K-shell x-ray-production cross sections in 6C, 8O, 9F, 11Na, 12Mg, and 13Al, by 0.75- to 4.5-MeV protons Page: 5,702
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VOLUME 44, NUMBER 9
K-shell x-ray-production cross sections in 6C, 80, 9F, 11Na, 12Mg,
and 13A1 by 0.75- to 4.5-MeV protons
Y. C. Yu, M. R. McNeir, D. L. Weathers, J. L. Duggan, and F. D. McDaniel
Department of Physics, University of North Texas, Denton, Texas 76203
Department of Physics, East Carolina University, Greenville, North Carolina 27858
(Received 10 April 1991; revised manuscript received 8 July 1991)
K-shell x-ray-production cross sections are reported for elements with K-shell x-ray energies between
277 eV (C) and 1487 eV (Al). The x-ray measurements were made with a windowless Si(Li) detector that
was calibrated for efficiency by comparing bremsstrahlung spectra from electron bombardment of thin
foils of aluminum, silver, and gold with theoretically determined bremsstrahlung spectral distributions.
The x-ray-production cross-section measurements are compared to first-order Born and perturbed-
stationary-state with energy-loss, Coulomb deflection, and relativistic corrections (ECPSSR) ionization
theories using single-hole fluorescence yields. The ECPSSR and first-order Born theoretical predictions
are, in general, in close agreement with each other and both generally fit the data quite well.
PACS number(s): 34.50.Fa, 34.70. +e
Atomic inner-shell ionization by incident charged par-
ticles has been discussed and examined extensively. The
literature [1-5] for K-shell x-ray studies with protons in-
dicates a lack of precise data for target atomic numbers
less than 13, however. Of the existing K-shell ionization
measurements in this region, the earlier measurements
used flow-mode proportional counters [6-11]. More pre-
cise measurements of cross sections have become possible
with the use of high-resolution Si(Li) detectors [12-14];
this is the type of instrument employed in the present
There are a number of reasons why the data presented
here have not been investigated extensively. First, the Be
window of standard Si(Li) detectors, for the most part, at-
tenuates all x rays below 1 keV. Even in the windowless
mode the detector efficiency curve is very steep in this re-
gion and is difficult to measure. Second, and perhaps of
equal importance, is the problem of low-energy contam-
inant x rays produced by the impurities which are present
on the carbon backings used for substrates to support the
evaporated targets. These impurities usually come from
the soap solution that is used as a surfactant in the
preparation of the carbon foils. In this paper, we will
outline the techniques that were used to overcome both
of these experimental problems.
There have been several theories proposed to explain
the measured cross sections. For K-shell ionization of an
atom, the direct ionization (DI) of a target electron to the
continuum has been shown to be a principal mode of in-
teraction for the region Z1 <<Z2 and v1 >2K (Ref.
), where Z1 and Z2 refer to the incident and target
atomic numbers, and v1 and V2K refer to the incident-ion
and target K-shell electron velocities, respectively. The
DI process has been described in the first-order Born ap-
proach by the plane-wave Born approximation 
(PWBA). For Z1 Z2 and v1 V2K, K-electron capture
(EC) to incident-ion bound states is important. The
Oppenheimer-Brinkman-Kramers theory as modified by
Nikolaev  (OBKN) has been used in the first-order
Born approach for the EC process. The ECPSSR theory
of Brandt and Lapicki for DI  and Lapicki and
McDaniel for EC  accounts for the energy loss (E)
and Coulomb deflection (C) of the projectile as well as for
the perturbed stationary states (PSS) and the relativistic
nature (R) of inner-shell electrons. This theory has ex-
tended the region of validity to Z1 < Z2 and v1 < v2K.
This paper reports x-ray production cross sections for
protons in the energy range 0.75-4.5 MeV on thin tar-
gets of 6C, 80, 9F, , Na, 12Mg, and 13A1. X-ray mea-
surements were made with a Link Analytical windowless
Si(Li) x-ray detector , which allowed the extension of
x-ray analysis down to carbon. The ranges of the Z1 /Z2
and V1 /v2K parameters investigated were 0.076
<Z1 /Z2 <0. 167 and 0.43 <v1 /v2K <2.35, respectively.
The experimental results are compared to the predictions
of the first-order Born approximation (PWBA for DI and
OBKN for EC) and the ECPSSR theory.
II. EXPERIMENTAL PROCEDURE
Experiments were performed using the 3-MV tandem
accelerator (NEC 9 SDH) at the University of North
Texas Ion Beam Modification and Analysis Laboratory
. Thin targets (see Table I) were prepared by vacuum
evaporation and deposition of the elements of interest
onto 5-ptg/cm2 carbon foils, except for magnesium, which
was evaporated onto gold backings. The impurities on
the carbon backings were mainly oxygen, sodium, and sil-
icon. These elements were removed by floating the car-
bon off in ultrapure water that was spiked with acetic
acid [21,22]. The cleaning procedure was repeated three
times in an ultrasonic bath. This technique essentially el-
5702 1991 The American Physical Society
PHYSICAL REVIEW A
1 NOVEMBER 1991
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Yu, Y. C.; McNeir, M. R.; Weathers, Duncan L.; Duggan, Jerome L.; McDaniel, Floyd Del. (Floyd Delbert), 1942- & Lapicki, Gregory. K-shell x-ray-production cross sections in 6C, 8O, 9F, 11Na, 12Mg, and 13Al, by 0.75- to 4.5-MeV protons, article, November 1, 1991; [College Park, Maryland]. (digital.library.unt.edu/ark:/67531/metadc139500/m1/1/: accessed February 20, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT College of Arts and Sciences.