Boron loaded plastic scintillator applied to active neutron measurements of waste drums

High efficiency neutron detectors are needed to do passive or active neutron measurement in order to characterize waste drum. In fact to measure prompt neutrons and fast neutrons, the cell should exhibit high detection efficiency and low mean lifetime of neutron inside its structures. At that time, this kind of cell uses only helium-3 gaseous detector inside a polyethylene structure. Several experiments were done using the "Promethee" facility available at the CEA Cadarache to evaluate and compare the efficiency of both boron loaded plastic scintillator and helium-3 detector. "Promethee" is in fact a passive and active neutron measurement cell using for the active part a GIN26 neutron generator that can emit up to 6×10⁷ n.s^-1. This generator works in pulse mode emitting typically during 200 μs with a repetition rate of 125 Hz. The geometry of the tested detector is a cylinder of 15 cm length and 2 inches diameter coupled to an XP2020 photomultiplier tube. Comparison between two kinds of detectors (boron loaded plastic scintillator and unloaded plastic scintillator) is done exhibiting that boron loaded plastic scintillators, despite their high gamma rays efficiency, could be also used instead of helium-3 gaseous detectors for waste cells measurements. It is possible to use this kind of detector in order to follow the neutron emission from the neutron generator due to its very fast recovery during and after the neutron emission.