Nuclear Chemistry and Radioactivity — Chemistry STD 11 Science — Question

i. Binding energy per nucleon $(\bar{B})$, for nucleus containing $( A )$ nucleons with binding energy (B.E.) is given as,
$
\overline{ B }=\text { B.E. } / A
$
ii. Mean binding energy per nucleon $(\overline{ B })$ for the most stable isotopes as a function of mass number is shown above. This plot leads to the following inferences:
a. Light nuclides: $(A<30)$

The peaks with A values in multiples of 4 . For example, ${ }_2^4 He ,{ }_6^{12} C ,{ }_8^{16} O$ are more stable.
b. Medium mass nuclides: $(30<A<90)$
$\overline{ B }$ increases typically from $8 MeV$ for $A =16$ to nearly $8.3 MeV$ for $A$ between 28 and 32 and it remains nearly constant $8.5 MeV$ beyond this and shows a broad maximum. The nuclides falling on the maximum are most stable which turns possess high values. ${ }^{56} Fe$ with $\overline{ B }$ value of $8.79 MeV$ is the most stable.

c. Heavy nuclides $(A>90)$
$\overline{ B }$ decreases from maximum 8.79 $MeV$ to $7.7 MeV$ for $A \cong 210,209 Bi$ is the stable nuclide. Beyond this, all nuclides are radioactive ( $\alpha$-emitters).