Z. Physik 266, 245-255 (1974) 9 by Springer-Verlag 1974 X-Ray Production by 1.5-11 MeV Protons R. Akselsson and T. B. Johansson Department of Nuclear Physics, Lund Institute of Technology, Lund, Sweden* Received July 23, 1973 Abstract. K-shell ionization and L x-ray production cross-sections by proton impact have been determined from measurements of K x-ray yields from thin targets of Ti, Fe, Co, Cu, Ni and Ag and of L x-ray yields from Au and Pb. The proton energies varied from 1.5 to 11 MeV. A Si(Li) semiconductor detector recorded the x-rays. The total error in the measured cross-sections is mostly less than 5 %. K~/K, ratios and L~,~,~/L, ratios have been determined. Ionization cross-sections have been compared with predictions of the plane-wave Born approximation (PWBA) and the binary-encounter approximation (BEA). Both theories describe the ionization quite well: PWBA is, however, better for higher proton energies whereas BEA is superior for lower energies. An empirical formula for ionization cross-sections is derived. Introduction Since their original discovery by Chadwick in 1912, heavy charged-particle induced characteristic x-rays have attracted continued interest and, in 1958, Merz- bacher and Lewis [1] published an extensive review article. Ionization cross-sections by heavy charged-particle impact have generally been compared with predictions of the plane-wave Born approximation(PWBA). This model describes the qualitative behaviour of the cross- sections as a function of the impinging particle energy quite well, but does not give a good quantitative description of the cross-section at low proton energies. At MeV energies, the model seems to be better, although available experimental results are scarce. Low-energy cross-sections appear to be better described by the semiclassical approach by Bang and Hansteen [2], who take the deflection of the proton in the Coulomb field of the nucleus into account. The binary-encounter model developed by Garcia [3] seems to provide ionization cross-sections in good agreement with ex- perimental data at both high and low energies. * Work supported in part by the Swedish Board of Technical Development. Most published experimental work has been done with low-energy protons. Modern work with proton energies above a few MeV are reported by Bissinger et al. [4, 5] using 2-28 MeV protons impinging on Ca, Ti, Ni and Ag and by Jarvis et al. [6] using 160 MeV protons impinging on 15 elements between Z=26 and 92. In addition, Watson et al. [7] have measured K or L x-ray cross-sections for 13 elements using 30- 80 MeV c~-particles. Very recently, Bearse et al. [8] measured K~ and L~ x-ray production cross-sections using 1 to 3.7 MeV protons for 11 and 10 elements respectively and Winters et al. /-9] studied inner shell ionization ofAr, Kr and Xe by 1.5 to 5.0 MeV protons. In these works errors of 10-20 % are reported. Measurements of ionization cross-sections in the 1950-ies were generally made using thick targets and scintillation detectors. The high resolution Si(Li) detectors now available provide superior conditions for this type of work. Ref. F1] contains references to the older literature, while references to later work can be found in Ref./-10]. Incentives to the present work were to extend the possibilities of comparing calculations of x-ray ioniza- tion cross-sections with precise measurements at MeV energies and to provide the sensitive method of elemental trace-analysis offered by using MeV protons