ENERGY DEPENDENCE. OF THE COEFFICIENTS IN THE CUSP ASYMMETRY STUDY BY SERIES EXPANSION

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ENERGY DEPENDENCE. OF THE COEFFICIENTS IN THE CUSP ASYMMETRY STUDY BY SERIES

EXPANSION

D. Berényi, L. Gulyás, A. Kövér, G. Szabó

To cite this version:

D. Berényi, L. Gulyás, A. Kövér, G. Szabó. ENERGY DEPENDENCE. OF THE COEFFICIENTS

IN THE CUSP ASYMMETRY STUDY BY SERIES EXPANSION. Journal de Physique Colloques,

1987, 48 (C9), pp.C9-231-C9-233. �10.1051/jphyscol:1987937�. �jpa-00227355�

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JOURNAL DE PHYSIQUE

Colloque C9, supplement au n012, Tome 48, decembre 1987

ENERGY DEPENDENCE. OF THE COEFFICIENTS IN THE CUSP ASYMMETRY STUDY BY SERIES EXPANSION

D. BERENYI, L. GULY~S, A .

KOVER

and G. S Z A B ~

I n s t i t u t e of Nuclear Research of the Hungarian Academy

( A T O M K I ) , of Science, Pf. 51, H-4001 Debrecen, Hungary

Abstract.

-

A comparison of the different experiments and recent theoretical calculations is given for the shape of the ncusp" in the electron spectrum by using the series expansion procedure for the characterization of the cusp shape.

I 1 1 1 1 1 1 1 1 I 1 1 1 1 1 1 1 1 I 1 1 1 1 1 1 1 1 I I

0.01 0.1 1 10

E(MeVlamulZ)

F i g . 1 . - The Bo~/Boo expansion series coefficient ratio on He target at different projectiles as a functlon of E(Mev/amu/Z) for light

projectiles.

In the study of "cuspn phenomenon in the spectra of electrons ejected in ion-atom collisions (see e. g. in [ I ] ) a number of

experimental and theoretical works were carried out on the shape of cusp. For the experimental characterization of the cusp shape, a series expansion and fitting procedure has been introduced [2,33 and more and more generally Used.

B0l

-0.7- -0.6- 0.5- 0.4- 0.3-

0.2 0.1

I

Experiments

+ H* Andersen e t a1 o ~ e ' '

xH+ 1

i

^r^H' ^Meckbache t a l

He2+ Guly6s e t al

I.n _----

^TheoriesCrothers and

I

^T ^McCann

r 1 :

-

Burgdorfer COW

I

! ' i

0

-

'

^\_\

'\. ^.

-

.-. -- _{-_}

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987937

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C9-232 JOURNAL DE PHYSIQUE

According to the above papers the measured intensity distribution of the electrons in the cusp Q(ve,€3,) can be expressed as follows

where ve is the velocity and €3, is the angle of the ejected electron and S(ve,Qe)is the spectrometer function. By taking into consideration the Taylor series expansion we have

and

where 8,' and veJ is the angle and velocity of the ejected electron in the projectile frame and vp is the velocity of the projectile.

Fig. 2.

-

The same as in Fig. i. but for heavy projectiles including.

Gulyas et al. and MecKbach et al. corresponding data for light projettiles.

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Recently a number of theoretical and experimental determination of the relative Boi parameters were carried out including ours [5] and seems to be quite justified to compare them with each other.

The above parameters were determined experimentally for the H+, ~ e ~ + - ~ e collisions as functions of the impact velocity by Meckbach et al. [3], by Andersen et al. [4] and by us [5]. In the paper of Andersen et al. the data concerned are also evaluated from the works of Dahl 161. Corresponding theoretical calculations, however, were also published recently by Burgdarfer 171 and Crothers and McCarry

C81.

As can be seen in Fig. 1. the data of Meckbach et al. and those of ours are in a rather good agreement with each other and they are not in a pronounced contradiction with the theories. The disagreement, however, is quite definite between MecRbach et al. and our data on one side and Andersen et al. values on the other side which so disagree with the above theories too. It is well known that the values of the Bnl parameters depend on the fitting region (in our case it was 0. 93!ve/vpi 1.07, and a similar region was used by Meckbach et al. ) .

The discrepancies may be caused by the different fitting regions used (one can determine the Bol parameter from Dahl's projectile frame data in a very small region around the peak) and also from assumptions on the analytical form of the S(ve, Re).

If we plot our and Meckbach et al. data together with the corresponding values for heavy ion impact ([9],

[lo]),

it can be seen that they are in a rather good agreement with each other. But at higher velocities the tendencies of the theoretical values are

different (see Fig. 2).

Some more details of the comparison is given in [ill.

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