(Formerly, Nuclear Science Centre)
New Delhi - 110067 India

about Radiation

Dr. S.P. Lochab * Mr. Debashish Sen  * Mr. Birendra Singh


Types of radiation

How Does it Affect ?


Effects of radiation



2010 Jan-Jun
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Website Maintained By:

Health Physics Group, IUAC

Inter University Accelerator Centre, Aruna Asaf Ali Marg, Post Box-10502, New Delhi-110067. India

Phone: +91-11-26893955  Ext. 131 (O), Fax: +91-11-26893666







ABOUT Radiation

Radiation is a process in which a body emits energy that propagates through a medium, or through empty space, to be absorbed by other bodies. It can be further classified as Ionizing and Non Ionizing radiation.Ionizing radiation consists of subatomic particles or electromagnetic waves that are energetic enough to detach electrons from atoms or molecules, ionizing them. The occurrence of ionization depends on the energy of the impinging individual particles or waves, and not on their number. An intense flood of particles or waves will not cause ionization if these particles or waves do not carry enough energy to be ionizing. Examples of ionizing particles are energetic alpha particles, beta particles, and neutrons. The ability of electromagnetic waves (photons)) to ionize an atom or molecule depends on their wavelength. Radiation on the short wavelength end of the electromagnetic spectrum � ultraviolet, x-rays, and gamma rays - is ionizing. Non-ionizing radiation refers to any type of electromagnetic radiation that does not carry enough energy per quantum to ionize atoms or molecules � that is, to completely remove an electron from an atom or molecule. Instead of producing charged ions when passing through matter, the electromagnetic radiation has sufficient energy only for excitation, the movement of an electron to a higher energy state. Near, visible light, infrared, microwave, radio waves, and low frequency RF (longwave) are all examples of non-ionizing radiation. The light from the Sun that reaches the earth is largely composed of non-ionizing radiation, with the notable exception of some ultraviolet rays. However, most ionizing radiation is filtered out by the atmosphere. Non-ionizing radiation is not mutagenic.




Types of radiation

Alpha (α) radiation consists of Helium-4 (4He) nuclei and is stopped by a sheet of paper. Beta (β) radiation, consisting of electrons, is halted by an aluminum plate. Gamma (γ) radiation, consisting of energetic photons, is eventually absorbed as it penetrates a dense material. Neutron (n) radiation consists of free neutrons which are blocked using light elements, like hydrogen, which slow and/or capture them.


Radiation Sources

1.  Natural sources

      -cosmic ray (radiation from outer spaces) and

      -terrestrial radiation (naturally occurring radioactive materials e.g. K-40, Rb-40

2.  Man made sources

      -X-ray machines

      -Radio isotopes

      -particle accelerators


How Does Radiation Affect?

Exposure to ionizing radiation produces free electrons by ionizing atoms/molecules. These ionized entities are chemically active and can form compounds, which interfere process of cell division and metabolism.


Biological Effects:


Ionizing Radiation

1.      Delay in cell division

2.      Chromosome Breaks

3.      Cell Death

4.      Gene Mutation


Non Ionizing Radiation

In terms of potential biological effects, the non-ionizing portion of the spectrum can be subdivided into:

  1. The optical radiation portion, where electron excitation can occur (visible light, infrared light)
  2. The portion where the wavelength is smaller than the body, and heating via induced currents can occur (MW and higher-frequency RF).
  3. The portion where the wavelength is much larger than the body, and heating via induced currents seldom occurs (lower-frequency RF, power frequencies, static fields).


Interaction of Radiations with Matter

    All radiation have energy, either K.E as in the case of moving charged particle, or inherent  

    energy as in case of EM radiation. When radiation passes through matter it may interact with  

    the material, transferring some or all of its energy to the atoms of the material.

    At atomic level the radiation can interact with

    1. Nuclear region

    2. Nuclear field or extra nuclear region

    3. Can pass straight through wide open spaces with in atom, without interaction.




Roentgen (R)

The roentgen is a unit used to measure a quantity called exposure. This can only be used to describe an amount of gamma and X-rays, and only in air. One roentgen is equal to depositing 2.58 x 104 coulombs per kg of dry air. It is a measure of the ionization of the molecules in a mass of air. The main advantage of this unit is that it is easy to measure directly, but it is limited because it is only for deposition in air, and only for gamma and x-rays.

