Volume 18, number 2
PHYSICS LETTERS
3. M.R.Cleland, J.Towsend and A.L.Hughes, Phys.
Rev. 84 (1951) 298.
4. H.Langhoff, P.Kilian and A.Flsmmersfeld, Z.
Phys. 165 (1961) 387.
5. S.D.Bloom, Phys. Rev. 88 (1952) 312.
LEVELS
OF
20Ne
FROM
15 August 1965
6. H.SlJ[tis and K.Siegbahn, Arkiv Fysik 4 (1952) 485.
7. J . C . J a e g e r a n d H . R . I b d m e , Proc.Roy.Soc.Lond.
148 (1935) "/08.
8. S.A.S.Brimberg, Phys. Rev. 87 (1952) 150.
RADIATIVE
IN 160
ALPHA-CAPTURE
C. VAN D E R LEUN, D. M. S H E P P A R D and P. J. M. SMULDERS
Fysisch Labo~to~ium R. U., Utlfecht, The NetherZmuis
Received 14 July 1968
R a d i a t i v e a l p h a - c a p t m ' e in 1 6 0 i s c o n s i d e r e d
to be the p r i n c i p a l p r o c e s s in the s t e l l a r p r o d u c tion of 20Ne. The r a t e of t h i s p r o c e s s d e p e n d s
c r i t i c a l l y on the proj~erUes of the 4.97, 5.62 and
. 5 . 7 9 MeV l e v e l s of ~'t~Ne [1]. The J ~ = 2- a s s i g n m e n t to the 4.97 MeV l e v e l e x c l u d e s t h i s l e v e l
f r o m c o n t r i b u t i n g to t h e s y n t h e s i s of 20Ne [2].
The i n v e s t i g a t i o n of the 1 6 0 ( a , ~ ) 2 0 N e r e a c t i o n ,
r e p o r t e d h e r e , w a s u n d e r t a k e n to d e t e r m i n e the
r e s o n a n c e s t r e n g t h s and v a r t i a l widths of the
" a s t r o p h y s i c a l l e v e l s of 20Ne" [3] at 5.62 and
5.79 MeV, with J ~ = 3- and 1" r e s p e c t i v e l y [4],
and a l s o t h o s e of the next l e v e l at 6.72 MeV,
'60(aN)2°Ne ; TARGETSi02
I
I
I
I
CHANNEL:(EyI-O7MeV)-(EypQ2MeV)
CRYSTALS:TWOlOxlOcmNoI
leO(a,n)21Ne
D'alcm
500 _
400
0-90"
o~2.490
1.319
O
=L
with J~ = 0 + [5].
F r o m the viewpoint of nuclear structure
s t u d i e s , t h e s e m e a s u r e m e n t s are a l s o of i n t e r e s t ,
s i n c e they e x t e n d the r e c e n t d e t e r m i n a t i o n s of the
r a d i a t i v e w i d t h s of the l o w - l y i n g 20Ne l e v e l s [6]
to the next h i g h e r e x c i t e d s t a t e s .
In the r a n g e s of i n t e r e s t 1 6 0 ( a , y)20Ne y i e l d
c u r v e s w e r e m e a s u r e d w i t h n a t u r a l SiO 2 and
CaO t a r g e t s . One of t h e s e i s given in fig. 1. The
two l o w e s t r e s o n a n c e s s t a n d out c l e a r l y , but the
t h i r d one i s p a r t i a l l y o b s c u r e d by t h e I 8 0 ( ~ , n)21Ne
r e s o n a n c e a t 2.47 MeV [7], which p r o d u c e s n e u t r o n - c a p t u r e g a m m a r a y s . M e a s u r e m e n t s of the
g a m m a - r a y s p e c t r a at the t h r e e r e s o n a n c e s conf i r m the a s s i g n m e n t to the r e a c t i o n u n d e r i n v e s tigation. So f a r , a s e a r c h f o r the doubtful l e v e l
at 6.17 MeV [8] h a s been i n c o n c l u s i v e .
