4.2 Principles of Radiation Protection (ALARA)
Radiation protection is a set of measures and principles designed to minimize the health risks associated with exposure to ionizing radiation.
The ALARA Principle
The central philosophy of radiation protection is the **ALARA** principle, which stands for "**As Low As Reasonably Achievable**". This means that every reasonable effort should be made to keep radiation exposure as far below the dose limits as possible.
The term "reasonably achievable" considers economic and social factors, but the primary goal is to ensure the benefits of the radiation source outweigh the risks associated with the exposure.
The Three Pillars of Protection
The ALARA principle is implemented through three fundamental measures for external exposure control:
- Time: The amount of radiation exposure is directly proportional to the time spent in a radiation field. Therefore, minimizing the time spent near a source is the simplest way to reduce your dose.
- Distance: Radiation intensity decreases significantly with distance from the source. This is due to the **inverse square law**, which states that intensity is inversely proportional to the square of the distance from the source. Doubling your distance from a point source reduces your dose rate to one-quarter of the original.
- Shielding: Placing a physical barrier between a person and a radiation source will reduce the dose. The effectiveness of the shielding material depends on its thickness, density, and atomic number, as well as the type and energy of the radiation. Common shielding materials include lead, concrete, and water.