Isomeric state and rotational band in 158Ho

HAL Id: jpa-00231273

https://hal.archives-ouvertes.fr/jpa-00231273

Submitted on 1 Jan 1976

HAL is a multi-disciplinary open access

archive for the deposit and dissemination of

sci-entific research documents, whether they are

pub-lished or not. The documents may come from

teaching and research institutions in France or

abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est

destinée au dépôt et à la diffusion de documents

scientifiques de niveau recherche, publiés ou non,

émanant des établissements d’enseignement et de

recherche français ou étrangers, des laboratoires

publics ou privés.

Isomeric state and rotational band in 158Ho

N. Rizk, J. Boutet

To cite this version:

ISOMERIC STATE

AND

ROTATIONAL

BAND IN

158Ho

N. RIZK

_(*)

and J. BOUTET

Institut des Sciences

Nucléaires,

BP

257,

38044 Grenoble

_Cedex,

France

(Reçu

le 1 er

avril 1976,

accepte

le 21 mai

₁₉₇₆₎

Résumé. 2014

Le noyau

impair-impair 158Ho

a été étudié au moyen des

réactions 159Tb(03B1, 5n)158Ho

et

_160Dy(p,

_3n)158Ho.

Un état

_isomérique

de _période

_T1/2

= _{(29 ± 3)} ns a été mis en évidence.

Une bande de rotation a été

_{développée jusqu’au spin}

16-. Abstract. 2014 The odd-odd 158Ho nucleus is studied

by means of the

_{reactions 159Tb(03B1, 5n)158Ho}

and

_160Dy(p,

_3n)158Ho.

The life-time of an isomeric state is measured as

_T1/2

= (29 _± 3) _ns. A

rotational band is

_developed

up to

_spin

16-.

Classification

Physics Abstracts

4.220 - 4.240

1. Introduction. - In the framework of

a

systematic

study

of the

_spectroscopy

of neutron-deficient hol-mium

_isotopes,

the level scheme of the odd-odd nucleus

i 58Ho

has been

investigated.

A

_{previous investigation by}

Stenstrom and

_{Jung [1]}

determined the

_{genetic relationships}

and half-lives of

15 "Ho

isomers.

_Recently

Abdurazakov et al.

_[2]

and Harmatz and

_Handley

_[3]

have

_investigated

the

decay

scheme of the nucleus

i58Er -+ 15 "Ho.

As a

result of their

_{investigations}

the

_ground

state

of

15 "Ho

is found to have

_spin

and

_parity

5 +

corres-ponding

to 67

_protons

and 91 neutrons with a p

7/2- [523] t

n

_3/2-

[521] T configuration.

An

iso-meric state

_(T1/2

= 27

min.) in

i58Ho

with _energy

67.3 keV is known which has been

_interpreted

as

having spin

and

_parity

2- and which

_corresponds

to

possible

configurations :

a

p

1/2+

[411] J.

n

_{5/2- [523]!}

Ref.

[2]

p

7/2 +

[404] !

n

3/2 -

[521]

f Ref.

[3]

p

7/2- [523] T n

3/2+

[402] ~

It is _{the purpose of this letter} to discuss the above

possibilities

and compare them with our data which concern the levels

of i 58Ho

studied

by

in beam

spec-troscopic

methods in the reactions

_(a,

xny)

and

(p, xny).

2.

_{Experimental procedure}

and results. - The in beam

_experiments

were carried out at the Grenoble

cyclotron.

For the

_159Tb(a,

_{5n) reaction,}

a

mono-isotopic

terbium foil

_target

of 5

_mg/cm2

was used.

The

_i60Dy(p,

_3n)

reaction was

performed

with a 5.5

_mg/cm2

_{85 %}

enriched

_160DY203

_target.

The

(*) Permanent address : _Department of _{Physics, University} of _{Ein-Shams, Cairo, Egypt.}

study

of excitation functions

_suggested

that

_alpha

and

proton

particle energies

of

_{approximately}

63 MeV and 43 MeV

_respectively

were the most favourable for the

_production

of

i58Ho.

Gamma lines

_belonging

to

TABLE I

Summary of

the

_experimental

results

L-198 JOURNAL DE PHYSIQUE - LETTRES

FIG. 1. -

Example of coincident spectrum (stop by 156.9 _keV-y).

FIG. 2. -

Example of coincident spectrum (115.1 keV-y).

1 s’Ho

and i59Ho

and their

_{daughter products}

were

observed in the

_spectrum

due to the

_{(a, 6n)}

and

_{(a, 4n)}

reactions.

The

_experimental

information consists of y-ray

spectra

(in

and out of

_beam),

the life-time of the iso-meric state measured

_using

the

_{cyclotron pulses}

and the

_prompt

and

_delayed

_y-y coincidences. The results of our

_experiments

are summarized in table I and in

_figures

_1~2,

3 and 4. In table I

_only

the

_energies

and the relative y-ray intensities for the lines of

i58Ho

and 158 Dy

are tabulated. A _{spectrum obtained}

_using

the

_delayed

coincidence method is

_presented

in

figure

1. In this

_figure

the 156.9 keV _y-ray is taken

as the _gate STOP.

Figure

2

gives

an

example

of the

prompt

coincidences for the 115.1 keV _y-ray. The

decay

curve for the 156.9 keV line

of 118 Ho

is shown

in

_figure

3.

