- Email: [email protected]
Levels in Al27 below 2.21 MeV
Volume 7, number 4
PHYSICS
LE T T E RS
which the p a r t i c l e s t r a v e r s e d both e l e c t r o d e s , t h e d i s t a n c e b e t w e e n t h e l a t t e r b e i n g 25 c m . In t h i s c h a m b e r the q u a l i t y of the t r a c k s , a s c a n be s e e n f r o m fig. 4, i s h i g h e r than t h a t of the t r a c k s shown in f i g s . 1, 2, 3. Despite all said above there is reason for bel i e v i n g t h a t t h e q u a l i t y of t r a c k s in c h a m b e r s in w h i c h the s t r e a m e r s d e v e l o p p e r p e n d i c u l a r to t h e p a r t i c l e p a t h ( " t r a n s m i s s i o n c h a m b e r " ) m a y be c o n s i d e r a b l y i m p r o v e d . It should be n o t e d t h a t in s u c h c h a m b e r s s h i f t of the t r a c k due to s i m u l t a n e o u s a c tion of the e l e c t r i c and m a g n e t i c f i e l d s (the s o c a l l e d [EB] e f f e c t ) should p r a c t i c a l l y be a b s e n t s i n c e
now b e i n g i n v e s t i g a t e d in c h a m b e r s of v a r i o u s s i z e s and d e s i g n . In c o n c l u s i o n we e x p r e s s o u r a p p r e c i a t i o n to A c a d e m i c i a n V e x l e r and I. V. C h u v i l o f o r t h e o p p o r t u n i t y to c a r r y out o u r i n v e s t i g a t i o n on the J I N R p r o t o n s y n c h r o t r o n , to A. A. K u z n e t s o v f o r a s s i s t a n c e in the e x p e r i m e n t s and to S. V. K a r d o n s k y , V . A . Ivanov and K. A. G a z a r i a n f o r p a r t i c i p a t i n g in the m e a s u r e m e n t s . References 1) A.I.Alikhanian. T . L . A s a t i a n i , E.M. Matevosian, J. Exptl. Theoret. Phys. (USSR) 44 (1963) 773. 2) Problems in Elementary P a r t i c l e Physics. A collection of lectures delivered at the spring school of physics at Nor-Amberd. Publishing House of the Arm. USSR Academy of Sciences (1963).
~I!B.
The h i g h e s t F o s s i b l e a c c u r a c y of m e a s u r e m e n t of the m o m e n t u m of p a r t i c l e s in s u c h c h a m b e r s i s
LEVELS
IN A127
1 December 1963
BELOW
2.21
MeV
B. H. A R M I T A G E , J. H. MONTAGUE , A. K. M. SIDDIQ * Atomic Energy Research Establishment, Harwell, Berks. , England and R. E. M E A D S Washington Singer Laboratories, University of Exeter, Devon, England
Received 25 October 1963
F o r s o m e t i m e i t h a s b e e n a c c e p t e d t h a t the f i r s t t h r e e e x c i t e d s t a t e s in A127 a r e a t 0.84, 1.01 and 2 . 2 1 MeV 1). R e c e n t l y , h o w e v e r , C i u f f o l o t t i and D e m i c h e l i s 2) have r e p o r t e d a d d i t i o n a l s t a t e s a t 1.65 and 1.83 M e V , p o p u l a t e d d u r i n g t h e d e c a y of Mg 27, and d i s c u s s e d t h e i r p r o p e r t i e s in t e r m s of the r o t a t i o n a l c o l l e c t i v e m o d e l . T h e i r a p p r o a c h w a s to s t u d y v r a y s in c o i n c i d e n c e with 1) g r o u n d s t a t e 7 r a y s f r o m the 0.84 MeV l e v e l , and 2) g r o u n d s t a t e y r a y s f r o m t h e 1.01 M e V l e v e l . S t a t e s a t 1.65 