The design of a multisource americium-beryllium (Am-Be) neutron irradiation facility using MCNP for the neutronic performance calculation.

The americium-beryllium neutron irradiation facility at the National Nuclear Research Institute (NNRI), Ghana, was re-designed with four 20 Ci sources using Monte Carlo N-Particle (MCNP) code to investigate the maximum amount of flux that is produced by the combined sources. The results were compared with a single source Am-Be irradiation facility. The main objective was to enable us to harness the maximum amount of flux for the optimization of neutron activation analysis and to enable smaller sample sized samples to be irradiated. Using MCNP for the design construction and neutronic performance calculation, it was realized that the single-source Am-Be design produced a thermal neutron flux of (1.8±0.0007)×10(6) n/cm(2)s and the four-source Am-Be design produced a thermal neutron flux of (5.4±0.0007)×10(6) n/cm(2)s which is a factor of 3.5 fold increase compared to the single-source Am-Be design. The criticality effective, k(eff), of the single-source and the four-source Am-Be designs were found to be 0.00115±0.0008 and 0.00143±0.0008, respectively.

Determination of aluminium, silicon and magnesium in geological matrices by delayed neutron activation analysis based on k0 instrumental neutron activation analysis.

In this work, concentrations of silicon, aluminium and magnesium in geological matrices were determined by Neutron Activation Analysis based on k0-IAEA software. The optimum activation and delay times were found to be 5 min and 15-20 min respectively for the determination of Si via (29)Si (n,p) (29)Al reaction. The adopted irradiation scheme did not work for the determination of magnesium. Each sample was irradiated under a thermal neutron flux density of 5.0 × 10(11) ncm(-2)s(-1). Cadmium covered activation indicated that a permanent epithermal irradiation site for research reactors would be very useful for routine determination of silicon in environmental samples.

Fuel burnup calculation of Ghana MNSR using ORIGEN2 and REBUS3 codes.

Ghana Research Reactor-1 core is to be converted from HEU fuel to LEU fuel in the near future and managing the spent nuclear fuel is very important. A fuel depletion analysis of the GHARR-1 core was performed using ORIGEN2 and REBUS3 codes to estimate the isotopic inventory at end-of-cycle in order to help in the design of an appropriate spent fuel cask. The results obtained for both codes were consistent for U-235 burnup weight percent and Pu-239 build up as a result of burnup.

Characterization of low power research reactor neutrons for the validation of k(0)-INAA standardization based on k(0)-IAEA software.

Channel Bsite2 of Ghana research reactor-1 has been characterized for k0-INAA application. Cadmium ratio and bare multi-monitor were used to determine flux parameters using 0.1%Au-Al, Fe, and Zr wire as flux monitors. The parameters determined were 18.36±1.91, 0.0479±0.012, 5.12×10(11)±0.42×10(11) ncm(-2)s(-1), 2.74×10(10)±0.14×10(10) ncm(-2)s(-1), 7.73×10(10)±0.16×10(10) ncm(-2)s(-1) and 16.75±1.58, -0.034±0.0028, 4.28×10(11)±1.71×10(11) ncm(-2)s(-1), 2.55×10(10)±0.15×10(10) ncm(-2)s(-1) respectively for thermal-to-epithermal flux ratio, alpha, thermal neutron, epithermal neutron and fast neutron flux using cadmium ratio and multi-monitor method accordingly. The k0-INAA performance assessment based on z-score distributions showed most results within |z|<2.

Statistical evaluation of environmental contamination, distribution and source assessment of heavy metals (aluminum, arsenic, cadmium, and mercury) in some lagoons and an estuary along the coastal belt of Ghana.

