Lecture Notes: Uranium Isotopes and Mass Spectrometry

Uranium Isotopes

• Uranium-235
• Uranium-238
  • Separation of isotopes based on mass differences
  • Uranium-238 has more neutrons, thus greater mass than Uranium-235

Mass Spectrometer Overview

• Used to separate isotopes due to different masses
• Historical use in WWII for uranium isotope separation

Steps in Mass Spectrometry

1. Ionization

• Electron is knocked off each isotope
• Formation of positive ions

2. Acceleration

• Ions accelerated over a potential difference (deltaV)
• Physics involved: work done = charge (q) × potential difference (deltaV)
• Kinetic energy of ion = 1/2 mv²
• Calculation of ion velocity:
  • v = √(2qV/m), where V = potential difference

Magnetic Field Interaction

• Ions enter a region with a uniform magnetic field (B) pointing out of the page
• Magnetic field representation: like viewing the tip of an arrow
• Magnetic force on ions: q(v x B)
  • Right-hand rule used to determine the direction of force
  • Force causes ions to move in a circular path

Circular Motion of Ions

• Magnetic force acts as centripetal force
• Radius of ion's path: r = mv/qB
• Relationship between mass and radius:
  • As mass increases, radius increases (m/q ratio)

Example: Uranium Isotopes in a Mass Spectrometer

• U-235 ion travels in a path with smaller radius
• U-238 ion travels in a path with a larger radius

Detection Stage

• Final part of the mass spectrometer process
• Separates ions based on mass using detected radii
• Modern spectrometers:
  • Do not typically separate isotopes
  • Used for obtaining very accurate mass measurements

Conclusion

• Mass spectrometry introduces fundamental concepts of measuring mass differences and separation techniques
• Modern applications focus on precise mass measurements

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Note: Additional content on modern mass spectrometers and their applications can be discussed in further lectures or videos.