Well, my envelope calc above has a boo boo, which I edited (left the original, but added the correction in orange, see above). Now it all makes a lot more sense. I'd run 20 minutes for the first run, and about the same for the second. Assuming I really caught all the gas on that second one (I did try harder to get it right) then the numbers actually agree pretty closely! Or, great for such a simple estimate.
In a way, that bit of accidental self-deception made this a more-honest experiment, I was expecting lots more (see the orignal math) but I reported what I did see....and a measurement beat a guess once again.
I will continue this series of tests and get some really good numeric measurements, rather than eyeballing the scope counts in 5 second sweeps -- with a little signal conditioning I should be able to push this signal into our multi-geiger (tm) counter/data aq. It seems obvious now that I should have made provision to flush the system better without having to take air through the system and pumps. I will add a fitting between pump outlet and test chamber so I can push shop air through there and get rid of last run's T and baseline every time.
It appears that running the fusor at record levels (twice the normal power input) for long times (4 times a normal run time) is bad for some of the pieces in there, I melted some things inside it seems, and will have to get in there and replace a quartz sleeve (or swap it end for end) on the feedthrough, if it didn't weld to the pyrex, in which case I have to make two more pieces. No big deal, and for sure that will flush the system, but if I can finde a T and a plug in my plumbing junk, I'll use that time to also add a flush port for shop compressed air to clean things out.
Late last night, what appeared to happen is that any T I'd pushed out too far (due to bleed air from the backing pump) didn't quite make it outdoors, and during a wait it simply found its way back up to the chamber, being lighter than the air it was mixed with, and the system being designed to slope down all the way to outdoors. So after the flush that reduced the counts, they went back up again. Hopefully I don't have issues with the stuff soaking into the plastic, or worse yet, the detector. I'll know soon enough, but it seems wise to go ahead and fix the issues I know about (messed up FT and need for flush port and signal conditioning so I can get real counts rather than eyeballs) and try some more times.
I can't do a beta spectrum very easily, as "there is no such thing" in reality. Betas have a continuum of energy levels, the rest of the fixed Q of the decay coming out as a neutrino in a variable ratio. So if I hooked a MCA up to this detector (possible, we are evaluating one now for purchase) all I would get is the classic "Square box" from zero energy up to the limit for T, which is 18 kev or so, pretty low. Here's the wiki on beta decay and
why I can't do a spectrum that means anything much.
This is a special detector head to even see energies that low, the window over the scintillator plastic (NE-102) is only a few microns thick to allow such low energy particles (electrons) through at all.
Tritium link at wikipedia. claims range in air to zero energy is only 6mm (for the few full-energy betas)...this is pretty "weak tea" as radiation goes.
But hey, I found the mistake and now it all lines up pretty close. I'd expect to count something less than half the decays because half or more would simply emit a beta away from the detector face -- it's all adding up pretty well (it kind of surprises me -- usually my back of envelope will only get me to the right order magnitude -- and this seems right to about 1 digit significance, a little better than that).
So, now I feel a little better myself. Nothing more to do but repeat a few times and get better numbers (or not) to see if this is viable for sure, but even after the correction, yes, it looks possible, and not even all that hard. There could be various ways to optimize T detection as well. In a proper box (light tight) you could eliminate the window, and arrange the scintillator to capture light from the full 4 pi angle of emissions too. This particular detector was designed for a fission plant (I guess they worry about low energy betas in those too -- T in the cooling water?) and isn't perfect for "best possible sensitivity" -- wouldn't need to be for what it was designed for - safety. We are no way into a range where the amount of T we can make is a safety issue!
Edit:
Thanks Alex for sending me a mail with the correct math. Maybe you should join, we evidently use some guys who understand the calendar
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.