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Submitted on 1 Jan 1987
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MEASUREMENT OF THE NUCLEAR gI FACTOR BY LASER OPTICAL PUMPING AND LARMOR
PRECESSION IN A FAST ATOMIC BEAM
J. Vialle, M. Carre, J. Lerme, M. Pellarin
To cite this version:
J. Vialle, M. Carre, J. Lerme, M. Pellarin. MEASUREMENT OF THE NUCLEAR gI FACTOR BY
LASER OPTICAL PUMPING AND LARMOR PRECESSION IN A FAST ATOMIC BEAM. Journal
de Physique Colloques, 1987, 48 (C7), pp.C7-679-C7-681. �10.1051/jphyscol:19877165�. �jpa-00226988�
JOURNAL DE PHYSIQUE
Colloque C7, suppl6rnent au n012, Tome 48, dkcembre 1987
MEASUREMENT OF THE NUCLEAR g, FACTOR BY LASER OPTICAL PUMPING AND LARMOR PRECESSION IN A FAST ATOMIC BEAM
J.L. VIALLE, M. CARRE, J. LERME and M. PELLARIN Laboratoire de SpectromBtrie Ionique et MolBculaire,
(CNRS UA-171 et Celphyra), Universite Claude Bernard Zyon-I, 43, Bd du 11 Novembre 1918, F - 6 9 6 2 2 Villeurbanne Cedex, France
The e x t r a c t i o n of t h e n u c l e a r d i p o l a r magnetic moment Mn from t h e hyper- + f i n e s t r u c t u r e c o n s t a n t s r e q u i r e s t h e c a l c u l a t i o n of t h e e l e c t r o n i c c o n t r i b u t i o n and t h i s l i m i t s t h e accuracy which moreover depends on t h e h y p e r f i n e anomaly. To over- come t h e s e d i f f i c u l t i e s , we p r e s e n t an o r i g i n a l method of determining t h e n u c l e a r Land6 f a c t o r g l f o r diamagnetic atoms. This new t e c h n i ue i s i l l u s t r a t e d w i t h two experiments uslng r e s p e c t i v e l y t h e odd-A i s o t o p e s 135,13qBa ( I = 312
-
t e s t e x p e r i - ment 111) and t h e odd-A i s o t o p e s 213,225Ra ( I = 112-
t h i s experiment was c a r r i e d o u t a t C.E.R.N. on l i n e w i t h t h e ISOLDE mass s e p a r a t o r ) . The method, based on t h e f a s t atomic beam l a s e r spectroscopy technique, c o n s i s t s of d e t e c t i n g t h e i n - f l i g h t Larmor p r e c e s s i o n of t h e n u c l e a r magnetic moment i n a s t a t i c f i e l d , v i a t h e f l u o r e s - cence induced by a r e s o n a n t l a s e r l i g h t .F i g u r e 1 : Schematic experimental set-up
The experiments a r e a s f o l l o w s ( s e e F i g u r e 1) : ~ a + i o n s (Ra') a c c e l e r a t e d t o e n e r g i e s i n t h e neighbourhood of 60 keV a r e converted i n t o a quasi-monokinetic n e u t r a l beam i n a charge-exchange c e l l . The atomic beam is overlapped by a c o l l i n e a r
l i g h t beam from a s i n g l e mode C.W. dye l a s e r , r e s o n a n t with t h e t r a n s i t i o n ' ~ ~ ( ~ = 3 / 2 ) + 1 ~ 1 ( ~ ' = ~ / 2 ) ( 1 ~ o ( ~ = l / 2 ) + ,'l' ( F ' = L / ~ ) ) . The o p t i c a l pumping produced
+
< -by t h e II-polarised (o - p o l a r i z e d ) l i g h t d e p l e t e s tlhe Zeeman s u b l e v e l s MF = 2 112 MF=-1[2) I l e a d i n g t o a very weak f l u o r e s c e n c e s i g n a l i f t h e l a s e r power i s s u f f i - c i e n t t o Induce s e v e r a l pumping c y c l e s b e f o r e t h e o b s e r v a t i o n zone ( s e e F i g u r e 2 ) .
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19877165
JOURNAL
DE
PHYSIQUEFigure 2 :
(A) O p t i c a l ~ u m p i n g produced by t h e It-polarized l a s e r l i g h t
r e s o n a n t w i t h t h e (F-312) + l p l (F1=l 12) t r a n s i t i o n of l j 5 , 1 3 7 ~ a (B) O p t i c a l pumping produced by t h e ~ + - ~ o l a r i z e d l a s e r li h t
r e s o n a n t w i t h t h e l ~ ~ ( F = l / 2 ) + l p l (F'-1 12) t r a n s i t i o n of 413:225Ra.
