X-ray Spectroscopy
4
4.1 What are X‐rays?
X‐rays are electromagnetic radiation: another region in the spectrum, along with ultraviolet, infrared,
visible etc. They are characterised by very short wavelengths, meaning high frequencies and high
energies. The wavelength range of the X‐ray region is 0.01 to 10 nm, compared to 400‐800 nm for
the visible region. This makes X‐ray photons up to 80000 times more energetic than visible radiation.
There are two other units commonly used in reference to X‐rays: another wavelength unit, the
Angstrom (Å) and the electron volt, a measure of energy (expressed as keV). Their relationship is
shown in Eqn 4.1.
10Å = 1 nm = 1.24 keV
Eqn 4.1
Note that the nm/keV relationship is inverse because wavelength and energy are inversely related.
X‐rays are produced in three ways:
1.
when high energy electrons collide with a surface, and are slowed down by the collision; the
loss of energy produces a continuous band of X‐ray wavelengths
2.
emissions from decaying radioactive nuclei
3.
emission of X‐rays from matter which has been irradiated with a X‐ray beam; the emitted
X‐rays are single wavelengths, and of different energies to the excitation beam
Processes 1 & 2 are employed in X‐ray sources, while process 3 produces fluorescent radiation,
exploited in the important analytical technique, X‐ray fluorescence, which this chapter concentrates
on.
4.2 Dangers associated with X‐ray use
The high energies associated X‐rays mean that they are potentially harmful to living organisms,
because of the chance that the energy will be absorbed by molecules in the organism. This can cause
destruction or alteration to the molecules absorbing the energy. The damage may be direct ‐ the
photon breaks bonds in an important molecule, or indirect ‐ the photon splits water, forming the
very reactive hydroxyl radical, which then reacts with an important biochemical substance.
If the species affected is genetic material, i.e. DNA, then the chance exists for mutated cells to
be produced, leading to the formation of cancers. The effect is cumulative: this is why there is a
limited number of body X‐rays that a person can have with in a set period of time. Too many
increases the number of damaged molecules and therefore, the chance of serious health
consequences.
There are a number of ways that limit the possible dangers associated with X‐ray use:

instruments using them are thoroughly sealed (usually with lead) so that no radiation should
escape

the seals are checked on a regular basis

where the instrument has removable panels which can, if opened, allow the X‐rays to escape,
then microswitches are employed which will trip out the X‐ray source within milliseconds,
eliminating substantial risk of accidental exposure

operators of X‐ray instruments wear radiation badges which are developed each month to
check the levels of exposure
4. X‐ray Spectroscopy
4.3 X‐ray spectroscopic techniques
X‐rays are used analytically in three different techniques:



X‐ray fluorescence (XRF) – where the emission of characteristic wavelength X‐rays from
matter irradiated by an X‐ray beam is used to identify and quantify particular elements
X‐ray diffraction (XRD) – where X‐rays are deflected through characteristic angles (diffracted)
by the crystal structure of the matter; this can be used for spectral fingerprinting, especially of
minerals
X‐ray absorption (XRA) – which is the familiar use of X‐rays to laypersons in medicine and
materials testing, where the varying density of matter causes variation in the absorption of the
X‐ray beam. Bones are denser than tissue and absorb more radiation, hence giving high
absorption, while defects (holes) in a metal component are picked by a X‐ray absorption scan
because the X‐rays pass unabsorbed through them
Only XRF – most useful for chemical analysis – will be examined in this course.
4.4 X‐ray fluorescence
As you might expect from the name, X‐ray fluorescence is a emission technique, where the radiation
measured from the sample is of different (and higher) wavelengths than the incident radiation.
A little bit of history (non‐examinable)
The 1895 discovery of X‐rays by Wilhelm Roentgen was also the discovery of X‐ray fluorescence,
though Roentgen did not do anything with this aspect of his work. In 1913, Henry Mosley showed
that the generated X‐rays were characteristic of particular elements, and that the wavelengths were
related to atomic number. It was this discovery by Mosley that caused the re‐ordering of the
elements in the periodic table away from atomic mass, and removed some of the anomalies in
Mendeleev’s table.
In the following decade, a number of physicists, including Mosley and the Bragg brothers,
struggled to design equipment that could efficiently generate fluorescent X‐rays, using electron
beams as excitation. In 1928, Glocker and Schreiber showed that using a beam of X‐rays to excite
fluorescence was a better way and actually carried out quantitative analysis of real samples.
However, this discovery did not lead to immediate developments because of problems in separating
different wavelengths (monochromation) and detecting the radiation.
In 1948, Friedman and Birks took some of the components of an X‐ray diffraction instrument
and built the first XRF spectrometer as would be recognised today. The first commercial instruments
were released in the 1950s, and the next two decades were dominated by improvements in
detection systems, particularly the silicon drift semiconductor detector discovered in 1970.
Generation of fluorescent X‐rays
As with other forms of spectroscopy that you are familiar with – eg UV/VIS, AAS, flame emission –
XRF deals with the electrons. In those other spectroscopic techniques, the electrons were simply
moved up and down in their orbitals, whereas in XRF, electrons are actually ejected from the atom.
A second difference is that in XRF it is the inner shell electrons that are affected, whereas in the
others, it is those in the outer shell.
The emitted radiation is produced after an inner shell electron (most commonly from one of
the first two shells – the old symbols K&L tend to be used rather than 1st and 2nd orbitals – in an
atom) is ejected entirely from the atom by incident X‐rays (Figure 4.1(a)).
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4.2
4. X‐ray Spectroscopy
This creates a "hole" in the electron shells, which is filled by electrons in higher shells. A cascade
effect can occur since an electron dropping down a level to fill a hole creates a hole which in turn, is
filed from a higher shell again (Figure 4.1(b)).
Since the electrons are moving to lower energy levels, they lose the excess energy in the form
of radiation (Figure 4.1(c)).
M shell
M&L
electrons
drop down
L shell
X‐ray
X‐rays
emitted
K electron
ejected
K shell
(a)
(b)
(c)
FIGURE 4.1 Electron transitions involved in X‐ray fluorescence
The transitions in XRF are given labels which identify them when a spectrum is recorded. The labels
indicate:


