BACKWARD EMISSION OF ENERGETIC PROTONS

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BACKWARD EMISSION OF ENERGETIC PROTONS

M. Avan, A. Baldit, J. Castor, G. Chaigne, A. Devaux, J. Fargeix, P. Force, G. Landaud, G. Roche, J. Vicente, et al.

To cite this version:

M. Avan, A. Baldit, J. Castor, G. Chaigne, A. Devaux, et al.. BACKWARD EMISSION OF ENERGETIC PROTONS. Journal de Physique Colloques, 1984, 45 (C4), pp.C4-25-C4-29.

�10.1051/jphyscol:1984403�. �jpa-00224068�

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B A C K W A R D EMISSION O F E N E R G E T I C P R O T O N S

M. Avan, A. Baldit, J. Castor, G. Chaigne, A. Devaux, J. Fargeix, P. Force, G. Landaud, G. Roche, J. Vicente, M. El Zoubidi, J.P. Didelez* and F. Reide*

Laboratoire de Physique Corpusculaire, B.P. 45, 63170 Aubière, France

*Institut de Physique Nucléaire, B.P. 1, 91406 Orsay Cedex, France Résumé - Nous avons mesuré les sections efficaces inclusives de production de protons énergétiques (80-180 MeV) à grand angle(76°,102°)induites par des protons de 200 MeV frappant des cibles de 6L i , Ï 7A 1 , 2 8S i , 58Ni et 1 9 7A u . Les données ont été interprétées en utilisant la représentation du "Quasi Two Body Scaling" et également comparées aux prédictions d'un modèle de cascades nucléaires classique.

Abstract - Backward energetic proton inclusive cross sections were measured for 2UU MeV protons hitting 6Li, 2 7A 1 , 2 8S i , S8Ni and 1 9 7Au targets. The data are analyzed using the Quasi Two Body Scaling picture and also com- pared with the predictions of a standard cascade code.(Outgoing proton energy : 80-180 MeV ; scattering angle : 76°, 102°).

Backward energetic proton inclusive cross sections were measured for 200 MeV protons on 6L i , 2 7A 1 , 2 8S i , 58Ni and 1 9 7Au targets using the Orsay synchrocyclotron accele- rator (Fig. 1 ) .

Fig. 1 - Inclusive proton spectra as a function of outgoing proton energy at mean angle (102°) for 6Li (•), 27A1 ( A ) , 58Ni (•), 1 9 7Au ( A ) .

Such measurements have been performed by other experimentalists with various beams (electrons, protons and heavy ions) in a wide range of energies (100 MeV to 1 GeV/

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984403

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C4-26 JOURNAL DE PHYSIQUE

n u c l e o n ) b u t t h e measurements o f t h e s c a t t e r e d p r o t o n a r e m o s t l y performed w i t h energy u p t o h a l f v a l u e o f t h e i n c i d e n t energy. I n o r d e r t o s t u d y t h e r e l e v a n c e of t h e v a r i o u s proposed mechanisms ( k n o c k - o u t on c l u s t e r s , n u c l e a r cascades, s i n g l e s c a t t e r i n g on nucleons w i t h l a r g e Fermi momentum . . . ) , we a r e s t u d y i n g e n e r g e t i c p r o t o n s up t o t h e k i n e m a t i c l i m i t .

The e x p e r i m e n t a l s e t - u p /1,2,3/ needs t o have a l a r g e acceptance b o t h i n momentum (300 - 700 MeV/c) and a n g l e ( % 10"). A bending magnet (1 m x 1 m a r e a ) w i t h two m u l t i w i r e p r o p o r t i o n n a l chambers i s s u f f i c i e n t t o r e c o n s t r u c t t h e t r a j e c t o r i e s

h

u s i n g t h e beam s p o t on t h e t a r g e t as o r i g i n ) and provides an energy r e s o l u t i o n o f MeV (FWHM)

.

P a r t i c l e i d e n t i f i c a t i o n i s o b t a i n e d u s i n g a Time o f F l i g h t Technique. To check a l l c a l i b r a t i o n s (momentum, acceptance, e f f i c i e n c y ) d a t a a t f o r w a r d a n g l e s (18"

-

24") were r e c o r d e d w i t h a CH2 t a r g e t t o g e t t h e f r e e p-p e l a s t i c c r o s s s e c t i o n ( F i g . 2) b e f o r e moving t h e whole system t o backward r e g i o n s (80"

-

110").

.

^phase^sh~ftanalysis (203 W )

r cur data

15 16 n \e w m 21 22 23 24 2s

0 (degree)

F i g . 2 - P r o t o n - p r o t o n e l a s t i c s c a t t e r i n g d i f f e r e n t i a l c r o s s s e c t i o n as a f u n c t i o n o f t h e s c a t t e r i n g angle..(&) o u r d a t a (.) phase s h i f t a n a l y s i s (200 MeV).

