The purpose of the experiment is to determine buildup factor for given source. The experiment
involves firing a narrow beam of gamma-rays at a material and measuring how much of the
radiation gets through. We vary the type of absorbing material as well as its thickness and
density by interposing iron, aluminum, and copper absorbers of different thicknesses t between
the source and the detector. Buildup factor is determined by using two geometries, first the
counts are taken for good and bad geometry and then buildup factor is determined from it.
Another method used for measuring build up factor is determining buildup factor by using multi
channel analyzer.
Build up factor:- The factor by which the total value of the quantity being assessed at the point
of interest exceeds the value associated with only primary radiation. The total value includes
secondary radiations especially scattered radiation.
The gamma-ray buildup factors for point isotropic sources in infinite homogeneous media have
been widely used in gamma-ray shielding calculations. Considerable effort has been devoted
to developing methods of calculating buildup factors taking into account multiple scattering
of gamma-ray. The data set of gamma-ray buildup factors was first developed by Goldstein
theoretical value by some factor called build up factor. This increase in intensity of gamma rays
at observation point is due to many effects one of which is scattering of gamma rays from some
material. Theoretical value by some factor called build up factor. This increase in intensity of
gamma rays at observation point is due to many effects one of which is scattering of gamma rays
from some material.
Buildup factors vary with a number of parameters such as the distance of penetration through
the attenuating medium; the geometric configuration of the attenuating medium, source and
detector position; the composition of the medium; the detector response function; and the energy
and direction of emission of the source photons, ideally taken to be monoenergetic and
isotropic.
Why Build Up Factor Is Needed:- when radiation is incident on some attenuator material then
beside some other process also take place. The collision processes depend very much on the type
of particles involved in the collision. Heavily ionizing particles such as, alpha particles or
protons are very easily stopped by a small amount of material because they leave a dense trail of
ions. They are not generally removed by a single collision but slowed with energy going into the
ionizing process. On the other hand, electrons scatter off other electrons and in this process, lose
energy and produce a gamma. Subsequently, the gamma may react with another electron to
produce an electron and gamma. This process is called a gamma cascade which is complicated
to calculate.
Due to these many processes radiation passed through attenuator is not only given by attenuation
constant but also by another constant called build up factor. This build up factor has a number of
uses in radiation shielding.
Attenuation:-. When radiation falls on some material then some of radiation is blocked by
material by some processes like stopping or blocking by its nucleus. This property is used in
radiation shielding of material. Material having higher cross section of radiation stopping is used
in radiation shielding.
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