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Four sample groups were prepared by adding different concentrations of naphthalene (NP) or of 2,6-diisopropylnaphthalene (DIN) as a secondary solvent (${{\rm S}_2}) in carborane-loaded toluene (TL)- and pseudocumene (PC)-based scintillators. The pulse-height spectra of the samples in response to ^137Cs\ \gamma -rays and to thermal neutrons were collected to study the light output (L) enhancement effect of ${{\rm S}_2}$. It is found that for all sample groups, $L$ increases to a plateau with the concentration of secondary solvent ([${{\rm S}_2}$]). As [${{\rm S}_2}] is increased from 0 to saturation concentration, L increases by 31–45% and 34–53% in response to ^{137}{\rm Cs}\ \gamma -rays and to thermal neurons, respectively. A first-order approximation model is proposed to fit to the experimental data. The enhancement factor ({k_h}$) and maximum L$ of each sample group are obtained from curve fitting. The Birks factor (kB) and electron equivalent energy (keVee) of each sample are calculated by a numerical method based on Birks formula. The L$ enhancement is discussed according to the percent changes of these parameters. In conclusion, the enhancement effect is attributed mainly to the fused double benzene-ring structure of NP and DIN, which has more delocalized electrons, and provides faster Förster resonance energy transfer paths than the single benzene-ring structure of TL and PC. Adding NP or DIN leads to a significant increase in absolute scintillation efficiency (S) values in response to ^{137}{\rm Cs}\ \gamma -rays and to thermal neutrons. [ABSTRACT FROM PUBLISHER]

Thin polymeric films are evaluated in this research as a potential replacement technology for radiation portal monitors where specific attention is given to the physical basis for neutron-photon discrimination.  It is shown that the difference in the energy deposition mechanics from charged particle reaction products and from the Compton scattered electrons allows for the effective discrimination between neutrons and gammas. One goal of this study was to establish optimal thickness for polymeric films that maximize the neutron interactions and simultaneously minimize the measured interaction of photons. Polymeric films ranging from 15~\mu\m to 600~\mu\m containing ^6LiF were fabricated and tested for their capability to satisfy criteria established by the Department of Homeland Security.  Results from Monte Carlo simulations with the GEANT4 code and data from measurements confirm the technical basis for our proposed understanding of neutron-photon discrimination characteristics for thin films. [ABSTRACT FROM AUTHOR]

Novel ^6Li-loaded polyester scintillation films have been designed and fabricated to detect thermal neutrons. Lithium fluoride crystals containing enriched ^6Li were synthesized and integrated into polyethylene naphthalate polyester matrix containing appropriate luminescent molecules. Thermal neutron capture by ^6Li ions produces charged particles with kinetic energy sufficient to ionize and subsequently excite the components of the polymeric matrix. This energy is transferred to secondary luminescent molecules, which produce net radioluminescence responses detectable by a photomultiplier tube. Design, production and characterization of these scintillation films are discussed herein. The films due to their thinness (<220\ \mum) and low atomic number components have low susceptibility to gamma induced scintillation and thus are effective discriminators for thermal neutrons. [ABSTRACT FROM AUTHOR]

A series of novel ^6Li-loaded plastic scintillation films have been designed and fabricated to detect thermal neutrons. Organolithium salts containing enriched ^6Li were synthesized and interspersed in a series of matrices comprising a polymer doped with an antenna fluor. Thermal neutron capture by ^6Li produces charged particles with kinetic energy which is sufficient to ionize and excite the polymeric matrix. This energy is collected by the antenna fluor, which produces a photonic response detectable by a photomultiplier tube. Design and optimization of these scintillation films is discussed herein. A current problem in the design and fabrication of polymeric composite materials is phase separation. The matrix is a low-dielectric aromatic polymer; hence, ionic molecules in the composite tend to phase-separate from the matrix and produce agglomerates which decrease the quantum efficiency by scattering and/or quenching the photonic response to thermal neutrons. Based on the experimental results, the importance of synthesizing polymers with high quantum yield and efficiency in energy migration and transport for making effective composite neutron scintillators is emphasized. [ABSTRACT FROM AUTHOR]