MeV and 1.83 MeV w e r e p o s t u l a t e d a s a r e s u l t of t h e s e m e a s u r e m e n t s , but e x a m i ' m t i o n of t h e d i r e c t s p e c t r u m s h o w e d no e v i d e n c e f o r g r o u n d s t a t e transitions from these levels. W i n t e r h a l t e r 3) h a s i d e n t i f i e d a s t a t e at 1.91 MeV in a s t u d y of t h e i n e l a s t i c s c a t t e r i n g of n e u t r o n s b y A1. T h e r e i s no e v i d e n c e in t h i s w o r k , h o w e v e r , f o r a s t a t e n e a r 1.65 MeV. T h i s l e t t e r d e s c r i b e s an a t t e m p t to c o n f i r m the e x i s t e n c e of t h e s e new s t a t e s , both t h r o u g h a s t u d y of the ~ - ~ c o i n c i d e n c e s p r o d u c e d in t h e d e c a y of * Attached from Pakistan Atomic Energy Commission. 274
Mg 27, and t h r o u g h a m e a s u r e m e n t of p r o t o n i n e l a s t i c s c a t t e r i n g by A1. A f t e r the p r e s e n t w o r k w a s c o m p l e t e d O p h e l and L a w e r g r e n 4) r e p o r t e d 7 - 7 c o i n c i d e n c e m e a s u r e m e n t s on v r a y s f o l l o w i n g the d e c a y of Mg27. T h e Mg 27 w a s p r o d u c e d by the M g 2 6 ( d , p ) M g 27 r e a c t i o n with 9 MeV d e u t e r o n s . No e v i d e n c e w a s found, h o w e v e r , f o r the e x i s t e n c e of s t a t e s found b y C i u f f o l o t t i and D e m i c h e l i s . D e c a y o f Mg27. Mg27 (9.6 m i n h a l f - l i f e ) w a s o b t a i n e d by i r r a d i a t i n g c y l i n d r i c a l s a m p l e s of A1 (25 m m r a d i u s x 13 m m ) with 14 MeV n e u t r o n s f r o m the H a r w e l l C o c k c r o f t - W a l t o n a c c e l e r a t o r . N e u t r o n c a p t u r e in A127 r e s u l t e d in t h e p r e s e n c e of 2.3 m i n A128. A s a c o n s e q u e n c e , e a c h s a m p l e w a s i r r a d i a t e d f o r 5 m i n , and b e f o r e c o u n t i n g f o r 20 m i n , a p e r i o d of 5 m i n w a s a l l o w e d to e l a p s e to e n a b l e a r e d u c t i o n in the p r o p o r t i o n of A128 to take place. r a y s a r i s i n g f r o m Mg27 d e c a y w e r e s t u d i e d with two 50 m m x 55 m m NaI c r y s t a l s and p h o t o m u l t i p l i e r s , u s i n g a c o n v e n t i o n a l c o i n c i d e n c e c i r c u i t of 0.1 ~s r e s o l v i n g t i m e . The c o u n t e r s w e r e p l a c e d
Volume 7, number 4
PHYSICS
a l o n g a c o m m o n a x i s a n d Mg 27 P r a y s w e r e a b s o r b e d by 6 m m A1 p l a c e d in f r o n t of the NaI c r y s tals. S p e c t r a of 7 r a y s in c o i n c i d e n c e with (1) 0.84 MeV 7 r a y s and (2)1.01 MeV 7 r a y s a r e shown i n f i g s . 