# Nootan Solutions Radioactivity ISC Physics Class-12 Ch-28

Nootan Solutions Radioactivity ISC Physics Class-12 Ch-28 Vol-2 Nageen Prakashan.  Step by step Solutions of Numericals of latest edition of Kumar and Mittal ISC Physics Part-2 Class-11 Nageen Prakashan Questions. Visit official Website CISCE for detail information about ISC Board Class-12 Physics.

## Nootan Solutions Radioactivity ISC Physics Class-12 Ch-28

 Class: 12 Subject: Physics Part-2 Chapter: 28 Radioactivity
 Board ISC Writer / Publications Nootan / Nageen Prakashan / Kumar and Mittal Topics Solved Numericals of page 959, 960

### Nootan Solutions Radioactivity ISC Physics Class-12 Ch-28 Vol-2 Kumar and Mittal

Henry Becquerel discovered radioactivity by accident. A Uranium compound was placed in a drawer containing photographic plates, wrapped in a black paper.

Due to nuclear instability, an atom’s nucleus exhibits the phenomenon of Radioactivity. Energy is lost due to radiation that is emitted out of the unstable nucleus of an atom. Two forces, namely the force of repulsion that is electrostatic and the powerful forces of attraction of the nucleus keep the nucleus together. These two forces are considered extremely strong in the natural environment. The chance of encountering instability increases as the size of the nucleus increases because the mass of the nucleus becomes a lot when concentrated. That’s the reason why atoms of Plutonium, Uranium are extremely unstable and undergo the phenomenon of radioactivity.

(i) Law of conservation of charge holds good in radioactivity.

(ii) The disintegration is accompanied by the emission of energy in terms of α, β and γ-rays either single or all at a time.

Emission of α- particle results in a decrease in its atomic number by 2 and a decrease in its atomic weight by 4.

Emission of β- particle results in an increase in its atomic number by 1 while its atomic weight remains unaffected.

Emission of γ- rays results neither in a change of atomic number nor in a change of atomic weight.

(iii) Each of the product disintegration is a new element having physical and chemical properties different from those of the parent atom.

(iv) Radioactivity is due to the disintegration of a nucleus.

(v) Rate of disintegration is not affected by the external conditions like temperature and pressure etc.

(a) Curie (Ci):- Radioactivity of a substance is said to be one curie if its atoms disintegrate at the rate of 3.7×1010 disintegrations per second.

(b) Rutherford (rd):- Radioactivity of a substance is said to be 1 Rutherford if its atoms disintegrate at the rate of 106 disintegrations per second.

#### Chain reaction :-

The above quoted fission reaction proceeding in an uncontrolled manner is known as chain reaction and forms the basis of atom bomb. Following conditions must be met with, for the chain reaction to proceed.

• The fissionable material should be larger than a certain minimum size.
•  The material should be highly pure.

#### Nuclear reaction :-

Fission reaction of  U92235can be made to proceed in a controlled manner by slowing down the three emitted neutrons. This is achieved by passing them through moderators. Heavy water and carbon rods can be used as moderators. A device in which the fission proceeds in a controlled manner is called a nuclear reaction.

Nootan Solutions Radioactivity ISC Physics Class-12 Ch-28

### (Page 1004, 1005)

Question 1:

The half-life of radium is 1600 years. What fraction of a simple of radium will be disintegrated after 6400 years ?

Question 2:

The half-life …………………….. 9 minutes.

Question 3:

…………………………..

………………………….

…………………………

Question 18:

The half-life  of a ………………………. 90 % of it.

Question 19:

……………………..

………………………..

…………………………..

Question 26:

Calculate the mass of ………………………… 6.02 x 10²³ mole¯¹.

—: End of Nootan Solutions Radioactivity :–

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