Describe what particles make up an $\alpha$-particle.
State the name of the particle with the same composition as an $\alpha$-particle.
The $\alpha$-particle decay of thorium-230 produces an isotope of radium. Deduce the number of neutrons in a neutral atom of this radium isotope.
Deduce the number of electrons in a neutral atom of this radium isotope.
The half-life of thorium-230 is 75 000 years. A radioactive sample contains $7.2 \times 10^{16}$ thorium-230 atoms. Determine how long it takes for the number of thorium-230 atoms to fall to $9.0 \times 10^{15}$.
When it decays, thorium-230 also emits gamma radiation ($\gamma$-radiation). On Fig. 8.1, sketch how the $\gamma$-radiation travels in the electric field.
Fig. 8.2 shows the electric field replaced by a magnetic field directed into the page. On Fig. 8.2, sketch the path of the $\gamma$-radiation in the magnetic field.