NUCLEAR
INSTRUMENTS
AND
METHODS
142 ( 1 9 7 7 )
5-8 ;
(~)
NORTH-HOLLAND
PUBLISHING
CO.
INNER SHELL IONIZATION RESEARCH IN THE INSTITUTE OF NUCLEAR RESEARCH IN DEBRECEN, HUNGARY
A. KOVI~R
Institute oJ'Nuclear Research, Debrecen, Hungary Data for the X-ray production cross-section for the K and L shells induced by electrons, positrons, protons and ~z-particles are presented and compared with different theoretical approaches.
There is a very active interest now in the field of inner electron shell ionization in charged particle-atom collisions. The vacancies are produced by projectiles such as electrons, positrons, protons and heavy ions. These measurements are motivated by both fundamental and practical as well as by instrumental reasons.
Our investigation in this field concerned the Xray production cross section for the K and L shells induced by electrons, positrons, protons and alpha particles. The number of experimental data for inner shell ionization by relativistic electrons (between 100 keV and 1 MeV) are rather limited even in the
IooolL
E (3 ¢1
E = 490 keY
E = 670key •
L~
Lo
for eleC:tron
•
o :o;ooO;,oo
for e l e c t r o n
0 for p o £ t r o n theory
100
1oo
~0-
1
1o -
(a) 1
10
-
100
---
Z~
]
(b) 10
I lO0
Z -""
Fig. 1. Comparison of cross sections for K shell ionization by el,~ctron and positron impact, with those according to the Kolbenstvedt theory at 670 and 490 keV.
I. T E C H N I C A L
DEVELOPMENTS
6
A. KOvER
case of the K shell. For the L shell ionization by electrons in this region there have been no papers up till now except ours. In our earlier measurements a magnetic beta-ray spectrometer was used to monochromatize the impinging electrons ~) as well as positrons 2) coming from a radioactive source. K shell ionization cross sections excited by electrons and positrons were measured in the case of seven elements (Ni, Y, Ag, Yb, Ta, Au, Pb). Fig. 1 shows the result of the comparison between qK for electrons and positrons as well as with Kolbenstvedt theory. The L shell ionization cross sections excited by electrons were measured for three elements (Yb,
Ta, pb)l).
In the case of these measurements the experimental errors were rather high, due to the target thicknesses (20--40 mg/cm 2) and the difficult experimental conditions. Therefore now a Cockcroft-Walton generator has been applied as an electron source, in the energy region of 300-600 keV3). In order to reduce the thickness,
mostly self-supporting targets were used. The thickness of our targets was about 100-400 ~g/cm2 4). The X-ray production cross section and yield ratios for the L lines and the total L shell were determined for Yb, Au and PbS). Fig. 2 shows the experimental data in the case of Pb compared with three different theoretical calculations, like BEA (Gryzinski 1965), Pessa and Newell (1971) and Kolbenstvedt (1975). Kolbenstvedt's method has been extended to the L shell. As can be seen the BEA theory describes the experimental data fairly well. The ionization cross sections have been calculated by the help of fluorescence yields. Unfortunately, complete series of these theoretical and experimental values are missing. Therefore we used the available experimental or theoretical values. Fig. 3 shows the yield ratios: Le/L ~, LJL~ and LJL,. The agreement with the BEA theory is fairly good. We also performed measurements in the field of o)
6
x }
L~I L,z
Li
(born)
C.~
11o
8zPb
7oYb
Ioo
t
I0' 9o
b) 10'
so! 7c
,¢
L~/L=
L. C J
6(
7,Au
Lp 5c
L,/L~
~- ~d 4c
c.)
z-'6ho,
3o
i0c
L~/L=
2o
io •
I
~
Lr
•
•
Lt
Fig. 2. X-ray production cross sections by electron impact for partial and total L-lines of Pb; ~ measured values; full line: BEA; dashed line: Pessa and Newell; dash-dotted line: Kolbenstvedt.
5'10
~
{
~
,}
LTIL=
~
Lt/L~
Fig. 3. Measured yield ratios (~) of the X-ray lines for Yb, Au and Pb.
