3) α = 220, ß = 40

Background radiation = 20 units
α + ß = 280 – 20 = 260
We know that when the paper is placed, all α radiation will be blocked.

So,
ß + background radiation = 60
ß + 20 = 60
ß = 40
α + ß = 260
α + 40 = 260
α = 220