Satish Pradhan Dnyanasadhana college, Thane ( Academic Year 2017– 2018 ) SEM-II Class- F. Y. B. Sc Subject-Physics Paper-II Topic- Radioactivity Presented By Ms. Ankita P. Angre Dept. of Physics

Radioactivity

What is mean by radioactivity? Radioactivity is the spontaneous disintegration of atomic nuclei. The nucleus emits α particles, ß particles, or electromagnetic rays during this process. After decaying, radioactive atoms “change” into other atoms

Marie Curie &Piere Curie (1898) Introduction Radioactivity The Phenomenon of spontaneous emission of radiation from radioactive substance is known as Radioactivity It is reversible, Self- disintegrating and spontaneous nuclear phenomenon. Name of the Scientist Discovery Becquerel (1896) Uranium Marie Curie &Piere Curie (1898) Thorium Polonium Radium Dabierne&Giesel (1899) Actinium E. Rutherford α&β- rays P. Villard (1909) 𝛾- rays

Radioactive Disintegration Experimental Observation A beam of radioactive rays from radioactive sample splits into three components in a strong electric and magnetic field. One type of radioactive rays are found to be Positively charged (α- particle) One type of radioactive rays are found to be negatively charged (β- particle) Penetrating power of β- particle is 100 times greater than α- particle Radioactive rays ionize the surrounding air Its affect the photographic plate When Radioactive rays hot the screen (zinc sulphide), they produce fluorescence 𝛾 rays are not deflected by electric and magnetic field. Fig. Discovery Of Radioactive Rays

Types Of Radioactivity Natural Radioactivity Artificial Radioactivity

Natural Radioactivity Radioactive Series

Radioactive Series Uranium Series Actinium Series Thorium Series Neptunium Series

Radioactive Series Actinium Series (A=4n+3) Uranium Series (A=4n+2 Neptunium Series (A=4n+1) Thorium Series (A=4n)

Table: Radioactive Series

Artificial Radioactivity

Radioactive Decay The Term natural Radioactivity applies to the spontaneous transformation of one nuclear species into another with emission of some particle α particle β particle γ particle

Neutron decays into a proton & an electron is given off Types of decays… 2 protons & 2 neutrons Neutron decays into a proton & an electron is given off Only Energy is release

α-decay When a radioactive nucleus (parent nuclei) X shows alpha decay it results in a formation a daughter element Y In α-decay process atomic number decrease by 2 & mass number decrease by 4 of parent nucleus. In α-decay total mass number and charge are conserved. Emission of alpha particle reduces the size of nucleus

α-decay Alpha particles consist of two protons and two neutrons, identical to the nucleus of a helium atom. A sheet of paper or a person’s surface layer of skin will stop them. Alpha particles are only considered hazardous to a person’s health if they are ingested or inhaled and thus come into contact with sensitive cells such as in the lungs, liver and bones.

A few examples of beta decay When an radioactive element disintegrate by the emission of beta particle i.e. emission of electron by neutron in the nucleus, It changes the neutron to a proton, It is because of the a loss of negative charge. In Beta decay the atomic number Z of the parent increases to Z+1 and atomic number remain same. Beta decay occurs in those elements with excess neutrons. A few examples of beta decay

They can travel a few feet in air but can usually be stopped by clothing or a few centimeters of wood. They are considered hazardous mainly if ingested or inhaled, but can cause radiation damage to the skin if the exposure is large enough. Unstable Neutron decays into a proton.

γ- decay Example

Properties of α-particle,β- particle and γ -rays

Law of Radioactive Disintegration

Half Life Period (𝜏) The half life period (𝝉) of a radioactive substance is defined as the time in which one half of the radioactive substance is disintegrated. At the end of the half life 𝝉 for a radioactive element only 50% of the remain unchanged . At the end 2 𝝉 only 25%….etc. Knowing the radioactive disintegration constant (λ) of the radioactive substance, half life of the radioactive substance can be determined and it is different for different materials Fig. radioactive curve of different radioactive substance

Average Life Period

Law of successive Disintegration: Growth and Decay

This equation gives the number of atoms in elements C at any instant.

Fig. Decay and Recovery Curve The Law of successive radioactive transformation can be represented graphically Fig. Decay and Recovery Curve

Radioactive Equilibrium Three kinds of radioactive Equilibrium Ideal Equilibrium Secular Equilibrium Transient Equilibrium

Ideal Equilibrium

Secular Equilibrium This is condition for secular Equilibrium

Transient Equilibrium transient equilibrium occur

Dating- Finding the age Radio-isotopes Generate electrical power : Nuclear fission is used to generate electricity as an alternative energy source. Dating- Finding the age Even the age of fossils or rocks can be determined by using radioactive isotopes.

Carbon occurs naturally in three isotopes. All of these atoms have the same number of protons but different numbers of neutrons. The number of neutrons and protons determines the mass, so the masses are different. 14C is radioactive. Application of radio-Isotopes Research Industry Medicine Agriculture Animal husbundary

Carbon dating Radioactive 14C acts chemically just like 12C, so it becomes incorporated into plants an animals. When the animal/plant dies the 14C begins to decay into 14N at a know rate, so we can determine how long ago the organism died. This is called Carbon Dating. It’s only good for about 50,000 years.

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