K. H. Abu Saleem

Identification of excited structures in proton unbound nuclei 173,175,177Au: shape co-existence and intruder bands

Abstract Excited states in the proton-unbound 173,175,177 Au nuclei were identified for the first time. Level structures associated with three different shapes were observed in 175 Au. While the yrast lines of 175 Au and 177 Au consist of a prolate band built upon the intruder 1/2 + [660] ( i 13/2 ) proton orbital, no sign of collectivity was observed in the lighter 173 Au isotope. Implications for the deformation associated with these structures are discussed with a focus on shape co-existence in the vicinity of the proton-drip line.

Diffraction efficiency and diffraction bandwidth of thermal-gradient and composition-gradient crystals

Measurements were made at the Advanced Photon Source at Argonne National Laboratory on the diffraction efficiency and diffraction bandwidth of a thermal-gradient crystal (Si) and a composition-gradient crystal (Si-Ge) to which a thermal gradient was applied. Gradient crystals are crystals in which the spacing between crystalline planes varies with the position in the crystal. This change in the crystal plane spacing is obtained by applying a thermal gradient to a single crystal or by growing a two-component crystal in which the ratio of the two components changes with position in the crystal. Measurements were made at two energies, 92.6 and 153 keV. Both crystals were 1-cm cubes. Laue diffraction (transmission diffraction) was used in all experiments. The thermal gradient was applied perpendicular to the [111] diffraction planes of the pure silicon crystal and perpendicular the [400] diffraction planes in the composition-gradient crystal (Si-Ge). The thermal gradient applied to the crystals was quite unif...

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.

Extending the region of triaxial superdeformation: Candidate TSD bands in 174Hf

Abstract Three, possibly four, regularly spaced rotational bands with large dynamic moments of inertia have been identified in 174 Hf. Their properties are consistent with known triaxial superdeformed bands of the Lu/Hf region. Calculations predict substantial triaxial deformation ( γ ≈±17°) for 174 Hf structures with deformation ϵ 2 ≈0.45, despite the fact that 174 Hf is eight neutrons away from the previously established N =94 triaxial superdeformed gap. Shell gaps at N =100 and 106 with γ ⩾15° are predicted for ϵ 2 ≈0.45, and are most likely responsible for the calculated TSD minima in 174 Hf.

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.

Performance of a Be Refractive Lens

The performance of a beryllium compound refractive lens (CRL) was tested in the energy range of 11.5 to 8.0 keV. The beryllium refractive lens consists of 50 aligned, 1‐mm‐diameter, hollow spheres in a solid block of beryllium, 30 mm × 20 mm × 55 mm. The minimum web between each hollow sphere was 0.10 mm. The measured focal length of the lens for x‐rays close to the axis of the beam was 147.7 cm +/− 2.0 cm at 10 keV and 120.2 +/− 2.0 cm at 9.1 keV. These values agree well with the theoretical values of 146.6 cm and 121.4 cm, respectively. The diameter of the best focus obtained at 10 keV was 35 μm horizontal and 45 μm vertical. For the modified version of the lens used in the 9.1 keV experiment these values were 25 μm horizontal and 35 μm vertical. The x‐ray beam cross section for the 10 keV and the 9.1 keV experiments were 0.50 mm × 0.50 mm and 0.30 mm × 0.30 mm, respectively. The enhancement of the flux (photons per sq. mm) was 50:1 at 10 keV and 80:1 in the 9.1 keV experiment.

Limits of the energy-spin phase space beyond the proton drip line: entry distributions of Pt and Au isobars

Abstract Entry distributions in angular momentum and excitation energy have been measured for several very proton-rich isotopes of Pt and Au. This is the first systematic study of the energy-spin phase space for nuclei near and beyond the proton drip line. Comparisons are made between the distributions associated with proton-unbound Au nuclei and more stable Pt isobars. In 173 Au the first evidence is seen for the limits of excitation energy and angular momentum which a nucleus beyond the proton drip line can sustain.

Possible Triaxial Superdeformation in 174 Hf

Four regularly spaced rotational bands with large dynamical moments of inertia, which are consistent with known superdeformed bands in the Lu/Hf region, have been identified in 174Hf. The states were populated in the 130Te(48Ca,4n) reaction at a beam energy of 194 MeV. The Gammasphere array detected the emitted gamma radiation. Ultimate cranker calculations predict substantial triaxial deformation (γ ≈ ±17°) for highly deformed 174Hf structures. However, 174Hf is eight neutrons away from the previously established N = 94 triaxial superdeformed shell gap. Shell gaps at N = 100 and 106 with γ ⩾ 15° are observed when e2 ≈ 0.45, which may be responsible for the predicted TSD minima in 174Hf.

Limits Of The Energy‐Spin Phase Space Beyond The Proton Drip Line: Entry Distributions Of Pt And Au Isobars

The systematic study of entry distributions populating proton‐rich Pt and Au isotopes indicates a limit in the excitation energy and angular momentum in the population of 173Au, a nucleus beyond the proton drip line.