Atomic Structure and Electromagnetic Radiation

Atomic Structure and Electromagnetic Radiation

RADIATION SCIENCE

CHAPTER 1

• atomic structure
• quantities and units of electromagnetic radiations
• x-ray and gamma rays
• primary and secondary radiations

✓Atomic Structure

• Atom definition: The smallest unit of matter that retains
• the chemical properties of an element.
• or
• An atom is the smallest particle that has all the properties
• of an element.
• Components
• The fundamental particles of an atom are the electron,
• the proton, and the neutron.
• o Nucleus: contains protons (positive charge) and
• neutrons (neutral, contribute to mass).
• o Electrons: Negatively charged particles orbiting the
• nucleus in shells/energy levels.
• The arrangement of electrons around the nucleus
• determines the manner in which atoms interact.Key properties
• o Atomic number (Z): Number of protons; determines
• element identity.
• o Mass number (A): Protons + neutrons.
• o Isotopes: Atoms with the same atomic number (Z) but
• different mass numbers (A) due to varying neutrons.
• o Electron binding energy: Energy required to remove
• an electron from its shell; higher closer to the
• nucleus.
• In their normal state, atoms are electrically neutral; the
• electric charge on the atom is zero.
• This is because the total number of electrons in the
• orbital shells is exactly equal to the number of protons in
• the nucleus. ✓Electromagnetic Radiation (EMR)
• Definition
• Electromagnetic radiation is energy transmitted through
• space or a medium in the form of oscillating electric and
• magnetic fields that are perpendicular to each other and
• to the direction of wave travel.
• It does not require a medium (can travel through

vacuum).

Travels at the speed of light (c = 3 × 10⁸ m/s in vacuum).2. Nature of Electromagnetic Radiation Dual nature (wave–particle duality):

• This principle states that electromagnetic radiation
• exhibit characteristics of both waves and particles.
• Wave-like behavior: Described by wavelength (λ),
• frequency (ν), velocity (c).
• Particle-like behavior: Exists as discrete packets of
• energy called photons (quanta).
• Properties of Electromagnetic Waves
• Transverse waves: Electric and magnetic fields oscillate
• at right angles to each other and to direction of
• propagation.
• Wavelength (λ): Distance between successive wave

peaks (meters).

• Frequency (ν): Number of cycles per second (Hertz, Hz).❖Velocity (c): Constant in vacuum, 3 × 10⁸ m/s.
• Photon energy (E):
• A photon is the smallest discrete packet (quantum) of
• electromagnetic radiation.
• Photon energy refers to the amount of energy carried by
• a single photon of electromagnetic radiation.
• It explains why higher-frequency radiation (like X-rays,
• gamma rays) is more penetrating and biologically
• hazardous than lower-frequency radiation (like radio
• waves).
• Electromagnetic Spectrum
• Electromagnetic radiation exists in a broad spectrum of
• wavelengths and frequencies:5. Characteristics Relevant to Radiation Science
• Ionizing radiation: High-energy EMR (X-rays, gamma rays,
• part of UV) can eject electrons from atoms → ionization.
• Non-ionizing radiation: Low-energy EMR (radio,
• microwave, IR, visible light) excites atoms but does not
• ionize.
• Penetration power: Depends on energy; gamma rays
• penetrate more deeply than X-rays.
• Interaction with matter: Absorption, scattering,
• transmission—important in imaging and radiation
• protection.6. Quantities and Units of Electromagnetic Radiations
• Electromagnetic radiation is quantified by its
• wavelength, frequency, velocity, and photon energy.
• In radiation science, additional quantities like
• exposure, absorbed dose, and equivalent/effective dose
• are used to measure its interaction with matter and
• biological effect.
• Since EMR (X-rays, gamma rays) is ionizing,
• additional radiation-specific quantities are defined:
• (a) Exposure
• o Measures ionizations (charges) produced in air by
• radiation.
• o Unit: Coulomb per kilogram (C/kg)
• (b) Air Kerma
• o Measures the energy of ionizations in the air.
• o Kerma is an acronym for Kinetic Energy Released per
• unit Mass
• o Unit: Gray (Gy)
• o 1 Gy = 1 joule/kg(c) Absorbed Dose
• o Energy absorbed per unit mass of material.
• o Unit: Gray (Gy)
• o 1 Gy = 1 joule/kg
• (d) Equivalent Dose
• o Absorbed dose that takes into account the impact of
• radiation type (quality factor).
• o Different radiations have different biological effects
• on tissue.
• o Unit: Sievert (Sv)
• (e) Effective Dose
• o Absorbed dose that takes into account tissue
• sensitivity (tissue weighting factor).
• o Unit: Sievert (Sv)
• Summary of Key Units
• Quantity Symbol Unit (SI) Common Use
• Wavelength λ meter (m) Wave property
• Frequency ν Hertz (Hz) Wave property
• Velocity c m/s Wave property
• Photon Energy E J, eV Photon property
• Exposure X C/kg Ionization in air
• Absorbed Dose D Gray (Gy) Energy absorbed
• Equivalent/Effective Dose H, E Sievert (Sv) Biological effect
• Primary and Secondary Radiations
• (a) Primary radiation:
• o The useful radiation beam emitted directly from the Xray tube or radioactive source.
• o Responsible for image formation in diagnostic
• radiology.
• (b) Secondary radiation:
• Radiation produced when primary radiation interacts
• with matter (e.g., patient’s body, equipment, walls).
• Types include:
• Scatter radiation: Deflected X-ray photons (major
• source of occupational exposure).• Characteristic radiation: Emitted when inner
• shell electrons are ejected and outer electrons
• fill vacancies.
• Secondary radiation reduces image quality and
• increases unwanted exposure; shielding and protective

measures are essential.