Nuclear Equations

IGCSE Edexcel Physics
7.1–7.8 Atomic structure, types of radiation and nuclear equations
Key Concepts: Atomic number (Z) = number of protons. Mass number (A) = protons + neutrons. Alpha ($\alpha$): $^4_2\text{He}$, mass −4, atomic number −2. Beta ($\beta^-$): $^0_{-1}\text{e}$, mass unchanged, atomic number +1. Gamma ($\gamma$): no change to nucleus, $^0_0\gamma$. Mass number and atomic number are conserved in nuclear equations.

Section A — Atomic Structure and Radiation Types

1. Define: a) atomic number, b) mass number, c) isotope. [3]
2. Complete the table for each type of radiation. [6]
TypeSymbolChargeMass (relative)Range in airStopped by
Alpha
Beta
Gamma
3. State which type of radiation is the most ionising and which has the greatest penetrating power. Explain why there is a relationship between these two properties. [3]

Section B — Alpha Decay Equations

4. State the changes to mass number and atomic number during alpha decay. [2]
5. Complete the nuclear equation for alpha decay of uranium-238: [2] $$^{238}_{92}\text{U} \rightarrow \;?\; + \;^4_2\text{He}$$
6. Radium-226 undergoes alpha decay. Write the complete nuclear equation. (Radium: Z = 88) [3]

Section C — Beta and Gamma Decay Equations

7. State the changes to mass number and atomic number during beta-minus decay. [2]
8. Complete the equation for beta decay of carbon-14: [2] $$^{14}_{6}\text{C} \rightarrow \;?\; + \;^0_{-1}\text{e}$$
9. Cobalt-60 undergoes beta decay followed by gamma emission: [2] $$^{60}_{27}\text{Co} \rightarrow \;^{60}_{28}\text{Ni} + \;?$$ State what the missing particle is.
10. Explain why gamma emission does not change the atomic number or mass number of the nucleus. [2]

Total marks: 27

Mark Scheme

1. a) Atomic number: number of protons in the nucleus [1]; b) Mass number: total number of protons + neutrons [1]; c) Isotope: atoms of the same element with the same number of protons but different numbers of neutrons [1] [3]
2. Alpha: $^4_2\text{He}$, charge +2, mass 4, a few cm in air, stopped by paper/skin [2]; Beta: $^0_{-1}\text{e}$, charge −1, mass ~0, ~1 m in air, stopped by a few mm aluminium [2]; Gamma: $^0_0\gamma$, charge 0, mass 0, very long range, reduced (not fully stopped) by thick lead/concrete [2] [6]
3. Alpha is most ionising [1]; gamma has greatest penetrating power [1]; high ionising power means energy is quickly transferred to air molecules, so the radiation does not travel far [1] [3]
4. Mass number decreases by 4 [1]; atomic number decreases by 2 [1] [2]
5. $^{234}_{90}\text{Th}$ [2]
6. $^{226}_{88}\text{Ra} \rightarrow ^{222}_{86}\text{Rn} + ^4_2\text{He}$ [3] (award 1 mark each for correct mass number, correct atomic number, correct symbol Rn)
7. Mass number unchanged [1]; atomic number increases by 1 [1] [2]
8. $^{14}_{7}\text{N}$ [2]
9. $^0_0\gamma$ (gamma photon) [2]
10. Gamma radiation is energy released as an electromagnetic wave [1]; no particles leave the nucleus, so the number of protons and neutrons is unchanged [1] [2]