EXPERIMENTAL W-VALUES IN GASEOUS XE, KR AND AR FOR LOW-ENERGY X-RAYS

A refined experimental method that allows absolute measurements of the W-value, i.e., the mean energy required to produce an electron-ion pa ir, in noble gases for X-rays is presented. The spectrum of the X-ray energy absorbed in the gas is obtained from proportional scintillation pulses, while the corresponding primary electron charge is collected on a rid and measured with an electrometer. The method is presently ca pable of an accuracy of 2 to 3%. The W-values measured for 5.9 keV X-r ays in xenon are 21.7 +/- 0.5 eV at 1250 mbar, 21.7 +/- 0.5 eV at 980 mbar, 21.5 +/- 0.6 eV at 800 mbar, 22.1 +/- 0.5 eV at 580 mbar and 21. 8 +/- 0.5 eV at 380 mbar and for 4.5 keV X-rays in xenon are 21.9 +/- 0.7 eV at 1250 mbar. For 5.9 keV X-rays in krypton the measured W-valu e is 24.0 +/- 0.7 eV at 1350 mbar and in argon is 25.8 +/- 0.6 eV at 1 280 mbar. The experimental results obtained are compared with experime ntal and calculated results available.