JEE PHYSICS MCQ: NUCLEI

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Application +4 | -1

Uranium -238 decays to Thorium -234 with half-life

5 \times 10^9 \mathrm{yr}

. The resulting nucleus is in the excited state and hence further emits

\gamma

-rays to come to the ground state. It emits

20 \gamma

-rays per second. The emission rate will drop to

5 \gamma

-rays per second in

View answer and explanation

Correct option: B

10^{10} \mathrm{yr}

Option B (

10^{10} \mathrm{yr}

) is correct because the emission rate drops to 5 γ-rays per second after two half-lives, which is

2 \times 5 \times 10^9 \mathrm{yr} = 10^{10} \mathrm{yr}

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