On the thermoluminescence characteristics of NaF and KCl.

Thermoluminescence (TL) properties of NaF and KCl are investigated in order to assess their suitability as radiation dosemeters for retrospective dosimetry. TL measurements were made on samples irradiated to different doses (1-20 Gy) and heated at a rate ranging from 0.4 to 4 °C/s in a TL/OSL reader. The TL glow curves of NaF, readout at 1oCs-1, exhibited six apparent peaks around 38.7 ± 1.4, 63.5 ± 0.5, 105.5 ± 0.4, 237.5 ± 0.8, 299.0 ± 1.0 and 347.5 ± 0.7 °C with a shoulder around 168.0 ± 2.3 °C. Those of KCl have three clearly identifiable peaks around 44.0 ± 0.3, 95.3 ± 0.8 and 160.5 ± 0.7 °C. Glow curve deconvolution, however, revealed that the glow curves of NaF and KCl are best fitted with nine and five glow peaks respectively. In NaF, all the peaks exhibited linearity of dose-response in the entire dose range considered in this study. Only the peaks around 95.3 ± 0.8 and 160.5 ± 0.7 °C exhibited linear dose-response in the entire dose range for KCl. In NaF, there was thermal quenching of the TL responses of the peaks around 63.5 ± 0.5, 105.5 ± 0.4 and 237.5 ± 0.8 °C, and thermal enhancement of responses for peaks around 299.0 ± 1.0 and 347.5 ± 0.7 °C. With respect to KCl, the TL responses of all the peaks exhibited thermal enhancement as heating rate was increased. The activation energies associated with the thermal enhancement and quenching of the peaks' TL responses are presented. The repeated use of an aliquot of NaF five times for dose measurements resulted in an acceptable variation in sensitivity, on the other hand the sensitivity of KCl decreased with increasing number of repeat use. The activation energy of the electron traps associated with the glow peaks in both crystals calculated in this study are comparable to previously published values. Both crystals can be used for retrospective dosimetry however change in sensitivity with repeat use of an aliquot will have to be accounted for in the case of KCl.

Optically stimulated luminescence of cowrie shells.

Characteristics of continuous wave optically stimulated luminescence (CW-OSL) and linear modulation OSL (LM-OSL) from three different types of cowrie shells are presented. Irradiated samples were optically stimulated at 72 mW/cm2 for CW-OSL and linearly ramped from zero to 72 mW/cm2 to obtain LM-OSL. The measured CW-OSL and LM-OSL curves of the shells are each determined to consist of three components namely fast, medium and slow components. The fast, medium and slow LM-OSL components peak at 17.0 ± 0.8, 45.0 ± 1.8 and 140.8 ± 6.7 s respectively for all samples. In addition, peak positions are independent of dose. The photoionization cross-sections of the OSL traps for the three components estimated from CW-OSL are similar to those determined using LM-OSL. The OSL of the three components increases linearly with dose. The coefficient of variation of responses from repeated measurements of same aliquot lies below 2.3%. The shells are thus potential materials for retrospective dosimetry.

Radon measurements by nuclear track detectors in dwellings in Oke-Ogun area, South-Western, Nigeria.

An indoor radon survey of a total of 77 dwellings randomly selected in 10 districts in Oke-Ogun area of Oyo state, South-western Nigeria was carried out using CR-39 detectors. The CR-39 detectors were placed in the bedrooms and living rooms and exposed for 6 months and then etched in NaOH 6.25 N solution at 90 °C for 3 h. Mean concentrations amount to 255 ± 47 and 259 ± 67 Bq m(-3) in the living rooms and bedrooms, respectively. The lowest radon concentration (77 ± 29 Bq m(-3)) was found in Igbeti, whereas the highest was found in Okeho (627 ± 125 Bq m(-3)). The annual exposure of dwellers was estimated to fall <10 mSv (6.4 and 6.5 mSv y(-1) n living rooms and bedrooms, respectively), which is the upper range of action levels recommended by the International Commission on Radiological Protection. The average excess lung cancer risk was estimated 24.8 and 25.2 per million person-years in both living rooms and bedrooms. It is believed that the high radon level in this part of the country may be attributed to its geographic location. The data presented here will serve as a baseline survey for radon concentration in dwellings in the area.

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.

Estimation of patients' organ doses and conceptus doses from selected X-ray examinations in two Nigeria X-ray centres.

