The effect of the aging of liquid organic scintillators used for gamma-neutron separation

Since the beginning of using liquid scintillators for gamma-neutron separation, there have been many articles dealing with long-term degradation especially due to oxygen presented during scintillator encapsulation. The effect of aging of liquid organic scintillators namely EJ301, EJ309 (both Eljen Technology), and new custom-made cocktails based on 1-Phenyl-3-(2,4,6-trimethylphenyl)-2-pyrazoline and 2,5-Bis(5-tert-butyl-benzoxazol-2-yl)thiophene fluors were investigated for more than half a year. The research was focused on the Compton edge shifting of gamma particles since the position is proportional to the light yield of the selected scintillator. Furthermore, the gamma-neutron separation was observed and quantified using FOM (Figure Of Merit) for samples prepared and filled under normal and nitrogen atmosphere during the mentioned period. All stated parameters of liquid scintillator NE213 manufactured by Nuclear Enterprises Limited opened more than three decades ago were measured and used for comparison.

Radiation portal monitors response to gamma radiation and to the detection capability of Orphan radioactive sources: Contribution of the Strass project

Radiation portal monitors are commonly used to detect and intercept unauthorized movement of nuclear and other radioactive materials at country borders. A total of twelve double-pillar portal monitors are present at the Greek-North Macedonian border, each containing two polystyrene scintillating detectors per pillar. Spatial and spectral response testing of the scintillating detectors to gamma radiation was performed by using different radioactive sources and comparing the measurement results with Monte Carlo simulations. A good agreement of the experimentally deduced activities of different point sources, needed for alarm triggering of the radiation portal monitors with Monte Carlo calculated values, was observed. Spectral results show no photopeaks in the spectra due to low resolution of these detectors. The broad peaks observed in the spectra correspond to the Compton edge. Measured spectra with a 137Cs source placed directly on the scintillating detector, at several positions away from the photo multiplier tube, show an energy shift of the Compton edge towards lower energies, as the source is moving away from the photo multiplier tube. The energy shift is due to light transfer mechanisms within the scintillator volume and therefore, it is only observed in optical simulations and not in gamma-ray particle simulations.

PROBING THE LIGHT SPEED ANISOTROPY WITH RESPECT TO THE COSMIC MICROWAVE BACKGROUND RADIATION DIPOLE

We have studied the angular fluctuations in the speed of light with respect to the apex of the dipole of Cosmic Microwave Background (CMB) radiation using the experimental data obtained with GRAAL facility, located at the European Synchrotron Radiation Facility (ESRF) in Grenoble. The measurements were based on the stability of the Compton edge of laser photons scattered on the 6 GeV monochromatic electron beam. The results enable one to obtain a conservative constraint on the anisotropy in the light speed variations Δc(θ)/c<3×10-12, i.e. with higher precision than from previous experiments.