Beta decay confusion

Hi

Can some one please help

Question 1

aM is atomic mass nM is nuclear mass Mp is parent atom Md is the
daughter atom
me is the mass of an electron
Can some please explain why the Q/c^2 formulae are :

Beta(minus) is Q/c^2 = aMp - aMd
Beta(plus) is Q/c^2 = Q/c^2 = aMp -(aMd - 2*me)

Question 2

Since beta decay is occuring in the parent Nucleus why are the
formulae working with neutral atom (parent) masses. I would have
expected the formulae to use nMp rather than aMp
I can see why there is a -me for beta(plus) but WHY 2me?

Thanks
.

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