August 9th 2014, mostly shield tests

[Doug Coulter]

Mostly, but the basic data is nice enough to share as well. At the beginning of the run, I hit > 5 million neutrons/second, probably averaged around 3 million over the run. Started at aroungd 2.2 e-3 mbar, ended at 1.9e-2 (cleanup and other issues).
Initial current limit was 15 ma (so I didn't get fried too badly running around with the survey meter discovering yet more leaks), and ended at 17ma (just to try and keep output up - the silver is super sensitive to the output right at the end of run, as you can see by the decay rate).

Basic data plots. Neutrons are green X, X rays are red X, lines are power supply, pressure, and calibration.

Had some troubles getting this up as a png at larger size. Perhaps along with cheating me on the "unlimited bandwidth" I've been paying for well over a decade, now the "unlimited space" is also done by a metric of "did you use more than some other user?" rather than the dictionary (and legal, you shits) meaning of "unlimited".

Someone find us another web host, this sucks.

Looks like silver hit ~ 2800 cpm. It generally tracks neutron output near the end of the run pretty close, by sheer co-incidence of how the various counters are (un) calibrated. In the closest we could do (at HEAS 2009) our neutron counter used here says 980 cpm/million neutrons/second. I generally mentally round that up to 1k counts/million to make life easier, but we're doing just a little better than we report due to that. Not enough to sweat in either direction.

We still have some leaks I didn't notice visually before, but it's getting better as far as the survey meter goes at the places it used to get pegged - the ones we found before, I've fixed. This has NOT produced a dramatic fall at the main system geiger counter at the op position, though. While the red and green (geiger and neutron) lines used to track, it looks like we've only gotten around 2-3x better on geigers than before.
Some of that has to be scatter from the still-existing couple of big leaks, but I'm going to have to start on the theory that some of it is from neutrons being captured in things that make hot gammas. We will continue to investigate that. Hopefully, I'll soon have at least a sloppy gamma spectrometer going again...that will tell the tale with no guessing required. Heck, even without a fancy histrogram spectrum, I can compare pulse heights on the scope with a known source (like Cs-137) and get a feel for the range of interest. After all, power supply is 50kv. Boron capture is more like 570kev...hydrogen is 2+ megs. I don't think I need 4k resolution to tell what's what on that range.

[Doug Coulter]

Added a few more sq inches of lead to a couple spots that had gone unnoticed before - the junction of the main window to the tank. While this appears to have cut back some on the rads at the op position, tiny leaks there (there's a pretty fierce particle beam hitting near the window) - are still enough to peg the survey meter at 100x (lowest sensitivity). More work to do - I'll wrap that whole mess in a removable piece of THICK lead now. But it's getting better. Not an especially astounding run - not super high neutrons even for what is now "idle mode" - but you can see where near the end I added gas, hit a current limit, took some back out - all the various plot traces line up sweetly and show you what happened there.

A little better at the op position, not so greeat right at the leak(s). But there are less and less of those.

Gawd, this is boring, hard, and not too safe as work goes - I'm itching to get on with our breakthrough. But our shielding was barely adequate to make 3m neuts/second kind of safe. Now that we found a factor of thousands...you can see why I want that op position counter to sit right at background (which BTW, stays the same if I put it entirely inside 2" thick lead blocks = it's all cosmics or internal counter contamination) - because 1000x or more of that - might not be great for my bod.
Sadl6y, there appears to be no way to gradually ramp up the "secret sauce" bunching - it's there or not - you get thousands or not - no middle ground I've yet found.