CAIE IGCSE Physics Relative Ionising Effects of Radiation

Practise explaining why alpha ionises more strongly than beta or gamma by comparing electric charge, kinetic energy and interaction time with atoms.

Exam points

state the ionising order alpha > beta > gamma and relate stronger ionisation to shorter range
explain alpha's stronger effect using its larger charge and stronger interaction with atomic electrons
use kinetic energy or lower speed to explain longer interaction time and more ionisation along the path

[Maximum number: 2]

Many household smoke alarms contain a sample of the radioactive isotope americium-241 (Am).

Americium-241 decays to an isotope of neptunium (Np) by alpha-particle ( $\alpha$ -particle) emission.

One reason for using an isotope that emits $\alpha$ -particles in a smoke detector is that $\alpha$ -particles are more strongly ionising than beta-particles ( $\beta$ -particles).

Explain why $\alpha$ -particles are more strongly ionising than $\beta$ -particles.

( $\alpha$ -particles have) more kinetic energy (than $\beta$ -particles)

B1

( $\alpha$ -particles have) more charge (than $\beta$ -particles)

B1

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5.2.2.4—Their relative ionising effects with question 1