Atomic physics - reaction and energy

[lingling]

The problem statement, all variables and given/known data

Which of the following reactions will release large amount of energy
(1) Nuclear fusion
(2) alpha - decay
(3) Nuclear fission
(4) gamma - decay

two of the options are:

B (1) and (3) only
D (1), (2), (3), (4)


2. Relevant equations
none


3. The attempt at a solution

I tried D but the solution says it should be B.
I don't understand why alpha - decay and gamma - decay do not give large amount of energy.

[rsk]

If alpha decay gave off large amounts of energy, poor old Alexander Litvinenko might have met with a quicker, albeit more dramatic, end than the lingering one he suffered.....

[RandallB]

You are correct all 4 do give off LARGE amounts of energy (joules or kilo-watt hours), but only if your measure of “large” is in comparison to the amount of mass lost.
All four use the same E=mc^2, so yes all for give a Large conversion to energy.

But I’m sure the context of the question refers to power of each process in the amount of energy released in a unit of time (work, watts, joules/sec).
Fission and Fusion converts much more mass much faster than decay does.