REINA() DE TRABALHO SOBRE FiSICA NUCLEAR NO BRASIL

XX RTFNB - Resumos - 02/09/97 19
The 7—ray spectroscopy of low- Z or very neutron defficient
evaporation residues is difficult because of the
strong competition among 'many open channels. Typically
2 to 5 particles are evaporated from a heavyion
reaction, in varied combinations of protons, neutrons
and alpha particles. A partial selection of specific
channels can be made by detecting and identifying
some or all of the evaporating particles. Indeed, the use
of ancillary charged particle detectors can significantly
improve the resolving power of 7—ray spectrometers.
The 7-spectroscopy group of the Pelletron Laboratory
has interest in the study of the A re. 100, 80 and 30
mass regions, which would benefit from the use of an
evaporation-- channel filtering device. The design of the
4x charged particle telescope array was based on ref. [1].
The system consists of 12 plastic phnswich scintillators,
disposed in the geometry of a dodecahedron. Each telescope
consists of a 0.1 mm thick fast scintillation decay
time BC400 AE detector bonded to a 10 mm thick
long decay time BC444 E detector. The detector faces
have a diameter of 2 cm. The E and AE detectors are
bonded toghether by the vacuum heat press technique
[2] in order to avoid the presence of a dead layer. The
target chamber also serves as a support for the detectors,
and has the shape of a semi-regular polyhedron
with 12 pentagonal and 20 triangular faces. It is built
of aluminum and is divided in two hemispheres excavated
inside in order Lo minimize 7 ray absorption. The
chamber has a diameter of 14 cm, and the whole system,
including the photornultiplier tubes and bases fits
in a sphere of 24 cm diameter. The 7-ray detectors are
aligried with the triangular faces.
[1]F. Lidiin, Nucl. Inst. and Meth. A288 (1990), 455
[2]C. A. Pruneau et at, Nucl. Inst. and Meth. A297
(1990), 404.
DSAM LIFETIMES IN THE DOUBLY ODD
NUCLEUS 134Pr
M. N. Rao, H.. V. RIBAS, N. H. MEDINA, M. A.
Rizzurro, E. W. CYBULSKA. J. R. B. OLIVEIRA
Department() de Fisica Nuclear, Institute de Fitica USP
F. ft. ESPINOZA-QUIFIONES
Departamento de Alien CCE, Universidade Estadual de
Lendrina, Londrina, PR, Brasil
1). BAZZACCO, S. LUNARDI, C. M. PETRACHE, ZS.
PODOLYAK, C. ROSSI ALVAREZ, T. SCANEERLA, C.
A.. UR
Dipartimento de Fisica and INFN„ Sezione di Padova,
Padova, Italy
R. VENTURELLI, D. DE ACuRA., G. DE ANGELIS, M.
DE POLL, E. FARNEA, A. OADEA, D. R. NAPOLI, L.
H. ZHU
INFN, Laborateri Nazionati di Legnero, Ugrian+, Italy
A. DEWALD, J. OARLESKE, P. VON BRENTANO.
Institut fiir Kernphysik der Universitat zu Koln, Kan,
Germany
Information on highly deformed rotational hands in the
doubly odd ' 34Pr nucleus has become available quite
recently [1,2]. One of these bands has been tentatively
assigned a r(h1v2) 3 0 v(I7/2,119/2) configuration, while
the other band is thought to have the ir(h1i/2) 3 0 vilayz
configuration. Thus one would expect the latter band
to have a more deformed nuclear shape.
The present note reports on a Doppler broadened lineshape
lifetime measurement in this nucleus. The rotational
bands in 134Pr were populated by bombarding a Aubacked
110Pd target with 130 MeV 'Si beam provided
by the XTU tandem accelerator of the Legnaro National
Laboratory. The GASP array, BOO inner ball and
the multi-telescope particle detector ball (ISIS) were
utilized in order to select the proton gated events. Data
were of sufficiently good statistics to obtain dean gated
spectra for the positive parity E2 band. The Doppler
broadened lineshapes for a cascade of 6 transitions in
this band were fitted for 5 of the 7 rings of detectors
(36°, 60°, 90°, 120° and 146") in the GASP array. The
analysis of data was performed with the computer code
LINESHAPE [3], assuming rotational-band side feeding
for each of the levels of interest. The slowing down
of the Pr recoiling nuclei was described with two sets
of electronic stopping, viz., shell-corrected Northcliffe-
Schilling and Ziegler's heavy-ion stopping powers.
[1]K.Ilausehild et.al ., Phys. Rev. C50 (1994) 707
[2]C.M.Petrache et al., Nucl. Phys. A.597 (3996) 106
[3]J.C.Wells and N.lt.Johnson, OItNL Report (1996),
unpublished
PRELIMINARY RESULTS FOR. THE I'La
NUCLEUS
M. A. RTZZUTTO, E. W. CYBULSKA, .1. B., B.
OLIVEIRA., R.. V. RIBAS, N. H. MEDINA, M. N.
Rao, W. A. SEALE, 0. ZAHN, C. FRANCA, 3.
A LCANTAII -Nrili,*EZ
Institato de Fisica, Universidade de san Paulo, Sao Paulo,
Brazil
. R. ESPINOZA-QUISIONES
Departamento de Pisicu - CCE, Universidade Estadual do
bondrina, Londrina, PR, Brazil
With the view of extending the systematics of odd and
odd-odd nuclei in the A = 130 - 140 mass region towards
to the N = 82 closed shell, the nucleus 1"La was
studied with in-beam -y-ray spectroscopy. The nuclei
in the region Z 50 and N re 80 are of interest because
the Fermi surface is close to the top of the neutron
intruder h1112 subshell and the proton one is at the
bottom of this subshell, causing a competition between
the neutron oblate and proton prolate driving forces.
This competition can result in shape transitions from
prolate (N = 73) to triaxial or oblate (N = 80) forms.