Q107 / 180 · AIIMS 2004 · Physics

Assertion : ${ }^{90} \mathrm{Sr}$ from the radioactive fall out from a nuclear bomb ends up in the bones of human beings through the milk consumed by them. It causes impairment of the production of red blood cells. Reason : The energetics $\beta$-particles emitted in the decay of ${ }^{90} \mathrm{Sr}$ damage the bone marrow.

  • Correct answer
    A
    If both assertion and reason are true and reason is the correct explanation of assertion
  • B
    If both assertion and reason are true but reason is not the correct explanation of assertion
  • C
    If assertion is true but reason is false
  • D
    If both assertion and reason are false.

Solution

Assertion is true. ${ }_{38}^{90} \mathrm{Sr}$ decays to ${ }_{39}^{90} \mathrm{Y}$ by the emission of $\beta$-rays. Sr gets absorbed in bones along with calcium. Reason is also true. ${ }^{90} \mathrm{Sr} \stackrel{\beta}{\longrightarrow}{ }^{90} \mathrm{Y}$ Strontium decays to Yitrium. This emits $\beta$-rays of very high energy. Sr does not emit $\gamma$-rays. The damage is by the $\beta$-rays only.

Hence, the correct answer is option: 'A'.

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