Summary on XRF

SUMMARY ON XRF

XRF works through the process of exciting electrons within an atom. Generally, waves of high energy and low frequencies are used (x-rays or gamma). When the electron within an atom becomes excited, it then ejects from the atom. As a result the atom becomes unstable and an electron from an outer shell must fill the spot. The difference in energy levels between the the electrons is then released in the form of photons. Each element releases a specific energy and that is how we are able to identify elements.

I must have read this summary about a thousand times by now. Yet, looking especially at what I underlined, " When an electron within an atom becomes excited, it then ejects from the atom", a question was raised. I was requested by Dr. McColgan to then find out what energy level is needed to eject the electron. Also, why does the HD Prime need three energy levels in the form of x-rays to complete its task? What amazed me was the lack of detail many articles went into about ejecting at electron.

Finally I found my answer.

First I have to say, let's forget about the math. To put it in simplest terms, we know that there are several shells within an atom including: K-shell, M-shell, and L-shell. Within each shell there are electrons, all of which have their own energy level (that is the closest we will get to math). To knock an electron out, all we need is for the x-ray to have an energy level at least the same amount as the electron we intend to knock out. 

So then why don't we just use a really high energy level to get all of the electrons to react?

Yes, by doing that you would get all of the elements to react and release electrons, but it would be very hard to identify all of the elements. Especially when looking at an energy level graph, all we would see is an overlapping of peaks. Thus, we would be unable to identify all of the elements, especially those that would only require a small amount of energy to react. That is why the HD Prime has three energy levels. As the energy output decreases, elements that require lower amounts of energy will react stronger and we will be able to see them. Also, with the three energy levels we will get K, L, and M series. This way if we are still getting overlapping we could look at a different series to identify the element.

Side note:

X-ray fluorescence has come a long way in the world of atomic physics. It amazes me what I have accomplished in these eight weeks. Thank you so much for the opportunity and I hope what I have recorded will help the next student along the way in his or her research.

Reference Samples and Data

Intro: 

You might remember awhile ago when I was testing the calibration of the machine by using a tile that contained 5 metal samples and a plastic sample. But, because m1y study focuses on both aqueous and soil samples, I need to test the limits of detection using liquid, certified reference materials. I have already tested lead, nickel, chromium, and cadmium using AA standards. I just bought arsenic, mercury, and antimony to test.

How checking the calibration of the machine works is by creating a sample in which you know the exact measurements in it. Using simple math you could calculate the ppm for an element you wish to put into a sample, measure it out in a syringe, and put it into the HNO3. Then when you run it through an x-ray analyzer, you would know what to expect for numbers. What we need to be cautious of is the LOD (limits of detection). The LOD tells us the lowest concentration (ppm) that an element can be examined in a sample. For my CRMs they are:

Sb= 6 ppm

As=.2 ppm

Hg=None

What this means is if I go below the LOD, the x-ray analyzer will not be able to pick up on the concentration. That is why we created a calibration sample that contains the following:

Sb= 9.89 ppm

As=10.10 ppm

Hg=10.04 ppm

Data:

A large concentration of the reference material was created.  I then put the reference material into four different measuring samples that were individually run through the x-ray analyzer. A total of nine data sets were collected throughout the four samples. The numbers calculated included:

Sb= 12.9, 13.3, 14, 13.3, 18.7, 14, 11.9, 16.1, 12.8 (ppm)

As= 2, 2.2, 2.2, 2.1, 2.2, 2.1, 2.3, 2.1, 2 (ppm)

Hg= 3, 3, 2.9, 2.6, 2.9, 3, 2.8, 3.1, 2.7 (ppm)

Conclusions:

The data does not seem very close to the expected values. Because of this, I now need to have the machine calibrated and adjust all values for experiments done.