NON DESTRUCTIVE CHEMICAL ANALYSIS
Corpuscular induced and X-ray or
γ-ray induced fluorescence
Notes by:
Dr Ivan Gržetić, professor
University of Belgrade – Faculty of Chemistry
Dual nature of the microscopic
material
In 1924, Louis de Broglie suggested that just as
light exhibits wave and particle properties, all
microscopic material particles such as electrons,
protons, atoms, molecules etc. have also dual
character. They behave as a particle as well as
wave.
 Radiation with enough energy to knock electrons
out of atoms and produce ions is called ionizing
RADIATION and includes particles (protons, alpha
particles, beta particles, accelerated ions) and
rays (x-rays and gamma rays).

Induced X-ray florescence

Primary (incidet) radiation that can induce
X-ray fluorescence could be dividet into
three major groups:
◦ Corpuscular induced fluorescence
◦ X-ray induced fluorescence (wave induced)
◦ γ-ray induced fluorescence (wave induced)
Corpuscular induced
fluorescence
Electrons, protons, alpha particles
or ions

The radiation associated with subatomic
particles, such as electrons, protons,
alpha particles or ions, which travel in
streams at various velocities. All such
particles have definite masses and have
radiation properties very different from
those of electromagnetic radiations, which
have no mass and travel as waves at the
speed of light.
Electron induced X-ray fluorescence
Common particles used for induced
fluorescence are electrons and protons.
 Electron induced X-ray fluorescence is
tightely bond to instruments like electron
microscopes equiped with appropriate
spectrometers for x-ray detection.

Scanning electron microscope - SEM
SEM with EDS and WDS
EDS – Energy dispersive
spectrometer
WDS – Wavelength dispersive
spectrometer
Electron sample intereaction
SAMPLE and SEM SIGNALS

Backscattered electrons are electrons which have been
emitted from the primary beam and have reacted elastically
with the sample's atoms. They are sent back almost in the
same direction as the one they came from, and with very little
energy loss. Chemical elements that have a high atomic
number produce more backscattered electrons than the ones
that have a low atomic number. The areas of the sample with a
high atomic number will thus look whiter than the ones with a
low atomic number (high phase contrast).
SAMPLE and SEM SIGNALS

Secondary electrons are emitted when the
primary beam that has lost a part of its own energy,
excites atoms of the sample. The secondary electrons
have a little energy (about 50 eV) divided up on a
large spectrum. Pictures obtained with the secondary
electrons mostly represent the topography of the
sample and they have very little phase contrast.
SAMPLE and SEM SIGNALS

X-ray emision is electromagnetic radiations
induced by primary (incident) radiation. The
energy of the secondary X-rays produced from
atomes present in the sample in SEM are usualy
between 0.5 et 30KeV.



Auger electrons
Continuum
...
SAMPLE and SEM SIGNALS

Intereaction volumen, depth of signal and
resolution
X-ray induced
fluorescence
Sample X-ray Intereaction
Saturation Depth or Penetration
Depth
The deeper the X-ray enters the sample, the more it
interacts with the sample’s atoms. An increasing portion of
the X-ray is absorbed by the sample until a specific depth is
reached beyond which the primary X-ray light can no
longer penetrate. This also applies to the fluorescent light
that must exit the sample in order to be detected.
 The lowest detectable sample layer is called the saturation
depth. The saturation depth depends on the intensity of the
X-rays, the wavelength (i.e., the type of detected atom) and
the density of the sample’s surroundings (the matrix). If
different elements are analyzed in the same surroundings,
the saturation depth increases according to the atomic
number of the element in question.

Saturation Depth or
Penetration Depth
Table of Saturation Depth or
Penetration Depth
28000 μm = 0,028 m = 28 mm ; (1 μm = 10-6 m) ; 3 mm = 3000 μm
Difference between electron and Xray impact volumen
Recommondation
The thicknes of the bulk sample should be
minimum 3 mm (5 mm).
 Thicker bulk samples are prefared for samples
made of light elements (10-15 mm minimum).
 Thin layers and film samples are treated totaly
different from bulk samples.

γ-ray induced
fluorescence
Radioactive sources
 γ-ray induced fluorescence is usualy used for Field-portable
x-ray fluorescence (XRF) also known as Hand held X-ray
analyser.
 The X-ray emitting sources usually contain nuclides that
decay by means of the electron-capture mechanism. During
the decay, a inner shell electron is captured by the neutrondeficient nucleus, transforming a proton in a neutron. This
results in a daughter nuclide that has a vacancy in one of its
inner shells, which results in the emission of corresponding
characteristic radiation.
 For example, when a 55Fe-nucleus (26 protons and 29
neutrons) captures a K-electron and becomes a 55Mn
nucleus, a Mn K-L3,2 (Mn-Kα) or KM3,2 (Mn-Kβ) photon will
be emitted.
Radioactive sources

An instrument may contain one or more
of the following radioactive isotopes:
Cadmium (Cd-109) source

The 109Cd source emits X-rays with energies of 22
and 25 keV when it decays to 109Ag in the two-step
nuclear process of electron capture and internal
conversion. In addition, a small portion (3.8%) of its
photon output is emitted at 88 keV. The 22- and 25keV emissions of this isotope may be used for the Kshell excitation of atomic numbers 22 (Ti) through 44
(Ru) and L-shell excitation of atomic numbers 67 (Ho)
through 94 (Pu).Additionally, an 88-keV co output will
excite K-shells up to lead. The isotope has a half-life of
1.24 years, meaning that after this time the source
activity is half its original value.
Americium (Am-241)

The 241Am is a source of 59.5 keV X-rays
allowing for the excitation of higher atomic
number elements. This isotope has generally been
used for the K-shell excitation of atomic numbers
45 (Rh) through 66 (Dy). However, 241Am is also
a source of lower excitations at approximately
13.95 and 17.7 keV (the neptunium L-lines).This
permits all elements from about atomic number
22 (Ti) through 94 (Pu) to be analyzed effectively
with only one radioisotope source. Furthermore,
the americium isotope has a half-life of 432 years
and therefore never requires replacement.
Useful range of X ray radioactive
sources
The range of
elements that
can be usefully
analyzed by
means of
various
radioactive
X-ray sources.
THE END