Cary N. Davids

Proton radioactivity from highly deformed nuclei.

Proton emission half-lives are calculated within the DWBA formalism for {sup 131}Eu and {sup 141}Ho assuming permanent quadruple deformation. The decay rates are consistent with a decay from either [411 3/2] or [413 5/2] Nilsson states for {sup 131}Eu and [523 7/2] Nilsson state for {sup 141}Ho.

Isovector pairing in odd-odd N = Z 50Mn

High-spin states in the odd–odd N=Z nucleus 5025Mn have been investigated. A sequence of states up to Jπ=6+ has been assigned as the T=1 analogue of the yrast band in 5024Cr for the first time. The differences in energy between levels in these bands are interpreted in terms of rotational alignments and the effect they have on the Coulomb energy of the nucleus. Comparisons with shell model calculations show that the Coulomb energy difference between the T=1 analogue structures is an important indicator of the competition between isovector pairing modes in N=Z nuclei and their isobars.

Identification of excited states in 140Dy.

Excited structures in the proton-rich nucleus 140 Dy have been established following the decay of an 8 − isomer. The excitation energy of the isomer is established to be 2.16 MeV with a half-life of 7.3 ± 1.5 µs. The isomer decays into the yrast line at the 8 + state, revealing a rotational band with a deduced deformation of β2 = 0.24(3). The isotope 140 Dy is the daughter of the deformed proton emitter 141 Ho. The new information obtained here supports the role of deformation in proton emission and the previous assignments of single-particle configurations to the two proton emitting states in 141 Ho. In addition, the reduced hindrance factor measured for the isomer is consistent with the trend observed in the N = 74 isotones.  2002 Elsevier Science B.V. All rights reserved.

First observation of excited structures in neutron-deficient 179Hg: evidence for multiple shape coexistence

Abstract Excited structures in the neutron-deficient nucleus 179 Hg have been established for the first time using the Gammasphere spectrometer in conjunction with the fragment mass analyzer. Competing states originating from three different minima associated with nearly spherical, oblate, and prolate deformations were found. This result can be contrasted with the situation in heavier odd-mass Hg isotopes where only two minima (oblate and prolate) have been seen. The implications of these three shapes at low spin and excitation energy are discussed in the general context of shape coexistence in this mass region.

Experiments with a radioactive 56Ni beam

Abstract A technique for producing a high-quality radioactive 56 Ni (T 1/2 =6.1 d ) beam via the two-accelerator method has been developed. Beam intensities of 2×10 7 56 Ni/s were extracted from the ion source and 2×10 4 56 Ni/s were delivered to the target. For a study of neutron transfer reactions in inverse kinematics, a high-efficiency detection system was built consisting of a large solid angle (2.8 sr), high-granularity Si detector array for measuring the outgoing protons in coincidence with the heavy reaction products identified with respect to mass A and nuclear charge Z in the focal plane of a recoil mass separator.

Study of radiative capture reactions with radioactive ion beams

A technique for separating and identifying reaction products from radiative capture reactions induced by radioactive ion beams has been developed. The {sup 18}F(p,{gamma}){sup 19}Ne and {sup 18}O(p,{gamma}){sup 19}F reactions have been measured in inverse kinematics by identifying the {sup 19}F and {sup 19}Ne reaction products with respect to mass and charge at forward angles in the Fragment Mass Analyzer. A total detection efficiency of 30% and a suppression factor for the incident beam relative to the (p,{gamma}) reaction products of better than 10{sup 12}:1 was achieved. Details of the detection technique, the beam monitoring procedure as well as experience in the use of polypropylene targets in experiments with radioactive beams are discussed.

Proton decay: spectroscopic probe beyond the proton drip line

Proton decay has been transformed in recent years from an exotic phenomenon into a powerful spectroscopic tool. The frontiers of experimental and theoretical proton-decay studies will be reviewed. Different aspects of proton decay will be illustrated with recent results on the deformed proton emitter 135 Tb, the odd-odd deformed proton emitter 130 Eu, the complex fine structure in the odd-odd 146 Tm nucleus and on excited states in the transitional proton emitter 145 Tm.

Nuclear pairing and Coriolis effects in proton emitters

Abstract.We introduce a Hartree-Fock-Bogoliubov mean-field approach to treat the problem of proton emission from a deformed nucleus. By substituting a rigid rotor in a particle-rotor model with a mean field, we obtain a better description of experimental data in 141Ho. The approach also elucidates the softening of kinematic coupling between particle and collective rotation, the Coriolis attenuation problem.

Prompt compound nuclear K X-rays in fusion reactions induced by a heavy projectile

Abstract Prompt K X-rays were studied in compound nuclear reactions induced by a heavy projectile. Total production cross sections and multiplicities of K X-rays were measured for the systems 32 S + 116, 120, 124 Sn by determining X-ray singles, X-ray—X-ray coincidence, and direct evaporation residue yields over the incident energy range 130 MeV ⩽ E lab ⩽202 MeV. We find a slow dependence of the multiplicities and cross sections on target mass and incident energy, establishing the prompt K X-ray yields as a useful indicator of the complete fusion cross section behavior induced by a heavy projectile in this mass region.

Decay Rate of Triaxially-Deformed Proton Emitters

The decay rate of a triaxially‐deformed proton emitter is calculated in a particle‐rotor model, which is based on a deformed Woods‐Saxon potential and includes a deformed spin‐orbit interaction. The wave function of the I = 7/2− ground state of the deformed proton emitter 141Ho is obtained in the adiabatic limit, and a Green’s function technique is used to calculate the decay rate and branching ratio to the first excited 2+ state of the daughter nucleus. Only for values of the triaxial angle γ < 5° is good agreement obtained for both the total decay rate and the 2+ branching ratio.