Analysis and simulation of the relative lethality of Auger-electron-emitting radionuclides with a liquid-scintillation counter

Abstract

Purpose: The efficiency of strand-break induction and the counting efficiency of a liquid-scintillation counter can both be described similarly in terms of Poisson statistics. The aim of this work is to relate these two concepts, developing a simple method to simulate with a liquid-scintillation counter the relative biological effects between two different electron-emitting radionuclides.Methods: A gel scintillator can be used to confine the decaying nuclei into nanoscale structures of liquid water (micelles). Because the fluorescing agents of the gel lay outside the micelle structure, the low-energy electrons emitted by the decaying nucleus lose part of their energy within the micelle structure before being detected, resulting in a negative increment of the counting efficiency. The difference in the counting efficiency between two gels with micelles of different characteristic sizes is applied to simulate the relative lethality of the radionuclides.Results: The results are only qualitatively successful. A better accuracy cannot be achieved for commercial liquid-scintillation spectrometers, which have two photomultiplier tubes of identical gain. Also the comparison cannot be extended to low-Z Auger-electron-emitting radionuclides such as 55Fe, since the micelle size effect is significantly increased by the interference of the L-Auger electrons.Conclusions: A liquid-scintillation counter with a gain decreased by a factor of 2.5 in one of the two photomultiplier tubes would be necessary to improve the simulation of the damaging efficiency.