- Email: [email protected]
A study of the T = 32 states of 17O
Volume 29B, number 1
PHYSICS
A STUDY
OF
THE
LETTERS
T = {
31 March 1969
STATES
OF
170
C. D E T R A Z * and H. H. DUHM Max-Planck-lnstitut fi~r Kernphys ik , Heidelberg, Germany Received 5 M a r c h 1969
Eight analogue T = { excited states in 170 have been identified with the 180(3He, Ot)170 reaction at E(3He) = 16 MeV. The l - t r a n s f e r values and spectroscopic factors are presented for four of these states.
In r e c e n t y e a r s , m u c h i n f o r m a t i o n . h a s b e e n o b t a i n e d c o n c e r n i n g t h e l o c a t i o n s and, to a l e s s e r e x t e n t , t h e s p i n s and p a r i t i e s of h i g h - i s o s p i n s t a t e s in light n u c l e i [1]. A s f o r the T = {, A = = 17 s t a t e s , s o m e 24 s t a t e s in 17N(Tz =~ ) [2], 5 s t a t e s in 1 7 0 ( Tz = ½) [3], 4 s t a t e s in 17F (T z = ½) [4] h a v e b e e n l o c a t e d so f a r ; the f o u r t h m e m b e r of t h e i s o b a r i c q u a d r u p l e t , 17Ne ( T z = = - {), h a s b e e n c h a r a c t e r i z e d a s a b e t a - d e l a y e d p r o t o n e m i t t e r and an a p p r o x i m a t e v a l u e of i t s m a s s (~:250 MeV) h a s b e e n o b t a i n e d [5]; t h e s p i n s and p a r i t i e s of t h e two l o w e s t - l y i n g T = {, A = 17
60
65 T
- - T
s t a t e s a p p e a r to be u n a m b i g u o u s l y c h a r a c t e r i z e d a s ½- and { - r e s p e c t i v e l y [6]. In o r d e r to o b t a i n m o r e i n f o r m a t i o n about t h e l o c a t i o n s , s p i n s and p a r i t i e s of the T = 5 a n a l o g u e s t a t e s of 1 7 0 , we h a v e s t u d i e d t h e 1 8 0 ( 3 H e , a ) 1 7 0 r e a c t i o n . T h e a d v a n t a g e of u s i n g t h i s r e a c t i o n f o r t h e study of the T = ~ s t a t e s is t h a t the Q v a l u e i s c l o s e to 0 MeV w h i c h p r o v i d e s a l m o s t optimal momentum matching conditions. Conseq u e n t l y the s t r o n g a n a l o g u e t r a n s i t i o n s should exhibit pronounced diffraction patterns allowing t h e d e t e r m i n a t i o n of t h e t r a n s f e r r e d a n g u l a r
70 T
Distance along the Focal Plane Ecm3 75 80 85 T 1 T ~
lSO(3He, a )170
"E
.U
,o
E ,40O
,
04 x
E3
A2
"I°Ni
=16MeV,5 °
I '~ ~|
He
~o
~, 3oo e~ if)
~ 2oo L
A1
A4
100 0
!
11
12
13
l
1
14 15 Excitation Energy in1~Z)Evle~
Fig. 1. 180(3He,Oz)lTo spectrum for excitation energies in 170 between 11 MeV and 15.5 MeV. The states labelled with a capital A are interpreted as the T = ~ analogue states in 170. The impurity groups arising from 12C and 160 contaminations in the target are indicated by the excitation energies of the residual nuclei.
* On leave from Institut de Physique Nucl6aire, Orsay, France. 29
Volume 29B, number 1
PHYSICS
160(3He,ot)150 l
t
i
i
I i
LETTERS
and 180(3He,(z)170
E3He=16MeV I
I ,
[ =0
Io 4 ('~.
." . 150519
103
=1
t'
",, ,:'.,506. ~
•
31 March 1969
i
"'+.
f=2 ' i
, i
*%
170, A3
*
1506.79
170, A 0 10 2
,+~f+f. ~7o,A s
~ ~t
"t+ fl
10 3
O"
~'/
I , I = I * 2 0 = 4 0 = 6C P eCM
,
(:7
I
*
)
I
102
"-'t
~
I
!' 'i.;,:°? -"
'( t',, ~
2(7 4 0 ° 6 0 * eCM
' ~'t
÷~
170' As
"J~ "t~" J
0o
I I
').*. ~ ~ t'
102 .
