1.

A U^(235) atom undergoes fission by thermal neutrons according to the following reaction U^(235)+nrarr""_(54)^(140)Xe+""_(38)^(94)Sr+2n Then Xenon undergoes four and Strontium undergoes two consecutive B decays and six electrons are detected. What is the atomic number of the two decay products of Xenon and Strontium?

Answer»

50, 36
58, 40
56, 42
57, 41

Solution :`U^(235)+n rarr ""_(54)^(140)Xe+""_(38)^(94)Sr+2n`
When `beta` particle is emitted, atomic number of daughter NUCLEI.
is increased by 1 and atomic MASS number remains the same.
Therefore, when `""_(54)^(140)Xe `undergoes four consecutive `beta` decays, the atomic number of final decay product is increased by 4 i.e., 58 and corresponding decay CHAIN is shown here,
`""_(54)^(140)Xerarr""_(55)^(140)CS rarr ""_(56)^(140)Bararr""_(57)^(140)La rarr ""_(58)^(140)Ce`
When `""_(38)^(94)Sr` undergoes two consecutive `beta` decays, the atomic number of final decay product is increased by 2. i.e. 40 and corresponding decay chain is shown below
`""_(38)^(94)Sr rarr ""_(39)^(94)Y rarr ""_(40)^(94)Zr`


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