An environmental pollution investigation was carried out to determine the concentrations of aluminum (Al), arsenic (As), cadmium (Cd), and mercury (Hg) (heavy metals) in the surface water and river water bed sediments of lagoons and estuaries along the coastal belt of Ghana. The study assessed the environmental pollution situation and evaluated their sources and distribution of these metals. The total concentrations of Al, As, Cd, and Hg were determined by the neutron activation analysis technique. Water and sediment samples were collected from the Benya, Fosu, and Narkwa lagoons in the Central Region and from the Pra estuary in the western part of Ghana. Some indices, such as contamination factor, pollution-load index, contamination degree, and geoaccumulation index, were used to assess eco-environmental quality of the sampling sites. The analysis indicated that the Fosu lagoon was fairly polluted with Cd. The investigation indicated a highly localized distribution pattern closely associated with the two pollution sources (garbage/solid waste dumps and industrial activities) along the coastal belt. The resulting environmental deterioration required a concerted evaluative effort by all stakeholders.

Design of boron carbide-shielded irradiation channel of the outer irradiation channel of the Ghana Research Reactor-1 using MCNP.

The MCNP model for the Ghana Research Reactor-1 was redesigned to incorporate a boron carbide-shielded irradiation channel in one of the outer irradiation channels. Extensive investigations were made before arriving at the final design of only one boron carbide covered outer irradiation channel; as all the other designs that were considered did not give desirable results of neutronic performance. The concept of redesigning a new MCNP model, which has a boron carbide-shielded channel is to equip the Ghana Research Reactor-1 with the means of performing efficient epithermal neutron activation analysis. After the simulation, a comparison of the results from the original MCNP model for the Ghana Research Reactor-1 and the new redesigned model of the boron carbide shielded channel was made. The final effective criticality of the original MCNP model for the GHARR-1 was recorded as 1.00402 while that of the new boron carbide designed model was recorded as 1.00282. Also, a final prompt neutron lifetime of 1.5245 × 10(-4)s was recorded for the new boron carbide designed model while a value of 1.5571 × 10(-7)s was recorded for the original MCNP design of the GHARR-1.

Investigating concentration distributions of arsenic, gold and antimony in grain-size fractions of gold ore using instrumental neutron activation analysis.

Instrumental neutron activation analysis (INAA) has been used to quantify concentrations of arsenic (As), gold (Au) and antimony (Sb) in grain-size fractions of a gold ore. The ore, which was taken from the Ahafo project site of Newmont Ghana Gold Ltd., was fractionated into 14 grain-size fractions using state-of-the-art analytical sieve machine. The minimum sieve mesh size used was 36mum and grains >2000mum were not considered for analysis. Result of the sieving was analysed with easysieve(R) software. The<36mum subfraction was found to be the optimum, hosting bulk of all three elements. Arsenic was found to be highly concentrated in<36-100mum size fractions and erratically distributed in from 150mum fraction and above. For gold, with the exception of the subfraction <36mum which had exceptionally high concentration, the element was found to be approximately equally distributed in all the size fractions but slightly "played out" in 150-400mum size fractions. Antimony occurrence in the sample was relatively high in <36mum size fraction followed by 600, 800, 400 and 36mum size fractions in that order. Gold content in the sample was comparatively far greater than arsenic and antimony; this is indicative of level of gold mineralization in the concession where the sample ore was taken. The concentration of gold in the composite sample was in the range 564-8420ppm as compared to 14.33-186.92ppm for arsenic and 1.09-9.48ppm for antimony. Elemental concentrations were correlated with each other and with grain-size fractions and the relationships between these descriptive parameters were established.

Neutron activation analysis for Dy, Hf, Rb, Sc and Se in some Ghanaian cereals and vegetables using short-lived nuclides and Compton suppression spectrometry.

A pseudo-cyclic instrumental neutron activation analysis (PCINAA) method has been developed to determine selected elements in various types of cereal and vegetable from Ghana using relatively short-lived nuclides (t1/2<80 s) and the Compton suppression counting. The samples were irradiated for 10 s at the Dalhousie University SLOWPOKE-2 research reactor facility (DUSR) and allowed to decay for 20 s, and counted for 40 s. The process is repeated every 50 s for 4 cycles to quantify Dy, Hf, Rb, Sc and Se through 165mDy, 179Hf, 86mRb, 46mSc, and 77mSe. The detection limits were generally of the order of 1.0 ng g(-1) except for Rb which is about 1 microg g(-1). Both precision and accuracy of the method were found to be good.

