Nuclear & Quantum Physics

Nuclear and quantum physics explores the behaviour of matter at the smallest scales — from the structure of the atom and radioactive decay to the wave-particle duality that challenges classical intuition. This section covers radioactivity, nuclear energy, quantum phenomena, and particle physics.

Topics Covered

Radioactivity

• Atomic structure — the nucleus (protons, neutrons), electron shells; nuclide notation ${}_Z^A X$
• Isotopes — same atomic number, different mass number; stability and the N/Z ratio
• Radiation types — alpha ($\alpha$: helium nucleus, highly ionising, stopped by paper), beta ($\beta^-$: electron, moderate ionisation, stopped by aluminium), gamma ($\gamma$: electromagnetic photon, weakly ionising, reduced by lead)
• Decay equations — $\alpha$ decay: ${}_Z^A X \to {}_{Z-2}^{A-4} Y + {}_2^4 \alpha$; $\beta^-$ decay: ${}_Z^A X \to {}_{Z+1}^{A} Y + {}_{-1}^0 \beta + \bar{\nu}_e$
• Half-life — $N = N_0 \left(\frac{1}{2}\right)^{t/t_{1/2}}$; activity $A = \lambda N$; decay constant $\lambda = \frac{\ln 2}{t_{1/2}}$
• Background radiation — sources (radon gas, cosmic rays, rocks, medical); measuring and subtracting
• Detection — Geiger-Müller tube, photographic film, cloud chambers

Nuclear Energy

• Mass-energy equivalence — $E = mc^2$; mass defect and binding energy
• Binding energy per nucleon curve — fission for heavy nuclei (A > 56), fusion for light nuclei (A < 56); iron-56 is the most stable
• Nuclear fission — splitting heavy nuclei (uranium-235, plutonium-239); chain reactions; controlled (reactor) vs. uncontrolled (weapon)
• Nuclear fusion — combining light nuclei (hydrogen isotopes); conditions required (high temperature, high pressure); the Sun’s energy source
• Calculations — determining energy released from mass difference: $\Delta E = \Delta m \times c^2$

Quantum Physics

• The photoelectric effect — photons with energy $E = hf$ eject electrons if $hf > \phi$ (work function); threshold frequency $f_0 = \frac{\phi}{h}$; why wave theory fails to explain instantaneous emission
• Einstein’s photoelectric equation — $hf = \phi + KE_{\max}$; the kinetic energy of the fastest electrons
• Photon model — light as quantised packets of energy; $E = hf = \frac{hc}{\lambda}$
• Wave-particle duality — De Broglie wavelength $\lambda = \frac{h}{mv} = \frac{h}{p}$; electron diffraction as evidence
• Energy levels — discrete atomic energy levels; excitation and de-excitation; photon emission $hf = E_{\text{upper}} - E_{\text{lower}}$
• Line spectra — emission and absorption spectra; identifying elements; the hydrogen spectrum

Particle Physics

• Fundamental particles — quarks (up, down, strange, charm, top, bottom), leptons (electron, muon, tau, neutrinos), gauge bosons (photon, W, Z, gluon)
• Hadrons — baryons (three quarks: proton = uud, neutron = udd) and mesons (quark-antiquark pair)
• Conservation laws — charge, baryon number, lepton number, strangeness (in strong interactions); using these to determine whether interactions are possible
• Antimatter — antiparticles with opposite charge and quantum numbers; pair production and annihilation ($E = 2mc^2$)

Study Tips

1. Practise decay equations — conserve both mass number (top) and atomic number (bottom) in every nuclear reaction.
2. Draw the binding energy per nucleon curve — label fission and fusion regions; explain why both release energy despite going in opposite directions on the curve.
3. Understand the photoelectric effect deeply — be able to explain why wave theory fails and the photon model succeeds. This is a common 6-mark explanation question.
4. Use conservation laws — for every particle interaction, check charge, baryon number, and lepton number. If any is violated, the interaction is impossible.
5. Know your constants — Planck’s constant $h = 6.63 \times 10^{-34}\,\text{Js}$, speed of light $c = 3.0 \times 10^8\,\text{m/s}$, $1\,\text{u} = 931.5\,\text{MeV}/c^2$.

How to Use These Notes

Follow the sidebar order. Each page provides physical principles, derivations, worked examples with calculations, and exam-style problems. Start with radioactivity, then nuclear energy, then quantum physics and particle physics.