Study of 188Pt with the 190Pt(p, t)188Pt reaction

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Submitted on 1 Jan 1978

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Study of 188Pt with the 190Pt(p, t)188Pt reaction

M. Vergnes, G. Rotbard, J. Kalifa, G. Berrier, J. Vernotte, Y. Deschamps, R.

Seltz

To cite this version:

STUDY

OF

188Pt

WITH THE

_{190Pt(p, t)188Pt}

REACTION

M.

VERGNES,

G.

ROTBARD,

J.

_KALIFA,

G.

BERRIER,

J.

VERNOTTE,

Y. DESCHAMPS and R. SELTZ

_(*)

Institut de

_Physique

_Nucléaire,

BP n°

_1,

91406

_Orsay,

France

(Reçu

le 23

_{juin 1978,}

_accepte

le 12

_{juillet 1978)}

Résumé. 2014 La réaction

190Pt(p, t)188Pt

a été étudiée à 25 MeV sur une cible enrichie

(35

%).

L’intensité de la transition fondamental ~ fondamental ne diffère pas, dans la limite des erreurs,

de celles observées pour les autres _{isotopes pairs} du Pt et le _premier état O+ est faiblement excité _{(5 %)} par rapport au fondamental. Il n’y a donc aucune indication d’un

_changement

de forme

_important

entre 190 et 188.

Abstract. -

The 190Pt(p, t) 18

8Pt reaction has been studied at 25 MeV _{on an}

enriched target

(35 %).

The g.s. ~ _{g.s. intensity} does not differ 2014 within the _error limits 2014 from those observed for the

other even Pt _isotopes and the low-lying O+ level is weakly excited

(5

%) as _compared with the _ground state. There is therefore, no indication of an

_important

_shape transition between 190 and 188.

Tome 39 ?

t’7

1 er SEPTEMBRE 1978

LE

JOURNAL

DE

_{PHYSIQUE LETTRES}

Classification

’

Physics Abstracts 21.10F 2013 25.50 2013 27.70

1. Introduction. - Kumar and

Baranger [1]

long

ago

predicted

the occurrence of an oblate to

_prolate

shape

transition in

_platinum

when

_going

from the

heavy

to the

_light

_isotopes.

_Kumar,

in more recent’ calculations

_[2],

concludes that

196pt

and

192Pt

are

oblate

and 186Pt

_prolate,

the

_shape

transition

_occurring

between

192pt

and

186Pt.

Another

calculation,

by

Gbtz et al.

_[3],

_predicts

the transition as

_occurring

between A = 192 and A = 190.

The

_(p,

_t)

reaction has

_proved

_{[4, 5]}

to be

_quite

sensitive to

_shape

transitions : when

_crossing

such a

transition there is an

appreciable

reduction of the

ground

state to

_ground

state transition

_strength

(reduced overlap)

the

_{missing strength}

_{corresponding}

to the observed

_{important population}

of a

_low-lying

0+ level which is described as a

shape

isomer.

The

_{(p, t)}

reaction has

_already

been studied

_[6]

on

196,194,192Pt

_targets.

We describe in the

_present

paper the result of the

(p,

t)

reaction on the rare

target 19 OPt.

2.

_Study

of the

_{(p, t)}

reaction. - The

(p,

t)

reaction has been studied

_using

a 25 MeV _proton beam from the

_Orsay

MP tandem and a

_{split pole}

_magnetic

spectrometer. The enriched Pt was

_produced

at the

Orsay

C.S.N.S.M.

_isotope

_separator SIDONIE. A

target was

_{prepared by}

_depositing

and

_drying

a

_droplet

of

_chlorhydrate

solution on a 50

Jlgjcm2

carbon

backing.

The Pt thickness of the _target was of the

order

of 70

_Jlg/cm2.

The resolution was 35 keV

(F.W.H.M.)

and the

_{peak shapes quite}

_{asymmetrical,}

due to evident _target

_{inhomogeneities.}

The

_{peak corresponding}

to the

_188Ptg.s.

is

_clearly

identified in the _spectra and the

_{corresponding}

_angular

distribution has a standard L = 0

shape

(Fig.

