Some of us have gotten some of the neutron detector tubes discussed here. I'm playing guinea pig and working on getting them going, but all my moderators are "busy" right now, so I needed another. The roughly correct dimensions for a moderator to get a high percentage of neutrons to thermal without losing them is about 7", which is the size of the Eberline Bonner Ball in that case used with bf3 tubes. But close is close, and I had some 6.5" diameter HDPE, which unfortunately was also UMHW, making it rather a task to do much with. The only way to cut that stuff is to melt it, more or less, with speeds and feeds beyond what many tools can manage. Twist drills screw into it instantly like a tap would, and you then lose both the drill and the piece. When drilling, you have to pull the drill out very often, or the molten plastic will stick it in there -- same result. And it's just a little too large to fit in my lathe without a chuck change I've been avoiding.
I discovered a modern Stanley spade bit goes through this like the wind -- as long as you pull the drill out every half inch, clear the chips, cool it off, repeat. Drilling and tapping for 4-40 screws to hold things on there was actually much harder as all I had in that size was twist drills -- and they tend to self-feed, cool, and stick. Tapping was easy, though. Due to experience with our 3He tube picking up EMI, apparently magnetic induction into the tube somehow, and because I had to cut the piece off with a chainsaw and got a sloppy cut -- I decided to go ahead and build this with a ground-able very low resistance shield with more or less full coverage. I used copper flashing for the top and bottom (so I can solder to it and mount a preamp box right over the tube), and Al flashing for the sides, as it's much cheaper and easier to work with. Neither will have much effect on neutrons.
Here's the parts, partway done, with that drill that really does work on this stuff -- at least if brand new and very sharp.
Here it is almost done. I'll bend up some Cu flashing for a preamp box to screw to the top and hold the preamp and HV input stuff. Since this pic was taken, I've niced it up a little by bashing the copper top and bottom to round them over where they stuck out a little bit. Nicely hides my lousy chain saw work.
Hopefully, I can get a decent test in before the end of the weekend -- I have one other major project I'm working on too -- an 8 core 3 ghz i7 computer, 12 gigs ram, 1 tb mag disk, 40gb SSD, 12 gigs ram -- doing the "build the computer" thing too. And oh -- it has a telsa card (NVidia) for doing very fast double precision floating point -- for simulations and neural net training tasks. I guess I just like hot rods.