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Lifetime of the 4f7 6s6p z6P 52 state of europium
Volume 20, number 2
PHYSICS LETTERS
r e f e r r e d to by K a d o m t s e v [10]. They a p p e a r to p r o v i d e an o t h e r e x a m p l e of p l a s m a heating by the c o n v e r s i o n of d i r e c t e d b e a m e n e r g y into e n e r g y of r a n d o m p l a s m a e l e c t r o n motion through the i n t e r m e d i a r y of c o o p e r a t i v e o s c i l l a t o r y p h en o m ena. The w r i t e r s w i s h to thank Dr. A. G a r s c a d d e n , Dr. J. M. J o n e s and Dr. A. Von E n g e l f o r helpful c o m m e n t s and Dr. J. E. D r u m m o n d for m a k i n g [6] a v a i l a b l e . One of us (W. T. K.) a l s o w i s h e s to thank the M i n i s t r y of Education, G o v e r n m e n t of N o r t h e r n I r e l a n d , f o r the a w a r d of a R e s e a r c h Studentship in the p e r i o d 1962-1965.
References 1. R.A.Bailey, Ph.D.Thesis, Belfast 1951.
LIFETIME
OF
THE
4f76s6p
1 February 1966
2. T.K. Allen, R.A. Bailey and K. G. Emeleus, Brit. J.Appl. Phys. 6 (1955) 320. 3. M.J. Kofoid and H.V. Cleva, J. Electron. Control 13 (1962) 525. 4. K.G. Emeleus, Adv. in electronics and electron physics, Vol.20 (Academic Press, New York and London, 1964) p.59. 5. W. T. Kennedy, Ph.D. Thesis, Belfast 1965. 6. R. Gerwin and D.J.Nelson, Boeing Scientific Research Labs. Rep. D 1-82-0332, 1964. 7. K.G.Emeleus, Proc. Phys. Soc. B64 (1951) 166, 8. O. Buneman, Phys. Rev. 115 (1959) 503. 9. J.M.Dawson, Nucl. Fusion Suppl., Part 3 (1962) 1033. 10. B.B.Kadomtsev, Plasma turbulence (Academic Press, New York and London, 1965). 11. T.K.Allen, Proc. Phys. Soc. (London) A68 {1955) 696. 12. A. Garscadden, E.M.H. Gray and K. G. Emeleus, Proc. 5th Intern. Conf. Ionisation Phenomena in Gases, Munich (1962) 1433. 13. A. Garscadden and E. M. H. Gray, Proc. Phys. Soc. (London) 80 {1962) 515.
z6P_5
STATE
OF
EUROPIUM
2
W. LANGE, J. LUTHER, A. S T E U D E L and H. W A L T H E R Institut f l i t E x p e r i m e n t a l p h y s i k A d e r Technischen Hochschule Hannover, Ger~lany Received 28 December 1965
The lifetime of the 4f76s6p z6P5 state of europium was measured by the method of zero field level crossing (Hanle effect). The following pi2~liminary value was derived: 7(z6P~) = (0.74 • 0.07) × 10-6 sec.
The z e r o fi e l d l e v e l c r o s s i n g (Hanle effect) s e e m s to be a r e l i a b l e method for the d e t e r m i n a tion of e x c i t e d s t a t e l i f e t i m e of a t o m s . So f a r this method was m a i n l y applied to alkaline e a r t h s or e l e m e n t s with s i m i l a r s p e c t r a . In the e x p e r i m e n t d e s c r i b e d in this l e t t e r it was p o s s i b l e to extend the m e t h o d to the 4f76s6p z6P_S s t a t e of 2 europium. An a t o m i c b e a m of n a t u r a l e u r o p i u m was exci t ed by an e l e c t r o d e l e s s high f r e q u e n c y d i s c h a r g e lamp, made of q u a r t z . The l a m p was f i l l e d with He of about t h r e e m m Hg and with Eu m e t a l . In o r d e r to get a s u f f i c i e n t vapor p r e s s u r e of E u the l a m p was heated to about 800°C. The high f r e quency p o wer was about 300 W at a f r e q u e n c y of 40 M c / s e c . By m e a n s of H e l m h o l t z c o i l s a v e r t i c a l m a g n e t i c fi el d could be applied to the a t o m s of the Eu b e a m . The h o r i z o n t a l component of the e a r t h ' s 166
