HEAVY ION SECONDARY BEAMS

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HEAVY ION SECONDARY BEAMS

R. Bimbot, S. Della-Negra, M. Manasijevic, P. Aguer, G. Bastin, R. Anne, H.

Delagrange, Y. Schutz, F. Hubert, Y. Gono, et al.

To cite this version:

R. Bimbot, S. Della-Negra, M. Manasijevic, P. Aguer, G. Bastin, et al.. HEAVY ION SECONDARY

BEAMS. International Conference on Heavy Ion Nuclear Collisions in the Fermi Energy Domain,

1986, Caen, France. pp.C4-241-C2-243, �10.1051/jphyscol:1986428�. �jpa-00225794�

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JOURNAL DE PHYSIQUE

Colloque C4, supplement au n o 8, Tome 47,

aoOt

1986

HEAVY I O N SECONDARY BEAMS

R. BIMBOT, S. DELLA-NEGRA, M. M A N A S I J E V I C * , P. AGUER*', G. B A S T I N * " , R. ANNE*"', H. D E L A G R A N G E * * * , Y. SCHUTZ"*, F. HUBERT'

,

Y. GONOt + and K. HATANAKA+ +

Institut d e Physique Nucleaire, BP 1, F-91406 Orsay, France 'IPN, Orsay and Boris Kidric Institute, Belgrade, Yugoslavia " " C S N S M , BP 1, F-91406 Orsay, France

*"GANIL, BP 5027, F-14021 Caen, France

'CENBG, Le Haut Vigneau, F-33170 Gradignan, France + + R I K E N , Wako-Shi, Saitama 351, Japan

A b s t r a c t : The p o s s i b i l i t y o f producing secondary beams o f r a d i o a c t i v e n u c l e i i s an i n - t e r e s t i n g a p p l i c a t i o n of medium and h i g h energy heavy i o n beams. A f t e r a f i r s t attempt a t CERN ( I ) , two experiments have been performed a t GANIL, u s i n g 44 MeV/u 4 0 ~ r ( 2 ) and 65 MeV/u 180 p r o j e c t i l e s . T h i s paper r e c a l l s t h e r e s u l t s o f t h e Ar experiment, and presents new data obtained w i t h t h e 180 beam.

1

.

EXPERIMENTAL TECHNIQUE

The r a d i o a c t i v e n u c l e i a r e produced i n a t h i c k t a r g e t o f a l i g h t element through p r o j e c t i l e fragmentation o r t r a n s f e r . The products e m i t t e d a t zero degree a r e separated from t h e rimary beam using a magnetic spectrometer o f l a r g e angle and e n e r gy acceptance (LISE~

.

The secondary beam i s t r a n s p o r t e d over 18 m and refocused i n a spot of diameter l e s s than 15 mm. The spectrometer i s composed o f two

d i p o l e s and 10 quadrupoles. I t i s described i n r e f . ( 3 ) . Beam d i a g n o s t i c s make i t p o s s i b l e t o v i s u a l i z e t h e beam p r o f i l e s i n several p o i n t s . A s o l i d s t a t e d e t e c t o r telescope (AE,E) i s placed a t t h e achromatic focus i n o r d e r t o analyse t h e i s o t o p i c composition o f t h e secondary beam. D e t a i l s about t h e experimental procedure can be found i n r e f . (2).

2. EXPERIMENTAL RESULTS 2.1. 40Ar beam

Secondary beams o f masses around 40 and energies around 34 MeV/u have been produced u s i n g a 99 mg/cmz Be t a r g e t . The y i e l d s I/Io (secondary/primary beam i n t e n - s i t y ) obtained ( 2 ) f o r these beams a r e given i n t a b l e 1.

Table 1 : Production y i e l d s ( I / I o ) f o r v a r i o u s secondary beams (S.B.) obtained from 4 0 ~ r and 180 primary beams.

