2012 Volume 61 Issue 8 Pages 415-427
The experimental determinations of W-value, the average energy required to produce an ion pair by a charged particle in gases, have been attempted by many researchers since just after the discovery of radiation. From these experiments, W has become to be established in many gases, and to be known as being almost constant for electrons and protons over a wide range of energy. Still at present, however, some of gases have no established values of W, and there are few data of W for heavy charged particles(ions), which is known to show the dependence on particle energies. Some important properties of W, such as dependences of particle Z and the gas pressure, are not sufficiently clear. In this article, the present status of W is reviewed, and the problems in measurements of W are discussed.