3. Data

_analysis

and results. - In the

course of

measurement of in and out of beam _{gamma spectra,}

an intense

_delayed

_{gamma line} at 156.9 keV was found

to

_decay

with a half-life of

₍₂₉

+

3)

ns. A

_comparison

of this value with those

assigned for

the isomeric states in odd-odd holmium

_isotopes

is

_given

in the

following

table. ’

164 Ho [4] 162 Ho [5, 6] 160Ho _[5] 158 Ho

Spin 6- 6- (5-)

T1/2 37.5 min. 68 min. 60 ns 29 ns

Energy 139 keV 106 keV 118.1 keV 156.9 keV

Thus,

while both the

162Ho

and

164Ho

nuclei

FIG. 3. - The

decay of the 156.9 keV _peak.

FIG. 4. - Plot of effective inverse moments-of-inertia associated

with individual cascade transitions for 158Ho and 16oHo.

configuration,

the isomeric state observed at 118.1 keV in

i60Ho

_apparently

has not this

_{configuration}

as

reported by Leigh, Stephens

and Diamond

_[5].

These authors indicated that the 6- state should also

occur in

l6oHo

and the rotational band observed is

probably

based on this state with the

_{configuration}

6 -,

p

7/2-

[523]

T

n

5/2+

_[642]

_T.

This conclusion was

based on the _{very great}

_similarity

between the _sequence

of _y-rays transitions in both

16’Ho

and

160Ho.

Moreover the oscillations in the _energy level

_spacings

for

162Ho

and

l6oHo

obtained

_{by plotting}

are in

_phase.

The isomeric state could be a 5 - state with the

_{configuration}

p

7/2-

[523] T

n

3/2+

[402] ~.

FIG. 5. - Proposed level scheme of 158Ho.

L-200 JOURNAL DE _{PHYSIQUE -} LETTRES

configuration

which shows _strong

_perturbation

_by

Coriolis

_coupling.

The

_increasing

_perturbation

of the

p

7/2- [523]

band with

decreasing

mass number is

indicated

_by

the variation of the

_strength

of

fluctua-tions in

_neighbouring

157 Ho

and

is9Ho

nuclei

_[7].

Figure

4 shows this in a

_plot

of

f(2 /)2

for

160Ho

and 158Ho. It is clear that the

_perturbation

in the

energy level

spacing

of

158Ho

is

stronger

than that

in 160Ho.

If we _suppose that the curves

(EI -

_{EI _ 1)/2}

I

must be in

_phase

in both

160Ho

and

_158Ho,

the

156.9 keV state of

_spin

5- must be

_assigned

as the

isomeric state in the

158 Ho

nucleus. The

spin

I = K = 6 -

might

be attributed _to the head of the

rotational band.

However,

two other

_assumptions

are also

_{possible :}

1)

The 6- state could be attributed as the isomeric

state and considered as the head of the rotational

band.

2)

The isomeric state could be

_assigned

as the 5

-state

_{by supposing}

a weak transition between the 6-and 5 - state. We could not see a _gamma line of such

low _energy with our

_experimental

_arrangement;

if _present, it is

_{undoubtedly highly}

converted and will be difficult to observe. In this case the _y-ray

of 72.9 keV could

_represent

the transition between the 7- and 6- states.

By

choosing

the

_spin

and

_parity

of the isomeric state as

_{5 -,}

a

_{possible configuration}

for this state is p

7/2- [523] T

n

3/2+

[402] 1.

According

to

Galla-gher-Moszkowski’s rule,

the 2- state of 67.3 keV

in 158Ho

is the lower member of the doublet.

However,

this situation leads to a different

_{interpretation}

from

that

_given

in refs.

_[2,

_3].

4. Conclusion. -

a)

The level scheme of

158Ho

proposed

on the basis of our

_experiments

is shown in

figure

5.

b)

The rotational band observed in

158Ho

is

highly perturbed by

Coriolis

_coupling.

This is due to the fact that the orbits of the _proton and neutron states

_originate

from

_high-j

shells of

_hll~z

and

_i13/2

respectively

and to the fact that with

_decreasing

A the

_perturbation

increases

_rapidly

in the

_neighbouring

odd-A nuclei.

Acknowledgments.

- It is

a

_pleasure

to thank

Dr. R.

_Piepenbring

and Dr. S. Andre for fruitful discussions and comments.

References

[1] STENSTRÖM, T. and JUNG, B., Nucl. _Phys. 64 ₍₁₉₆₅₎ 209.

[2] ABDURAZAKOV, A. S., GROMOV, K. Ya., ZHELEV, Zh. T., KALIN-NIKOV, V. G., LIPTAK, Ya., NAZAROV, U. K. and

URBA-NETS, Ya., Sov. J. Nucl. _Phys. 8 (1969) 367.

[3] HARMATZ, B. and HANDLEY, T. _H., Nucl. Phys. A 191 (1972)

497.

[4] JØRGENSEN, M. H., NIELSEN, O. B. and SKILBREID, O., Nucl.

Phys. 84 (1966) 569.

[5] LEIGH, J. R., STEPHENS, F. S. and DIAMOND, R. M., Phys.

Lett. 33B (1970) 410.

[6] EKSTRÖM, C., NORELAND, T., OLSMATS, M. and WANNBERG, B.,

Nucl. Phys. A 135 ₍₁₉₆₉₎ 289.

[7] DIAMOND, R. M., International _Conference on the _Properties