Estimation of Radiation Dose Rate Levels around a Nuclear Establishment in Abuja, North Central, Nigeria

The radiation monitoring around Nuclear Technology Centre, Nigeria Atomic Energy Commission, Sheda-Abuja has been carried out using RDS-200 Universal Survey meter. Areas monitored included Gamma Irradiation Facility, Central Workshop, Radioactive Waste Management Build ing under Construction, proposed Radioisotope Plant site, Power Supply Station, SHESTCO Advanced Laboratories, Xechem Pharmaceutical Plc, Staff Housing Estates and NAEC Researchers’ Hostel. It was observed that the dose equivalent rate varied from 0.106 ± 0.032 to 0.212 ± 0.036 μSv/h with a mean of 0.149 ± 0.032μSv/h.These results though slightly above the standard background radiation of 0.133 μSv/h, they are below the ICRP maximum permissible limit of 0.57μSv/h and may not pose any danger to the radiation workers , the general public and the environment. This work also revealed that the dose rate at the Nuclear Technology Centre (NTC) is essentially from natural background radiation. Th is implies that there is adequate shielding for all the radioactive sources. It is safe and there has possibly been no contamination from the activit ies of the centre on its environment.


Introduction
Radiat ion, because of the adverse health effect when persons are over exposed to ionizing radiat ion, is feared by many people worldwide and Nigerians are no exempt ion. This concern is even much higher with inhabitants living at close proximity to nuclear establishments. What most people do not realize is that radiation is present everywhere, in everything in our environment and even in our bodies. There is cosmic radiation made up of protons, alpha particles and heavy nuclei bombard ing the earth from space. They interact with at mosphere resulting into large numbers of gamma rays, neutrons and mesons contributing high radiation dose burden to man even at sea level [1]. Other natural rad iation includes the terrestrial gamma rays fro m land, sea and walls of houses we live. We are also internally exposed fro m radiation emitted by radio-nuclides absorbed into the body through the food we eat and milk we d rin k. Examples of such radio-nuclides are potassium -40, heavy elements and carbon-14. Although generally the background radiation contributes more than 60% of the annual rad iation dose burden to man, however the radiation levels in most places are too weak to cause any deleterious effects on man. Therefore, there is no need to fear radiat ion but to understand the properties, make use of it and reduce the exposure to dose level wh ich the society judged as acceptable with minimu m associated risk. As long as the contribution from the artificial radio-nuclides does not push the annual dose equivalent level beyond 1mSv , then there is no need to fear radiat ion. Although the level of dose burden from natural rad iation is low, there is still a level of risk, though small, is not zero. It has been reported [2] that averagely the radiation exposure rate lies in the range of 0.08-0.15μSv/hr. According to [3] about 95% of the world's population is assumed to live in areas of normal background radiation with outdoor dose rate ranging fro m 0.024 to 0.160 μGy/h. The harmfu l effects of radiation can be categorized into deterministic radiat ion (Tissue reaction) and non deterministic radiation risks. Determin istic effects have threshold dose below which effects are not probable such as erythema, rad iation dermatitis, alopecia etc whereas non deterministic effects have no threshold dose and include carcinogenesis and genetic effects. The objective of radiation protection is to define how one can protect individual, their descendants and human race in the entirety against the potential risks of ionizing rad iation [4]. The public and radiation workers receive various doses of ionizing radiation fro m both naturally occurring and man made sources. The level of doses received depends on the occupation, level of radiation in the environ ment and where an indiv idual lives. Depending on where an individual lives, some people receive an exposure in the range of 1mSv per year fro m cosmic radiat ion fro m outer space and fro m naturally occurring isotopes in the ground, air, food and water [5]. Radiat ion fro m many sources is omnipresent on the earth surface, consequently man is continuously irradiated. The level of the natural radioactiv ity in the soil and in the surrounding environment as well as the associated external exposure due to the gamma radiation depends primarily on the geological and geographical conditions of the region [6]. The geological and geographical defin ition of an environment dictate to a good degree the radionuclides contained in the soil and rocks there. [7]. Soil contains small quantities of radioactive elements along with their progeny [8]. This paper presents the radiation level and the gamma equivalent dose rate, cancer and heritable risks effects to the radiation workers and the non rad iation workers working and liv ing with in Sheda Science and Technology Comp lex, Sheda and the general public living around this nuclear establishment. The values obtained for radiation fro m this work will form part of the baseline data for environ mental radiation in the Federal Capital Territory, Abuja which up till now to the best of our knowledge is not available. The data could also be used (in the future) to assess the impact of research activities on the environment.

