Understanding Neutron Radiography Post Exam Reading VIII-Part 2a of 2A

Effect of Photon Energy on Attenuation
Absorption characteristics will increase or decrease as the energy of the x-
ray is increased or decreased. Since attenuation characteristics of materials
are important in the development of contrast in a radiograph, an
understanding of the relationship between material thickness, absorption
properties, and photon energy is fundamental to producing a quality
radiograph. A radiograph with higher contrast will provide greater probability
of detection of a given discontinuity. An understanding of absorption is also
necessary when designing x-ray and gamma ray shielding, cabinets, or
exposure vaults.
The applet below can be used to investigate the effect that photon energy has
on the type of interaction that the photon is likely to have with a particle of the
material (shown in gray). Various materials and material thicknesses may be
selected and the x-ray energy can be set to produce a range from 1 to 199
KeV. Notice as various experiments are run with the applets that low energy
radiation produces predominately photoelectric events and higher energy x-
rays produce predominately Compton scattering events. Also notice that if the
energy is too low, none of the radiation penetrates the material.
Charlie Chong/ Fion Zhang