exotic nuclei structure and reaction noyaux exotiques ... - IPN - IN2P3

Lifetime measurement of first 2 + state in 74 Zn
IPNO Participation: B. Mouginot, M. Niikura, M. Assié, F. Azaiez, S. Franchoo, F. Ibrahim, J. A. Scarpaci,
I. Stefan D. Verney, I. Matea
Collaboration : Institut fur Kernphysik, Darmstald (Germany), Universitaet zu Koeln, Cologne
(Germany), CSNSM (France), GANIL (France), Laboratori Nazionali di Legnaro (Italy), NIPNE Bucarest
(Romania), Institute of Nuclear Research Debrecen (Hungary), University of Sofia (Bulgaria),
Flerov Laboratory Dubna (Russia)
Les noyaux riches en neutrons autour de 78 Ni sont actuellement intensément étudiés par des équipes de
physique et astrophysique nucléaire de part le monde. Nous rapportons ici la mesure du temps de vie des
états excités dans les isotopes de 72, 73, 74 Zn par la technique du PLUNGER différentiel. Ces mesures nous
permettront de contraindre les modèles nucléaires et de répondre aux questions liées au caractère
magique du 78 Ni.
Introduction
The neutron-rich isotopes in the vicinity of 78 Ni are
in the focus of modern nuclear physics and
astrophysics studies [1-7]. This is a report on the
lifetime measurement of exited states in neutronrich
Zn isotopes using differential PLUNGER
technique with the aim of constraining models that
tend to predict the degree of magicity of 78 Ni.
Experiment description
The experiment was performed at the GANIL
facility. The primary beam used was 76 Ge at 60
A.MeV. Maximum intensity used was 2 eµA. The
secondary 74 Zn beam at 30 MeV was produced in
the CLIM target and selected using LISE
spectrometer [11] and delivered on the PLUNGER
device placed in the first image focal point of the
spectrometer – D4. The beam impinging on the
target contained 75% 74 Zn, 20% 73 Zn and 5%
72 Cu. PLUNGER device consisted in 30 mg/cm 2
CD 2 target and 55 mg/cm 2 Be degrader.
two rings around the target, first at 45° and second
at 135° compared with the beam direction. The
reaction products were transmitted to the end of
the spectrometer, D6, were the products impinge
on a (dE,E) system. For a precise time of flight
(ToF) measurement, two MCP (Multichannel plate)
were used, one placed in front of the PLUNGER
device, second in front of the (dE,E) system. The
ToF measurement allows an accurate velocity
measurement for the nuclei traveling between the
PLUNGER degrader and and the (dE,E) system.
The velocity of the reaction products is necessary
for Doppler correction of the measured gamma
decay in EXOGAM detectors.
For PLUNGER calibration purposes the 30+
charge state of the primary beam was selected
The distance between the target and the degrader
Fig. 2: Background subtracted gamma spectra
measured at 45° (upper image) and 135°
compared with beam direction. We see gamma
lines from 72,73,74 Zn.
Fig. 1: The Cologne PLUNGER device
could be changed between 0 – 40 mm with a 10
um precision. The target was surrounded by eight
EXOGAM clovers. The detectors were placed in
with the LISE spectrometer and sent on the target.
This allowed for the lifetime measurement of the
first 2+ state in 76 Ge.
The center-of-mass gamma spectra corrected for
the velocity of 74 Zn are shown in Fig. 2. The
spectra were obtained when the target and
degrader were touching eachother. We clearly see
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