Year
2008
Abstract
We present an improved method for measuring time-correlated neutron and photon events from fission sources. These correlations are unique for a specific radioactive material and can be interpreted as material signatures. The goal of this work is to explore the feasibility of using the method to accurately identify radioactive materials such as special nuclear material (uranium, plutonium) and typical spontaneous fission sources (Cf-252, Am-Li, Am-Be, etc). A digital pulse shape discrimination method was applied to correctly identify the different particles detected, while retaining time-correlation information with ns resolution. The novelty of the approach is in the use of a 250 MHz digitizer that allows real-time data acquisition even for very high count rates. The measurements for various source-detector distances were carried out and compared to Monte Carlo simulations performed with the MCNP-PoliMi code. MCNP-PoliMi has the capability of simulating coincidences on an event-by-event basis and has been successfully used in the past. In the experiments, different measurement configurations were investigated to assess the effect of the sourcedetector distance. Specifically, symmetric and asymmetric configurations were used, with and without lead shielding. The results obtained are very encouraging, because they show unique features for the given source and geometry.