53 On-Line Nuclear Orientation N. J . Stone
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Clarendon Laboratory, Parks Road, Oxford ΟΧ2 3PU, United Kingdom
A brief survey is given of the technique and its limiting parameters. Recent results on moments of proton rich iodine isotopes show shape coexistence and the presence of the g [404] intruder orbital for A ≥ 118. 9/2
As a t e c h n i q u e f o r m e a s u r i n g n u c l e a r moments and i n v e s t i g a t i n g n u c l e a r l e v e l s t r u c t u r e , low temperature n u c l e a r o r i e n t a t i o n has long been k e p t from a r e a s o f c u r r e n t a c t i v i t y i n l o w e n e r g y n u c l e a r p h y s i c s by t h e h a l f l i f e l i m i t a t i o n c a u s e d b y needs o f sample p r e p a r a t i o n and c o o l i n g t o b e l o w 1 K. The d e v e l o p m e n t o f He/ He d i l u t i o n r e f r i g e r a t o r s c a p a b l e o f c o n t i n u o u s l y m a i n t a i n i n g t e m p e r a t u r e s o f o r d e r 10 mK i n t h e p r e s e n c e o f h e a t f l u x o f o r d e r 1 opened up t h e p o s s i b i l i t y o f u s i n g t h e method o n - l i n e t o s o u r c e s o f a c t i v e i s o t o p e s . The m a g n e t i c h y p e r f i n e i n t e r a c t i o n e x p e r i e n c e d by n u c l e i o f a l l e l e m e n t s when p r e s e n t as d i l u t e i m p u r i t i e s i n f e r r o m a g n e t i c m e t a l s i s a q u a s i - u n i v e r s a l method o f p r o d u c i n g a p p r e c i a b l e p o l a r i z a t i o n a t s u c h t e m p e r a t u r e s . More r e c e n t l y s i n g l e c r y s t a l s o f n o n - c u b i c m e t a l s have come t o t h e f o r e as s u i t a b l e s o u r c e s f o r e l e c t r i c q u a d r u p o l e a l i g n m e n t , a l t h o u g h t h e t e m p e r a t u r e r e q u i r e d i s o f t e n l o w e r t h a n 10 mK. A f i n a l n e c e s s a r y i n n o v a t i o n has b e e n t h e d e v e l o p m e n t o f i m p l a n t a t i o n t e c h n i q u e s t o i n t r o d u c e n u c l e i o f many e l e m e n t s , w h e t h e r c h e m i c a l l y c o m p a t i b l e o r n o t , i n t o h o s t l a t t i c e s s u c h t h a t a m a j o r p r o p o r t i o n o f t h e i m p l a n t s come t o r e s t i n e s s e n t i a l l y undamaged s u b s t i t u t i o n a l s i t e s and e x p e r i e n c e l a r g e h y p e r f i n e i n t e r a c t i o n s . Such samples a r e t h i n , w i t h l i t t l e s e l f - a b s o r p t i o n f o r a l p h a - and b e t a particles . The c o m b i n a t i o n o f t h e s e t h r e e d e v e l o p m e n t s h a s l e d t o t h e o n - l i n e n u c l e a r o r i e n t a t i o n method (OLNO). A f u r t h e r advance