Monitoring Radiation Doses Resulting from Naturally Occurring Radioactive Materials Resulting from Mineral extraction - Oil and Phosphate Extraction as an Example

Abstract

Extracting minerals from the ground results in bringing in other materials that are sometimes unwanted, but their presence is inevitable, among these materials are what are known as Naturally Occurring Radioactive Materials (NORM). In this research, an attempt is made to monitor these materials in two different areas of mineral extraction, which are oil and phosphate. Seven soil samples were collected from the dry or semi-dry surface layer of a number of water collection pits associated with oil production in some Libyan oil fields (Z₁, Z₂, Z₃, Z₄, H₁, H₂ and S₁), and three samples of phosphate fertilizer used in fertilizing agricultural lands in Libya (raw Tunisian fertilizer-F3, raw Moroccan fertilizer-F2 and Tunisian compound fertilizer-F3) and one sample of normal soil for comparison. The radiation detection of these samples was carried out using a gamma ray spectroscopy device with a high purity germanium (HPGe) detector with an efficiency of 40% located in the protection building of the Tajoura Nuclear Research Center. The radioactivity of the samples, a number of hazard indicators and the concentration of emitted radon gas (arithmetic only) were calculated. Sample H₁ (oil) recorded the highest readings, where the radioactivity of 238U, 232Th and 40K was 3.21x10⁵±566.5, 1.46x10⁵±382.9 and 7.44x10³±86.2 Bq/kg, respectively, and an effective equivalent dose (AEDE) of 291.95±17.05mSv/y, while the radon gas flux rate was 65.15±8.07 Bq/m².s. Sample S₁ recorded the lowest readings, where the radioactivity of 238U, 232Th and 40K was 1240±35.24 and 240.5±15.49. 330.05±18.16 Bq/kg, respectively, and an annual effective equivalent dose of 0.96±0.97 mSv/y, while the radon gas flux rate was 0.031±0.17 Bq/m².s.

For phosphate fertilizer samples, significantly lower readings were recorded compared to oil soil samples. The highest readings were recorded for raw Tunisian fertilizer, where the radioactivity of ²³⁸U, ²³²Th, and ⁴⁰K was 267.55±16.35Bq/kg, 3.21±1.79, and 248.9±15.77, respectively. The effective equivalent dose (AEDE) was 0.123 mSv/y, while the radon gas flux rate was calculated as 0.839±0.028 Bq/m².s. When comparing these results, especially for the oil samples, with the results of normal soil samples and the global average for normal soil, was found that these samples are saturated with NORM to the real danger.