Computed Tomography (CT)
is a powerful nondestructive evaluation
(NDE) technique for producing 2-D and
3-D cross-sectional images of an object
from flat X-ray images. Characteristics
of the internal structure of an object
such as dimensions, shape, internal defects,
and density are readily available from
Photon Induced Positron
& Distributed Source Positron Annihilation
Photon Induced Positron
Annihilation (PIPA) involves penetrating
materials with a photon beam. This process
creates positrons, which are attracted
to nano-sized defects in the material.
Eventually, the positrons collide with
electrons in the material and are annihilated,
releasing energy in the form of gamma
rays. The gamma ray energy spectrum creates
a distinct and readable signature of the
size, quantity and type of defects present
in the material.
Distributed Source Positron
Annihilation (DSPA) uses a positron source
emitter to deposit positrons into the
subject material. The process is similar
to PIPA after the positrons are deposited
and attracted to nano-sized defects in
PIPA and DSPA technologies
detect fatigue, embrittlement, and other
forms of structural damage in materials
at the atomic level, before cracks appear.
PIPA and DSPA can also accurately determine
the remaining life of various materials
and are more precise than any other existing
flaw detection technology on the market.
Neutron Radiography is
an imaging technique which provides images
similar to X-ray radiography. The difference
between neutron and X-ray interaction
mechanisms produce significantly different
and often complementary information. While
X-ray attenuation is directly dependent
on atomic number, neutrons are efficiently
attenuated by only a few specific elements.
For example, organic materials or water
are clearly visible in neutron radiographs
because of their high hydrogen content,
while many structural materials such as
aluminium or steel are nearly transparent.
At the present time, Neutron Radiography
is one of the main NDT techniques able
to satisfy the quality-control requirements
of explosive devices used in aerospace
and defense programs.
X-ray Diffraction (XRD)
X-ray diffraction is a versatile, non-destructive
technique that reveals detailed information
about the chemical composition and crystallographic
structure of natural and manufactured
A crystal lattice is a
regular three-dimensional distribution
(cubic, rhombic, etc.) of atoms in space.
These are arranged so that they form a
series of parallel planes separated from
one another by a distance d, which varies
according to the nature of the material.
For any crystal, planes exist in a number
of different orientations - each with
its own specific d-spacing.
When a monochromatic X-ray
beam with wavelength lambda is projected
onto a crystalline material at an angle
theta, diffraction occurs only when the
distance traveled by the rays reflected
from successive planes differs by a complete
number n of wavelengths.
By varying the angle theta,
the Bragg's Law conditions are satisfied
by different d-spacings in polycrystalline
materials. Plotting the angular positions
and intensities of the resultant diffracted
peaks of radiation produces a pattern,
which is characteristic of the sample.
Where a mixture of different phases is
present, the resultant diffractogram is
formed by addition of the individual patterns.
Based on the principle
of X-ray diffraction, a wealth of structural,
physical and chemical information about
the material investigated can be obtained.
A host of application techniques for various
material classes is available, each revealing
its own specific details of the sample
X-ray fluorescence is
a technique of chemical analysis. The
technique involves aiming an X-ray beam
at the surface of an object; this beam
is about 2 mm in diameter.
The interaction of X-rays with an object
causes secondary (fluorescent) X-rays
to be generated. Each element present
in the object produces X-rays with different
energies. These X-rays can be detected
and displayed as a spectrum of intensity
against energy: the positions of the peaks
identify which elements are present and
the peak heights identify how much of
each element is present.
This is often used by
museum curators to study ancient objects
because measurements are non-destructive
and usually the whole object can be analyzed,
rather than a sample removed from one.