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Question

The atomic mass of uranium 92U238 is 238.0508 u, that of thorium 90Th234 is 234.0436 u and that of an alpha particle 2He4 is 4.0026 u. Determine the energy released when αdecay converts 92U238 into 90Th234. [1u×c2=931.5 MeV]

A
1.1 MeV
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B
4.3 MeV
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C
8.2 MeV
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D
15.9 MeV
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Solution

The correct option is B 4.3 MeV
The given decay is represented as,

92U238 90Th234+2He4

The energy is released due to the difference in mass between the reactants and the products.

92U238238.0508u90Th234234.0436u+2He44.0026u238.0462u

The mass defect is given by,

Δm=238.0508u238.0462u

Δm=0.0046u.

Energy released, E=Δm×c2

E=0.0046 u×c2

We know that, 1u×c2=931.5 MeV

E=0.0046×931.5 MeV

E=4.28 MeV4.3 MeV

Hence, option (B) is correct.
Why this Question?

ZXA Z2YA4+ 2He4+Q

Q value: It is defined as the energy released during the decay process.

Q value = (rest mass energy of reactants - rest mass energy of products)

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