Industrial Machinery News

Archive for the ‘X-Ray Theory’ Category

The property of being absorbed by matter is very important for the application of x-rays in contaminant detection. Because higher density objects have smaller subatomic distances, they absorb more x-rays than lower density ones do. In reality, it is impossible to quantitatively examine the ability of materials absorbing x-rays without going into complex considerations on their subatomic structure. The following chart, as an example, shows how water in liquid phase absorbs x-rays as a function of x-ray energy. It should be noted that the graph is non linear.

Absorption in water.

In the graphs, :/D is the mass attenuation coefficient, and :en/D is the mass energyabsorption coefficient (defined in ICRU report 33, 1980). The graphs have been taken from NIST Physics Laboratory, Physical Reference Data (See http://Physics.nist.gov/PhysRefData).

If we consider a solid material, like glass lead, we can observe that there are points of

discontinuity because, at certain energies, x-rays match the energy of the orbital of the

atoms.

Absorption in glass lead.

To a first approximation, the mass attenuation coefficient varies as the third power of the atomic number of the absorber. (See X-Ray Fluorescence Spectrometry Second Edition, Ron Jenkins, edited by JohnWiley & Sons, Inc, section 1.1).

It is not our intention to go any further into this subject. We only wanted to show that considerations about the nature of the materials are essential in the design of an x-ray inspection machine. This is true for every part of the machine that can be exposed to x-rays, either in an active or in a passive mode.