Analysis of 226Ra content and 222Rn exhalation rates in soil samples from Wukro, Tigray, using SSNTDs

Background: Radon gas, a decay product of radium, poses potential health risks due to its radioactive properties. Understanding radium content and radon exhalation rates in soil is essential for assessing environmental safety and radiological hazards.

Materials and Methods: Soil samples were collected from various locations in Wukro, Tigray, and analyzed using LR-115 type-II plastic film track detectors. Measurements included radium concentration, mass exhalation rates, and surface exhalation rates.

Results and Discussion: The radon mass exhalation rates ranged from 0.18 × 10⁻⁷ Bq.kg⁻¹.d⁻¹ to 0.82 × 10⁻⁷ Bq.kg⁻¹.d⁻¹, with a mean of 0.48 × 10⁻⁷ Bq.kg⁻¹.d⁻¹. Surface exhalation rates varied from 0.38 × 10⁻⁶ Bq.m⁻².d⁻¹ to 1.72 × 10⁻⁶ Bq.m⁻².d⁻¹, averaging 1.02 × 10⁻⁶ Bq.m⁻².d⁻¹. Radium concentrations ranged from 0.33 to 1.47 Bq.kg⁻¹, with an average of 0.87 Bq.kg⁻¹. A significant positive correlation between radium content and radon exhalation rates was observed, indicating a direct relationship between these variables. Clay soils exhibited the highest radium concentrations, while sandy soils had the lowest. All measured values were below the safety limit of 370 Bq.kg⁻¹ recommended by OECD and UNSCEAR, suggesting no significant radiological risk in the study area.

Conclusion: This study highlights the importance of monitoring natural radiation levels for environmental safety. The findings provide a baseline for future studies and emphasize the need for continuous assessment to detect any long-term changes in soil radioactivity.

Methods
In this study, twelve soil samples were collected from various locations of the study area by grab sampling method. Sealed Can technique has been used. Following collection, collected soil samples were crushed into fine powder to ensure uniformity and consistency. Obtained soils were then sieved using a 200 micron-mesh size. For each measurement, 200 grams of fine powder was placed at the base of a cylindrical can with dimensions of 8 cm x 12 cm and sealed tightly and stored for duration of four months in order to reach equilibrium with its decay product. A piece of LR-115 Type-II plastic track detector, measuring 2 cm × 3 cm, was affixed to the inner surface of the cylindrical can, approximately 0.65 meters away from the surface of the samples. After exposure time of 4 months, the LR-115 detectors were removed and chemically etched in a solution of 2.5N NaOH at a temperature of 70°C for one hour and half. After this chemical treatment, the detector tracks which represent interactions between alpha particles and the detector surface were then counted using an optical microscope at a magnification of 400x.