;..t* , 9 ',
I '
150
!f++~
°' i!
'
$. 5.24 ¢ ** .
10 3
(,
I
unassorted f value
i
I
i
I
*
I
I
2 0 = 4 0 o 6 0 ° 0C M
i
Qo
I
*
I
l
I
2(:7 4 0 = 6 0 = OCM
Fig. 2. Angular distributions for the (3He, a) reactions on 160 and 180. The absolute cross sections are determined to about an accuracy of 25% for both isotopes. The dotted curves are the DWBA calculations using the following parameters: V Wvo1 r rc a rw aw [MeV l [MeV] [fm] [fm] [fm] [fm] [fm] 3He bound state
165 238
9.96 30.
1.22 1.226
1.3 1.3
0.8 0.626
2.17 1.342
1.25
1.3
0.65
~.=0
m o m e n t u m . In a d d i t i o n to the l = 1 t r a n s i t i o n s , one e x p e c t s to o b s e r v e p o s i t i v e p a r i t y T = s t a t e s , s i n c e the 1 8 0 g r o u n d s t a t e i s known to h a v e s i z a b l e p r o t o n p a r t i c l e - h o l e c o m p o n e n t s [8]. The e x p e r i m e n t w a s p e r f o r m e d w i t h a 16 MeV 3He b e a m f r o m the H e i d e l b e r g EN T a n d e m Van de G r a a f f a c c e l e r a t o r and a b r o a d r a n g e m a g n e t i c s p e c t r o g r a p h f o r the a n a l y s i s of the a p a r t i c l e s . T h e t a r g e t s w e r e m a d e by e v a p o r a t i o n of about 80 / ~ g / c m 2 of t u n g s t e n on a 30 / ~ g / c m 2 c a r b o n b a c k i n g and o x y d a t i o n of the t u n g s t e n in an 1 8 0 atmosphere. The targets contained typically 10 g g / c m 2 of 1 8 0 and about 6 ~ g / c m 2 of 1 6 0 , t h e r a t i o of the two i s o t o p e s b e i n g d e t e r m i n e d by a study of e l a s t i c s c a t t e r i n g . Fig. 1 presents a typical a-particle spectrum at f o r w a r d a n g l e s . T h e T = ~ l e v e l s a r e i d e n t i f i e d t h r o u g h the u s u a l c r i t e r i a of the e n h a n c e d e x c i t a t i o n and n a r r o w l i n e width a s c o m p a r e d to the w e a k l y e x c i t e d n e i g h b o u r i n g T = ½ s t a t e s and by t h e i r e n e r g y c o r r e s p o n d e n c e w i t h the p a r e n t s t a t e s in 17N. T h e e n e r g y c a l i b r a t i o n w a s p r o v i d e d by the l o c a t i o n of n e i g h b o u r i n g 1 5 0 s t a t e s r e s u l t i n g f r o m the 1 6 0 c o n t a m i n a n t in t h e t a r g e t . 30
0.8 0.695
T h e e x c i t a t i o n e n e r g i e s of the 1 5 0 s t a t e s w e r e t a k e n f r o m the c o m p i l a t i o n of W a r b u r t o n et al. [9], and f r o m s o m e m o r e r e c e n t d a t a [10]; t h e y a r e a c c u r a t e to within a few keV o r l e s s . T a b l e 1 l i s t s the p o s i t i o n s of the o b s e r v e d T = ~ s t a t e s in 170. F o r c o m p a r i s o n w i t h the 17N l e v e l s c h e m e , the c o r r e s p o n d i n g e n e r g y d i s t a n c e s to the l o w e s t T = ~ s t a t e s in 1 7 0 and 17F a r e a l s o given. The l a b e l l i n g of i s o b a r i c m u l t i p l e t s f r o m 0 to 10 a c c o r d i n g to the known 17N s t a t e s is o n l y f o r the s a k e of c l a r i t y . T h e o r d e r i n g of l e v e l s in 1 7 0 m i g h t be r e v e r s e d when l e v e l s a r e v e r y c l o s e , a s f o r the 2 - 3 and 5-6 d o u b l e t s . Fig. 2 s h o w s the a n g u l a r d i s t r i b u t i o n s of the 1 7 0 a n a l o g u e s t a t e s and, f o r c o m p a r i s o n , of s o m e 1 5 0 s t a t e s e x c i t e d in t h e s a m e e x p e r i m e n t . F o r l = 0 and l = 1 t r a n s f e r s , the 1 5 0 and 1 7 0 a n g u l a r d i s t r i b u t i o n s a r e quite s i m i l a r . T h e s h a p e of the l = 2 a n g u l a r d i s t r i b u t i o n s i s l e s s c h a r a c t e r i s t i c , but it h a s b e e n shown [7] t h a t the e x c i t a t i o n f u n c t i o n s of the l = 2 t r a n s i t i o n s in 1 6 0 ( 3 H e , a ) 1 5 0 e x h i b i t f l u c t u a t i o n s at f o r w a r d a n g l e s for i n c i d e n t 3He e n e r g i e s c l o s e to 16 MeV. T h e D W B A c a l c u l a t i o n s fit the l = 0 and l = 1 d i s -
