DEVELOPMENT OF A SEMIEMPIRICAL EXPRESSION FOR LIGHT GAIN FACTORS IN GAS SCINTILLATION PROPORTIONAL-COUNTERS

An attempt is made to develop a semi-empirical expression for light ga in factors in single wire anode (SWA) gas scintillation proportional c ounters (GSPC) as a function of various other counter parameters like operating voltage, anode and cathode radii, filling gas mixture and it s pressure. Experimental data of charge gain and light gain factors ha s been taken from four GSPCs having anode diameters ranging from 25 mu m to 1.7 mm and operated with Ar or Ar + 2.5% N-2 mixture. First the quality of our experimental data has been investigated by fitting the values of charge gain factors from one of the four GSPCs to four diffe rent semi-empirical expressions selected from the literature which hav e been developed for charge gain factors in ordinary ionization propor tional counters and which are suitable for experimental verification. Subsequently, assuming appropriate functional forms of electron excita tion and ionization coefficients and using derived or assumed values o f some other unknown parameters, the relevant integrals have been eval uated. Then the assumed values of unknown parameters are adjusted in s uch a way that the calculated values of light gain factors are compara ble to the experimental values. Thus a correlation between the light g ain factors and other counter parameters is established. The values of the effective electron excitation coefficients as a function of elect ric field strength per unit pressure in Ar + 2.5% N-2 from these GSPCs having considerably different electric field gradients have also been estimated.