L SUBSHELL IONIZATION OF Eu AND Gd BY PROTON, DEUTERON AND ALPHA BOMBARDMENT

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L SUBSHELL IONIZATION OF Eu AND Gd BY PROTON, DEUTERON AND ALPHA

BOMBARDMENT

A. Jesus, J. Ribeiro, J. Lopes

To cite this version:

A. Jesus, J. Ribeiro, J. Lopes. L SUBSHELL IONIZATION OF Eu AND Gd BY PROTON,

DEUTERON AND ALPHA BOMBARDMENT. Journal de Physique Colloques, 1987, 48 (C9), pp.C9-

235-C9-238. �10.1051/jphyscol:1987938�. �jpa-00227356�

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JOURNAL DE PHYSIQUE

Colloque C9, suppl6ment au

n"12,

Tome

4 8 ,

dbcembre

1987

L SUBSHELL IONIZATION OF Eu AND Gd BY PROTON, DEUTERON AND ALPHA BOMBARDMENT

A.P. JESUS*,**, J.P. R I B E I R O * ~ " " ~

and

J.S. LOPES*""

' c e n t r o de Fisica Nuclear, Complexo 11 do INIC, Avenida Gama Pinto

2 , P - 1 6 9 9

Lisboa Codex, Portugal

"Departamento de Fisica da Universidade Nova de Lisboa, Lisboa, Portugal

"""Departamento de Fisica da Universidade de Lisboa. Lisboa, Portugal

RESUME

Oes s e c t i o n s e f f i c a c e s de p r o d u c t i o n de rayons L-X o n t i t 6 mesuries pour Eu e t Cd s u r une zone d 1 6 n e r g i e comprise e n t r e 0.2 e t 0.9 MeV u - l pour l a c o l l i s i o n du p r o t o n e t du deuteron, e t e n t r e 0.2 e t 0.45

MeV u - l pour l a c o l l i s i o n de l a p a r t i c u l e alpha. Les r a i e s La

,

L y e t L y 2,3 o n t s e r v i i l a con- v e r s i o n des s e c t i o n s e f f i c a c e s de p r o d u c t i o n de rayons X en s e c t i o n s e f f i c a c e s d ' i o n i s a t i o n q u i s o n t comparies 2 l a t e o r i e ECPSSR.

ABSTRACT

L X-ray p r o d u c t i o n c r o s s s e c t i o n s have been measured f o r Eu and Gd i n t h e energy range 0.2 t o 0.9

MeV u - I f o r p r o t o n and deuteron impact and 0.2 t o 0.45 MeV u - l f o r a l p h a - p a r t i c l e impact. La

,

Lyl and LY2,3 l i n e s were used t o c o n v e r t from X-ray p r o d u c t i o n t o s u b s h e l l i o n i z a t i o n c r o s s s e c t i o n s t h a t a r e compared w i t h t h e ECPSSR t h e o r e t i c a l values.

INTRODUCTION

In the last few years L shell ionization by light ions has been the subject of considerable theoretical and experimental work (1-6).

Theories based on PWBA have been improved by the incorporation of the binding and Coulomb defletion effects and by taking into account the effects of relativity and projectile energy loss on the ionization cross sections. Vacancy transfer me- chanisms (7,8) have been proposed to account for the experimental L2 subshell ionization enhancement and they induce a significant improvement for projectiles with atomic number Z1 '2. However, for L subshell cross sections some discrepancies remain unexplained; the atomic parametres used in the conversion from X-ray production to ionization introduce a further source of uncertainty that difficults the comparison between experiment and theory (9,lO).

Experimental results for deitterons and alpha-particles are very scarce, while for protons results from different authors show large variations (6). More experi- nental work is clearly needed, in particular alpha to deuteron and deuteron to pro-

ton cross section ratios as they can test the binding and Coulomb defflection effects rather accurately (10-12).

In this work we measured Eu and Gd L X-ray production cross sections induced by protons and deuterons, w ~ t h energies from 0.2 to 0.9 MeV u-'

,

and by alpha- particles, in the energy range 0.2 to 0.45 MeV u - I , and compare the ionization cross sections with Brandt and Lapicki ECPSSR theory (1).

