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ManualX-ray fluorescenceManual remote experimentProject e-Xperimenteren+

J.M.Mulder, J. Snellenburg

19-01-2006



Manual X-ray fluorescence

page 2 of 15

Colofon


Manual remote experiment

Project e-Xperimenteren+

Stichting Digitale Universiteit

Oudenoord 340, 3513 EX Utrecht

Postbus 182, 3500 AD Utrecht

Phone 030 - 238 8671

Fax 030 - 238 8673

E-mail [email protected]

Author(s)

J.M.Mulder, J. Snellenburg

Copyright

Stichting Digitale Universiteit

De Creative Commons Naamsvermelding-GeenAfgeleideWerken-NietCommercieel-licentie is van

toepassing op dit werk. Ga naar http://creativecommons.org/licenses/by-nd-nc/2.0/nl/om deze

licentie te bekijken.

Date

19-01-2006

http://creativecommons.org/licenses/by-nd-nc/2.0/nl/

http://creativecommons.org/licenses/by-nd-nc/2.0/nl/




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Table of contents

1 Introduction 4

2 Theory 4

3 Setup 5

3.1 Schematic view 5

3.2 Pictures 6

4 Remote interface 8

4.1 Settings 8

4.2 Measure 10

4.3 Calibrate 11

4.4 Analyse 12

4.5 Journal 13

5 Constants and parameters 14

6 References 14




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1 Introduction

This manual explains the working of a remotely controlled X-ray fluorescence experiment.

X-ray fluorescence is a technique that can be used to determine the surface composition of a

sample non-destructively. Related to this technique are various processes such as attenuation of x-

rays in materials, absorption, fluorescence yields, coherent and incoherent scattering.

In this experiment some of these processes can be studied using a241

Am source.

The experimental setup is located at the Vrije Universiteit Amsterdam and is maintained by the

Physics student laboratory. The web-experiment can be accessed from practically any location in

the world, provided the user’s system meets the minimum system requirements as listed in

Appendix A. Before starting the experiment it is recommended to formulate a research plan to work

as productively as possible. To this end, besides reading this manual, it may help to study the

background theory available on the website to find out what the possibilities and limitations are of

online experimenting.

2 Theory

X-ray fluorescence occurs when an electron from the inner electron shell of an atom (molecule) is

ejected by a high energy X-ray photon. The absorption of x-ray photons can be described by the

law of Lambert-Beer . The created hole is filled up by an electron from one of the outer shells (an

electron from the L, M, …state). The energy difference from this transition is emitted as a

fluorescence photon.

Fig. 2.1: A Bohr-atom with filled K and L shells and one electron in the M shell.

These energies are characteristic for each element. A measurement of emitted fluorescence

photons coming from a target results in fluorescence spectrum. The composition of the exposed

target can be determent by comparing the energies in this spectrum with the known transition

energies of all elements. See the table of emission energies.

http://www.english.vu.nl/home/index.cfm

http://www.nat.vu.nl/edu/

http://www.nat.vu.nl/webexperiments/rontgen/index.html

http://en.wikipedia.org/wiki/Beer-Lambert_law

http://en.wikipedia.org/wiki/Beer-Lambert_law

http://www.nat.vu.nl/webexperiments/rontgen/index.html

http://www.nat.vu.nl/edu/

http://www.english.vu.nl/home/index.cfm




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An electron from the L to the K shell is a Kα transition and from the M to the K shell is a Kβ

transition. For an introduction to the theory of fluorescence see refs. 1, 2 and 3.

Elements you should be familiar with are (notations of) electron states, characteristic lines, selection

rules, fluorescence and intensity yield, absorption and scattering of x-rays.

3 Setup

3.1 Schematic view

The most important parts of the experimental setup are the x-ray source, the target materials and

the x-ray detector. (Fig. 3.1)

Fig. 3.1: schematic overview of experimental setup

X-ray source

The x-ray source is a241

Am (10 mCu). The x-ray spectrum of this source together with the

identification of some peaks is shown in fig. 3.2.

The target materials

In the target wheel different materials can be selected. For the list of materials that can be chosen

see 4.1: Remote interface settings

The x-ray detector

Specifications of the detector (type XR-100CR) can be found in ref. 4.

If an x-ray photon interacts with the silicon plate in the x-ray detector, it produces a number of

electron/hole pairs depending on the energy of this photon. This results in a short signal pulse.

After amplification these pulses are selected on height, counted and stored by the MCA. The

resulting x-ray spectrum is then read by the computer.

