Needing more than a spark test?

Last comment on liquification of hydrogen. If you precool the compressed hydrogen to liquid nitrogen temperature 77K, then the expanding hydrogen will cool, and eventually reach liquid temperatures. (If you do everything right!) Helium has an even lower inversion point, which made it the last gas to be liquified
 
I wonder if this has anything to do with why liquid He is jacketed with liquid N2 in MRI magnets? I have always wondered why that is more efficient than just having better insulation.
 
The solid-state lab I slaved in as a grad student had a gas blend that consisted of nitrogen plus about 3% hydrogen. It was called "forming gas" and was used when you wanted a reducing atmosphere but didn't like the idea of exploding furnaces.

Later on when I worked in a lab associated with a fab (actually making money at the time), we periodically had test drills that simulated things like hydrogen leaks. The alarm sound for that was pretty distinctive, kind of a rising/descending whistle. Fortunately I never heard one in a real leak situation.

Fabs use other really nasty gasses and chemicals in addition to hydrogen. Some spontaneously combust in air, some will combust and release arsenic oxide, some are just plain poisonous. We took fire drills and other types of emergency drills very seriously.....
 
I have a few updates regarding this project. The first is that I pulled the trigger on a 40CF argon tank and regulator. The regulator has a ball-type flowmeter but, since I also now have a MEMS based flow sensor that can measure very low flow rates (it maxes out at 30 SCCM) the ball flowmeter is kind of superflous -- at least, when its being used to operate a detector tube. Though for inert-gas welding it will be useful.

The tank cost a little less than $100. One reason for buying it now: to avoid paying a tariff, if they really are imposed. I didn't see any reason to include a photo of it, everyone's seen gas bottles :)

The second is that I just received the PCBs I designed for testing the 3mm^2 Osram PIN diode for use as an x-ray detector. It was laid out so I could attach a thermoelectric cooler to the back of the board:

PIN detector board.JPG

The amplifier is a composite design -- a JFET front end feeding a low-noise opamp. The feedback capacitance is 330 femtofarads, formed with three series-connected 1pf capacitors (C5,C7 and C8). The PIN diode is labeled "PD1". The "sealing area" denotes where a gasket will go if the TEC is used -- the idea is to seal the detector in an enclosure that contains some desiccant beads to remove water that would otherwise condense on the board and cause leakage problems, electrically speaking.

The pulse coming out of the TIA will be pretty fast, so to make it compatible with my existing MCA code the board also has a low-pass filter network to smooth and slow down the pulse. The opamp package is a dual, and the second amplifier just buffers the output of the low-pass filter.

The design also includes an option to install a temperature and moisture sensor, that's what the 4 connections on the lower right edge of the board are for. That also will only be installed if the TEC is used. Hopefully not!

Finally, an atmospheric-pressure gas proportional detector requires about twice the voltage that my PMT needs (~2KV). None of the HV capacitors in my home-made HV power supply, nor the ones on my detector board, are rated for 2KV. The other thing is that the BNC connectors aren't, either. I bought some SHV connectors that are good to 5KV but they are panel-mount types so not compatible with my existing PCB anyway. It won't take much to change my existing PCB design to accommodate the SHV connectors, though.

I have a 0-4KV power supply I scored a long time ago that will be used for this application, but it's a bit noisier than what the Theremino folks recommend (it's specified to have about 15mV of noise+ripple, and something on the order of tens of microvolts is recommended). I earlier mentioned a "noise eater" design I've simulated so that circuit also will go on the redesigned interface board. That is, IF I decide to proceed with making this kind of detector. It does have one nice feature: it's not light-sensitive, unlike PMTs and PIN photodiodes.
 
Back to the original question, a chemical analysis to determine alloy is about 250 $ as of a few months ago.

You can also do a hard quench (cold water) followed by hardness test. I recently had a bar from McMaster fail to harden. I was able to approximate the carbon content using the quench-and-test method. Using the diameter to search through the catalog, I deduced the sent 12L14 rather than 4140.

I bought a book on quantitative analysis. Identifying an alloy would be a whole hobby by itself. In principal, not difficult but there are lots of steps in which you must add a reactant, observe the precipitate, filter or centrifuge, and make decisions about what to do next. Big flow charts and lots of fussy details. Still, it's more reliable than any alternative, or so I am told
 
ericc said:
I saw an interesting video. Is there anything of use for this project:

Click to expand...
That device apparently can analyze radioactive isotopes due to the higher-energy xrays produced by their decay, typically in the ~100Kev to 600 Mev range. The thing is passive, in that it only detects radioactive elements. Radioactive iron, nickel and cobalt aren't going to be present to any great degree in alloys us machinists want to work with, so we're trying to use a different effect, similar to UV fluorescence, to do the analysis.

One big challenge is that the x rays of interest to us are at the low end of the sensitivity range for many x ray detectors, primarily due to the fact that the scintillator crystals are moisture-sensitive. So they have to be inside a hermetically sealed package, which absorbs most, if not all, of the x rays of interest. Here's a discouraging factoid. The thickness of kitchen-style aluminum foil is sufficient to attenuate the low-energy XRF-generated x rays emitted by iron by about 50%! Specially-built detectors are available, but for far more than the $325 Amazon is asking for the Radiacode 102.

The goal has been to provide a more-accurate test than the old spark test, but remain affordable for hobbyist types willing to spend some time making something.

Technology marches on, so, who knows, at some point maybe there will be the equivalent of a "Mr. Fusion" (channeling "Back to the Future" here) that can do what we want, and is offered as a prize in a McDonald's Happy Meal......but probably not in my lifetime!
 
durableoreo said:
Back to the original question, a chemical analysis to determine alloy is about 250 $ as of a few months ago.

You can also do a hard quench (cold water) followed by hardness test. I recently had a bar from McMaster fail to harden. I was able to approximate the carbon content using the quench-and-test method. Using the diameter to search through the catalog, I deduced the sent 12L14 rather than 4140.

I bought a book on quantitative analysis. Identifying an alloy would be a whole hobby by itself. In principal, not difficult but there are lots of steps in which you must add a reactant, observe the precipitate, filter or centrifuge, and make decisions about what to do next. Big flow charts and lots of fussy details. Still, it's more reliable than any alternative, or so I am told
Click to expand...
There are XRF "guns" available that can do the job, in just a few minutes. But they cost a LOT. I just browsed Amazon and found a few in the mid $20K and up range. Group buy investment, anyone ?:grin:
 
I watched the video, and there was a comment about detecting secondary x-rays. Also, he was talking about resolution down to the 20-30 kev range. This seems to be a useful range. The GAGG had one side exposed. That is an interesting point about moisture, though.
 
ericc said:
I watched the video, and there was a comment about detecting secondary x-rays. Also, he was talking about resolution down to the 20-30 kev range. This seems to be a useful range. The GAGG had one side exposed. That is an interesting point about moisture, though.
Click to expand...
20 Kev is about 4X too high for what we need. The iron x-ray lines that Am-241's 60Kev gammas can excite are about 6Kev.

I have a PMT/scintillator that can go down to 20Kev and it doesn't work at all for detecting iron's 6Kev x rays.
 
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