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987938

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JOURNAL DE PHYSIQUE

EXPERIMENT

The experimental set-up has been described in detail elsewhere (13) and the experimental procedure is the same that we used in ref. 9. The statistical uncertainty was generally better than 1% for L a . Dead time and target thickness corrections (12) never exceeded 5% and 10% respectively.

RESULTS AND DISCUSSION

Results for L a , L and Ly,, production cross sections and an estimate of Yl

the percentual error are presented in table 1. For deuterons and alpha-particles we are unaware of results published in numerical form in the energy range covered in this work. For protons in Gd at 1 MeV the results of Avaldi et a1.(14) agree with ours within the quoted errors.

Atomic parametres used in the conversion of X-ray production into ionization cross sections were taken from the tables of Krause(l5) and Scofield(l6). Compa- rison between our experimental results and ECPSSR theory is made in the figures.

In figure 1 we can see that the plateau predicted by the theory for the L1 ionization cross section, due to the extra node of the 2s atomic wave function, is present and, indeed, enhanced in the experimental results. At both the lowest and the highest energy points, experiment is about 30% above the theoretical curve.

For Au the use of relativistic Hartree-Slater wave functions (3) improves the agreement between theory and experiment, predicting a more clearly defined plateau.

In figure 2 it is shown that, for L 2

,

the experimental points at the lowest velocity are a factor of 2 and 2.5 above the theory for deuterons and alphas respectively and for L 3 about 30% above for the two projectiles. Results of the comparison with theory for protons are similar to

those for deuterons, suggesting that the Coulomb deflection and energy loss effects

(in spite of corresponding to a correction factor of 6 for Gd L1 subshell bombar- ^6x10'- ded by protons with 0.2 MeV) are well ta-

ken care of by the ECPSSR theory for all 2 4 0 - the subshells. In figure 3 ratios of

alpha to deuteron cross sections are dis-

played; we can infer that the binding ef- _Eu -

fect is not the origin of the discrepan- ^Gd

-

t h

cies between theory and experiment. A

-

vacancy transfer mechanism from the L1 I I I I

I

0.30 0.40 0.50 0.601RB

to the L q subshell prior to X-ray emis- Fig.1 L, ionization Q-oss sections irduced sion has been proposed (7,s) ; the corres- bv Protons plotted against the r e d u d inci-

dent velocity, corrected for relativistic ponding cross sections for protons and am3 binding effects,

deuterons are very small, but are somewhat

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Table 1. L X-ray production cross sections (in b) for proton, deuteron and alpha impact on Eu and Gd. Numbers in parenthesis give the error in percent for the line in question and the lines below. The notation ab' stands for a xlOib. Errors for ratios of cross sections obtained from the table are generally smaller than 4%.

r Energy

MeV u-1 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.60 0.70 0.80 0.90 1.00

Fig.2 Ratios of exprimental and theoretical a) deuteron-!.rduced and b) alpha-induced cross sections f o r Lp and L3 subshells plotted against the reduced incident velocity, corrected f o r r e l a t i v i s t i c and binding effects, F,RB. Theoretical values are calculated a m r d i n g to ECPSSR theory of Srandt and Lawicki.

0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.60 0.70 0.80 0.90 1.00

PROTONS

I

DEUTERONS

I

ALPHAS

*a I ^*YI I ^{O Y ~ P}

I

*a

I

*Y1 I Y I ^aa

I

Y

I*-

E U R O P I U M

G A D O L I N I U M

5.02-2(13) 7.08-2 1.17-l(12) 1.13-1 1.33-1

1.84-2(15) 3.81-2(13) 6.75-2 9.20-2(12) 1.17-1 1.62-1 9.97-3(15)

1.58-2(13) 2.61-2 3.13-2(12) 3.97-2 4.58-2 4.64-2 6.86-2 5.73-2 1.06-1 1.26-1 2.09-l(8)