1 and 2 r e s p e c t i v e l y . A f t e r s u b t r a c t i o n of the r a n d o m c o i n c i d e n c e s no p e a k s a r e o b s e r v e d in e i t h e r y s p e c t r u m f o r an e n e r g y > 200 keV. A low c o n t i n u o u s b a c k g r o u n d i s o b s e r v e d , h o w e v e r , which i s a t t r i b u t e d to the 15 h o u r Na 24 a c t i v i t y p r o d u c e d b y the A127(n,c}Na 24 r e a c t i o n . In both s p e c t r a a b r o a d d i s t r i b u t i o n p e a k i n g a t a p p r o x i m a t e l y 150 keV i s o b s e r v e d , but the i n t e n s i t y of t h i s d i s t r i b u t i o n i s about 4 t i m e s h i g h e r f o r the y s p e c t r u m in c o i n c i d e n c e with 0.84 MeV y r a y s than f o r the s p e c t r u m in c o i n c i d e n c e with the 1.01 M e V 7 r a y s . The d i f f e r e n c e b e t w e e n t h e s e two s p e c t r a c a n be a t t r i b u t e d to r e a l c o i n c i d e n c e s b e t w e e n 0.17 MeV 7 r a y s , c a s c a d i n g f r o m the 1.01 MeV l e v e l , and 0.84 MeV g r o u n d s t a t e 7 r a y s . A c o n s i d e r a b l e s h a r p e n i n g of the low e n e r g y p e a k o c c u r r e d on r e m o v a l of the a b s o r b e r , s u g g e s t i n g that a t t e n u a t i o n of the y r a y s by the a b s o r b e r was p a r t l y r e s p o n s i b l e f o r the width of the d i s t r i b u t i o n .
15C
zloc
0,84
Al~'7 McV ~'
•.*•
• "•.',.•'.•....•.•..• ."
TOTAL A|27 I'O1 M c V
SC
COINCIDENCES 1~24 1"37 MeV
• . ** • ,•. , • %•, ° ,*• • • •. . •., .,.•.***,• • • •°.••..., RANDOM
x~ r •*•* • ******************************************************* "',**, ,**,*•,-° • . . . . . . .
COINCIDENCES ....•._ _•.**. . . . . . . .
REAL CO,NC,DENCCS/ O
1December 1963
2DO ,sc z ~oo
AE27 O84
u
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$ o
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TOTAL
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I
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so
CO/NCIDENCE
RANDOM
S
Mg 24
McVI AII~2:V . .
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.
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COINCIDENCES
U ..
2
.
50 /
o
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,~
,
.
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REAL
2b 3o 4o C"ANNEL NUMBER--
COINCIDENCE
so
60
Fig. 2. Spectrum of y rays in coincidence with 1.01 MeV y rays. the i n t e n s i t y of t n e 0.17 MeV ~ r a y . A s i m i l a r c o n c l u s i o n c a n be d r a w n f r o m an e x a m i n a t i o n of the ~, s p e c t r u m in c o i n c i d e n c e with the 1.01 MeV ~ r a y w h e r e t h e r e i s no e v i d e n c e of 7 r a y s c a s c a d i n g f r o m l e v e l s at 1.65 and 1.83 MeV t h r o u g h the 1.01 MeV level.
20C
U
LETTERS
'i''"'"'"".'.'.';'..'.'"'."" .'"'";""-"''"'.'.","J'.".'""'"'".'..., t 2s so ~s ,oo ,2s CHANNEL
NUMBER
Fig. 1. Spectrum of y rays in coincidence with 0.84 MeV rays. T h e r e i s no e v i d e n c e in the 7 s p e c t r a f o r r e a l c o i n c i d e n c e s with 0.84 MeV g r o u n d s t a t e 7 r a y s , e x c e p t f o r 0.17 MeV 7 r a y s . If l e v e l s at 1.65 MeV and 1.83 MeV a r e p o p u l a t e d d u r i n g the d e c a y of Mg27, then ~ r a y s c a s c a d i n g t h r o u g h the 0.84 MeV l e v e l would be expected. An u p p e r l i m i t to the i n t e n s i t y of 0.81 and 0.99 MeV :~ r a y s , in c o i n c i d e n c e • with 0.84 M e V ~ r a y s , can be p l a c e d a t 0.02 t i m e s
