Gamma Radiation

What are gamma rays?

      A gamma ray is a packet of electromagnetic energy--a photon. Gamma photons are the most energetic photons in the electromagnetic spectrum. Gamma rays (gamma photons) are emitted from the nucleus of some unstable (radioactive) atoms

What are the properties of gamma radiation?

     Gamma radiation is very high-energy ionizing radiation. Gamma photons have about 10,000 times as muchenergy as the photons in the visible range of the electromagnetic spectrum.



     Gamma photons have no mass and no electrical charge--they are pure electromagnetic energy.
Because of their high energy, gamma photons travel at the speed of light and can cover hundreds to thousands of meters in air before spending their energy. They can pass through many kinds of materials, including human tissue. Very dense materials, such as lead, are commonly used as shielding to slow or stop gamma photons.


     Their wave lengths are so short that they must be measured in nanometers, billionths of a meter. They range from 3/100ths to 3/1,000ths of a nanometer.
 

 
 
 
About Gamma Radiation

- The coulomb per kilogram (C/kg) and is the amount of radiation required to create 1 coulomb of charge of each polarity in 1 kilogram of matter.



- The Gray(Gy) which has units of (J/kg) and is the amount of radiation required to deposit 1 joule of energy in 1 kilogram of any kind of matter.



 Shielding

   

 Shielding from gamma rays requires large amounts of mass. They are better absorbed by materials with high atomic numbers and high density, although neither effect is important compared to the total mass per area in the path of the gamma ray. For this reason, a lead shield is only modestly better (20-30%) as a gamma shield than an equal mass of another shielding material such as aluminum, concrete, or soil; the lead's major advantage is in its compactness.

 

 

 

Matter interaction

 

      The total absorption coefficient of lead (atomic number 82) for gamma rays, plotted versus gamma energy, and the contributions by the three effects. Here, the photoelectric effect dominates at low energy. Above 5 MeV, pair production starts to dominateWhen a gamma ray passes through matter, the probability for absorption in a thin layer is proportional to the thickness of that layer. This leads to an exponential decrease of intensity with thickness. The exponential absorption holds only for a narrow beam of gamma rays. If a wide beam of gamma rays passes through a thick slab of concrete the scattering from the sides reduces the absorption.

 

     Here μ = nσ is the absorption coefficient, measured in cm−1, n the number of atoms per cm3 in the material, σ the absorption cross section in cm2 and d the thickness of material in cm.

Video shows Gamma Radiation

Credit : stoller-eser , wikipidia