O-LevelPhysicsNuclear Physics5054/21 · Oct/Nov 2025 · Q89 Marks

The nuclide notation for the radioactive isotope radon-222 is 222 Rn. An atom of radon-222 decays by the emission of an alpha particle (α-particle).

(a)Describe how the composition of an atom of radon-222 differs from that of an atom of radon-224.[2]
(b)Radon-222 decays to an isotope of polonium (Po). Complete the nuclide equation for the decay of radon-222. 222 Ra → α + Po[3]
(c)(i)Describe what is observed when the detector is at position J and when it is at position K.[2]
(c)(ii)Explain what these observations show about the structure of a gold atom.[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2025). The mark or mark type is shown in brackets.

[C1] different numbers of neutrons / nucleons
[A1] radon-222 / it has two fewer neutrons (in the nucleus) / radon-222 has 136 neutrons and radon-224 has 138 neutrons
[B1] 4 / 2 (α)
[B1] 218 (Po)
[B1] 84 (Po)
[B1] count rate at detector J is not zero/is small or some alpha particles are deflected through large angles
[B1] detector K has larger/very large detection rate or most / nearly all alpha particles pass straight the gold sheet / are undeflected by the gold sheet
[B1] there is a concentration of charge in the atom
[B1] most of the mass of an atom is concentrated into a very small volume or most of the (volume of an) atom is empty space or atom has a dense nucleus

On Oracle Prep you can write or photograph your own answer and have it marked by AI against this mark scheme, with feedback on what you missed.