Volume 29B, number 1
PHYSICS
LETTERS
31 March 1969
Table 1 Summary of the properties of the T =-32, A = 17 levels including the locations, spins, parities and spectroscopic factors obtained in the present 180(3He,a)170 experiment. Ex [keVl in 170 Energy distance [MeV] to the lowest T=~state in spin spectroscopic and factor state this previous no. experiment value [3] 17N(Tz -_ 3_) 2 [2] 170(Tz = ½) 17F(Tz = _ ½)b) In-transfer parity C2S 0
11082±
6
11075-6
O.00
0.00
0.00
1
1
12471±
5
12469~-5
1.37
1.389
1.360
1
!-c) 3-c)
0.49 0.27
0
½+
0.096
2
(~+)
0.39
2
12950±
8
12948+5
1.85
1.868
3
12 994 ~
8
12 996 ± 5
1.91
1.912
4
13 640 ± 5
13 635 ~- 5
5
14219=e
8
2.54
2.558
3.13
3.137 3.200
6
14282 ~- 12
3.21
7
a)
3.65
15 101=e 8
4.01
9
a)
4.22
10
a)
4.47
8
2
1.865
3.115
4.019
a) No evidence was found for the excitation of these levels at the expected excitation energies, b) F r o m the compilalation of ref. 1. c) Spin assignments f r o m ref. 6. t r i b u t i o n s of 1 7 0 q u i t e w e l l . T h e l = 2 fit i s l e s s satisfactory. T h e s p e c t r o s c o p i c f a c t o r s shown in t a b l e 1 were calculated assuming a spectroscopic factor C2S = 4 f o r t h e 6.18 MeV p , h o l e s t a t e in 150. A s e x p e c t e d [11] t h e low~est a n a l o g u e s t a t e A o c o n t a i n s a l a r g e f r a c t i o n of t h e p~ s t r e n g t h . H o w e v e r , t h e s p e c t r o s c o p i c f a c t o r C 2 S = 0.49 l i e s s o m e w h a t b e l o w t h e s u m r u l e l i m i t C2S (T =~ )=~ f o r an i n e r t 1 6 0 c o r e , e v e n though the u s u a l DWBA p r o c e d u r e of v a r y i n g t h e w e l l depth of t h e bound s t a t e p o t e n t i a l often o v e r e s t i m a t e s t h e s p e c t r o s c o p i c f a c t o r s f o r t h e a n a l o g u e s t a t e s [13]. T h e t r a n s i t i o n to the ~ - A 1 s t a t e c a r r i e s r o u g h ly one fifth of t h e p o s s i b l e p , s t r e n g t h . T h e r e f o r e , t h i s l e v e l m a y be i d e n t i f i e d ~ts a p r e d o m i n a n t l y [180~.+, ( p , ) - i ] 4 _ s t a t e a s p r e d i c t e d by t h e o r e t i c a l calcu'katlons [11,12]. T h e r e m a i n i n g p~ s t r e n g t h w o u l d be e x p e c t e d at h i g h e r e x c i t a t i o n e n e r g i e s . H o w e v e r , t h e p r e s e n c e of e l a s t i c a l l y s c a t t e r e d 3 H e - p a r t i c l e s p r e c l u d e d t h e o b s e r v a t i o n of a p a r t i c l e g r o u p s in t h i s r e g i o n . T h e l a r g e v a l u e s of t h e s p e c t r o s c o p i c f a c t o r s for the positive parity states imply a relatively l a r g e a m o u n t of 2 p - 2 h p r o t o n c o n f i g u r a t i o n in t h e 1 8 0 g r o u n d s t a t e w a v e function. T h i s i s c o n s i s t e n t with the r a t h e r s m a l l s p e c t r o s c o p i c f a c t o r o b s e r v e d f o r t h e ½- A o s t a t e . T h e r a t i o of 2s½ to l d ~ s t r e n g t h s e e m s v e r y r e a s o n a b l e ; it i s s i m i l a r to t h e r a t i o of 2s,_ and ld_~ n e u t r o n c o m p o n e n t s in 1 8 0 , a s calcul~tted by 17~edlich [14] a n d Kuo and B r o w n [15]. •
~
°
.
