Question

Which radiations emitted by the radioactive substance have little effect on photographic plate on ZnS screen ?

Answer 1

Bacquerel (1886) discovered that uranium salts emit some active rays called radioactive rays and the property itself was known as radioactivity. Potassium uranyl sulphate was the first compound in which radioactivity was observed. Madame Curie et al. (1898) found that thorium and radium are also radioactive substances.

Rutherford (1899) proved that there are two types of radiation i.e. -and -rays carrying (+) ve and (-) ve charge respectively. Willard (1900) discovered the third type of radiation, i.e. -rays which is neutral. Characteristics of these three types of radiation are given below.

Characteristics of -rays

(a) -rays
Nature: particle
Symbol : 
Charge : +2 unit
Mass:  (4 units)
Velocity : 
Ionizing power : maximum
Penetrating power : checked by  thin Al-foil (least)
Effect on photographic plate ZnS screen : effect more
Kinetic energy : maximum

(b) -rays
Nature: particle
Symbol : 
Charge : -1 unit
Mass:  (no mass)
Velocity : 
Ionizing power :less
Penetrating power : checked by  thin Al-foil (less)
Effect on photographic plate ZnS screen : very little effect
Kinetic energy : less

(c) -rays
Nature: electromagnetic radiation
Symbol : 
Charge : 0
Mass: 0
Velocity : 
Ionizing power : least
Penetrating power : passed through even  thin steel sheet
Effect on photographic plate ZnS screen : nearly no effect on ZnS
Kinetic energy : ×