Portable Irradiator by plutonium-beryllium source for manganese sulphate bath efficiency measurements

One of the main issues encountered by research laboratories working on primary standardization of neutron sources without using high flow neutron field generators is the difficulty in reaching satisfactory specific activity levels on manganese sulphate (MnSO₄) solutions that can be used in determining primary standard system efficiency of neutron sources. An efficient system is required to ensure the enhanced precision of the Manganese Sulphate Bath (MSB) method. The purpose of this work is therefore to provide an alternative irradiation system for the MnSO₄ solution to be used in efficient determination of MSB, based on plutonium-beryllium (α, n) source, neutron emit. Computational simulations using Monte Carlo code were performed to establish the main characteristics of the system allowing for optimal Mn-driven neutron capture efficiency. Among the four simulated geometries (cubic, cylindrical, half-moon and double parallelepiped) and three volumes (84,5 cm³, 100 cm³ and 169 cm³), half-moon with 84,5 cm³ of MnSO₄ solution was the best option to be built, reaching 6,41 % (± 0,02 %) of probability that one single neutron interacts with one single ⁵⁵Mn nuclei. Manganese sulphate solution activity measurements were performed with a Hyperpure Germanium detector to validate the new irradiation system. The results showed an average efficiency of 5,742 x 10^-4 and standard relative uncertain of 0,63 % (coverage factor k=1) for the MSB. The efficient value obtained in this work compared with the values determined by LEITE (2010) which used an ²⁵²Cf neutron source showed a relative difference of 0,07 %, which is in agreement with the anticipated thought of this work. This alternative dosimetric method demonstrated the utility of neutron sources for the irradiation of solutions in primary standard laboratories without the need of the use of costly nuclear reactors or particle accelerators. (author)