o f t h e t e c h n i q u e h a s b e e n t h e c o m b i n a t i o n w i t h NMR, w h i c h u s e s r e s o n a n t r f p e r t u r b a t i o n o f t h e n u c l e a r p o l a r i z a t i o n , y i e l d i n g moment v a l u e s t o a f e w p a r t s i n 10 . The w i d e r a n g e o f e l e m e n t s i n w h i c h m a g n e t i c p o l a r i z a t i o n and e l e c t r i c a l i g n m e n t o f r a d i o a c t i v e n u c l e i have b e e n o b s e r v e d i s shown i n f i g u r e 1, w h i c h g i v e s a l s o t h e number o f i s o t o p e s i n w h i c h NMR/ON h a s b e e n d e t e c t e d . As w i t h c o n v e n t i o n a l n u c l e a r o r i e n t a t i o n , o n - l i n e work c a n y i e l d t h e s t r e n g t h o f t h e h y p e r f i n e i n t e r a c t i o n , deduced f r o m t h e t e m p e r a t u r e depen dence o f t h e r a d i a t i o n a n i s o t r o p y . F o r t h e m a j o r i t y o f e l e m e n t s i n F i g . 1 h o s t m e t a l s may be c h o s e n i n w h i c h t h e m a g n e t i c f i e l d , o r e l e c t r i c f i e l d g r a d i e n t , i s k n o w n , a l l o w i n g e x t r a c t i o n o f t h e n u c l e a r moment. T y p i c a l l y e x t r a c t e d moments a r e a c c u r a t e t o 5-10%, p o s s i b l y s u b j e c t t o v a r i o u s s y s t e m a t i c e r r o r s . By c o n t r a s t , NMR/ON g i v e s p r e c i s e unambiguous r e s u l t s . S i m u l t a n e o u s l y t h e d i f f e r e n t d e g r e e s o f a n i s o t r o p y shown b y d i f f e r e n t t r a n s i t i o n s i n t h e same d e c a y c o n t a i n i n f o r m a t i o n on t h e s p i n s o f t h e n u c l e a r l e v e l s and t h e m u l t i p o l a r i t i e s and m i x i n g r a t i o s o f t r a n s i t i o n s l i n k i n g them. T h i s s e p a r a t i o n c a n be s e e n i n t h e f a m i l i a r e x p r e s s i o n f o r t h e a n g u l a r d i s t r i b u t i o n f r o m an a x i a l l y o r i e n t e d ensemble 3
l+
4
W(0,T) = 1 + Z B ( T ) A P ( c o s 6 ) À
À
x
where Β (Τ) a r e t h e t e m p e r a t u r e dependent o r i e n t a t i o n p a r a m e t e r s o f t h e 0097-6156/ 86/ 0324-0350506.00/ 0 © 1986 American Chemical Society
Meyer and Brenner; Nuclei Off the Line of Stability ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
53.
On-Line Nuclear Orientation
STONE
H
li
It
Ni
Mg
/
Magnetic
4
Number of resonated isotopes and isomers
/ Κ
Co
/
/
Ti
Sc
V
Rb
/
Sr
/
Y /
α
Bo
Fr
R*
/
/
Zr
/
3
U 1
Hi
Ac
Rl
Tc
4
R«
w4
3
/
/
/
Ht
/
Co
5
Ni
Cu
1
/ \ Cd
Pd
Rh
3
Ot
lr
4
1
/ \ Zn
Al
Si
G*
Go
N
0
P
s
/
/
As
Pt
4
/ \ ta
1
Au
10
6
Sb
5 /
?
ΤΙ
Pb
li
1
Nt
Cl
Ar /
Ir
1
/
St
F
/
St
3
/
Ru
c
Β
/ Tt
Kr /
/
4
1
Xt
6 / \ Po
\ At
R
Tm
Yb
lu
r
2
3
Ho
/
Ct
1
Th
Fig.
