. Discussions in connection with this correction formula may help in interpreting and clarifying those ex periments reported in the literature which have hitherto remained in discrepancy and ambiguity.更多还原