Proton inelasHc scattering by A127. L e v e l s in A127 at 0.84, 1.01, 2.21 and 2.73 MeV have b e e n o b s e r v e d with 9.9 MeV p r o t o n s f r o m the H a r w e l l T a n d e m G e n e r a t o r . The i n e l a s t i c a l l y s c a t t e r e d p a r t i c l e s w e r e a n a l y s e d with the b r o a d r a n g e s p e c t r o g r a p h 5), and d e t e c t e d i n Ilford K2 n u c l e a r e m u l s i o n s . S p e c t r a of i n e l a s t i c a l l y s c a t t e r e d p r o t o n s w e r e r e c o r d e d at v a r i o u s o b s e r v a t i o n a n g l e s (45 ° , 90 ° 120 ° ) and in each c a s e e x p o s u r e of 200 #C and 5000 !~,C w e r e m a d e . The l o n g e r e x p o s u r e s e n a b l e d a s e a r c h to be m a d e f o r g r o u p s l e a d i n g to s t a t e s at 1.65, 1.83 and 1.91 MeV, and the s h o r t e r e x p o s u r e s e n a b l e d g r o u p s to the w e l l known s t a t e s to be s c a n n e d . A t y p i c a l s p e c t r u m i s shown in fig. 3; no e v i d e n c e b e i n g p r o v i d e d for the e x i s t e n c e of s t a t e s in the r e g i o n 1.5-2.0 MeV. In t a b l e 1, u p p e r l i m i t s a r e p l a c e d on the i n t e n s i t y of g r o u p s in the 1 . 5 - 2 . 0 MeV r e g i o n r e l a t i v e to g r o u p s a s s o c i a t e d with s t a t e s at 0.84, 1.01, 2.21 and 2.73 MeV. The r e s u l t i s in a g r e e m e n t with o t h e r p u b l i s h e d w o r k on the A127(p,p')A127 r e a c t i o n 1). A l l the l o w - l y i n g s t a t e s in A127 should be a p p r e c i a b l y e x c i t e d by p r o t o n i n e l a s t i c s c a t t e r i n g with 9.9 MeV p r o t o n s . T h e r e i s no r e a s o n to e x p e c t that a n y group c o r r e s p o n d i n g to one of t h e s e s t a t e s would be i n h i b i t e d with r e s p e c t to the o t h e r s 275
Volume 7, n u m b e r 4
PHYSICS
PROTON 8.O [
8,5 12OO~
r
LETTERS
1 D e c e m b e r 1963
ENERGY (M,V) 7,5 i
6"5
7.0 l-
McV 0 b - 9 0 °
Et-9.91
cla(o.o)
A'~(O.S,)
& a: B o o
Ata7(,<~,) z o i-
~ 4oo
si2eO.77 )
G.
II x25 200
.
L.-,I .....
42
.,:'. ....
40
'.-.-..~
}I'.r l
.,........................ -~- ...... . ........ ...; "............~:...... 38 36 34 32 30 DISTANCE ALONG PLATE (CMS)
L
.....
28
~__._ . . . . . . . . . . . . . . . .
26
J
24
Fig. 3. Spectrum of protons obtained by bombarding an A127 target with 9.91 MeV protons. The energies in MeV of the excited states corresponding to the outgoing proton groups ar e shown. Table 1 Relative intensity for scattering to levels in A127 at various observation angles Excitation energy (MeV) Relative intensity 120 ° 90 ° 45 °
r
0.84
f
2 200 4 200
1.01
1.65
1.83
1.91
4 200 5 600 5 500
<1.5 <1.5 <4
<1.5 <1.5 <4
<1.5 <1.5 <4
by a f a c t o r of 103 o r 104. It s e e m s u n l i k e l y , t h e r e f o r e , that an y s t a t e s e x i s t in A127 b e l o w 2.2 1 M e V e x c e p t f o r t h o s e at 0.84 and 1.01 M e V .
sor for Mr. the
276
T l , i s p r o b l e m w a s s u g g e s t e d to u s by P r o f e s W. E. B u r c h a m to w h o m we a r e a l s o i n d e b t e d s e v e r a l h e l p f u l d i s c u s s i o n s . We w i s h to t h an k Peter Thorpe for valuable assistance during experiment.
