Ok, still a lot to do. I used to labor under the mis-impression that X or gamma ray photons worked similar to light (since after all, they're photons). Well, that's not quite the case, due to the sheer energy being far higher per photon than chemical bonding kinds of energies (thousands or 100 thousands volts versus 1-3 volts). When you put out an X ray "beam" well, it's not like a flashlight - it's more like a flashlight in fog. Light goes "everywhere", due to compton scattering (and other things). Unlike visible light, this effect does lower the energy of the photons some - knocking out electrons from air and other atoms does that due to the higher energy photon's ability to do it vs visible light - but not enough to make something really unsafe into something safe.
Not knowing that is my excuse for having done a relatively sloppy job on parts of this, and I'm sticking by it. But now I know, so there's no excuse.
Here's one side of the fusor. I got that fairly well - there are leaks that aren't obvious in the picture (like out through the end of some feedthrough) but in general, this side is pretty tight (I'll do more anyway).
- Left side of fusor when facing the front from the op position.
I should note that most of these SS flanges are so thick they might as well be shielded with lead. SS isn't as good per cm, but I'm not using inch thick lead, either.
One obvious leak here is that little piece of coax with the probe on it. Yes, that's enough to make a difference. But this side is no longer the main offender.
You can see the recently
almost-done neutron oven in this pic. I still need to attach the bottom part more firmly to the tank, so it doesn't lift off when I pull the top off. It's painted black because that's graphite paint to lube things a bit, but it's still on the sticky side. I'll probably solder on some tabs to the copper part and put baling wire (yes!) under the thing to hold it down.
But the main priority now is this side - I cheesed out and left major areas of the thin tank metal completely alone, as it's real work to handle all the warts and bumps well. Further, the tubes that stick out tend to leak pretty badly themselves. So it's not just the sides of the tank, it's those pipes too. Lots of fiddly work required here - and to make matters more fun, it's quite a tight fit between this side and my big lathe and mill.
- The bad side.
The partly shielded HV FT you can see on the upper left of the tank is one of our faraday probes. This FT failed for HV - internal arc tracks, but is fine for this use, other than yes, ceramic slows down X rays pretty close to "none at all". And the X rays come right out of the end as well. The yellow box on the upper right is our primary neutron detector - while I DID use the box from an old CD ionization chamber/detector (you know, the kind that only read off zero after you're dead), it's just a box. The real detector is a hornyak button from Eljen, and a photomultiplier with our fine-wine preamp, running on its own wall wart and integrated, regulated power supply. It's by far the most stable detector in our, well, stable of various sorts of neutron detectors. We have a 3He one, a B10 one, some BF3's...none are as good for this. We don't need the sensitivity of the others at this point, we need accuracy and reliability, and the hornyak gives us that. Along with count rates that don't swamp preamps and counters...
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.