1).

The

_{corresponding experimental}

_Q

value is deter-mined as

_{Q = - 7 150}

_{± 10}

keV to be

_compared

to

the Wapstra and Bos [7] value Q

= - 7193 _{± 23 keV.}

The _presence of an

_{important background}

due to

the

_(p,

_t)

reaction on all the other Pt

isotopes

and

impurities

present in the _target makes it _very difficult with the

_relatively

_poor resolution of the _present

experiment

to extract the

_angular

distributions of excited states of

188pt.

It has however been

possible

to extract the

_angular

distribution of the first excited

Oi

level at 800 keV. Its

_shape

is

_compared

to that of the

_ground

state in

_figure

1. The ratio

is 5

_%.

As we shall see later another

0+

level has been

observed in the heavier Pt

_isotopes

around 1.6 MeV.

In 18Spt

we have been able to _put a firm

limit,

R 2

%,

for any 0+ level in the excitation range between 1.5 and 2 MeV.

L-292

/ ~

-JOURNAL DE PHYSIQUE - LETTRES

FIG. 1. -

Experimental angular distributions of the tritons in the

_190Pt(p,

_t)188Pt reaction, for the _ground state and the first

excited 0+ level. The curves _{represent the average shape} of the

angular distributions _{(all practically identical)} measured in the

present experiment for all _{the g.s.} - _g.s. transitions of the heavier _Pt

isotopes. The vertical bars _{correspond only} to the statistical

uncer-tainties. For the excited 0+ level an additional source of _uncertainty,

except for the _point at _8lab = _5°,

may be due to the estimate of the substracted background.

3.

_{Isotopic composition}

of the

_target.

- The enrich-ment

of 19 opt

in the

_platinum

used to _prepare the _target

was unknown. A direct

_comparison

of the intensities

on the _g.s. -~ _g.s. transitions

_(for

_each

_-isotope)

_in

the

_(p,

_t)

reaction on

_respectively

the enriched and a

natural Pt

_target

_gave the relative

_proportions

of the

192,194,195,196,198Pt

_isotopes

in the _target.

However,

due to the

_rarity

of

190pt

in the natural Pt

_(0.012

7

_%)

the g.s. -~ _g.s. transition is not observed. It was there-fore necessary to determine the relative amount

of 19 OPt as

_compared

with one of the other

_isotopes.

The measurement was

_performed

_by

activation

analysis.

The material of the

target

and a

_sample

of natural Pt were irradiated

together

_during

3

_days

in a

thermal neutron flux of

1012

_n/cm2/s.

The obser-vation and

_intensity

measurement,

using

Ge(Li)

detectors,

of the 539 keV _{y ray} emitted in the

_decay

of

’9’Pt

₍₃

_days)

_permitted

determination of the relative amount of

190pt

in the two

_samples.

A

chemical

_separation

of

_gold

from

_platinum

was then

performed

and the

_intensity

measurement of the 158 keV _{y ray emitted in the}

_decay

of199 Au

_{(3.15 days)}

permitted

determination of the relative amount

of 198pt

in the two

_samples.

Using

both the activation and the

_(p,

_t)

_results,

it is

possible

to determine the

_composition

of the _target

given

in table I. The abundance of

190pt

is 35 ± 3.5

_%.

From _{these results the g.s.} ~ _{g.s. relative intensities}

can be determined.

TABLE I

Isotopic

composition

of

the target

(%)

4. Discussion. - The relative

g.s. -~ _{g.s. intensities}

for all the stable Pt targets, normalized to 100 for the

_{194Ptg.s. -+ 192Ptg.s.}

transition,

are

compared

in

table II. It is clear that no

_important

variation is

observed

_although

there is

_possibly

an indication of a

slight

increase for the two

_lighter

_targets. This

result,

as well as the small relative value

(5 %)

of the

popu-lation

of the first

_low-lying

0+

level,

indicates that no

significant shape

transition occurs between A = 190

and A =

_188,

_so

that 188 Pt

has _a

shape

similar to that of the heavier Pt

_isotopes.

