Needing more than a spark test?

Like Graham, some things have delayed my work on an XRF setup. A trashed-out rental, damaged by drug-addled tenants, has required some serious work. And, unfortunately, some serious money to address. In the (few) spare moments I have right now I've been working on the enclosure/shield for the detector and signal conditioning boards, but it's been slow going.

Some information I recently found suggests that the noise coming out of the detector diode can be greatly reduced by going to a zero-bias mode, something to experiment with when I have more time. In that situation it will behave more like an x-ray "solar cell". Dropping the noise floor, if it can be done without significantly lowering its sensitivity to x-ray photons, would be a good step forward.

On the bright side, my wife and I have received our second Covid vaccination. Takes some of the stress out and permits the thought of visiting family members we haven't seen in over a year.
 
Mark - so sorry you have to deal with fixing up damage like that!
I can feel OK by things like storm damage, or natural events, even the consequences of my own mistakes, but damage from other humans behaving badly brings resentment, anger, and sadness.
I too am looking at some XRF stuff, the partly assembled ADC lash-up, which recently shared with adventures in layout fluid. Unfortunately both have to stay put in the face of tax accounts and house structure repairs/changes.

Bias noise was something I feared. Reverse biased diodes have always been an excellent source of noise, especially zeners, and especially avalanche types. A multi-doped PIN photo-diode would have some potential for noise. Some noise diodes are guaranteed to have loud wide-band Gaussian white noise up to many GHz. From what you say about it, I will likely arrange bias to be variable, and maybe include some filtering to take out the noise at bandwidths above what we need to reproduce the pulse .

I have had vaccination #1. The second will be due in about 4 weeks, but already I feel much safer. A couple of days back, there were zero COVID deaths in Scotland, and zero in London, with only 7 patients in ICU. Theis does not mean "its over", because any one infected fool in a society that has decided they are back to life in 2019 just starts a whole new wave, and you have to go back to the beginning, as has happened in France.

We now know that those vaccinated not only can survive better. It seems COVID never really gets started in them. Not only do they not get ill, they also are not infectious, and cannot pass it on! I'm pleased you got there. Removing that background stress really does make a difference to one's life!
 
While searching around for information on PIN diodes as radiation detectors I came across this. Suggests we're not totally nuts (maybe).:geek:

I also found that Mouser carries a number of large-area PIN diodes, including a through-hole version of the X100-7 (although its P/N is given as a PS100R-7). It runs about $107. The PC50-7-TO8 is 50mm^2 and costs $62.86, but it would be necessary to remove the glass window. I think that would be possible, by making a special pot chuck to hold it in your lathe and cut off the top portion where the window is. The diode would be very sensitive to light so it probably would not be suitable for a portable XRF system.
 
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rwm said:
Any body still working on this?
R
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Yes indeed! This is one of my best interests. For a while, it has to go behind quite a lot of other stuff. My life got kind of complicated through 2020, mostly changes forced from the COVID thing. At the same time, I took on construction of a new outbuilding workshop. Even now, most of my electronics/chemistry stuff is in wraps, but I have acquired a binocular microscope of the right power to help handle those tiny parts. I had expected that, now I have retired, there would be time and space to do more of what I please. I have found that to have that happen, one has to clear down all that stuff one had left to "do later", and then start actively directing life towards one's favourite project.

I have sought to find a A/D converter that comes in a package somewhat larger, to make it easier for hand PCB assembly, but unfortunately, the chips that really do the trick well come in packages with 0.5mm pin pitch. The one I have mounted to the little computer is of that sort.

Right now, most of us still have to become experts at observing sparks, and the best we get from that is a binary choice guess at the metal hardness, with some small clues if there is high carbon content. Heat treatable hardening alloys remain a big guess, unless one keeps known steel marked and labeled from the beginning, including off-cuts. Who can afford a hardness tester, like as shown off by Stefan Gotteswinter? I know I can assume parts of ex-brake discs are cast-able semi-steel, and I can tell which bits among my stash are titanium, but for me, there is no substitute for really knowing what stuff is some random chunk of steel..

