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.

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.

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

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.

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.

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.

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.

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

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

General pattern: ^{A}{Z}X \rightarrow ^{A}{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).

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

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.

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

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.