Abstracts for Experiments with AYEball

exp 545

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.

exp 557

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.

exp 577

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.

exp 561

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.

exp 475

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.

exp 541

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.

exp 525

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.

exp 549

Sean's Radium run

exp 559

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.

exp 547

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.

exp 571

We propose to study the nucleus 226U...

exp 515

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.

exp 579

24Mg run