Radioactivity | Physics for JEE Main & Advanced PDF Download

First time Henri Bacqueral observed that there are certain substance which Emitts radiation on their own and named this phenomenon as "RADIOACTIVITY " and the substance are known as "RADIOACTIVE SUBSTANCE ".

The common radioactive elements are 
URANIUM; RADIUM; POLONIUM; THORIUM, etc 

Uranium salt (potassium Uranium sulphate) was the first compound found to be radioactive. 
Tritium  is the lightest radioactive element.

Madam curie and piere curie isolated  polonium and radium from pitch blend 

Rutherford  observed that three kinds of rays are emitted by radioactive elements and named them as alpha ray,bita ray and gama ray .

1.one type of rays were deflected towards the negative plate which indicates that they carry  positive charged partials  and are called alpha rays. These rays were found to be consists of positively charged partials He  ion (Hellium nucleus).

2.The second type of Ray were deflected towards the positive electrode  which shows that these are negatively charged partials  these are called bita rays. These partials have the same (e/m) value as the cathode ray. Therefore bita partials were considered to be stream of electron.
(e/m)=1.758820×10^11

3.Third type of rays were not deflected at all and therefore they are neutral. These are called gama rays. These rays are regarded as energy electromagnetic wave. Having no charge and negligible mass.

Radioactivity is a nuclear phenomenon 

ALPHA EMISSION 
In an alpha emissions removal of 2 protons and 2 neutrons at a time from the nucleus. So,mass number is reduced by 4 unit and atomic number is reduced by 2 unit 

BITA  EMISSION ARE OF TWO TYPES 
1.Bita emissions (positron emission)
2.Bita -- emissions (simply bita emission)

1.Bita emission --- in this case inside the Nucleus when a proton is converted into neutron a new type of partials is formed called positron .

Positron is equivalent to electron in mass but the charge is opposite to electron 
Mass of positron =1/(1837) amu 
Charge on positron = 1
                                            In this case atomic number is reduced by 1 unit but there is no change in mass number. 

2.BITA --EMISSION 
In this case inside the Nucleus when a neutron is converted into proton a new type of partials is formed called  bita partial which is equivalent to electron. 
              When a bita partials is ejected from the nucleus as a result charge inside the Nucleus is increased by 1 unit. So, removal of bita partials means atomic number is increased by 1 unit but mass number remains the same. 

GAMA EMISSION 
In gama emission there is no change in atomic number and mass number but energy is reduced during gama emission.
Since gama rays is an electromagnetic wave and wave is a form of energy.

Number of alpha partials emitted =change in.                                                                                 mass
                                      4
Number of bita particals emitted =2×(number of alpha particals)-(change in atomic number)



Note: emission of 1 alpha and two bita partials gives the  isotopes

Isotope:Isotope are those particals which have same atomic number but different mass are called Isotope.