Rossi-α experiment in the IPEN/MB-01 research reactor

One major objective of this work is to experimentally estimate the following kinetic parameters on the IPEN/MB-01 research reactor at São Paulo: The effective neutron delayed fraction, β _eff, the prompt neutron generation time, Λ, and the ratio β _eff/Λ. In order to achieve our goal, we will use a microscopic noise technique called Rossi-α method. This method is based on the statistical nature of the fission-chain process. Using a coincidence acquisition system, the rationale is to experimentally determine the probability distribution of detecting neutrons from the same chain. Through a least-squares fit of this distribution we estimate the prompt neutron decay constant α = (β _eff- ρ)/Λ. The a parameter will be measured for three sub-critical levels using three different source configurations, and the ratio β _eff/ Λ is obtained via a extrapolation to ρ = 0. A specific acquisition system for Rossi-α measurements has been developed in order to achieve our objective. This system is based on a multichannel sealer controlled by virtual instruments that records the timing of all neutron events, allowing data analysis during the acquisition. The first measurements were performed using two BF ₃ detectors positioned at the center of IPEN/MB-01 reactor core. In the future the same measurements described above will be performed using ³He and photodiode detectors. The photodiode detectors have been developed by the Reactor Physics Division of IPEN. In this work we will present a preliminary set of Rossi-α measurements performed on the IPEN/MB-01 research reactor at São Paulo.