The assessment of radionuclides in selected granite quarry sites in Ohimini and Gwer-East Local Government Areas of Benue State was carried out using a 76 × 76 mm NaI (TI) detector crystal optically coupled to a photomultiplier tube (PMT). The detector is enclosed in a 6 cm lead shield with cadmium and copper sheet and data acquisition was done by Canberra Nuclear Products (Meastro) at Center for Energy Research Training, Ahmadu Bello University, Zaria. These sites include Anmuda, Awulema and Ikpayongo quarry sites with five samples from each site making a total of fifteen samples. From the preliminary investigation, the mean absorbed dose in Anmuda, Awulema and Ikpayongo are 12.3 nGy/h, 17.27 nGy/h and 18.87 nGy/h respectively and the corresponding Mean Annual Effective Dose equivalent are 0.15 mSv/y, 0.21 mSv/y and 0.25 mSv/y which are actually below the recommended safe values. The result of the assessment of radionuclides in granite samples includes Radium-226 (226Ra), Thorium-232 (232Th) and Potassium-40 (40K). The mean activity concentration in Anmuda for 40K is 86.717 ± 4.656 Bq/kg, that of 226Ra is 7.862 ± 3.728 Bq/kg and 232Th is 5.280 ± 1.505 Bg/kg, in Awulema, 40K is 155.656 ± 5.074 Bq/kg, 226Ra is 3.614 ± 4.220 Bq/ kg and 232Th is 8.478 ± 3.842 Bq/kg and in Ikpayongo 40K is 329.737 ± 9.405 Bq/kg, 226Ra is 5.394 ± 5.032 Bq/kg and 232Th is 7.067 ± 3.820 Bq/kg. The mean absorbed dose in Anmuda, Awulema and Ikpayongo are 10.6094 nGy/h, 13.845 nGy/h and 21.212nGy/h. The mean annual effective dose equivalent in Anmuda is 0.13 mSvy- 1, Awulema is 0.16 mSvy-1 and Ikpayongo is 0.25 mSvy-1. The average value falls within the global range of outdoor radiation exposure given by UNSCEAR-2000 publication.

Radiation is defined as the transfer of energy through space and matter in the form of wave and particle. Natural and artificial sources of ionizing radiation are present in the environment in which we live. Naturally occurring radionuclides are present in air we breathe, the food we eat and the water we drink and have resulted in adverse health consequences on the public. Human can be exposed to radionuclide from natural and artificial sources through human activities such as mining and drilling. The artificial sources also include human activities such as nuclear and atomic bomb testing, nuclear reactor explosions, mining activities, industrial waste and effluent from factories as reported by Agba et al. in 2006. International Atomic Energy Agency (IAEA) estimation shows that over 85% of radiation dose received by man are derived from the naturally occurring radionuclides while the remaining 15% is from cosmic rays and nuclear processes all around the globe. Over exposure to radiation could cause adverse health effects such as leukemia, chromosomal breakage, bone necrosis, bone cancer, mutation of genes, cataracts of eye lens etc. The mining of mineral resources such as granite, limestone, marbles etc can facilitate the release of radioactive materials from the host material (ores) into the environment since most minerals (ores) co-exist with naturally occurring radionuclides. On the earth, natural radioactive mineral deposits are available in many suitable geological environments. The high exposure level of these radionuclides in such an area may be harmful to people residing in the region. The greatest contribution to human exposure comes from natural background radiation.

The energy transferred by ionizing radiation to the mass per unit volume, is called absorbed dose. The probability of affecting the human health is directly related to the absorbed dose. The worldwide average natural dose to humans is about 2.4 mSv per year (UNSCEAR, 2000). The major natural radionuclides of concern are Thorium-232 (²³²Th) and Radium-226 (²²⁶Ra) and their decay products as well as Potassium-40 (⁴⁰K). Thorium and Uranium primarily undergo alpha and beta decay and are not easily detectable. However, many of their daughter products are strong gamma emitters. Gamma rays are more penetrating than alpha or beta particles and are most often used to characterize the terrestrial component of the natural radiation environment. Thus, the gamma ray emissions from ²³²Th and ²³⁸U radioactive daughter products are used to estimate their concentrations. Granite is the best-known igneous rock which has extensive applications. Granite is used to make many objects that we encounter in life daily. These include counter tops, floor tiles, paving stone, stair, building veneer, and cemetery monuments. At the same time granite is a natural source of radioactivity like most natural rocks. The main part of the radioactivity in this kind of samples is attributed to the potassium-40 radioisotope. ⁴⁰K exists in a standard relation with total potassium content, with a natural abundance of 0.012%. Granites contain also some dozens of parts per million (ppm) of Uranium and Thorium as well. Granite quarries produce massive amount of dust particles and such dust particles increase the level of Radon gas. The main way of saving the humans from radiation injuries is to protect it from exposure to radiation and this is why radiation monitoring and measurement are very essential in our society today

With Regards,
Sara Giselle
Associate Managing Editor
Journal of Medical Physics and Applied Sciences