Levels in 192Os excited by the (p, p') and (d, d') reactions

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Levels in 192Os excited by the (p, p’) and (d, d’)

reactions

J. Jastrzebski, R. Kaczarowski, J. Lukasiak, S. André, J. Treherne

To cite this version:

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1383

LEVELS IN

192Os

EXCITED BY THE

_(p,

_p’)

AND

_(d,

_d’)

REACTIONS

_(*)

J.

_JASTRZEBSKI,

R.

KACZAROWSKI,

J. LUKASIAK

Institute for Nuclear

_{Research, Department}

of

_Physics,

05-400

_Swierk,

Poland and

S.

_ANDRÉ,

J. TREHERNE

Institut des Sciences

_Nucléaires,

BP

_257,

38044 Grenoble

_Cedex,

France

(Reçu

le

_{23 juillet}

_1976,

_accepté

le 23 aofit

₁₉₇₆₎

Résumé. 2014 Les niveaux

d’énergie

de 192Os ont été etudies par réactions (p, p’) et _{(d, d’).}Les

spectres 03B3 et les coincidences 03B3-03B3 ont été _enregistrésà des _énergiesde protons de 16 MeV et de deutons de _23,2MeV. En dehors des niveaux

_déjà

connus, des états de _{parité négative}ont été observés. La

possibilité d’une forme triaxiale pour ce noyau est _envisagée. Abstract. 2014

The energy levels of 192Os were studied _bythe _{(p, p’)}and _{(d, d’)}reactions. _Single

gamma ray spectra and 03B3-03B3 coincidences were measured at 16 MeV _(protons)and 23.2 MeV (deute-rons) incident energy. Negative parity states were observed in addition to _previouslyknown levels. The _possiblityof the triaxial _shapefor this nucleus is discussed.

LE JOURNAL DE PHYSIQUE TOME _37,DTCEMBRE 1976, F

Classification

Physics Abstracts

4.220

1. Introduction. -

Levels of the heaviest stable osmium

_isotope

192 Os

are known from the

_decay

of 5.9 s isomeric state in this

_nucleus,

excited

_by

the

(n, n’)

reaction

_[I],

from Coulomb excitation

experi-ments

_{[2, 3]}

and

from 192Re

_[1]

and 192Ir

_[4]

_decays.

This _paper_reportsthe results obtained

_during

in-beam studies

of 191Ir

_{by (p,}

_2n)

and

_{(d, 3n)}

reactions

on

a 1920S

_{target [5].}A number of gamma transitions

could be attributed to the _targetexcitation.

2.

_Experimental

_procedure

and results.

-2.1 EXPERIMENTAL SET-UP. - The metallic Os

target

(enriched

to

_{99 %}

_{192 Os),}

_{approximately}

20

_mg/cm2

thick,

deposited

on 2

mg/cm2

mylar backing

was

irradiated with 16 MeV

_protons

and 23.2 MeV

deu-terons from the Grenoble variable energy

cyclotron.

Single

gamma-ray spectra and y-y coincidences were

measured with 45 and 77

cm’

_Ge(Li)

detectors. Details of the

_{experimental arrangement}

were

publi-shed

_previously

_[6]

and will not be further discussed here.

The list of _gammalines

_belonging

to

1920s

is

presented

in table I. Attribution of the transitions

to this nucleus was made on the basis of coincidences

with lines

_placed

in the

_decay

scheme of the 5.9 s

isomeric

_{state [1].}

Some

_typical

coincidence _spectraare shown in

figure

1.

2.2 LEVEL scmvtE. - The level scheme deduced

from the coincidence data is

_presented

in

_figure

2a. This scheme is in

_good

_agreementwith that

_proposed

in ref.

_[1].

At most three levels of the rotational bands built on the

ground,

[(111: = 22+ and 44+ states

are

fed

at the

projectile

energies

used. But we

report a

_{3 -,}

1 341 keV state and the first member of its rotational band

_(1’

=

4-, E

= 1 560.6

keV).

Our attribution of

spin

and

_parity

to these levels is based on their

_decay

modes and on the

_negative

_parity

state

_systematics

in the even Os nuclei

_shown

in

figure

3.

Figure

2b shows the cross-sections for the excitation of some levels

in 192OS.

Their relative values are based on the

_intensity

balance for each level. The absolute

cross-section was estimated

_{by comparison}

of the

intensities of the transitions

_feeding

the

191Ir

_ground

state in the

_(p,

_2n)

and

_(d,

_{3n) reactions,}

with the

cross-sections

_predicted

for these reactions

_by

the

_hybrid

model

_[7].

For

_{bombarding energies}

near the maximum

of the excitation function these

_predictions

should be

correct within 20

_%

accuracy.

