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Dosimetry for Cell Irradiation using Orthovoltage 40-300 kV X-Ray Facilities
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HUMAN EXPOSURE TO BACKGROUND RADIATION IN ORTUM, KENYA
F O Wanjala1, N O Hashim1, D Otwoma2
1Kenyatta University, Physics Department, P. O. Box 43844-00100, Nairobi, Kenya.
Radiation Protection Dosimetry
|December 2, 2019
Summary
Radon (222Rn) and its decay products are the primary cause of lung cancer in non-smokers. This study measured radon levels in homes in the United States and found that levels were higher in the winter than in the summer.
Area of Science:
- Environmental Science
- Radiological Health
- Geochemistry
Background:
- Terrestrial radionuclides, including Uranium-238 (238U), Thorium-232 (232Th), and Potassium-40 (40K), are naturally occurring and contribute to background radiation.
- Understanding the distribution and concentration of these radionuclides in soil is crucial for assessing potential environmental and health impacts.
- The absorbed dose rate (ADRA) in air at 1 meter above ground is a standard metric for evaluating external gamma radiation exposure from terrestrial sources.
Purpose of the Study:
- To determine the activity concentrations of 238U, 232Th, and 40K in soil samples from Ortum.
- To measure the absorbed dose rate (ADRA) in air at 1 meter above ground in Ortum.
- To assess the suitability of local soil and rocks for use based on radionuclide concentrations.
Main Methods:
- Gamma-ray spectrometry was employed to measure the activity concentrations of 238U, 232Th, and 40K in soil samples.
- The absorbed dose rate (ADRA) in air was calculated based on the measured activity concentrations and established conversion factors.
- Depth profiles of radionuclide concentrations were analyzed to understand their distribution within the soil.
Main Results:
- Soil activity concentrations in Ortum ranged from 33-85 Bq kg-1 for 238U, 20-67 Bq kg-1 for 232Th, and 148-1019 Bq kg-1 for 40K.
- Average activity concentrations were 40 ± 1.43 Bq kg-1 (238U), 56 ± 1.46 Bq kg-1 (232Th), and 425 ± 19.24 Bq kg-1 (40K).
- The average ADRA in air at 1 m above ground was 112 ± 29.6 nGy h-1. Activity concentrations of 232Th and 238U decreased with depth, while 40K increased.
- Average soil radionuclide concentrations were higher than global averages, but still below recommended safety thresholds.
Conclusions:
- The soil and rocks in Ortum exhibit terrestrial radionuclide concentrations that are generally higher than world averages.
- Despite higher-than-average concentrations, the measured activity levels for 238U, 232Th, and 40K remain below established safety thresholds.
- The soil and rocks in Ortum are recommended for general use, as the radiological risk associated with their terrestrial radionuclide content is deemed acceptable.
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