Occupational exposure to natural radiation.

Area of Science:

• Occupational health and safety
• Radiation protection
• Environmental science

Background:

• Natural radiation sources contribute to occupational radiation exposure.
• Work involving minerals with elevated activity and high radon daughter concentrations are key concerns.
• Current regulations allow exemptions for low-activity natural radioactive substances.

Purpose of the Study:

• To assess potential significant radiation doses from work with naturally low-activity minerals.
• To determine activity concentration thresholds requiring radiological supervision.
• To investigate radon daughter concentrations in various workplaces.

Main Methods:

• Investigated five factories working with minerals below regulatory exemption levels.
• Developed models to correlate mineral activity with effective dose equivalent (gamma, radon daughters, long-lived activity).
• Measured radon daughter concentrations in seventy workplaces.

Main Results:

• Activity concentrations of 0.3 Bq g-1 for thorium-232 and 1 Bq g-1 for uranium-238 were identified as thresholds where airborne dust exposure could reach one-tenth of the worker dose limit.
• Some workplaces exhibited radon daughter concentrations approaching or exceeding occupational exposure limits.
• Highest radon concentrations were observed in areas with poor ventilation.

Conclusions:

• Radiological supervision may be necessary for minerals with thorium-232 concentrations above 0.3 Bq g-1 and uranium-238 above 1 Bq g-1.
• Elevated radon daughter concentrations in workplaces pose a significant occupational exposure risk, particularly in poorly ventilated areas.
• Further attention to natural radioactivity in occupational settings is warranted.