An atomic battery wrist watch uses ( { }_{61}^{147} mathrm{Pm} ) as a source of ( beta )-p…

An atomic battery wrist watch uses ( { }_{61}^{147} mathrm{Pm} ) as a source of ( beta )-particle ( left(t_{1 / 2}=2.62right. ) years) for energy required for its operation. How long would it take for the rates of ( beta )-emission in the battery to reduced by ( 5 % ) of its original value?
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