1
Electric
Ft
2
/
Mb
Nb
/
Mn
Cr
1
1 /
/
\
351
/
Pr
/
Pa
/ Nd
U
/
Pm
/
Sm
/ Hp
/ Eu
/ Pu
An
/ Gd
Cm
/
Tb
Ik
/
/
Ci
/
Ho
/
Es
/
Er
1
/
Fm
Md
No
Ir
1. Elements studied by low temperature nuclear o r i e n t a t i o n (magnetic and e l e c t r i c ) and by NMR/ON.
parent state and are d i r e c t i o n a l d i s t r i b u t i o n c o e f f i c i e n t s d e s c r i b i n g the decay sequence pKRA7 Q . A schematic OLNO experiment i s shown i n F i g . 2. The primary a c c e l e r a tor beam s t r i k e s a target incorporated i n the i o n source of an isotope separator, where heavy i o n beams can produce a wide range of isotopes pre dominantly on the proton r i c h side of the N/Z s t a b i l i t y l i n e . Alternatively a s p a l l a t i o n source or a neutron beam can be used with advantage to reach a d d i t i o n a l neutron r i c h isotopes. The a c t i v i t i e s desorb from the target, are i o n i s e d , and enter the separator. Ions of a chosen mass are focussed and pass through a s l i t i n the f o c a l plane. Leaving the separator, having been accelerated through a p o t e n t i a l of 50 - 100 kV, they enter a cold (4 K) beam tube and are implanted i n t o a target f o i l , u s u a l l y of i r o n , attached by a copper c o l d f i n g e r to the mixing chamber of a d i l u t i o n r e f r i g e r a t o r and main tained close to 10 mK. The target f o i l i s magnetised to provide an axis of p o l a r i z a t i o n f o r the implanted n u c l e i which are oriented i n the magnetic hyperfine f i e l d . What are the c r i t i c a l parameters of such a system? C l e a r l y we are concerned with the a t t a i n a b l e temperature, the e f f e c t i v e n e s s of the low temp erature implantation, the required p a r t i c l e f l u x and the c o n d i t i o n that the n u c l e i , i n i t i a l l y random, become p o l a r i z e d before they decay. Each of these i s b r i e f l y considered. The current lowest f u l l y o n - l i n e temperature i s 10 mK, but, f o r some what longer h a l f - l i v e s , c l o s i n g o f f the r e f r i g e r a t o r a f t e r implantation can give r e s u l t s to ^ 7 mK i n about 30 m (see F i g . 4 ) . The Bonn group, who were
Meyer and Brenner; Nuclei Off the Line of Stability ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
352
NUCLEI OFF THE LINE OF STABILITY
ACCELERATOR BEAM
ill
TARGET ION SOURCE B, applied SEPARATOR
t
TARGET T=0 01K
T=tK
DETECTORS
Fig.
2.
Schematic o n - l i n e n u c l e a r
o r i e n t a t i o n experiment.
the f i r s t t o o p e r a t e o n - l i n e t o a n i s o t o p e s e p a r a t o r , have shown f o r many s y s t e m s t h a t i m p l a n t a t i o n b e l o w 4K i s a t l e a s t as e f f e c t i v e i n p r o d u c i n g h i g h l y s u b s t i t u t i o n a l i m p l a n t s as room t e m p e r a t u r e i m p l a n t a t i o n [HER78]. NMR/ON i n f u l l y OLNO i m p l a n t e d s y s t e m s h a s b e e n o b s e r v e d i n L e u v e n [VAN85ajj . A c r u c i a l parameter i n implanted source p r e p a r a t i o n i s the t o t a l i m p l a n t d o s e . F o r o n - l i n e work t h e f l u x o f i m p l a n t i o n s i s v e r y low as we a r e f a r f r o m any s t a b l e beam. E v e n a f l u x o f 1 0 i o n s s~ g i v e s o n l y 1 0 i o n s / d a y , w e l l b e l o w t h e l i m i t i n g c o n c e n t r a t i o n o f o r d e r 0.1 a t o m i c p e r c e n t i f i m p l a n t a t i o n i s a t 50 KeV o r a b o v e . A v a l u a b l e f e a t u r e o f OLNO i s t h a t a sequence o f i s o t o p e s may be s i m u l t a n e o u s l y s t u d i e d as t h e p r i m a r y i m p l a n t decays towards the s t a b i l i t y l i n e . T h i s f r e q u e n t l y makes a c c e s s i b l e i s o t o p e s of e l e m e n t s w h i c h do n o t r e a d i l y f o r m i o n beams. Nuclear o r i e n t a t i o n i s a s i n g l e s counting technique i n which the measured e f