Question

Which type of nuclear decay is the following radioactive isotope likely to undergo?

All known stable isotopes are shown on the graph. The points form what is know as the "belt of stability".

If a radioactive isotope is above the belt of stability, think about what type of decay would decrease its N/Z ratio. If an unstable isotope is below the belt of stability, think about what type of decay would increase its N/Z ratio. If a radioactive isotope is off the chart (Z > 83), think about what type of decay would decrease Z the most.

Answer 1

The radioactive isotope, \({ }_{85}^{213}\) At has atomic number \(83(Z=83)\). The number of neutrons \(=213-85=128\)

For this element, the atomic number is greater than \(83 .\) Hence, to come into the belt of stability, the atomic number should be decreased.

The atomic number and mass number of an element decreases when it undergoes alpha decay. When an alpha particle is ejected, the atomic number decreases by 2 units and the mass number decreases by 4 units.

The alpha decay of \({ }_{85}^{213}\) At results \({ }_{83}^{209} \mathrm{Bi}\)

$$ { }_{85}^{213} \mathrm{At} \rightarrow{ }_{83}^{209} \mathrm{Bi}+{ }_{2}^{4} \mathrm{He} $$

Therefore, the radioactive isotope, \({ }_{85}^{213}\) At undergoes alpha decay to convert into a stable nuclide.