Subatomic Physics – Quasi mono-energetic Neutron beams
At the iThemba LABS, quasi-monoenergetic neutrons are typically produced in the D-line (neutron) facility by the 7Li(p,n)7Be or 9Be(p,n)9B reactions. iThemba LABS has excellent beam quality even at high currents. Even at 200 MeV virtually single-turn extracted, nanosecond-pulsed beam can be delivered making a background free interval between pulses possible. The time between beam pulses at 200 MeV is 33ns, but by letting through one in 7 pulses, this can be increased to 235ns
A collimator fan (parallel walls and a quadratic opening of 5×5 cm2 in size) makes possible measurements for neutron emission angles of 0°, 4°, 8°, 12° and 16°. Carbon absorbers are used to remove charged particles contaminating the neutron beam. The available flight paths extend from about 5m to about 10m. The time intervals between successive proton beam pulses can be enlarged from about 50 to 360ns using an electrostatic deflector system. At the maximum distances, these time intervals correspond to frame-overlap neutron energies of about 4.0 MeV. In recent experiments at 120 MeV using a 10mm thick Be target, a quasi-monoenergetic (peak) neutron flux of about 6.5 x 104 neutrons cm-2 s-1 was obtained at 0°.
Neutron spectra at 0 – and 16 – degrees from 200MeV protons on a Lithium target in the D-line vault.