Measurement of M-shell X-ray production induced by protons of 0.3–0.7 MeV on W, Au, Pb, Bi, Th and U L. Rodr  ıguez-Fern andez * , J. Miranda, J.L. Ruvalcaba-Sil, E. Segundo, A. Oliver Instituto de F  ısica, Universidad Nacional Aut onoma de M exico, Apartado Postal 20-364, 01000 Mexico, D.F. Mexico Abstract M-shell X-ray production cross-sections of the elements 74 W, 79 Au, 82 Pb, 83 Bi, 90 Thand 92 Uinducedbyprotonswere measured in the energy range 0.3–0.7 MeV in steps of 50 keV. X-rays were registered by a Si(Li) detector. Values measured for the cross-sections of the most intense M-shell X-ray lines are presented. The measured X-ray production cross-sections are compared with PWBA and ECPSSR theoretical calculations. Results indicate the ECPSSR theory underestimates the experimental cross-sections for low energy protons. Ó 2002 Elsevier Science B.V. All rights re- served. PACS: 34.50 Keywords: X-ray production cross-sections; PIXE; M-shells 1. Introduction The X-ray production cross-section induced by protons decreases strongly for energies lower than 1 MeV. This strong change in the cross-section is one of the bases for many low energy PIXE ap- plications, such as thin film thickness determina- tion, since the X-ray production drops steeply near the end of the proton path, thereby increasing the sensitivity to changes in depth profiles [1]. For this reason an accurate knowledge of the X-ray production cross-sections is required to achieve reliable results during the analysis. Reliable semi- empirical cross-sections for the K and L shells are available [2,3] and those are good enough for many of the PIXE applications. The detection of M-shell X-rays is useful for the measurement of very heavy elements using low energy particles. Although,therearefitstoexperimentaldataofM- shell X-ray production cross-sections [4], the M- shell X-rays induced by charged particles have not been studied as much as K and L shells. In this work is presented the measurement of the M-shell X-ray production cross-sections in- duced by protons on the elements 74 W, 79 Au, 82 Pb, 83 Bi, 90 Th and 92 U at energies between 0.3 and 0.7 MeV in steps of 50 keV. Experimental values for the most intense M X-ray lines are reported. The results are compared with the plane wave Born approximation (PWBA) [5,6] and the ECPSSR theory [7]. 2. Experimental Theprotonbeamwasproducedbythe0.7MeV Van de Graaff accelerator at the Instituto de Nuclear Instruments and Methods in Physics Research B 189 (2002) 27–32 www.elsevier.com/locate/nimb * Corresponding author. 0168-583X/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII:S0168-583X(01)00989-2