T h e w e a k A3, A5, A 6 and A 8 s t a t e s do c o r r e s pond to e x c i t e d s t a t e s in 17N, a s shown in t a b l e 1. Their uncharacteristic angular distributions, h o w e v e r , do not a l l o w an / - t r a n s f e r a s s i g n m e n t . T h e s e s t a t e s m i g h t be i d e n t i f i e d a s t h e n e g a t i v e p a r i t y s t a t e s p r e d i c t e d in t h i s r e g i o n [11,12] w h o s e c o l l e c t i v e c o m p o n e n t s in t h e w a v e f u n c t i o n s c a n n o t be s t r o n g l y p o p u l a t e d in the (3He, a) reaction. We l i k e to t h a n k C. S c h m i d t f o r v a l u a b l e h e l p in the p e r f o r m a n c e of t h e e x p e r i m e n t . One of u s (C.D.) t a k e s t h i s o p p o r t u n i t y to e x p r e s s h i s g r a t i t u d e to P r o f . W. G e n t n e r f o r the kind h o s p i t a l i t y e x t e n d e d to h i m at the M a x - P l a n c k - I n s t i t u t e .
.
References 1. J. Cerny, Ann. Rev.of Nucl.Science 18 (1968) 27. 2. V . P . Hart, E. Norbeck and R. R. Carlson, Phys• Rev. 137 (1965) B17. 3. C.A. Barnes, E. G. Adelberger, D.C. Hensley and A. B. McDonald, private communication to J. Cerny, quoted in ref. 1. 4. For complete references, see ref. 1. 5. R.A. Esterlund, R. Me Pherson, A.M. Poskanzer and P. L. Reeder, Phys. Rev. 156 (1967) 1094. 6. J . R . Patterson, H. Winkler and C. S. Zaidius, Phys. Rev. 163 (1967) 1051; E. G. Adelberger and C. A. Barnes, Phys. Letters 23 (1966) 474; M. G. Silbert and J. C. Hopkins, Phys. Rex,. 134 {1964) B16; G. M. Temmer, Dubna Symposium 1968, p.249. 31
Volume 29B, number 1
PHYSICS
7. H.Schimetzek, Diplomarbeit, Max-Planck-Institut fiir Kernphysik, Heidelberg (1966) unpublished. 8. J . R . Erskine et al., Phys. L e t t e r s 14 (1965) 915; E . R o s t , Phys. L e t t e r s 21 (1966) 87; C. O. Lennon et al., Phys. L e t t e r s 28 (1968) 253; C. Schmidt and H. H. Duhm, to be published. 9. E . K . Warburton, J.W. Olness and D. E. Alburger, Phys.Rev.140 (1965) B1202.
32
LETTERS
31 March 1969
10. D.E. Alburger and E . K . Warburton, Phys. Rev. 152 (1966) 914. 11. B. Margolis and N. de Takacsy, Can. J. Phys. 44 (1966) 1431. 12. M. Soga, Nucl. Phys. 89 (1966) 697. 13. R. Stock and T. Tamura, Phys. L e t t e r s 22 (1966) 304 and r e f e r e n c e s therein. 14. M. Redlicht, Phys. Rev. 110 (1958) 468. 15. T . T . S . K u o and G.E. Brown, Nucl. Phys. 85 (1966) 40.
