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1. β – emission.

2. Atomic increases to one unit. But mass number remains constant

3. The parent atom comes to ground state by emitting gamma ray.

4. P → n + e⁺ + ν

Atomic number decreases by one unit. But mass number remains constant.

a. 1. α particle.

b. Mass number decreases to 4 and atomic number decreases to 2

c. penetrating power of the particle is very small in air:

(i) Mass of α particle is

4. Hence penetrating power of the particle is small.

d. Towards A (left) Flemings left hand rule is used.

1. It is electron

2. When α is emitted, mass number decreases to 4 and atomic decreases by 2.

3. To get stability, β is emitted from the nucleus.

1. The splitting of heavy nucleus into two nucleus is called fission.

2. E = 200 Mev

= 200 × 10^-6 ev

E = 200 × 10⁶ x 1.6 x 10^-19J

= 3.2 x 10^-11J.

3. Number of fission

\(n=\frac{Total\,energy}{energy\,per\,fission}\) = \(\frac{1\times10^6}{3.2\times10^{-11}}\)

= 3.3 x 10¹⁰

1. R = R₀ A^1/3 .

2. Density of nucleus = (mass of the nucleus)/ (volume of the nucleus)

\(\frac{mA}{\frac{4}{3}\pi R^3}=\frac{mA}{\frac{4}{3}\pi R^3_0A}\) = \(\frac{m}{\frac{4}{3}\pi R_0^3}\)

This shows that nuclear density is independent of mass number.

\(R=R_0A_\frac{1}{3}\)

1. fission 

2. fission 

3. fission 

4. fusion

The decay rate R at a certain time t and the number of undecayed nuclei N at the same time are related by R = λN 

The decay rate of a sample is experimentally measurable quantity and is given a specific name: activity. The SI unit for activity is becquerel, named after the discoverer of radioactivity, Henry Becquerel. 

1 becquerel is simply equal to 1 disintegration or decay per second. 

There is also another unit named “curie” that is widely used and is related to the SI unit as: 

1 curie = 1 Ci = 3.7 × 10¹⁰ decays per second 

= 3.7 × 10¹⁰ Bq.  

On the atomic scale, mass is measured in atomic mass units (u). By definition, 1 atomic mass unit (1u) is 1/12th mass of one atom of ¹²C; 1u = 1.660563 × 10^–27 kg. 

Nuclides with the same atomic number Z, but different neutron number N are called isotopes. 

Ex : Nuclides with the same A are isobars and those with the same N are isotones. 

Ex : (i) Isobars  (ii) Isotones

Most elements are mixtures of two or more isotopes. The atomic mass of an element is a weighted average of the masses of its isotopes. The masses are the relative abundances of the isotopes. 

An atom has a nucleus. The nucleus is positively charged. The radius of the nucleus is smaller than the radius of an atom by a factor of 104. More than 99.9% mass of the atom is concentrated in the nucleus. 

A nucleus contains a neutral particle called neutron. Its mass is almost the same as that of proton. 

The atomic number Z is the number of protons in the atomic nucleus of an element. The mass number A is the total number of protons and neutrons in the atomic nucleus; A = Z+N; Here N denotes the number of neutrons in the nucleus. 

A nuclear species or a nuclide is represented as ^A_ZX, where X is the chemical symbol of the species. A nucleus can be considered to be spherical in shape and assigned a radius. Electron scattering experiments allow determination of the nuclear radius; it is found that radii of nuclei fit the formula R = R₀ A^1/3, 

where R₀ = a constant = 1.2 fm. This implies that the nuclear density is independent of A. It is of the order of 10¹⁷ kg/m³. 

Neutrons and protons are bound in a nucleus by the short-range strong nuclear force. The nuclear force does not distinguish between neutron and proton.