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Well done! DSP Students

Over the last few months, PhD students linked to the DSP have graduated/completed their research work.

1. Christiaan Brits has graduated with a PhD degree from Stellenbosch University in December 2019. Christiaan’s
work focussed on the electric quadrupole transition strength which is a fundamental quantity to probe the collective
behaviour in nuclei and is a basic observable in studies of nuclear structure. Experimental measurements of this
transition strength provide powerful information on quantities such as deformation, the interaction between protons
and neutrons, and the vanishing and emergence of shell gaps. The much improved values of the transition strength
between nuclear states in 194-Platinum provide important constraints for nuclear theory. The measurement on 14-
Carbon lays the foundation for improved future experiments to address the apparent inconsistencies in the
understanding of the nuclear structure in this nucleus.

2. Kgashane Malatji has graduated with a PhD degree from Stellenbosch University in December 2019. Kgashane’s
projects focussed on two parts. Several samarium isotopes show discrepancies in the persistence of the nuclear
scissors resonance, which may hint at interesting underlying physics and possibly impact the production of elements
in the universe. The importance of nuclear structure effects is apparent from tantalum isotopes. With very few
exceptions most heavy nuclei are produced in neutron capture processes, which take place in stars and supernovae.
New nuclear data allow for astrophysical relevant capture cross-sections to constrain the production of 180-Tantalum due to the photodisintegration process. This solves the long-standing question on which process is
primarily responsible for the production of 180-Tantalum.

3. Munirat Bashir defended her PhD thesis entitled “Design, construction and characterisation of a low-level
radioactivity counting system based on gamma-ray spectrometry with LaBr3:Ce scintillator detectors” at Stellenbosch University. In this work, the GEANT4 Monte Carlo toolkit was used to design a passive water shielding to reduce background radiation, and a new low-activity measurement system constructed. In addition a novel method of background reduction was employed by using photon time-of-flight to reduce background for environmental sample studies.

4. Wiggert Brümmer’s project was to learn more about the astrophysically important of 18Ne(4He,1H)21Na reaction.
Direct measurements with 18-Neon and 4-Helium are extremely challenging as both nuclei are gases and 18-Neon is
radioactive. Valuable information from the 1-Hydrogen decay following the 24Mg(1H,3H)22Mg reaction was studied, as in both cases the intermediate nucleus is 22-Magnesium. Corrections to time-reversed measurements of the cross section were calculated from this measured data that will in future replace theoretical values in the large programmes that synthesize the production of elements in the cosmos.

5. All carbon is produced in exploding stars from unstable 8-Berylium and 4-Helium, into a resonant excited state of 12-Carbon, named the Hoyle state. The excited states just above the Hoyle state are still of critical astrophysical
importance, and remain a challenge for many nuclear-structure models. In this region are at least one broad state but the number and nature of the states is still unclear. It is this energy region that was investigated by Kevin Li,
meticulously analysing a new 14C(1H,3H)12C data set simultaneously with several other data sets. He could
determine the energy and width of a state and establish the need for it to be recognised in future data compilations.