the shell from which the electron was ejected – K or L, very rarely M
the shell from which the filling electron came – the Greek letters , , and  indicate that the
filling electron came from 1, 2 or 3 shells respectively, from the hole
Transitions from KL, MK, ML and NL shells produce radiation of X‐ray energy for most
elements (except the very light ones).
CLASS EXERCISE 4.1
(a) What are the two transitions shown in Figure 4.1?
Draw the transitions corresponding to the labels K and L.
(b)
N
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M
L
K
4.3
4. X‐ray Spectroscopy
Why are these labels important? There are important trends in wavelength and intensity that can be
followed for these transitions (shown in Table 4.1), which can help identify the presence of species in
a sample, and also are a shorthand way of referring to certain characteristic emissions.
TABLE 4.1 Energy and intensity trends for X‐ray fluorescent photons
Trend
Behaviour
Energy for a given element
K > K >> L > L
Intensity for a given element
K > K >> L > L
Energy for a given transition
Increases with increasing atomic number (see Figure 4.2 & Table 4.2)
CLASS EXERCISE 4.2
Explain the order of energies for the four transitions.
TABLE 4.2 Energies (keV) of selected element XRF lines
Element
K
K
L
L
Ca
3.69
4.01
0.34
0.35
Cr
5.41
5.95
0.57
0.58
Fe
6.40
5.06
0.71
0.72
Sn
25.19
25.48
3.44
3.66
Pb
74.22
84.92
10.55
12.61
100
80
K
60
keV
40
20
L
0
10
20
30
40
50
60
70
80
90
Atomic Number
FIGURE 4.2 Energies of K and L transitions vs atomic number
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4.4
4. X‐ray Spectroscopy
Given that the K line is the most intense for each element, there might seem to be little use for the
other lines. Qualitatively they help in making a definite identification, but they also have use
quantitatively because for reasons of excitation and detection, there are limits on which elements
can be analysed by their K line. This is covered in more detail later.
4.5 XRF instrumentation
There are two basic designs of XRF instruments, mainly due to the development of the
wavelength‐selective semiconductor detectors described above. These two instrument types are
known as:

wavelength‐dispersive – the older type, using a conventional monochromator‐based design to
separate the fluorescent wavelengths (Figure 4.3)

