What nuclear decay can be stopped by aluminum?
Alpha and beta rays.
All types of radiation from nuclear decay can be stopped by aluminium if it is thick enough.
Personal experience; at least 30 cm from Sr 90 isotope (beta source).
Alpha particles can be absorbed by a thin sheet of paper or by a few centimetres of air.
Beta particles travel faster than alpha particles and carry less charge, so they interact less readily with the material through which they pass. They can be stopped by a few millimetres of aluminium.
Gamma rays are highly penetrative. Many centimetres of aluminium would be required to absorb energetic gamma rays.
It is important to note that aluminium is susceptible to the Bremsstrahlung effect (responsible for "extra radiation" within the metal). The Bremsstrahlung effect is seen primarily by alpha and beta radiation.
Conclusion: Alpha and beta can be stopped easily by aluminium.