Chapter Six: X-Rays

6.1 Discovery of X-rays

• Discovered in late 1895 by German physicist W.C. Roentgen.
• Utilized a cathode ray tube similar to fluorescent light bulbs.
• Observed a green fluorescent light through a heavy paper cover indicating a new "invisible light" or ray.
• Named it X-ray, representing an unknown quantity in mathematics.
• X-rays shown to pass through human tissue, leaving bones and metals visible.
• First practical application in early 1896, used in the US for medical imaging like bone fractures.

6.2 Production of X-rays

• X-ray tube is a vacuum tube designed to produce X-ray photons.
• Invented by Sir William Crookes (Crookes tube).
• Uses high voltage (30 to 150 kV) causing ionization of residual air and electron beams from cathode to anode.
• Produces X-rays when electrons hit the target due to the Bremsstrahlung effect.
• Radiation energy consists of a line and continuous spectrum.

6.3 Properties of X-rays

• Travel in straight lines.
• Not deflected by electric or magnetic fields.
• High penetrating power.
• Blacken photographic film.
• Cause fluorescent materials to glow.
• Can produce photoelectric emission.
• Ionize gases they pass through.

6.4 Continuous Spectrum

• Generated when electrons accelerate towards the target and lose kinetic energy through collisions.
• Produces a continuous spectrum with a sharp cut-off wavelength.
• Minimum wavelength depends on the accelerating voltage.

6.5 Characteristic X-Ray Spectrum

• High voltage allows electrons to eject core electrons of the target.
• Filling of vacant states in K-, L-, or M-shells emits X-rays.
• Characteristic sharp lines due to specific energy levels of electrons.

6.6 X-Ray Diffraction

• X-ray reflection from atomic planes (Bragg's law).
• Constructive interference produces diffractogram patterns.

6.7 Moseley's Experiment

• Investigated X-ray spectra of elements from aluminum to gold.
• Found series of high intensity peaks specific to each element.
• Correlated peaks with atomic number of elements, forming the basis for modern periodic table arrangement.
• Used Bohr model to explain characteristic radiation origin.
• Moseley’s work led to corrections in periodic table and prediction of undiscovered elements.

Example: Characteristic X-ray Spectrum of Copper

• Calculation of frequency and minimum potential for Kα lines.
• Uses atomic number (Z=29) and formulas for frequency in K and L series.