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VOLUME 36, NUMBER 8
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
M. C. Andrews,* F. D. McDaniel, and J. L. Duggan
Department of Physics, North Texas State University, Denton, Texas 76203
P. D. Miller, P. L. Pepmiller, H. F. Krause, and T. M. Rosseel
Physics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830
L. A. Rayburn
Department of Physics, University of Texas at Arlington, Arlington, Texas 76019
R. Mehta and G. Lapicki
Department of Physics, East Carolina University, Greenville, North Carolina 27858
(Received 27 April 1987)
L- and M-shell x-ray production cross sections have been measured for thin solid targets of neo-
dymium, gadolinium, holmium, ytterbium, gold, and lead by 25-MeV Cq (q = 4,5,6) and by
32-MeV 160q + (q = 5,7,8). The cross sections were determined from measurements made with
thin targets (less than 2.25 pg/cm2). For projectiles with one or two K-shell vacancies, the target
x-ray production cross sections were found to be enhanced over those for projectiles without a K-
shell vacancy. The sum of direct ionization to the continuum (DI) plus electron capture (EC) to
the L,M,N, ... shells and EC to the K shell of the projectile have been extracted from the data.
The results are compared to the predictions of first Born theories, i.e., plane-wave Born approxi-
mation for DI and Oppenheimer-Brinkman-Kramers formula of Nikolaev for EC, and to the
ECPSSR that accounts for energy loss and Coulomb deflection of the projectile as well as for rela-
tivistic and perturbed stationary states of inner-shell electrons.
I. INTRODUCTION
Interest in inner-shell ionization in ion-atom collisions
has resulted in major advances both theoretically and ex-
perimentally.' This information is important in the de-
velopment of tokamaks,2 plasma physics,3 ion implanta-
tion,4 and in particle-induced x-ray emission (PIXE).5'6
Initially, the majority of the experimental work was
done using low-atomic-number ions, primarily protons,
to ionize K-shell electrons from target atoms.7 With the
development of high-resolution Si(Li) detectors and the
increased availability of heavy-ion beams, ionization
measurements have been extended to the L shell8'9 and
M shell. 10
At the time when advances were being made in the ex-
perimental studies, several theories were proposed to de-
scribe the dynamics of an ion-atom collision. The
plane-wave Born approximation (PWBA),11,12 the
binary-encounter approximation (BEA),'3 and the semi-
classical approximation (SCA) (Ref. 14) were successful
in describing direct ionization (DI) of the target K shell
by protons. Later the PWBA was modified5',16 for low
relative velocity effects of enhanced target electron bind-
ing and Coulomb deflection which increase with Z1 /Z2
where Z1 and Z2 are the atomic numbers of the projec-
tile and target atoms, respectively.
In addition to DI, electron capture (EC) of target elec-
trons to vacancies in the projectile can play an impor-
tant part in ionization.17 The first Born calculations use
the PWBA to describe DI and the Oppenheimer-
Brinkman-Kramers (OBK) theory'8 as modified by Niko-
laev'9 (OBKN) to describe electron capture. Using the
perturbed-stationary-states (PSS) approach that was used
in DI calculations20,21 for K-shell ionization, Lapicki and
Losonsky22 have developed another approach to EC,
also called ECPSSR, where energy loss (E), Coulomb
deflection (C), and refinements for target relativistic
effects (R) have been taken into account.23 It has been
improved and extended to the L and M shells by Lapicki
and others.24-28
In the present paper we report the simultaneous mea-
surement of L- and M-shell x-ray production for projec-
tiles of 25-MeV 12C + (q =--4,5,6) and 32-MeV 160q +
(q =5,7,8) incident upon thin (less than 2.25 g/cm2)
targets of 60Nd, 64Gd, 67Ho, 70Yb, 79Au, and 82Pb. The
purpose of this work was to make independent deter-
minations of the L- and M-shell x-ray production cross
sections and then compare them to predictions of the
first Born and ECPSSR theories. Preliminary L-shell x-
ray production cross sections have been previously re-
ported.9 These earlier data have been improved by using
more refined data analysis techniques as discussed in Sec.
II B.
S1987 The American Physical Society
PHYSICAL REVIEW A
OCTOBER 15, 1987
36 3699
