CORRELATIONS IN THE MOTIONS OF MOLECULAR FRAGMENTS TRAVERSING THICK FOILS

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CORRELATIONS IN THE MOTIONS OF

MOLECULAR FRAGMENTS TRAVERSING THICK FOILS

D. Nir, A. Mann, B. Rosner

To cite this version:

D. Nir, A. Mann, B. Rosner. CORRELATIONS IN THE MOTIONS OF MOLECULAR FRAG-

MENTS TRAVERSING THICK FOILS. Journal de Physique Colloques, 1979, 40 (C1), pp.C1-350-

C1-351. �10.1051/jphyscol:1979175�. �jpa-00218455�

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JOURNAL DE PHYSIQUE Colloque C1, supplkment au no 2 , Tome 40, fkvrier 1979, page C1-350

CORRELATIONS I N TEE MOTIONS OF MOLECULAR FRAGMENTS TRAVERSING THICK FOILS

D. N i r , A. Mann, B. Rosner

Physics Department, Technion, Haifa, I s r a e l

+ + +

&u&. Des faisceaux d'ions molhcul4res D

,

D2 et D3

2

300 e t 400 keV/atome, s o n t

u t i l i s e s pour rechercher l a c a r r e l a t i o n dans les mouvements des fragments molhculaires dans une f e u i l l e d ' o r de 180 pg/cm2

.

Les p r o b a b i l i t h s de d i t e c t e r un nombre quelconque de fragments e t les d i s t r i b u t i o n s angulaires i n t h g r a l e s sont dhtermi&es en u t i l i s a n t une ou- v e r t u r e iris v a r i a b l e c i r c u l a i r e devant l e detecteur, controlee de l l a x t C r i e u r de la chambre de c o l l i s i o n . Un d i t e c t e u r de c o n t r s l e e s t u t i l i s g pour la normalisation. Les r i s u l t a t s montrent une augmentation de 50% de l a probabilith de dgtecter tous l e s fragments d'ions molhculaires aux f a i b l e s angles. La donnhe d'ions D+ e s t raisonnablement

bien r e p t o d a i t e - p a t une forme t r h s sifnpliffge d'iin potentief de s i l l a g e sans aacun l5bre. La donn66-de

Df.

montre que l e p b t e n t i e l de s i l l a g e pour ce cas e s t plus f o r t que c e l u i e s p i r i ;ip a r t i r d3un fragment entrainant.

Abstract. Molecular ion beams D+, D2

+

and D+

,

a t 300 and 400 keV/Atom, were used t o i n v e s t i g a t e t h e c o r r e l a t i o n i n the motions

02

t h e molecular fragments i n s i d e a 180 pg/cm2 t h i c k Au f o i l . The p r o b a b i l i t i e s of detecting any number of fragments and t h e i n t e g r a l angular d i s t r i b u t i o n s were determined using a v a r i a b l e round iris aperture i n f r o n t of t h e detector, controlled from outside t h e s c a t t e r i n g chamber. A monitor detector was used f o r normalization. The r e s u l t s show a 50% enhancement of t h e p r o b a b i l i t y f o r detecting a l l t h e molecular ions fragments a t small angles. The d a t a of D: ions is reasonably w e l l reproduced by a very simplified form of a wake p o t e n t i a l without any f r e e parameters. The data of D; shaw t h a t t h e wake p o t e n t i a l f o r t h i s case i s stronger than the one expected from one leading fragment.

Correlations i n the angular d i s t r i b u t i o n s with a much l a r g e r enhancement, i s observed f o r D3

+

of t h e fragments of H+ and H ions have been shown

+

2 3 ions (see Fig. 2).

f o r high p r o j e c t i l e energies and very t h i n carbon I n t h i c k t a r g e t s t h e dominant e f f e c t is f o i l s [I], [2]

.

I n t h e present work w e e x h i b i t t h e multiple s c a t t e r i n g 133 and neglecting t h e a new and d i f f e r e n t aspect of these c o r r e l a t i o n s Coulomb explosion we g e t t h e equation of motion

+ + +

f o r fragments of D

,

D2, and D3 ions a t low bombarding energies and a 180 p g / m t h i c k Au 2

target* Simultaneous measurements of t h e angular p and r denote t h e transverse coordinate of a d i s t r i b u t i o n s of a l l the fragments of the molecular s c a t t e r e d atomic p r o j e c t i l e and a s c a t t e r e d ions were performed by using a v a r i a b l e iris molecular fragment respectively.

