engleski

Statistical fluctuations on the ionization yield of low-energy photons absorbed in polyatomic gases

The statistical fluctuations of the number of ion pairs created by monoenergetic photons in several polyatomic gases and gas mixtures were derived by iterative deconvolution of measured pulse height spectra obtained by means of the proportional counter. The response of the proportional counter to the unit charge (the single-electron spectrum) has been determined precisely, making possible the measurement of the number of electrons created per absorbed photon. W values (mean energy per ion pair), generalised Fano factors and primary ion pair distribution characteristics have been derived as functions of incident photon energy for ten polyatomic gases, mostly alkanes, and two tissue-equivalent gas mixtures. Monoenergetic photons having an energy equal to 0.277 keV (carbon K_alpha line), 1.49 keV (aluminium K_alpha line) and 5.89 keV (55^Fe) have been used throughout the experiment. It is shown that the primary distribution of ion pairs in all investigated gases and gas mixtures is asymmetrical and more peaked than the Gaussian distribution for low-energy incident photons, approaching the Gaussian shape for 6 keV photons.

ionization; low-energy photrons; polyatomic gases

nije evidentirano