F.A. Balogun

OCCURRENCE OF NATURAL RADIONUCLIDES AND FALLOUT CESIUM-137 IN DRY-SEASON AGRICULTURAL LAND OF SOUTH WESTERN NIGERIA

The radioactivity of the Opa river — irrigated farmlands in the south western Nigeria was determined using an HpGe based, low-level passive gamma-counting system. With the exception of two isotopes, the main radionuclides analysed in the sample were the progenies of238U and232Th. The other two isotopes were the naturally occurring40K and the anthropogenic137Cs. The result obtained showed elevated levels of radioactivity from all detected radionuclides compared to the published data for this area. Enhanced levels of naturally occurring radionuclides is attributed to the use of phosphatic fertilizers for dry season vegetable cultivation along this river banks. The presence of the fission product137Cs could be traced to the fallouts occasioned by the various French nuclear tests in the Sahara desert, and probably, some effect of the more recent nuclear reactor accident at Chernobyl in 1986.

TL response of a natural fluorite

Abstract A batch of a naturally occurring fluorite (CaF 2 ) from the Middle Benue Valley region of Nigeria has been studied in some detail for its thermoluminescence (TL) properties. TL glow peaks are observed at 119, 144 and 224°C at a heating rate of 10°C s −1 . The TL response is observed to increase with increasing dose, as expected, over the dose range examined. Variations are observed in the decay curves of the various glow peaks with storage at room temperature. While the lower temperature peaks are observed to decay, enhancement of the TL signal is observed for the 224°C glow peak when stored for four weeks. A low-level radioactivity measurement showed no evidence of self-irradiation from naturally occurring radionuclides. UV exposure was suppressed by storage in a black sealed container to exclude sunlight contribution to the observed TL response. A scheme involving the formation of large defect complexes, from smaller ones, during storage, as possible route leading to loss of signal in low temperature glow peaks and a corresponding enhancement at higher temperature, is suggested.

Angular variation of scattering volume and its implications for Compton scattering tomography

Abstract If quantitative and qualitative precision is to be achieved in X-/ γ -rays Compton scattering densitometry and tomography, the volume of interaction within which a useful signal is collected must be well defined and accurately estimated. This work presents a numerical study of the variation of scattering angles and collimator sizes. The effect of choosing back-scattering angles for measurement in both the densitometry and tomographic modes of this technique is studied. A symmetry is observed between the volume at forward and back scattering angles. A symmetry exists, however, within the scattering angle range 90±30°. It is proposed that the best volume/spatial resolution in Compton scattering densitometry/tomography is obtainable within the above mentioned scattering angle range.

INAA in the determination of the elemental constituents of a natural fluorite

A complementary use of the comparative and the semi-absolute variations of instrumental neutron activation analysis (INAA) has enabled us to determine 22 different elements in a sample of natural fluorite originating from the younger granite province of Nigeria. The mineral has a brownish purple appearance with some veinlets having a deep purple coloration. Of all the 22 elements measured, Fe (851.36 ppm), Sb (7.69 ppm), Ag (87.4 ppm), Hg (2.71 ppm) and Se (1.97 ppm) are found to be exclusive to the veinlets while Au (109.15 ppm), Co (2.15 ppm) and W (173.20 ppm) are concentrated in the main matrix of the fluorite. With the aid of the semi-absolute method, it was possible to measure the Au concentration in the IAEA Soil-7 reference material to be 56.83±5.87% ppm. A qualitative electron microprobe analysis (EMA) showed that the bulk of the matrix is composed mainly of Ca and F, as expected.

Radiological study of soils in oil and gas producing areas in Delta State, Nigeria

Measurements of radioactivity concentrations in soils around the oil and gas producing areas in Delta State of Nigeria were carried out using a high-purity germanium detector gamma-ray spectrometer. Soil samples were collected from 20 locations from the study area and analysed. The radionuclides detected are traceable to the primordial series of (238)U and(232)Th as well as (40)K and traces of globally released (137)Cs. The specific activity values ranged between 7 and 60 Bq kg(-1) with a mean of 24±2 Bq kg(-1) for (238)U; while for (232)Th the range was 7-73 Bq kg(-1) with a mean of 29±3 Bq kg(-1). Relatively higher specific activity values were recorded in (40)K with a range of 15-696 Bq kg(-1), while the mean was 256±37 Bq kg(-1). However, a relatively low-specific radioactivity was obtained from(137)Cs with a range of 1-25 Bq kg(-1) and a mean of 7±1 Bq kg(-1). The estimated dose equivalent obtainable per year from these levels of radioactivity is <5 % of the recommended safe level of 1 mSv per annum. Therefore, the area and the use of the soils as building materials may be considered safe.

