Excitation and decay properties of the |31− ⊗ 31−; 2+〉 state in 208Pb

Prq

Parr

Pergamon

Vol. 38, pp. 63-64, 1997 0 1997 Elsevier Science Ltd in Great Britain. All nghts reserved 0146.6410/97 $32.00 + 0.00

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Phys.,

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Excitation and Decay Properties /3i 8 31; 2’) State in 208Pb* J. ENDERS,

P. VON

NEUMANNXOSEL,

V. Yu. PONOMAREVT fir

tnslitut

Kemphxsik,

Schlossgarrensrr.

of the

and

Technische

9, D-64289

A. RICHTER

Hochschule

Darmstndr,

Darmsmdr,

Grrman\

Abstract A nuclear

resonance

on quasiparticle-phonon

model

the experiment

In the low-energy be interpreted

spectra

should

modes

be degenerate

established

vibrations

of states

doubly-magic

phonon

an excitation MeV)

like (p,p’y)

E3 transition We propose detectors compared

state

Recent

like the Euroball

with the equipment

state.

close to the endpoint

energy

first 3- state

whether

model

calculation

(QPM)

series of (7,~‘)

of the experimental

performed

to

of two-octupole-

to identify

a two-step

was mainly = 5.241

phonon

-~ at (4.086

such excitations

Coulomb

excitation

on the high-spin

focused

members

scattering

of

probes

on the O+ member

MeV exhibits

using the nuclear efficient

composite increase

a strong

two-

by the observation

an

multiplet

the nonresonant

fluorescence germanium sensitivity

weak E2 excitations

in

energies,

the experimental with a Euroball

06 DA665

63

Dubna,

at the full energy is small),

(which

the branch

and here the background

is

to the

is large.

In

or not, we did a quasiparticle-phonon

feasibility Cluster

on the basis of results

at the S-DALINAC.

from a

For a concise

see e. g. [7-91.

1, by the Heisenberg-Landau

Research,

will be a sizable decay branch

occurs

background

could be successful

for Nuclear

resonance high-purity

in the detection

even rather

transition

setup as well as the results

Institute

.5-)

experiments.

at fairly low photon

contract

l-

coupling

to the decay of the 6+ member

some years ago, so that

experiment

under

12: 83;;

the octupole

the interest

[6] s h ow a striking

the ground-state

and estimated

measurements

*Supported by the BMBF Planck-Forschungspreis. ‘Permanent address: Joint

using highly

and therefore

a NRF

phonon

On the other hand, non-selective

of the two-octupole-phonon

has to be measured

order to judge

e.g.

neutron

of the quadruplet

scattering

Whereas

phonon

lead to a splitting

[4].

available

of the 2+ member

to the single-phonon

in inelastic

of

states

sparse. state -

at E,

can

12: 8 2:; O+, 2+, 4+) is well

have been undertaken

the O+ state

module

in photon

the possible

on octupole-octupole

which was assigned

experiments

Cluster

which

phonon is at a much higher energy

Here the attention

to look for the 2+ member

nuclei are now accessible

summary

oberved,

states

case for the study

On the one hand,

which has been indentified

[5].

test

collective

shown to belong to ‘07Pb

to the one-phonon

The signature

strongly

the quadrupole

As it was shown recently,

technique

available

at the GSI some years ago, focusing

and (n,n’-y) have been used.

component,

mea-

of two or even three

picture

and octupole

an outstanding

many attempts

parity

the phonons

excitations

O+, 2+, 4+, 6+ is rather

represents

was subsequently

of the multiplet.

