Comparison of proton and helium induced M subshell X-ray production cross sections with the ECUSAR theory D.D. Cohen a,⇑ , E. Stelcer a , J. Crawford a , A. Atanacio a , G. Doherty a , G. Lapicki b a Australian Nuclear Science and Technology Organisation, Locked Bag 2001, Kirrawee DC, NSW 2232, Australia b Department of Physics, East Carolina University, Greenville, NC 27858, USA article info Article history: Received 18 February 2013 Received in revised form 29 April 2013 Accepted 27 May 2013 Available online 19 July 2013 Keywords: Protons He ions X-rays PIXE M-subshell ECUSAR abstract M subshell X-ray production cross sections have been measured for Ma 12 ,Mb 1 ,Mc,M 2 –N 4 and M 1 –O 23 transitions representing all five M subshells. These experimental cross sections have been compared with the ECUSAR theory of Lapicki and four parameter fits are given to the experiment to theory ratios cover- ing the proton and helium ion energy range from 0.5 to 3 MeV on thin W, Au, Pb, Th and U targets. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction Particle induced X-ray emission (PIXE) has been used by many laboratories for many years to characterise a broad range of sam- ples. Current PIXE detection systems are readily capable of measur- ing X-rays between 1 and 20 keV and hence through the characteristic X-rays from K and L shells cover most elements in the periodic table for aluminium upwards. For common heavy ele- ments with characteristic X-rays in the 1–5 keV region it has be- come more important to better understand and theoretically predict the numerous M shell lines which often overlap with light- er element K and L shell lines. M shell ionisation cross sections have been measured for more than a quarter of a century [1]. More recently the focus has shifted to more accurate measurements of the five M subshell X-ray production cross sections [2–8] to better quantify these and to make comparisons with theory across all five subshells. The ECPSSR theory developed over the years by Brandt and Lapicki [9] and applied specifically to the M shell [10], has more re- cently been extended to the ECUSAR theory [11]. Here the experi- mental and the ECUSAR X-ray production cross sections are compared for dominant lines in each of the five M subshells for slow proton and helium ion impact on selected high atomic number targets from W to U. This covers the X-ray energy range 1.1–5.5 keV. Proton energies between 0.5 and 3 MeV and helium ion ener- gies between 0.5 and 2 MeV were used to provide M subshell cross sections for 0.3 < n Mi < 3, where the reduced velocity n Mi = 2v 1 /(h Mi v 2 Mi ), was defined by Brandt and Lapicki [12] and distinguishes between the slow (n Mi < 1) and the fast (n Mi > 1) collision regimes. 2. Experimental conditions Five Mylar foils with thin metal coatings evaporated on their front surfaces were used as targets. Table 1 gives the metal film characteristics including typical detector efficiencies and self absorption for the corresponding M line energies. Target thick- nesses were calibrated to ±5% by standard Rutherford backscatter- ing (RBS) techniques. Self-absorption corrections for these thin targets were generally less than 6% and ion energy losses for the lowest proton and helium ion energies (0.5 MeV) were less 5 and 19 keV, respectively. Each target was bombarded with 10–20 nA of beam current for between 20 and 60 lC of ion charge. This was sufficient to keep counting statistical errors for each major M subshell peak below 10%. A modern VORTEX X-ray detector was used with a 25 lm beryllium window and a 400 lm thick silicon chip. 3. Results Fig. 1 shows a theoretical M shell PIXE spectrum without the background for 3 MeV protons on U. It was generated in the 0168-583X/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.nimb.2013.05.094 ⇑ Corresponding author. E-mail address: dcz@ansto.gov.au (D.D. Cohen). Nuclear Instruments and Methods in Physics Research B 318 (2014) 11–14 Contents lists available at ScienceDirect Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb