What is the alpha decay equation for argon-39?

Answer 1

Argon-39 undergoes beta decay, rather than alpha.

The equation for the beta decay of 39Ar:

1839Ar --> 1939K + -10e

where the e is an electron or beta particle.

In order to undergo alpha decay, an atom has to have a mass greater than at least nickel.

Answer 2

39/18 Ar --> 35/16 S + 4/2 He

All you do for any alpha decay equation is subtract 2 from the bottom fraction and subtract 4 from the top fraction. Then you get the bottom number fraction and look for that number on the 'Periodic Table of Elements' and you place the subtracted fraction after the arrow and add the symbol of the element in front of it. Some problems are also shown like this:

39/18 Ar --> 35/16 S + 4/2 He

On problems like these, all you simply do is look at Ar and S. If you add 2 to the bottom fraction of S and 4 to the top fraction of S, you get 39/18 Ar. So all you have to add at the end is 4/2 He.