Safety From External Radiation Hazard

Study Notes

Radiation Safety

Radiation sources outside the body include α, β, X, γ, and neutrons, which can penetrate to sensitive organs.
Alpha radiation is not typically considered an external radiation hazard since it cannot penetrate the outer skin layers.

ALARA Principle

ALARA stands for "As Low As Reasonably Achievable," aiming to avoid unnecessary radiation exposure.
Three basic protective rules in radiation safety:
- Time: Minimize time spent near a radioactive source to reduce dose.
- Distance: Maximize distance from the source to decrease dose rate.
- Shielding: Use barriers to absorb radiation, depending on the type of radiation.

Distance and Inverse Square Law

As distance from the source increases, the dose rate decreases.
If distance from the source doubles, the dose rate reduces to 1/4 of its original value.
If distance from the source triples, the dose rate reduces to 1/9 of its original value.

Shielding

Shielding materials depend on the type of radiation:
- Alpha radiation: Easily absorbed by thin sheets of paper.
- Beta radiation: Shielded by low Z materials like Perspex (not lead) to avoid secondary x-rays.
- Gamma and X-ray radiation: Attenuated exponentially by materials, with the dose rate decreasing with increasing shield thickness.
- Neutron radiation: Materials with high hydrogen content (e.g., paraffin, water, concrete) and elements with high capture for thermal neutrons (e.g., boron, cadmium) are used.

Half-Value Layer (HVL)

HVL is the thickness required to reduce radiation intensity to one half its incident value.
High purity lead brick is ideal for X-ray and gamma ray shielding.

Neutron Shielding Materials

Materials with high hydrogen content (e.g., paraffin, water, concrete) slow down incident neutrons through elastic scatter.
Elements with high capture for thermal neutrons (e.g., boron, cadmium) are used to capture moderated/thermalized neutrons.
Borated Polyethylene is a good shield for n-capture reactions, made from high-density polyethylene plastic with 5% boron content.

Description

Learn about external radiation hazards from sources like α, β, X, γ, and neutrons, and how to stay safe. Understand the principle of ALARA - As Low As Reasonably Achievable, which emphasizes minimizing radiation exposure as much as possible.