Energy calibration of the 6 MV EN Tandem accelerator of iThemba labs (Gauteng) and measurement of 16O + 16O elastic scattering

Abstract

The beam energy stability and reproducibility of the newly refurbished 6 MV EN tandem accelerator of iThemba LABS (Gauteng) (formerly the Schonland Research Institute) has been investigated, followed by an angular distribution measurement of 16O + 16O elastic scattering at ELab = 30 MeV. The 90˚ beam momentum-analysing magnet system was calibrated using two methods. In one method, the 27Al(p,n)27Si reaction was used to determine the proton beam energy from the known neutron emission sharp-threshold of 5.802 ± 0.001 MeV protons. In the other method, the energy of alpha-particles measured at a large backward scattering-angle (θLab = 170° ± 2°) from the 12C(16O,α)24Mg* reaction exciting low-lying states in 24Mg* were used to infer the energy of the incident 16O beam. The reaction-product alpha-particle energy was obtained by bracketing with known energies from a thin 241Am α-source. The beam energy measurements were then used to determine the analyser magnet constant. An angular distribution for the elastic scattering of identical particles 16O + 16O was measured at a laboratory energy ELab = 30 MeV, as a test of the calibrated accelerator. The scattering cross-section was measured with the aid of a high resolution ΔE-E gas-ionisation detector. The new elastic-scattering data are consistent with the previously measured values. The optical model theoretical calculation reproduces reasonably well the measured data over the whole angular range as expected.