Rossi-alpha 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, betaeff, the prompt neutron generation time, lambda, and the ratio betaeff/ lambda. In order to achieve our goal, we will use a microscopic noise technique called Rossi-alpha 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 alpha = (betaeff-rho)/lambda. The alpha parameter will be measured for three sub-critical levels using three different source configurations, and the ratio betaeff/ lambda is obtained via a extrapolation to rho = 0. A specific acquisition system for Rossi-alpha measurements has been developed in order to achieve our objective. This system is based on a multichannel scaler 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 BF3 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-alpha measurements performed on the IPEN/MB-01 research reactor at São Paulo.