In this study, organ and conceptus doses of patients undergoing chest, abdomen and skull radiograph examinations at two Nigeria X-ray centres, Niger State General Hospital (NGH) and Two-Tees (TTX), are reported. Air kerma was measured, and entrance surface dose (ESD) and half-value layer estimated for each set of tube potential (kV(p)), focus to skin distance and current-time product (mAs) used for each of the patients included in this study. Results show that the mean air kerma in the two centres are similar for the three projections considered in this study. Organ doses ranged from <0.01 to 2.18 mGy in NGH and from <0.01 to 1.29 mGy in TTX for examinations of the abdomen, from <0.01 to 0.20 mGy in NGH and from <0.01 to 0.13 mGy in TTX for examinations of the skull and from <0.01 to 3.90 mGy in NGH and from <0.01 to 1.96 mGy in TTX for examinations of the chest. Generally, no significant difference is seen between the organ doses of male and female patients. In NGH, organ doses are generally greater than those from TTX for the three examinations. The mean ESDs for examinations of the chest postero-anterior, abdomen antero-posterior (AP) and skull AP are, respectively, 5.37, 6.28 and 4.24 mGy in NGH, and 5.82, 5.33 and 4.76 mGy in TTX. The ESDs reported in this study, except for examinations of the chest, are generally lower than comparable values published in the literature. Conceptus doses were also estimated for female patients using normalised published conceptus dose data for abdomen examinations. The estimated conceptus doses were >1 mGy even when the conceptus was located 12 cm below the surface of the abdomen.

Radiological parameters and radiation doses of patients undergoing abdomen, pelvis and lumbar spine X-ray examinations in three Nigerian hospitals.

Thermoluminescent dosemeters (TLDs) have been used to measure the entrance surface doses (ESDs) of patients undergoing pelvis, abdomen and lumbar spine diagnostic X-ray examinations in Nigeria. A total of three public hospitals and 171 patients were included in this investigation. The ages of the patients involved were from 40 years to 85 years, while their weights ranged from 64 kg to 73 kg. Mean, median, first and third quartiles of ESDs are reported. The results showed that in most cases, for each of the examinations, the individual ESD values are found to be comparable with, and higher than, those from Ghana and Tanzania, respectively. The mean ESD values are also found to be within the range of mean ESD values that have been previously been reported from countries outside Africa. When compared with the European Community (EC) reference values, the mean ESDs were found to be below the reference values in only two of the hospitals. The ranges found in this work are high and this indicates more attention needs to be given to X-ray facilities in the country. This also suggests that radiographic departments need to review their radiographic practices in order to bring their doses to optimum levels. Effective doses were also calculated from the ESD values. The mean effective doses were found to be generally low when compared with those found in the literature from other countries including two African countries. The radiographic parameters used for all the patients were also compared with the European criteria. It is recommended that the tube filtration at one hospital be increased. The importance of good regulatory activities and trained personnel is stressed in this work. Apart from the fact that the data provided in this work will be useful for the formulation of national guidance levels, they also provide patient dosimetry information on healthcare level IV countries.

Survey of radiological techniques and doses of children undergoing some common x-ray examinations in three hospitals in Nigeria.

A dosimetric survey has been carried out in order to investigate typical radiation doses for children undergoing a number of common x-ray examinations in Nigeria. The results presented in this work are derived from the data of 226 children from three different hospitals included in the survey. Assuming the sample is representative of national practice patterns, pediatric chest examinations are the most frequent radiological examinations. Doses were measured by attaching thermoluminescent dosimeters to the patient's skin to determine entrance surface dose (ESD). The mean and standard deviation of the individual ESD values are reported. Comparisons were made between these doses and diagnostic reference levels, and also between the doses and those from other countries. The mean ESD values in the present work are found to be generally higher than those found in an UNSCEAR document and the NRPB diagnostic reference levels. The ratio of maximum ESD to minimum ESD, a parameter that characterizes ESD variation, was found to be less than 10 in each of the hospitals, while across the three hospitals the ratio was found to be greater than 10. The reasons for the high mean ESD and the variations in patients' ESD values have been discussed in terms of regulatory control, personnel, difference in radiological techniques, performance of x-ray facility, film processing condition, and the type of film-screen combination used. The results presented in this work will form part of the baseline data needed for deriving national guidance levels of pediatric radiological examination. In addition, it will also serve as a source of additional information on pediatric patient dosimetry. Suggestions are given on how to reduce doses to pediatric patients during x-ray examinations, especially in developing countries.

Whole-body doses of occupationally exposed female workers in Nigeria (1999-2001).

