Question

In fission of $U-235$, the percentage of mass convened into energy is about:

• A. $0.1\%$
• B. $0.25\%$
• C. $0.3\%$
• D. $2\%$

Answer 1

Answer: (A)

$0.1\%$

Answer 2

The fission reaction of $U ^{235}$ is as follows : ${ }_{92} U ^{235}+{ }_{0} n^{1} \longrightarrow{ }_{92} U ^{236} \longrightarrow { }_{56} Ba ^{144}+{ }_{36} Kr ^{89}+3_{0} n^{1}+$ energy The mass of ${ }_{92} U ^{235}+{ }_{0} n^{1} =234.99 \,amu +1.01 \,amu$ $=236.00 \,amu$ $=143.87 \,amu +88.90 \, amu +3 \times 1.01 \, amu$ $=2358 \,amu$ Similarly, the mass of ${ }_{56} Ba ^{144}+{ }_{36} Kr ^{89}+3_{0} n^{1}$ $\therefore \Delta m=$ mass defect $=236-235.8=0.20 \,amu$ Hence, $\%$ of mass converted to energy $=\frac{0.20}{236} \times 100 \approx 0.085 \approx 0.1 \%$