PHYSICS
A STUDY
OF
THE
LETTERS
T = {
31 March 1969
STATES
OF
170
C. D E T R A Z * and H. H. DUHM Max-Planck-lnstitut fi~r Kernphys ik , Heidelberg, Germany Received 5 M a r c h 1969
Eight analogue T = { excited states in 170 have been identified with the 180(3He, Ot)170 reaction at E(3He) = 16 MeV. The l - t r a n s f e r values and spectroscopic factors are presented for four of these states.
In r e c e n t y e a r s , m u c h i n f o r m a t i o n . h a s b e e n o b t a i n e d c o n c e r n i n g t h e l o c a t i o n s and, to a l e s s e r e x t e n t , t h e s p i n s and p a r i t i e s of h i g h - i s o s p i n s t a t e s in light n u c l e i [1]. A s f o r the T = {, A = = 17 s t a t e s , s o m e 24 s t a t e s in 17N(Tz =~ ) [2], 5 s t a t e s in 1 7 0 ( Tz = ½) [3], 4 s t a t e s in 17F (T z = ½) [4] h a v e b e e n l o c a t e d so f a r ; the f o u r t h m e m b e r of t h e i s o b a r i c q u a d r u p l e t , 17Ne ( T z = = - {), h a s b e e n c h a r a c t e r i z e d a s a b e t a - d e l a y e d p r o t o n e m i t t e r and an a p p r o x i m a t e v a l u e of i t s m a s s (~:250 MeV) h a s b e e n o b t a i n e d [5]; t h e s p i n s and p a r i t i e s of t h e two l o w e s t - l y i n g T = {, A = 17
60
65 T
- - T
s t a t e s a p p e a r to be u n a m b i g u o u s l y c h a r a c t e r i z e d a s ½- and { - r e s p e c t i v e l y [6]. In o r d e r to o b t a i n m o r e i n f o r m a t i o n about t h e l o c a t i o n s , s p i n s and p a r i t i e s of the T = 5 a n a l o g u e s t a t e s of 1 7 0 , we h a v e s t u d i e d t h e 1 8 0 ( 3 H e , a ) 1 7 0 r e a c t i o n . T h e a d v a n t a g e of u s i n g t h i s r e a c t i o n f o r t h e study of the T = ~ s t a t e s is t h a t the Q v a l u e i s c l o s e to 0 MeV w h i c h p r o v i d e s a l m o s t optimal momentum matching conditions. Conseq u e n t l y the s t r o n g a n a l o g u e t r a n s i t i o n s should exhibit pronounced diffraction patterns allowing t h e d e t e r m i n a t i o n of t h e t r a n s f e r r e d a n g u l a r
70 T
Distance along the Focal Plane Ecm3 75 80 85 T 1 T ~
lSO(3He, a )170
"E
.U
,o
E ,40O
,
04 x
E3
A2
"I°Ni
=16MeV,5 °
I '~ ~|
He
~o
~, 3oo e~ if)
~ 2oo L
A1
A4
100 0
!
11
12
13
l
1
14 15 Excitation Energy in1~Z)Evle~
Fig. 1. 180(3He,Oz)lTo spectrum for excitation energies in 170 between 11 MeV and 15.5 MeV. The states labelled with a capital A are interpreted as the T = ~ analogue states in 170. The impurity groups arising from 12C and 160 contaminations in the target are indicated by the excitation energies of the residual nuclei.
* On leave from Institut de Physique Nucl6aire, Orsay, France. 29
Volume 29B, number 1
PHYSICS
160(3He,ot)150 l
t
i
i
I i
LETTERS
and 180(3He,(z)170
E3He=16MeV I
I ,
[ =0
Io 4 ('~.
." . 150519
103
=1
t'
",, ,:'.,506. ~
•
31 March 1969
i
"'+.
f=2 ' i
, i
*%
170, A3
*
1506.79
170, A 0 10 2
,+~f+f. ~7o,A s
~ ~t
"t+ fl
10 3
O"
~'/
I , I = I * 2 0 = 4 0 = 6C P eCM
,
(:7
I
*
)
I
102
"-'t
~
I
!' 'i.;,:°? -"
'( t',, ~
2(7 4 0 ° 6 0 * eCM
' ~'t
÷~
170' As
"J~ "t~" J
0o
I I
').*. ~ ~ t'
102 .
