A determination of the average energy required to produce an ion pair for alpha-particles in air and for X-rays.

Measurements of the W-velues(electron volts/ion pair; e.v./i.pr.), for alpha-particles emitted by a Am-241 source of energy E = 5.36 Mev, were done in puro nitrogen, argon, dry air and in N[2]-O[2] gas-mixture, using the conventional parallel plate ionisation chamber connected to a vibrating reed electrometer. The W-values obtained were : 36.4 +/- 0.4/0.5, 26.36 +/- [0.1] [0.14] and 35.1 +/- [0.17] [0.27] e.v./i.pr. in pure nitrogen, argon and dry air respectively. The value of W-of air for alpha-particles has been redetermined. Careful measurements of the W-value of air dependence on the air composition have been studied. Validity of the Wm-value equation for alpha-psrticles in gas-mixture (e.g. N[2]-O[2]), was investigated at different percentages of each component of that mixture. A gas flow proportional counter was designed and constructed to know how many X-ray, emitted by an Fe-55 source of energy E = 5.9 Kev,can be tolerated by such a counter . The data obtained ware required to calculate the W- value of different gases. In pure nitrogen, that value of W was found to be 32.06 +/- [0.79] [1.05] e.v./i.pr. A third peak was observed on the right hand side of the main energy peak (Mn- K X-ray peak),in the pulse height spectrum produced in the Ar-CH[4] gas mixture irradiated by Fe-55 X-ray source. The phenomenon was referred to as a Third peaking phenomenon. Characteristics of that phenomenon were studied as a function of gas purity, counter lengths and source activities. It was found that the third peaking phenomenon is independent of the gas purity and counter lengths. It is a counting rate dependence (i.e. the pulse height spectrum of the third peak varies proportionally with the source activities)