f e c t s a r e t y p i c a l l y o f o r d e r 10 p e r c e n t ( b u t may be much l a r g e r ) . I n d i v i d u a l measurements a c c u r a t e t o 1 p e r c e n t w i l l g e n e r a l l y g i v e u s e f u l results. T h i s r e q u i r e s p e r h a p s 3 x 1 0 ^ c o u n t s t o be r e c o r d e d , i f some a l l o w ance i s made f o r b a c k g r o u n d s u b t r a c t i o n . I t i s s i m p l e t o mount f o u r l a r g e G e ( L i ) d e t e c t o r s , i n p a i r s , a t θ = 0 and θ = π/2 r e l a t i v e t o t h e p o l a r i s a t i o n a x i s and a b o u t 7 cm. f r o m t h e s o u r c e . The combined p h o t o p e a k e f f i c i e n c y i s t h e n a p p r o x i m a t e l y 3 p e r c e n t a t each a n g l e , so t h e d e s i r e d r e c o r d e d c o u n t r e q u i r e s 10 d i s i n t e g r a t i o n s feeding the observed t r a n s i t i o n . An i m p l a n t a t i o n r a t e o f ΙΟ* n u c l e i p e r s e c o n d , t h a t i s , a s s u m i n g a 1 p e r c e n t s e p a r a t o r e f f i c i e n c y , a r e a c t i o n y i e l d o f 10 n u c l e i p e r second, w i l l give the r e q u i r e d c o u n t s i n 100 s e c o n d s f o r a t r a n s i t i o n f e d i n 100 p e r c e n t o f d e c a y s . It is c l e a r n o t o n l y t h a t measurements c a n be made by OLNO when i m p l a n t a t i o n r a t e s f a l l as l o w as 100 n u c l e i p e r s e c o n d f o r s t r o n g l y f e d t r a n s i t i o n s , b u t a l s o t h a t a t h i g h e r r a t e s weak t r a n s i t i o n s c a n be s t u d i e d w i t h a d e q u a t e a c c u r a c y to y i e l d u s e f u l i n f o r m a t i o n . NMR/ON r e q u i r e s t h a t r e s o n a n t d e s t r u c t i o n o f t h e a n i s o t r o p y be detected. The f a c t t h a t a sequence o f c o u n t s as a f u n c t i o n o f c h a n g i n g f r e quency i s n e c e s s a r y means t h a t t h i s p r e c i s i o n method w i l l be r e s t r i c t e d t o n u c l e i w i t h i m p l a n t a t i o n r a t e s g r e a t e r than 10 per second, although a l l t r a n s i t i o n s i n t h e d e c a y o f t h e r e s o n a t e d i s o t o p e c a n be combined t o g i v e t h e t o t a l resonance s i g n a l . 6
l
6
4
6
3
Meyer and Brenner; Nuclei Off the Line of Stability ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
1 1
53.
On-Line Nuclear Orientation
STONE
353
1
On implantation i n t o the cold f o i l the n u c l e i are i n i t i a l l y 'hot i . e . u n p o l a r i s e d . They approach thermal e q u i l i b r i u m with the f o i l l a t t i c e tempera ture through the Korringa r e l a x a t i o n mechanism v i a the conduction e l e c t r o n s . A r e l a t i o n s h i p of the form T i T ( h v ) = C where C i s a constant f o r a s p e c i f i c host and hv i s the Zeeman s p l i t t i n g has been e s t a b l i s h e d to give estimates of T i to about a f a c t o r of two. T y p i c a l values at 10 mK l i e i n the range Is-1000s. The h a l f l i f e T i must be _> T i . The leading o r i e n t a t i o n parameter B 2 i s given approximately f o r low degrees of p o l a r i s a t i o n by B 2 = 1 (hv/kT) /5. U s e f u l NO measurements r e q u i r e t y p i c a l l y B2(min) = 0.2, g i v i n g a maximum use f u l temperature of Τ(max) = Ihv/k, f o r which T i = C/[(hv) T(max)] = C k / I ( h v ) = 2 χ lO'+C/KhvP where C i s i n MHz sK and hv i n MHz. For i r o n host C = 5 χ 10 . The average value of B 2 , taking the s i m p l i f y i n g assumption of a nuclear s p i n temperature % approaching the l a t t i c e temperature T as (1/T)^(t) = 1/T ( l - e / i ) is B = B ( T ) [2X /(1 + 3X + 2X2)j where X = Ti/Ti£n2 and B ( T ) i s the f u l l e q u i l i b r i u m l i m i t . For cases with higher degrees of p o l a r i s a t i o n a b e t t e r approximation i s B α 1/T and we have B 2 = B2(Τγ)[x(1+X)] . Results f o r B 2 / B 2 ( T ^ ) are shown i n f i g u r e 2 as a f u n c t i o n or X. These r e l a t i o n s allow estimates to be made of the mean p o l a r i s a t i o n achieved f o r any combination of host C values, hyperfine s p l i t t i n g and h a l f l i f e . The l i m i t i n g case i s found by p u t t i n g Τ(max) equal to the lowest a t t a i n a b l e temperature. This gives hv(min), hence Ti(min) and Τχ(min). For d i f f e r e n t elements the hyperfine f i e l d v a r i e s from 100 T, and with v a r y i n g nuclear spins and moments each case must be considered s e p a r a t e l y . 2
