Brigitte Mouanda

Discrimination methods between neutron and gamma rays for boron loaded plastic scintillators

Boron loaded plastic scintillators exhibit interesting properties for neutron detection in nuclear waste management and especially in investigating the amount of fissile materials when enclosed in waste containers. Combining a high thermal neutron efficiency and a low mean neutron lifetime, they are suitable in neutron multiplicity counting. However, due to their high sensitivity to gamma rays, pulse shape discrimination methods need to be developed in order to optimize the passive neutron assay measurement. From the knowledge of their physical properties, it is possible to separate the three kinds of particles that have interacted in the boron loaded plastic scintillator (gamma, fast neutron and thermal neutron). For this purpose, we have developed and compared the two well known discrimination methods (zero crossing and charge comparison) applied for the first time to boron loaded plastic scintillator. The setup for the zero crossing discrimination method and the charge comparison methods is thoroughly explained, and the results on those boron loaded plastic scintillators are discussed.

Study of a new boron loaded plastic scintillator (revised)

Neutron detection research using plastic scintillators has recently led to instrument development for several applications and particularly for nuclear material characterization. In particular, plastic scintillators exhibit a fast time response and a high efficiency for fast neutrons spectrometry. The use of boron loaded plastic scintillators has been also proposed in order to reduce dead time for fission neutron coincidence counting. We report here on the study of a new and low-cost boron loaded plastic scintillator. Further, a simulation study was performed, including light production and transport in this kind of scintillator. Its characteristics have been measured in terms of light response, photon and neutron induced signals. An experiment has been carried out using the ion beam of a Van de Graaff accelerator at Saclay so as to determine the Birks parameters of the scintillators. These parameters were obtained for proton (between 1-2 MeV) and alpha particles (between 3.1 MeV and 5.4 MeV). The correlation between the experimental data and the simulation predictions has been studied for the neutron response of these scintillators. In addition, performances of this scintillator are compared with those of commercially available boron loaded plastic scintillator (BC454 from Bicron, Newbury, OH).

Surface characterization of a potential photoactive LC coupling agent

Abstract Azo dye molecules were grafted onto a silicon wafer surface in order to generate a potentially orienting substrate interface for liquid–crystal (LC) layers. This coupling agent was synthesized by reaction between 4-[bis(2-hydroxyethyl)amino]-4′-nitro azobenzene (DR19) and 3-(triethoxysilyl)propyl isocyanate (TESPI). The 1 H-NMR, IR spectra of the silylated compound confirmed that nucleophilic addition between the carbonyl group of TESPI and the hydroxyl functions of DR19 had occurred. In this article, the silanization conditions are described and the thin layers obtained characterized using Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and X-ray reflectivity.