Question

BE/nucleon relation with mass number

• A. first decreases then increases
• B. first increases then decreases
• C. increases
• D. decreases

Answer 1

Answer: (B)

The binding energy per nucleon for light nuclei is very small.
The variation of average binding energy per nucleon with mass number $A$ is shown in figure.
Average binding energy per nucleon for light nuclei like
${}_1{H}^1,{}_1{H}^2,{}_1{H}^3$ is small.
For mass numbers ranging from $2$ to $20$, there are sharply defined peaks corresponding to ${}_{2}H{e}^4,{}_6{C}^{12},{}_8{O}^{16}$ etc.
The binding energy curve has a broad maximum in the range $A=30$ to $A=120$ corresponding to average binding energy per nucleon $=8.5MeV$.
The peak value of the maximum is $8.8MeV/$ nucleon for ${}_{26}F{e}^{56}$.
As the mass number increases, the binding energy per nucleon decreases gradually falling to about, $7.6MeV$ per nucleon for ${}_{92}{U}^{238}$.