26 Nuclear Instruments and Methods in Physics Research B56/57 (1991) 26-29 North-Holland L-shell X-ray production cross sections in ,Ca, 26Fe, 28Ni, 29Cu, and 32Ge by 0.75 to 4.5 MeV 7Li+ ions zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONML MR. McNeir, Y.C. Yu, D.L. Weathers, D.K. Marble, J.L. Duggan and F.D. McDaniel Department of Physics, University zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA of North Texas, Denton, Texas 76203, USA G. Lapicki Department of Physics, East Carolina Umi~ersi~, Greenville, North Carolina 27858, USA L-shell X-ray production cross sections are presented for selected elements with X-ray energies between 341 and I188 eV. X-ray measurements were made using both a windowless Si(Li) and a windowless high purity Ge detector. The efficiency of the Si(Li) detector was determined by comparing bremsstrahlung spectra from electron bombardment of thin foils of aluminum, silver, and gold with theoretically determined bremsstrahhmg spectral distributions. The efficiency of the Ge detector was determined by no~ali~ng K-shell X-ray measurements to the Si(Li) detector. The me~mements are compared to the first Born and the ECPSSR theories. The ECPSSR theory is shown to be in much closer agreement with the data. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQP 1. Introduction zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA The ionization of inner-shell electrons by fast ions and the associated emission of characteristic X-rays has been studied extensively for the past few decades, dur- ing which time several theoretical models of the processes have been examined. These theories have not been tested to any large extent for L-shell X-ray pro- duction for binding energies less than 1.2 keV. The development of windowless X-ray detectors has made these meas~emen~s possible. While extensive tables of proton induced X-ray cross sections have been pub- lished [1,2], there has been much less work performed with other light ions [3]. L-shell X-ray production by helium and deuterons have each received some attention [3-6). There are, however, few measurements using lithium ions f3,7], and none at the low binding energies considered in this paper. Two main processes contribute to the ionization of inner-shell electrons: direct ionization (DI) and capture of the electron (EC) by the passing ion [8]. These processes have been treated quantum mechanically by the Born appro~mation. The calculation for DI is per- formed with the plane wave Born appro~mation (PWBA) [9]. The EC contribution is found using an idea developed by Oppenheimer, Brinkman, and Kramers and calculated by Nikolaev (OBKN) [lo-121. An extension beyond the first Born approximation is the ECPSSR theory [13,14], which incorporates the en- ergy loss and Coloumb deflection of the ion, along with the orbital perturbation and relativistic velocity of the electron, into the framework of the PWBA and OBKN formulae. This paper reports the measurements of L-shell X-ray production cross sections for singly ionized 7Li ions in the energy range 0.75-4.5 MeV incident upon selected elements with low L-shell binding energies. These mea- surements are compared to calculations from the stan- dard quantum mechanical theory of ionization (PWBA + 0BK.N) [9-121 as well as the approach of Brandt and Lapicki (ECPSSR for DI) [13] and Lapicki and Mc- Daniel (ECPSSR for EC) [14]. 2. Experiment A windowless, lithium drifted silicon detector and a windowless, high purity ge~a~um detector from LINK Analytical [15] were used for X-ray detection. Each detector was 30 mm2 in area with a 3 mm active depth. The detectors could be operated in three possible con- figurations: a beryllium window, an ultrathin window of aluminum on formvar, or no window at all. For the windowless mode, each detector had a pair of magnets mounted in front of the crystal face to deflect low energy, charged particles. The unique feature of such detectors is that they can measure X-rays down to approximately 200 eV [16]. This low energy capability gives an excellent opportunity to compare experimental measurements with theoretical predictions in an energy region that has been inaccessible because of the Be window attenuation in the standard Si(Li) detector. The detectors were equipped with the LINK Analytical 2040 pulse processor [15] that interrogates incoming pulses, 0168-583X/91/$03.50 0 1991 - Elsevier Science Publishers B.V. (North-Holland)