X-rays from Beamline Monochromator Reference Sample on Mössbauer Driver Investigation High Resolution Monochromator 1 Si 3 1 APD Si 3 1 1 Si 5 1 1 Sample under Investigation Si 5 1 1 High Resolution Monochromator Reference Sample on Mössbauer Driver X-rays from Beamline Monochromator APD M e a s u r e m e n t o f L o n g - l i v e d I s o t o p e s u s i n g S t r o b o s c o p i c D e t e c t i o n o f S y n c h r o t r o n R a d i a t i o n M e a s u r e m e n t o f L o n g - l i v e d I s o t o p e s u s i n g S t r o b o s c o p i c D e t e c t i o n o f S y n c h r o t r o n R a d i a t i o n Fig. 1. Experimental setup for both experiments. N u c l e a r r e s o n a n t e l a s t i c s c a t t e r i n g o f s y n c h r o t r o n r a d i a t i o n p r o v i d e s i n f o r m a t i o n o n t h e h y p e r f i n e i n t e r a c t i o n s b e t w e e n n u c l e i a n d t h e i r su rr ou nd in gs [1 ]. Tr ad it io na ll y, th is in fo rm at io n is deduced from the time response of the radiation to th e nu cl ea r ex ci ta ti on . In th es e ex pe ri me nt s it is i m p e r a t i v e t h a t t h e t i m e b e t w e e n t w o s u c c e s s i v e b u n c h e s i s l a r g e r t h a n t h e d e c a y t i m e o f t h e nuclear ensemble. We present here an alternative t o t h i s m e t h o d , c a l l e d s t r o b o s c o p i c d e t e c t i o n , i n w h i c h t h e c o n s t r a i n t o n t h e b u n c h m o d e i s si gn if ic an tl y re li ev ed , an d wh ic h ha s th e po te nt ia l for providing complementary information. S t r o b o s c o p i c d e t e c t i o n i s p e r f o r m e d i n t h e he te ro dy ne se tu p , me an in g th at tw o sa mp le s ar e put in the beamline: the sample under investigation a n d a s i n g l e - l i n e r e f e r e n c e s a m p l e w i t h k n o w n ch ar ac te ri st ic s. Th e re fe re nc e sa mp le is gi ve n a vari able velo city and thus its reso nanc e ener gy is shifted by the Doppler-shift. The spectra are then taken as a function of the velocity of this reference sa mp le . I n nu cl ea r re so na nt s ca tt er in g ex pe ri me nt s, i t i s c r u c i a l t h a t t h e d a t a c o r r e s p o n d i n g t o n o n - s c a t t e r e d p h o t o n s i s n o t i n c o r p o r a t e d i n t h e s p e c t r u m b e c a u s e t h e n u m b e r o f n o n - s c a t t e r e d p h o t o n s i s s e v e r a l o r d e r s o f m a g n i t u d e l a r g e r t h a n t h e n u m b e r o f n u c l e a r r e s o n a n t l y s c a t t e r e d p h o t o n s . T h i s i s r e l a t e d t o t h e l i n e w i d t h o f t h e n u c l e a r e x c i t e d l e v e l , w h i c h i s s e v e r a l o r d e r s o f m a g n i t u d e s m a l l e r t h a n t h e b a n d w i d t h o f t h e s y n c h r o t r o n r a d i a t i o n , e v e n a f t e r t h e b e s t h i g h r e s o l u t i o n m o n o c h r o m a t o r . B e c a u s e t h e n u c l e a r r e s o n a n t l y s c a t t e r e d p h o t o n s a r e d e l a y e d d u e t o the lifetime of the nuclear excited level, they can be separated from the non-scattered photons by time- g a t i n g . T y p i c a l l y i n s t r o b o s c o p i c d e t e c t i o n , t h e fundamental frequency of this time-gating is equal to or is a multiple of the bunch frequency [2]. The intensity, integrated within the periodic set of time- w i n d o w s a s a f u n c t i o n o f t h e D o p p l e r v e l o c i t y i s ca ll ed th e st ro bo sc op ic sp ec tr um . Th is sp ec tr um consists of several stroboscopic order components, e a c h r e s e m b l i n g a c o n v e n t i o n a l M ö s s b a u e r spectrum. A s p e c i f i c p r o p e r t y o f s t r o b o s c o p i c d e t e c t i o n i s t h a t the bunch mode is decorrelated fro m the li fet im e of the nu cle ar is om er . T he r ep et it io n fr eq ue nc y of the bunches is only restricted b y t h e t i m e r e s p o n s e o f t h e d e t e c t o r . T h e r e f o r e , i t i s p o s s i b l e to study systems with a lifetime t h a t i s m u c h l o n g e r t h a n t h e bunch period, even longer than t h e c i r c u l a t i o n p e r i o d o f t h e e l e c t r o n s i n t h e s t o r a g e r i n g . T o i l l u s t r a t e t h a t r e s o n a n c e s o f l o n g - l i v e d i s o t o p e s c a n b e d e t e c t e d u s i n g s t r o b o s c o p i c 46 Fig. 1 Fig. 2. Stroboscopic spectra of two 181 Ta metal- foils with a bunch-mode of (a) 203 single bunches and (b) 1/12 filling + 10 single bunches. F i g u r e 2 F i g . 