Determination of toxic elements in waters and sediments from River Subin in the Ashanti Region of Ghana.

Waters and sediments of Subin River, which flows through the industrial and commercial areas of Kumasi in the Ashanti region of Ghana, were geochemically investigated to ascertain heavy metal pollution levels due to anthropogenic activities. The study shows preoccupying pollution levels that constitute a threat to public and ecological systems. The waters of Subin River are neutral to slightly basic, inferred from pH values of 6.89-7.65). Electric conductivity (EC) of the waters ranges from 822 to 1,821 mus/cm and the range of total dissolved solids (TDS) is from 409 to 913 mg/l. Toxic elements contents of sediments and waters from 10 sites along the river were analysed by instrumental neutron activation analysis (INAA), and Al, As, Cd, Cr, Cu and Zn were determined. The concentrations of Al, As, Cd, Cr, Cu and Zn in the waters range between 4.02-15.18, 0.007-0.16, 0.002-0.05, 0.001-0.019, 1.32-7.04 and 4.28-10.2 mg/l, respectively. The contamination factors (CF) computed for the elements indicate that with the exception of sampling site S10, the sediments are polluted with Cd. Chromium contamination in the sediments is observed at S6 and S7, where the CF values were 1.39 and 1.52, respectively. The pollution load indices (PLI) were low (<1) and ranged from 0.14 to 0.75, suggesting that the overall sediment column of the river is not polluted.

Biomonitoring of airborne heavy metals along a major road in Accra, Ghana.

Lichens collected in an unpolluted forest (background) in November 2004, transplanted at 41 sampling sites along the Madina-Tetteh Quarshie road, retrieved in February 2005 and analysed were found to contain higher concentrations of Manganese (Mn), Vanadium (V), lead, Cadmium (Cd), Chromium (Cr) and Nickel (Ni) than in the background area. Observations showed that of all the heavy metals studied, Manganese concentrations were highest at all sampling points with maximum values around a traffic light, an intersection and car fitting/mechanic workshops. Significant correlations were found between Ni and Mn, Mn and Cr and Mn and V. Statistical analysis also revealed a relatively even dispersion of the studied elements on the eastern side of the road than on the western side.

Simultaneous use of neutron transmission and reflection techniques for the classification of crude oil samples.

Neutron attenuation and reflection characteristics of three crude mineral oil samples from West Africa were determined using 37 GBq 241Am-Be source in a single set-up and compared with those of paraffin (oil) and benzene, an aromatic compound. Based on the trends of measured data which are similar to those exhibited by paraffin but different from those associated with benzene, the crude oil samples could be classified as paraffinic. The total hydrogen content and weight ratios (O+C)/H and C/H determined for the crude oil samples using the transmission and reflection techniques are not only independent of the technique but are also consistent with literature values of thermal reflection technique.

Characterization of neutron flux spectra in irradiation sites of MNSR reactor using the Westcott-formalism for the k0 neutron activation analysis method.

For the general applicability of the k0-NAA method to deal with "non-l/v" (n,gamma) reaction nuclides, the modified spectral index r(alpha) square root (Tn/T0) and g(Tn) factor for monitoring neutron temperature Tn for the inner and outer irradiation sites of the Ghana MNSR reactor (GHARR-1) were measured using the Cd-ratio method. Using the measured Cd ratio for lutetium and the modified spectral index, the reduced resonance integral of lutetium s0,Lu was also calculated. The computed result of 1.64 was in good agreement with the reported value of 1.67. Based on the assumption that the definitions of reaction rates in the Westcott-formalism and in Nisle's unified formulation are equal, a theoretical verification of the accuracy of the measured modified spectral indices for our data and those reported in the literature for other research reactors was carried out. Employing 197Au, 96Zr and 94Zr as "1/v" monitors, the theoretical values which depend on the choice of the monitor, followed the trend for measured values of the sub- to epi-cadmium flux ratio f for nine irradiation sites of four different research reactors. The computed and experimental modified spectral indices for the different flux ratios associated with irradiation sites within the range 18.8-152 fitted well to a simple exponential relationship. Calculated and measured data are in good agreement when appropriate correction factors are used.