On the normalization of the positron-impact direct ionization cross-section in the noble gases

Difficulties in the normalization of the positron-impact direct ionization cross-sections due to differences among the various data for electron impact ionization are discussed. Consequently, the cross-sections of Kara et al. (J. Phys. B 30 (1997) 3933) and of Moxom et al. (Can. J. Phys. 74 (1996) 367) have been renormalized using more recent and accurate data for electron impact ionization from Sorokin et al. (Phys. Rev. A. 58 (1998) 2900; 61 (2000) 022723). The new normalization for Ne, Kr and Xe lowers the cross-sections by 19%, 8% and 14% respectively, while that for Ar increases the cross-section by 2%