Between Mark and myself, I think we have already wrung out the viable circuits, and it remains to press home actual experimental construction. I have an ADC mounted on a Raspberry Pi, and I can poll it with crude single test code snippets. Mark has being doing rather more in digging up alternative photo-diodes choices, but we have both purchased the kit that comes with one fitted. One of my major aims is to have an outcome that can be readily be acquired and put together by almost any HM member, as low cost and convenient as possible, with all software simply downloadable. There would be an element of machining or ad-hoc fabrication with hand tools. If at all possible, I am trying for ready-assembled electronics. Some of the chips I would use can be had already mounted on PCBs as "evalulation" kits.

Another major chunk needed in the end is a whole lot of information. From circuit design, and descriptions, through the whole process of putting it together, and how to test it. There has to be, at least, some sort of manual, or collection of PDFs with pictures. Any folk here who actually make one may be able to throw in a few pictures.

Hang in there Robert - we will definitely be getting back to this.
 
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rwm said:
Any body still working on this?
R
Click to expand...
Yes, but slowly due to our rental rehab that is still going on (hopefully to be concluded soon), plus general summer-time distractions. Toward that, I've continued making my aluminum enclosure to (1) keep 60Hz noise out of my now-unshielded detector and (2) keep 60Kev gamma rays inside it. The box has two partitions, separated with another aluminum plate that will have a hole milled in it to allow the fluorescence photons to strike the detector. The hole will be ringed with my Am241 sources. The opposite exterior wall is hinged and will be held closed with a clasp, used to install samples for analysis.

I still need to come up with a mounting scheme for my detector and signal-conditioning board. It probably will be a couple of nylon plates with grooves milled in them to hold the boards in place. It would have been smart to make my signal conditioning board the same size as the detector board but I wasn't thinking that far ahead :(.

Here's a photo of my enclosure-in-progress, partially disassembled to show most of what I mentioned above:

IMG_1608.JPG
The clasp (sitting on top of the enclosure) was purchased at a local hardware store.
 
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Regarding Graham's comment about my looking at alternate detectors, I'm just thinking about the possibility that the large-area PIN detectors we have will turn out to be just too noisy to give us anywhere near the energy resolution we need. There may be ways to improve it, by reducing the dark current (by reducing or eliminating the bias voltage), but we really won't know until we have some lashups to play with. I can just about guarantee that the first working version won't come up to snuff.

I didn't mention it in my previous response, but I also bought myself a nice birthday present this summer that should come in handy. It's a "real" lunchbox-style DSO, 2 channel 1GSPS/100MHz BW 'scope. Made by Hantek. My little hand-held 'scope is pretty limited in bandwidth (and functionality), plus the connectors are quite fragile -- nowhere near as robust as BNC's or SMA's. I'm always afraid I'll bugger up the connectors so I never disconnect the probes on that one. The thing that put me over the edge was the need for an external trigger to debug some Ardunino I2C bit-bang code, and the hand-held doesn't have that.

I've been lusting after a NanoVNA but can't justify it (quite) yet. If I come up with a PCB design that needs 50 ohm striplines....well, the pocketbook will quickly open....
 
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@graham-xrf I'd recommend you look at using hot air soldering for fine pitch stuff. For the longest time I put off SMT stuff. I bought some solder paste and a hot air gun. Works a treat. Bought the hot air gun off AliExpress. Was very inexpensive for its capabilities. If you have some components that are sensitive to heat, they also have low temperature lead free solder paste. If only making one or two boards, just use a sharpened toothpick to dab some on. Or get a narrow gauge blunted hypodermic needle and syringe. Also works well. I've also bought SMT to through hole adapter boards. Then you can use the "more modern" parts with the tiny footprints.
 
I have had good luck using a toaster oven as a reflow oven. The board shop I use will provide a solder stencil at no extra cost. Took some practice to get the temp cycle right but any issues can usually be fixed with a hot air gun or a fine point on the soldering iron. The nice thing about reflow is that it is fast. I can put several in the oven depending on the size of the boards. I used to avoid surface mount components and now I find that I am working to avoid thru-hole components.
 
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