iGCSE Physics (0625) 5.2.3 Radioactive decay Paper 4 -Exam Style Questions- New Syllabus
▶️ Answer/Explanation
Correct Answer: Time taken for half the nuclei (in any sample) to decay.
Detailed solution: The half-life is a key statistical measure used in nuclear physics to describe the rate of radioactive decay. It specifically refers to the time interval required for exactly half of the unstable radioactive nuclei in a given sample to undergo a decay process. This time value is constant for a specific isotope, regardless of the initial sample size or environmental conditions.
Correct Answer: $_{92}^{234}\text{U} + _{-1}^{0}\beta$
Detailed solution: In a $\beta$-decay process, a $\beta$-particle (which is a fast-moving electron) is emitted. The $\beta$-particle has a nucleon number of 0 and a proton number of -1, denoted as $_{-1}^{0}\beta$. To conserve both the total nucleon number and the total proton number across the equation, the new nucleus must have the same nucleon number ($234 = 234 + 0$) and a proton number that is one higher ($91 = 92 – 1$), identifying the new element as Uranium ($\text{U}$).
Correct Answer: A neutron changes to a proton (plus an electron).
Detailed solution: During $\beta$-emission, the fundamental change inside the unstable nucleus is driven by the weak nuclear force. Specifically, a single neutral neutron transforms into a positively charged proton, which remains bound in the nucleus, and a negatively charged electron (the $\beta$-particle), which is immediately ejected. This explains why the atomic number increases by 1 while the mass number remains completely unchanged.
Correct Answer: $\alpha$-particles have greater kinetic energy and greater charge than $\beta$-particles.
Detailed solution: Ionisation occurs when radiation strips electrons away from neutral atoms. An $\alpha$-particle consists of two protons and two neutrons, giving it a relative charge of +2 compared to a $\beta$-particle’s charge of -1. This larger charge exerts a much stronger electromagnetic force on surrounding atomic electrons. Furthermore, due to their significantly larger mass, $\alpha$-particles typically carry greater kinetic energy, allowing them to interact more intensely with matter as they pass through it.