ionizing radiation

Introduction to Ionizing Radiation

  • Date: January 19, 7:41 PM
  • Course: OEHS 6750 - Ionizing Radiation (10-08-21)

Basic Atomic Structure

  • Atomic Structure: Essential for understanding ionizing radiation.
    • Components of an Atom:
    • Nucleus: Contains neutrons and protons
      • Neutrons: Neutral charge
      • Protons: Determine atomic number
    • Electrons: Found in rings around the nucleus
    • Definitions:
    • Ionization: Removal of an electron from an atom, creating an ion pair.
      • Results in a negatively charged electron and a positively charged residual atom.
    • Consequences of Ionization:
      • Can lead to cell injury or death.
      • Alters cell reproduction, division, and may cause mutations, leading to outcomes such as cancer.

Types of Ionizing Radiation

Overview of Radiation Types

  • Focus on:
    • Alpha Radiation
    • Beta Radiation
    • Positron Radiation
    • Neutron Radiation
    • X-Rays
    • Gamma Rays

Alpha Radiation

  • Nature: Consists of helium nuclei (2 protons and 2 neutrons).
    • Charge: +2
    • Mass: Heavy compared to other forms.
    • Energy: 4 to 8 mega electron volts (MeV).
    • Range: Limited range (cannot travel more than 60 microns in tissue). Shielding is easy (e.g., skin).
  • Sources: Common isotopes include uranium and radium.
  • Linear Energy Transfer (LET): High, with a quality factor of 20.

Beta Radiation

  • Nature: High-speed electrons emitted from the nucleus, can be positively or negatively charged.
    • Mass: Much lighter than alpha particles.
    • Energy: 0.1 kiloelectron volts (keV) to 5 MeV.
    • Range: Can travel in air for several feet; limited range in tissue (few millimeters).
    • Quality Factor: 1.
  • Sources: Common isotopes include tritium, carbon-14, strontium-90, and phosphorus-32.
  • Hazards: Can cause damage through ingestion or inhalation, easily shielded by materials such as glasses.

Gamma and X-Rays

  • Nature: Consist of photons ejected from the nucleus with no charge.
    • Energy Level: Typically in the range suitable for ionization.
    • Range: Unlimited, similar to the speed of light.
    • Quality Factor: 1, low compared to particle radiation.
  • Shielding Needs: Requires materials such as concrete or lead.
  • Common Emitters: Potassium-40, iodine-131, cobalt-60.

Neutron Radiation

  • Nature: Free neutrons emitted from the nucleus usually as a byproduct of nuclear fission.
    • Stability: Man-made and unstable; decay occurs through beta emission.
    • Quality Factors: Varies based on speed—slow (thermal), intermediate, and fast.
  • Neutron Activation: Ability to initiate radioactivity in other substances, including human tissue.

Electromagnetic Spectrum and Ionizing Radiation

  • Positioning in Spectrum: Ionizing radiation appears on the right side of the electromagnetic spectrum, characterized by higher frequency, shorter wavelength, and high energy.
  • Types and Effects: The energy from ionizing radiation can produce ionization in materials.
    • Decay Rates: Different isotopes have distinct half-lives affecting control strategies and decay rates.

Control of Ionizing Radiation

Risk Assessment and Application

  • Key factors in assessing risk: source, intensity, and duration of exposure.
  • Exposure Types: Chronic exposure versus acute effects.
    • Chronic exposure (long-term) linked to cancer and organ failure.
    • Acute effects, such as gastrointestinal issues from exposure to high doses.

Measurement Units

  • Units of Exposure:
    • Roentgen (R): Measures ionization in air due to x-rays and gamma rays.
    • Radiation Absorbed Dose (rad): Measures energy absorbed per mass of matter (measured in Joules/kg).
    • Dose Equivalent (rem): Adjusted based on quality factor; helps assess biological effects.
  • Relationships:
    • extDoseEquivalent(rem)=extDose(rad)imesextQualityFactorext{Dose Equivalent} (rem) = ext{Dose} (rad) imes ext{Quality Factor}

Biological Effects of Radiation

  • Acute Effects:
    • Severe tissue damage, particularly to rapidly dividing cells.
    • Key organs impacted include the gastrointestinal system.
  • Delayed Effects:
    • Increased cancer risk, cataracts, and reproductive effects.
  • Dose Benchmarks:
    • 25 rads: No observable effects.
    • 50-300 rads: Severe health issues may be observed.
    • Lethal dose (LD50): Approximately 600 rads.