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Abstract: A prototype gas-filled proportional counter (PC) based on micro-scale tungsten wire and carbon fiber, and nano-scale carbon nanotube (CNT) anodes was built and tested with a 90Sr source. Tungsten anodes of 500μm down to 4μm diameter were used to observe the gradual decrease in operating voltage for the proportional region with a decreasing anode diameter. The 40nm diameter CNTs anodes ranged in length from 35 to 105μm. The absolute detection efficiency was measured at ∼10−6%. An electrostatic computer model was used to predict the resulting electric field associated with a single CNT in the coaxial configuration. For a single anode coaxial design the model predicted that the electric field was insufficient for secondary ionizations which contributed to a low amplitude signal and that the small volume of the ionization region resulted in the low absolute detection efficiency. To overcome the problems of low absolute detection efficiency and operational issues with the single anode, CNT arrays were investigated. Electrostatic modeling of 100nm×40μm long CNTs in an array with a 50μm pitch conducted for a parallel plate configuration indicated that each anode functioned independently. [Copyright &y& Elsevier]

Abstract: The absolute total and absolute peak detection efficiencies of gamma ray detector materials NaI:Tl, CdZnTe, HPGe, HPXe, LaBr3:Ce and LaCl3:Ce were simulated and compared to that of polyvinyltoluene (PVT). The dimensions of the PVT detector were 188.82cm×60.96cm×5.08cm, which is a typical size for a single-panel portal monitor. The absolute total and peak detection efficiencies for these detector materials for the point, line and spherical source geometries of 60Co (1332keV), 137Cs (662keV) and 241Am (59.5keV) were simulated at various source-to-detector distances using the Monte Carlo N-Particle software (MCNP5-V1.30). The comparison of the absolute total detection efficiencies for a point, line and spherical source geometry of 60Co and 137Cs at different source-to-detector distance showed that the absolute detection efficiency for PVT is higher relative to the other detectors of typical dimensions for that material. However, the absolute peak detection efficiency of some of these detectors are higher relative to PVT, for example the absolute peak detection efficiency of NaI:Tl (7.62cm diameter×7.62cm long), HPGe (7.62cm diameter×7.62cm long), HPXe (11.43cm diameter×60.96cm long), and LaCl3:Ce (5.08cm diameter×5.08cm long) are all greater than that of a 188.82cm×60.96cm×5.08cm PVT detector for 60Co and 137Cs for all geometries studied. The absolute total and absolute peak detection efficiencies of a right circular cylinder of NaI:Tl with various diameters and thicknesses were determined for a point source. The effect of changing the solid angle on the NaI:Tl detectors showed that with increasing solid angle and detector thickness, the absolute efficiency increases. This work establishes a common basis for differentiating detector materials for passive portal monitoring of gamma ray radiation. [Copyright &y& Elsevier]

Manganese dioxide coated polyvinyltoluene (PVT) scintillating and extractive scintillating (ES) resins, which can be used to simultaneously separate and quantity radioactivity in aqueous solutions, were applied toward environmental screening applications. Off-line screening, utilizing a commercially available liquid scintillation counter (LSC) and on-line screening using a modified hand-held survey meter was evaluated in the laboratory for quantification of 99TcO4− and uranium in groundwater. The detection efficiencies for uranium with the MnO2 coated PVT resin were determined to be 17–37% and 7–27% for the LSC and survey instrument, respectively. The loading efficiency of the uranium out of groundwater ranged from 16% to 26%. In contrast, the detection efficiencies for 99Tc with the ES resin were determined to be 2–14% and 2–3% for LSC and hand-held survey meter, respectively, while the loading efficiency of the 99TcO4− in groundwater acidified to pH 2 was nearly 100%. [Copyright &y& Elsevier]

Extractive scintillating resins, which are used to simultaneously separate and quantify radioactivity in aqueous solutions, were developed for low-level alpha radiation monitoring of natural waters. Resins were investigated with bis(2-ethylhexyl)methane-diphosphonic acid (H2DEH[MDP], Dipex®) extractant, which has a strong affinity for tri-, tetra- and hexavalent actinides in dilute acids. Extractive scintillating resins were manifested (1) as a mixed bed of scintillating resin and extraction chromatographic resin and (2) by diffusing the organic fluor 2-(1-naphtyl)-5-phenyloxazole into macroporous polystyrene chromatographic resin, then coating with H2DEH[MDP], or by coating H2DEH[MDP] on scintillating polyvinyltoluene beads. The scintillation light was detected with a modified Hidex Triathler to allow for continuous flow measurements. The average detection efficiencies were 51.7±2.6% and 65.8±10.1% for natural uranium and 241Am, respectively, for the extractant coated scintillator. The resin was stable for solution flow of up to 1000 ml resulting in rapid real-time quantification of natural uranium in groundwater down to 30 μg/ml. [Copyright &y& Elsevier]