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INVESTIGATION OF PERIPHERAL FISSION PROCESSES AT 30 MeV/u WITH 40Ar
E.-M. Eckert, K. Hildenbrand, U. Lynen, W. Müller, H. Rabe, H. Sann, H.
Stelzer, R. Trockel, R. Wada, P. Lhénoret, et al.
To cite this version:
E.-M. Eckert, K. Hildenbrand, U. Lynen, W. Müller, H. Rabe, et al.. INVESTIGATION OF PE-
RIPHERAL FISSION PROCESSES AT 30 MeV/u WITH 40Ar. Journal de Physique Colloques, 1986,
47 (C4), pp.C4-105-C4-107. �10.1051/jphyscol:1986414�. �jpa-00225780�
JOURNAL DE PHYSIQUE
Colloque C4, supplement au n o 8 , Tome 47, aoQt 1986
INVESTIGATION OF PERIPHERAL FISSION PROCESSES AT 30 MeV/u WITH 4 0 A r
E.-M. E C K E R T , K.D. H I L D E N B R A N D * , U. L Y N E N " , W.F. J. ~ L L E R * , H.J. RABE', H. S A N N * , H. STELZER*, R. T R O C K E L * , R. W A D A * , P. L H ~ N O R E T '
,
R. LUCAS",
C. M A Z U R * * , C. N G ~ *,
M. RIBRAG*.,
E. TOMASI*
,
C. CERRUTI*,
A. D E M E Y E R * and D.
GUINET' 'Univ. Frankfurt, Inst. fiir Kernphysik, August-Euler Strasse 6 , D-6000 Frankfurt, F.R.G.
'GSI, Postfach 110541, 0-6100 Darmstadt, F.R.G.
"CEN-saclay, F-91191 Gif-sur-Yvette, France
'"'~nstitut de Physique Nucleaire de Lyon, 43 Boulevard du 11 novembre 1918, F-69622 Villeurbanne Cedex, France
A b s t r a c t
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Using t a r g e t s of Th, Au, and Ta and an "'Ar-beam o f 30MeV/u b i n a r y f i s s i o n e v e n t s have been measured i n c o i n c i d e n c e w i t h an outgoing p r o j e c t i l e fragment. For p e r i p h e r a l c o l l i s i o n s t h e l i n e a r momentum and t h e a z i m u t h a l a n i s o t r o p y have been d e t e r - mined. The c o r r e l a t i o n between t h e l i n e a r momentum t r a n s f e r and t h e v e l o c i t y of t h e p r o j e c t i l e g i v e s i n d i c a t i o n s f o r two r e a c t i o n machanism.
The mechanisms of heavy i o n r e a c t i o n s change from deep i n e l a s t i c c o l l i - s i o n s o r complete f u s i o n a t low bombarding e n e r g i e s t o a hydrodynamical behaviour a t r e l a t i v i s t i c e n e r g i e s . I n t h e i n t e r m e d i a t e energy r e g i o n between 20 and 100 fleV/u t h e d i f f e r e n t p r o c e s s e s a r e however not y e t w e l l known.
A t t h e cyclosynchrotron SARA i n Grenoble heavy t a r g e t s , such a s Ta, Au and Th were used t o measure t h e t r a n s f e r of e n e r g y , l i n e a r and a n g u l a r momen- tum by ""r p r o j e c t i l e s i n p e r i p h e r a l f i s s i o n p r o c e s s e s .
P e r i p h e r a l c o l l i s i o n s were s e l e c t e d r e q u i r i n g a p r o j e c t i l e fragment w i t h 2>=12, which were i d e n t i f i e d w i t h an i o n i s a t i o n chamber ( I C ) a t a n g l e s between 6'- 13'. The d i r e c t i o n of t h e p r o j e c t i l e fragment t o g e t h e r w i t h t h e beam a x i s determined t h e r e a c t i o n p l a n e . A s e t o f 10 l a r g e a r e a p a r - a l l e l p l a t e d e t e c t o r s ( 20'<0<160°), measured t h e t i m e o f f l i g h t , t h e energy and t h e p o s i t i o n of heavy t a r g e t fragments.
Because of t h e small s o l i d a n g l e of t h e I C ( R = 6 msr) we t r i e d t o o b t a i n b e t t e r s t a t i s t i c s u s i n g an a n n u l a r I C and PPD (each o f them c o n s i s t i n g of 12 e-lements) and a s e t o f 6 q u a d r a t i c PPD's t o measure most o f t h e p r o j e c - ti1 fragments w i t h a AE
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time of f l i g h t t e c h n i q u e . Furthermore 6 t e l e -Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1986414
JOURNAL
DE
PHYSIQUEscopes were used to measure the charge and the energy of light-particles at angles between 13' and 120'.
In order to determine the angular momentum transferred to the target, we measured the azimuthal anisotropy (ratio of the yield at 180" and 9 0 ' ) of the fission fragments in relation to the reaction plane. Fig.1 shows, that this anisotropy is twice higher for Au than for Th.
Fig. 1
The azimuthal anisotropy for Th and Au
In addition the linear momentum p l l transferred to the target was deter- mined by measuring the folding angle of the two fission fragments, which were detected in coincidence with the projectile fragments. In Fig.2 the dependence of the azimuthal anisotropy on the linear momentum of the tar- get is shown. Because of the lower fission barrier of Th in relation to Au the anisotropy at low p l is higher for Au than for Th.
Fig. 2
The anisotropy in dependence of the linear momentum trans- ferred to the target for Th and Au
P, O F FlSSlONING SYSTEM (GEV/C)
In Fig.3 the correlation between the energy per nucleon of the projectile fragment and the folding angle of the fission fragments is shown. The arrow indicates p, ,=0. The folding angle of 120' corresponds to about 4 GeV/c. Projectile fragments with Zt17 remain at their initial velocity (30MeV/u) and therefore only small linear momenta can be transferred to the target. This reaction mechanism can be understood in the framework of fragmentation processes1.
With decreasing charge of the projectile fragment the linear momentum of the target increases and at the same time the energy per nucleon of the projectile is reduced.
For Z=8 this second process dominates, but there also remains a contribution of frag- mentation.
REFERENCES
Fig. 3
The energy per nucleon of the projectile fragment in dependence of the folding angle of the two fission fragments for Th
