Initial performance of sealed straw modules for large area neutron science detectors
Alternative neutron detection technologies must be considered, to overcome limitations imposed by a depleting 3He supply. We have developed a detector technology based on close-packed arrays of boron-coated straws (BCS) in two configurations: (1) each is 4 mm in diameter and 1 m long, and are packaged in groups of 7 that fit inside a single sealed aluminum tube (1.27 cm in diameter, 1 m long); (2) each is 7.5 mm in diameter and 2 m long, and are packaged in groups of 7 that fit inside a single sealed aluminum tube (2.54 cm in diameter, 2 m long). It thus allows operation of the straw detectors in sealed mode, for indefinite periods of time, and in vacuum environments, as required in neutron scattering instruments. The sealed detector modules form a large area (e.g., 1×1 m2, 2×1 m2) neutron imager. Initial testing of the sealed straw detector bundles showed promising results in straw decoding, detector life time, longitudinal resolution, and gas gain stability. The 3D resolution is expected to be 4 mm × 4 mm × 4 mm in configuration #1 and 2.5 cm × 2.5 cm × 2.5 cm in configuration #2, throughout the entire imaging area. Negligible gas gain change was seen over the long test period, in different sealed straw detectors. In addition to facilitating operation in vacuum, another advantageous aspects of the sealed straw detector bundle technique are high portability and structural versatility. Detector modules are easy to transport and detector arrays can be easily installed and tailored to a multitude of different scattering experimental setups. The depth of the detector array can be easily tailored to the desired neutron wavelength and the size and configuration of panels varied of a wide range while utilizing the same elemental modules.
Pie-Shaped boron-coated straws with enhanced neutron sensitivity
The boron-coated straw (BCS) neutron detection technology has been proposed as an attractive 3He replacement solution in a series of applications in homeland security, neutron science, and safeguards. In order to improve the neutron detection efficiency of the BCS, while maintaining manufacturability, Proportional Technologies, Inc. is introducing a modified BCS with significant performance benefits. The proposed pie-like shape consists of any desired number of arc segments, and an equal number of septa walls, which are radially oriented, and extending a desired distance towards the center of the geometry. Each septum is essentially a segment of the wall that has been collapsed onto itself, resulting in a rigid surface, coated on both sides. The area coated on the septa is added to the area coated on the arc segments, thus offering a significant benefit in sensitivity. Compared to a round straw of the same diameter, the coated wall area of the proposed shape with 12 septa is 3 times larger, assuming the septa are equal in length to each of the arc segments. We present laboratory measurements with two prototype detectors that demonstrate stable operation, a neutron sensitivity that is nearly 3 times higher than that measured in a simple BCS with no septa walls, and adequate energy resolution to effectively discriminate against gamma rays.
Heavy metal adsorption from industrial wastewater by PAMAM/TiO2 nanohybrid: Preparation, characterization and adsorption studies
Abstract This study investigates the removal of heavy metals from industrial wastewater using TiO 2 nanoparticles modified with poly-amidoamine dendrimer (PAMAM, G 4 ). The metal ions Cu 2 + , Pb 2 + , and Cd 2 + were selected as model pollutants. FTIR, SEM, BET surface area and Zeta potential measurements, and Dispersion Observing methods have been employed for characterizing the synthetic nanohybrid and these techniques indicated that the PAMAM loaded on to TiO 2 have been favorably synthesized. The effects of several parameters including initial metal ion concentration, temperature, pH solution, the nanohybrid dosage and contact time were studied. The experimental data were analyzed using equilibrium isotherm and kinetics models. The adsorption process was studied using isotherm, kinetics, and thermodynamics models. The analysis shows that the Langmuir isotherm and pseudo-second-order kinetics are appropriate models for the adsorption process. The thermodynamic parameters illustrate that the absorption is endothermic and spontaneous. The findings suggest that the nanohybrid is a good super absorbent for the removal of heavy metals from industrial effluents.