Stable & Unstable Nuclei

Q1. Why does the strong nuclear force become repulsive at separations less than approximately 0.5 fm?

Multiple Choice · 1 point

• · To prevent electrons from entering the nucleus
• · To prevent nucleons from being pushed too far apart
• · To prevent nucleons from collapsing into one another
• · To counteract the weak nuclear force at short range

Q2. A nucleus undergoes alpha decay. Which of the following correctly describes the change in proton number Z and nucleon number A?

Multiple Choice · 1 point

• · Z decreases by 1, A decreases by 1
• · Z decreases by 2, A decreases by 4
• · Z decreases by 4, A decreases by 2
• · Z decreases by 2, A decreases by 2

Q3. Which of the following is a correctly balanced equation for β⁻ decay?

Multiple Choice · 1 point

• · ¹⁴₆C → ¹⁴₇N + ⁰₋₁e + v̄ₑ
• · ¹⁴₆C → ¹⁴₇N + ⁰₋₁e + vₑ
• · ¹⁴₆C → ¹⁴₅B + ⁰₋₁e + vₑ
• · ¹⁴₆C → ¹⁴₇N + ⁰₊₁e + vₑ

Q4. Before the neutrino was hypothesised, which conservation law appeared to be violated in beta decay?

Multiple Choice · 1 point

• · Conservation of charge
• · Conservation of nucleon number
• · Conservation of energy
• · Conservation of momentum only

Q5. Put the following in order to explain why the neutrino was hypothesised to exist.

Ordering · 2 points

• 1. Experiments showed beta particles were emitted with a continuous range of kinetic energies
• 2. If only the beta particle and daughter nucleus were products, energy conservation would demand a fixed kinetic energy
• 3. The missing energy suggested an undetected third particle was carrying away the remainder
• 4. Pauli proposed the existence of the neutrino to account for the missing energy and momentum