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The Micromegas is a type of ionising radiation detector that consists of a gas chamber sandwiched between two parallel plate electrodes, with the gas chamber divided by a Frisch grid into drift and amplification gaps. Investigators have applied it to a number of different applications, such as charged particle, X-ray and neutron detection. A Micromegas device has been tested as a neutron beam monitor at CERN and is expected to be used for that purpose at the Spallation Neutron Source (SNS) under construction in Oak Ridge, TN. For the Micromegas to function effectively as neutron beam monitor, it should cause minimal disruption to the neutron beam in question. Specifically, it should scatter as few neutrons as possible and avoid neutron absorption when it does not contribute to generating useful information concerning the neutron beam. Here, we present the results of Monte Carlo calculations of the effect of different types of wall materials and detector gases on neutron beams and suggest methods for minimising disruption to the beam.

Composite neutron scintillators consisting of neutron-insensitive fluorescent dopant particles (e.g. ZnS:Ag) embedded in a matrix material containing isotopes with high neutron cross sections that emit energetic charged particles (e.g. 6Li) are a popular method for neutron detection in a variety of applications. The size and volume doping fraction of the fluorescent dopant particles and the densities of both dopant particles and the matrix material determine the characteristics of the pulse-height spectrum of emitted light and the probability that capture of a neutron will result in scintillation. In this work, we characterise the effects of these parameters for ZnS:Ag particles in a lithiated glass matrix using a Monte Carlo simulation of composite neutron detectors that we have constructed.

Boron neutron capture therapy (BNCT) is a cancer brachytherapy based upon the thermal neutron reaction: 10B(n,alpha)7Li. The efficacy of the treatment depends primarily upon two conditions being met: (a) the preferential concentration of a boronated compound in the neoplasm and (b) an adequate fluence of thermal neutrons delivered to the neoplasm. The boronated amino acid, para-boronophenylalanine (BPA), is the agent widely used in clinical trials to deliver 10B to the malignancy. Positron emission tomography (PET) can be used to generate in vivo boron distribution maps by labeling BPA with the positron emitting nuclide fluorine-18. The incorporation of the PET-derived boron distribution maps into current treatment planning protocols is shown to provide improved treatment plans. Using previously established protocols, six patients with glioblastoma had 18BPA PET scans. The PET distribution maps obtained were used in the conventional BNCT treatment codes. The isodose curves derived from the PET data are shown to differ both qualitatively and quantitatively from the conventional isodose curves that were derived from calculations based upon the assumption of uniform uptake of the pharmaceutical in tumor and normal brain regions. The clinical course of each of the patients who eventually received BNCT (five of the six patients) was compared using both sets of isodose calculations. The isodose contours based upon PET derived distribution data appear to be more consistent with the patients' clinical course.

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 methodology for simulating a neutron detector's pulse-height spectra (PHS) utilizing semiempirical equations for the light yield nonproportionality of organic scintillators is described. Using these simulations, suitable material synthesis techniques are established for optimizing the performance of neutron scintillators. A MATLAB program suite was developed to automate the process of generating the PHS by pairing these semi-empirical equations with results generated using Monte Carlo radiation transport code (MCNPX) particle track (PTRAC) output files. This is accomplished by first calculating the energy deposited in a detector from each charged-particle reaction product generated from a neutron absorption event by postprocessing the MCNPX PTRAC output files. The energy deposited from each charged particle is then used in semiempirical light yield equations to determine the fluorescent light energy output by each charged particle. Finally, the individual contributions from each charged particle are recombined to accurately simulate the pulse generated from the neutron absorption event. [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]