Reactivity measurements and neutron spectroscopy in the MUSE-4 experiment

Reactivity measurement gives access to an important parameter in reactor physics, which can be achieved by many experimental techniques. This paper describes our current efforts to develop and test a method which makes use of the Pulsed Neutron Source technique. To do so, the MASURCA fast neutron reactor was coupled to the pulsed neutron generator GENEPI. For various subcritical configurations, the decay of the neutron population which follows a neutron burst was recorded using in-core fission chambers. The analysis relies on the distribution of time intervals between fission events belonging to the same fission chain. An excellent agreement is found between the measured reactivities and the expected ones, from a near criticality configuration down to very deep subcritical levels. The second part of the paper is devoted to the measurement of the neutron energy distribution. A proportional counter was used to measure the energy deposition of the neutrons in the 3He active gas. A calibration of the counter response allows us to reconstruct the neutron flux at the detector location. A reasonable agreement is found with a Monte Carlo prediction. This gives us a direct test of the stochastic approach to the neutron transport. (authors)