74 First Results at Système Accélérateur Rhône-Alpes (SARA) with a He-Jet Coupled to a High-Current Mass Separator Source 1
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R. Beraud, A. Charvet, R. Duffait, A. Emsallem, M. Meyer, T. Ollivier, N. Redon, J. Genevey, A. Gizon, N. Idrissi, and J. Treherne Downloaded via UNIV OF CALIFORNIA SANTA BARBARA on July 22, 2018 at 11:30:45 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.
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Institut de Physique Nucléaire (et IN2P3), Université Lyon 1, 43 boulevard du 11 Novembre 1918, F. 69622 Villeurbanne Cédex, France Institut des Sciences Nucléaires (IN2P3 et USMG), 53 avenue des Martyrs, F. 38026 Grenoble Cédex, France
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We report on the performances of a He-jet connected to a Bernas-Nier ion source. After a brief description of the system we give the first spectroscopic results on very neutron deficient rare-earth isotopes. Among the techniques used to study the nuclear structure all over the mass surface, in-beam γ -spectroscopy and isotope separator on-line (ISOL) are the two most important ones. The first one gives access to high spin physics whereas the second one is mainly related with low-spin states at lower energy depending on available decay energy. The ISOL systems allow to investigate nuclear species produced with very small cross-sections since the products can be studied in a very low background environment. The use of intense beams and the development of fast and efficient ISOL systems are both necessary to study nuclei far off the valley of stability. In this paper I will explain our motivations concerning the technical choice of a He-jet coupled to a mass separator and then give our first results. 2- Experimental facility 2.1 SARA (Sy stème Accélérateur Rhône-Alpes) This facility is composed of two cyclotrons, a K=90 compact one and a K=160 separated sector one which is operating siiice 1982. An ECR ion source is now commonly used for the production of C,N,0 and Ne beams up to 40 MeV/u energy. The layout of the beam lines, as shown in fig. 1, allows to use also the first cyclotron alone when high intensity, moderate energy beams are needed. This is a common mode of operation to carry out spectroscopic studies by means of fusion-evapo ration reactions. Fig. 1 : General layout of the SARA machine arid experimental areas. 0097-6156/ 86/ 0324-0490506.00/ 0 © 1986 American Chemical Society
Meyer and Brenner; Nuclei Off the Line of Stability ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
74.
BERAUD ET AL.
First Results with a He-Jet
491
2.2 L a y o u t of the on-line isotope separator A s c h e m a t i c plan view of the new on-line separator l o c a t e d on beam line C is given in f i g u r e 2. The beam f r o m the a c c e l e r a t o r enters the H e - j e t r e c o i l chamber through a t h i n N i w i n d o w ( 2 m g / c m ) , bombards tbe t a r g e t and is then stopped in a beam-stopper composed mainly of i r o n , lead and polystyrene in order to p r e v e n t f r o m both neutron and γ background. The ion-source of the separator is f e d by a capillary t r a n s p o r t i n g the r e c o i l s t h e r m a — lized in the H e - j e t c h a m b e r . The separator beam is e x t r a c t e d a t r i g h t angle to the axis of the beam line and then t r a v e l s in a 120° magnet of index n=1/2. F r o m the f o c a l plane the mass-separated beam is then t r a n s p o r t e d by means of a 6m long Einzel lens t o a w e l l - s h i e l d e d c o l l e c t i o n c h a m b e r . A p r o g r a m m a b l e t a p e - t r a n s p o r t device c a r r i e s the a c t i v i t y t o the c o u n t i n g s t a t i o n where X - r a y s , γ-rays and p a r t i c l e s are d e t e c t e d . The o v e r a l l p e r f o r m a n c e of the separator is mainly d e t e r m i n e d by the quality of the m a g n e t . The r e s o l u t i o n is nowadays 1000 F W H M a t mass 100 and the s e p a r a t i o n 17 m m b e t w e e n A=100 and A = 1 0 1 . It is planned t o i m p r o v e the r e s o l u t i o n by changing mechanically the e n t r a n c e and e x i t magnet boundaries. 2
F i g . 2 : L a y o u t of isotope separator in beam line C. The numbers i n d i c a t e : (1) H e - j e t r e c o i l c h a m b e r , (2) beam-sto'pper, (3) ion-source, (4) analysing m a g n e t , (5) Einzel lens f o r t r a n s p o r t of mass-separated b e a m , (6) t a p e - t r a n s p o r t and c o u n t i n g s t a t i o n , (7) p o w e r / c o n t r o l rack of t a p e - t r a n s p o r t , (8) p o w e r / c o n t r o l of mass-separa~ tor.