4

is the wake aperture whose control was outside t h e s c a t t e r i n g p o t e n t i a l which expresses t h e influence of t h e chamber. A monitor detector was us& t o normalize leading fragment on t h e t r a i l i n g one. Let tl be the angular d i s t r i b u t i o n s . . Assuming no corre- t h e e x i t time from t h e f o i l ; we multiply eq. 1 l a t i o n between fragments, we can use the scatterifig by $ and i n t e g r a t e overtime. For t h e

;

^which

probability of D on t h e same t a r g e t t o evaluate

+

multiply

6

i n t h e the r e s u l t i n g equation we the expected probability f o r measuring s e v e r a l

+ +

fragments of D2 and D3 ions.' The r a t i o of t h e measured probability and t h e expected p r o b a b i l i t y should be a constant i n an absence of correlations.

Fig. l a shows t h e r a t i o of p r o b a b i l i t i e s f o r .two Eragments detection (denoted C2) and Fig.

16

shows the r a t i o s f o r one fragment d e t e c t i o n

(denoted C1)

.

An enhancement i s observed i n t h e p r o b a b i l i t y 'of detecting a l l the fragments of D: a t small s c a t t e r i n g angles. A s i m i l a r phenomenon

s u b s t i t u t e its expression i n terms of p r e s u l t i n g from a direct'.'"+ategration of eq. 1. Neglecting second order terms we g e t t h e transverse energy conservation law

Equation 2 shows t h a t t h e t r a t 4 i n g fragment i s l o s i n g k i n e t i c energy equal t o

e+(G

^{i f}^{i t}

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979175

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Rig. 1: Angular d i s t r i b u t i o n of :D fragments (See d e t a i l s i n t h e t e x t ) .

c2.0-i

U

leaves t h e wake p o t e n t i a l well i n s i d e t h e f o i l . It

. . . -

0" Iris Opening Angle (degrees

-

0.5" lo 1.5' 2" 2.5O

L

a l s o shows how the transverse energy depends on t h e impulse of t h e wake force. For t h i c k f o i l s and low

I I I I I

dl 0 . 2 0.3 0.4 0.5 0.6

8"

^ReducedIris Opening Angle

p r o j e c t i l e energy t h e multiple s c a t t e r i n g i s t h e dominant e f f e c t and i s l a r g e r than t h e o t h e r terms i n eq. 2. The angular d i s t r i b u t i o n t h e r e f o r e can be calculated from t h e t a b l e s of multiple s c a t t e r i n g theory [3]. Changing the angular v a r i a b l e from (b/v,, ) t o (;/v,, ) we get foi' the i n t e g r a l angular d i s t r i b u t i o n

v,, is the longitudinal p r o j e c t i l e velocity. F is taken from t h e t a b l e s of multiple s c a t t e r i n g theory. This expression has no f r e e parameters.

The curved dashed l i n e i n Fig. l a s h w s t h e t h e o r e t i c a l predi=tion f o r :D fragments. For D3

+

OD iris Opening Angle (degrses)

-

0.5' I* 1.5' 2' 2.5O

0 I I I I

O!I 0!2 0.3 0.4 0.5 0.6

8

Reduced Iris Opening Angle

Fig. 2: Angular d i s t r i b u t i o n of D: fragments (See d e t a i l s i n t h e t e x t ) .

REFERENCES

[ I ] D.S. Gemmel, J. Remillieux, J.C. Poizat, M.J. Gaillard, K.E. Holland and Z. Vager, Phys. Rev. L e t t .

2

(1975). 1420.

123 Z. Vager, D.S. Gemmel and B.J. Zabran-ski, Phys. Rev.

& &

(1976) 638.

[3] P. Sigmund and K.B. Winterbon, Nucl. I n s t . Meth,

2

(1974) 541.

fragments we f u r t h e r assumed t h a t t h e two

t r a i l i n g fragments a r e independent of each other.

The curved dashed l i n e i n Fig. 2 shows t h i s t h e o r e t i c a l prediction.