;..t* , 9 ',
I '
150
!f++~
°' i!
'
$. 5.24 ¢ ** .
10 3
(,
I
unassorted f value
i
I
i
I
*
I
I
2 0 = 4 0 o 6 0 ° 0C M
i
Qo
I
*
I
l
I
2(:7 4 0 = 6 0 = OCM
Fig. 2. Angular distributions for the (3He, a) reactions on 160 and 180. The absolute cross sections are determined to about an accuracy of 25% for both isotopes. The dotted curves are the DWBA calculations using the following parameters: V Wvo1 r rc a rw aw [MeV l [MeV] [fm] [fm] [fm] [fm] [fm] 3He bound state
165 238
9.96 30.
1.22 1.226
1.3 1.3
0.8 0.626
2.17 1.342
1.25
1.3
0.65
~.=0
m o m e n t u m . In a d d i t i o n to the l = 1 t r a n s i t i o n s , one e x p e c t s to o b s e r v e p o s i t i v e p a r i t y T = s t a t e s , s i n c e the 1 8 0 g r o u n d s t a t e i s known to h a v e s i z a b l e p r o t o n p a r t i c l e - h o l e c o m p o n e n t s [8]. The e x p e r i m e n t w a s p e r f o r m e d w i t h a 16 MeV 3He b e a m f r o m the H e i d e l b e r g EN T a n d e m Van de G r a a f f a c c e l e r a t o r and a b r o a d r a n g e m a g n e t i c s p e c t r o g r a p h f o r the a n a l y s i s of the a p a r t i c l e s . T h e t a r g e t s w e r e m a d e by e v a p o r a t i o n of about 80 / ~ g / c m 2 of t u n g s t e n on a 30 / ~ g / c m 2 c a r b o n b a c k i n g and o x y d a t i o n of the t u n g s t e n in an 1 8 0 atmosphere. The targets contained typically 10 g g / c m 2 of 1 8 0 and about 6 ~ g / c m 2 of 1 6 0 , t h e r a t i o of the two i s o t o p e s b e i n g d e t e r m i n e d by a study of e l a s t i c s c a t t e r i n g . Fig. 1 presents a typical a-particle spectrum at f o r w a r d a n g l e s . T h e T = ~ l e v e l s a r e i d e n t i f i e d t h r o u g h the u s u a l c r i t e r i a of the e n h a n c e d e x c i t a t i o n and n a r r o w l i n e width a s c o m p a r e d to the w e a k l y e x c i t e d n e i g h b o u r i n g T = ½ s t a t e s and by t h e i r e n e r g y c o r r e s p o n d e n c e w i t h the p a r e n t s t a t e s in 17N. T h e e n e r g y c a l i b r a t i o n w a s p r o v i d e d by the l o c a t i o n of n e i g h b o u r i n g 1 5 0 s t a t e s r e s u l t i n g f r o m the 1 6 0 c o n t a m i n a n t in t h e t a r g e t . 30
0.8 0.695
T h e e x c i t a t i o n e n e r g i e s of the 1 5 0 s t a t e s w e r e t a k e n f r o m the c o m p i l a t i o n of W a r b u r t o n et al. [9], and f r o m s o m e m o r e r e c e n t d a t a [10]; t h e y a r e a c c u r a t e to within a few keV o r l e s s . T a b l e 1 l i s t s the p o s i t i o n s of the o b s e r v e d T = ~ s t a t e s in 170. F o r c o m p a r i s o n w i t h the 17N l e v e l s c h e m e , the c o r r e s p o n d i n g e n e r g y d i s t a n c e s to the l o w e s t T = ~ s t a t e s in 1 7 0 and 17F a r e a l s o given. The l a b e l l i n g of i s o b a r i c m u l t i p l e t s f r o m 0 to 10 a c c o r d i n g to the known 17N s t a t e s is o n l y f o r the s a k e of c l a r i t y . T h e o r d e r i n g of l e v e l s in 1 7 0 m i g h t be r e v e r s e d when l e v e l s a r e v e r y c l o s e , a s f o r the 2 - 3 and 5-6 d o u b l e t s . Fig. 2 s h o w s the a n g u l a r d i s t r i b u t i o n s of the 1 7 0 a n a l o g u e s t a t e s and, f o r c o m p a r i s o n , of s o m e 1 5 0 s t a t e s e x c i t e d in t h e s a m e e x p e r i m e n t . F o r l = 0 and l = 1 t r a n s f e r s , the 1 5 0 and 1 7 0 a n g u l a r d i s t r i b u t i o n s a r e quite s i m i l a r . T h e s h a p e of the l = 2 a n g u l a r d i s t r i b u t i o n s i s l e s s c h a r a c t e r i s t i c , but it h a s b e e n shown [7] t h a t the e x c i t a t i o n f u n c t i o n s of the l = 2 t r a n s i t i o n s in 1 6 0 ( 3 H e , a ) 1 5 0 e x h i b i t f l u c t u a t i o n s at f o r w a r d a n g l e s for i n c i d e n t 3He e n e r g i e s c l o s e to 16 MeV. T h e D W B A c a l c u l a t i o n s fit the l = 0 and l = 1 d i s -
