Comprehensive Study Notes: Nuclear Chemistry & Radiation

Nuclear Chemistry in Medical Context

• Nuclear chemistry underpins diagnostic & therapeutic techniques in hospitals and imaging centers (e.g.
  • PET, SPECT, radiotherapy, tracer studies).
• Specialists who handle these materials are called radiation (or nuclear medicine) technologists.

Natural Radioactivity

• Definition: Spontaneous emission of radiation from an unstable nucleus to achieve greater stability.
• Elemental stability trends
  • For atomic numbers $\le 19$: most isotopes are stable.
  • For $Z \ge 20$: one or more isotopes usually exhibit instability because nuclear forces cannot fully counteract proton–proton repulsion.
• Key term – Radioisotope
  • Any isotope with an unstable nucleus.
  • Notation always includes the mass number: ex. Carbon-14 $(^{14}_{6}\text C)$ used in archaeological dating.

Stable vs. Radioactive Isotopes (Representative Table)

• Magnesium: stable $^{24}<em>{12}\text{Mg}$; radioisotopes $^{23}</em>{12}\text{Mg}, ^{27}_{12}\text{Mg}$.
• Iodine: stable $^{127}<em>{53}\text{I}$; radioisotopes $^{125}</em>{53}\text{I}, ^{131}_{53}\text{I}$.
• Uranium: no stable isotopes; common radioisotopes $^{235}<em>{92}\text U, ^{238}</em>{92}\text U$.

Types of Radiation Emitted

• Alpha (α) Particle
  • Symbol: $^{4}_{2}\text{He}$ (identical to a helium nucleus).
  • Composition: 2 protons + 2 neutrons.
  • Mass number: 4; charge: $2^+$.
  • Relatively low penetration energy.
• Beta (β) Particle
  • Symbol: $^{0}_{-1}e$.
  • High-energy electron produced when a neutron → proton + electron.
  • Mass number: 0; charge: $1^-$.
• Positron (β⁺)
  • Symbol: $^{0}_{+1}e$.
  • Antimatter counterpart of the electron; created when a proton → neutron + positron.
  • Mass number: 0; charge: $1^+$.
• Gamma (γ) Ray
  • Symbol: $^{0}_{0}\gamma$.
  • Pure high-energy electromagnetic radiation.
  • Mass number & charge: 0.
  • Usually accompanies α, β, or β⁺ emissions as the nucleus relaxes from an excited (metastable, “m”) state to a lower-energy state.
• Auxiliary Particles
  • Proton: $^{1}_{1}\text H$, charge $1^+$.
  • Neutron: $^{1}_{0}n$, charge 0.

Consolidated Properties (Table-style)

• Mass numbers & charges (from Table 5.2)
  • α: $A=4,\; q=+2$
  • β: $A=0,\; q=-1$
  • β⁺: $A=0,\; q=+1$
  • γ: $A=0,\; q=0$
  • p⁺: $A=1,\; q=+1$
  • n⁰: $A=1,\; q=0$

Sample Exercise 1 – Recall of Data

• Required: Give both mass number & charge for each particle.
  • α → 4, $2^+$
  • β⁺ → 0, $1^+$
  • β → 0, $1^-$
  • n → 1, 0
  • γ → 0, 0

Biological Effects of Radiation

• Ionizing radiation interacts with biological molecules, creating ions/radicals → cellular damage.
  • Greatest sensitivity: rapidly dividing tissues (bone marrow, skin, reproductive organs) & cancer cells.
  • Therapeutic application: high doses intentionally destroy malignant tissue with comparatively smaller collateral damage to slower-dividing normal tissue.
• Potential health consequences
  • Malignant tumors, leukemia, anemia, heritable genetic mutation.

Radiation Protection Principles

• Shielding materials
  • α: stopped by paper or ordinary clothing.
  • β: require heavy clothing, lab coats, gloves.
  • γ: need dense shielding, e.g. lead or thick concrete.
• Additional safety doctrines: Minimize exposure time & maximize distance.
• Penetration data (Table 5.3)
  • Travel in air: α (2–4 cm) < β (200–300 cm) < γ (≈500 m).
  • Tissue depth: α (0.05 mm), β (4–5 mm), γ (≥50 cm).
  • Typical emitters: α (Ra-226), β (C-14), γ (Tc-99m).
• Sample Exercise 2 – Shielding Identification
  • Heavy clothing → α & β.
  • Paper → α.
  • Lead → α, β, γ.
  • Lab coat → α & β.
  • Thick concrete → α, β, γ.