2
2
3
2
2
4
_ t
L
T
L
2
2
2
L
2
L
2
Fig. 3 . Mean value of B 2 as a f u n c t i o n of T i / T i r a t i o . Upper curve f o r large a n i s o t r o p i e s (>10%), lower f o r s m a l l . The r e s u l t s of these c o n s i d e r a t i o n s l i m i t current methods of OLNO. Representative estimates of lower l i m i t h a l f - l i v e s are given i n Table 1, assuming i r o n host and taking I=g=l. These should be taken as a guide only, v a r i a t i o n s with I and g being i n d i c a t e d . I t i s seen that, f o r many elements, l i m i t i n g l i f e t i m e s are less than 1 minute. In e f f e c t t h i s means a range of 15-25 isotopes per element above Ζ ^ 30. Comparison of OLNO with other methods of moment and l e v e l s t r u c t u r e study has been given b r i e f l y i n [ST085]. Most a l t e r n a t i v e moment measurements require considerably higher count r a t e s . When working f u r t h e r from s t a b i l i t y decay schemes are o f t e n poorly e s t a b l i s h e d and, as Q values f o r decay i n crease, they become more complex. The occurrence of isomers i s r e l a t i v e l y frequent, which has the advantage of populating s t a t e s of a wide range of s p i n values and the drawback of producing complicated parentage f o r t r a n s i tions lower i n the daughter decay scheme. The over a l l r e s u l t i s that nuclear
Meyer and Brenner; Nuclei Off the Line of Stability ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
354
NUCLEI OFF THE LINE OF STABILITY
TABLE 1 L i s t i n g f o r each element of the temperature at which B 2 = 0.2 i n i r o n host, the estimated Ύ\ a t that temperature and hence the minimum h a l f - l i f e a c c e s s i b l e . In Table, I = g = 1 i sassumed, see footnotes • Element
B
hf (T)
Τ
T i1
max (mK) +
at Τ max = T, (min)
Element
B
hf (T)
2
T i1
Τ max (mK) +
seconds* 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53
Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I
-13.2 -12.2 -8.7 -6.6 -22.8 -33.9 -28.7 -23.4 -21.8 -19. 1 -9.4 6.0 34.4 69 84 66 5.4 -10 -22.6 -27.4 -26.6 -25.6 -31.7 -49 -55.7 -54.7 -44.7 -39.2 -28.7 8.5 23.4 68. 1 1 14.6
4.8 4.5 3.2 2.5 8.4 12.4 10.5 8.5 8.0 7.0 3.4 2.2 12.6 25.2 30.7 24 1.9 3.7 8.3 10.0 9.7 9.4 11.6 17.9 20.4 20.0 16.3 14.3 10.5 3.1 8.5 24.9 41.9
3
1.0 χ 10 1.3 χ 10 3.5 10 7.8 χ 10 194 59 97 179 222 330 2.8 χ 10 1.1 χ 10 57 7 4 8 1.4 χ 10 2.3 χ 10 200 112 122 137 72 20 13 14 26 38 97 3.8 χ 10 180 7 1.5
3
3
3
3
3
3
3
3
3
54 55 56 57 58 62 63 65 66 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 88 90 92 94 96
Xe Cs Ba La Ce Sm Eu Tb Dy Er Tm Yb Lu Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn Ra Th U Pu Cm
160 27.6 8.5 -46 41 314 148 380 610 768 625 125 61 -63 -64 -69 -75 -109 -147 -128 -115 -84 -18.5 26.2 119.1 238 254 170 12.7 31 56 1 13 S b based on c o m p a r i s o n o f t h e i r measured g - f a c t o r s w i t h c a l c u l a t i o n s b a s e d on n e i g h b o u r i n g odd-A n u c l e i w h i c h y i e l d g = 1.06(3) f o r t h e f o r m e r c o n f i g u r a t i o n and g = 0 . 8 2 ( 3 ) f o r t h e l a t t e r . The p r e s e n t i m p r e c i s e measurement, g = ± 0.87(9) i n S b needs t o be i m p r o v e d u s i n g t h e NMR/ON t e c h n i q u e , b u t 1 2 2
v s
1 2 0
l l S
1 1 6
Meyer and Brenner; Nuclei Off the Line of Stability ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
356
F i g . 4.