energy‐dispersive – uses a special detector which doesn't require a monochromator (Figure
4.4)
sample
holder
emitted
radiation
single 
many s
excitation
X-rays
detector
path
detector
collimator
X-ray
source
dispersing
crystal
FIGURE 4.3 Schematic diagram of a wavelength‐dispersive XRF instrument (with moving detector)
The wavelength‐dispersive instrument uses a monochromator where the emitted wavelengths are
diffracted by a crystal at different angles. “Conventional” spectroscopic instruments, such as UV‐VIS
spectrophotometers, are designed so that the diffraction medium rotates and one wavelength at a
time leaves the exit slit. In XRF instruments which are designed for high resolution work, both the
diffracting crystal and the detector unit move around a circular track (known as a goniometer),
picking up one wavelength after another. ICP emission instruments also use this design.
FIGURE 4.4 Schematic diagram of a energy‐dispersive XRF instrument
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4.5
4. X‐ray Spectroscopy
The eneergy‐dispersive instrumeent has a keey componen
nt that makkes it very different to the
t older
wavelength‐dispersivve design: its semicond
ductor deteector has th
he unique ability to bee able to
or physical se
eparation. Itt is thus a
distinguiish between photons of different eneergy withoutt the need fo
single‐deetector multtichannel insttrument, witth the advan
ntages that su
uch a configu
uration bringgs:

sim
mplicity

sp
peed

co
ost

sizze
dispersive instruments can
c be small benchtop designs,
d
or even
e
hand‐held battery‐‐powered
Energy‐d
XRF deviices, capablee of being ussed in the fieeld or in the factory
f
(as sh
hown in Figu
ure 4.5). They are not
as accurrate as a lab
boratory devvice, but havve obvious convenience advantages (think abou
ut an ion‐
selectivee electrode vs
v a HPLC fo
or measuringg nitrate). They
T
can also
o be used to
o analyse larrge items
which caannot be fitteed into a con
nventional in
nstrument. Examples
E
of this include valuable works of art
and anciient artefacts unearthed in archaeolo
ogical excavaations (see Figure 4.6).
Ho
owever, wavelength‐disspersive insttruments arre
still impo
ortant becau
use they aree more sensittive and havve
better rresolution th
han energy‐‐dispersives. The “bestt”
XRF insstruments in
n terms off absolute performancce
remain w
wavelength‐‐dispersive, and
a can costt in excess of
o
$300,000
0!
on source
Radiatio
The X‐raay tube conssists of a heaated wire caathode, whicch
emits electrons. Th
hey are acceelerated tow
wards to th
he
m
known
n as the target ‐ and th
he
anode ‐ a block of metal
us
collision releases energy in the form of a continuou
m of X‐rays. A schematiic diagram of
o the tube is
spectrum
shown in
i Figure 4.7 below. Th
he tube is evacuated to
t
avoid ccomplication
ns caused by ionisattion of gaas
moleculees.
FIGUREE 4.5 Portablle energy disspersive
XRF insttrument (courrtesy of InnovX
Xsys)
FIGURE 4.6
4 Portable energy
e
disperssive XRF instru
ument used to
o analyse a reeligious paintin
ng in position (Kriznar
et al, 9th Internationall Conference on
o NDT of Art))
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4.6
4. X‐ray Spectroscopy
window
X-rays
target
electrons
cathode
FIGURE 4.7 Schematic diagram of an X‐ray tube
There are three variables that affect the output of an X‐ray tube (as shown in Figure 4.8):

applied voltage between the electrodes

current

the material used on the surface of the target exposed to the electron beam.
Target anodes are made from a block of copper, with a coating of another metal on the surface
which takes the electron impact. The block is water‐cooled to remove the heat which accumulates as
part of the collision process. Metals commonly employed as the contact surface are rhodium,
tungsten and molybdenum. Heavier elements generate more radiation, as can be seen in Figure
4.8(c).
FIGURE 4.8 Effect on X‐ray tube output of (a) tube current (b) applied potential and (c) target element (from
Bertin, Introduction To X‐ray Spectrometric Analysis, Plenum).
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4.7
4. X‐ray Spectroscopy
CLASS EXERCISE 4.3
Complete the table below, to summarise Figure 4.8.
Tube Variable
Wavelength Range
Intensity
Voltage
Current
Target element
The continuous spectrum shown in Figure 4.8 is not quite accurate, as the real output has two or
more peaks superimposed. These are due to X‐ray fluorescence processes occurring in the atoms of
the target. These may cause an interference in XRF that must be allowed for or removed, or can be
used as a monochromatic source of X‐rays, if appropriate filtering is available, as occurs in XRD.
Rhodium, for example, the target metal in the XRF instrument in this department, emits lines at 2.7,
2.8, 3.0, 20.2 & 22.7 keV.
The only option for many years to the X‐ray tube was a radioactive source, which generated a
range of X‐ray wavelengths, without the need for electrical power. However, the problems of
radioactive sources and the lower output intensities reduced the usability of these sources.
Traditionally, X‐ray tubes require large quantities of electrical power: typical operating
conditions may be 35kV and 30 mA (1.05 kW), necessitating connection to the mains power supply.
Low current X‐ray tubes (10‐100 uA) have been recently developed which have allowed battery‐
powered portable devices for field analysis and small desktop instruments, such as the Minipal we
have.
CLASS EXERCISE 4.4
What would be the main disadvantage of these low current X‐tubes?
Voltage is the most important variable in X‐ray fluorescence because it is determines the energy of
the exciting photons, and therefore which elements will be excited. The keV unit for X‐ray energy is
related to the voltage needed to excite a particular element line. An electron accelerated towards a
positive electrode with a voltage equal to that keV value (in kV) has the energy contained in that X‐
ray. To excite the element that generates that fluorescent X‐ray typically requires a tube voltage
twice the keV value.
EXAMPLE 4.1
The K line of calcium has an energy of 3.69 keV. What tube voltage needed to excite this line?
2 x 3.69 = 5.38 kV.
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4.8
4. X‐ray Spectroscopy
CLASS EXERCISE 4.5
The X‐ray tube in our instrument has a maximum voltage of 30kV. What is the maximum atomic
number for an element that can have its K line excited (see Figure 4.2)?
Detectors
There are three common X‐ray detectors:



semiconductor
gas‐filled/flow/proportional
scintillation
Semiconductor detectors are used in energy‐dispersive devices, while the other two are used
together in wavelength‐dispersive instruments. The reason that two detectors are required in WD
instruments is that neither covers the full range of X‐rays. Their mechanism of operation is described
below.
SEMICONDUCTORS
The most recent development in X‐ray detection is the silicon drift detector (using semiconductor
technology). The precise means by which X‐rays are detected by such a device are beyond the scope
of this course. The most important aspect of this detector is its ability to produce an output (a
current pulse) that is proportional to the energy of the incoming photon.
It can do this for polychromatic radiation equally well, when linked with pulse‐height counting
equipment. This sums the number of pulses of each amount of current (e.g. 1, 1.1, 1.2 uA) and so the
final spectrum is really a plot of number of pulses vs current. A correlation between energy and
current must be made by some internal setting in the detector, eg a current pulse of 1.2 uA is created
by a photon of 2.5 keV energy.
This unique ability means that energy‐dispersive instruments do not need a monochromator
with the all the multi‐channel‐type advantages that brings. The two major limitations are:


resolution ‐ the ability to distinguish between photons of similar but not identical energy is not
perfect
sensitivity – there is a maximum count rate (in our instrument, it is 60,000 per second) above
which the detector is overloaded
It is not clear why similar detectors have not been developed in other regions of the electromagnetic
spectrum, especially the UV‐VIS where so many instruments operate.
PROPORTIONAL (OR FLOW) COUNTERS
X‐rays have sufficient energy to ionise atoms. This ability is exploited in a number of detectors, which
use a chamber filled with an inert gas, such as argon, and electrical plates which collect the ions that
are produced.
The chain reaction may generate hundreds of electrons and ions from the one photon. The
degree to which the chain reaction proceeds depends on the applied voltage between the collector
plates and the energy of the photons. The most commonly used voltage range is 800‐1000V, where
the response of the detector is approximately linear which voltage. This region is known as the
proportional region, and a detector using this behaviour as a proportional counter.
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4.9
4. X‐ray Spectroscopy
A typical proportional counter is shown below in Figure 4.10. A small flow of gas is normally passed
through the detector to keep it at a constant pressure. The gas is 90% argon/10% methane. These
detectors are also known as flow counters. Proportional counters are most suited to X‐ray photons
from 1.5‐25Å (because these detectors are used in WD instruments, wavelength is the usual unit),
which in terms of X‐ray fluorescence, come from the lighter elements.
X-rays
gas in
anode
cathode
FIGURE 4.9 Schematic diagram of a proportional flow counter
SCINTILLATION COUNTERS
The term 'scintillation' means the generation of multiple photons of visible light from matter, which
has absorbed a higher energy photon, e.g. an X‐ray. Certain crystalline substances possess this
property. The most widely used scintillation crystal is sodium iodide, which has been doped
(contaminated) with a about 0.2% thallium iodide. Some organic substances, often in solution, are
also used.
Each X‐ray photon that enters the scintillation chamber can produce thousands of visible
wavelength photons. These are measured by a conventional photomultiplier tube.
Scintillation counters are best used for shorter wavelength X‐rays, from heavier elements, and
so complement proportional counters in their range of operation.
Figure 4.10 shows the ranges available from each type of detector. Where they overlap,
neither works perfectly, and unfortunately, this is the region in XRF where the commercially
important metals such as iron, chromium and manganese produce lines.
Å ()
0.5
1.0
1.5
2.0
2.5
5
10
20
Scintillation
Flow
FIGURE 4.10 Detector ranges
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4.10
4. X‐ray Spectroscopy
4.6 Qualitative analysis
XRF is an ideal qualitative technique for elements above sodium, because of its limited sample
preparation. Solids are in fact more easily analysed than solutions. Granular solids need only be