Volume 29B, number 1
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LETTERS
31 March 1969
Table 1 Summary of the properties of the T =-32, A = 17 levels including the locations, spins, parities and spectroscopic factors obtained in the present 180(3He,a)170 experiment. Ex [keVl in 170 Energy distance [MeV] to the lowest T=~state in spin spectroscopic and factor state this previous no. experiment value [3] 17N(Tz -_ 3_) 2 [2] 170(Tz = ½) 17F(Tz = _ ½)b) In-transfer parity C2S 0
11082±
6
11075-6
O.00
0.00
0.00
1
1
12471±
5
12469~-5
1.37
1.389
1.360
1
!-c) 3-c)
0.49 0.27
0
½+
0.096
2
(~+)
0.39
2
12950±
8
12948+5
1.85
1.868
3
12 994 ~
8
12 996 ± 5
1.91
1.912
4
13 640 ± 5
13 635 ~- 5
5
14219=e
8
2.54
2.558
3.13
3.137 3.200
6
14282 ~- 12
3.21
7
a)
3.65
15 101=e 8
4.01
9
a)
4.22
10
a)
4.47
8
2
1.865
3.115
4.019
a) No evidence was found for the excitation of these levels at the expected excitation energies, b) F r o m the compilalation of ref. 1. c) Spin assignments f r o m ref. 6. t r i b u t i o n s of 1 7 0 q u i t e w e l l . T h e l = 2 fit i s l e s s satisfactory. T h e s p e c t r o s c o p i c f a c t o r s shown in t a b l e 1 were calculated assuming a spectroscopic factor C2S = 4 f o r t h e 6.18 MeV p , h o l e s t a t e in 150. A s e x p e c t e d [11] t h e low~est a n a l o g u e s t a t e A o c o n t a i n s a l a r g e f r a c t i o n of t h e p~ s t r e n g t h . H o w e v e r , t h e s p e c t r o s c o p i c f a c t o r C 2 S = 0.49 l i e s s o m e w h a t b e l o w t h e s u m r u l e l i m i t C2S (T =~ )=~ f o r an i n e r t 1 6 0 c o r e , e v e n though the u s u a l DWBA p r o c e d u r e of v a r y i n g t h e w e l l depth of t h e bound s t a t e p o t e n t i a l often o v e r e s t i m a t e s t h e s p e c t r o s c o p i c f a c t o r s f o r t h e a n a l o g u e s t a t e s [13]. T h e t r a n s i t i o n to the ~ - A 1 s t a t e c a r r i e s r o u g h ly one fifth of t h e p o s s i b l e p , s t r e n g t h . T h e r e f o r e , t h i s l e v e l m a y be i d e n t i f i e d ~ts a p r e d o m i n a n t l y [180~.+, ( p , ) - i ] 4 _ s t a t e a s p r e d i c t e d by t h e o r e t i c a l calcu'katlons [11,12]. T h e r e m a i n i n g p~ s t r e n g t h w o u l d be e x p e c t e d at h i g h e r e x c i t a t i o n e n e r g i e s . H o w e v e r , t h e p r e s e n c e of e l a s t i c a l l y s c a t t e r e d 3 H e - p a r t i c l e s p r e c l u d e d t h e o b s e r v a t i o n of a p a r t i c l e g r o u p s in t h i s r e g i o n . T h e l a r g e v a l u e s of t h e s p e c t r o s c o p i c f a c t o r s for the positive parity states imply a relatively l a r g e a m o u n t of 2 p - 2 h p r o t o n c o n f i g u r a t i o n in t h e 1 8 0 g r o u n d s t a t e w a v e function. T h i s i s c o n s i s t e n t with the r a t h e r s m a l l s p e c t r o s c o p i c f a c t o r o b s e r v e d f o r t h e ½- A o s t a t e . T h e r a t i o of 2s½ to l d ~ s t r e n g t h s e e m s v e r y r e a s o n a b l e ; it i s s i m i l a r to t h e r a t i o of 2s,_ and ld_~ n e u t r o n c o m p o n e n t s in 1 8 0 , a s calcul~tted by 17~edlich [14] a n d Kuo and B r o w n [15]. •
~
°
.
