Ionizing and non-ionizing radiations are

harmful to the living beings. Radiation

shields protect people and the

environment from the harmful

effects of ionizing radiations.

Disadvantages of ionizing radiations are

(i) These cause a microscopic damage

to living tissue. These  result in skin

burns on excessive exposures.

(ii) These cause cancer.

(iii) These cause tumor.

(iv) These cause genetic damage at low exposures.

Types of Electromagnetic Radiations

  Two types, ionizing and Non-ionizing

Ionizing Radiations

Radiations with sufficiently high energy are ionizing radiations.  Ionizing radiation are Alpha particles, beta particles, gamma rays, and X-rays.

Effects of ionizing radiations

Both ionizing and non-ionizing radiations are

(a)    Harmful to organisms
(b)   Can result in changes to the
(i) Natural environment
(ii) Can disturb the ecological balance.
(c) Move an electron to a higher orbital of a big atom like calcium atom in bones.
(d) Knock an electron from the small atom, ionize the atom ( skin atoms).

Relative abilities of ionizing radiations to penetrate solid matter

  1.  A sheet of paper stops Alpha particles (α).
  2.  An aluminum plate stops Beta particles (β).
       c.  Deep matter dampens Gamma radiations (γ).

Sources of ionizing radiations

Ionizing radiations come from
 (i) Radioactive materials
(ii) X-ray tubes
(iii) Present in the environment.

Harmful effects

These radiations can cause damage to
(i) Living tissue
(ii)Skin burns
(iii) Death at high doses
(iv) Cancer
(v) Tumors

(vi)Genetic damage at low doses

Examples of ionizing radiations

  1. Gamma rays 
Gamma rays are Generation of Gamma rays is from
(i)  Nuclear reactions
(ii)  Nuclear explosions
(iii) Come from the sun
X-rays have a wavelength smaller than 10 Nano meters. A smaller `wavelength corresponds to a higher energy. It is clear according to the equation E=h⋅c/λ.
Where E is energy of 1 photon
h is Planck’s constant
c is the speed of light
λ is wavelength.
Energy of 1 photon, E = λν
An X-ray PHOTON collides with an atom, it may cause two effects
(i) It moves an electron to a higher orbital level in case of larger atoms (like calcium atoms).
(ii) It may knock an electron from the atom in small atoms (atoms of soft tissues of human body). Hence X-rays absorption is different in different atoms in a
(i) Human body
(ii)Other bodies.
This absorption difference between bone and soft tissue, allows physicians to examine structure in the human body.


The energy of non-ionizing radiation is less. It does not produce charged ions when passes through a matter. Hence less harmful than the ionizing radiations. These are electromagnetic radiations.

Examples of non-ionizing radiations

  1. Production of Radio waves is by
(i) Lightning
(ii) Astronomical objects
 Radio waves find use
(i) For fixed and mobile radio communication,
(ii) Broadcasting,
(iv) Radar and other navigation systems,
(v) Satellite communication,
(vi) Computer networks and innumerable other applications
Long radio waves (3 to 30 kHz), used only for radio signals. Shorter waves (3 to 30 Hz), used in TV.

Special features of radio waves 

Radio waves carry signals for television, cellular phones and radar signals. Radio waves
(i) 3 km to 300 m wavelength for AM Radio
(ii) 300 m to 30 m wavelength for TV
(iii) 30 m to 3 m wavelength FM Radio
(iv) 3 m to 30 cm wavelength for Cell phone
(v)Use of shorter, near infrared waves is in TV’s remote control.
  1. Thermal radiation (heat) or infra radiations

Infrared radiation comes from a common

(i) Household radiator
(ii) Electric heater
(iii) By a glowing incandescent light bulb
(iv) From a human body
(v) Sun
(vi) Boiler furnace
(vii) Heat exchangers
(viii) IC engines
(ix) Gas turbines
(x)  Steam turbines
(xi) Nuclear reactors
(xii) Air craft engines.
Infrared radiations has heat that we feel from
(i) Sunlight
(ii) A fire
(iii) A radiator
(iv) Microwaves
(v) Human body gives infrared radiations of mostly 10 microns.

Infrared Radiations from Human Body

 Human body emits mostly infra-red radiations. Net energy lost by a human being is 100 W or 100 J/s. The total energy radiated in one day is about 9 MJ, or 2000 kcal (food calories).  Humans lose energy by convection and evaporation.
  1. Visible radiations
The visible spectrum is located between 380 nm–750 nm wavelengths.
(i) Red (670–770 nm),
(ii) Orange (592–620 nm)
(iii) Yellow (578–592 nm)
(iv) Green (500–578 nm)
(v) Blue (464–500 nm)
(vi) Indigo (444–464 nm)
(vii) Violet (444-380 nm).
The energy of the photon is inversely proportional to the wavelength.  Lowest energy is for red and highest for blue.

Physical sizes of waves

S. No.

Type of wave

Size of wave

Radio waves
Gamma rays

 Parameters of a radiation

Energy, Wavelength and Frequency
Use of energy is for X- ray.
Microwave refers to Wavelength of a radiation
Use of  Frequency is for a radio wave.
These is a mathematical relation between these.

Applications of non ionizing radiations 

(i)  microwaves
(ii)  Television, radios, telephones, remote and cell phones.

Application of ionizing radiations

(i). Medical applications – Use of Ionizing radiations is for diagnosis and treatment.
(a). Doctors use X-rays  to find broken bones and to locate cancers.
(b). Research work
Researchers use radioactive atoms to determine the age of materials.

 Reduction of Harmful effect of Radiations 

(i) Reducing the time of exposure

(ii) Inverse square law reduces bad effect with increasing distance.

(iii)  Provide a biological shield. It is a mass to absorb radiations. It surrounds a

reactor giving radiations. This shield reduces the radiations to a safe level for human beings.


Irradiance is ionizing radiations incident on the surface per unit area per unit time.

It is in W/m2. Irradiation is use of high energy radiations for

(i) Medical treatment

(ii) Sterilization of food and preservation of food.

(iii) X-rays and other high energy radiations kill cancer cells and shrink tumors.

(iv) Sterilizing milk/foodstuff

(v) Inducing polymerization of monomers

(vi) Vulcanization of rubber

The term irradiation usually EXCLUDES the exposure to non-ionizing radiation. Non-ionizing radiations are from microwaves, cellular phones. Radio and TV transmitters give these electromagnetic waves.

Spectral irradiance

It is energy incident for a particular one frequency only. Its units will be W/m/nm or W/m3.

Intensity of radiation

 Amount of energy emitted/m2 s /unit solid angle. The radiation from a surface has different intensities in different directions. The intensity of radiation normal to the surface is intensity of normal radiation.

Applications of irradiation


Used in sterilization, diagnosis and cancer treatment.

Industrial chemistry

Irradiation cross links polymers.


(i) Irradiation prevents sprouting of onions, garlic and potatoes.

(ii) Appropriate irradiation produces sterile insects.

(iii) Irradiation approves the fitness of meat and poultry products.              Q. ANS Radiation