Simulation and Design of a Simple and Easy-to-use Small-scale Neutron Source at Kyoto University

AbstractA simple and easy-to-use compact neutron source based on a low power level proton accelerator (proton energy 3.5 MeV and 0.35kW beam power) at Kyoto University was designed with the conception of low cost, compact size, high safety and intensive thermal neutron flux via Monte Carlo method with PHITS code. By utilizing (p, n) reactions in a beryllium target coupled to a polyethylene moderator and graphite reflector with a wing configuration, this facility is expected to produce time-averaged thermal neutron fluxes suitable for neutron scattering and development of instrumentation, and play a role in educating students in neutron science and performing research with neutrons. Borated polyethylene (BPE) and ordinary concrete were combined to shield the neutron and photon. By using niobium as target backing and water as cooler, it is promising to cope with the problem of thermal damage and hydrogen embrittlement damage. The sizes of moderator and reflector are optimized to have thermal neutron flux as high as possible, while keeping the low ratio of fast neutron flux to thermal neutron flux. The neutron and gamma dose equivalent rates were evaluated and the current shielding configuration is acceptable

Solving the degeneracy of the lepton-flavor mixing angle theta_atm by the T2KK two detector neutrino oscillation experiment

If the atmospheric neutrino oscillation amplitude, sin^2 2theta_atm is not maximal, there is a two fold ambiguity in the neutrino parameter space: sin^2 theta_atm>0.5 or sin^2 theta_atm<0.5. In this article, we study the impact of this degeneracy, the so-called octant degeneracy, on the T2KK experiment, which is a proposed extension of the T2K (Tokai-to-Kaimoka) neutrino oscillation experiment with an additional water cherenkov detector placed in Korea. We find that the degeneracy between sin^2 theta_atm= 0.40 and 0.60 can be resolved at the 3sigma level for sin^2 2theta_rct>0.12 (0.08) for the optimal combination of a 3.0^circ off-axis beam (OAB) at SK (L=295km) and a 0.5^circ OAB at L=1000km with a far detector of 100kton volume, after 5 years of exposure with 1.0(5.0) time 10^21 POT/year, if the hierarchy is normal. We also study the influence of the octant degeneracy on the capability of T2KK experiment to determine the mass hierarchy and the leptonic CP phase. The capability of rejecting the wrong mass hierarchy grows with increasing sin^2 theta_atm when the hierarchy is normal, whereas it is rather insensitive to sin^2 theta_atm for the inverted hierarchy. We also find that the 1sigma allowed region of the CP phase is not affected significantly even when the octant degeneracy is not resolved. All our results are obtained for the 22.5 kton Super-Kamiokande as a near detector and without an anti-neutrino beam.Comment: 23 pages, 9 figure