A charge particle of $2 \mathrm{\mu C}$ accelerated by a potential difference of $100 \mathrm{V}$ enters a region of uniform magnetic field of magnitude $4 \mathrm{mT}$ at right angle to the direction of field. The charge particle completes semicircle of radius $3 \mathrm{cm}$ inside magnetic field. The mass of the charge particle is  $\_\_\_\_\_\_\_\times {10}^{-18} \mathrm{kg}$ .