ground into a powder, while fixed‐shape materials only require a polish.
The technique is non‐destructive which means that valuable samples can be analysed without
risk of damage. This allied with the portability of an energy‐dispersive instrument means that works
of art and archaeological items can be scanned in situ.
Emission lines (weak and strong) for elements are well‐known, and it is easy to identify the
components of a mixture. The rules of intensity trends for the various lines must be followed (Table
4.1). If a line which corresponds to the K emission of a particular element is found, then the K line
must also be present, and at about 20‐40% of the intensity of the K line.
XRF is a surface technique: only the top 100 um (or so) of the sample is analysed. Therefore,
for a true overall picture of the sample, it must be made homogenous. However, for a sample with
intentional layers, e.g. chrome‐plated steel, only the surface would be analysed, whereas a technique
which relied on solution or powder samples, would require that the coating layer be separated.
It is not the most sensitive technique, but the newer instruments are able to detect much
lower concentrations than before. Typically it will be able to detect concentrations of 10 mg/kg for
elements with K lines present, and about ten times this for those with only L lines sufficiently well for
qualitative purposes.
The technique does not discriminate at all between different forms of the same elements.
Iron gives exactly the same set of wavelengths, regardless of whether it is in steel, iron ore, aqueous
solution or an ionic salt.
Figure 4.11 shows an XRF spectrum, recorded using an energy‐dispersive instrument, of a dust
sample. It illustrates the ability of the technique to identify the presence of a wide range of elements.
FIGURE 4.11 XRF spectrum of a dust sample (from Christian & O'Reilly, Instrumental Analysis, Allyn & Bacon)
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4.11
4. X‐ray Spectroscopy
CASE STUDIES OF SOME UNUSUAL APPLICATIONS FOR XRF1
The authentication of Victoria Crosses
The medals for the highest military honour in Commonwealth countries are made from two melted
cannons from the Crimean War (1860s). Because of the value (monetary and emotional) of the
medals, they can only be analysed by a totally non‐destructive technique. The cannons have a very
specific elemental content, and this allows potential forgeries to be identified. Medals in a number of
New Zealand collections were analysed, compared with those of known origin in the Australian War
Museum and authenticated.
The examination of ancient artefacts from an archaeological excavation
XRF was used to determine the composition of gold figurines, weapons, paint from wall murals and
clay pots excavated on the Greek island of Thera in the remains of the 1500 BC city Akrotiri which
was destroyed by a volcanic eruption in similar circumstances to the Roman city of Pompeii.
Analysis of the pigments used in a medieval religious painting
To assist with future restoration, a large painting from the 15th century in a church in Seville, Spain,
was analysed on location by XRF to identify the pigments.
4.7 Quantitative analysis
In many respects, quantitative analysis by XRF is the same as other techniques. Standards are
prepared, an optimum line (preferably K) chosen to maximise sensitivity and calibration graphs
drawn to find the answer.
However, XRF is a technique which suffers very severely from matrix interference. As stated
above, the iron K peak may occur at exactly the same position, regardless of the matrix, but its
intensity will be very different from sample to sample. This is particularly the case when analysing
solids, since the matrix is very concentrated. The causes of the interference include:

matrix components absorbing the excitation radiation so that the amount of radiation available
to excite the analyte is reduced

matrix components absorbing the analyte fluorescence – particular prominent where elements
a few atomic number lower than analyte are present, eg when analysing nickel (atomic number
28) in steel, the high concentration of iron (AN 26) will reduce the Ni K line intensities
significantly, compared to a sample of the same concentration of Ni with no iron

fluorescence of matrix components, particularly from heavier elements, can cause additional
excitation of the analyte,

