Measurements of W-values for alpha particles in tissue-equivalent gases

The W-values (average energy loss per ion pair) were measured by a modified Jesse method on four kinds of tissue-equivalent gases for α particles of ²⁴¹Am. The chart recorder followed by electrometer figuring in Jesse's apparatus was replaced by a 'peak holder' circuit and pulse height analyzer, which made it possible to observe the pulse height distribution directly. The measurements resulted in 31.1eV for Rossi's TE gas, 28.5eV for Shonka's TE gas, 27.2eV for propane-butane-air mixture and 27.1eV for a new TE gas. Strickler's equation which has been used to predict the W-values of binary gas mixtures was modified into a form applicable to the case of mixtures of three or more gases. The estimated W-values of Rossi's TE gas and propane-butane-air mixture obtained with the extended equation agree well with the measured results. (author)