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[en] Recent advances in science and technology of materials fabrication, engineering of work functions, and micrometer gap machining between emitter and collector are making thermionic conversion/converter (TEC) of solar energy an emerging technology. As the converter is the lightest of all devices with highest direct power conversion density (per unit area of the converting surface), it has, potential for substituting photovoltaic technology to a large extent and for deployment in space as a power source. This article summarizes the current efforts/technologies in the field, and discusses their inherent merits and demerits towards realizing the goal of achieving high conversion efficiency and simulation of performance evaluation of a solar TEC. We also discuss the use of both metals and nanomaterials, critical roles of work functions of both emitter and collector, collector temperature, absorptivity and emissivity of the surfaces, radiation losses, and use of both metals and nanomaterials in the efficiency of conversion of solar energy. We further deal with the role of correcting thermionic emission current density equation in the simulation of solar TEC performance. We discuss briefly the possible methods of space-charge control in future in a solar TEC. (author)
[en] Highlights: • Concentrations of the natural radionuclides 226Ra, 232Th, and 40K were measured. • 10 tile samples of different brands have been analyzed using Gamma ray spectroscopy. • Activity concentrations in Bq/kg were determined using a High purity Germanium detector. • Radiological hazard indices such Raeq, Dr, AEDE, Hex, Hin, Iγ and Iα were evaluated. - Abstract: Activity concentration of 10 different brands of tiles made in Nigeria were analyzed using High purity Germanium gamma detector and its hazard indices such as absorbed dose rate, radium equivalent activity, external Hazard Index (Hex), internal Hazard Index (Hin), Annual Effective Dose (mSv/y), Gamma activity Index (Iγ) and Alpha Index (Iα) were determined. The result showed that the average activity concentrations of radionuclides (226Ra, 232Th and 40K) content are within the recommended limit. The average radium equivalent is within the recommended limit of 370 Bq/kg. The result obtained further showed that the mean values for the absorbed dose rate (D), external and internal hazard index, the annual effective dose (AEDR) equivalent, gamma activity index and Alpha Index were: 169.22 nGyh−1, 0.95 and 1.14, 1.59 mSv/y, 1.00 Sv yr−1 and 0.34 respectively. The result established that radiological hazards such as absorbed dose rate, internal hazard, annual effective dose rate, gamma activity index and Alpha Index for some samples are found to be slightly close or above international recommended values. The result for the present study was compared with tiles sample from others countries, it was observed that the concentration of tiles made in Nigeria and other countries are closer, however recommends proper radiation monitoring for some tiles made in Nigeria before usage due to the long term health effect.
[en] The activity concentration of 226Ra, 232Th and 40K was measured in commonly building materials used in Nigeria from commercial supplier using High Purity Germanium Gamma (HPGe) detector. The mean activity concentrations in the samples were found to be 51.5±9.3, 72.46±17.65 and 217.05±44.31Bqkg-1 for 226Ra ,232Th and 40K respectively. The highest radium equivalent (Raeq) of 273.9 Bqkg-1 was noted in Perfect Super fix White Cement (Nigeria) but found to be<370 Bqkg-1as the recommended dose limiting safe value for bulk media as presumed, the highest value of internal hazard index (Hin) and external hazard index (Hex) of 0.894 and 0.744 respectively were also <1. The absorbed dose rate (DR) with a value of 122.52 nGyh-1 noted in ceramic tile sample is higher than the weighted population world average value of 80 nGyh-1 by a factor of 1.53. The highest annual effective dose rate (AEDR) of 0.601 mSvy-1 reported in PNT ceramics but was found to be less <1 mSvy-1. The investigated materials have the values of Hin, Hex and AEDR greater than 0.5 but less than 1, showing that the dose impact exceeds the exemption dose level of 0.3 mSvy-1 for AEDR but complies to the upper limit of dose principle of 1mSvy-1
[en] Inadequate public water supply by the Water Board in Abuja has forced the public to source for groundwater as the only alternative for consumption without consideration for radiological risk. The radiological risk for cancer mortality of uranium in Immigration Headquarters Gosa and Federal-Housing Lugbe groundwater water samples were measured and compared with Water Board and hand-dug well water samples from the same area using inductively coupled plasma mass spectrometry. The highest radiological risks for cancer mortality and morbidity were found to be low, with highest values of 1.24 × 10"-"7 and 1.64 × 10"-"7 obtained from Federal-Housing Lugbe borehole. The chemical toxicity risk of "2"3"8U in drinking water over life time consumption has a mean value of 4.0 × 10"-"4 μg kg"-"1 day"-"1 with highest value of 6.0 × 10"-"3 μg kg"-"1 day"-"1 obtained from Federal-Housing Lugbe. Significantly, this study inferred that the "2"3"8U concentrations reported in groundwater based-drinking originated from sheared zone of magmatic metamorphosed basaltic dyke intrusion. Due to the low risk values found in the water samples when compared with the International Reference Standard, radiological and chemical toxicity risks values may not pose any health risk to the public that rely on groundwater in the area. (author)