INNER SHELL I O N I Z A T I O N
RESEARCH
7
PWBA
~glntp,xl
•
T~ ~.'"'" PWBAB t J~...'"~~f'~ -PWBABC T ~';'-/C ?/ BEA
~o
to
T/./"
t/::;~y
1
2 Cu(e,x)
.'" ,'Z
{/'-
.
/
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-
/
~./ 101
/
/i/"
/
/
O/
, /BEA
/ ~2~. ~PWBABC /
/
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0/
_
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,~ oo//
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'
i
~1/
10--~~ T#~ ~,
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/ - ?/
" Present measurements
OLin et at(1973) a Mc Knight et at(197z,) oMc Daniet et a[(1975) • Present measurements
: ,.':i//
'71
10-2
I/ I
1,0
2,0
3,0
E [MeV] 10-q
Fig. 4. Proton impact K ionization cross sections for In. The different theoretical approaches (BEA, PWBA, PWBAC, PWBAB, PWBABC) are shown as curves.
,
3,0
2,0
~,0
i
4,0
E[MeV]
Fig. 5. Alpha impact K-shell ionizations for Cu. The curves represent the different theoretical approaches (BEA, PWBA, PWBABC). The PWBABC curves calculated for ~+ are also presented.
~Mc{ I0 x I0~I
tL. ~La 79 Au
i
J
5-
IX 1/400
,'
i
,i
" --
-~0
i~s..'.IL, .."".....i
MF~
°'°""----''"f60
L ................
-" I~0
260
( channel )
Fig. 6. L and M shell X-ray spectra of Au, bombarded by singly ionized carbon. 1. T E C H N I C A L DEVELOPMENTS
8
A. KOVER
inner shell ionization by heavy charged particles such as protons and alpha particles, accelerated by our 5 MV Van de Graaff generator. The data for the inner shell ionization cross section are available only for selected elements over limited energy regions even in tile case of proton bombardment. There are disagreements between the theoretical and experimental data. K shell ionization cross sections have been determined for Cr, Cu and In. In this case the projectiles were protons in the energy region of 0.9-2.5 MeV6). The results are compared with different theoretical approaches, namely the semiclassical binary encounter approximation (BEA)7,8). The planewave Born approximation (PWBA) 9) as well as PWBA with Coulomb deflection correction (PWBAC), PWBA with binding energy correction (PWBAB), PWBA with binding energy and Coulomb deflection correction (PWBABC)I°). Fig. 4 shows the results in the case of an In target. Summarizing the results we can say that the accuracy of the measured data, at this moment does not give the possibility to discriminate between the different theories.
Fig. 5 shows the results in the case of a Cu target bombarded by alpha particles6). Recently we have obtained some preliminary resuits in the case of heavy ion impact, such as singly ionized carbon. Fig. 6 shows the X-ray spectra of Aul~). References 1) S. A. H. Seif el Nasr, D. Ber6nyi and Gy. Bibok, Z. Physik 267 (1974) 169. 2) S. A. H. Seif el Nasr, D. Ber6nyi and Gy. Bib6k, Z. Physik 271 (1974) 207. 3) B. Schlenk, D. Ber6nyi, S. Ricz, A. Valek and G. Hock, Acta Phys. Hung., to be published. 4) B. Schtenk, D. Ber6nyi, S. Ricz, A. Valek and G. Hock, 2nd Conf. on Inner shell ionization phenomena, Freiburg (1976) Abstracts p. 227. 5) B. Schlenk, D. Berenyi, S. Ricz, A. Valek and G. Hock, J. Phys. B: Atom Molec. Phys., to be published. 6) E. Koltay, D. Ber6nyi, I. Kiss, S. Ricz, G. Hock and J. Bacso, Z. PhysikA278 (1976) 299. 7) j. D. Garcia, R. J. Fortner and T. M. Kavanagh, Rev. Mod. Phys. 45 (1973) 111. 8) j. D. Garcia, E. Gerjuoy and J. E. Welker, Phys. Rev. 165 (1968) 66. 9) G. S. Khandelwal, B.-tt. Choi and E. Merzbacher, At. Data I (1969) 103. 10) G. Basbas, W. Brandt and R. Laubert, Phys. Rev. A7 (1973) 983. t t) E. Koltay, D. Berenyi and J. V6gh, private communication.