Lecture-1

                                Radiation Sources

        What is the definition of Radiation Protection?

  —Radiation protection may be defined simply as effective measures employed by radiation workers to safeguard patients, personal, and the general public from unnecessary exposure to ionizing radiation.

  —Example of ionizing radiation:

         X ray, γ ray

           Objectives

               By the end of this lecture you have learnt:

    ØSource of radiation

                 Natural (background) source

                 Manmade(Artificial) source

   ØBiological damage potential of radiation

                 Meaning of biological effect

                Radiation interaction with atom

                Type of biological effect

           Source of radiation 

                Human beings are continuously exposed to source of ionizing radiation.

                Source of ionizing radiation may be:

                 I.Natural (background) source

                 II.Manmade(Artificial) source

             I.Natural background source

              The natural source of ionizing radiation have always been a part of the human environment since   the formation of the universe.

           Background radiation comes from three main sources:

            1.Cosmic radiation

            2.Radiation from terrestrial sources

            3.Internal, radioactivity in the body

          Cosmic radiation

   —Comes from the sun and beyond the solar system

   —Cosmic Radiation collides with proton nucleus creating secondary particles thus destroying the nucleus

                                                    

     Questions     

             1.How the Earth could be protected from cosmic rays?

             2.Compare between dose rate at sea-level and at high altitudes?

 

          2. Terrestrial radiation

   —Radiation from radioactive materials occurring naturally in the earth's crust.

   —The rocks and soil of the Earth’s strata contain small quantities of the  radioactive element,    such  as uranium-239, radium-226, and thorium-232, which emit   densely ionizing radiations.

             Approximately 55% of the gross common exposure of human beings to the natural background radiation comes from radon

              Question:

           High indoor concentration of radon have the potential to cause serious health hazards for human, how?

          3. Internal, radioactivity in the body

          The tissues of the human body contain many naturally existing radionuclide that have been ingested  from various foods or inhaled as particles in the air.

       For example: potassium-40, carbon-14, hydrogen-3

             II.Manmade(Artificial) radiation

               There are several sources of human exposure that have arisen only over the last 100 or less. These are:

    —Diagnostic radiology

    —Therapeutic radiology

    —Use of radioisotopes

    —Radioactive waste

    —Atmospheric fall-out

    —Occupational exposure

 

             Biological damage potential of radiation

   —What biologic effect means?

                     Radiation Causes Ionizations of ATOMS

                     which may affect

              Thus, all biological damage effects begin with the consequence of radiation interactions with the atoms forming the cells. As a result, radiation effects on humans proceed from the lowest to the highest levels as noted in the above list.

              Even though all subsequent biological effects can be traced back to the interaction of radiation with atoms, there are two mechanisms by which radiation ultimately affects cells. These two mechanisms are commonly called

1.Direct effect

2.Indirect effect

   —Direct effect:

                                                                          

                    If radiation interacts with the atoms of the DNA molecule, or some other cellular component critical to the survival of the cell, it is referred to as a direct effect. Such an interaction may affect the ability of the cell to reproduce and, thus,survive.           

                                             

  

   —Indirect effect

                 When radiation interacts with water, it may break the

                 bonds that hold the water molecule together, producing

                 fragments such as hydrogen (H) and hydroxyls (OH).

                 These fragments may recombine or may

                interact with other fragments or ions to form compounds,

                such as water, which would not harm the cell.

                However, they could combine to form toxic substances,

                such as hydrogen peroxide (H2O2), which can

                contribute to the destruction of the cell.

Biological Effect

        The effects of radiation on the human body as a whole arise from damage to individual cells, but the two types of change have quite different results.

       1.Deterministic effect.

       2.Stochastic effect.