- BTI's last gasp
Still some issues. This is the one I'm testing the 3/4" carbon/ceramic composite grid on, and "it acts funny". But it definitely works somewhat. It acts so strange compared to what I'm used to (which is why it was taken out of the big tank for the VA Tech demo) I'm going to put in an old standby and kind of see how much of the difference is the grid, and how much the rest of everything.
This was run off the "little" Spellman supply 40kv at 12.5 ma max. For I'm not sure how long, I was just fooling around with the gas flow situation and trying to adjust the main valve so I could run the mass spec (now on the pump side of that valve) at the same time. Had some success with that.
After that, I ran down and ran the big boy, just to hear those counters scream (and to find out if I had to do repairs on the feedthrough again). Ran it all over the map, and all the way to 2.5kw input power -- not for long as that melts things quick. Base pressure was 7e-9 mbar before I started, nice. Well, it ran just fine at all power levels, and I tried something for fun -- magnets with various alignments and strengths. I did find something interesting doing that, other than that you have to be real careful not to focus an electron beam onto things in the tank (they evaporate).
One is that (not so big a surprise) at a gas pressure just under where it will normally self-run, with some magnetic field, you can make it run at lower pressures. The thing that WAS a suprise is that the obvious field orientations you'd think would do something didn't, much, but an oblique field (roughly 45 deg from the grid axis) not only made it run, but made it make more neutrons than with the same volts/ma but a little more gas so it would run without the magnet. In other words, more Q. But aligning the magnet along or across the grid axis -- no good. Going to have to put one on a wiggle stick and sacrifice it moving it around in there and see what I can see. In no case did a mere 1.5k gauss 3" speaker magnet do anything I could notice. But a stack of 12k gauss 2" diameter by 2" long sure did. (gauss measured at the magnet face).
Oh, whatever was making the FT act bad last time was "fixed" by letting it sit for a week or more in high vacuum. Nothing I need to do, which is always nice.
That run made a ton of neutrons. Silver was 1646, but In was 240 cpm at the end. I didn't time this one either, and near the end of run was running low power, cool-down mode, so that's why the silver/indium ratio is low, most likely. The silver really is short memory stuff, so the last minute or 30 seconds has a lot to do with how hot that measures, where the indium with longer half life integrates a whole run better -- and is better for this if, and only if, you make enough neutrons to get it to count well out of background (which takes a lot more than for silver).
Now that I know the upstairs guy makes neutrons for certain, I can use it as a low power source to finally get the rest of my neutron detectors tested and working, along with those new ones Bill found when they get here.
And I only stabbed myself once with a screwdriver. A good day!