m a g n e t i c f i el d was c o m p e n s a t e d by two o t h e r c o i l s . The f l u o r e s c e n t light of the b e a m was m e a s u r e d by a p h o t o m u l t i p l i e r , the d i r e c t i o n of the applied e x c i t i n g light b e a m , the d i r e c t i o n of the applied m a g n e t i c f i el d and the d i r e c t i o n of o b s e r v a t i o n b ei n g mutually orthogonal. No p o l a r i z e r s have b e e n u s e d e i t h e r for e x c i t a t i o n or for o b s e r v a t i o n . The t h e o r e t i c a l t r e a t m e n t of this e x p e r i m e n t a l a r r a n g e m e n t is done by Rose and C a r o v i l l a n o [1]. Fig. 1 shows the e l e c t r o n i c s e t - u p of the app a r a t u s . The s i g n a l of the p h o t o m u l t i p l i e r is a m p l i f i e d by a d.c. a m p l i f i e r and i n t e g r a t e d by an o p e r a t i o n a l a m p l i f i e r . The s i g n a l is i n t e g r a t e d f o r one second, then the digital v o l t m e t e r is t r i g g e r e d by the t i m e b a s e g e n e r a t o r and the output voltage of the i n t e g r a t o r is m e a s u r e d . The value is punched out by a tape p e r f o r a t o r . The digital v o l t m e t e r s i g n a l s by a pulse that the m e a s u r e -
Volume 20, number 2
P H YS I C S L E T T E RS
sta~rigger pulse Fig. 1. Schematic diagram of the electronic part of the apparatus. m e n t has been done. This pulse is u s e d to stop and to r e s e t the i n t e g r a t o r , to change the m a g n et i c f i el d of the H e l m h o l t z c o i l s by a c e r t a i n amount and to r e s t a r t the t i m e base g e n e r a t o r . A f t e r an i n t e r v a l of about 200 m s e c the i n t e g r a t o r is s t a r t e d again and the whole c y c le is r e p e a t e d (200 m s e c a r e n e c e s s a r y f o r the m a g n e t i c f i el d to adjust i t s e l f to its s e t point). In this way the dependence on the m a g n e t i c f i e l d of the i n t e n si t y of the light s c a t t e r e d by the Eu a t o m s was m e a s u r e d f o r s e l e c t e d m a g n e t i c f ie ld v a l u e s in the r a n g e f r o m -2.00 to +3.00 g a u s s . T h e s e points w e r e followed through in r i s i n g and f a ll in g o r d e r consecutively. In s e v e r a l e x p e r i m e n t s this was done for a t i m e i n t e r v a l b e t w e e n 5 and 20 m i n u t e s . The value fo r the i n t e n s i t i e s of the s c a t t e r e d light f o r c o r r e s p o n d i n g m a g n e t i c f i e l d s have been added a f t e r w a r d s by a c o m p u t e r . A l i n e a r c o m b i n a t i o n of a L o r e n t z i a n and a d i s p e r s i o n s h a p e d c u r v e was f i t t e d to the s u m m e d - u p s i g n a l by a l e a s t s q u a r e fit. It t u r n e d out that the line shape was always m o r e than 95% L o r e n t z i a n . A ty p i c al r e sult is shown in fig. 2. F r o m the r e s u l t s of t h e s e m e a s u r e m e n t s the following p r e l i m i n a r y value f o r the l i f e t i m e has been d e r i v e d , u s in g the R u s s e l l - S a n n d e r s g j value f o r the 4f76s6p z6P_5 state: 2
T(z6P~) = (0.74 ± 0.07) × 10 -6 s e c . (The n a t u r a l i s o t o p e s of Eu both have a n u c l e a r spin of ~. B e c a u s e I = J = } the g F f a c t o r s f o r the v a r i o u s h y p e r f i n e s t r u c t u r e s t a t e s a r e ident i c a l at low m a g n e t i c f i e l d s and no c o r r e c t i o n s fo r the h y p e r f i n e s t r u c t u r e s p l i t t i n g have to be considered.)
1 February 1966
At l a t e r s t a g e s of the e x p e r i m e n t s a l s o a Nuc l e a r Data E n h a n c e t r o n was u s e d f o r s o m e m e a s u r e m e n t s . In this c a s e the m a g n e t i c field was c o n t r o l l e d by the s w e e p of the E n h a n c e t r o n . The r e s u l t s a c h i e v e d with this d e v i c e a r e in good a g r e e m e n t with the m e a s u r e m e n t s d e s c r i b e d above.
-o$
-o,3
-o2
-o,1
o
o,I
o,2
oF
o$
:ignal Fig. 2. Magnetic field dependence of the intensity of the light scattered from an atomic beam of natural Eu. The signal is plotted in arbitrary units. The measurements at Ho = +3.00 and -2.00 gauss are omitted in this figure.
