The mass defect ($ \Delta m $) is the difference between the mass of the reactant and the sum of the masses of the products. $$ \Delta m = M(^{238}U) - [M(^{234}Th) + M(^{4}He)] $$ $$ \Delta m = 238.050 - [234.043 + 4.003] $$ $$ \Delta m = 238.050 - 238.046 = 0.004 \, u $$
The Q-value is given by $ Q = \Delta m \times 931.5 \, MeV/u $. $$ Q = 0.004 \times 931.5 = 3.726 \, MeV $$
Since $ 1 \, MeV = 1000 \, keV $: $$ Q = 3.726 \times 1000 = 3726 \, keV $$
Final Answer: 3726
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