NEET Physics Nuclei Questions Solved


A radioactive sample is α-emitter with half life 138.6 days is observed by a student to have 2000 disintegration/sec. The number of radioactive nuclei for given activity are
(a) 3.45×1010               (b) 1×1010
(c) 3.45×1015               (d) 2.75×1011

(a) Activity of substance that has 2000 disintegration/sec
=20003.7×1010=0.054×10-6ci=0.054 μci
The number of radioactive nuclei having activity A
N=Aλ=2000×T1/2loge2=2000×138.6×24×36000.693=3.45×1010

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