Polonium (`_84^210`Po`) 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`