59 Spectroscopy and Measurement of Electromagnetic Moments in Po 198,200,210
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Κ. H . Maier Hahn-Meitner-Institut Berlin, D-1000 Berlin 39, Glienicker Str. 100, Federal Republic of Germany 210
π
+
-
-
The quadrupole coupling constants for the Po Ι =8 , 11 , 13 isomers in Bi have been measured, and Q(11 ) = 82(2) fm and Q(13 ) = 90(2) fm normalized to Q( Po8 ) = 57 fm are deduced. In beamγ-spectroscopyof Po showed the (πh 9/2 8 ) π(h9/2i13/2 11 ) and (vi 13/2 12 ) isomers. TheB(E28 ->6 )and Q(8 ) in Po to Po are discussed, a sudden drop is found for the B(E2) in Po. TheB(E3,11 ->8 )rises very steeply in the light Po isotopes. -
-
2
210
+
198,200
-
198
2
2
2
2
+
+
+
+
+
210
198
-
+
This c o n t r i b u t i o n covers work done with the Nuclear S t r u c t u r e Group a t Lawrence Livermore N a t i o n a l Laboratory and a t the Hahn-Meitner-Institut a t B e r l i n . The former uses the t r i t o n beam of the Los Alamos tandem f o r γ-spectroscopy i n beam t o measure f a i r l y b a s i c p r o p e r t i e s of simple few p a r t i c l e 208 states very c l o s e t o Pb. There are s t i l l many gaps i n our knowledge, p a r t i c u l a r l y on neutron p a r t i c l e and proton hole states, a few of these could be f i l l e d by t h i s unique setup f o r γ-spectroscopy with n e u t r o n r i c h t r i t o n p r o j e c t i l e s . Here I w i l l cover recent measurements of the quadrupole moments +
2 1
f o r the 8 , 11" and 13" isomers i n ° P o . At HMI we use the heavy i o n beams 208 from VICKSI f o r spectroscopy of n u c l e i f u r t h e r away from Pb t o observe the gradual t r a n s i t i o n from pronounced s i n g l e p a r t i c l e s t r u c t u r e t o i n c r e a s i n g l y 19 8 20 0 c o l l e c t i v e behaviour. As example spectroscopy of * Po i s presented 210 here. We can then look i n t o the systematics of Po-isotopes from magic
Po
with N=126 down t o N=114 with a few holes i n the 1 1 3 / 2 neutron s h e l l and t h e r e f o r e diminished s t a b i l i t y of s p h e r i c a l shape. 209 A s i n g l e c r y s t a l of t r i t o n s with about
B i metal was struck by a p u l s e d beam of 15 MeV
1 ns pulsewidth. The bismuth
c r y s t a l was heated t o 478±5 Κ
to avoid e f f e c t s from r a d i a t i o n damage. I t s c-axis p o i n t e d a t t o the beam i n the plane of the two detectors a t 15e and 90°. F i g . 1 gives the r e l e v a n t 210 0097-6156/ 86/the 0324-0392506.00/ p a r t of the Po l e v e l scheme. For high energy0 l i n e s from the 11 and 3
© 1986 American Chemical Society
Meyer and Brenner; Nuclei Off the Line of Stability ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
59.
Spectroscopy and Measurement of Electromagnetic Moments
MAIER
4372 4324
-13"
yf
393
93ns
-11" R(t)
2
1
0
P o
1 =
13"
E
y
=
1473
KeV
0.20
1522.9*
1475.1* 0.00 -0.20
>'
2849
0.20
yf
•11"
20.4ns
o.oo -0.20
1292.2*
0.20 0.00 -0.20 300
1557
y
1473
\,83.7*
1427
\ ,46.5
1181
yr
•8*
96.0ns
•6
+
42.6ns
•4
+
1.53ns
time[ns]
Fig. 2
245.3
Measured quadrupole modulation p a t t e r n s
1181.4
210
Fig. 1
Isomers i n
Po. *used
f o r measuring Q
yf
•o*
13" l e v e l s c o a x i a l Ge-detectors with 6 mm +
+
f o r the 83.7 keV 8 -*6 t r a n s i t i o n ,
l e a d absorbers were used, whereas
l y i n g between the B i - and Po- K
a
and
Κβ X-rays, p l a n a r detectors were employed. F i g . 2 shows the quadrupole modulation p a t t e r n s 1/2[N(158° ,t)/N(90°,t)-1] and the r e s u l t s are presented 17
i n the t a b l e . The f i e l d gradient f o r Po i n B i eq(PoBi) = 11.7·10 normalized by c a l c u l a t i n g Q ( P o 8 ) = 57 f m from the measured 2 1 0
+
2
2
V/cm [l]
is
210 +
+
B(E2,8 ->·6 ) assuming pure h9/2 c o n f i g u r a t i o n s . As the s t r u c t u r e of q u i t e pure t h i s i s the best n o r m a l i z a t i o n a v a i l a b l e . Mahnke e t a l .
Meyer and Brenner; Nuclei Off the Line of Stability ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
Po i s [ 2 ] got
394
NUCLEI OFF THE LINE OF STABILITY
14.5(15)· 10
17
V/cm
2
from the same procedure f o r
208
Po which i s l e s s safe on
the nuclear model assumption. 210 Table 1: Quadrupole
moments i n
Po. The c o u p l i n g constants are f o r PoBi a t +
+
478(5) K. * C a l c u l a t e d as reference from B(E2,8 -*6 ) JQ|present
|Q|(ref.
57*
57*
2
level
e Qq/h
8+
160.7(10) MHz
11"
229(4)
13"
MHz
253(4)
MHz
81(2) fm
2
90(2) fm
2
3)
82(19) fm
2
62(11) fm
2
In d e t a i l the time d i s t r i b u t i o n of the 83.5 keV l i n e at e a r l y times i s not reproduced by the f i t ,
due to feeding from the 11" isomer. However, the
d i s t a n c e t o the next pronounced
s t r u c t u r e , a t which a l l n u c l e a r spins are i n
phase again i s p r a c t i c a l l y independent of t h i s . Feeding from 13" i n t o 11" i s weak and spread out i n time and t h e r e f o r e unimportant. V a r i a t i o n s of the f i t t e d range and other parameters
changed the r e s u l t s f o r the frequencies by
