ESTIMATION METHOD FOR ALPHA-PARTICLE COUNTING EFFICIENCY FOR SCINTILLATION FLASKS

A simulation method to estimate counting efficiencies for Rn-222 and R n-230 collected in a scintillation flask has been studied. The concept of this Monte Carlo calculation was based on a relationship between a residual range of an alpha particle colliding with a scintillator and an output-pulse-height distribution. The relationships were investiga ted using collimated beams of Am-241 because the pulse-height distribu tions differed not only with residual ranges but with distances betwee n the collision point and the window of the flask. Using the distribut ions, counting probabilities for various alpha energies were estimated . The simulation for the counting efficiency was carried out using the following procedure: (1) a radiating point is determined by two rando m functions; (2) a radiating direction of an alpha particle is determi ned by other two random functions; (3) a counting probability for the alpha particle is calculated by the pulse-height distributions determi ned by the residual range at the collision point; and (4) the calculat ing cycle from (1) to (3) is repeated 100,000 times. The method was ve rified against experimental values for a standard Rn-222 gas and then adapted to Rn-220. This method is very useful and effective because co unting efficiencies of various scintillation flasks for various alpha particles can be estimated.