How X-rays are Produced: Charged particles are rapidly decelerated, transforming kinetic energy into high-frequency electromagnetic radiation (X-rays).
X-rays vs Gamma Rays: Overlapping frequency spectra; differ in origin (X-rays from Bremsstrahlung, gamma from decay or particle collisions).
Soft X-rays: Used in medical imaging, generally lower energy than gamma rays.
X-ray Tubes
Function: Accelerate electrons in high-voltage field, decelerate with metal anode collisions (e.g., tungsten).
Thermionic Emission: Electrons emitted from a heated source.
Preventing Overheating: Rotating anode or cooling systems.
Collimation: Straighten beams for precise targeting, minimize exposure.
X-ray Spectra
Braking Radiation: Produces broad wavelengths with characteristic sharp lines.
Cause: Incident electrons knock out low-energy level electrons in anode atoms.
Ionising Radiation
Effects: Can ionize DNA, causing damage/mutations.
Radiotherapy: Destroys cancer cells while minimizing healthy tissue damage.
X-ray Attenuation Mechanisms
Attenuation: Gradual decrease in X-ray beam energy/intensity through matter.
Materials: Different materials attenuate differently (e.g., bone vs soft tissue).
Absorption Mechanisms
Simple Scattering: Low-energy X-rays reflect off atoms/molecules.
Photoelectric Effect: X-rays absorbed by electrons, resulting in photoelectron emission.
Compton Effect: X-rays lose energy through inelastic interactions with electrons.
Pair Production: High-energy X-rays create electron-positron pairs in atom fields.
X-ray Imaging
Contrast Media: High attenuation materials (e.g., barium, iodine) for imaging soft tissues.
Applications: Blood flow, digestive system imaging through use of contrast media.
Computerised Axial Tomography (CAT)
3D Imaging: Uses multiple 2D X-ray images to construct 3D images.
Benefits: Better resolution, distinguishes between overlapping tissues.
Drawbacks: Longer exposure time, higher radiation dose.
Medical Tracers
Use in Medicine: Radioactive isotopes form compounds for specific body locations.
Gamma Emitters: Preferred due to low ionizing nature.
Examples: Fluorine-18 for PET scans, Technetium-99m for organ monitoring.
Gamma Cameras
Function: Detect gamma photons from tracers in body.
Collimation: Only detect photons in specific direction.
Process: Photons interact with scintillation crystal, producing visible photons detected and amplified.
Positron Emission Tomography (PET)
3D Imaging: Uses gamma cameras to construct accurate 3D images from photon emissions.
Tracer Example: Fluorodeoxyglucose locates areas with high respiration rates.