Design of a versatile and compact moderator for the CNA HiSPANoS neutron source

The use of thermal neutron radiation is widespread across numerous fields. While nuclear reactors are the most extended and intense source of such neutrons, moderated radioactive sources are often used as a much lower neutron flux alternative. An intermediate option are Compact Accelerator Neutron Sources (CANS) like HiSPANoS at the Centro Nacional de Aceleradores (CNA), for which we have designed a neutron moderator. Different options of the proton or deuteron beam energy, the neutron producing reaction and the moderator geometry/composition have been studied in detail through Geant4 Monte Carlo simulations, aiming at both versatility (for different applications) and compactness (because of limited space in the HiSPANoS hall). The proposed solution is a ∼ 40x40x40 cm 3 polyethylene moderator based on the 7 Li(p,n) reaction featuring both an irradiation cavity and a beam exit, as well a γ -ray shielding. A set of proton beam energy and geometrical configurations are defined for achieving different performance in terms of thermal purity (more 98% is achievable in both field and beam) and neutron flux (maximum values of 8 ⋅ 1 0 7 and 1 ⋅ 1 0 5 n/cm 2 / s ).