Materials and Methods
This study was conducted between October and November, 2011, in and around Nuclear Technology Centre (NTC). NTC is situated in Sheda, Abuja. It is also 75 km southwest of the Federal Capital Territory (FCT), Abuja and about 35 km fro m the Nnamd i A zikwe International Airport, Abuja. NTC is in the vicinity of the National Food Reserve Agency Strategic Grains Reserve Facility, Nat ional Agricultural Seeds Council; National Automotive Council site, Nigerian Educational Research and Development Council, Federal Min istry of Works Highway Materials and Geotechnics Testing Laboratories. Also the Nat ional Mathematical Centre lies to the South West while Nat ional Fire Academy, Nat ional Co-operative Management Develop ment Centre and Federal Govern ment College lies to the South East. NTC is in the transitional zone between the basement complex rocks of the North-Central part of Nigeria and the Bida Sand stone basin lying to the South. The rocks consists mainly of gran ite, are exposed only along river channels [9].
The RDS-200 Un iversal Survey Meter is an excellent, portable mu ltipurpose radiation meter for a wide range of applications. It is especially designed for situations where accurate measurements at low dose rate levels are of importance. The meter has an interface for the external gamma p robes GMP-12H/12L or beta/contamination measurement probe GMP-11/ 15. A connector for the attachment of the meter to a PC is located at the bottom part of the meter and is equipped with protective cover. The RDS-200 utilizes field -proven measurement electronics and can also be used as a local display unit with the RADOS AAM-90 Area Monitoring System. The meter measures γ-radiation and beta radiation with an external probe detector It also measures equivalent dose rate within 0.05 μSv/h-10 μSv/h The meter was calibrated by the National Institute of Radiat ion Protection and Research, University of Ibadan, Ibadan-Nigeria. Read ings were obtained between the hours of 1200 and 1600 hours. Eighteen (18)  Radiat ion (BKG). These areas record high population flux throughout the day. The monitor was suspended in air at one meter above the ground level. [10]. At least five readings were taken in each location and the mean values were recorded.

Results and Discussion
Data for the mean dose rates of the areas measured are presented in Table 1 [12]. Figure 1. Shows that the dose rate values of NTC I, SHESTCO academic and Staff Quarters areas are higher than the NTCII (inside the Gamma Irradiat ion Facility) radiation dose rate value. This imp lies that inhabitants of those areas are not subjected to increased radiation exposure and higher risks fro m the radiation facility. The background radiation observed at the surveyed areas could be attributed only to natural sources (cosmic and terrestrial). The geology of the town suggests that the soil in Abuja has a large deposit of granite. It is well known that granites contain high concentrations of uranium, thoriu m and potassium [13]. The total mean dose rate of the surveyed areas was found to be lower than that of a similar institution at GAEC, Ghana [12]. Also, the dose rate is lower than that reported for Minna which is just about 100 Km away fro m the study area; this may be due to the fact that they have similar geology [8,9]. Ilorin and Offa values, 0.132uSv/hr and 0.134 uSv/hr respectively, [14,15] are found to be comparable with that obtained in this work. Table 2 illustrates the estimated fatality cancer risk to adult workers per year which ranges fro m 6.26 X 10 -6 to 12.50 x 10 -6 with heritable effect risk to adult workers ranged fro m 1.53 x 10 -6 .to 3.05 x 10 -6 . Also, the total detrimental risk to adult workers ranges fro m 6.41 x 10 -6 to 12.80 x10 -6 . It could be inferred that annual effective dose values compares well with world average of annual effect ive dose of 480uSv/h [11]. On the average, WTP recorded the highest level of risks to its workers and thus it could be inferred that the likelihood of a worker within WTP transferring heritable effects fro m a radiation induced to their offspring is high.

Conclusions
The exposure rates have been computed for the various Nuclear Technology Centre and Sheda Science and Technology Complex locations using in situ measurement method. This work revealed that the calculated average annual effective dose is comparab le to the worldwide average annual effective dose. This exp lains the acceptable level of safety culture being practiced in the centre. The results from this work will form the baseline data which will be useful in assessing contribution to radiation in the environment fro m future activ ities of the Nuclear Technology Centre.