Yes, you happen to be correct but you can’t just say that. Different isotopes of each of these elements can be many orders of magnitude more active. If I could summon a few grams of any isotope of carbon (like C-20 that decays in microseconds), I could kill you with radiation poisoning instantly.

Anyway, it’s β⁻ decay so they are all affected, plus some α from secondary products that will be mostly received by Simon.

Unless Alvin’s ²³⁵U is above critical mass, in which case they all die very quickly.