iGCSE Physics (0625) 5.2.2 The three types of nuclear emission-Exam Style Questions- New Syllabus
▶️ Answer/Explanation
Detailed solution:
The count rate remains $2000\text{ counts/minute}$ with paper, meaning no $\alpha$-particles are present as they would be absorbed.
The rate drops to $1200\text{ counts/minute}$ with $5\text{ mm}$ of aluminium, indicating $\beta$-particles are being emitted and absorbed.
Since $1200\text{ counts/minute}$ still pass through the aluminium, $\gamma$-radiation must also be present due to its high penetrating power.
Therefore, the source emits both $\beta$-particles and $\gamma$-rays, making Option C the correct choice.
▶️ Answer/Explanation
Detailed solution:
Beta-particles ($\beta^{-}$) are high-speed electrons emitted from the nucleus, not electromagnetic waves like gamma rays or X-rays.
They possess a relative charge of $-1$, making statement D correct, and they are highly ionising, making statement B correct.
During $\beta$-decay, a neutron changes into a proton ($n \to p + e^{-}$), which increases the proton number $Z$ by $1$.
Because the proton number defines the identity of an atom, the strontium-89 changes into a different element, making statement C correct.
Therefore, statement A is the only incorrect claim, as beta radiation consists of particles with mass and charge, not electromagnetic radiation.
▶️ Answer/Explanation
Detailed solution:
Alpha particles ($\alpha$) consist of two protons and two neutrons, giving them a relative charge of $+2$.
This is the largest electric charge among the three emissions, as beta particles ($\beta$) have a charge of $-1$ and gamma rays ($\gamma$) have $0$ charge.
The high charge and large mass of alpha particles cause them to interact strongly with atoms, making them the most ionising.
Stronger ionisation occurs because the $+2$ charge easily pulls electrons away from nearby atoms during collisions.
Therefore, Row C correctly identifies that alpha radiation is the most ionising due to having the largest electric charge.