No abstract available

[en] The ⁸⁶Kr+²³⁸U reaction has been studied at krypton beam energies about 30 MeV above the Coulomb barrier. Reaction products were detected by an array of 32 photovoltaic cells coupled to the AFRODITE γ-ray detector array at iThemba LABS. A symmetric fission component has been observed at about 600 MeV total kinetic energy. This could possibly be due to fusion-fission with a cross section of 35±20 mb

No abstract available

[en] In intermediate-mass systems, collective excitations of the target and projectile can greatly enhance the subbarrier capture cross section σ_cap by giving rise to a distribution of Coulomb barriers. For such systems, capture essentially leads directly to fusion [formation of a compound nucleus (CN)], which then decays through the emission of light particles (neutrons, protons, and alpha particles). Thus, the evaporation-residue (ER) cross section is essentially equal to σ_cap. For heavier systems, the experimental situation is significantly more complicated owing to the presence of quasifission (QF) (rapid separation into two fragments before the CN is formed) and by fusion-fission (FF) of the CN itself. Thus, three cross sections need to be measured in order to evaluate σ_cap. Although the ER essentially recoil along the beam direction, QF and FF fragments are scattered to all angles and require the measurement of angular distributions in order to obtain the excitation function and barrier distribution for capture. Two other approaches to this problem exist. If QF is not important, one can still measure just the ER cross section and try to reconstruct the corresponding σ_cap through use of an evaporation-model code that takes account of the FF degree of freedom. Some earlier results on σ_cap obtained in this way will be reanalyzed with detailed coupled-channels calculations, and the 'extra-push' phenomenon discussed. One may also try to obtain σ_cap by exploiting unitarity, that is, by measuring instead the flux of particles corresponding to quasielastic (QE) scattering from the Coulomb barrier. Some new QE results obtained for the ⁸⁶Kr + ²⁰⁸Pb system at iThemba LABS in South Africa will be presented

[en] A summary of recent results of research at iThemba LABS is given. This includes high-resolution measurements of the fine structure of isoscalar giant quadrupole resonances, a new programme to measure fusion barrier distributions for reactions leading to the formation of superheavy elements, measurements of high-energy γ-rays from (p,γ) reactions using the AFRODITE array of HpGe clover detectors, and a comparison of the vibrational band structures of ¹⁶⁰Yb, measured with the AFRODITE array, with the X(5)-β²ⁿ model. A summary of future developments is given

[en] When a left-handed and a right-handed nuclear system form in angular momentum space, a pair of nearly degenerate rotational bands is observed. To identify chiral symmetry most important is to establish near-degeneracy not only in excitation energies of the partner bands, but also in their intra-band and inter-band B(M1) and B(E2) transition probabilities. This needs dedicated lifetime measurements. Such measurements were performed for four bands of "1"9"4Tl. Two of these have very close near-degeneracy and form a prime candidate for best chiral pair. The lifetime measurements confirm the excellent near-degeneracy in this chiral pair. (paper)

[en] The upcoming detector facility aims at developing new state-of-the-art particle detectors as well as providing hands-on training to postgraduate students using both analog and digital signal processing from nuclear radiation detectors. The project is two-fold and aims at developing: 1) ancillary detectors to be coupled with the new GAMKA array at iThemba LABS. Of particular interest to our group is the determination of nuclear shapes, which depend on the hyperfine splitting of magnetic substates; 2) PET scanners for cancer imaging using a cheaper technology. Performance of NaI(Tl) inorganic scintillator detectors has been evaluated using PIXIE-16 modules from XIA digital electronics. Gamma-ray energy spectra were acquired from ⁶⁰Co and ¹³⁷Cs radioactive sources to calculate the detector resolution as well as to optimize the digital parameters. The present study focuses on improving and optimizing the slow and fast filter parameters for NaI(Tl) detectors which can eventually be used in the list mode of data aquisition.

[en] A search for isomeric states was performed in the nucleus 60140Nd80 using in-beam γ-ray spectroscopy and the 126Te(18O,4n) reaction. Prompt and delayed γ-ray coincidences were measured with the AFRODITE spectrometer using the pulsed beam delivered by the Separated Sector Cyclotron of iThemba LABS. One new isomer was identified, with spin-parity Iπ=20+ and lifetime T1/2≥400 ns, at an excitation energy Ex=7430 keV. The lifetime of the 10+ isomer at Ex=3619 keV was determined to be 32.9(1.8) ns, confirming the previously reported value. The configuration of the Iπ=20+ isomer is assigned based on configuration-dependent cranked Nilsson-Strutinsky (CNS) calculations as a state π(d5/2g7/2)10+-4xν(h11/2-2)10+, with the spin vectors of the six holes in the 64146Gd82 core fully aligned

[en] The DIAMANT-AFRODITE combination has been used to investigate incomplete fusions reactions via the ¹³C+¹⁷⁰Er entrance channel. The intensity of ¹⁷⁶Hf (populated via the α 3n exit channel) is ∼8% of ¹⁷⁸W (populated via 5n evaporation) which is ∼8 times stronger than that expected from complete fusion. Moreover, 2αxn exit channels leading to Yb nuclei are observed with intensities that are ∼30-to-40% of ¹⁷⁶Hf, for which no yield is expected from complete fusion. A comparison of the intensities from the two-α- and one-α-gated data is consistent with fragmentation of the ¹³C beam into (α-α-α-n) which suggests that the population of Yb nuclei results from fusion (or ''massive transfer'') of one the break-up α-particles. A campaign of measurements is scheduled for late 2007 with further investigations planned for 2008, including the continuation of the study of superdeformation in ³²S

[en] Analyzing powers have been measured for the ⁴⁰Ca(p-vector,pα)³⁶Ar reaction at an incident energy of 100 MeV for coplanar scattering angles corresponding to zero recoil momentum of the residual nucleus. Predictions based on the distorted wave impulse approximation fail to reproduce the data