三双符合比-切伦科夫方法中β核素壁效应的影响

Influence of wall effect on detection efficiency ofβ-emitters in TDCR-Čerenkov method

为分析三双符合比-切伦科夫(TDCR(Triple-to-double Coincidence Ratio)-切伦科夫)方法中壁效应对效率计算的影响。首先,对β粒子在溶液到瓶壁过程的输运进行分段分析,得到不同能量的粒子在不同材料中的沉积能谱与所产生的切伦科夫光子数的关系式,并对其进行了计算上的简化,进一步完善TDCR-切伦科夫效率的计算模型;之后利用Geant4计算了β在介质和瓶壁中的沉积谱,得到考虑了壁效应的切伦科夫光子数与β能量的关系曲线以用于对核素的效率计算;最后开展了多种纯β核素的实验测量以验证考虑壁效应后的计算模型的准确性。结果显示:考虑壁效应后的TDCR-切伦科夫方法与液闪方法的结果在不确定度范围内一致,且对高能β核素,其结果与液闪之间的相对偏差由原方法的0.47%降低至0.02%(^(90)Y),0.64%降低至−0.16%(^(32)P),表明考虑壁效应后的TDCR-切伦科夫方法对高能β核素的测量结果更准确。

[Background]The triple-to-double coincidence ratio-Čerenkov(TDCR-Čerenkov)method can be applied to the activity measurement of radionuclides by detecting theČerenkov photons produced in a nonscintillation solution.The computation of the detection efficiency of this method is based on the premise that the energy of emittedβis completely deposited in the solution.However,this precondition is ideal and does not apply to the actual measurement because of the counting loss caused by the restrictions of a finite solution and the wall of the counting vial(i.e.,wall effect).[Purpose]This study aims to analyze the influence of the wall effect on the computation of detection efficiency.[Methods]The transport process of emittedβfrom the solution to the vial wall was analyzed in sections.Thereby the relationship between the number ofČerenkov photons and the deposition energy spectra of emittedβwith different energies in different matrices was obtained.This relationship was used to further improve the calculation model of the TDCR-Čerenkov method.Subsequently,the calculation model was simplified to reduce the required time.Geant4 calculated the deposition spectra of emittedβin different matrices,subsequently,the efficiency of different nuclides was calculated using curves of the number ofČerenkov photons vs.the energy of the emittedβ.To verify the accuracy of the improved calculation model,measurements were carried out on a variety of pureβ-emitters.[Results]The results derived from the improved TDCR-Čerenkov method are in good agreement with those of the TDCR-LS method.Especially for high energyβ-emitters,the relative deviation of the results between the TDCR-Čerenkov and TDCR-LS methods is reduced from 0.47%for the original method to 0.02%(^(90)Y),and 0.64%to−0.16%(^(32)P).[Conclusions]The TDCR-Čerenkov method is more accurate when considering the wall effect in the activity measurement of high-energyβ-emitters.