2.21
2.73
5 4001 3 800 10 000 5 700 9 100 4 900
References 1) P . M . Endt and C. Van der Leun, Nuclear Phys. 34 (1962) 1. 2) L.Ciuffolotti and F. Demichelis, Nuclear Phys. 39 (1962) 252. 3) D.Winterhalter, Nuclear Phys. 39 (1962) 535. 4) T.R.Ophel and B.T. Lawergren, Physics Letters 6 (1963) 230. 5) B. H. Armitage and R. E. Meads, Nuclear Phys. 33 (1962) 494.
PHYSICS
LE T T E RS
which the p a r t i c l e s t r a v e r s e d both e l e c t r o d e s , t h e d i s t a n c e b e t w e e n t h e l a t t e r b e i n g 25 c m . In t h i s c h a m b e r the q u a l i t y of the t r a c k s , a s c a n be s e e n f r o m fig. 4, i s h i g h e r than t h a t of the t r a c k s shown in f i g s . 1, 2, 3. Despite all said above there is reason for bel i e v i n g t h a t t h e q u a l i t y of t r a c k s in c h a m b e r s in w h i c h the s t r e a m e r s d e v e l o p p e r p e n d i c u l a r to t h e p a r t i c l e p a t h ( " t r a n s m i s s i o n c h a m b e r " ) m a y be c o n s i d e r a b l y i m p r o v e d . It should be n o t e d t h a t in s u c h c h a m b e r s s h i f t of the t r a c k due to s i m u l t a n e o u s a c tion of the e l e c t r i c and m a g n e t i c f i e l d s (the s o c a l l e d [EB] e f f e c t ) should p r a c t i c a l l y be a b s e n t s i n c e
now b e i n g i n v e s t i g a t e d in c h a m b e r s of v a r i o u s s i z e s and d e s i g n . In c o n c l u s i o n we e x p r e s s o u r a p p r e c i a t i o n to A c a d e m i c i a n V e x l e r and I. V. C h u v i l o f o r t h e o p p o r t u n i t y to c a r r y out o u r i n v e s t i g a t i o n on the J I N R p r o t o n s y n c h r o t r o n , to A. A. K u z n e t s o v f o r a s s i s t a n c e in the e x p e r i m e n t s and to S. V. K a r d o n s k y , V . A . Ivanov and K. A. G a z a r i a n f o r p a r t i c i p a t i n g in the m e a s u r e m e n t s . References 1) A.I.Alikhanian. T . L . A s a t i a n i , E.M. Matevosian, J. Exptl. Theoret. Phys. (USSR) 44 (1963) 773. 2) Problems in Elementary P a r t i c l e Physics. A collection of lectures delivered at the spring school of physics at Nor-Amberd. Publishing House of the Arm. USSR Academy of Sciences (1963).
~I!B.
