Chapter 4, Problem 2STP

Interpretation Introduction

Interpretation:

The new atom formed from the decay of Neptunium’s decay needs to be determined.

Concept introduction:

There are $25$ known radioactive isotopes of neptunium molecular weights ranging from $(225-244)$. The most stable is $\mathrm{Np}-237$.

Answer to Problem 2STP

Correct answer: The correct option is (A).

Explanation of Solution

Reason for correct option: The primary decay of neptunium by electron capture with the emission of $\alpha -paticles$ produces isotopes of Uranium as $U$.

The primary decay for $\mathrm{Neptunium}-237$ goes with $\alpha -paticles$ emission and for the heavier isotopes of $\mathrm{Neptunium}-237$ decays to plutonium with $\beta -decay$. $\mathrm{Neptunium}-237$ then decays to protactinium then to uranium and finally decays to form $bismuth-209$ and $thallium-205$. This decay chain is known as neptunium series.

The correct option is (A).

Conclusion

Reasons for incorrect options: Neptunium doesn’t decay to the $Np$, $U$ as they are of heavier molecular weights than the $\mathrm{Neptunium}-237$ and hence cannot decay to a heavier mass after emission of energy.

Option (B ): $Np$ is of heavier mass.

Option (C ): $Th$ isn’t produced in the decay.

Option (D ): $U$ isn’t the right option as its molecular weight is heavier than the isotope of $\mathrm{Neptunium}-237$.