Nuclear and Particle Physics
Nuclear and Particle Physics in GATE PH tests nuclear size and binding energy, the semi-empirical mass formula, radioactive decay, nuclear reactions, cross sections, conservation laws, the quark model, and basic particle classifications. Questions often turn on a mass defect or a conserved quantum number.
Core rules and concepts
- Binding energy: BE = [Zm_p + (A-Z)m_n - M_nucleus]c². The mass defect is converted using 1 u = 931.5 MeV/c².
- The semi-empirical mass formula includes volume, surface, Coulomb, asymmetry, and pairing terms. Pairing favours even-even nuclei.
- Beta decay conserves charge, baryon number, and lepton number. Beta-plus emission competes with electron capture and requires a nuclear mass excess above the daughter plus two electron masses.
- Nuclear reaction Q-value: Q = (initial mass - final mass)c². A positive Q-value means energy is released.
- Quark content: proton = uud, neutron = udd, mesons are quark-antiquark pairs. Strong interactions conserve strangeness; weak interactions need not.
Worked example
The deuteron has m_p = 1.007276 u, m_n = 1.008665 u, and m_d = 2.013553 u. The mass defect is Δm = 1.007276 + 1.008665 - 2.013553 = 0.002388 u. Using 931.5 MeV/u, BE = 0.002388 × 931.5 ≈ 2.225 MeV. This is the deuteron binding energy.
Traps that cost marks
- Using atomic masses where nuclear masses are required, or vice versa.
- Forgetting the electron-mass correction in beta-plus decay.
- Confusing the threshold energy with the Q-value.
- Assuming strangeness is conserved in weak decays.