Radioactivity and Nuclear Chemistry Notes

Radioactivity

  • Radioactivity is the emission of subatomic particles or high-energy electromagnetic radiation by the nuclei of certain atoms.
  • Radioactive atoms undergo a process called radioactive decay.

Types of Radioactivity

  • Alpha ($\alpha$) decay
  • Beta ($\beta$) decay
  • Gamma ($\gamma$) ray emission
  • Positron emission
  • Electron capture

Isotopes and Nuclides

  • A nuclide refers to a particular isotope of an element when discussing nuclear properties.

Alpha ($\alpha$) Decay

  • Alpha decay occurs when an unstable nucleus emits an alpha particle (composed of two protons and two neutrons).
  • Example:
    • Parent nuclide → Daughter nuclide + α particle
    • ^{224}{88}Ra \rightarrow \space ^{220}{86}Rn + ^4_2He

Nuclear Equations

  • Represent emission of particles.
  • Sum of atomic numbers and mass numbers must be equal on both sides.

Ionizing and Penetrating Power

  • Ionizing power: Ability of radiation to ionize other molecules and atoms.
  • Penetrating power: Ability of radiation to penetrate matter.

Beta ($\beta$) Decay

  • Beta decay occurs when an unstable nucleus emits an electron.
  • A neutron is converted into a proton and an electron.
  • Example:
    • Parent nuclide → Daughter nuclide + β particle

Gamma ($\gamma$) Ray Emission

  • Gamma rays are high-energy photons.
  • Gamma ray emission occurs in conjunction with other types of radiation.
  • Excited nuclide → Stable nuclide + Photon

Positron Emission

  • Positron emission occurs when an unstable nucleus emits a positron (the antiparticle of an electron).
  • A proton is converted into a neutron.
  • Parent nuclide → Daughter nuclide + Positron

Electron Capture

  • Electron capture occurs when a nucleus assimilates an electron from an inner orbital.
  • A proton is converted into a neutron.
  • Parent nuclide + Electron → Daughter nuclide

Predicting Type of Radioactivity

  • Nucleon: proton or neutron.
  • Stability depends on balance between attractive strong forces and repulsive electrostatic forces.

Valley of Stability

  • High N/Z ratio: Beta decay (too many neutrons converted to protons).
  • Low N/Z ratio: Positron emission or electron capture (too many protons converted to neutrons).

Magic Numbers

  • Nuclei with certain numbers of nucleons (2, 8, 20, 28, 50, 82, N=126) are uniquely stable.

Radioactive Decay Series

  • Atoms with Z > 83 are radioactive and decay in one or more steps.
  • Primarily involves alpha and beta decay.

Detecting Radioactivity

  • Film Badge Dosimeter
  • Geiger-Muller Counter
  • Scintillation Counter

Kinetics of Radioactive Decay

  • Radioactive decay follows first-order kinetics.
  • Nuclides decay exponentially with time.

Integrated Rate Law

  • ln(\frac{Nt}{N0}) = -kt

Half-Life

  • t_{1/2} = \frac{ln(2)}{k}

Radiocarbon Dating

  • Uses the decay of Carbon-14 to estimate the age of organic materials.

Uranium/Lead Dating

  • Uses the decay of Uranium-238 to Lead-206 to estimate the age of rocks.

Nuclear Fission

  • Nuclear fission is the splitting of a heavy nucleus into lighter nuclei.

Nuclear Power

  • Chain Reaction
  • Control rods
  • Fuel rods

Converting Mass to Energy

  • Products of nuclear reaction have less mass than reactants.

Mass Defect and Nuclear Binding Energy

  • Mass defect: Difference in mass between a nucleus and its separate components.
  • Nuclear binding energy: Energy corresponding to the mass defect.

Nuclear Binding Energy per Nucleon

  • E = mc^2

Nuclear Fusion

  • Nuclear fusion is the combination of two light nuclei to form a heavier one.

Nuclear Transmutation

  • Nuclear reactions result in transformation of one element into another.

Measuring Radiation Exposure

  • Curie (Ci): unit measuring number of decay events (3.7 × 10^10 decay events per second).
  • Gray (Gy): unit describing energy absorbed by body tissue (1 J of energy per kg of tissue).
  • Rad: corresponds to 0.01 Gy.
  • Rem: dose in rads multiplied by biological effectiveness factor (RBE).

Applications of Radioactivity

  • Diagnostic and therapeutic techniques in medicine.
  • Irradiation of food.

Diagnosis in Medicine

  • Radiotracer: Radioactive nuclide attached to a compound to track movement.

Radiotherapy in Medicine