# Physics Class 12 NCERT Solutions: Chapter 13 Nuclei Part 3

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Q: 6. Write nuclear reaction equations for

(i)

(ii)

(iii)

(iv)

(v)

(vi)

(vii)

Answer:

is a nucleus of helium and is an electron . In every, there is a loss of protons and neutrons. In every decay, there is a loss of proton and a neutrino is emitted from the nucleus. In every , there is a gain of proton and an antineutrino is emitted from the nucleus.

For the given cases, the various nuclear reactions can be written as:

(i)

(ii)

(iii)

(iv)

(v)

(vi)

(vii)

Q: 7. A radioactive isotope has a half-life of T years. How long will it take the activity to reduce to (A), (B) of its original value?

Answer:

Half-life of the radioactive isotope

Original amount of the radioactive isotope

(A) After decay, the amount of the radioactive isotope

It is given that only remains after decay. Hence, we can write:

But

Where,

Decay constant

Time

Since

Hence, the isotope will take about years to reduce to of its original value.

(B) After decay, the amount of the radioactive isotope

It is given that only remains after decay. Hence, we can write:

But

Since,

Hence, the isotope will take about years to reduce to of its original value.