Abstracts for Experiments with AYEball
We propose to extend information on excited states in N=Z nuclei beyond
82Mo towards 100Sn. It is known that the deformed shell
gaps play a vital role in stabilizing nuclear shapes at particular values of Z,
N, and angular momentum. When we come near these shell gaps, we get abrupt
changes in nuclear shape due to the polarizing infulences of high angular
momentum nuclear orbits. The special nature of N=Z nuclei means that these
effects are particularly dramatic since the neutrons and protons are filling the
same orbits. The production of these N=Z nuclei is difficult as they lie far
from stability and have production cross-sections which are typically less than
10-4 of teh fusion cross-section. Accordingly, thses nuclei can only
be studied in recoil-gamma coincidence experiments. This requires the use of the
FMA, the newly commissioned Daresbury-ANL ion chamber, and a large array of
gamma-ray detectors loaned from the Eurogam equipment pool.
We propose to study the experimental problems associated with the production of
N=Z nuclei around 100Sn utilizing a "double" reaction, where a
primary beam is used to produce residues which will have suffucient recoil
energy to induce further fusion reactions on a secondary target leading to a
production of exotic final products in the vicinity of A~100. Based on our
estimates , a 58Ni beam and targets of 12C and
40Ca will produce ~ 100-500 secondary residues/hour at the PPAC
detector. It is the goal of this experiment to understand the secondary
production rate and isotopic yields as well as determine the backgrounds
resulting from these projectile target combinations.
We propose to study the single-particle energies and neutron-neutron two-body
interactions with respect to the 100Sn core. In-beam gamma-ray
transitions in 103Sn will be detected in an array of 20 Ge
detectors. Reaction channel selection will be obtained using the FMA with the
ion chamber placed at the focal plane as well as with the Vanderbilt array of
neutron detectors downstream of the target.
It is proposed to use the FMA in order to identify gamma-ray transitions in the
doubly odd 110Sb and 110I, and even-even 110Xe
isobars. A 240-MeV beam of 58Ni will be used to bombard targets of
56Fe and 58Ni.
We propose to study the N=Z nucleus 68Se using the FMA coupled to the
AYEball Ge detector array. The Daresbury-ANL ion chamber will be used behind the
focal plane of the FMA for Z-identification of the residual nuclei.
The aim of this proposal is to make the first study of an odd-odd N=Z nucleus in
the 28-50 shell in order to probe the role of the T=0 pair in the structure of
such nuclei. The nucleus will be studied via the gamma rays emitted in a
near-barrier fusion evaporation reaction, using the FMA to detect the recoil and
the new ionization chamber to allow both mass and charge identification. A
parallel theoretical effort will be made to apply the isospin invariant IBM
framework to this class of nuclei.
It is proposed to study the low-lying structure of the neutron-deficient
isotope, 200Rn, using the 176Hf(28Si,4n)
reaction. Gamma-ray transitions between excited states in 200Rn will
be identified by mass tagging using the FMA and by the observation of
X-rays. The deduced level scheme will be used to address the predictions of a
ground-state deformed shape for this nucleus, thereby testing the predictions of
a new region of deformation.
Sean's Radium run
Recent Nilsson-Strutinsky calculations by Nazarewicz using a Woods-Saxon
potential have indicated that another region of superdeformation should exist
for Hg isotopes with N<=98. The calculations indicate that the states in the
SD well become yrast between I=30 and 40 h. This is the spin region for which
the SD states are calculated to be yrast for the known SD region of Z=80 and
N>=110. Presently, no excited states are known in Hg isotopes of A<180. This
is due to the fact that cross-sections to make these nuclei are small (<5mb)
and fission dominates in heavy-ion fusion reactions. As a first step in looking
for SD bands in these nuclei, we propose to establish the lower lying excited
states in these nuclei using the recoil-decay tagging technique where gamma rays
emitted from excited residues are correlated with the charged particle
radioactivity of their decay.
In the penultimate month of operation at the Nuclear Structure Facility,
Daresbury, the unique opportunity occurred to couple together the Eurogam ge
detector array with the recoil separator and the Edinburgh Double-Sided Silicon
Detector (DSSD). The basic principle of the Recoil-Decay Tagging (RDT) method
was to correlate charged-particle radioactive decays having a unique signature
(alpha, delayed proton, direct proton) with preceding implanted ions which in
turn were in fast delayed coincidence with gamma rays emitted at the target
position. New in-beam gamma-ray spectroscopy information was obtained for the
highly neutron-deficient isotopes 180,109Te, 109I, and
114Xe. The FMA offers a factor of ~5 improvement in recoil detection
efficiency which presents a great opportunity to study in-beam gamma-ray
spectroscopy of highly neutron-deficient emitting charged particles from their
ground states.
We propose to study the nucleus 226U...
We have used "standard" in-beam gamma-ray spectroscopy techniques to study the
high-spin states of A=181 through 187 Au isotopes. To study the next lighter
ones, it will be necessary to gate on the actual Au recoils or on emitted
charged particles. We propose to use the FMA in conjunction with an array of Ge
detectors around the target to study 179Au. The main purpose of the
experiment is to locate and study properties of the intruder
proton i13/2 state. In particular, we are interested in the trend of the
energy and deformation characteristics of the proton i13/2 orbital,
comparing TRS calculations that predict the departure of the intruder state from
the low energy spectrum of states at some point.
24Mg run