The h i g h e s t F o s s i b l e a c c u r a c y of m e a s u r e m e n t of the m o m e n t u m of p a r t i c l e s in s u c h c h a m b e r s i s
LEVELS
IN A127
1 December 1963
BELOW
2.21
MeV
B. H. A R M I T A G E , J. H. MONTAGUE , A. K. M. SIDDIQ * Atomic Energy Research Establishment, Harwell, Berks. , England and R. E. M E A D S Washington Singer Laboratories, University of Exeter, Devon, England
Received 25 October 1963
F o r s o m e t i m e i t h a s b e e n a c c e p t e d t h a t the f i r s t t h r e e e x c i t e d s t a t e s in A127 a r e a t 0.84, 1.01 and 2 . 2 1 MeV 1). R e c e n t l y , h o w e v e r , C i u f f o l o t t i and D e m i c h e l i s 2) have r e p o r t e d a d d i t i o n a l s t a t e s a t 1.65 and 1.83 M e V , p o p u l a t e d d u r i n g t h e d e c a y of Mg 27, and d i s c u s s e d t h e i r p r o p e r t i e s in t e r m s of the r o t a t i o n a l c o l l e c t i v e m o d e l . T h e i r a p p r o a c h w a s to s t u d y v r a y s in c o i n c i d e n c e with 1) g r o u n d s t a t e 7 r a y s f r o m the 0.84 MeV l e v e l , and 2) g r o u n d s t a t e y r a y s f r o m t h e 1.01 M e V l e v e l . S t a t e s a t 1.65 MeV and 1.83 MeV w e r e p o s t u l a t e d a s a r e s u l t of t h e s e m e a s u r e m e n t s , but e x a m i ' m t i o n of t h e d i r e c t s p e c t r u m s h o w e d no e v i d e n c e f o r g r o u n d s t a t e transitions from these levels. W i n t e r h a l t e r 3) h a s i d e n t i f i e d a s t a t e at 1.91 MeV in a s t u d y of t h e i n e l a s t i c s c a t t e r i n g of n e u t r o n s b y A1. T h e r e i s no e v i d e n c e in t h i s w o r k , h o w e v e r , f o r a s t a t e n e a r 1.65 MeV. T h i s l e t t e r d e s c r i b e s an a t t e m p t to c o n f i r m the e x i s t e n c e of t h e s e new s t a t e s , both t h r o u g h a s t u d y of the ~ - ~ c o i n c i d e n c e s p r o d u c e d in t h e d e c a y of * Attached from Pakistan Atomic Energy Commission. 274
Mg 27, and t h r o u g h a m e a s u r e m e n t of p r o t o n i n e l a s t i c s c a t t e r i n g by A1. A f t e r the p r e s e n t w o r k w a s c o m p l e t e d O p h e l and L a w e r g r e n 4) r e p o r t e d 7 - 7 c o i n c i d e n c e m e a s u r e m e n t s on v r a y s f o l l o w i n g the d e c a y of Mg27. T h e Mg 27 w a s p r o d u c e d by the M g 2 6 ( d , p ) M g 27 r e a c t i o n with 9 MeV d e u t e r o n s . No e v i d e n c e w a s found, h o w e v e r , f o r the e x i s t e n c e of s t a t e s found b y C i u f f o l o t t i and D e m i c h e l i s . D e c a y o f Mg27. Mg27 (9.6 m i n h a l f - l i f e ) w a s o b t a i n e d by i r r a d i a t i n g c y l i n d r i c a l s a m p l e s of A1 (25 m m r a d i u s x 13 m m ) with 14 MeV n e u t r o n s f r o m the H a r w e l l C o c k c r o f t - W a l t o n a c c e l e r a t o r . N e u t r o n c a p t u r e in A127 r e s u l t e d in t h e p r e s e n c e of 2.3 m i n A128. A s a c o n s e q u e n c e , e a c h s a m p l e w a s i r r a d i a t e d f o r 5 m i n , and b e f o r e c o u n t i n g f o r 20 m i n , a p e r i o d of 5 m i n w a s a l l o w e d to e l a p s e to e n a b l e a r e d u c t i o n in the p r o p o r t i o n of A128 to take place. r a y s a r i s i n g f r o m Mg27 d e c a y w e r e s t u d i e d with two 50 m m x 55 m m NaI c r y s t a l s and p h o t o m u l t i p l i e r s , u s i n g a c o n v e n t i o n a l c o i n c i d e n c e c i r c u i t of 0.1 ~s r e s o l v i n g t i m e . The c o u n t e r s w e r e p l a c e d
