# A-level Physics (Advancing Physics)/Binding Energy/Worked Solutions

**1. Deuterium (an isotope of Hydrogen with an extra neutron) has a nuclear mass of 2.01355321270 u. What is its binding energy?**

Total mass of neutron and proton is 1.00727647 + 1.00866492 = 2.01594139 u

Mass defect = 2.01594139 - 2.01355321270 = 0.002388178 u = 3.965662187 x 10^{-30} kg

**2. Uranium-235 has a nuclear mass of 235.0439299 u. It contains 92 protons. What is its binding energy?**

235 - 92 = 143 neutrons

Total mass of baryons is (92 x 1.00727647) + (143 x 1.00866492) = 236.9085188 u

Mass defect = 236.9085188 - 235.0439299 = 1.8645889 u = 3.096222181 x 10^{-27} kg

**3. How would you expect H-2 and U-235 to be used in nuclear reactors? Why?**

H-2 is used in experimental fusion reactors, since it has a smaller nucleus than Iron-56.

U-235 is used in fission reactors, since it has a much larger nucleus than Iron-56.