- Imagine that you're Indiana Jones.
And in one of your
archeological adventures,
you find a mysterious object.
You want to know what it is, right?
But at the same time, you
don't want to remove a sample
from the object for analysis
because it's cultural heritage.
And you don't want to damage
what's been safely preserved
for hundreds or thousands of years.
How awesome would it
be if we could find out
what the object is made of
without causing any damage to it?
It turns out, we can!
We can use a method called
X-ray fluorescence, or XRF.
And this is the topic of today's video.
(upbeat music)
Hi everyone. I'm Maria Baias
and I'm a heritage scientist
who wants to share with you
her passion for cultural heritage.
In a previous video,
we've learned about the
electromagnetic spectrum.
We've seen there that X-rays
are very high energy
electromagnetic waves.
In today's video, we will
learn how these X-rays
are used in a scientific method called
X-ray fluorescence, or XRF.
We use XRF in cultural
heritage to find out
what objects of cultural
heritage are made of.
We will start by learning how XRF works,
and then we will move on to learn about
applications of XRF in art.
And if you stay until the end,
I will share with you
the kind of XRF studies
that made me fall in
love with this method.
And why I think this is the
coolest scientific method
that can be used for
the analysis of artwork.
So let's dive into the
science of X-ray florescence.
First, we'll have a
look at the general idea
of how XRF works when we
want to analyze an object.
And the object we'll take as
example here is a painting.
Let's say, for example, we want to analyze
the blue pigment in this painting.
So what we do is bring the XRF
instrument close to the area
of the painting we want to investigate,
in this case the blue pigment,
and we irradiate that area with X-rays.
After we send the beam
of X-rays to that area,
we then record with
the help of a detector,
the radiation emitted as a response
to the irradiation with X-rays.
What we're recording is
the X-ray fluorescence.
And we'll see exactly what
that is in a few seconds.
This recorded signal is then analyzed
and after the analysis, we can find out
which chemical elements
are present in the sample.
There are different
types of XRF instruments.
Here is one example of an XRF
analyzer, which is portable.
That means that we can
record the experiments
even in more remote locations
like archeological sites.
The entire experiment can
be as fast as few seconds
or longer lasting several minutes.
That's the general idea of the method.
Now let's see what happens at atomic level
when we irradiate a sample with X-rays.
This is the structure of the atom
that we've discussed in a previous video.
Just a quick reminder
that the atom is composed
of the nucleus in the center
and surrounding the nucleus,
we find the electrons.
And the electrons are
located in different shells
corresponding to different energy levels
with the inner most shell
being the lowest energy shell.
So when we irradiate the
sample with an X-ray beam
in response to those X-rays
one electron from the inner
shells is removed from the atom.
With this electron out of the
atom, now there's a vacancy
in one of the inner shells of the atom.
And because the inner shells are the ones
with the lowest energy
and the electrons prefer to
occupy those shells first,
an electron from the outer
shell comes to the inner shell,
and takes the place of the electron
that was kicked out by the primary X-ray.
When the outer shell electron
moves to the inner shell,
an energy is released in the
form of X-ray florescence.
This energy is then
recorded by the detector.
And by analyzing this energy,
we can find out which elements
are present in the sample.
Let's see now, how and why
we can identify the elements
based on this energy.
As we discussed earlier,
the electrons are located
on different shells
corresponding to different energy levels
with the inner shell
being the lowest in energy
and the outermost shell
being the highest in energy.
Moving from the inner to the outer shell,
these shells are named K, L, M, N, O
and there's a maximum number of electrons
that each shell can have
as shown on the right.
Why that is so, it's a
topic for a future video.
What we're interested in here
is the movement of electrons
from one shell to another
as response to irradiation with X-rays.
So now let's place the
electrons back in their shells.
And we've seen before how
upon irradiation with X-rays,
an electron from the L
shell move to the K shell
to take the place of the
electron that was kicked out.
But it doesn't have to be
an electron from the L shell
that takes its place.
It can be an electron from
any of the outer shells
that takes the place of
the electron that left.
And here you can see how an
electron from the M shell
moves to the K shell.
When an electron from an outer
shell moves to the K shell,
the X-ray florescence will be a K-X-ray.
And if the electron is coming
from the shell next to it,
the irradiation will be a K-Alpha X-ray.
If the electron comes from
the second next shell,
the transition will be a K-Beta.
Similarly, when an electron
moves to an L shell,
the X-ray florescence will be an L-X-ray
and that can be Alpha, or Beta, or Gamma
depending on which shell
the electron is coming from.
Why is this important?
It's because the X-ray fluorescence
associated with each of these transitions
has a precise energy value.
This energy is given by
the energy difference
between the inner shell
and the outer shell.
And in this example,
if we're looking at the K-Beta transition,
the energy of the X-ray florescence
is given by the energy between
the K shell and the M shell.
This is very important
because these energies
are specific to each element.
They're like fingerprints
for the elements.
Once we know the values of these energies
recorded by the detector,
we can identify the elements
that are present in the sample.
In our example, once we know
which elements are present,
we can identify which pigments
were used in painting the
blue regions of the painting.
And we can do that for all
other pigments in the painting.
Isn't it great how we can use science
to identify which pigments the artists
used in creating their paintings?
And in the same way,
we can find out which elements are present
in other heritage objects.
We can find out what these elements are
based on the energy released
during the electron transition
from one shell to another.
But how do we get these energy values?
Once the X-ray florescence is detected,
we can obtain spectra that contain peaks
at different energy values.
Here's an example of an XRF spectrum.
In an XRF spectrum,
there are peaks that show
up at different energies.
And since we've already
seen that each element
has a specific energy value,
by checking the energies
where we have peaks in the spectrum,
we can identify which elements
are present in the sample.
Moreover, by analyzing the
intensities of each peak,
we can obtain quantitative information
about the different
elements in the sample.
We can find out how much
of each element is present.
And once we know which
elements we have in our sample
and how much of each, we can
put this information together
to identify the material.
This is how we can learn
which materials were used
in creating tangible
heritage like paintings,
mosaics, sculptures,
coins, and many others.
And now, here's what I
promised you in the beginning.
Why I love XRF for the
analysis of artwork.
It's because besides
the elemental analysis
and getting information
about what kind of elements
are present in the sample,
and in which quantities,
we can also record XRF
mapping of artworks.
So if we analyze a painting with XRF,
we can obtain a full two-dimensional
map of that painting,
showing the distributions
of different elements in the painting.
If you want to see some examples
of these 2D XRF maps of painting,
check out the links in the
video description below,
where I added the links
to two different studies
that were done by scientists
from the Metropolitan
Museum of Art in New York,
where they analyze paintings
using the XRF method.
If you enjoyed learning
about X-ray fluorescence
and its applications in the
field of cultural heritage,
then please give this video thumbs up.
And now I'm curious to hear from you
if you could analyze with XRF
any object or site of cultural heritage.
What would you choose?
Let me know your answer in
the comments below the video.
I'm really curious to hear what object
or cultural heritage
site you would choose.
Today we focused on the XRF method.
In the future we will come back to XRF
so we can see what kind of case studies
XRF is being applied to in the
field of cultural heritage.
If you don't want to miss those videos,
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Thank you for watching and
I'll see you next time.
Bye.
(upbeat music)
