HIGH SPIN STATES OF THE ODD-ODD 110In NUCLEUS

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HIGH SPIN STATES OF THE ODD-ODD 110In

NUCLEUS

R. Béraud, A. Charvet, R. Duffait, M. Meyer, J. Genevey, J. Tréherne, A.

Genoux-Lubain, F. Beck, T. Byrski

To cite this version:

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JOURNAL DE PHYSIQUE CoZZoque CIO, suppldment au n012, Tome 41, ddcembre 1980, page ~ 1 0 - 159

R. Beray$, A . Charvet, Duffait, M. Meyer, J . ~ e n e v e ~ * , J. ~ r ~ h e r n e * , A . ~enoux-~ubain*!"' F. Beck and T. Byrski

.

I n s t i t u t de Physique Nuclkaire (IN2P3), Universitd CZaude Bernard Lyon-I, .43, bouZevard du 12 novembre 1918, 69622 V i i leurbanne Cedex, France.

I n s t i t u t des Sciences NucZe'aires de GrenobZe, (USMG e t IN2P31 53, m e des Martyrs, **38026 GrenobZe cedex France.

Centre de Recherches NucZdaires de Strasbourg IINZP31, 23, rue du Loess, Cronenbourg, 67037 Strasbourg cedex, France.

Abstract. The high-spin s t a t e s of the odd-odd llO1n nucleus have been investigated i n the 1 0 0 ~ o ( 1 4 ~ , 4ny) reaction and observed up to 5.6 MeV e x c i t a t i o n energy. An intense AI = 1 cascade has been found from 7- t o 14- and has been interpreted i n the frane of the a x i a l r o t o r + two q ~ a s i ~ a r t i c l e s model including Coriolis interaction.

I. Introduction

Recent studies have begun to explore the high spin s t r u c t u r e of doubly odd-transitional nu- c l e i i n p a r t i c u l a r within the Au-T1 region

''

2, and around the s h e l l c l o s u r e Z = 50 3' 4). This inve s

-

tigation is a p a r t of a m o r e systematic investiga- tion of odd-odd s i l v e r a n d indium nuclei excited through heavy-ion reactions. The i n t e r e s t of odd- odd nuclei such a s indium i s the possible existence of a s o called "conflicting ~ a s d " ~ ) : the q u a s i - p a r t i - c l e s that give r i s e to collective bands i n neighbou- r i n g odd-A nuclei have opposite behaviours i n the f r a m e w o r k of the r o t o r

+

q u a s i p a r t i c l e model. Namely, the TT g9,2 o r b i t a l l e a d s to a coupled band s t r u c t u r e (A I = l ) w h e r e a s the V h l l/2 o r b i t a l a c - counts f o r decoupled bands AI = 2. In lo81n ( a s i n 196a198Tl), such a conflicting c a s e gives r i s e to a s i m p l e sequence of 41 = 1 l e v e l s i n t e r p r e t e d i n the f r a m e of the r o t o r

+

two quasi-particle model including Coriolis interaction.

2. Experimental p r o c e d u r e and r e s u l t s The levels of l 1°1n have been excited

14

u s i n g the l o O ~ o ( N, 4 n ~ ) l 1°1n reaction. E x p e r i -

i n t r i n s i c Ge detector w e r e used i n the y - r a y experiments. The y - r a y yield h a s been m e a s u r e d a s a function of bombarding e n e r g y within the r a n g e 55-75 MeV. The m a x i m u m of l 1°1n production occured a t 62 MeV. This e n e r g y h a s been s e l e c t e d f o r a l l i n beam experiments. A single y - r a y s p e c - t r u m i s shown i n fig. 1. The m a i n p a r a s i t i c lines a r e those of 109,I 10Cd, 1 091n and 107 *g.

7

About 2 . 1 0 ' b i p a r a m e t r i c 2048 x 2048 chan- nel Y - Y coincidence events have been r e c o r d e d . The t i m e resolution of prompt events w a s 1 5 ns, Accidental coincidences (delay t i m e of about 60 n s ) a s a l s o out of b u r s t coincidences have been s i m u l t a - neously r e c o r d e d . No evidence f o r a n i s o m e r i c s t a t e h a s been observed.

The angular distributions w e r e m e a s u r e d a t five angles ranging f r o m 0" to 90° with r e s p e c t t o the b e a m direction. The normalization w a s deduced f r o m s p e c t r a r e c o r d e d by a fixed Ge(Li) d e - t e c t o r . The l i n e a r polarization of 'lO1n Y-rays w a s m e a s u r e d using the f i v e g e r m a n i u m d e t e c t o r s

,

Compton p o l a r i m e t e r d e s c r i b e d i n r e f e r e n c e 6. The experimental value of the polarization p i s dedu- c e d f r o m the coincidences s c a t t e r e r plus horizon- m e n t s w e r e c a r r i e d out by m e a n s of the Grenoble

t a l a n a l y s e r s ( N ) and s c a t t e r e r plus v e r t i c a l ones ISN cyclotron. The MO t a r g e t e n r i c h e d t o 97% i n H

2 (N

v

) through the r e l a t i o n : 'OONO c o n s i s t e d of a l mg/crn foil deposited on a

2

l e a d backing of about 30 mg/cm

.