Volume 7, number 4
PHYSICS
a l o n g a c o m m o n a x i s a n d Mg 27 P r a y s w e r e a b s o r b e d by 6 m m A1 p l a c e d in f r o n t of the NaI c r y s tals. S p e c t r a of 7 r a y s in c o i n c i d e n c e with (1) 0.84 MeV 7 r a y s and (2)1.01 MeV 7 r a y s a r e shown i n f i g s . 1 and 2 r e s p e c t i v e l y . A f t e r s u b t r a c t i o n of the r a n d o m c o i n c i d e n c e s no p e a k s a r e o b s e r v e d in e i t h e r y s p e c t r u m f o r an e n e r g y > 200 keV. A low c o n t i n u o u s b a c k g r o u n d i s o b s e r v e d , h o w e v e r , which i s a t t r i b u t e d to the 15 h o u r Na 24 a c t i v i t y p r o d u c e d b y the A127(n,c}Na 24 r e a c t i o n . In both s p e c t r a a b r o a d d i s t r i b u t i o n p e a k i n g a t a p p r o x i m a t e l y 150 keV i s o b s e r v e d , but the i n t e n s i t y of t h i s d i s t r i b u t i o n i s about 4 t i m e s h i g h e r f o r the y s p e c t r u m in c o i n c i d e n c e with 0.84 MeV y r a y s than f o r the s p e c t r u m in c o i n c i d e n c e with the 1.01 M e V 7 r a y s . The d i f f e r e n c e b e t w e e n t h e s e two s p e c t r a c a n be a t t r i b u t e d to r e a l c o i n c i d e n c e s b e t w e e n 0.17 MeV 7 r a y s , c a s c a d i n g f r o m the 1.01 MeV l e v e l , and 0.84 MeV g r o u n d s t a t e 7 r a y s . A c o n s i d e r a b l e s h a r p e n i n g of the low e n e r g y p e a k o c c u r r e d on r e m o v a l of the a b s o r b e r , s u g g e s t i n g that a t t e n u a t i o n of the y r a y s by the a b s o r b e r was p a r t l y r e s p o n s i b l e f o r the width of the d i s t r i b u t i o n .
15C
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TOTAL A|27 I'O1 M c V
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1December 1963
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60
Fig. 2. Spectrum of y rays in coincidence with 1.01 MeV y rays. the i n t e n s i t y of t n e 0.17 MeV ~ r a y . A s i m i l a r c o n c l u s i o n c a n be d r a w n f r o m an e x a m i n a t i o n of the ~, s p e c t r u m in c o i n c i d e n c e with the 1.01 MeV ~ r a y w h e r e t h e r e i s no e v i d e n c e of 7 r a y s c a s c a d i n g f r o m l e v e l s at 1.65 and 1.83 MeV t h r o u g h the 1.01 MeV level.
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Fig. 1. Spectrum of y rays in coincidence with 0.84 MeV rays. T h e r e i s no e v i d e n c e in the 7 s p e c t r a f o r r e a l c o i n c i d e n c e s with 0.84 MeV g r o u n d s t a t e 7 r a y s , e x c e p t f o r 0.17 MeV 7 r a y s . If l e v e l s at 1.65 MeV and 1.83 MeV a r e p o p u l a t e d d u r i n g the d e c a y of Mg27, then ~ r a y s c a s c a d i n g t h r o u g h the 0.84 MeV l e v e l would be expected. An u p p e r l i m i t to the i n t e n s i t y of 0.81 and 0.99 MeV :~ r a y s , in c o i n c i d e n c e • with 0.84 M e V ~ r a y s , can be p l a c e d a t 0.02 t i m e s