Meyer and Brenner; Nuclei Off the Line of Stability ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
492 2.3.
NUCLEI OFF THE LINE OF STABILITY He-jet
c o u p l e d to
ion-source
A s c h e m a t i c v i e w of the H e - j e t r e c o i l c h a m b e r and i n t e g r a t e d s k i m m e r i o n - s o u r c e is shown in f i g u r e 3. T h e r e c o i l c h a m b e r is e i t h e r of m u l t i c a p i l l a r y or sheet t y p e as d e s c r i b e d in [ P L A 81]. The collection volume ( 0 = 12mm, length=100 mm) is made of an Aluminium cylinder and connected to the main stainless c a p i l l a r y . It is placed in the m i d d l e of the H e p r e s s u r i zed reaction chamber and He gas is fed through a temperature controled bubbler. D i f f u s i o n pump aerosols were mainly used in the experiments reported here. For monitoring of the beam, a Faraday cup f i x e d behind a 4 m g / c m Havar window was used. 2
F i g . 3 : S c h e m a t i c v i e w of H e - j e t integrated skimmer ion-source
The ion- source is of Bernas-Nier type and is described in more details in [CHA 67]. The extracted
r e c o i l c h a m b e r and
c u r r e n t may be Λ / 5 m A , a l l o w i n g thus o u t g a s i n g or t a r g e t e v a p o r a t i o n . A n i m p o r t a n t a p p l i c a t i o n is the use of c a r r i e r gas a n d / o r c h e m i c a l p r o d u c t s w h i c h may g i v e v o l a t i l e c o m p o u n d s of r e f r a c t o r y e l e m e n t s . A high flow p u m p i n g s y s t e m c o m p o sed of t w o r o o t s and a p r i m a r y p u m p (3000 m / h - 350 m / h - 120 m / n ) is used t o _ ^ k i m o f f the H e f r o m the s k i m m e r box w h e r e the p r e s s u r e is m a i n t a i n e d a r o u n d 10 t o r r . T h e s k i m m e r is a f l a t s t a i n l e s s s t e e l p l a t e w i t h a c i r c u l a r hole φ 1,2 m m in the m i d d l e . 3
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3. Results 3.1
T h e decay
of 12s
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4
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T b [OLL
85]
112 T h e a c t i v i t y was p r o d u c e d by b o m b a r d i n g ^ a s e l f - s u p p o r t i n g 2 m g / c m Sn t a r g e t ( e n r i c h e d to 88 %) w i t h a 191 M e V C I b e a m . T h e r e c o i l s , s t o p p e d in 1 bar H e p r e s s u r e , w e r e t r a n s p o r t e d v i a a 6 m l o n g c a p i l l a r y to the t a p e - t r a n s p o r t s y s t e m . A t the c o u n t i n g p o s i t i o n , m e a s u r e m e n t s including γ -ray multianalysis d e c a y s ( t y p i c a l l y 8x2 s and 8x10 s), Ύ - Χ and Ύ-Ύ c o i n c i d e n c e s w e r e c a r r i e d out with intrinsic G e d e c t e c t o r s . P a r t i c l e spectra were simultaneously measured with a 500 μηη Si d e t e c t o r ; no s i g n i f i a n t p a r t i c l e a c t i v i t y was o b s e r v e d . T h e Ύ-ray s w e r e a s c r i b e d to T b decay on the basis of f o l l o w i n g e x p e r i m e n t a l e v i d e n c e : i) a l l t h e s e γ - r a y s a r e in c o i n c i d e n c e w i t h K X - r a y s of G d (see f i g u r e 4). ii) the a v e r a g e m e a s u r e d h a l f - l i f e of the m o s t intense γ - l i n e s is (12 ± 1) s. 2
a
Meyer and Brenner; Nuclei Off the Line of Stability ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
74.
BERAUD ET A L .
First Results with a He-Jet
493 12s
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