2 ( a ) Fig. 2(b) Romain Coussement, Riet Callens and Inge Serdons Instituut voor Kern- en Stralingsfysica, K.U. Leuven, Belgium E-mail: romain.coussement @ fys.kuleuven.ac.be d e t e c t i o n , w e p e r f o r m e d t w o m e a s u r e m e n t s a t b e a m l i n e B L 0 9 X U o n 181 T a . T h e l i f e t i m e o f t h e iso mer ic sta te in a sin gle 181 Ta nuc leu s is 8.7 μ s. W e u s e d t w o 181 T a m e t a l f o i l s w i t h r e s p e c t i v e thicknesses of 3.8 μ m and 2.8 μ m. The decay time of the tota l nuc lea r ens emb le was abo ut 15 time s sho rte r tha n the lif eti me of the iso mer ic sta te in a single nucleus [3]. W e p e r f o r m e d t w o e x p e r i m e n t s , b o t h i n a velocity range of about 2 mm /s. The bunch mode i n t h e f i r s t e x p e r i m e n t w a s t h e 2 0 3 - b u n c h m o d e , w h i c h h a s a b u n c h s e p a r a t i o n o f 2 4 n s . T h e second experiment was performed in the 1/12 filling + 1 0 s i n g l e b u n c h e s m o d e . A p i c t u r e o f t h e e x p e r i m e n t a l s e t u p o f b o t h e x p e r i m e n t s c a n b e found in . The delayed count rate in the first e x p e r i m e n t w a s 6 c o u n t s p e r m i n u t e a n d i n t h e second experiment this was 18 counts per minute. T h e s e l o w c o u n t r a t e s a r e c a u s e d b y t h e n a r r o w l i n e w i d t h o f t h e n u c l e a r e x c i t e d l e v e l , w h i c h i s l i n k e d t o t h e l a r g e l i f e t i m e . T h e h i g h e r d e l a y e d count rate for the second experiment can be linked to a bett er effi cien cy of the aval anch e phot odio de d e t e c t o r [ 4 ] a n d a b e t t e r h i g h - r e s o l u t i o n monochromator. s h o w s t h e e x p e r i m e n t a l s p e c t r a . Because we are only interested in the resonance of t h e z e r o t h s t r o b o s c o p i c o r d e r , t h e s h a p e o f t h e t i m e - w i n d o w s i s n o t c r u c i a l . I n o r d e r t o o p t i m i z e fr om po in t of vi ew of st at is ti cs , th ey ar e ta ke n as b r o a d a s p o s s i b l e . F o r t h e f i r s t e x p e r i m e n t ( ) , t h e f i r s t s t r o b o s c o p i c o r d e r s p e c t r u m component is out of the velocity range, and hence, onl y the zer oth ord er stro bos cop ic res ona nce can b e o b s e r v e d . I n t h e s e c o n d s p e c t r u m , s e v e r a l stro bosc opic reso nanc es are gene rate d with in the v e l o c i t y r a n g e . T h e s e c o n s t i t u t e t h e n e g a t i v e sidebands in the spectrum ( ). I n c o n c l u s i o n , w i t h t h e s e t w o e x p e r i m e n t s w e d e m o n s t r a t e d t h e p o t e n t i a l o f s t r o b o s c o p i c detection to contribute to the research on long-lived i s o t o p e s . T h e r e b y , t h e s t r e n g t h o f s t r o b o s c o p i c detection is that there is no inherent restriction s on the lifetime of the nuclear levels to be investigated. References [ 1 ] E . G e r d a u a n d H . d e W a a r d , H y p e r f i n e Interact. 123-125 (2000) and references therein. [ 2 ] R . C a l l e n s , R . C o u s s e m e n t , C . L ’ a b b e , S . N a s u , K . V y v e y , T . Y a m a d a , Y . Y o d a , a n d J . Odeurs, Phys. Rev. B 65 (2002) 160404(R); R. C a l l e n s , R . C o u s s e m e n t , T . K a w a k a m i , J . Ladriere, S. Nasu, T. Ono, I. Serdons, K. Vyvey, T. Yamada, Y. Yoda and J. Odeurs, Phys. Rev. B 67 (2003) 104423. [ 3 ] A . I . C h u m a k o v e t a l . , P h y s . R e v . L e t t . 7 5 (1995) 549. [ 4 ] A . Q . R . B a r o n , H y p e r f i n e I n t e r a c t i o n s 1 2 5 (2000) 29. 47 3 5 0 4 0 0 4 5 0 5 0 0 5 5 0 3 0 0 C o u n t s – 1 0 0 . 5 1 – 0 . 5 V e l o c i t y ( m m / s ) ( b ) C o u n t s – 1 – 0 . 5 0 0 . 5 1 5 0 7 0 9 0 1 1 0 1 3 0 1 5 0 V e l o c i t y ( m m / s ) ( a )
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