Potassium -40 can decay in three modes. It can decay by β–-emission, β+-emission or electron capture.
(a) Write the equations showing the end products.
(b) Find the Q-value in each of the three cases. Atomic masses of 
are 39.9624 u, 39.9640 u and 39.9626 u respectively.
a) Equations:
1) 
[β- emission]
2) 
[β+ emission]
3) 
[electron capture]
b)
,
where c2 = 931.5 MeV/u
case 1:
case 2:
Case 3:
Note: For energy calculations we use the masses of the nuclei of the reactions but as we are given atomic masses we add and subtract appropriate number of electrons to get the above expressions. For more details, one should look through the derivation of Q value for the three cases.
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