X-Ray Physics & Radiation Safety – Vocabulary Review

X-Ray Machine Components

• Control panel : on/off, indicator light, exposure switch, adjusts kVp, mA, and time
• Extension arm : suspends/positions tube head; houses high-voltage wires
• Metal housing : lead-lined case around tube; shields & grounds stray radiation
• Insulating oil : absorbs heat produced in tube
• Tube-head seal : aluminum or leaded glass window permitting x-ray exit; filters weak photons
• Aluminum filtration disks : remove low-energy photons; required total filtration ≥1.5\,\text{mm} (<70\,kVp) or ≥2.5\,\text{mm} (≥70\,kVp)
• Lead collimator : restricts beam size; rectangular opening = greatest dose reduction
• PID (cone) : lead-lined cylinder that directs the primary beam toward receptor

Basic Atomic Structure

• Matter : anything with mass & space
• Fundamental unit : atom → nucleus (protons +1, neutrons 0) + orbiting electrons -1
• Atomic number (Z) : # protons
• Mass number : protons + neutrons
• Electron shells : K,L,M,N,O,P,Q (max 7); K has strongest binding energy, Q the weakest
• Binding energy keeps electrons in orbit
• Molecule : 2 + atoms joined by chemical bonds
• Neutral atom : equal protons = electrons
• Ion pair : positive ion (atom minus e⁻) + free negative e⁻

Radiation Fundamentals

• Radiation : energy transmission as waves/particles
• Ionizing radiation types : particulate (e⁻, α, β, protons), electromagnetic (x,  rays)
• Key wave terms • Velocity = 3\times10^{8}\,m/s (in vacuum) • Wavelength = crest-to-crest distance • Frequency = waves/sec
• Primary radiation : useful beam from anode target
• Secondary (scatter) : arises after primary interacts with matter; e.g. Compton scatter

CATNAP Quick-Recall

• CATNAP = Cathode (negative) → Anode (positive)
• Cathode (inside tube head): filament + focusing cup (−)
• Anode : tungsten target embedded in copper stem (+)
• Electron flow : cathode → anode → patient

Electrical Parameters

• Voltage : potential difference driving e⁻ from cathode to anode; measured in V (kVp clinically)
• Amperage : e⁻ quantity per second; measured in A (mA clinically)
• Thermionic emission : release of e⁻ from heated cathode filament

X-Ray Interactions

• Compton scatter : photon hits outer e⁻ → ejects e⁻ (ionization) + lower-energy scattered photon

Biological Effects of Radiation

• Stochastic (no threshold; probability↑ with dose): cancer, genetic mutations
• Non-stochastic (threshold; severity↑ with dose): erythema, cataract, hair loss
• Determining factors (dose-response)
  • Total dose ↑ → damage↑
  • Dose rate ↑ → damage↑
  • Tissue amount exposed ↑ → damage↑
  • Cell sensitivity ↑ (mitotic/immature) → damage↑
  • Age ↓ (younger) → damage↑
• Latent period : exposure → first detectable effect
• Period of injury : cellular dysfunction/death
• Recovery : cellular repair; may be incomplete
• Somatic mutation : body cells; not heritable (e.g. skin cancer)
• Genetic mutation : reproductive cells; heritable (e.g. congenital malformations)

Radio-Sensitivity

• Most resistant : muscle, nerve, mature bone & cartilage
• Least resistant : lymphocytes, bone-marrow stem cells, reproductive germ cells
• Four critical organs (dentistry) : skin, thyroid, lens of eye, bone marrow

Units & Protection

• Roentgen (R) : exposure unit measuring ionization in air (2.58 × 10⁻⁴ C/kg)
• RAD (Radiation Absorbed Dose) : energy absorbed (1 rad = 0.01 Gy)
• Collimator : lead; rectangular shape = max exposure reduction