Speaker
Description
The Helium and Lead Observatory 1 Kiloton (HALO- 1kT) is a lead-based detector to study electron neutrinos emitted in supernova events. It is proposed to follow the same-purpose lesser sensitive HALO detector located at SNOLAB, Ontario, Canada. The sensitive to electron neutrinos make HALO-1kT (and also the current HALO detector)) unique in the sense that all other detectors with capability to detect supernova neutrinos are sensitive to anti-electron neutrinos through charged-current inverse beta-decay such as the Super-Kamiokande, LVD, IceCube and KamLAND.
HALO-1kT sensitivity to supernova neutrinos is larger than that for HALO due to
its proposed 12-fold target-mass increase relative to HALO and a more efficient neutron detection.
The detector will consist of 1 kt of lead (208Pb with 82 protons and 126 neutrons). Neutrinos from supernova will interact with the lead via inverse beta-decay process producing bismuth or lead in high-excited states (the excitation states depend on the income neutrino flauvor). The daughter nuclei emit neutrons during de-excitation. Polyethene moderator materials are used to slow down the neutrons which are then detected by 3He proportional counters. The outer most layer of lead consists of a reflector made of graphite due to lower neutron absorption cross section and thermalization efficiency. The purpose of this reflector is to recover neutrons that would other otherwise escape detector . The processes involved are
CC: ʋe + 208Pb → 207Bi + n + e- -10.3 MeV
ʋe + 208Pb → 206Bi + 2n + e- -18.4 MeV
NC: ʋx + 208Pb → 207Pb + n -7.4 MeV
ʋx + 208Pb → 206Pb + 2n -14.1 MeV
I am currently working on the design of the graphite layer which will work as moderator and reflector to redirect some of the neutrons back into the detector lead block. This will increase the detection efficiency by up to 50% (as an example, it is currently 28% in HALO). Geant4 simulations have been used to tune the thickness and grade of the graphite to be used. I found that the optimal thickness is ~15 cm, and as for the graphite grade, it should, ideally, be of Nuclear-Reactor quality.