A s u r v e y of the r e s o m m c e d ~ i s g i v e n in
t a b l e 1. The 28Si(e, T)$2S r e s o n a n c e at 2 6 1 8 , 4
keV [9], m e a s u r e d with the s a m e t a r g e t , w a s
u s e d for the e n e r g y c a l i b r a t i o n . The "VNe e x c i tation e n e r g i e s a r e c a l c u l a t e d w i t h the r e a c t i o n
Q value, Q = 4729.7 ~- 0.5 k e V [10]. The r e s o n a n c e s t r e n g t h s , d e t e r m i n e d f r o m the y i e l d of a
thick SiO 2 t a r g e t , i n d i c a t e that the c o n t r i b u t i o n
134
30C
z
/
0
U
20C
1
1~16
100
O
0
O0
11
1.2
O0
1.3
~Ea(MeV)
,i.i4 ,{~
[
t
i
245
2.50
2.55
Fig. 1. Yield curve of the 160(a,y)Z0Ne reaotio~ m e a s ured with a SiO2 target. Tim p~mts r e p r e l e s t the ~um
of the ~mmher of pulses ~
in two 10 × 10 cm ~ NaI
crystals, positto~0ed as clos e t o t h e target as possible
(D = 1 cm) at 90 ° with respect to the proton beam. The
gamma-ray channel, 0.9 MeV wide, was ~ l y
ad,
justed to l n o ~
prtmm-fly the trausltS~m to "~Ne(1.63).
Room-bao~
has beem ~ .
The detted line
sivas ~the s]:mpe Of the ( u , a ) r ~ a ~ a c e as measured
with a higher s e t t t ~ of the Bmmna-ray channel.
Volume 18, number 2
PHYSICS LETTERS
15 August 1965
Table 1
Resonances in the reaction 160(~ ,7)20Ne.
E~
20Ne*
(keV)
(keV)
main decay (in perc.)
1116 + 4
1319+3
2490m8
5623 + 4
< 15
100
5785±3
6722+8
18±5
< 10
82+5
100
7o
(2J + 1)FrFr,/I"
~1
j ~ a)
(meV)
1.4 + 0.4
12
33
3-
+ 3
±16
I+
I'~, b)
F~ c)
(meV)
(meV)
0.20
2.6 3
>13X10
19X106
4.0
33
e2d)
0.006
>0.9
0.7
a) Literature values [4, 5]. The spin and parity of the 1319 keV resonance were confirmed in an angular distribution
measurement of the ground-state transition.
Fol >>rv[12], therefore r [ ro/r-- .
cb)) The
wldihs" of the first two resonances are calculated from r~,, using the relation r ~ / r = 0.077 and <3 × 10 "~,
respectively [12]; for the 2490 keV resonance r,v is given in ref. 7; this value is in hgreement with cur rough
estimate of 15 ± 7 keV.
d) Calculated with ~'o = 1.2 fro.
Table 2
Transition strengths in 20Ne.
Ea(keV)
ET(MeV)
Transition
Ji " Jf
Type
1116
(5.62)
3.98 ± 0.03
5.81 + 0.06
4.17 ;k 0.03
6.62-* O
5.62 --* 1.63
5.79--, 0
5.79 --~ 1.63
3---* O+
3- --, 2+
1---* 0+
1- --* 2+
5.13 + 0.04
6.72 --~ 1.63
0+ --* 2+
E3
E1
E1
E1
M2
E2
1319
2490
r ~ (meV)
0.017 a)
0.20 b)
0.7
3.3
~ 0.016
34
IM 12 = r 7 / F ~ w
10
6.3 x 10-6
7.2 X 10-_~
9.2 X 10-5
~< 0.12
3.8
a) Calculated with the branching ratio given in ref. 13.
b) Within the experimental errors, this value is in agreement with recent lifetime measurements [6,13].
of the 5.79 MeV l e v e l to the s y n t h e s i s of 201~e
might be an o r d e r of magnitude higher than that
of the 5.62 MeV l e v e l . The l a s t c o l u m n s of table 1
give the p a r t i a l widths deduced f r o m the r e s o n a n c e s t r e n g t h s . The l a r g e 82 of the 5//9 MeV
l e v e l i s c o n s i s t e n t with the l a r g e v a l u e s found
for other l e v e l s in the s a m e r o t a t i o n a l band.
