| 摘要 |
An instrument and method for selectively detecting alpha particles emitted simultaneously by radium A and radium C' which are derived from radon includes a device for sampling air through a filter which retains the alpha-emitting aerosols, a detector preferably CR 39, in which the alpha particles corresponding to the respective energies of the alpha emissions of radium A and of radium C' are selectively using the track diameter discrimination method. Either a single or a multiple collimator system can be adopted. Collimators are composed of simple parts allowing the flexible adjustment of the geometric efficiency. If a multiple collimator is adopted, it will provide advantage of reducing the volume while improving the overall efficiency. An appropriate thickness can be chosen for the absorber attached to the collimator so that the energy difference between alphas from RaA and RaC' can be enhanced. This enhancement will contribute to the resolution for separating RaA and RaC' by using an ordinary image analysis system.
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