Two Ge(Li) d e - p = - l N~

-

N~ Q(E) NV + NH t e c t o r s having a n efficiency of 15% a n d an X - r a y

w h e r e Q(E) i s the polarization sensitivity of the (X) P r e s e n t a d d r e s s : I. E. N. Alger, A l g e r i a

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c10- 160 JOURNAL DE PHYSIQUE

p o l a r i m e t e r . The A 2 , A 4 and p coefficients ex- t r a c t e d f r o m those m e a s u r e m e n t s a r e l i s t e d i n t a - ble 1. A typical N - N s p e c t r u m showing evi-

V

H

dence f o r the polarization sign i s displayed i n fig.

2. The e l e c t r o n s p e c t r u m of 'lO1n h a s been m e a - s u r e d with the help of the ISN orange s p e c t r o m e t e r a t

ren noble"!

The r r K values e x t r a c t e d f r o m t h i s experiment support the previous a s s i g n m e n t s deduced f r o m angular distributions and polarization

m e a s u r e m e n t s . The level scheme deduced f r o m avaiIable experimental evidence is given i n fig. 3. The ground s t a t e h a s been previously m e a s u r e d t o

t

be 7 7). Above the g. S. and the f i r s t positive

p a r i t y s t a t e s is observed a n intense c a s c a d e w h e r e s t a t e s f r o m 7- to 14- a r e connected with A I = 1 transitions. The E l multipolarity of the 1337 k e V transition establishes the positive p a r i t y of the c a s - cade s t a r t i n g with spin 12 a t 3512 keV.

1 0 0 14

F i g u r e 1

-

y - r a y s p e c t r u m of the MO( N, 4ny ) reaction a t 62 MeV

, , ,

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Table 1

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Energies, intensities, angular distribution coefficients, linear polarization and multipolarity of y-rays assigned to 1101n.

a ) This very low energy transition has not been observed with an intrinsic Ge X-detector because of i t s l a r g e conversion coefficient but i t s existence i s required to explain the coincidence results

b) Relative y -ray intensities a t 62 MeV bombarding energy corrected for angular distribution. Energy (intensity) uncertainties a r e about 0.2 keV (10%) for intense transition (Iy> 20) and 0.5 keV ( 2 0 % ) for the other ones.

Figure 3

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Level scheme of 'lO1n obtained from this study

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C10- 162 JOURNAL DE PHYSIQUE

3. Discussion

The m o r e striking f e a t u r e is t h e p r e s e n c e of a n intense AI

=

1 c a s c a d e of negative p a r i t y levels a s i t h a s been observed i n lo81n. Due to the p r e s e n c e of l e v e l s with spins higher than 10, this s c h e m e c a n - not be explained a s T T9/2 ~

B

vh14y multiplet s t a t e s

8). Potential e n e r g y calculations f o r odd indium isotopes indicate a s m a l l p r o l a t e equilibrium def o r

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mation. T h e r e f o r e , a s i n lo81n and i n odd-odd thal- liurn, we apply the two quasi-particles+axial r o t o r model including Coriolis interaction. The quasi- p a r t i c l e e n e r g i e s of neutron a n d proton, the pairing coefficient U. and the deformation have been e x t r a c -

J

ted f r o m constrained H.F. calculations on 106,110 Cd p r e s e n t e d i n a r e c e n t paper 1°). T h e s e band mixing calculations have been p e r f o r m e d by taking into a c - count a l l proton and neutron o r b i t a l s situated within one MeV on both s i d e s of the F e r m i level. The r e s i - dual interaction between the valence proton and neu- t r o n h a s been neglected i n our calculation. C o m p a r i - son between experiment and theoretical calculations is given i n figure 4 f o r both lo81n and 'lO1n. The model accounts f o r the special n e a r n e s s of the 7- and 8- s t a t e s i n llO1n.

The e x p e r i m e n t a l sequence i s relativelywell reproduced except a slight e n e r g y expansion of the calculated level s c h e m e ; it should be noted that no f r e e adjustable p a r a m e t e r i s enclosed i n our c a l c u - lations. The inclusion of a v a r i a b l e m o m e n t of iner- tia o r the attenuation of the Coriolis i n t e r a c t i o n should l e a d to a bundhing of the s t a t e s l ) . The coe- x i s t e n c e of E2 a n d M1 t r a n s i t i o n s accounts that this sequence looks like a rotational band based on the 8- l e v e l composed predominantly of K = 6 , 7, 8 band- mixing a r i s i n g f r o m ~ h ( n n = 3 / 2 . 5/2, 7/2) ~ ~ / ~@

(R = 9/2) s t a t e s . The positive p a r i t y band

=g9/2 P +

built on the 12 s t a t e located a t 3512 keV cannot be explained i n this p u r e two-quasi p a r t i c l e s

+

r o t o r model.

1xi

conclusion the Coriolis i n t e r a c t i o n appears to be dominant a l s o i n doubly odd t r a n s i t i o n a l nuclei in p r e s e n c e of high-j unique p a r i t y orbital, on the a s s u m p t i o n that the proton-neutron i n t e r a c t i o n i s weak.

R e f e r e n c e s

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(1979) 194

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Genevey J . , T r e h e r n e J . , Beck F . , B y r s k i T. Contribution t o t h i s conference

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,

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,

and F a e s s l e r A .

,

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