Thanks for the comment. I am glad you enjoyed the quiz.
I appreciate your suggestion regarding 'gamma', but within physics, the 'γ' is used to describe photons as a whole and not merely gamma rays (the 1905 discovery of photons by Einstein should be sufficient to lead to 'photons', while gamma rays—discovered by Rutherford in 1900 and which, admittedly, also use the 'γ' symbol—are not a larger class of elementary subatomic particles).
An alpha particle is subatomic in that it is smaller than at atom, being a composite particle (a doubly ionized helium nucleus). It is true that 'alpha particle' is not defined especially rigorously, but for the purposes of this quiz (and Rutherford's discovery/Rutherford and Royds' proof in 1907), an alpha particle is subatomic.
I appreciate your suggestion regarding 'gamma', but within physics, the 'γ' is used to describe photons as a whole and not merely gamma rays (the 1905 discovery of photons by Einstein should be sufficient to lead to 'photons', while gamma rays—discovered by Rutherford in 1900 and which, admittedly, also use the 'γ' symbol—are not a larger class of elementary subatomic particles).