Nuclear Radiation and Radioisotopes (Quick Reference)

Fundamental forces

• Four fundamental forces: gravity, electromagnetic, strong nuclear, weak nuclear.
• Gravity: keeps us on Earth.
• Electromagnetic: example = magnets sticking to fridge door.
• Strong interaction: binds protons in the nucleus; too many protons can make a nucleus unstable.
• Weak interaction: involved in certain decay processes.

Atomic structure, isotopes, and radioactivity

• Nucleus is dense; protons repel via Coulomb force, but the strong force holds them together.
• If a nucleus is unstable, it emits energy (radiation) to become more stable.
• Isotopes: same element (same Z) but different neutron number (A differs).
• Natural isotopes example: Carbon-12, Carbon-13, Carbon-14; among them, some are radioactive (radioisotopes).
• Radioisotopes in medicine: Iodine-131 used to diagnose and treat thyroid conditions; thyroid concentrates iodine; imaging and therapy work via gamma emissions and targeted uptake.

Types of radiation and their properties

• Alpha particle: $^4_2\mathrm{He}$ (two protons, two neutrons; mass 4; charge +2).
  • Range: in air ~2–4 cm; in tissue ~1 cm.
  • Shielding: easy (paper, regular clothes).
  • Internal danger: highly damaging locally if ingested or inhaled.
• Beta particle: electron $e^-$ (mass ~0; charge -1).
  • Range: in air ~200–300 cm; in tissue a few mm.
  • Shielding: heavier protection (thick clothing, gloves, goggles).
• Positron: $e^+$ (mass ~0; charge +1).
  • Similar range to beta; used in PET imaging.
• Gamma radiation: $\gamma$ (mass 0; charge 0).
  • Highly penetrating; requires dense shielding (lead, concrete).
  • No mass change; energy emitted as photons.

Nuclear decays and how they change the nucleus

• Alpha decay: $^{A}<em>{Z}X \rightarrow {}^{A-4}</em>{Z-2}Y + {}^{4}_{2}\mathrm{He}$
  • Atomic number decreases by 2; mass number decreases by 4.
• Beta decay (β−): $^{A}<em>{Z}X \rightarrow {}^{A}</em>{Z+1}Y + e^-$
• Positron emission (β+): $^{A}<em>{Z}X \rightarrow {}^{A}</em>{Z-1}Y + e^+$
• Gamma emission: $^{A}<em>{Z}X \rightarrow {}^{A}</em>{Z}X + \gamma$
  • Z and A unchanged; energy emitted as gamma ray.
• Example balancing: For $^{251}<em>{98}\mathrm{Cf}$ undergoing alpha decay: $^{251}</em>{98}\mathrm{Cf} \rightarrow {}^{247}<em>{96}\mathrm{Cm} + {}^{4}</em>{2}\mathrm{He}$; check that total Z and total A are conserved.

Isotopes, radioisotopes, and medical use

• Isotopes have same Z, different N (e.g., Carbon-12, -13, -14).
• Radioisotopes in medicine: Iodine-131 used for thyroid imaging and therapy; thyroid uptake concentrates iodine, enabling imaging and targeted cell killing.
• Radioisotopes are useful when properly controlled and shielded.

How far radiation travels and how to shield it (energy and safety)

• Alpha: least energy among common types; safe to block with a sheet of paper; dangerous if ingested.
• Beta: more penetrating; requires thicker shielding (clothing, gloves, goggles).
• Gamma: most penetrating; needs dense shielding (lead, concrete); even slow gamma can pass through body.
• Distance and shielding summarize protection needs:
  • Alpha: paper/clothes enough.
  • Beta: thick clothing, gloves, goggles.
  • Gamma: lead or concrete shielding.

Measuring radiation and safety equipment

• Measurement device: Geiger counter – counts individual disintegration events.
• Background radiation: always present; routine checks ensure contamination is detected.
• Safety dosimetry: badges and rings worn to monitor exposure; regular calibration by a safety office.
• Units of radioactivity and dose:
  • Becquerel (Bq): $1\ \mathrm{Bq} = 1\ \text{disintegration s}^{-1}$
  • Curie (Ci): $1\ \mathrm{Ci} = 3.7 \times 10^{10}\ \mathrm{disintegrations\, s^{-1}}$
  • Rad (rad) and Gray (Gy): $1\ \mathrm{Gy} = 100\ \mathrm{rad}$; $1\ \mathrm{rad} = 0.01\ \mathrm{Gy}$
  • Rem (rem) and Sievert (Sv): $1\ \mathrm{Sv} = 100\ \mathrm{rem}$; $1\ \mathrm{rem} = 0.01\ \mathrm{Sv}$
• Typical annual exposure in the US:
  • Background ~ 0.2 mSv; from air, water, and food ~ 0.3 mSv (banana example shows potassium-40 intake).
• Lethal dose measure: RD50 ~ 5 Sv for humans (50% mortality in population at this dose).
• Practical note: high-altitude travel increases cosmic radiation exposure; everyday devices (iPad, cell phone) contribute negligible exposure by comparison.
• Dose monitoring in practice: badges and rings track exposure; alerts trigger work stoppage when limits are reached.

Origins of elements and how new elements are made

• Elements originate from cosmic processes:
  • Big Bang produced mainly hydrogen, helium, and lithium; these light elements accounted for ~99% of atoms initially.
  • Stars fuse light elements into heavier ones up to iron-56 (Fe, Z=26, A=56).
  • Heavier elements are produced in supernova explosions via extreme temperatures and pressures.
• Human-made elements: beyond about element 108 (historical), created by bombarding nuclei in labs; these have very short lifetimes and decay rapidly into lighter elements.

Quick practical recall prompts

• Identify the four fundamental forces and give one everyday example for two of them.
• For each radiation type (α, β, γ, β+), state: particle involved, mass/charge, typical range, and shielding.
• State how Z and A change in α, β−, β+, and γ emissions.
• Interpret a simple nuclear reaction balance: ensure total Z and total A are conserved.
• Distinguish units: Bq, Ci, Gy, rad, Sv, rem.
• Explain why bananas are slightly radioactive and what potassium-40 contributes to daily exposure.
• Explain why heavy elements beyond iron are produced in supernovae, not in ordinary stars.