The mass of a helium atom () is , while the masses of a free neutron and proton are and respectively — Nuclear Chemistry and Radioactivity Chemistry Question
Question
The mass of a helium atom (${}_{2}^{4}He$) is $4.0026\text{ amu}$, while the masses of a free neutron and proton are $1.0087\text{ amu}$ and $1.0078\text{ amu}$ respectively. Assuming electron mass is negligible, what is the approximate binding energy per nucleon in the helium nucleus? (Given $1\text{ amu} \approx 931.5\text{ MeV}$)
Answer: A
💡 Solution & Explanation
Expected mass = $2(1.0078) + 2(1.0087) = 4.0330\text{ amu}$. Actual mass = $4.0026\text{ amu}$. Mass defect $\Delta m = 0.0304\text{ amu}$. Total Binding Energy = $0.0304 \times 931.5 = 28.31\text{ MeV}$. B.E. per nucleon = $28.31 / 4 \approx 7.07\text{ MeV}$.
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