Investigation of the role of neutron transfer in the fusion of 32,34S with 197Au,208Pb using quasi-elastic scattering

Excitation functions for quasi-elastic scattering have been measured at backward angles for the systems 32,34S+197Au and 32,34S+208Pb for energies spanning the Coulomb barrier. Representative distributions, sensitive to the low energy part of the fusion barrier distribution, have been extracted from the data. For the fusion reactions of 32,34S with 197Au couplings related to the nuclear structure of 197Au appear to be dominant in shaping the low energy part of the barrier distibution. For the system 32S+208Pb the barrier distribution is broader and extends further to lower energies, than in the case of 34S+208Pb. This is consistent with the interpretation that the neutron pick-up channels are energetically more favoured in the 32S induced reaction and therefore couple more strongly to the relative motion. It may also be due to the increased collectivity of 32S, when compared with 34S

Clean recoil implantation of the 100Pd/Rh TDPAC probe using a solenoidal separator

The synthesis and recoil implantation of the 100Pd/Rh probe for time differential perturbed angular correlation (TDPAC) spectroscopy using the solenoidal reaction product separator SOLITAIRE has been demonstrated for the first time. The separator suppres

A low-pain assessment model for laboratories and tutorials

Continuous assessment motivates students to become engaged with coursework, but presents challenges for staff due to the workload involved in marking and delivering feedback. Care must be taken to avoid students concentrating on simply accumulating marks, to the detriment of learning. We present a Checkpoint assessment model which strives to find a balance between these factors, and show how the Checkpoint model can be applied in tutorial and laboratory environments. Based on an evaluation of changes to student attitudes and performance within a large first-year physics course, we conclude that the Checkpoint model is effective at improving both student satisfaction and results

Fusion around the barrier for 7Li + 12C

Fusion cross-sections for the 7Li + 12C reaction have been measured at energies above the Coulomb barrier by the direct detection of evaporation residues. The heavy evaporation residues with energies below 3 MeV could not be separated out from the a-particles in the spectrum and hence their contribution was estimated using statistical model calculations. The present work indicates that suppression of fusion cross-sections due to the breakup of 7Li may not be significant for 7Li + 12C reaction at energies around the barrier

SABRE and the Stawell Underground Physics Laboratory: Dark Matter Research at the Australian National University

The direct detection of dark matter is a key problem in astroparticle physics that generally requires the use of deep-underground laboratories for a low-background environment where the rare signals from dark matter interactions can be observed. This work reports on the Stawell Underground Physics Laboratory – currently under construction and the first such laboratory in the Southern Hemisphere – and the associated research program. A particular focus will be given to ANU’s contribution to SABRE, a NaI:Tl dark matter, direct detection experiment that aims to confirm or refute the long-standing DAMA result. Preliminary measurements of the NaI:Tl quenching factor and characterisation of the SABRE liquid scintillator veto are reported.I.M. and F.N acknowledge travel support from AINSE for their attendance at the ANU quenching factor measurements. This research was supported by the Australian Research Council, grant numbers DP170101675, LE160100080, LE170100162 and LE190100196

Expressions of Inner Freedom

This study investigates the fusion and scattering of nuclei at energies spanning the Coulomb barrier. The coupling of the relative motion of the nuclei to internal degrees of freedom can be thought to give rise to a distribution of potential barriers. ¶ Two new methods to extract representations of these potential barrier distributions are suggested using the eigen-channel model. The new techniques are based on measurements of quasi-elastic and elastic backscattering excitation functions, from which the representations are extracted by differentiation. A third method utilizing transfer excitation functions is introduced using qualitative arguments. The techniques are investigated experimentally for the reactions 16O + 92Zr, 144,154Sm, 186W and 208Pb. The results are compared with barrier distribution representations obtained from fusion data. The methods are further explored using the systems 40Ca + 90,96Zr and 32S + 208Pb, for which scattering and fusion excitation functions have been measured. The new barrier distribution representations are consistent with the one from fusion. They are direct evidence of the effects of the internal degrees of freedom on channels other than the fusion channel. ¶ ..

Detection and tracing of the medical radioisotope

The transport and radioecology of the therapeutical radioisotope 131I has been studied in Canberra, Australia. The isotope has been detected in water samples and its activity quantified via characteristic J-ray photo peaks. A comparison of measurements on samples from upstream and downstream of the Canberra waste water treatment plant shows that 131I is discharged from the plant outflow into the local Molonglo river. This is consistent with observations in other urban environments. A time-correlation between the measured activities in the outflow and the therapeutical treatment cycle at the hospital identifies the medical treatment as the source of the isotope. Enhanced activity levels of 131I have been measured for fish samples. This may permit conclusions on 131I uptake by the biosphere. Due to the well-defined and intermittent input of 131I into the sewage, the Canberra situation is ideally suited for radioecological studies. Furthermore, the 131I activity may be applied in tracer studies of sewage transport to and through the treatment plant and as an indicator of outflow dilution following discharge to the environment