Evaluation of Gross Alpha and Gross Beta Radioactivity in Crude Oil Polluted Soil, Sediment and Water in the Niger Delta Region of Nigeria

The evaluation of gross alpha and beta activities in crude oil contaminated soil, sediment and water samples was conducted in ten oil polluted environment of Delta State using Gas-flow proportional counter. Samples were collected from the oil polluted environment in each oil field and samples were prepared and analyzed following standard procedures. The mean gross alpha and beta activities obtained are 331.4 ± 24.5 Bq kg-1 and 11,335 ± 112 Bq kg-1 respectively for soil, 259.2 ± 17.6 Bq kg-1 and 4508 ± 96 Bq kg-1 respectively for sediment, and 1.00 ± 0.09 Bq kg-1 and 20.3 ± 1.7 Bq kg-1 respectively for water. The estimated average values of the total annual effective dose equivalent (AEDET (α,β)), the total annual gonadal dose equivalent (AGDET (α,β))), and the total excess lifetime cancer risk (ELCRT (α,β)) are 10.64 mSv y-1, 0.037 μSv y-1 and 0.037 μSv y-1 respectively. The gross alpha and beta activities values obtained in soil and sediment were relatively high compared to values reported in some parts of the country and other regions and countries of the world. The radiological risk parameters examined show that AEDET (α,β) and AGDET (α,β) are above recommended permissible limits while ELCRT (α,β) is within the recommended permissible limit. The overall results obtained in this study indicate that the environmental samples have been radiologically impaired due to the crude oil spillage. An appropriate remediation technique was therefore recommended to remediate the polluted soil, sediment, and water to their near original state.

Study of CdZnTeSe Gamma-Ray Detector under Various Bias Voltages

Cadmium zinc telluride selenide (CdZnTeSe) is a new semiconductor material for gamma-ray detection and spectroscopy applications at room temperature. It has very high crystal quality compared to similar materials such as cadmium telluride and cadmium zinc telluride. The consistency of peak position in radiation detection devices is important to practical applications. In this paper, we have characterized a CdZnTeSe planar detector for bias voltages in the range of -20 V to -200 V and amplifier shaping time of 2, 3 and 6 μs. The peak position of the 59.6-keV gamma line of 241Am becomes more stable as the absolute value of the applied voltage increases. The best energy resolution of 8.5% was obtained for the 59.6-keV gamma peak at -160 V bias voltage and 3-μs shaping time. The energy resolution was relatively stable in the -120 V to -200 V range for a 6-μs shaping time. Future work will be focused on the study of the peak position and energy resolution over time.

Characterization of CdZnTeSe Nuclear Detector Chemically Etched in Bromine Methanol

Semiconductor nuclear radiation detectors made from tertiary and quaternary compounds of cadmium telluride (CdTe) can operate at room temperature without cryogenic cooling. One of such materials that have become of great interest is cadmium zinc telluride selenide (CdZnTeSe). Compared to other CdTe-based materials, such as cadmium zinc telluride (CdZnTe), CdZnTeSe can be grown with much less Te inclusions and sub-grain boundary networks. Chemical etching is often used to smoothen wafer surfaces during detector fabrication. This paper presents the characterization of CdZnTeSe that is chemically etched using bromine methanol solution. Infrared imaging shows that the wafer has no sub-grain boundary networks that often limit detector performance. The current-voltage (I-V) characterization experiment gave a resistivity of 4.6 × 1010 Ω-cm for the sample. The I-V curve was linear in the ±10 to ±50 volts range. An energy resolution of 7.2% was recorded at 100 V for the 59.6-keV gamma line of 241Am.

Study of Chemical Etching and Chemo-Mechanical Polishing on CdZnTe Nuclear Detectors

Cadmium zinc telluride (CdZnTe) semiconductor has applications in the detection of X-rays and gamma-rays at room temperature without having to use a cooling system. Chemical etching and chemo-mechanical polishing are processes used to smoothen CdZnTe wafer during detector device fabrication. These processes reduce surface damages left after polishing the wafers. In this paper, we compare the effects of etching and chemo-mechanical polishing on CdZnTe nuclear detectors, using a solution of hydrogen bromide in hydrogen peroxide and ethylene glycol mixture. X-ray photoelectron spectroscopy (XPS) was used to monitor TeO2 on the wafer surfaces. Current-voltage and detector-response measurements were made to study the electrical properties and energy resolution. XPS results showed that the chemical etching process resulted in the formation of more TeO2 on the detector surfaces compared to chemo-mechanical polishing. The electrical resistivity of the detector is of the order of 1010 Ω-cm. The chemo-mechanical polishing process increased the leakage current more that chemical etching. For freshly treated surfaces, the etching process is more detrimental to the energy resolution compared to chemo-mechanically polishing.

Analysis of Te and TeO₂on CdZnTe Nuclear Detectors Treated with Hydrogen Bromide and Ammonium-Based Solutions

Surface defects caused during cutting and polishing in the fabrication of cadmium zinc telluride (CdZnTe) nuclear detectors limit their spectral performance. Chemical treatments are often used to remove surface damages and defects. In this paper, we present the analysis of Te and TeO2 species on the surfaces of CdZnTe nuclear detectors treated with hydrogen bromide and ammonium-based solutions. The CdZnTe wafers were chemo-mechanically polished in a mixture of hydrogen bromide in hydrogen peroxide and ethylene glycol, followed by a chemical passivation in a mixture of ammonium fluoride and hydrogen peroxide solution. X-ray photoelectron spectroscopy showed significant conversion of Te to TeO2, thus producing a more chemically stable surface. The resistivity of the CdZnTe samples is in the order of 1010 ohms-cm. The current for a given applied voltage increased following the passivation and decreased after a 3-hour period. Results from spectral response measurements showed that the 59.5-keV gamma-peak of Am-241 was stable under the same channel for the surface treatment processes.

On the Role of Electrodes in Introducing Airflow Distortion in Residential Oil Burners

Computational Fluid Dynamics (CFD) simulations of airflow through a retention head residential oil burner were carried out to study the velocity field near and around the fuel spray. The simulations revealed (as expected, based on some previous experimental measurements) the velocity flow field to be far from axisymmetric. Moreover, the center of the swirling airflow was found to be at some radial distance away from the physical centerline of the flame tube. Since it was suspected that the two electrodes just upstream of the retention ring of the burner might be responsible for this flow distortion, additional CFD simulations were then carried out for the cases of no electrodes and 4-electrodes. The results clearly show that all flow distortions (velocity deviations from axisymmetric value) vanish when no electrodes are present and that the flow distortions are reduced by a factor of 2 when two additional dummy electrodes (for a total of 4 electrodes) are included in the burner design. Furthermore, for the 4-electrode case, the eccentricity of the swirling airflow is reduced by almost a factor of 3 as compared to the base design case of 2-electrodes.