Question

${S}^{32}$ absorbs energy and decay into which element after two $\alpha$-emissions?
A. Carbon
B. Aluminium
C. Oxygen
D. Magnesium

Answer 1

Alpha is emitted by alpha decay. Alpha decay is the disintegration of the parent nucleus to a daughter nucleus through the emission of helium atoms. So to solve this problem, first write the decay of ${S}^{32}$ where ${S}^{32}$ is the parent nucleus. Then, write the decay for the daughter nucleus obtained through earlier decay. The daughter nucleus obtained now, will be the element obtained after two $\alpha$-emissions.

Complete step-by-step answer:
Alpha decay is given by,
$_{Z}^{A}{X} \rightarrow _{Z-2}^{A-4}{Y} + _{2}^{4}{He}$
After first alpha emission, ${S}^{32}$ decays as given below,
$_{16}^{32}{S} \rightarrow _{14}^{28}{Si} + _{2}^{4}{He}$
Now, the second alpha emission will be,
$_{14}^{28}{Si} \rightarrow _{12}^{24}{Mg} + _{2}^{4}{He}$
Hence, after two $\alpha$-emissions ${S}^{32}$ decays to ${Mg}^{24}$ which is magnesium.

So, the correct answer is “Option D”.

Additional Information: Radioactive elements are unstable, hence they emit radiations to achieve stability. The parent nucleus emits $\alpha$, $\beta$, or $\gamma$ particles while disintegrating into daughter nuclei. This daughter nucleus again disintegrates to form a stable nucleus. Alpha decay is the phenomenon of emission of alpha particles from the radioactive nucleus. Beta decay is the phenomenon of emission of either electron or positron from the radioactive nucleus. Gamma decay is the phenomenon of emission of gamma photons from the radioactive nucleus.

Note: In practice, this type of decay is only observed in the nuclides considerably heavier than nickel. Alpha particles are emitted by all the heavy radioactive nuclides occurring in nature. Examples of these heavy radioactive nuclides include thorium, uranium, etc. Alpha particles are also emitted by transuranic elements like neptunium, americium, etc. After an alpha decay, the daughter nucleus is often left in an excited energy state.