The f u l l and broken l i n e s r e p r e s e n t t h e Zeeman s u b l e v e l s connected by t h e e x c i t i n g l i g h t and t h e spontaneous emission r e s p e c t i v e l y .
A s t a t i c magnetic f i e l d Bp + p e r p e n d i c u l a r t o t h e q u a n t i z a t i o n a x i s which determines t h e
n
o r a+ c h a r a c t e r of t h e l i g h t , i s a p p l i e d j u s t b e f o r e t h e o b s e r v a t i g n zone.The i n - f l i g h t p r e c e s s i o n of t h e a l i g n e d ( o r i e n t e d ) n u c l e a r magnetic moment Mn around
fto
r e p o p u l a t e s t h e s u b l e v e l s MF = 2 112 (MF=-112) p e r i o d i c a l l y a s a func- t i o n of Bo a t t h e e x i t of t h e electromagnet, and t h e f l u o r e s c e n c e s i g n a l appears a s a f r i n g e d p a t t e r n from which t h e gI-value can be deduced. More p r e c i s e l y t h e f l u o r e s - cence s i g n a l t a k e s t h e form : S = A + B c o s ( 2 + ) (S = A' + B' cos +) where+
= (gI uNBo/hv) I f (x)dx. UN i s t h e n u c l e a r magneton, v t h e atomic v e l o c i t y , Bof(x) t h e magnetic f i e l d a t p o s i t i o n x a l o n g t h e beam p a t h , Bo b e i n g t h e maxi- mum f i e l d i n t h e electromagnet where f ( x ) = 1. To avoid t h e very arduous determina- t i o n of f ( x ) , we adopt a comparative method where t h e f r i n g e d p a t t e r n of a second atom o r i s o t o p e , f o r which t h e g1-value i s known, i s used t o c a l i b r a t e t h e magnetic f i e l d .Typical r e c o r d i n g of t h e f l u o r e s c e n c e s i g n a l f o r t h e 2 2 5 ~ a i s o t o p e s is d i s - played i n F i g u r e 3. 1 3 7 ~ a and 1 3 5 ~ a i s o t o p e s were used t o c a l i b r a t e t h e magnetic f i e l d d u r i n g t h e Ra-ex eriment which i s t h e f i r s t d i r e c t measurement of t h e n u c l e a r magnetic moments of 2199225Ra. The r e s u l t s u 1 ( 2 1 3 ~ a ) = 0.6133(18) y~ and
l . ~ I ( 2 2 5 ~ a ) =
-
0.7338(15) UN provide an a c c u r a t e t e s t of a b - i n i t i o and semi-empirical c a l c u l a t i o n s from o p t i c a l h y p e r f i n e s t r u c t u r e s i n Ra I and Ra 11. This work, submit- t e d t o P h y s i c a l Review L e t t e r s , was c a r r i e d o u t i n c o l l a b o r a t i o n w i t h : E. ARNOLD W. BORCHERS'1,
H.T. DUONG 2 ) , P. JUNCAR 3 ) , S. LIBERMAN 2 ) , W. NEU I ) , R. NEUGART l f , E.W. OTTEN I ) , J. PINARD 2 ) , G. ULM 4 ) , K. WENDT and t h e ISOLDE C o l l a b o r a t i o n , C.E.R.N. Geneva, Switzerland.'1
U. ~ ~ ~ l ~ 4 ~ ~ l ~ ~ ~ ~ l , > t , l t ~ ~ ~ l ~ + ~ , l , , , ! l , t , l , , , . l , , ;
0 2 4
6CURRENT (A)
Figure 3 : Fluorescence s i g n a l obtained with 2 2 5 ~ a a s a function of t h e magnet current.
1 ) I n s t i t u t fiir Physik, U n i v e r s i t i t Mainz, 6500
-
Mainz, Fed. Rep. of Germany, 2) Laboratoire A i m s Cotton, 91405 Orsay Cedex, France,3) I n s t i t u t National de MBtrologie du C.N.A.M., 75141 Paris Cedex 03, France, 4) C . E . R . N . 1211 - Geneva 23, Switzerland.
Reference
/ 1 / M . CARRE, J. LERME and J . L . VIALLE, J . Phys.
