Aidan Byrne

Shape coexistence in very neutron-deficient Pt isotopes

Yrast bands in 176Pt(N=98) and 178Pt have been identified. The level scheme of 176Pt changes from a quasi-vibrational pattern to that of a well deformed rotor, at very low spins, a behaviour similar to that attributed to shape coexistence in the light Hg isotopes. Analysis of The 176-188Pt yrast bands supports a shape coexistence interpretation, the excitation energy of the intruder state behaving as predicted by Wood, (1981).

Production of terbium-152 by heavy ion reactions and proton induced spallation.

Terbium-152 (Tb-152) is of potential value as a radiotracer for radiolanthanides in positron emission tomography. We report the production of Tb-152 by heavy ion reactions at the ANU Tandem accelerator, and by the spallation method at the CERN proton accelerator using the on-line ISOLDE separator, obtaining microcurie and millicurie yields, respectively. After purification, a phantom image in PET is obtained which shows the feasibility of using Tb-152 for monitoring the kinetics of Tb-149 and other radiolanthanides. However, the current availability of this radioisotope will be restricted to major nuclear physics research centres.

Energy dependent saturation width of swift heavy ion shaped embedded Au nanoparticles

P.K. and M.C.R. thank the Australian Research Council for support. P.K., R.G., D.J.S., and M.C.R. were supported by the Australian Synchrotron Research Program, funded by the Commonwealth of Australia via the Major National Research Facilities Program.

Non-yrast states and shape co-existence in light Pt isotopes

Abstract Low-lying states in the even-even light platinum isotopes 176Pt, 178Pt, 180Pt and 182Pt have been populated using β+ /EC decay from parent gold nuclei, created in (HI,xn) reactions. State energies, spins and parities and γ-ray branching ratios were determined using γ-ray and electron spectroscopy. Whereas non-yrast states were observed in 178Pt, 180Pt and 182Pt, none were seen in 176Pt. The excitation energies of the observed states are analysed in terms of a band-mixing model, yielding the moments of inertia of the unperturbed bands. Branching ratios and ground-state-band quadrupole moments are calculated and compared with experimental values. The results indicate that the two lowest-lying 0+ states in each of the light Pt isotopes are formed from the mixing of two intrinsic states of different deformation, and other low-lying states can be described as admixtures of rotational states built on these intrinsic states, and on γ-vibrational states.

Structural modification of swift heavy ion irradiated amorphous Ge layers

Swift heavy ion (SHI) irradiation of amorphous Si (a-Si) at non-perpendicular incidence leads to non-saturable plastic flow. The positive direction of flow suggests that a liquid phase of similar density to that of the amorphous solid must exist and accordingly a-Si behaves like a conventional glass under SHI irradiation. For room-temperature irradiation of a-Si, plastic flow is accompanied by swelling due to the formation of voids and a porous structure. For this paper, we have investigated the influence of SHI irradiation at room temperature on amorphous Ge (a-Ge), the latter produced by ion implantation of crystalline Ge substrates. Like a-Si, positive plastic flow is apparent, demonstrating that liquid polymorphism is common to these two semiconductors. Porosity is also observed, again confined to the amorphous phase and the result of electronic energy deposition. Enhanced plastic flow coupled with a volume expansion is clearly responsible for the structural modification of both a-Si and a-Ge irradiated at room temperature with swift heavy ions.

Energy depression of high-spin core-excited states in radon nuclei

Inclusion of the effective residual interaction determined from empirical two-body spectra accounts for most of the energy depression of high-spin core-excited isomers in the Rn isotopes.

Nanoscale density fluctuations in swift heavy ion irradiated amorphous SiO2

We report on the observation of nanoscale density fluctuations in 2 μm thick amorphous SiO2 layers irradiated with 185 MeV Au ions. At high fluences, in excess of approximately 5 × 1012 ions/cm2, where the surface is completely covered by ion tracks, synchrotron small angle x-ray scattering measurements reveal the existence of a steady state of density fluctuations. In agreement with molecular dynamics simulations, this steady state is consistent with an ion track “annihilation” process, where high-density regions generated in the periphery of new tracks fill in low-density regions located at the center of existing tracks.

Transverse BGO Compton suppression shield

The performance of a Compton suppressed Ge spectrometer, that utilizes a transverse BGO suppression shield, is presented. A comparison of the experimental measurements and Monte Carlo calculations is made.

Monte Carlo calculations for asymmetric NaI(Tl) and BGO compton suppression shields

A simple Monte Carlo model is used to calculate the response of a NaI(Tl) Compton suppression shield of an asymmetric design. The results are compared with source measurements. The predicted response at low energies is only obtained when coincidence techniques are used to remove incident γ-rays which have energies below that of a nominally mono-energetic source. The Monte Carlo model is then applied to a BGO shield to predict its response as a function of size and other parameters.

IMPLANTATION-INDUCED AMORPHIZATION OF INP CHARACTERIZED WITH PERTURBED ANGULAR CORRELATION

The perturbed angular correlation (PAC) technique has been used to characterize the implantation-induced crystalline-to-amorphous transformation in InP. Radioactive 111In probes were first introduced in InP substrates which were then irradiated with Ge ions over an ion-dose range extending 2 orders of magnitude beyond that required for amorphization. Crystalline, disordered and amorphous probe environments were subsequently identified with PAC. The dose dependence of the relative fractions of the individual probe environments were determined, a direct amorphization process consistent with the overlap model was quantified and evidence for a second amorphization process via the overlap of disordered regions was observed. Given the ability to differentiate disordered and amorphous probe environments, a greater effective resolution was achieved with the PAC technique compared with other common analytical methodologies.