Time-resolved pile-up compensation in PIXE analysis with list-mode collected data

In order to improve the accuracy of the PIXE analysis with respect to the p ile-up problem, a technique to analyse PIXE spectrums suffering from File-u p has been developed. It is based on the well-known relationship N-a . N-b . tau = N, where N-a and N-b are the count rates in two primary peaks, tau is the pile-up interval and N is the count rate in the resulting pile-up pe ak. This relationship, however, only holds for a constant count rate, a con dition rarely encountered in practice. In order to compensate the spectrum for the pile-up effects despite a varying count rate, the X-ray energy sign al together with the current are collected in list-mode event-by-event, gro uped in time steps, enabling a time-resolved analysis of the spectrum. The above relationship can then be applied at every time step, here 10 ms, duri ng which the count rate is considered constant. A formula to determine a co mpensation factor, (1 + C), is inferred, that enables compensation for pile -up in the final spectrum. Also a simplified technique is proposed, where o nly the beam current is multiscaled for the duration of the experiment. The dependence of tau on the X-ray energy was determined by pulse generator ex periments as well as by beam for a number of elements. Examples of the meth od are demonstrated for various degrees of instability in the beam, and wit h and without a beam deflection system. (C) 1999 Elsevier Science B.V. All rights reserved.