Rad (radiation absorbed dose)

The rad is a unit used to measure a quantity called absorbed dose. This relates to the amount of energy actually absorbed in some material, and is used for any type of radiation and any material. One rad is defined as the absorption of 100 ergs per gram of material. The unit rad can be used for any type of radiation, but it does not describe the biological effects of the different radiation.

Rem (roentgen equivalent man)

The rem is a unit used to derive a quantity called equivalent dose. This relates the absorbed dose in human tissue to the effective biological damage of the radiation. Not all radiation has the same biological effect, even for the same amount of absorbed dose. Equivalent dose is often expressed in terms of thousandths of a rem, or mrem. To determine equivalent dose (rem), you multiply absorbed dose (rad) by a quality factor (Q) that is unique to the type of incident radiation.

Curie (Ci)

The curie is a unit used to measure radioactivity. One curie is that quantity of radioactive material that will have 3.7x1010 transformations in one second. Often radioactivity is expressed in smaller units like: thousandths (mCi), one millionth (mCi) or even billionths (nCi) of a curie. The relationship between becquerels and curies is 3.7 x 1010 Bq in one curie.


Effects of radiation

The harmful effects of exposure to radiation are due largely to its ionizing effects. Atoms and molecules contain electrons that can be removed from their orbits rather easily. For example, if a beta particle passes through an atom, it has the ability to repel any electrons in its path, ejecting them from the atom.

The bonds that hold atoms together in molecules are made of electrons. A molecule of water, for example, consists of oxygen and hydrogen atoms held together by electrons. If radiation passes through or very near a molecule of water, it may cause electrons to be ejected from the molecule. When that happens, the water molecule may fall apart. The same process occurs in any kind of molecule, including proteins, lipids, nucleic acids, and carbohydrates, the molecules of which living organisms are constructed.

Damage to molecules of this kind can have two general effects. First, when essential molecules are destroyed, an organism is no longer able to carry on all the normal functions it needs in order to stay alive and to function properly. A person, for example, may become sick if essential enzymes (substances that speed up chemical reactions) in his or her body are destroyed.

Some of the symptoms of radiation sickness include actual burns to the skin, nausea, vomiting, and diarrhea. The specific effects observed depend on the kind of radiation to which the person was exposed and the length of exposure. For example, a person exposed to low doses of radiation may experience some of the least severe symptoms of radiation sickness and then get better. A person exposed to higher doses of radiation may become seriously ill and even die.

Exposure to radiation can have long-term effects as well. These effects include the development of various kinds of cancer, leukemia being one of the most common types. Damage to a person's deoxyribonucleic acid (DNA) can also cause reproductive defects, such as children who are born deformed, blind, mentally impaired, or with other physical or mental challenges. (DNA is a complex molecule in the nucleus of cells that stores and transmits genetic information.)





The Health Physics Group in the Centre was set up primarily for monitoring and ensuring radiation safety of the Accelerator facility as is mandatory by the Atomic Energy Regulatory Board. The activities of the group have grown in the direction of radiation research beyond the routine regulatory duties. Over a decade, this group has produced excellent output in research and given the required support towards radiation safety.


There are around 20 universities and around 30 research scholars, working with the health Physics group on various interdisciplinary research activities. A few NGO's and some Government Agencies have also used these facilities. The universities associated with this group are from all over the country.  Atomic Energy Regulatory Board (AERB) has accredited Low Background Counting System for radioactivity analysis such as 226Ra, 232Th, 40K. Indian Environmental Radiation Monitoring network (IERMON) was installed with the help of BARC. We are putting our best efforts to make these activities par excellence in co-ordination with the Atomic Energy Regulatory Board (AERB) and the various universities involved with the health physics group.


Research activities and facilities:

  • Low Background Counting System (HPGE & Atomtex)

  • Dosimetry of neutron and Gamma using Conducting Polymers and SSNTD�s

  • Low Beta Counting Setup

  • MRF and RF Enhancement Setup for Hall Effect Studies & Dosimetry

  • Four Probe Setup

  • Development of new Thermoluninescence Materials & its Dosimetry Applications.

  • Development of Conducting Polymers

  • Microscope for Track Measurements

  • Alpha source for Thickness Measurement

  • Centrifuge machine

  •  Muffle furnace (12000C)

  • Spark counter

  • TLD Reader

  • Electronic Balance

  • G M Counter

  • Distillation Set up

  • Gamma Chamber