ABSTRACT
The range of the α particles from uranium has been difficult to determine directly on account of the smallness of the activity of the thin films of the substance. The scintillation method was adopted in order to count the number of α particles from a known weight of active material. A small quantity of the material under examination was finely powdered in an agate mortar, and then mixed with alcohol or ether and deposited as a thin uniform film on a thin sheet of aluminium or glass. The efficiency of the zinc sulphide screen was tested by counting the number of α particles emitted from a definite quantity of radium C. The number of scintillations observed was found to be 8 per cent, less than the actual number of α particles incident on the screen. In the case of uranium and thorium minerals, where the scintillations are on the average brighter than those from uranium, the counting was relatively easy.
