Production of Characteristic X Rays by Low-Energy Protons

Abstract

The cross sections for the production of characteristic x rays emitted by targets bombarded with lowenergy protons have been measured for a number of elements. Scintillation counters capable of resolving x rays with quantum energies as low as 2 keV were used as detectors. X rays from K, L, and M shells were observed and the behavior of the production cross section for these was measured as a function of incident proton energy. Proton beams with energies between 100 and 500 keV produced by the Lawrence Radiation Laboratory (LRL) Cockcroft-Walton accelerator were used for the bombardments. The ionization cross sections for the shells have also been computed using measured or extrapolated values of the appropriate fluorescence yields. The experimental results for i£-shell ionization are in good agreement with previous measurements for a number of elements. The dependence of the iT-shell ionization cross section on atomic number (Z) and on the energy of the bombarding protons is also in accord with the theoretical predictions provided that the deflection of the bombarding particle by the Coulomb field of the nucleus is taken into account. The measured Z-shell ionization cross sections are smaller than the values predicted by a Born approximation calculation in which Coulomb effects are neglected. No calculations are available for If-shell ionization cross sections so only a qualitative explanation of their behavior is presented.

Thorium and uranium M-shell x-ray production by 0.4–4.0 MeV protons and 0.4–6.0 MeV helium ions

“…decreasing energy, the first Born approximation increasingly overestimates all data while the ECUSAR underestimates them to the same degree. The oldest set of measurements of Jopson et al [12] for uranium bombarded by 0.2-0.5 MeV protons bucks this trend in the data versus the ECUSAR as an exception. 2) and others [5,17,19,21] to the first Born approximation [35][36][37][38][39][40] and the ECUSAR theory [26,27].…”

“…Since the cross sections for the individual M-shell line cross sections are rarely found [15,20], in the following our data for the total M shell are compared with others [5,[12][13][14][15][16][17][18][19][20][21], and displayed against the prediction of the first Born approximation [35][36][37][38][39][40] and the ECUSAR theory [26,27]. The M-shell x-ray production cross sections by protons are shown in figure 5 for thorium and uranium.…”

“…References compiled by Lapicki [6] and Paul et al [7,8] report about 180 K-shell cross sections, while tables of Hardt and Watson [9], Sokhi and Crumpton [10] and Orlic et al [11] list some 130 L-shell cross sections for these targets. M-shell articles [5,[12][13][14][15][16][17][18][19][20][21] report approximately 210 x-ray production cross sections for thorium and uranium.…”

Thin carbon foils for the elimination of charging effects in proton induced x-ray emission spectrometry

“…Several experimental modifications for minimizing the charge buildup on the sample target and reducing the bremsstrahlung have been proposed. The evaporation of a conductor onto the sample (3,4) or mixing the sample with a conducting compound (5) are unsatisfactory because the sample can be readily contaminated. An increase in the pressure of the sample chamber has also been shown to be effective ( 6), but this also increases the probability of contaminating the sample.…”

L-shell x-ray production cross sections of Ni, Cu, Ge, As, Rb, Sr, Y, Zr, and Pd by (0.25–2.5)-MeV protons

“…The two primary processes responsible for inner-shell ionization are direct ionization (DI) Jopson et al (1962) and the copper data of Khan et al (1964Khan et al ( -1966. Among the later studies ' Winters et al ' (1973) taken from Refs.…”