⚛️Intro to Applied Nuclear Physics Unit 9 – Radiation Safety and Health Physics

Key Concepts and Terminology

• Ionizing radiation transfers enough energy to remove electrons from atoms or molecules, creating ions
• Non-ionizing radiation does not have sufficient energy to ionize atoms or molecules but can still cause biological effects
• Radioactivity is the spontaneous emission of radiation from unstable atomic nuclei
• Half-life is the time required for half of a given quantity of a radioactive substance to decay
• Absorbed dose measures the amount of energy deposited in a material per unit mass, expressed in grays (Gy) or rads
  • 1 Gy = 1 joule per kilogram (J/kg)
  • 1 rad = 0.01 Gy
• Equivalent dose accounts for the varying biological effectiveness of different types of radiation, expressed in sieverts (Sv) or rems
  • Calculated by multiplying the absorbed dose by a quality factor (QF) specific to the type of radiation
• Effective dose is the sum of the equivalent doses to each organ or tissue, weighted by the tissue weighting factor, expressed in Sv or rem

Types of Radiation and Their Properties

• Alpha particles consist of two protons and two neutrons (helium nuclei) emitted from heavy radioactive nuclei
  • Highly ionizing but short range, easily stopped by a sheet of paper or skin
  • Hazardous if inhaled or ingested due to high linear energy transfer (LET)
• Beta particles are high-energy electrons or positrons emitted from radioactive nuclei during beta decay
  • More penetrating than alpha particles but less ionizing, can be stopped by a few millimeters of aluminum or plastic
• Gamma rays are high-energy electromagnetic radiation emitted from excited atomic nuclei
  • Highly penetrating, requiring dense materials like lead or concrete for shielding
  • Interact with matter through photoelectric effect, Compton scattering, and pair production
• X-rays are similar to gamma rays but originate from electron transitions in atoms rather than nuclear transitions
• Neutron radiation occurs when free neutrons are emitted from nuclear reactions or spontaneous fission
  • Can be highly penetrating and cause activation of stable nuclei, creating radioactive materials

Biological Effects of Radiation

• Radiation can cause direct damage to biomolecules (DNA, proteins, lipids) through ionization or excitation
• Indirect damage occurs when radiation interacts with water molecules, producing free radicals that react with biomolecules
• Deterministic effects have a dose threshold and severity increases with dose (skin erythema, cataracts, sterility)
  • Result from extensive cell death and tissue damage
• Stochastic effects have no dose threshold and probability increases with dose (cancer, genetic mutations)
  • Result from mutations in individual cells that survive and proliferate
• Acute radiation syndrome (ARS) occurs after whole-body exposure to high doses (>1 Gy) in a short time
  • Symptoms include nausea, vomiting, fatigue, and potentially death depending on dose
• Chronic radiation exposure can lead to increased risk of cancer, cataracts, and other long-term health effects

Radiation Detection and Measurement

• Gas-filled detectors (ionization chambers, proportional counters, Geiger-Müller tubes) measure ionization produced by radiation in a gas
  • Ionization current or pulse height is proportional to the energy deposited by the radiation
• Scintillation detectors use materials that emit light when exposed to radiation (NaI, plastic, liquid scintillators)
  • Light is converted to electrical signals by photomultiplier tubes or photodiodes
• Semiconductor detectors (silicon, germanium) measure electron-hole pairs created by radiation in a semiconductor material
  • Provide excellent energy resolution for gamma and X-ray spectroscopy
• Neutron detectors often rely on nuclear reactions that produce charged particles (BF3, 3He, fission chambers)
• Thermoluminescent dosimeters (TLDs) and optically stimulated luminescence (OSL) dosimeters measure accumulated dose over time
• Film badges and pocket dosimeters provide personal dose monitoring for radiation workers

Radiation Protection Principles

• Time, distance, and shielding are the three primary methods for reducing radiation exposure
  • Minimize time spent in radiation areas
  • Maximize distance from radiation sources (inverse square law)
  • Use appropriate shielding materials (lead, concrete, water) to attenuate radiation
• ALARA (As Low As Reasonably Achievable) principle guides radiation protection practices
  • Justification: Benefits of a practice involving radiation exposure should outweigh the risks
  • Optimization: Radiation doses should be kept as low as reasonably achievable, considering economic and societal factors
  • Limitation: Radiation doses should not exceed established limits for workers and the public
• Contamination control involves preventing the spread of radioactive materials and decontaminating affected areas
• Proper waste management and disposal practices are essential to minimize environmental impact and public exposure

Dosimetry and Exposure Limits

• External dosimetry measures dose from radiation sources outside the body using personal dosimeters (film badges, TLDs, OSLs)
• Internal dosimetry assesses dose from radioactive materials inside the body through bioassay measurements (urine, feces, whole-body counting)
• Occupational dose limits for radiation workers are typically 50 mSv/year whole-body effective dose
  • Limits for lens of the eye, skin, and extremities are higher due to lower tissue weighting factors
• Public dose limits are typically 1 mSv/year above background radiation to ensure minimal risk
• Dose constraints are set lower than dose limits to optimize protection and prevent approaching limits
• Collective dose is the sum of individual doses in a population, expressed in person-Sv or person-rem
  • Used to assess population exposure and potential health effects

Safety Procedures and Equipment

• Radiation areas should be clearly marked with signs and barriers to control access
• Personal protective equipment (PPE) such as lab coats, gloves, and respirators may be required in certain areas
• Fume hoods and glove boxes provide containment for working with radioactive materials
• Radiation surveys using portable detectors (Geiger counters, ion chambers) monitor work areas and identify contamination
• Decontamination procedures involve removing or reducing radioactive contamination from surfaces, equipment, and personnel
  • Methods include washing, wiping, and using specialized decontamination agents
• Emergency response plans outline procedures for accidents, spills, or releases of radioactive materials
  • Includes evacuation, containment, and notification of appropriate authorities

Regulatory Framework and Standards

• International Commission on Radiological Protection (ICRP) provides recommendations and guidance on radiation protection principles
• International Atomic Energy Agency (IAEA) establishes safety standards and promotes peaceful use of nuclear technology
• National regulatory agencies (NRC in US, CNSC in Canada, AERB in India) oversee licensing, inspection, and enforcement of radiation safety regulations
• Regulations cover areas such as occupational dose limits, public exposure, radioactive material handling, and waste disposal
• Radiation safety officers (RSOs) are responsible for implementing and overseeing radiation protection programs within organizations
• Regular training and education for radiation workers ensure understanding of risks, safety procedures, and regulatory requirements
• Recordkeeping and reporting requirements maintain transparency and accountability in radiation safety practices