Primary beam 44 MeV/u 4 O ~ r 65MeV/u 180 65 MeV/" 180 Target 99 m g / c m d l ~ Be 567mg/cm2 Be 1026 mg/cm2 Be S.B. 1 8 ~ 1 7 ~ 1 6 ~ 1 7 ~ I/Io 10-4 3.10-4 2.10-6 4.10-6

lo-a

0.5.10-6 1/10

...

5.10-5 2.10-6 n, 10-4 210-4 5.10-6 S.B. 3 8 ~ r 3 9 ~ r 1% 1 5 ~ 1 4 ~ 1 6 ~ S.B. 3% 38s 13B 128 118 Ill0 10-4 0.6.10-5 1.5.10-~ 10-6 4 5.104

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C4-242

JOURNAL

DE

PHYSIQUE

2.2.1. Production of 50 MeV/u secondary beams

- - * - - - * - - - * - - -

Using a 567 mg/cm2 Be t a r g e t , various secondary beams of about 50 MeV/u have been produced

i n

t h e mass range 10-18.

An

example of t h e beam r o f i l e s observed a t

E

t h e achromatic focus i s given in f i g . l a . The emittance of a

1 C

secondary beam has been measured using t h e beam p r o f i l e s i n two d i f f e r e n t positions, and i s equal t o 30

+

6 a mm.mrad.

D O + ' 1 1 1 I 1 1 1 - j

Fig. 1 : Horizontal (H) and v e r t i c a l ( V ) b e a m r o f i l e s observed a t t h e LISE achromatic focus. The i n t e n s i t y collected on each wire i s plotted versus t h e wire posi- tion d. Note t h a t the wire spacing i s equal t o 1

mm

f o r vertical p r o f i l e s and t o 1.5

mm

f o r t h e horizontal ones. a . Won purified 16C beams produced in a

567 mg/cm2 o r in a 1036 mg/cm2 Be t a r g e t ( s i m i l a r p r o f i l e s a r e observed f o r both t a r g e t s ) .

b. Secondary beams produced in a 1036 mg/cmz Be t a r g e t and purified with a

150 mg/cm2 A1 degrader. The horizontal

-

l y centered peak contains almost pure 16C, t h e peak on the r i g h t i s a mixture of several components, t h e main ones being 1% and 138. I > TOO Ez340-700 0 14-40 e (20%) 10 20 30 40 50 60 70 80 A E (MeV)

Fig. 2 : Bidimensional p l o t showing the i s o t o p i c composition of a secondary beam obtained in t h e following conditions :

65 P.leV/u 180

+

567 mg/cm2 Be ;

Bp = 2.44 Tm ; ABplBp =

+

0.17 %.

The abundances of t h e main components a r e given in parenthesis.

The isotopic composition of a secondary beam optimized f o r 1 7 ~ production i s shown in f i g . 2. Such bidirnensional p l o t s , associated with primary beam i n t e n s i t y measurements a r e used t o determine the production y i e l d f o r each isotope, and f o r each value of the mapnetic r i g i d i t y Bp. The resulting curves a r e presented in f i g . 3 , and t h e maximum production r a t e s deduced from these curves, a r e given in t a b l e ?.Note the r e l a t i v e l y high yields f o r lb-17PI and 1 4 ~ , and a l s o t h e odd even e f f e c t s in the production of the couples 15c-I6c and

I ~ B - I ~ B .

The s i g n i f i c a n t y i e l d f o r 1 8 ~ i s i n t e r e s - t i n g t o remark,firstly because i t i s a r e l a t i v e l y exotic nucleus, and secondly because i t can be produced only through a t r a n s f e r (charge exchange) reaction.

