W (the average energy to form an ion pair) for 5.4 MeV Am alpha particles in a Rossi-type tissue equivalent (T.E.) gas, argon and methane was determined to an accuracy better than 0.27, using a new automated data handling system. A vibrating reed electrometer and current digitizer were used to measure the current produced by com¬pletely stopping the alpha particles in a large cylindrical ionization chamber. A multichannel analyzer, operating in a slow multiscaler mode, was used to store pulses from the current digitizer.
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