The work described in this note is based on the national dose registry of radiation workers in Nigeria kept by the Federal Radiation Protection Service. In each of the three years (1999-2001) used for this analysis, the number of male radiation workers was more than that of female radiation workers in both medicine and industry. The ratio of the number of female radiation workers to that of their male counterparts, however, is smaller in industry. The mean of the annual doses of all radiation workers increased from 3.6 mSv in 1999 to 4.7 mSv in 2000 and to 7.7 mSv in 2001. This increase was a result of the yearly increase in mean annual doses to radiation workers in industry. In the industrial category, the mean annual doses of female radiation workers were higher than those of their male counterparts in 1999 and 2001 in both occupation categories. In 2000, while the mean annual doses were the same for both male and female radiation workers in the medical category, the mean annual dose of male radiation workers was higher than that of female radiation workers in industry. Female radiation workers received the highest annual doses in 1999 and 2001. These results indicate the need for the regulatory authority to pay more careful attention to the control of female radiation workers' exposures.

Review of the radioactive waste management system in Nigeria.

The management of radioactive waste in Nigeria from early 1960 to date is reviewed. As in many developing countries, waste management in Nigeria has been shown to be ineffective. The factors that are responsible for this ineffectiveness are identified and discussed. The steps being taken by and the opportunities available to the newly established Nigerian Nuclear Regulatory Authority towards addressing this problem of ineffectiveness are discussed. The efforts of this newly set up body towards managing the resultant radioactive wastes that will be generated during the use of a reactor and an accelerator that will soon be commissioned in Nigeria are also mentioned. Likely ways of further addressing the problems militating against waste management in developing countries are suggested.

Analysis of occupational doses of workers on the dose registry of the Federal Radiation Protection Service in 2000 and 2001.

In 2000 and 2001 about 279 and 221 radiation workers, respectively, were monitored by the Federal Radiation Protection Service, University of Ibadan, in Nigeria. The distribution of the occupational doses shows that the majority of workers received doses below 4 mSv in each of the two years. The radiation workers in the two years are classified into two occupational categories: medicine and industry. The mean annual effective doses, collective doses and the collective dose distribution ratios for workers in each category and the entire monitored workers were calculated. The mean annual effective doses were compared with their corresponding worldwide values quoted by UNSCEAR. In each of the two years, a few workers in industry received doses higher than 50 mSv. The collective dose distribution ratio was found to be about 0.49, which is very close to the highest value of 0.5 in the range of values considered by UNSCEAR as normal for this parameter. This suggests that extra measures have to be taken, particularly in industry, to ensure that the proportion of workers at risk does not go outside this normal range. The occupational doses were also modelled by both the log-normal and Weibull distributions. Both distributions were found to describe the data in almost the same way.

Scattered doses to different parts of cancer patients during radiotherapy treatment in Nigeria.

The doses over various parts of the body of 7 patients with cancers of the pharynx, breast and cervix during radiotherapy treatment with a megavoltage 60Co therapy machine were measured using LiF TL dosemeters. The doses on the surface of the patients outside the primary beam were found to vary with a maximum of 366 mGy at the abdomen of a cervix cancer patient to a minimum value of 1.1 mGy at the left arm and left leg of a pharynx cancer patient. The observed variations in the doses were attributed to the difference in patients' tumour location, exposure and anatomy. In the treatment of pregnant women and women of childbearing age, the results presented will be a good starting point for estimation of fetus doses and doses to organs outside the planning region.

Comparison of entrance surface doses of some X ray examinations with CEC reference doses.

Entrance surface dose (ESD) measurements have been carried out in Nigeria as part of the ongoing dose reduction programme. Thermoluminescence dosemeters (TLD) were used to measure skin entrance doses for four common radiographic views in three hospitals. The mean ESD for the PA chest examination in all the participating hospitals was in the range 0.12 - 4.46 mGy. The mean ESD for the AP skull. PA skull and LAT skull were 8.55, 5.17 and 6.97 mGy respectively. The mean ESD values are greater than the CEC reference doses, except for rooms 1 and 2 in UCH where the entrance surface doses for PA chest examination are below the CEC reference dose. The QA test results show non-compliance of the accuracy of tube voltage with acceptance limit in three rooms. The timer accuracy is also not within the acceptance limit in two rooms. The reproducibility of both the kVp and timer in all the rooms is good.

Models for the comparative equivalence of scattering properties of elemental filters used in diagnostic radiology.

While the equivalence of different filter materials commonly considered useful in diagnostic radiology can be obtained in terms of the overall transmitted primary photons, the scattering characteristics are not the same. In this work, comparative models that relate the scattered photons produced from one-filter material with those from another have been developed. The comparison of the results of simulation of the scattering properties of these equivalent filter materials using the Monte Carlo technique with those from the models developed in the study are in reasonable agreement.