Fitted Empirical Reference Cross Sections for K-Shell Ionization by Alpha Particles

Abstract

On the basis of our collection of experimental x-ray and Auger production cross-section data for H and He ions, we present a table of best-fitted cross sections for K-shell vacancy production (direct ionization plus electron capture) by 4He ions on all elements from 6C to 92U. Experimental values are first convened (if necessary) to vacancy production cross sections using fluorescence yields with an approximate correction for the effect of multiple ionization. These values are then normalized, i.e., divided, by an improved version (due to Benka et al.) of the ECPSSR theory by Brandt and Lapicki, to which a correction for electron capture by the projectile (following Lapicki and McDaniel) has been added. Since we have found empirically that the normalized cross sections (which describe the deviation of theory from experiment), at a certain scaled projectile speed, depend only on the ratio of projectile and target atomic numbers, we can use the data for both He and H ions as input. The normalized values are averaged, fitted by a polynomial, and multiplied by theory to produce best reference cross sections. Discrepant data sets are rejected using a statistical criterion which compares the deviations found to the errors stated in the original publications. The error assigned to the cross section consists of a calculated random contribution and an estimated systematic contribution that describes the limitations of the method. A list of the experimental input data (for 1H, 2H, 3He, and 4He projectiles) and a table showing the consistency or inconsistency of these data are also given.