Polonium `(._84^210Po)` emits `._2^4He` particles and is converted into lead (`._82^206Pb`). This reaction is used for producing electric power in a space mission. `Po^210` has half-life of `138.6` days. Assuming an efficiency of `10%` for the thermoelectric machine, how much `.^210Po` is required to produce `1.2xx10^7J` of electric energy per day at the end of `693 days`. Also find the initial activity of the material.
Given : Masses of nuclei
`.^210Po=209.98264` amu, `.^206Pb=205.97440` amu, `._2^4He=4.00260` amu,
`1 am u=931 MeV//c^2` and Avogadro's number` = 6xx10^23//mol`