Robin van Spaandonk wrote:
How are you going to judge the results? I assume that from a whole swag of test kits, the results will vary from no tracks / cm^2 to perhaps 100 or more / cm^2.
If you get no tracks, you did the etching wrong. When you do it right there are always some tracks from the cosmic background. You have to have another chip outside the cell to measure that background. When the experiment works well there are lots more than 100 per cm^2. There are so many you need a computerized SEM to count them. In some cases there are thousands of pits but they are not caused by neutrons, according to the Russians, because they look different. What causes them is a matter of contention. Distinguishing those holes from the ones caused by neutrons is also disputed.
. . . which then also raises the question, what does one do for a control?
A chip outside the cell, as I said. This is a crucial issue. Another difficulty is ensuring that you etch both the control and the sample with the same procedures and concentration of etchant. The concentration changes over time as you use the stuff.
To simplify, you etch for a while, then photograph the chip in various ways with a light microscope or SEM. Then etch it again, photograph again, and repeat until you get to the bottom of the pits. If you etch too much in the first round you etch away the entire pit. You have to repeat these steps for the control and the sample.
Pam is now using a different kind of light microscope that reduces the need for multiple etchings.
- Jed
