Monte Carlo simulations of the iThemba LABS neutron beam facility

Master Thesis


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University of Cape Town

The iThemba LABS neutron beam facility is currently being used for various applications of fast neutron studies, such as measurements of fission cross sections, the biological effectiveness of high-energy neutrons, calibration of detectors used for dose monitoring in space and aircrafts, and the development of neutron dose monitors. Neutron beams with energies up to 200 MeV are produced at iThemba LABS by irradiating thin targets of 7Li and 9Be with protons from the separated-sector cyclotron. The neutrons are collimated to produce a beam with a diameter of about 50 mm at a flight path of 7.7 m from the target. The collimator geometry is designed to maximize the central part of the beam resulting in a beam with a uniform intensity throughout its diameter and a small penumbra. Secondary neutrons produced from the interactions of the primary charged particles with structural parts e.g. beampipes, shielding wall, target holder, etc. have been observed in the measured neutron fluence spectra. The Monte Carlo radiation transport code FLUKA were used to study the effects of secondary neutrons on the neutron fluence spectra. Results obtained from the calculations were compared with those obtained experimentally.

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