The g a m m a - r a y e n e r g i e s m e a s u r e d at the
t h r e e r e s o n a n c e s a r e l i s t e d in table 2. Since j1r
i s known for a l l l e v e l s involved in the decay,
the type of r a d i a t i o n i s u n a m b i g u o u s for a l l t r a n s i t i o n s to o r f r o m a ff~ = 0 + level. The amplitude
m i x i n g r a t i o of the 4 . 1 " / g a m m a ray, x =
-0.03 ± 0.04, was d e t e r m i n e d f r o m the a n a l y s i s
of double and t r i p l e a n g u l a r c o r r e l a t i o n m e a s u r e m e n t s at the 1319 keV r e s o n a n c e . The 3.98
MeV t r a n s i t i o n i s known to have n e a r l y pure
E1 c h a r a c t e r [13].
The I MI 2 - v a l u e s of the E1 t r a n s i t i o n s fall on
the low Side of the I M[ 2 - d i s t r i b u t i o n for T - f o r bidden E1 t r a n s i t i o n s in A = 2 0 - 4 0 n u c l e i [11].
T h i s might r e f l e c t on the T - s p i n p u r i t y of these
r e l a t i v e l y l o w - l y i n g 20Ne l e v e l s . The s t r e n g t h of
the 3.98 MeV E1 t r a n s i t i o n is i n s u f f i c i e n t l y low
for the i n t e r f e r e n c e of any AK = 2 inhibition.
The s t r e n g t h of the 5.13 MeV i n t e r b a n d E2
t r a n s i t i o n , which f a l l s within the n o r m a l r a n g e
of E2 s t r e n g t h s i n A = 20-40 nuclei, i s about
a factor of four l o w e r than those of other r e -
cently m e a s u r e d i n t r a - b a n d E2 t r a n s i t i o n s in
20Ne [6].
This i n v e s t i g a t i o n was p a r t l y s u p p o r t e d by the
j o i n t p r o g r a m of the "Stichting voor F u n d e m e n teel Onderzoek d e r M a t e r i e " and the " N e d e r l a n d s e
O r g a n l s a t i e voor Z u i v e r Wetenschappelijk O n d e r zoek".
1. E.M.Burbidge, G.R.Burbidge, W.A.Fowler and
F.Hoyle, Revs.Mod.Phys.29 (1957) 547.
2. H.E.Gove, A.E.Litherlaud and M.A.Clark, Nature
191 (1961) 1381.
3. Expression from the Ch,lk River vocabulary, p r i vate communication.
4. J.A.Kuehner, Phys. Rev.125 (1962) 1650.
5. J.R.Cameron, Phys. Rev. 90 (1963) 839.
6. H.C.Evans, M.A.Eswaran, H.E.Gove, A.E.
Litherland and C. Broude, Can. J. Phys. 43 (1965) 82.
7. T.W.Bc~ncr, A.A.Kraus, J.B.Marion and J . P .
Schiffer, Phys. Rev. 102 (1956) 1348.
8. E.Almqvist and J.A.Kuehner, Proc.Rutherford
Jubilee Conf. (1961) 795.
9. P.J.M.Smulders, Physica 30 (1964) 1197.
1O. J.H.E.Mattauch, W.Thiele and A.H.Wapstra,
Nuclear Physics, to be published.
11. C.Van der Lcun, l>roc.Kansas Conf.o~ LowMedium Mass Nuclei (1964) 109.
12. E. A l m q v i s t and J. A. Kuehner, N u c l e a r P h y s . 56
(1964) 145.
13. A.E. Litherl~nd, Nuclear structure and electromagnetic interactions, ed. N. MacDonald (Oliver
and Boyd, Edinburgh, 1965) p.61.
135