K-Shell Ionization Cross Sections of Selected Elements from Fe to As for Proton Bombardment from 0.5 to 2.0 MeV

Abstract

The problem with which this investigation is concerned is that of making experimental measurements of proton-induced K-shell x-ray production cross sections and to study the dependence of these cross sections upon the energy of the incident proton. The measurements were made by detection of the characteristic x-rays emitted as a consequence of the ionization of the K-shell of the atom. The method for relating this characteristic x-ray emission to the x-ray production cross section is discussed in this work.The measurements made in this investigation have a twofold use. First, they add to needed information for testing of theoretical calculations of inner atomic electron shell ionization by ion impact. There are three basic theories which describe inner shell ionization processes. Two of these theories, the Binary Encounter Approximation (BEA) and the Plane Wave Born Approximation (PWBA), apply to the proton energy range studied in this work. The BEA is a semi-classical treatment, and the PWBA is a quantum mechanical treatment.Corrections have been suggested to the PWBA to account for the change in the binding energy of the ionized shell caused by the penetration of the incident ion into this shell. Thisgives three theoretical predictions applicable to this work.Two of the theories, the BEA and the PWBA with binding energy corrections, give nearly equivalent predictions for the ionization cross section of an element when bombarded by protons in the energy range investigated in this work.The PWBA predicts cross sections which may differ from the other predictions by as much as a factor of two. Because of insufficient data to totally test these three theories, itis not known which theory best predicts the ionization cross sections for the range of proton energies studied in this work.The measurements made here compliment existing data and aid in the testing of these theories.The second use of these measurements is in the field of application of x-ray analysis. High resolution non-dispersive Since the available data is limited, the measurements of this work are a useful contribution to the information needed for studies in x-ray analysis techniques.The K-shell ionization and x-ray production cross sections for Fe, Co, Cu, Zn, Ga, Ge, and As were measured for proton impact in the range 0.5 to 2.0 MeV. Several of these elements were chosen for this investigation because of the need for x-ray production cross sections to facilitate the characterization of materials used in semi-conductor devices.The ionization cross sections for Fe, Co, Cu, Zn, Ga, Ge, andAs were found to be 242 23, 173 15, 94.1 7,8, 70.9 6.9, 56.4 4.6, 36.5 2.7 and 27.1 2.1 barns respectively at 2.0 MeV.These measurements agree to within less than 17 per cent with the predictions of the BEA and the PWBA with binding energy corrections.The predictions o6f the PWBA exceed the measured values by as much as a factor of two at the maximum deviation.It is concluded from a study of the energy dependence of these cross sections that the BEA and PWBA with bi...

Oxygen inducedK-shell ionization of selected elements from sulphur to bromine

“…The data of Table 3 shows the very good agreement of absolute cross sections of this work and the measurements of Bearse et al [25]. The agreement with the results of other authors [26][27][28][29] is not as good, but the values are still within the range of stated uncertainties. It is interesting to note that the common method to determine Si(Li) detector efficiencies with calibrated radioactive sources might lead to too small efficiencies especially at low X-ray energies [31] and thus to increased X-ray production cross sections.…”

“…We have checked our normalization procedure by measuring with the same experimental equipment proton induced K-shell ionization cross sections of Ti, Fe, Co and Ni at 1.0, 2.0 and 5.0 MeV bombarding energies, where cross section measurements of other authors [26][27][28][29] were available. For the comparison shown in Table 3, only measurements with thin targets and Si(Li) X-ray detectors were selected and all ionization cross sections were normalized to the fluorescence yields given by Bambynek et al [-25].…”

Energy dependence of the x-ray production cross sections of Cu and Ag for 150 to 800 keV proton and He+ bombardment

“…The K-shell ionization cross section of 800 keV protons on Cu was taken as normalization value. The weighted mean x-ray cross section from thin target measurements [18,19,20] for 1 MeV protons is (5.49_+0.4)b. To get the cross section for 800 keV this value was multiplied with the factor o-(0.8 MeV)/a(1 MeV) of the PWBABC theory.…”

Trace element analysis of fluids by proton-induced x-ray fluorescence spectrometry

“…Garcia allows for the nuclear repulsion of the incident proton. Very recently, several experimental groups (27)(28)(29)(30)(31)(32)(33) have reported measurements of absolute K-shell ionization cross-sections for a wide range of target elements and proton energies. From this work, we have extracted the data at 2.0 and 2.5 MeV, and compare them with the two theories as a function of Z in Figures 5 and 6.…”