Alpha-1 Use Procedures

(Please note, this is a work in progress and will be updated as time goes on.)

Instrument Basics.

The Alpha-1 is a basic theta-two-theta diffractometer with the benefit of an incident beam monochromator, and a fast linear detector.  It can generate very high resolution diffraction patterns in a minimum amount of time.  The x-ray tube stays fixed and the sample and detector rotate to collect the diffraction pattern.

The Alpha-1 has an incident beam programmable divergence slit prefix module, a rotating sample stage, and diffracted beam optics. Each of these will need to be configured to suit your particular measurement.

Incident Beam Optics Setup.

1. Figure out what your starting angle will be. Then choose a divergence slit accordingly.  If you look on the chart on the side of the instrument, it will tell you what slit to use.  Most people starting at 17deg or above will use a 1/2 degree divergence slit.  Keep in mind this slit is computer controlled.

2. Choose your anti-scatter slit.  The anti scatter slit is always twice the size of the divergence slit.  Thus, if you use a 1/2 degree divergence slit, you will need a 1 degree anti-scatter slit.  The anti-scatter slit is a manual device, so you will need to insert it.  Remember, it only goes in one way.

3. Soller slit. Choose either the 0.04 (recommended) or 0.02 radian soller slit. DO NOT DROP IT!!!

4. Mask. Choose the mask to fix the beam size according to your sample diameter. Most people will use the 10mm or 15mm mask.

Diffracted Beam Optics Setup.

5. The diffracted beam side is easy. It has one slit... unfortunately it's also called an anti-scatter slit.  The difference is that the angle is much much larger.  Most people will use the 5.5 degree diffracted beam anti-scatter slit.

Sample Preparation

You will either load a powder mount, a wafer mount or a low-background mount. That's it.  It is vital to ensure your sample is positioned exactly at the top of the powder and wafer mounts.  People using the low-background mounts should only have a monolayer of powder.  These samples are not designed for thick (greater than 100micron) samples.

6. Load the sample in the sample spinner stage and raise the lever to lock it in position. Do not forget to raise the lever.

Inside Datacollector

7. The program should be logged on.

8. Verify the Incident Beam Settings.  Make sure the optics are what you want. 

(programmable divergence slit, fixed, 1/2 degree anti-scatter slit, 1 degree, soller slit 0.04 radians, beam mask 10mm or 15mm)

9. Verify the Diffracted Beam Settings.  (anti-scatter slit 5.5degrees).

10. Increase the voltage and current to their operating settings. of 45kV and 40mA... this is found in the Instrument Settings Folder just to the left of Incident Beam Optics.

Setting up a Measurement.

11. Go to File>New Program. Use program type "Absolute Scan"

12. Choose the angle ranges you desire. General settings are 20-80 degrees continuous

13. Choose a step size and count time... these are rolled into a scan rate.  General settings are 0.04 degrees and 4 seconds. Don't worry if it changes the numbers on you.

14. Save the program

Making a Measurement

15. Go to Measure>Program. Open your program.

16. Give your file a name, and a folder to go to.

17. Verify that the instrument is at full power, the doors are closed, and your sample is raised up into position.

18. Hit "OK" to begin your measurement.

Return to stand-by when measurement is complete

Lower the power of the x-ray tube to 40 kV and current to 20 mA.