A c l a s s i c a l a n a l y s i s o f t h e backward d a t a i s g i v e n i n t e r m o f a s t a n d a r d cascade code /3,4,5,6/. I t has been p o s s i b l e t o reproduce q u a l i t a t i v e l y t h e d a t a o b t a i n e d w i t h l g 7 ~ u t a r g e t and 200 MeV i n c i d e n t p r o t o n s ( F i g . 3 ) .

U n f o r t u n a t e l y , when u s i n g a Fermi gas model, h i g h nucleon momenta a r e n o t i n c l u d e d i n t h e c a l c u l a t i o n . I n o u r case (200 MeV

-

l g 7 A u ) , t h e Fermi momentum d i s t r i b u t i o n i s l i m i t e d t o 300 MeV/c.

I n t h e most r e c e n t t h e o r e t i c a l approach developed by G u r v i t z /7,8/ a l a r g e amount o f d a t a pA + p ' X , A;A2 + p ' X t a k e n w i t h h i g h i n c i d e n t energy 0.6

-

1.0 GeV/A and 90" < e', < 180" ( 0

,

s c a t t e r i n g a n g l e ) shows an u n i v e r s a l one n u c l e o n momentum d e n s i t y d i s t r i b u t i o n ' n ( k ) which appears t o be t h e same f o r medium and heavy n u c l e i

(A g 2 0 ) . T h e Quasi Two Body S c a l i n g (QTBS) i s an i n t e r e s t i n g approach.

The e x p e r i m e n t a l i n c l u s i v e c r o s s s e c t i o n s a r e expressed i n terms o f o n - s h e l l pp, pn c r o s s s e c t i o n and a q u a n t i t y G(kmin). G(kmin), f o r a s i n g l e s c a t t e r i n g mechanism

s i m p l y reads : ^(X1

G(kmin) =

q

n ( k ) kdk mi n

kmin i s t h e mirnimum momentum o f t h e s t r u c k nucleon N i n t h e r e a c t i o n p

+

N + p ' + N ' .

On F i

.

4, we have p l o t t e d ( f u l l l i n e ) The " u n i v e r s a l " G(kmin) f i t t i n g a l a r g e amoung o f h i g h energy d a t a . C l e a r l y a s c a l i n g reglme 1s reached.

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0 0.2 0.4 0.6 a8 1.

krnin (GeV/c)

Fig. 4

-

Solid curve i s t h e " i n t e g r a t e d d i s t r i b u t i o n " G ( k m i n ) ... . .. f i t t i n g high energy d a t a .

The values of G(kmin) obtained from : our d a t a (200 MeV proton) f o r 6 L i (r), 27Al ( A ) , 58Ni (7) and 19?Au (A) a t 10ZO.

Cordell d a t a (180 MeV/nucleon) f o r 1 8 1 ~ a a t t h r e e angles (120' (m), 150' (n) and 90"

(++)I.

Electron d a t a f o r 4He ( 0 ) and _'+N (+)

.

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C4-28 JOURNAL DE PHYSIQUE

We have a l s o p l o t t e d G(kmin) e x t r a c t e d from o u r data /9/ and from o t h e r ones /10,11/. A s c a l i n g regime i s a l s o reached a t i n c i d e n t energies o f about 200 MeV.

However t h i s l a s t regime i s d i f f e r e n t from t h e one observed above 600 MeV/A ( h i g h energies d a t a ) /9/.

This may question t h e existence o f a s i g n i f i c a n t amount o f a l a r g e momentum compo- nent i n n u c l e i /9/. Up t o now, QTBS theory i n c l u d e s f i n a l s t a t e i n t e r a c t i o n b u t neglects d i s t o r s i o n o f the i n c i d e n t proton and s t r u c k nucleon.

We a r e a t t h e moment beginning a p-y coincidence experiment. We measure the y r a y e m i t t e d by t h e r e s i d u a l nucleus using a High P u r i t y Ge d e t e c t o r i n coincidence w i t h t h e backward s c a t t e r e d proton.The i d e n t i f i c a t i o n o f t h e r e s i d u a l n u c l e i provides p r e c i s e i n f o r m a t i o n s on the amount o f e x c i t a t i o n t r a n s f e r r e d t o the system, which i n t u r n should e n l i g h t e n the i n t e r a c t i o n mechanisms. P r e l i m i n a r y r e s u l t s are shown i n F i g u r e 5 where a l l t h e r e s i d u a l nucleus c o n t r i b u t i o n s have been added ( t a r g e t

" ~ i , s c a t t e r i n g angle 7 6 " ) .

F i g . 5

-

I n c l u s i v e p r o t o n spectrum versus outgoing p r o t o n energy ( e )

-

p-y coincidence spectrum versus outgoing p r o t o n e n e r g y .

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