(*) This work was _performedwithin the Grenoble-Swierk collaboration.

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1384

FIG. 1. -

Typical coincidence spectra.

FIG. 2. -

a) Levels in 1920s excited in _{(p, pJ}and _(d,_d)reactions.

b) Absolute cross-sections _{(in mb)}for the excitation of some levels. FIG. 3. - Level

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1385

TABLE I

(a) Energy error is 0.1 keV for strong and well resolved lines and Gan attain 0.8 keV for weak or _badlyresolved transitions.

(b) Values are _givenfor 16 MeV and 23.2 MeV incident energy

of protons and deuterons, respectively. Uncertainties in the least

significant figures are _givenin _parentheses.

0 Line observed in coincidence _spectra_only. (d) Complex line.

’e) Estimated from the coincidence _spectra. ,

(f ) Calculated from the branching ratio of transitions _deexciting the given level [1].

(9) Out of energy range.

3. Discussion. - The 3- and 4-

states in

1920S

at 1 341 keV and 1 560.6 keV

_respectively

were not

found in the

_decay

studies

_[1,

_3,

_4].

It seems

_likely

that the former is identical to the

_{3 -,}

1 333 keV state

observed in the inelastic

_scattering

of a

particles

and

reported

by

Baker et al.

_[3]

_during

the

_preparation

of our note.

Comparison

of the

_branching

ratios for the

decay

of 3 - state with the

_predictions

of the

_Alaga

rule is

presented

in table II. The best _agreementis found

TABLE II

for the

_assumption

of K = 3 for the level considered. This

_supports

the

_{interpretation}

of the 3 - state as

the

_octupole

one, as in the

_lighter

osmium

_isotopes

_[8].

However,

the 3- state in

1920S

_decays

also to the

[(IX = 02+

(205.8 keV)

level with _a

branching

ratio :

B(El,

1 135.2

_keV)/B(El,

852.0

_keV)

= 0.11. So in

this case K is not a

good

_quantumnumber. This fact may be due to the

_triaxiality

of the

112 Os

nucleus. Such

_assumption

can also

_explain

the inversed order

of [(I1t = 22+ and 04 + levels

_(cf.

_Fig.

₃₎

in this

_isotope.

Acknowledgements.

- Our thanks

are due to

Dr. N. Kaffrell for his comments on

192mos

_decay.

References

[1] KAFFRELL, N. and HERZOG, W., unpublished data, quoted after

SCHMORAK, M. R., Nucl. Data Sheets 9 ₍₁₉₇₃₎195.

[2] MILNER, W. T., MCGOWAN, F. K., ROBINSON, R. L.,

STEL-SON, P. H. and SAYER, R. O., Nucl. Phys. A 177 (1971) 1.

[3] BAKER, P. T., KRUSE, T. H., HARTWIG, W., LEE, I. Y. and

SALADIN, J. X., Nucl. Phys. A 258 (1976) 43.

[4] PRASAD, R., CHATURVEDI, L., CHATURVEDI, S. N. and

NIGAM, A. K., Nucl. Phys. A 243 ₍₁₉₇₅₎317.

[5] ANDRÉ, S., JASTRZEBSKI, J., KACZAROWSKI, R., LUKASIAK, J., RIVIER, J., SEBILLE-SCHÜCK, C. and TREHERNE, J., Proc.

Symposium on _HighlyExcited States in _Nuclei,Jülich

(1975) p. 67 and to be published.

[6] ANDRÉ, S., BOUTET, J., RIVIER, J., TREHERNE, J., JASTRZEBSKI, J.,

LUKASIAK, J., SUJKOWSKI, Z. and _{SEBILLE-SCHÜCK, C.,} Nucl. Phys. A 243 ₍₁₉₇₅₎229.

[7] BLANN, M. and _{MIGNEREY, A.,}Nucl. _Phys.A 186 (1972) 245.

[8] YAMAZAKI, T., NISHIYAMA, K. and HENDRIE, D. L., Nucl.

Phys. A 209 ₍₁₉₇₃₎153 ;

HOCHEL, R., DALY, P. J. and HOFSTETTER, K. J., Nucl. _Phys.A

211 (1973) 165 ; YATES, S. W., CUNNANE, J. C., HOCHEL, R.

and DALY, P. J., Nucl. Phys. A 222 ₍₁₉₇₄₎_{301 ;}

YATES, S. _{W., CUNNANE,}J. C. and DALY, P. J., Phys. Rev. C 11

(1975) 2034 ; YATES, S. W., CUNNANE, J. _C.,DALY, P. J., THOMPSON, R. and SHELINE, R. _K.,Nucl. _Phys.A 222