New run info, mass spectra. Tritium!

[Doug Coulter]

Did a run tonight, as I'm expecting guests soon and I wanted to make sure all was working well. Well, it wasn't, but I did get some things of interest while trying to get all the measuring gear to work right (again). That was mass spectra that show some reaction products -- this is supposedly impossible according to Richard Hull, but obviously he didn't calculate something right, and I refute it thus:
Here is a screen shot from the mass spectrometer pre run. This had been pumping down for days, and baked earlier in the day a little, then allowed to cool. I took this one in binned mode, as it integrates over each line lots longer and lowers the noise floor to about e-15 indicated (arb units). The rest are in analog mode, quicker but not as sensitive to very small amounts of things.

Screenshot of mass spec pre running

The system was reading about 3e-8 mbar at the time, I've seen it as low as about 9e-9 today.
Now, after running about 12 minutes (I was fiddling with broken detectors and not keeping the parameters close to best), then pumping back down to just where the mass spec would work again, it looked like this:

First post run spectrum, pressure high enough to smear resolution a little bit, around 1e-5 mbar

Here's one after about a minute more pumping (turbo still at standby revs, but forepump going and connected)

After some pumping

And the last one I took after a lot more pumping.

Pumped back down to e-7 or so

The important thing to note here is the line at 6 that shows up, not big, but definitely there, and I guess you'll have to take my word for it, when I just let in some D, it's not there unless I run the fusor.

So, that run made quite measurable amounts of tritium! Silver didn't get very hot (~800 cpm, indium about 300 -- the ratio goes down with longer runs due to indium's longer half-life), as near the end of the run I was still fooling with detectors and the pressure wasn't in range for the best operation -- either too high or too low most of this run. I find that there's a sweet spot, that with only a little attention it's easy to stay on. But while crawling on the floor, not so easy!
I'll get that pesky b10 tube working yet, I want stereo on my audio neutron indicator! Sadly, my data aq software also has some issues just now, so I've got more work to do, could be the idiot between the keyboard and screen -- but perhaps also Dave should have put in some helpful error indicators? I'll grouse, as I paid him close order of $10k to finish writing that stuff, and golly, it's supposed to work and be at least Doug proof. As Jon pointed out -- doing this off a huge budget and in limited time, you have to expect some of this -- in fact, even with the usual perks, you have to expect some of this. But, progress, and nice proof of fusion. And after sitting a month or so, collecting dust, the thing just fired right back up, which is kind of nice.

[Joe Jarski]

OK, dumb question... Why does T show up as 6 AMU? Is it assumed that the charge is +2 instead of +1 so it acts like 6 instead of 3?

[Doug Coulter]

Not dumb, just inexperience. It can only have charge +1 (still the one proton). It's T2+. You can't see it at 3, because there's always HD+ there, no matter what, and it swamps that out (note the scale is log and factor ten doesn't span much height). So we're seeing T2+, which is mass/charge ratio of 6 or thereabouts. That slot is just dead if I just let in D and don't run the HV on the fusor. Some of the 4 could be TH+, but then that'd be swamped out too by DD+. Then there's that otherwise hard to explain line at 5 too, which I have to assume is TD+.

Or it's something no one has been able to come up with a decent other explanation for so far - mass 12, charge 2 could do that (same ratio), but...we know there's carbon in there from the other lines, but this ionizer should do that if its going to without the fusor having run, and it doesn't show up under other conditions. I haven't tried capturing the pump output and checking it for radioactive, after all, as we worked out on another thread, it's a fraction of a cc total gas, and this is a tiny fraction of that. I don't have a clue how you'd even try to do that.

Mass spectra can be hard to read for even a chemist, because things can live in molecular flow conditions that just don't, in normal conditions. OH, H3O, COH, all kinds of things that wouldn't be stable in air are stable just by themselves if they don't hit a tank wall or something else before getting into the analyzer -- though most things do bang around a bit before they find that screened off hole. That's one reason you see all those lines on both sides of the water line at 18. Stuff that would react instantly with almost anything can, well, just not happen to hit anything to react with, so you see them, and it takes practice to interpret these. The instrument came with some "handy tips" to help with that.

[Joe Jarski]

Oh yeah, makes sense now. I was thinking of the T being monatomic as it went through the mass spec, then the mass to charge ratio would be the same as mass 6 +2. That would probably show up as mass 3 though, now that I think about it. The mass spec probably assumes that it's ionizing everything to +1. I'm all set now - I just have to remember all of the various combinations that these things can exist.

[Doug Coulter]

Riiight -- you should see the spectra if you let in a little acetone, zillions of lines of "parts of acetone" and "bizarre combinations of parts of acetone", or anything else easy to bust up into pieces with even a gentle ionizer, which this is. That big-heavy stuff in the first plot is a tiny bit of oil from the motor on my conductance valve, for example. Which is coming out of there next time I crack the system -- don't need it and the uncertainty that causes anymore.

In this case, I'm assuming most of this isn't the really bizarre stuff for one main reason. The system sat at 1e-2 mbar for awhile, which gave everything plenty of time to bang into everything before I could start the mass spec up. Notice the continuum in all but the first plot? That's because there's so much gas in there that some makes it through the analyzer no matter what, to hit the detector, being bounced around by neutrals -- viscous flow or nearly. So this is mostly relatively stable compounds (as these things go) here -- everything has sorta had a chance to resolve some, bounced off tank walls (which are famous for promoting recombinations into semi-stable stuff).

