Science/Engineering/Technical forums

We recently obtained one of these guys. They're very cool. The only thing I've gotten better spectra out of was a carefully tweaked "gallon jug" 6" NaI detector and an URSA II, but by comparison...this stacks up pretty decently.
Here it is with a sample of recently refined U ore on top, taking a spectrum. I then asked to identify what it was: And here's the resulting spectrum after plotting with my linux software. I could have blown this up much larger, but since there are only 256 bins (one special for "out of range" or "cosmics" there's really not much point at least for posting, looking at it carefully and using the cursor to get gnuplot to ID the lines accurately, that's another story. Here's the result (I will be posting the source code someplace under software real soon - check back if this hasn't had a link to it added yet). Here is thorium metal, about 1.8 grams we bought at a yard sale... Now for something really hot. We scored some torbernite, this is a fist-sized chunk placed green side down on the detector. It overflowed and quit after 200 seconds. I don't keep this one indoors! You can see it out on the porch with any gamma detector right through the lead pig I keep it in! The unit identifies it as natural U and radium. The theory is this is from Oklo and is very old natural reactor waste, more or less. It's not something you want real close to you for long, it's also giving off tons of radon and has contaminated the inside of the pig with radon daughters. Wash hands after handling with gloves, this stuff. Of course, this wouldn't be complete without showing Cs-137 from our .25 uC calibration source: You get about the same results from a new-old stock spark gap tube, but those are louder yet, even though they are on the old side, since they started out 4 times as hot as this.
More coming...as soon as I can.
These units have been going for the ~$300 range on ebay, with various faults. I can say that missing the battery cover and the knob are no big deal - you almost need a crowbar to get the batteries out, and if you look at the pic above, you'll see I just put a little silicone tubing over the sharp knob holder to make it easy on the fingers. If you have the PC software, even the screen doesn't have to work well - just well enough to navigate the menus, and you're golden. It looks much better on the PC anyway, and that way you have long term storage as well. While the unit will hold quite a few spectra and other data...it's battery backed and may fail if that battery goes down, and it isn't labeled past a time stamp. Obviously, on a PC you can make the name more meaningful, just for starters.

Now to really put it through the grinder. I took two spectra, one with a pound of potassium nitrate on it, and one just background. Here they are. It takes a good examination to see the difference, but it's there. FWIW, it ID's the KNO3 correctly, but also ID's my background the same. Who knows? It's a wood shop and not that far from a woodstove...but I do see a difference here with a known sample on it. Barely. And here it is with that pound of "stump remover" on top: These posts aren't yet showing all this can do. It also has survey and dose modes (your choice of Gy, Sv, and Rem), which my software handles, but enough for one post right now. I plan to put on a coat and take it for a ride in survey mode along with a vidcam so we can look at my campus and see what's hot (I already know - we have some pretty hot rocks here sticking out of the sides of the hills). Most of the "hot" stuff we've collected is kept far away from living quarters...I only keep some very small samples in the shop, and even those are in lead pigs, and kept away from where I usually am.

All these were taken with the setting at 1.5 MeV full scale. Our unit also has a 3 MeV full scale...might be interesting on the fusor later on.

This is very cool stuff indeed!

Do you have any information / guesses on how it determines pulse heights? Analog preprocessing / peak holding also, or everything handled digitally?

Philipp

I have only guesses based on the age and what people were up to then, but no actual knowledge yet. This one works perfectly so I'd be nuts to take it apart - I've seen pix of a partially disassembled one, and this thing is packed with boards, multiple layers and on at least 4 sides. We will soon have one of the not-perfect ones in our hot little hands, so I'll look inside that one - I believe Peter Schmelcher also got one that requires repair - he's a good engineer and will be looking inside, perhaps I can get him to report here instead of just in email. Given what's supposedly wrong with unit #2 (Bill's), I can probably fix it - or it doesn't actually need fixing. The previous buyer returned it for "lack of ability to hold calibration". Well, NaI has one heck of a temperature coefficient (15% over temperatures humans frequently encounter) so this (supposedly bad) one demands a recalibration quite often - that's not an actual problem! It's attention to detail by the original designer. Mine does that too, every few hours, which in my experience isn't on the long side, actually. The big jugs take hours to adjust to the temperature differential between down and upstairs here and drift with widened lines the entire time. It's actually a fairly big deal and very important to get right if you want good looking spectra. This unit appears to have at least a clock that runs all the time, and maybe a thermistor as well. Good for them, that's how to do it right.

I suspect an old school trick here - a wideband delay-line so parts of the circuit can "know the future" compared to other parts. Expensive but effective. This way, you can have a "slow" but accurate peak detector before the delay line, and catch the exact peak as it comes out the other end of the delay. I've seen that before in top of the line but no longer working NIM bin stuff (one had over 20 meters of coax in it for that). Hopefully, it's not full of house-numbered-only parts. We'll see, and I'll report when we do. This one's not super good at the very low energy scale, but that's not really an issue for what I want it for, which is fusor emanations that no one else has been able and/or willing to look for. EG, I need it a lot, but not for very long, to find out a couple of crucial bits of information to enlighten myself (which I will of course, share once I know what I'm talking about). I'm guessing, based on age, that it's a z80 or z8000 based unit, maybe early 68k, but that's a guess - it's on the slow side as computers go. To make it run on a pair of D cells was pretty advanced for those times, I suspect the power circuitry is full of fancy tricks (to boost from 1.8v or so at EOL of two D cells to 5v and then phototube voltages-regulated) that you can now just buy in a cheap chip.

After that, all's fair, and we'll take a look inside. The fact that it is telling me the truth pretty accurately when I know what I'm feeding it is enough for me at the moment. I won't be going into the prospecting biz (no one wants what you'd mostly find with this anyway), and I kind of doubt I want to get into X ray fluorescence for false precious metal detection (since you need a whale of an X ray source, not good to be around, for that). Bill wants one to prospect around the high-tech junkyards he likes to frequent, and there's no telling what he might find with one. We've seen some pretty strange stuff in those - and after all, that's where my fusor chamber came from, it was once a scanning electron microscope.

Of course, there's always the prospect of hooking in one of the big jugs and getting really much better spectra at the high energy end of things - or the thin-crystal one I have for the other end. But that can wait till I do the desired survey of fusor output under various conditions. This is lacking in past efforts as a bunch of neutrons are not good for the health of the NaI::Tl crystal scintillator - you can activate it (either the I or the Tl) and the thing becomes near-useless for awhile after that. So no one's done it in any sort of definitive way. I'm going to fix that! As my email sig says, "why guess when you can know?". I'd rather do it homebrew, as we are both trying to do - but also, I'm keeping my eyes on the fusion prize. That has to come first.

In a way, this might be like astronomy - every time some investigator gets a new capability, things take a big leap forward in that field. Perhaps we get lucky too...