2004 AIPMT NucleiNuclear Fusion and Mass Defect Easy Question 57 of 77 in Nuclei

If in a nuclear fusion process the masses of the fusing nuclei be $m_1$ and $m_2$ and the mass of the resultant nucleus be $m_3$, then

A $m_3 = |m_1 - m_2|$
B $m_3 \lt (m_1 + m_2)$
C $m_3 \gt (m_1 + m_2)$
D $m_3 = m_1 + m_2$

The answer is B.

Solution

In nuclear fusion, two light nuclei combine to form a heavier nucleus, and a large amount of energy is released.
The product nucleus is more stable (it has a higher binding energy per nucleon) than the fusing nuclei.
By Einstein's mass-energy relation, the energy released comes from a loss of mass: $E = \Delta m\, c^2$, where $\Delta m = (m_1 + m_2) - m_3$.
Since energy is released, $\Delta m \gt 0$.
So the mass of the product is less than the sum of the masses of the reactants: $m_3 \lt (m_1 + m_2)$.

Concept Mass defect in fusion

Nuclei in past papers

77 questions from this chapter have appeared across 26 exam years.