Nuclear Reactions & Equations

• Radioactive decay: spontaneous breakdown of unstable nucleus with emission of radiation.
• Balancing rules (conservation laws):
  • Sum of mass numbers $\Sigma A$ equal on both sides.
  • Sum of atomic numbers $\Sigma Z$ equal on both sides.

Alpha Decay Mechanics

• General pattern: $^{A}<em>{Z}X \rightarrow ^{A-4}</em>{Z-2}Y + ^{4}_{2}He$.
  • $A$ decreases by 4, $Z$ decreases by 2.
• Worked example – Americium-241 in smoke detectors
  1. Incomplete: $^{241}<em>{95}\text{Am} \rightarrow ^{?}</em>{?}Y + ^{4}_{2}He$.
  2. Mass # of Y: $241-4=237$.
  3. Atomic # of Y: $95-2=93$ ⇒ element = Neptunium (Np).
  4. Balanced: $^{241}<em>{95}\text{Am} \rightarrow ^{237}</em>{93}\text{Np} + ^{4}_{2}He$.

Beta (β⁻) Decay Mechanics

• General pattern: $^{A}<em>{Z}X \rightarrow ^{A}</em>{Z+1}Y + ^{0}_{-1}e$.
  • Mass unchanged; atomic # increases by 1.
• Example – Yttrium-90 (arthritis / cancer treatment)
  • $^{90}<em>{39}\text{Y} \rightarrow ^{90}</em>{40}\text{Zr} + ^{0}_{-1}e$.
• Sample Exercise 3 – Cobalt-60 (radiotherapy)
  • $^{60}<em>{27}\text{Co} \rightarrow ^{60}</em>{28}\text{Ni} + ^{0}_{-1}e$.

Positron (β⁺) Emission Mechanics

• General pattern: $^{A}<em>{Z}X \rightarrow ^{A}</em>{Z-1}Y + ^{0}_{+1}e$.
  • Mass unchanged; atomic # decreases by 1.
  • Converts a proton to neutron, important in PET imaging radioisotopes (e.g. $^{18}\text F$).

Gamma Emission Mechanics

• Denoted by $\gamma$ or “m” (metastable) following mass #.
• Pattern: $^{A}<em>{Z}X^{m} \rightarrow ^{A}</em>{Z}X + ^{0}_{0}\gamma$.
  • Only energy released; $A$ & $Z$ unchanged.

Summary of Radiation Types & Nuclear Stability

• α, β⁻, β⁺, γ emissions all yield daughter nuclei closer to the band of stability.
• Multiple decay modes may proceed sequentially until a stable configuration is reached.

Production of Artificial Radioisotopes (Particle Bombardment)

• Stable targets are struck by high-speed particles (α, p⁺, n⁰) in accelerators or reactors.
• Example: $^{10}<em>{5}\text B + ^{4}</em>{2}He \rightarrow ^{13}<em>{7}\text N + ^{1}</em>{0}n$ producing $^{13}\text N$ (PET tracer).
• Sample Exercise 4 – Ni-58 Bombardment
  1. Start: $^{58}<em>{28}\text{Ni} + ^{1}</em>{1}p \rightarrow ^{?}<em>{?}\text{Co} + ^{4}</em>{2}He$.
  2. Mass conservation: $58+1 = ? +4 \Rightarrow ?=55$.
  3. Charge conservation: $28+1 = ? +2 \Rightarrow ?=27$ (Co).
  4. Balanced: $^{58}<em>{28}\text{Ni} + ^{1}</em>{1}p \rightarrow ^{55}<em>{27}\text{Co} + ^{4}</em>{2}He$ (radioactive cobalt-55 formed).

Practical & Ethical Considerations

• Medical benefit: diagnostic accuracy, targeted cancer therapy.
• Safety duty: adhere to ALARA (As Low As Reasonably Achievable) for patient & staff exposure.
• Environmental stewardship: proper handling & disposal of radioactive waste to prevent contamination and genetic impact on future generations.