L- and M-shell x-ray production cross sections of Nd, Gd, Ho, Yb, Au, and Pb by 25-MeV carbon and 32-MeV oxygen ions Page: 3,701
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L- AND M-SHELL X-RAY PRODUCTION CROSS SECTIONS ...
S--- Background (1 74o)
5 10000 -
--- ------ ---- ---- - -- - -- ---- - -----
1.0 1.5 2.0 2.5 3.0
X-RAY ENERGY (KeV)
FIG. 1. A typical M-shell spectrum of gold bombarded by
25-MeV carbon ions. The triangles are the fit of six Gaussian
peaks (solid curves) plus a linear and nearly constant back-
ground (dashed line). These peaks are labeled with the symbol
of target atoms (gold plus aluminum and silicon contaminants)
and dominant x-ray transitions (with x-ray energies given in
keV). Some target transitions (M3--sN1, etc.) are obscured by
fluorescence yield (+5%), target thickness (+7%), and
x-ray yield uncertainties ( 10 or 20%), the overall un-
certainty in the x-ray cross sections is +15% for pt > 2.5
.tg/cm2 and 23% for pt <2.5 tg/cm2. To the extent
that these thin targets represent single-collision condi-
tions, the cross sections are a good approximation of the
cross sections for vanishingly thin targets.
Because the L-shell spectra were much less contam-
inated with low-atomic-number elements, the uncertain-
ties in the x-ray yields were only +2% for all targets.
The uncertainty in the efficiency of the Si(Li) detector is
also better known (+3%) in the L-shell energy region.
Combining these values with those for fluorescence yield
and target thickness, the overall uncertainty in the L-
shell x-ray cross sections is +10% for all measurements.
Effective M-shell x-ray production cross sections as a
function of target thickness are plotted in Fig. 2 for
different charge state ions.34 Similar results were ob-
tained for the L-shell spectra. The L-shell data for car-
bon and oxygen ions for the thinnest targets are present-
ed in Tables I and II, respectively. The M-shell data for
carbon and oxygen ions for the thinnest targets are
presented in Tables III and IV, respectively. The thick-
ness dependence of the yield must be carefully interpret-
ed because the electron configuration of the projectile in-
side a solid target is not well understood.35 Early studies
by Hopkins36 and Groeneveld et al.37 indicated that tar-
get x-ray yields, from ions which first passed through the
carbon backing of the target foil and had more K-shell
vacancies, were considerably enhanced over the target
x-ray yields when the beam was incident on the target
side of the foil.
8 0 Au
GOLD TARGET THICKNESS ( pg/cm2)
FIG. 2. Enhancement of the effective target M-shell x-ray
production cross sections, MX, occur with the decreasing
thickness of the target and for increasing ion charge state (Ref.
34). The slight rise of the 5 + cross sections (zero K-shell va-
cancies) is attributed to the relative increase in target contam-
ination as the thickness decreases. The much greater increase
for the 7 + (one K vacancy) and the 8 + (two K vacancies) re-
sults are due to EC to the projectile K shell. The dashed line
represents the cross section for DI plus EC to the L,M, ...
shells in the ECPSSR formalism. Representative error bars are
shown. The filled (e), half-filled (Q), and empty circles (0) of
the data correspond to the filled, half-filled, and empty K shell
that the projectile brings into the collision.
This dependence of x-ray yields on projectile charge
state and target thickness have also been investigated by
Gray et al38 and McDaniel et al.39 They measured tar-
get K-shell x-ray yields for projectiles with zero, one,
and two K-shell vacancies as a function of target thick-
ness. By varying the number of projectile K-shell vacan-
cies and target thicknesses, they controlled the amount
of K-shell to K-shell EC from the target to the projectile.
Both groups found that x-ray yields were strongly
influenced by the presence of projectile inner-shell va-
cancies and that the projectile charge state would equili-
brate at large target thicknesses. McDaniel et al.39
compared their results favorably with the ECPSSR.
McDaniel et al. 26 later extended this investigation to the
production of L-shell x rays and found similarly good
agreement. McDaniel et a. 26,39 used the thinnest possi-
ble targets (approximately 1 kpg/cm2), which approxi-
mated single-collision conditions, to extract DI and EC
The variation of M-shell x-ray production cross sec-
tions with projectile inner-shell vacancies has recently
been measured10,32,40 and compared to the first Born and
ECPSSR theories. Again it was found that the ECPSSR
was in good agreement with the data.
In Figs. 2-6 the filled circles represent target cross
sections o0) for projectiles with no K-shell vacancies,
while the half-filled circles and open circles show target
cross sections for projectiles with one o"(1) and two ao(2)
K-shell vacancies, respectively. Whereas the u(O) results
in Fig. 2 are constant within statistical limits for all but
the thinnest targets, the a(1) and r(2) results rise
out I I
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Andrews, M. C.; McDaniel, Floyd Del. (Floyd Delbert), 1942-; Duggan, Jerome L.; Miller, P. D.; Pepmiller, P. L.; Krause, H. F. et al. L- and M-shell x-ray production cross sections of Nd, Gd, Ho, Yb, Au, and Pb by 25-MeV carbon and 32-MeV oxygen ions, article, October 15, 1987; [College Park, Maryland]. (digital.library.unt.edu/ark:/67531/metadc139494/m1/3/: accessed September 20, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT College of Arts and Sciences.