Proton inelasHc scattering by A127. L e v e l s in A127 at 0.84, 1.01, 2.21 and 2.73 MeV have b e e n o b s e r v e d with 9.9 MeV p r o t o n s f r o m the H a r w e l l T a n d e m G e n e r a t o r . The i n e l a s t i c a l l y s c a t t e r e d p a r t i c l e s w e r e a n a l y s e d with the b r o a d r a n g e s p e c t r o g r a p h 5), and d e t e c t e d i n Ilford K2 n u c l e a r e m u l s i o n s . S p e c t r a of i n e l a s t i c a l l y s c a t t e r e d p r o t o n s w e r e r e c o r d e d at v a r i o u s o b s e r v a t i o n a n g l e s (45 ° , 90 ° 120 ° ) and in each c a s e e x p o s u r e of 200 #C and 5000 !~,C w e r e m a d e . The l o n g e r e x p o s u r e s e n a b l e d a s e a r c h to be m a d e f o r g r o u p s l e a d i n g to s t a t e s at 1.65, 1.83 and 1.91 MeV, and the s h o r t e r e x p o s u r e s e n a b l e d g r o u p s to the w e l l known s t a t e s to be s c a n n e d . A t y p i c a l s p e c t r u m i s shown in fig. 3; no e v i d e n c e b e i n g p r o v i d e d for the e x i s t e n c e of s t a t e s in the r e g i o n 1.5-2.0 MeV. In t a b l e 1, u p p e r l i m i t s a r e p l a c e d on the i n t e n s i t y of g r o u p s in the 1 . 5 - 2 . 0 MeV r e g i o n r e l a t i v e to g r o u p s a s s o c i a t e d with s t a t e s at 0.84, 1.01, 2.21 and 2.73 MeV. The r e s u l t i s in a g r e e m e n t with o t h e r p u b l i s h e d w o r k on the A127(p,p')A127 r e a c t i o n 1). A l l the l o w - l y i n g s t a t e s in A127 should be a p p r e c i a b l y e x c i t e d by p r o t o n i n e l a s t i c s c a t t e r i n g with 9.9 MeV p r o t o n s . T h e r e i s no r e a s o n to e x p e c t that a n y group c o r r e s p o n d i n g to one of t h e s e s t a t e s would be i n h i b i t e d with r e s p e c t to the o t h e r s 275
Volume 7, n u m b e r 4
PHYSICS
PROTON 8.O [
8,5 12OO~
r
LETTERS
1 D e c e m b e r 1963
ENERGY (M,V) 7,5 i
6"5
7.0 l-
McV 0 b - 9 0 °
Et-9.91
cla(o.o)
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.
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42
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.,........................ -~- ...... . ........ ...; "............~:...... 38 36 34 32 30 DISTANCE ALONG PLATE (CMS)
L
.....
28
~__._ . . . . . . . . . . . . . . . .
26
J
24
Fig. 3. Spectrum of protons obtained by bombarding an A127 target with 9.91 MeV protons. The energies in MeV of the excited states corresponding to the outgoing proton groups ar e shown. Table 1 Relative intensity for scattering to levels in A127 at various observation angles Excitation energy (MeV) Relative intensity 120 ° 90 ° 45 °
r
0.84
f
2 200 4 200
1.01
1.65
1.83
1.91
4 200 5 600 5 500
<1.5 <1.5 <4
<1.5 <1.5 <4
<1.5 <1.5 <4
by a f a c t o r of 103 o r 104. It s e e m s u n l i k e l y , t h e r e f o r e , that an y s t a t e s e x i s t in A127 b e l o w 2.2 1 M e V e x c e p t f o r t h o s e at 0.84 and 1.01 M e V .
sor for Mr. the
276
T l , i s p r o b l e m w a s s u g g e s t e d to u s by P r o f e s W. E. B u r c h a m to w h o m we a r e a l s o i n d e b t e d s e v e r a l h e l p f u l d i s c u s s i o n s . We w i s h to t h an k Peter Thorpe for valuable assistance during experiment.
2.21
2.73
5 4001 3 800 10 000 5 700 9 100 4 900
References 1) P . M . Endt and C. Van der Leun, Nuclear Phys. 34 (1962) 1. 2) L.Ciuffolotti and F. Demichelis, Nuclear Phys. 39 (1962) 252. 3) D.Winterhalter, Nuclear Phys. 39 (1962) 535. 4) T.R.Ophel and B.T. Lawergren, Physics Letters 6 (1963) 230. 5) B. H. Armitage and R. E. Meads, Nuclear Phys. 33 (1962) 494.