A COMPARATIVE STUDY OF ELEMENTAL COMPOSITION OF HUMAN BREAST MILK AND INFANT MILK SUBSTITUTES

Instrumental neutron activation analysis (INAA) and protoninduced X-ray emission (PIXE) analysis have been employed to determine the concentration of 13 elements in human breast milk, various infant formulas, and locally produced cereals from Nigeria, as well as from various infant formulas and natural cow and goat milk available in the UK. The study shows that if the locally produced cereal is to be used on a regular basis for babies in Nigeria, then their diet must be supplemented with essential trace elements. Furthermore, parents should be discouraged from giving their infants cow and goat milk because of the high concentration of major elements compared to human breast milk.

Influence of pre-irradiation annealing and Lix–Co(1−x)–O thin film deposition on the TL response of soda lime glass

Abstract Effects of pre-irradiation annealing and deposition of a thin film of Li x –Co (1− x ) –O on soda lime glass substrate are studied using the thermoluminescence technique, at low gamma radiation doses. Simple but similar glow curves were obtained with a single glow peak in all cases. Glow peaks occurred within the temperature range of 266 and 288 °C depending on sample treatment and gamma dosage. Within the studied gamma radiation dose range of 0.86–4.29 mGy, the heated soda lime glass consistently showed the highest TL response, while that from the film deposited sample was the least. At a dose of 0.86 mGy, a 41.8% enhancement and a 56.7% loss in signal over those from ordinary soda lime glass were recorded for annealed and film deposited samples respectively. Peak shift to higher temperatures were also observed in the two treated samples, relative to blank. These we have attributed to the increased diffusion of alkali ions in the annealed glass and exchange of impurity ions between the Li x –Co (1− x ) –O thin film and the soda lime glass substrate, at high temperatures, resulting in increased formation of points and complex defects that could be either killer or radiative traps.

Neutron induced gamma-ray emission tomography

Abstract Radioactivity induced in a neutron irradiated material may be considered as a distributed radioactive source suitable for imaging using computerized gamma-ray emission tomography. The resulting image reveals the distribution of an element of interest in a given plane of the imaged object. Therefore the technique, neutron induced gamma-ray emission tomography, provides information about the elemental composition and distribution. This is demonstrated by imaging the distribution of sodium in a pellet of freeze-dried sea water and a section of human bone using the gamma-ray emitted by Na-24 produced in the presence of a number of other gamma-ray emitting nuclides. Application of a dual energy scattering correction algorithm developed for this purpose resulted in a 44% increase in contrast for the lower energy gamma-rays (1.36 MeV), where the effect of scattering was pronounced and only 14% for the higher energy line (2.75 MeV) emitted by the same nuclide.

Determination of the elemental constituents of a natural dolerite using NIRR-1

Elemental characterization of natural dolerite obtained from South Western Nigeria has been carried out using Nigeria Research Reactor-1 (NIRR-1) located at the Centre for Energy Research and Training (CERT), Ahmadu Bello University, Zaria. The measurements showed the presence of aluminum, calcium, magnesium, titanium and iron with concentrations 69,990+/-3499, 61,140+/-8.0, 38,330+/-3929, 13,880+/-1804 and 8319+/-150 ppm, respectively, as the major elements. In addition, 16 other elements, in minor and trace quantities, including Th, a radioactive rare earth element and five other rare earth elements La, Ce, Sm, Dy and Lu were identified. The presence of the rare earth elements may be a confirmation of the previous argument that the observed single but broad glow peak in the glow curve of this rock is rather an overlap of more than one glow peak. The presence of Th suggests the possibility of internal radioactivity in the rock, a necessary criterion for using a material for luminescence dating. Thus, this work indicates that dolerite can be used for luminescence dating if properly developed for the purpose.

Study of the Nutritional Status of Maternal Breast Milk in Preterm Infants in Nigeria

Instrumental neutron activation analysis (INAA) and proton induced X-ray emission (PIXE) analysis were used to determine the concentration of 13 elements in the breast milk collected within the first week of lactation and after morning feed from 16 pre-term mothers and 20 term mothers. The results of the study show that pre-term milk has a significantly higher concentration of Cl, Cu, Fe, K, Mg, Mn, Na and Zn while term mothers have a significantly higher concentration of P and Br. No significant differences were, however, found in the mean concentration of Al, Ca, I and Rb. Furthermore, the mean concentration for most of the elements found in the breast milk fall within the range of the concentrations obtained for the commercial infant milk formulae.