4.98-1 7.39-l(7) 1.32+0 1.99+0(6) 2.62+0 4.48+0 6.73+0 9.51+0 1.28+1 1.64+1

1.44-l(10) 3.48-1 (8) 6.91-1 1.05+0(7) 1.65+0 2.33+0(6) 3.11+0 5.05+0 7.28+0 1.03+1 1.36+1

3.11-l(10 8.79-l(8)) 1.78+0 3.21+0(7) 4.97+0 7.00+0(6) 7.52-3(15)

1.61-2(13) 2.39-2 2.93-2(12) 3.35-2 3.95-2 4.53-2 5.73-2 7.76-2 7.36-2 1.50-1 5.52-2(10)

1.58-l(8) 4.13-1 6.54-l(7) 1.24+0 1.64+0(6) 2.42+0 3.70+0 6.19+0 8.77+0 1.18+1 1.45+1

1.25+0(8) 2.49+0 3.57+0(7) 5.45+0 7.24+0(6) 9.76-3(15)

2.43-2(13) 4.55-2 6.88-2(12) 1.08-1 1.55-l(11) 2.14-1 3.65-1 4.73-1 7.17-l(10) 9.67-1 1.36-2(13)

3.05-2 5.00-2(12) 8.14-2 1.30-l(11) 1.64-1 2.68-1 4.14-1 6.21-l(10) 8.28-1 1.09+0

2.63-2(15) 6.28-2(13) 1.15-1 2.67-l(12) 3.56-1 5.04-l(11) 8.82-2(13) 1.63-1 2.22-l(12) 3.81-1 5.20-l(11) 1.01-2(13)

1.82-2 2.16-2 3.19-2 4.31-2(12) 3.73-2 3.23-2 4.84-2 7.23-2 9.09-2 1.78-1

3.34-3(15) 9.51-3(13) 2.67-2 4.20-2(12) 8.10-2 1.04-l(11) 1.70-1 2.04-1 3.63-1 5.85-l(10) 8.28-1 1.1310

1.07-l(10) 2.78-l(8) 5.62-1 9.56-l(7) 1.50+0 2.13+0(6) 2.9OtO 4.69+0 7.03+0 9.46+0 1.25+1 3.12-3(15) 7.55-3(13) 1.60-2 2.05-2 3.27-2 3.35-2(12) 3.71-2 3.51-2 4.70-2 7.87-2 1.04-1 1.78-1

8.87-3(15) 1.70-2(13) 3.76-2 7.02-2(12) 9.43-2 1.39-1 1.87-l(11) 3.23-1 4.62-1 6.18-l(10) 9.34-1

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C9-238 JOURNAL

DE

PHYSIQUE

higher for alphas as they vary with

z12.

That may explain partially the differen-

ces in the ratios of figure 3 for L 1 - t h

H H --exp and L 2 subshells, but not the L 2 expe-

rimental enhancement. The inclusion of second order corrections might improve the agreement between experiment and

theory as lower ul/u2 and ug/u2 ra- 0.7 tios are predicted (4) at low energies,

for Au. The uncertainty in the atomic parameters used adds some difficulty to

the comparison between experiment and _I _I ₁ _I

1

theory. The present experimental results ^0.30 ^0.35 ^0.40 ^0.45 5

Fig.3 Ratios of alpha to deuteron-indm and the theoretical values would come to ionization cross sections, lotted against the reduced incident velocity, 5 . Full and fair agreement if different atomic para- _dashedlines are ~ S S R theoretical values

and best linear fits to the q b t a l

meters were used, particularly the term _points,respectively.

wSyl15% higher and f I 2 a factor of 2

higher (where the symbols have their usual meanings). A factor of 2 cannot be con- sidered very high taking into account the differences between theoretical and expe- rimental Coster-Kronig values (9,171. It should be refered that theoretical calcu- lations are made for a single-hole unperturbed atom and experimental results pertain to photoionization, where multiple ionization is negligible. It is clearly desira- ble to have other independent ways of estimating the atomic parameters for atoms bombarded by ions (17).

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