T h e w e a k A3, A5, A 6 and A 8 s t a t e s do c o r r e s pond to e x c i t e d s t a t e s in 17N, a s shown in t a b l e 1. Their uncharacteristic angular distributions, h o w e v e r , do not a l l o w an / - t r a n s f e r a s s i g n m e n t . T h e s e s t a t e s m i g h t be i d e n t i f i e d a s t h e n e g a t i v e p a r i t y s t a t e s p r e d i c t e d in t h i s r e g i o n [11,12] w h o s e c o l l e c t i v e c o m p o n e n t s in t h e w a v e f u n c t i o n s c a n n o t be s t r o n g l y p o p u l a t e d in the (3He, a) reaction. We l i k e to t h a n k C. S c h m i d t f o r v a l u a b l e h e l p in the p e r f o r m a n c e of t h e e x p e r i m e n t . One of u s (C.D.) t a k e s t h i s o p p o r t u n i t y to e x p r e s s h i s g r a t i t u d e to P r o f . W. G e n t n e r f o r the kind h o s p i t a l i t y e x t e n d e d to h i m at the M a x - P l a n c k - I n s t i t u t e .
.
References 1. J. Cerny, Ann. Rev.of Nucl.Science 18 (1968) 27. 2. V . P . Hart, E. Norbeck and R. R. Carlson, Phys• Rev. 137 (1965) B17. 3. C.A. Barnes, E. G. Adelberger, D.C. Hensley and A. B. McDonald, private communication to J. Cerny, quoted in ref. 1. 4. For complete references, see ref. 1. 5. R.A. Esterlund, R. Me Pherson, A.M. Poskanzer and P. L. Reeder, Phys. Rev. 156 (1967) 1094. 6. J . R . Patterson, H. Winkler and C. S. Zaidius, Phys. Rev. 163 (1967) 1051; E. G. Adelberger and C. A. Barnes, Phys. Letters 23 (1966) 474; M. G. Silbert and J. C. Hopkins, Phys. Rex,. 134 {1964) B16; G. M. Temmer, Dubna Symposium 1968, p.249. 31
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7. H.Schimetzek, Diplomarbeit, Max-Planck-Institut fiir Kernphysik, Heidelberg (1966) unpublished. 8. J . R . Erskine et al., Phys. L e t t e r s 14 (1965) 915; E . R o s t , Phys. L e t t e r s 21 (1966) 87; C. O. Lennon et al., Phys. L e t t e r s 28 (1968) 253; C. Schmidt and H. H. Duhm, to be published. 9. E . K . Warburton, J.W. Olness and D. E. Alburger, Phys.Rev.140 (1965) B1202.
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10. D.E. Alburger and E . K . Warburton, Phys. Rev. 152 (1966) 914. 11. B. Margolis and N. de Takacsy, Can. J. Phys. 44 (1966) 1431. 12. M. Soga, Nucl. Phys. 89 (1966) 697. 13. R. Stock and T. Tamura, Phys. L e t t e r s 22 (1966) 304 and r e f e r e n c e s therein. 14. M. Redlicht, Phys. Rev. 110 (1958) 468. 15. T . T . S . K u o and G.E. Brown, Nucl. Phys. 85 (1966) 40.