The detector can be placed at different angles. The angle between the x-ray source and the x-ray

detector can be varied from 40 to 180 degrees.

X-ray source




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3.2 Pictures

Below some pictures of the setup.

Legend:

A X-ray detector

B X-ray source

C Target wheel

D Power supply x-ray detector and preamplifier

E Multi channel analyzer

F Stepper motor control unit

G web-cams

X-ray detector with power supply Multi channel analyzer (MCA)




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Overview of the experimental setup

Close-up of x-ray detector, target wheel and x-ray source.




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4 Remote interface

Below is a description of the software interface of the experiment. The panel is organized into

several tabs:

1. Settings

2. Measure

3. Calibrate

4. Analyse

5. Journal

Each tab is described in the next paragraphs.

4.1 Settings

Various experimental parameters can be adjusted:

The angle between the detector and X-ray source

Normally set at an angle of 40 degrees for fluorescence measurements and 180 degrees for

absorption measurements. A change of this angle has to be confirmed with the confirmation button

which appears below this control.

A type of target One can choose targets with known materials such as copper, iron, zirconium for calibration

purposes, or targets with a priori unknown compositions like the sand from the shores of the Dutch

island of Texel to analyse their content. Also some compounds can be chosen such as brass or a

euro coin for this purpose.

A pinhole

A pinhole is only used with absorption measurements. During fluorescence measurements it should

always be set to none.

Webcam views

Two types of web cam views can be chosen: an upper view of the setup and a side view of the

chosen target in front of the source.




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Figure 4.1: screenshot of the “SETTINGS” tab in the remote panel overview.

– Set angle detector – X-ray source: a new angle can be set by changing the value or by

dragging the arrow in the picture control to a new position. The actual change to this new

position is done by clicking the confirm button, which appears when an change is first initiated

– Confirm: clicking this button will result in moving the x-ray detector to the new position.

– Choice target: with this popup button you can select one of the following materials:

0. empty 8. 0.13 mm Silver

1. 0.021 mm Copper 9. 0.53 mm Nickel

2. 0.052 mm Copper 10. 0.51 mm Iron

3. 0.10 mm Copper 11. 0.19 mm Aluminum

4. 0.22 mm Copper 12. Euro coin (50 cts)

5. 0.9 mm Lead 13. Sand (from the sea bottom of Texel)

6. 0.5 mm Tantalum 14. 0.4 mm Zirconium

7. 1.0 mm Tin 15. Brass

– Choice pinhole: You can choose between the following diameters: 2, 4, 8, and 16 mm. None

should always be selected for fluorescence measurements.

– Large image: when selected the color will change to blue and a large image is displayed.

– Small image: when selected the color will change to blue and a small image is displayed.

– Camera upper view: shows an upper view of the experimental setup

– Camera targets and carrousel: shows a part of the target wheel and the x-ray detector




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4.2 Measure

The measured energy spectrum of the X-ray detector is displayed. This energy spectrum is

measured with a Multi Channel Analyzer (MCA). Controls of this instrument are: start or stop the

measurement, clear memory (and graph), number of channels to set the resolution of the energy

spectrum and preset time to set the measuring time. When set to zero the measurement can only

be stopped manually. The measured time corrected for dead time is shown in the lower indicator.

The indicator “Measurement settings and variables” shows all the settings of the displayed energy

spectrum. The data can be saved and previously measured spectra can be read. Read MCA buffer

control displays the last measured energy spectrum that is still in the buffer.

Figure 4.2: screenshot of the “MEASURE” tab in the remote panel overview.

– Energy spectrum: the current energy spectrum is displayed here. Number of photons against

channel number (or against energy in keV if the MCA is calibrated).– Preset time [sec]: the preset live time to measure the energy spectrum. If zero the measuring

time is infinite.

– Measured time [sec]: the measured live time that has past.

– Measurement settings and variables: Information about the displayed energy spectrum.

– Start measurement: Starts the measurement until the preset time is reached or the

measurement is stopped manually.

– Stop measurement: stops the measurement.

– Empty MCA buffer and graph: clears the buffer of the multi channel analyzer and the graph.

– Number of channels: determines the resolution of the measurement. Possible values are 256,

512, 1024, 2048, 4096 and 8192 channels.

– Read MCA buffer: reads the buffer of the MCA.




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– Write data to file: Saves the displayed energy spectrum in a data file and the information shown

in “measurement settings and variables” indicator in an info file.