You'll see this firsthand soon, and it's a real eye opener on what the conditions are as seen by the stuff in there, I promise. Fun to let in a little of this or that, so you know what you put in, and see what this shows as a result. Very enlightening about how it all works.

[chrismb]

Doug,

Great work on the metrology and fusing. But there is one more thing you need to get clear of and that is 3D+ ions.

3H+, a protonated hydrogen ion, is the commonest ion in the universe, so someone arguing against your result might raise that possibility. The way to eliminate this might be to repeat the exact same experiment, but not use 'fusible' voltages and run at just a few kV instead, see if there are any persistent 3D+ ions formed during ionisation.

http://en.wikipedia.org/wiki/Trihydrogen_cation

[Doug Coulter]

Yup, that's a possibility, and one I'll check. Seems somewhat unlikely due to the fact that it had minutes at fairly high pressure and no volts before I could fire up the mass spec, but until checked out, any possibility is .... a possibility for sure. Since it's not hard to check for, why not just do it? My sig on other boards goes:
Why guess when you can know? Measure!

What I've found is that already-charged stuff has plenty of time and mechanisms to get uncharged before I can turn on the mass spec; I have to take it down to 1e-5 mbar or below from the operating pressure of maybe 1.6e-2 before the thing will read anything but straight lines -- it's a long quadrupole with plenty of chances for a produced ion to collide with stuff down the length.
So you'd be assuming we had lots of D2 (definitely) that somehow picked up a D+ right at the mass spec ionizer. Most of the D2 getting there picks up a charge itself, so wouldn't combine with another + charge in my experience but -- this isn't that loud a signal. So, I'll just check and we will see what we see.

I do know we don't see the line at either 5 or 6 when just letting in some D and running the uWave ionizer, which beats on things fairly brutally.

[chrismb]

Maybe the other way [or second way] to test is to fill with just hydrogen and see if you get a mass=3 peak.

After reading that link I put in, I think it would be important to do at least some form of investigation like that, to see if the fusor environment at fusible voltages produces these species because these ions were originally discovered in exactly these kinds of discharge experiments.

I think this whole issue is unique to you, Doug, because of your ultra-clean test environment. Whereas others would see these ions strip and revert to neutrals, I can imagine that in your ultra-clean setup they will bounce around a good while and could drop straight into your mass spectrometer because of the long MFPs [I think, maybe, they can successfully bounce off the walls without loosing ionisation because of the mass/velocity differentials with the wall atoms]. This is just speculation, of course...

[Doug Coulter]

Well, at any rate I intend to do the test, hopefully tomorrow, with pure D because I have that, and don't have pure H. Not that hard to do, and I agree, it's important to be sure. I will run an equivalent energy (but lower voltage) discharge in a grid at below fusion levels, not the microwave ion source, because in past tests where I've made a long run sealed off, it has happened that neutrons have continued to come out at low levels even after main power was removed, but the ion source still running -- and you could turn it on and off and turn the neutron production on and off -- not a whole lot of them, but it appears things in that microwave source can get to pretty high energies somehow. My guess, and that's all this is, is that some of the fusion byproducts are enough easier to make fuse than plain D that this is possible, because I've seen it a few times, but only after a run, never before.

So if I run at say 5kv (where I generally don't see any neutrons above the detector noise, that takes about 16kv) and don't get the 6 line, will that satisfy? I'd have to do it at a little bit (but not much) higher pressure to do that. Paschen's law is pretty steep, so it wouldn't be much higher -- say 2e-2 instead of 1.6e-2 (indicated, as we know, that gage reads high on hydrogen).

What (little) I know of surface science is that no, if anything hits a tank wall, it sticks and loses any charge. To keep a surface even moderately free of adsorbed gas atoms for even a few seconds takes ridiculously good vacuums of a few orders magnitude better than my best ever. I'm sure a few particles do get straight in to the analyzer, even miss the screen wires, but probably not enough to measure -- it's a tiny (and deep) hole in a big tank, so the odds are things have gone around and bounced some to find their way in. What I saw was too high a fraction to account for it that way. What I didn't do, but might try tomorrow if I think of it again, is turn off the ion source. After that much time and pumping (it does take about a minute to get to where the mass spec can run with the turbo still idling but the forepump reconnected) I'd have to suppose that every single particle in there has bounced off a tank wall and become neutral (probably a few million times, but I didn't run that math, just memory from some stuff in the Lesker tech notes), as the MFP is short even at e-6 given the time involved from stimulus to measurement.

We'll just see what we see, and let the chips fall where they fall -- I prefer to do good science. Without running a discharge, I never see 5 or 6, as I've done that to test how pure my gas is (particularly after moving it to other tanks than the one I bought). In fact, what I found is that they cheated me by about one of the claimed 9's of purity, evidently they didn't bake and outgas the supply tank thoroughly enough...

At any rate, I'll try whatever I think of, based on what we've discussed here and what the first tests show me. As my sig on other boards says "Why guess when you can know? Measure!"

It's been a hectic week here, hoping to catch a little lab time and fun this weekend, and I'll report, of course. Sigh, frozen pipes, more snow, dead battery in the truck...you name it.

[chrismb]

So if I run at say 5kv (where I generally don't see any neutrons above the detector noise, that takes about 16kv) and don't get the 6 line, will that satisfy?

Personally, I think it'd be a 98% show - i.e. I would accept it myself. But it's not me you're gonna have to satisfy!