2.2.2. Production and purification of 34 MeV/u secondary beams

- A - - - * - - - * - - - A - - - - A A - - - A -

Secondary beams have been produced around 34 MeV/u from the 65 MeV/u 180 beam using a 1036 mg/cm2 Be t a r g e t . Due t o t h e increase

i n

t a r g e t thickness, t h e Bp d i s t r i b u t i o n f o r each isotope i s now much broader. As a consequence, t h e individual yields f o r a given Bp value a r e lower than w i t h the 567 mg/cm2 t a r g e t (see t a b l e 1 ) . The influence of the t a r g e t nature was studied using 1138 mg/cm2 A1 and 1350 mg/cm2 Ni t a r g e t s which lead t o the same energy f o r secondary beams. This study showed t h a t

Be

t a r g e t s a w more e f f i c i e n t by a f a c t o r 2.5 r e l a t i v e t o A1 and 5 r e l a t i v e t o Mi t a r g e t s f o r t h e production of secondary beams of masses not very f a r from t h e p r o j e c t i l e one. These numbers correspond t o almost equivalent cross sections in the three t a r g e t s .

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This study shows t h a t t h e b e s t p u r i f i c a t i o n o f a given secondary beam can o n l y be obtained by a c a r e f u l s e l e c t i o n o f t a r g e t thickness, magnetic f i e l d i n f i r s t d i p o l e , Bp acceptance, degrader thickness and magnetic f i e l d i n second dip01 e.

x I0 600

-

a.

-

SO0

-

400

-

10-5

-

0

-

600

-

_b.

-

SO0

-

16c

-

400

-

300

-

200

-

I . I . . I . I . , 1

>

700 I 0 0

a

70- 700 0 54- 70 2.4 2 6 2.4 2 6 2.8 2 4 2 6 2 8 o . a " a l a " BplTm) 600

-

C.

-

F i g . 3 : V a r i a t i o n o f t h e p r o d u c t i o n r a t i o 500

I f f secondary beams w i t h t h e magnetic

r i g i d i t y Bp, f o r a Bp acceptance of

+

1.67% 400

-

(65 MeV 180 + 567 mg/cm2 Be).

References

1. A. F l e u r y e t a l , Nucl. I n s t r . and Yeth. 810-11 (1985) 369 2. R. Bimbot e t a1

,

Z. Phys. A322 (1985) 44-

3. R. Anne e t C. S i g n a r b i e u x , G A N ~ ~ r e p o r t RA/NJ 278-82 (1982) With such t h i c k t a r g e t s , a beam

200

obtained f o r a given Bp value i s now compo-

sed o f a l a r g e number o f n u c l i d e s , as can 1 0 0

o

-

b 1 > 7 0 0

-

b

m

40-700

-

u

1 4 - 4 0

-

be seen i n f i g . 4a. An e f f i c i e n t p u r i f i c a - 0 0 ,

,

t i o n can be performed by u s i n g a wedge de- ₀ ₁₀ _{20 30} ₄₀ ₅₀I ₆₀l ₇₀l ₈₀1 grader (achromatic) placed between t h e two

dipoles. A f t e r going through t h i s degrader, PE (MeV) secondary beams a r e dispersed by t h e second F i g . 4 : Same as f i g . 2 f o r a 1036 d i p o l e according t o t h e i r new magnetic r i g i -

i$?%

Be t a r g e t

d i t y . T h i s can be seen i n f i g . l b where a a. u n p u r i f i e d beam ( B l p = 2.248 Tm, beam p r o f i l e obtained a t t h e focus i n these ABplBp =

+

0.22 % )

c o n d i t i o n s i s displayed. By s e t t i n g t h e pro- b. 1 6 ~ p u r i f i e d beam (same B l p

,

150 p e r value o f t h e second d i p o l e magnetic mg/cm2 A1 i n t e r m e d i a t e degrader, f i e l d , a s p e c t a c u l a r p u r i f i c a t i o n o f 1 6 ~ i s B2p = 2.114 Tm, ABp/Bp = t 2.78 % ) achieved, as shown i n f i g . 4b. This i s made c. secondary beam obtained w i t h t h e w i t h n e g l i g i b l e i n t e n s i t y l o s s f o r 1 6 ~ . same B l p and ABp/Bp values, and Another t u n i n g o f d i p o l e 2 s e l e c t s a m i x t u r e B2p = 2.154 Tm.

of beams corresponding t o t h e same magnetic r i g i d i t y a f t e r going through t h e degrader (see f i q . 4c).