– Read data from file: reads previously saved data- and info-file from disk and displays it in the

“energy spectrum” graph and “measurement settings and variables” indicator.

4.3 Calibrate

This tab gives the possibility to calibrate the x-axis of the measured energy spectrum. The X-ray

emission energies of all selected known targets, of which energy spectra are measured, are shown

in the upper indicator/control. On the right side of this tab you give input for at least two channel

numbers with each a selected X-ray emission energy. After pressing in sequence the buttons

”Determine straight line fit” and “calibrate x-axis” the x-axis will be calibrated and changed into

energy in keV. This is also done for the spectra under the other tabs. The extra controls “cursor

active” will activate an extra cursor. Snap to channel means that the cursor is locked to each point

of the energy spectrum.

Figure 4.3: screenshot of the “CALIBRATE” tab in the remote panel overview.

– X-ray emission energies in keV: here all the emission energies are shown of all the known

target materials of which energy spectra are measured.

–

spectrum: displays all the line spectra of the known materials in the upper popup control.




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channel number (or against energy in keV if the MCA is calibrated).

– Slope: a parameter of the linear fit.

– Intercept y-as: a parameter of the linear fit.

– Mean squared deviation: goodness of the linear fit.

– Cursor active: if selected a cursor is shown in the graph and a active value in the linear fit.

– Channel number: the position of the cursor in the graph.

– Energy value keV: here the channel number is set to the emission energy values in keV’s.

– Snap to channel: If selected the cursor is locked to a channel number.

– Determine straight line fit: A fit is made with the channel numbers and the energy values

corresponding to the active cursors.

– Calibrate x-axis: After a fit is calculated all energy spectra will be shown in keV.

4.4 Analyse

On this tab the energy spectrum and a panel with all elements and the corresponding X-ray

emission energies is displayed. By selecting elements from this panel it is possible to investigate

which elements contribute to the energy spectrum. When an element is selected (clicked on) a line

spectrum with the tabulated X-ray energies from this element is shown in the graph. The RESET

ALL button will remove all selected elements from the graph.

Figure 4.4: screenshot of the “ANALYSE” tab in the remote panel overview.


channel number (or against energy in keV if the MCA is calibrated).




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– Elements: here an element can be selected, which results in colored lines in the upper energy

spectrum at the specific energy values (keV’s) given in this table. All selected elements are also

set in the legend on the right hand side of the graph

– Reset all: clears all colored lines of the chosen elements in the upper graph

4.5 Journal

In this tab you can enter items to your lab journal. This is done by selecting a “Journal Item” and

“Journal Status” from the lists at the top of this tab and entering a text in the field “Journal Text”.

Optionally you can add a reference to an earlier journal entry or log entry. This is done by clicking

the entry in the list box at the bottom of the tab or entering its number in the “reference” field. By

clicking the button “Submit”, the journal entry is added to the log.

Note that some actions are automatically logged.

Figure 4.5: screenshot of the “JOURNAL” tab in the remote panel overview.

– Journal Item: here it is possible to choose a category for your journal entry.

– Journal Status: here you can choose a qualification of your journal entry.

– Journal Text: here the actual text of the journal entry can be typed.

– Reference: You can refer to an earlier journal entry or experiment log entry by clicking in

the table of entries or choosing a number in the Reference field.

– Submit: by clicking the button Submit the journal entry is added to the experiment log.




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5 Constants and parameters

Name Description Value / range, error,

unit

X-ray source241

Am 10 mCu

Source/detector

angle

The angle between the x-ray source and the

x-ray detector.

40 to 180 degrees

Efficientie

detector

Ref. 3

Emission

energies of all

elements

http://www.nat.vu.nl/webexperiments/rontgen/

download/tabel.pdf

Size pinholes Diameter pinhole (lead) 2,4,8 and 16 mm

6 References

1. R. Tertian and F. Claisse, Principles of Quantitative X-ray Fluorescence Analysis

2. B. Dziunikowkski, Energy dispersive X-ray Fluorescence Analysis

3. http://en.wikipedia.org/wiki/X-Ray_fluorescence

4. Website of Amptek (http:/www.amptek.com/xr100cr.html)

http://www.nat.vu.nl/webexperiments/rontgen/download/tabel.pdf


http://en.wikipedia.org/wiki/X-Ray_fluorescence

http://www.amptek.com/xr100cr.html

http://www.amptek.com/xr100cr.html

http://en.wikipedia.org/wiki/X-Ray_fluorescence






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