particle size variations, which cause differences in the contact area between sample and
incoming X‐rays and also the scattering of the fluorescent photons
To counter the matrix interference, a number of familiar (and not so familiar) techniques have been
employed, but by far and away, the most important is matrix‐matched standards. The normal
drawback with this method is the availability of certified reference materials (standards of exactly
known composition), but for some of important XRF‐using sectors (metals, minerals, ceramics) this is
not really a problem as such materials are readily available.
1
The complete articles are downloadable from the subject webpage. The details are not examinable but you may be
required to give an outline of the study and why XRF was useful.
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4.12
4. X‐ray Spectroscopy
For the other areas (eg soil) there are the normal methods of dealing with interferences:

standard addition – the most obvious method, but not as easy to do with solid samples;
generally a borax melt (see Sample preparation) will have to be used to ensure homogeneity

internal standard – not usually employed to deal with matrix interference; in this case, the
properties choice is an element ± 2 in atomic number from the analyte

scattered X‐ray standardisation – where a wavelength of excitation radiation (eg the Rh line)
scattered to the detector is used in the same way as an internal standard
There is a new development from one instrument manufacturer – Panalytical – known as
standardless analysis, where a large database of many different types of materials (of known
composition) is built into the software. A highly sophisticated mathematical modelling process
compensates for interferences by the elements detected in the scan. It is not perfect in terms of
accuracy, but the great majority of samples and analytical purposes, it is sufficiently good.
4.8 Practical aspects
SAMPLE PREPARATION
As mentioned above, variations in particle size can affect intensity. Therefore, all standards and
samples need to be in a similar physical form and treated equally. Metals should be cleaned,
granular material ground into a fine powder. Powdered material is often pressed into a disc, most
requiring some type of binding agent to hold them together.
A common method for powdered material is the borax fusion disc, where an approximately
10% mixture of sample in borax (Na2B4O7) is heated to melting (above 1000C) and poured into a
metal tray to cool. The effect is to break down the sample matrix to some extent, and provide a
more homogeneous mix. It does, however, dilute the sample and reduce line intensities.
USE OF HELIUM
Lighter elements than calcium require a helium atmosphere for best sensitivity because the low
energy photons generated by these elements are absorbed by air.
FILTERS
These are placed between tube and sample, and absorb a particular range of X‐rays which would
otherwise interfere with the sample spectrum. The tube lines can be removed by this method, but at
the expense of a good deal of sensitivity. Trial and error is the best way to determine whether a
filter is necessary, and if so, which one.
TUBE VOLTAGE & CURRENT CONTROL
The importance of tube voltage has been discussed above. With current which only affects intensity,
it might be expected that the highest current possible is the best choice. However, this is not the
case, as a current that is too high will generate a large broad background “bump” in the spectrum.
This is particularly the case if the sample has high concentrations of light elements.
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4.13
4. X‐ray Spectroscopy
Revision Questions
1.
What procedures are used to ensure the safety of operators of X‐ray spectrometers?
2.
Describe the effect on the output of an X‐ray tube of (a) current and (b) voltage?
3.
How does the spectrum from a X‐ray tube with a tungsten target differ from that of one with a
copper target, assuming the peak intensity is equalised?
4.
Why do X‐ray spectrometers commonly use both flow and scintillation detectors?
5.
Draw a diagram showing the transitions occurring that resulting in the production of K and L
photons.
6.
How do wavelength‐ and energy‐dispersive XRF instruments differ?
7.
Why is XRF such a good qualitative technique?
8.
What quantitative technique would you recommend for the analysis of lead‐containing rocks?
Explain your answer.
Answers on following page
What You Need To Be Able To Do

define important terminology

explain how X‐rays are generated

outline the health and safety aspects of X‐ray use

distinguish between the three types of X‐ray spectroscopy

describe common X‐ray sources

outline the principles of operation of common X‐ray detectors

draw schematic diagrams and explain the function of each component for typical energy‐ and
wavelength‐dispersive XRF instruments

explain the electronic transitions which produce X‐ray photons by fluorescence

describe practical aspects of qualitative analysis by XRF

describe practical aspects of quantitative analysis by XRF

list advantages and disadvantages of XRF
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4.14
4. X‐ray Spectroscopy
Answer guide for revision questions
Where the answer can be found directly in your notes, a reference to them will be provided.
1.
p4.2
2.
Figure 4.2
3.
Different positions of the Ka & Kb lines superimposed on the broad continuous spectrum
4.
p4.9
5.
Lb
Ka
6.
Wavelength‐dispersive: two detectors, moving along circular path; energy dispersive: single
detector, no moving parts
7.
p4.11
8.
Matrix‐matching impossible, so use of source emission line as internal std possible if intense
enough; otherwise std addition or added internal std
AIT
4.15