Reference
1. M.E. Rose and R. L. Carovillano, Phys. Rev. 122 (1961) 1185.
167
PHYSICS LETTERS
r e f e r r e d to by K a d o m t s e v [10]. They a p p e a r to p r o v i d e an o t h e r e x a m p l e of p l a s m a heating by the c o n v e r s i o n of d i r e c t e d b e a m e n e r g y into e n e r g y of r a n d o m p l a s m a e l e c t r o n motion through the i n t e r m e d i a r y of c o o p e r a t i v e o s c i l l a t o r y p h en o m ena. The w r i t e r s w i s h to thank Dr. A. G a r s c a d d e n , Dr. J. M. J o n e s and Dr. A. Von E n g e l f o r helpful c o m m e n t s and Dr. J. E. D r u m m o n d for m a k i n g [6] a v a i l a b l e . One of us (W. T. K.) a l s o w i s h e s to thank the M i n i s t r y of Education, G o v e r n m e n t of N o r t h e r n I r e l a n d , f o r the a w a r d of a R e s e a r c h Studentship in the p e r i o d 1962-1965.
References 1. R.A.Bailey, Ph.D.Thesis, Belfast 1951.
LIFETIME
OF
THE
4f76s6p
1 February 1966
2. T.K. Allen, R.A. Bailey and K. G. Emeleus, Brit. J.Appl. Phys. 6 (1955) 320. 3. M.J. Kofoid and H.V. Cleva, J. Electron. Control 13 (1962) 525. 4. K.G. Emeleus, Adv. in electronics and electron physics, Vol.20 (Academic Press, New York and London, 1964) p.59. 5. W. T. Kennedy, Ph.D. Thesis, Belfast 1965. 6. R. Gerwin and D.J.Nelson, Boeing Scientific Research Labs. Rep. D 1-82-0332, 1964. 7. K.G.Emeleus, Proc. Phys. Soc. B64 (1951) 166, 8. O. Buneman, Phys. Rev. 115 (1959) 503. 9. J.M.Dawson, Nucl. Fusion Suppl., Part 3 (1962) 1033. 10. B.B.Kadomtsev, Plasma turbulence (Academic Press, New York and London, 1965). 11. T.K.Allen, Proc. Phys. Soc. (London) A68 {1955) 696. 12. A. Garscadden, E.M.H. Gray and K. G. Emeleus, Proc. 5th Intern. Conf. Ionisation Phenomena in Gases, Munich (1962) 1433. 13. A. Garscadden and E. M. H. Gray, Proc. Phys. Soc. (London) 80 {1962) 515.
z6P_5
STATE
OF
EUROPIUM
2
W. LANGE, J. LUTHER, A. S T E U D E L and H. W A L T H E R Institut f l i t E x p e r i m e n t a l p h y s i k A d e r Technischen Hochschule Hannover, Ger~lany Received 28 December 1965
The lifetime of the 4f76s6p z6P5 state of europium was measured by the method of zero field level crossing (Hanle effect). The following pi2~liminary value was derived: 7(z6P~) = (0.74 • 0.07) × 10-6 sec.
The z e r o fi e l d l e v e l c r o s s i n g (Hanle effect) s e e m s to be a r e l i a b l e method for the d e t e r m i n a tion of e x c i t e d s t a t e l i f e t i m e of a t o m s . So f a r this method was m a i n l y applied to alkaline e a r t h s or e l e m e n t s with s i m i l a r s p e c t r a . In the e x p e r i m e n t d e s c r i b e d in this l e t t e r it was p o s s i b l e to extend the m e t h o d to the 4f76s6p z6P_S s t a t e of 2 europium. An a t o m i c b e a m of n a t u r a l e u r o p i u m was exci t ed by an e l e c t r o d e l e s s high f r e q u e n c y d i s c h a r g e lamp, made of q u a r t z . The l a m p was f i l l e d with He of about t h r e e m m Hg and with Eu m e t a l . In o r d e r to get a s u f f i c i e n t vapor p r e s s u r e of E u the l a m p was heated to about 800°C. The high f r e quency p o wer was about 300 W at a f r e q u e n c y of 40 M c / s e c . By m e a n s of H e l m h o l t z c o i l s a v e r t i c a l m a g n e t i c fi el d could be applied to the a t o m s of the Eu b e a m . The h o r i z o n t a l component of the e a r t h ' s 166