NUCLEI O F FT H E LINE O F
T e m p e r a t u r e dependence
STABILITY
o f γ-anisotropy f o r o r i e n t e d I i s o t o p e s .
Meyer and Brenner; Nuclei Off the Line of Stability ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
53.
357
On-Line Nuclear Orientation
STONE
f a v o u r s t h e CI5/2 p r o t o n s t a t e , f o u n d as g r o u n d s t a t e i n a l l odd-A i s o t o p e s lll-121
S b e
I_. I n g | l ç a n d 5 3 1 5 7 we h a v e r e s u l t s o n two i s o m e r s f o r e a c h mass number. The h i g h s p i n i s o m e r ( a s s i g n e d 7" o n t h e b a s i s o f l e v e l s f e d i n d e c a y ) h a s μ = ± 4.2(2)nm i n b o t h c a s e s . This i s d i s t i n c t i v e of the d i s t o r t e d π (404) 9/2"*" o r b i t a l w h i c h , c o u p l e d t o ν (532) 5 / 2 " w o u l d g i v e Ι = 7"", μ = 4.8nm. The o c c u r r e n c e o f t h i s o r b i t a l a t l o w e x c i t a t i o n i s d i r e c t l y i n d i c a t i v e of large e q u i l i b r i u m deformation associated with the s o f t m i d - s h e l l n e u t r o n number. The l o w s p i n i s o m e r ( 2 ~ ) shows a moment i n I , ± 1.9(3)nm, w h i c h i s c l e a r l y l a r g e r t h a n f o u n d f o r l e v e l s o f t h e same Ι in I ± 1.23(3)nm and I ± 1.14(8)nm |])EJ83] . A p o s s i b l e e x p l a n a t i o n for this v a r i a t i o n i s that i n l S we a r e c l o s e t o t h e s h e l l m o d e l c o n figuration |jg /2,vhi1/2J2" ^schmidt -2.5nm) w i t h r e l a t i v e l y s m a l l e q u i l i b r i u m d e f o r m a t i o n , s u g g e s t i n g t h a t t h i s i s o t o p e i s a d r a m a t i c example o f i s o m e r i s a t i o n w i t h m a r k e d l y d i f f e r e n t d e f o r m a t i o n i n t h e two i s o m e r s . The same c o n f i g u r a t i o n Qrg7/2> h l l / 2 ] 2 " h a s b e e n p r o p o s e d f o r ^ f S b y ! (^meas ~1·9 nm) and C a l l a g h a n e t a l h a v e shown t h a t d e t a i l e d c o r r e c t i o n s t o t h e S c h m i d t moment r e d u c e t h e c a l c u l a t e d v a l u e t o - 1 . 9 5 ( 5 ) n m [CAL74] . The moment o f I ( 1 ) a t ± 0.93(9)nm l i e s c l o s e r t o t h e d e f o r m e d analogue C s ( l ) Q r ( 4 2 0 ) | , v ( 4 1 1 ) i ] μ = 0.67 nm, t h a n t o t h e s p h e r i c a l S b ( l ) Qrds/2, v d ] μ = + 2.3(2)nm. 1
1
5
π
1
1
8
π
1
2
0
1 2 i +
1
1
8
=
7
v
=
1 2 2
1 2 I +
1 2 0
+
+
+
3 / 2
References [CAL74] P.T. Callaghan et al. Nuclear Physics A221 1 (1974). [DEJ83] J. de Jong and H. Postma, Hyp. Int. 15/16 69 (1983). [HER78] P. Herzog et al. Nucl. Inst. and Meth. 155 421 (1978). [KRA71] K. Krane, Los Alamos Report LA4677 (1971). [STO85] N.J. Stone, Hyp. Int. 22 3 (1985). W [ OU85] J. Wouters et al. Hyp. Int. 22 527 (1985). [VAN85a]D. Vandeplassche et al. Hyp. Int. 22 483 (1985). [VAN85b]E. Van Walle et al. Hyp. Int. 22 507 (1985). RECEIVED July
18, 1986
Meyer and Brenner; Nuclei Off the Line of Stability ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
