Introduction

Before you go further, give us a call at (602) 965-9613 to reserve a session on the Ion Beam Accelerator. If the phone is unattended, leave your number, and we will get back to you as soon as possible.

To understand the operation of the analysis, you should have already read the Reading on X-rays, Earth, Moon and Mars. In this activity, you will be using accelerated protons to analyse a specimen using PIXE. The principle of PIXE is discussed in the Reading

Welcome to Mars!

The following images are all rather large, and will take a while to load, especially if you are using a modem. However, they are well worth the wait! If you know how to save the images you have loaded with your browser, you might well save them on your hard disk. You will probably be wanting to show these impressive images to your friends.

• First, take a glorious panoramic view of Mars. (Use your browser's scroll bars to change your point of view.)

• Now, watch the rover deploying the APXS against one of the martian rocks.

• Here, the rover is seen analysing the martian soil. Can you see the APXS being deployed from the back of the rover?

• There is a lot more about the Mars Pathfinder at the NASA web site devoted to this project. You are bound to find it interesting, but don't get distracted, there is work to be done!

Remote Analysis on Earth

If you are using a Netscape Navigator Browser, you will see the spectrum on the screen updating every few seconds (dependent on the speed of your connection).

Other browser users can reload the screen periodically to see the progress of the analysis. (If the control screen or the button bar at the bottom is not in full view on your browser window, drag the lower right corner of your browser window to maximize its size.)

Analysis is being performed at the facility using both PIXE (the technique you will use) and RBS (Rutherford Backscattering Spectrometry). It is possible that you will be watching an analysis using the latter technique.

You might be interested in a description of the principles of RBS, which can be found in Fundamentals of Surface and Thin Film Analysis by L. Feldman and J. Mayer (North-Holland, New York, 1986).

Performing your Own Analysis

You will also have been given a user name and password. When you first try to control the accelerator, your browser will return with "Authorization Failed". This is because the system sees your Patterns password, which it does not authorize. You can then select to "Retry", and can then enter your Analysis User name and Password.

Read the following brief description of the controls you will need to perform an analysis, and then, at the scheduled time, perform the analysis .

In the lower-most frame you will see a series of buttons:

• The "Acquire" button switches the analysis on and off. When you start the analysis, the previous analysis is cleared from memory, so you should have saved it if you want to keep it.

• The "Save" button saves the spectrum you have just acquired. Your User name and current run number appear in red, in the central box near the top of the screen. When a "Save" has been successfully performed, this changes to yellow.

• The arrow buttons move the cursors. The cursors identify the X-ray line corresponding to the energy at which they are located. The Ka, Kb, La and Lb lines of all elements are included in the data base. (Ka is used for K_alpha etc). Qualitative analysis of the specimen is possible in this way. (On slow web links, it is however rather time- consuming. Faster feedback is currently being developed.)

• The red and yellow buttons select which cursor will be moved by the arrow buttons. (It is possible to move both red and yellow simultaneously)

• The "Exit" button returns control to the Ion Beam Lab. You are however free to regain contol again by pressing "Analysis" again.

(602) 965-9613.

Go on to the PIXE Reading

Activity by Cecil Churms, National Accelerator Centre, Faure, South Africa