m a g n e t i c f i el d was c o m p e n s a t e d by two o t h e r c o i l s . The f l u o r e s c e n t light of the b e a m was m e a s u r e d by a p h o t o m u l t i p l i e r , the d i r e c t i o n of the applied e x c i t i n g light b e a m , the d i r e c t i o n of the applied m a g n e t i c f i el d and the d i r e c t i o n of o b s e r v a t i o n b ei n g mutually orthogonal. No p o l a r i z e r s have b e e n u s e d e i t h e r for e x c i t a t i o n or for o b s e r v a t i o n . The t h e o r e t i c a l t r e a t m e n t of this e x p e r i m e n t a l a r r a n g e m e n t is done by Rose and C a r o v i l l a n o [1]. Fig. 1 shows the e l e c t r o n i c s e t - u p of the app a r a t u s . The s i g n a l of the p h o t o m u l t i p l i e r is a m p l i f i e d by a d.c. a m p l i f i e r and i n t e g r a t e d by an o p e r a t i o n a l a m p l i f i e r . The s i g n a l is i n t e g r a t e d f o r one second, then the digital v o l t m e t e r is t r i g g e r e d by the t i m e b a s e g e n e r a t o r and the output voltage of the i n t e g r a t o r is m e a s u r e d . The value is punched out by a tape p e r f o r a t o r . The digital v o l t m e t e r s i g n a l s by a pulse that the m e a s u r e -
Volume 20, number 2
P H YS I C S L E T T E RS
sta~rigger pulse Fig. 1. Schematic diagram of the electronic part of the apparatus. m e n t has been done. This pulse is u s e d to stop and to r e s e t the i n t e g r a t o r , to change the m a g n et i c f i el d of the H e l m h o l t z c o i l s by a c e r t a i n amount and to r e s t a r t the t i m e base g e n e r a t o r . A f t e r an i n t e r v a l of about 200 m s e c the i n t e g r a t o r is s t a r t e d again and the whole c y c le is r e p e a t e d (200 m s e c a r e n e c e s s a r y f o r the m a g n e t i c f i el d to adjust i t s e l f to its s e t point). In this way the dependence on the m a g n e t i c f i e l d of the i n t e n si t y of the light s c a t t e r e d by the Eu a t o m s was m e a s u r e d f o r s e l e c t e d m a g n e t i c f ie ld v a l u e s in the r a n g e f r o m -2.00 to +3.00 g a u s s . T h e s e points w e r e followed through in r i s i n g and f a ll in g o r d e r consecutively. In s e v e r a l e x p e r i m e n t s this was done for a t i m e i n t e r v a l b e t w e e n 5 and 20 m i n u t e s . The value fo r the i n t e n s i t i e s of the s c a t t e r e d light f o r c o r r e s p o n d i n g m a g n e t i c f i e l d s have been added a f t e r w a r d s by a c o m p u t e r . A l i n e a r c o m b i n a t i o n of a L o r e n t z i a n and a d i s p e r s i o n s h a p e d c u r v e was f i t t e d to the s u m m e d - u p s i g n a l by a l e a s t s q u a r e fit. It t u r n e d out that the line shape was always m o r e than 95% L o r e n t z i a n . A ty p i c al r e sult is shown in fig. 2. F r o m the r e s u l t s of t h e s e m e a s u r e m e n t s the following p r e l i m i n a r y value f o r the l i f e t i m e has been d e r i v e d , u s in g the R u s s e l l - S a n n d e r s g j value f o r the 4f76s6p z6P_5 state: 2
T(z6P~) = (0.74 ± 0.07) × 10 -6 s e c . (The n a t u r a l i s o t o p e s of Eu both have a n u c l e a r spin of ~. B e c a u s e I = J = } the g F f a c t o r s f o r the v a r i o u s h y p e r f i n e s t r u c t u r e s t a t e s a r e ident i c a l at low m a g n e t i c f i e l d s and no c o r r e c t i o n s fo r the h y p e r f i n e s t r u c t u r e s p l i t t i n g have to be considered.)
1 February 1966
At l a t e r s t a g e s of the e x p e r i m e n t s a l s o a Nuc l e a r Data E n h a n c e t r o n was u s e d f o r s o m e m e a s u r e m e n t s . In this c a s e the m a g n e t i c field was c o n t r o l l e d by the s w e e p of the E n h a n c e t r o n . The r e s u l t s a c h i e v e d with this d e v i c e a r e in good a g r e e m e n t with the m e a s u r e m e n t s d e s c r i b e d above.
-o$
-o,3
-o2
-o,1
o
o,I
o,2
oF
o$
:ignal Fig. 2. Magnetic field dependence of the intensity of the light scattered from an atomic beam of natural Eu. The signal is plotted in arbitrary units. The measurements at Ho = +3.00 and -2.00 gauss are omitted in this figure.
Reference
1. M.E. Rose and R. L. Carovillano, Phys. Rev. 122 (1961) 1185.
167