A nucleus of mass 218 amu in free state decays to emit an α-particle. Kinetic energy of the α-particle emitted is 6.7 MeV. The recoil energy (in MeV) of the daughter nucleus is

(a) 1.0              (b) 0.5
(c) 0.25            (d) 0.125

(d) Using conservation of momentum Pdaughter=Pα
EdEα=mαmdEd=Eα×mαmd=6.7×4214=0.125 MeV

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