Ionizing Radiation Safety and Biological Effects

Ionizing Radiation Fundamentals

Radiation is defined as a form of energy transmission through space.

Ionizing Radiation Characteristics

Ionizing radiation is capable of producing ions in the atoms of matter with which it comes into contact. Its primary characteristics include:

• Energy: Greater than 1.23 MeV.
• Cumulative Power: It collects dose effects over time.
• Detection: It is not detectable by human senses.
• Nature: It can be corpuscular or consist of electromagnetic (EM) waves.

Types of Ionizing Radiation

• Alpha (α): Stopped by a sheet of paper and travels only a few inches.
• Beta (β): Stopped by aluminum or several meters of air.
• Gamma (γ) and X-rays: Stopped by lead or concrete shielding.
• Neutron: Stopped by hydrogen-rich materials.

Non-Ionizing Radiation

These belong to the Electromagnetic Field (CEM) spectrum and do not possess enough energy to ionize matter.

Radiation Measurement Units

Historical and International Units

Old Units:

• Radioactivity: Curie (Ci)
• Radiation-absorbed: Rad
• Biological effects: Rem

Current International Units (SI):

• Radioactivity: Becquerel (Bq)
• Radiation-absorbed: Gray (Gy)
• Biological effects: Sievert (Sv)

Radiological Magnitudes

Absorbed Dose (D): This is the energy imparted by ionizing radiation (RI) per unit mass of irradiated material (1 Gray = 1 J/kg).

Dose Equivalent (DE): This is the absorbed dose modified by weighting factors, representing the radiation received by a tissue or organ. The formula is DE = D * Q * FP.

Weighting Factors (Q) for Radiation Types

• X-rays, Gamma, and Beta: 1
• Alpha rays and Neutrons: 10
• Heavy nuclei: 20

Weighting Factors (FP) for Organs and Tissues

• Gonads: 0.20
• Bone marrow: 0.12
• Skin: 0.01
• Rest of the body: 0.05

Biological Effects of Radiation Exposure

Several factors influence the onset of biological effects:

• Intensity and irradiation time.
• Pervasiveness.
• Radiosensitivity of the affected tissue.

Classification of Biological Effects

Random or Stochastic Type:

• Cancer
• Malformations and hereditary diseases
• Malignant tumors
• Leukemia

Not Random or Deterministic Type:

• Instant death (> 50 Gy)
• Intestinal form (5 - 50 Gy)
• Hematologic form (2.5 - 5 Gy)
• Asymptomatic (> 2.5 Gy)

Radiosensitivity and Cellular Impact

The radiosensitivity of a cell depends on its reproductive activity:

• The least radiosensitive cells are those that are reproduced the least (e.g., the nervous system).
• The most radiosensitive cells are those that are reproduced the most (e.g., reproductive cells).

Radiation Protection and Safety Rules

Zoning and Classification

• Controlled Areas: Areas where it is not unlikely that doses exceed 3/10 of the Annual Dose Limit (WMD). These are designated for Type A Workers.
• Supervised Areas: Areas where it is unlikely that doses exceed 3/10 of the Annual Dose Limit (WMD). These are designated for Type B Workers.

Safety Protocols and Monitoring

• Appointment of a competent person in radiation protection.
• Adherence to Permissible Dose (RDPRI) standards.
• Staff Monitoring: Dosimetry is required for Type A workers; area dosimetry is mandatory for Type B workers.
• Regular medical surveillance.

General Protective Techniques

• Removal of the radiation source.
• Reducing the exposure time.
• Using appropriate shields.
• Use of Personal Protective Equipment (PPE).
• Implementation of containment measures.

Permissible Dose Limits and Regulations

• Whole Body: For uniform whole-body exposure, the annual effective dose limit is 20 mSv.
• Partial Exposure: For individual organs or tissues, the annual equivalent dose limit is 500 mSv, except for the lens of the eye, which is 150 mSv.
• Pregnancy: For pregnant women, it must be ensured that the dose to the embryo does not exceed 5 mSv.
• Public: The annual effective dose limit for individual members of the public is 1 mSv.