Nuclear Physics Concept Page - 9

Definition

The properties of beta particles

1. Beta particles are the fast moving electrons emitted from the nucleus of an atom.
2. Although beta-particle and the cathode rays both are the fast moving electrons, but they differ in their origin. Beta-particles are given out from the nucleus of the atom while cathode rays are given out from its orbital electrons.
3. The speed of Beta particles is of the order of 108${10}^8$ m/s.
4. Beta particles ionise the gas through which they pass.
5. Penetrating power of Beta-particles is more than that of alpha particles. 
6. Beta particles affect a photographic plate.

Definition

The properties of gamma radiations

1. Gamma radiations are the electromagnetic waves like X-rays and light, but they differ from X-rays and light in wavelength.
2. The speed of Gamma-radiations is the same as the speed of light.
3. The ionising power of Gamma-radiations is very low.
4. Gamma radiations affect a photographic plate.
5. Gamma radiations cause fluorescence when they strike a fluorescent material.

Definition

Differentiate between alpha, beta and gamma radiations

Property	α$\alpha$-Particle	β$\beta$-Particle	γ$\gamma$-Particle
Nature	Stream of positively charged particle i.e. helium nuclei	Stream of negatively charged particles, i.e. energetic electrons	Highly energetic electromagnetic radiation
Speed	Nearly 107ms−1${10}^7{ms}^{-1}$	About 90% of the speed of light or 2.7×108ms−1$2.7\times {10}^8{ms}^{-1}$	3×108ms−1$3\times {10}^8{ms}^{-1}$ in vacuum
Penetrating Power	Small (3 to 8cm in air)	Large (Up to few metre in air)	Very Large (Up to a few hundred metre in air)

Definition

Define background radiations and identify its sources

Background radiations are the radioactive radiations to which we are exposed even in the absence of an actual radioactive source.
There are two sources of background radiations:
1. Internal source: The radioactive substances such as potassium (K-40), carbon (C-14) and radium present inside our body.
2. External source: Cosmic rays, naturally occurring radioactive elements such as radon-222 and solar radiations.

Example

Explain the applications of radio-isotopes

The applications of radio-isotopes are as follows:
1. Cobalt-60 is extensively employed as a radiation source to arrest the development of cancer.
2. Iodine-131 has proved effective in treating hyperthyroidism.
3. In industry, radioactive isotopes of various kinds are used for measuring the thickness of metal or plastic sheets; their precise thickness is indicated by the strength of the radiations that penetrate the material being inspected.

Definition

Radioactivity and Artificial radioactivity

Radioactivity is the term used to describe the natural process by which some atoms spontaneously disintegrate, emitting both particles and energy as they transform into different, more stable atoms. This process, also called radioactive decay, occurs because unstable isotopes tend to transform into a more stable state. Radioactivity is measured in terms of disintegrations, or decays, per unit time. Common units of radioactivity are the Becquerel, equal to 1 decay per second, and the Curie, equal to 37 billion decays per second.
When the radioactive isotope is generated during the nuclear reaction, it is termed as artificial radioactivity.

Definition

Uses of radioactivity

1. Medical use: Many diseases such as cancer are cured by radio therapy. Sterilization of medical instruments and food is another common application of radiation.
2. Scientific use: Alpha particles emitted from the radio isotopes are used for nuclear reactions.
3. Industrial use: Radio isotopes are used as fuel for atomic energy reactors.

Definition

Radioactivity

The substance which disintegrate (or decay) by the spontaneous emission of radiations, are called the radioactive substances.
Eg. uranium, radium, polonium, thorium, actinium etc.
And the phenomenon which they exhibit is called radioactivity.

Definition

Various kinds of radioactive decay occurring in nature

Radioactivity is a nuclear phenomenon in which an unstable nucleus undergoes a decay. This is referred to as radioactive decay. Three types of radioactive decay occur in nature :
(i) α$\alpha$-decay in which a helium nucleus 42He${}_2^{4}He$ is emitted.
(ii) β$\beta$ decay in which electrons or positrons (particles with the same mass as electrons, but with a charge exactly opposite to that of electron)are emitted.
(iii) γ$\gamma$-decay in which high energy (hundreds of keV or more) photons are emitted.Each of these decay will be considered in subsequent sub-sections.

Law

Law of radioactive decay

We have dNdt=−λN${\displaystyle \frac{dN}{dt}}=-\lambda N$
dNN=−λdt${\displaystyle \frac{dN}{N}}=-\lambda dt$
Integrating both sides,
∫NN0dNN=−λ∫tt0dt${\int }_{N_0}^N\frac{dN}{N}=-\lambda {\int }_{t_0}^{t}dt$
ln(NN0)=−λt$ln({\displaystyle \frac{N}{N_0}})=-\lambda t$
N=N0e−λt$N=N_0{e}^{-\lambda t}$
This is the law of radioactive decay

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