Based

to the sum of the individual

between

of quadrupole

of its first excited,

[3]. The transition

the quadruplet,

is proposed

in *‘sPb.

from previous

natural

a harmonic

according

interactions

the information

[2] f or references).

was performed

estimates

collective,

of two-quadrupole

efforts,

Therefore,

(see e.g.

of the multiplet

(NRF)

“sPb

because

detectors

vibration

D ue to the coupling Within

energies

with spin and parity

and less collective.

phonon

research

[l].

occur.

and residual

energy of 2.615 MeV, whereas

in this nucleus experiment

states

the coupling

nucleus

excitations

one finds

nuclei, and the coupling

has been a topic of recent a multiplet

nuclei

multi-phonon

Whereas

and countrate

(or phonons)

and have excitation

in spherical

Cluster

seems feasible.

but anharmonicities

of the multiplets.

using Euroball

two-octupole-phonon

calculations

of spherical

as surface

elementary

excitations,

The

experiment

the long-sought

surements

these

fluorescence

with the aim to identify

Russia

program,

and through

a hIax_

64

J. Enders et al.

B(E1)=0.35

mW.u.

2.615

31

B(E2)=0.11

W.U. Fig.

v

0.000

The QPM

1: Energies and transition

phonon

Ol+

calculations

residual interaction

-

which are presented

and admixture

have been performed

144Sm showing

agreement

reasonable

B(E2; [3; @ 3~1 2+ +

within a few days. calculations,

in detail in [2] -

for the two-phonon

with experimental 0:)

While a very collective

data.

= 0.11 W.U., E3 transition

The transition

strength

of the strongly

the nonresonant

measurement

peak-to-background -

background

site to a simple

ratio for the transition

3 g target mass, electron

the transition method

well established

new tool for the investigation Many stimulating

discussions

acknowledged.

as a selective

of excitation

into the GEANT

[2] J. Enders

simulated

of dipole

10m3 W. u. Other decay

and decay properties Germanium

vol. 2, Benjamin,

(1992)

preprint

Thus, the

presents itself now as a due to

detectors. S. W. Yates, and M. Yeh are

Reading/MA

96/33

1208

Prog. Part. Nucl. Phys. 38, these proceedings Prog. Part. Nucl. Phys. 38, these proceedings

et al., Phys. Rev. Lett 76 (1996)

2029

et al., Phys. Lett B, in press GEANT3,

the signal of

of even weak E2 transitions

137

[6] J. Eberth,

R. Brun et al., program

the

of the experiment

package. Nuclear Structure,

et al., Prog. Part. Nucl. Phys. 37 (1996) 349

Herzberg

at the

to estimate

(J. E.) thanks K. Schweda and N. Huxel for their helpful

Yeh et al., Phys. Rev. Lett. 76 (1996)

[8] P. von Brentano

experiments

parameters

excitations,

with J. Gerl, G. Graw, H. J. Wollersheim,

et al., Z. Phys. A341

[7] P. von Neumann-Cosel,

in (7,~‘)

35 PA and 8 days of beam time -

[5] U. Kneissl

[lo]

x

to the ground-state

[lo] background

For reasonable

probe

et al., Nucl. Phys. A, in press; IKDA

[3] H. J. Wollersheim

191 R.-D.

= 0.35

compared

by the

and El decay

be clearly visible above the background.

of composite

One of the authors

(11 A. Bohr, B. Mottelson,

[4] Minfang

2+ -+ 3;)

to observe

nuclei observed

Carlo

in “sPb

state should

the recent progress in the development

introduction

level is predicted

of the high multipolarity,

towards lower photon energies.

of spherical Monte

beam currents of about

to the single-phonon

of NRF,

gratefully

background

With the same

in the nuclei g6Zr and

to the 2: state) can be neglected.

We compared Darmstadt

increasing

The

of the basic

For ‘OsPb one finds for the ground

of B(E1; [3; @ 3;]

transition

because

multiplets

to the one-phonon

1) is rather large, but far more difficult

(e.g.

as follows:

strengths

which is quite small but still observable

(as shown in Fig. branches

can be summarized

the energies and excitation

the partial decay width is rather small because

to dominate.

in the quasiparticle-

with other 2+ states has been taken into account.

ansatz similar calculations state transition

strengths for the decay of the

as obtained

model calculation.

has been chosen to reproduce

surface vibrations,

is found

2+ state in “‘Pb

two-phonon

CERN

report DD/EE/84-1

(1995)

(1975)