If there is a

_shape

_transition,

it should therefore occur between A = 188 and

A = 186. This is in

agreement with the

_striking

discontinuity

observed at this

_place

in the VMI

treatment

_[8]

of the

_experimental

_energies

and with the

shape

transition observed

_{recently [9]}

for the odd

isotopes

between 187pt

and

185pt:

Besides the

_low-lying

first 0+

_level,

_interpreted

_by

us

_[10]

as

corresponding mainly

to a two

_{phonons y}

vibration,

another

_higher-lying

0+ level has been observed

_{[6, 10]}

in

_{194,192,190Pt,}

its

_population

_being

of the order of 6

_%

of the

_ground

state one and its

energy

being practically

the same in the 3

_isotopes

(respectively

1 546,

1 617 and 1 670

_keV).

It is

_clear,

from the limit we have been able to fix for _any 0+

level

in 188Pt

between 1.5 and 2 MeV

_(R

2

_%),

that the

_population

of this level

_{drops significantly}

in 188Pt.

- Such an

_effect,

as well as the similar

_ground

state to

ground

state

intensities

observed in the _present

experiment

for all the Pt

_targets,

is

_correctly

pre-dicted

_by

Iachello and Scholten

_[11]

in the

_interacting

bosons model of the Pt nuclei.

-TABLE II

L-293 STUDY OF 188pt WITH

_{THE , ~ 9°Pt(p,}

t)188pt REACTION

Acknowledgments.

- The authors

gratefully

acknowledge

the C.S.N.S.M. SIDONIE

_separator

group,

particularly

M.

Meunier,

M.

Ligonniere

and G.

Moroy

for the

_preparation

of the enriched

190pt

and Y.

_Legoux,

from the

I.P.N.,

for the fabrication of the

_target

and her

_{help during}

the activation

analysis.

References

[1] KUMAR, K. and BARANGER, M., Nucl. Phys. A 122 (1968)

273.

[2] KUMAR, K., Proceedings of Conf. on _{properties of} nuclei far from stability, Leysin CERN _Report 1970 (70-30), p. 779.

[3] GÖTZ, U., PAULI, H. C., ALDER, K., JUNKER, K., Nucl. Phys.

A 192 (1972) 1.

[4] HINDS, S., BJERREGAARD, J. H., HANSEN, O. and NATHAN, O.,

Phys. Lett. 14 (1965) 48.

BJERREGAARD, J. H., HANSEN, O. and NATHAN, O., Nucl.

Phys. 86 (1966) 145.

MAXWELL, J. R., REYNOLDS, G. M. and HINTZ, N. _{M., Phys.} Rev. 151 (1966) 1000.

DEBENHAM, P. and HINTZ, N. M., Phys. Rev. Lett. 25 (1970)

44.

[5] VERGNES, M. _N., ROTBARD, G., GUILBAUT, F., ARDOUIN, D.,

LEBRUN, C., FLYNN, E. R., HANSEN, D. and _ORBESEN, S. D.,

Phys. Lett. 72B (1978) 447.

[6] VERGNES, M., ROTBARD, G., KALIFA, J., VERNOTTE, J.,

BER-RIER, G., SELTZ, R., SHARMA, H. L. and HINTZ, N. M., B.A.P.S. II, 21, 8 (1976) 976 and to be _published. [7] WAPSTRA, H. and Bos, K., Atom. Data Nucl. Data Tables

19 (1977) 215.

[8] MARISCOTTI, M. A. _{J., SCHARF-GOLDHABER,} G. _{and BUCK,} B.,

Phys. Rev. 178 (1969) 1864.

[9] BOURGEOIS, C. et al., Cargèse Conférence 1976 _{(CERN Report} 76-13, p. 456).

[10] VERGNES, M., Proceedings of the _{Colloque Franco-Japonais}

and INS _{Symposium, Tokyo-Dogashima (Institute} for Nuclear _{Study, University} of _{Tokyo, 1976), p.} 61-75.