Needing more than a spark test?

[rwm]

This is great! So what do you think is causing the counts with the Am 241 removed? I agree that your steel counts might be buried in the Am241 counts. Can you give us any indication of the KeV on the X axis?

 

[homebrewed]

This is great! So what do you think is causing the counts with the Am 241 removed? I agree that your steel counts might be buried in the Am241 counts. Can you give us any indication of the KeV on the X axis?

I think a lot of the background counts are simply due to noise. I had the trigger level set pretty low to show both "peaks".
If the iron peak is hidden in the Am241 background signal that suggests the right most spectrum is in the 6Kev range.

The distribution from the noise could be the result of my pulse discrimination code -- it rejects pulses that are either too long or too short. But that's speculation on my part. These results need to sink in some, and likely will prompt additional experimentation to figure out what's really going on here.

I put a piece of copper in the sample chamber and didn't see a huge difference so that Am241 "junk" really needs to be addressed!

 

[rwm]

Still a landmark step in this process!

 

[WobblyHand]

Despite the false "stuff" a major step forward! Pretty encouraging, if you ask me.

 

[graham-xrf]

I think it is all fabulous, and I am envious. Real stuff changes when you take out the sources. Just excellent!

So now to think about what we see.
Without the sources, the pile of counts to the left could be anything, even a mains field leak noise hum.
It's cluster of counts to the left means that it has a consistent interference signal level.

It also infers that the smaller crowd to the right are either real returns from material it encountered, or from the Am241 radiation itself.
The latter is less likely since photons cannot "go around corners", but we know that when they start out, they can go sideways right through stuff.

I am mindful that most smoke detector sources material are fixed onto a little disc made of steel, so I designed that they get glued down into the bottom of a little lead bucket about the diameter of a pen. I was heartened to discover a Mr Pete video on machining lead, right next to another where a lead body pen is actually made. Not my thing, but that is where the idea came from.

If we don't care about the weight, then the entire sources carrier and photodiode front mount could be made of lead, but I thought aluminium, with the little lead mugs set into it. Then I thought "what if it is sensitive enough to see aluminium"? I then thought to use plastic, it being mostly carbon and hydrogen. Lead everywhere is the bonkers sure-fire solution. We can use aluminium with lead inserts, provided the line of sight from the aluminium structure can't see the PIN diode, which is achieved by the presence of the little lead box collimator around it.

From our previous posts, and the contribution from @RJSakowski, I think 2mm thick walls is enough.

But back to what Mark is doing. I see this problem as a little detail. What we see is a real achievement, and it's great!

 

[WobblyHand]

Truly fantastic results thus far.

Another possibility for positioning the sources might be to 3d print the complex shape and use lead inserts. For a single use one could print the punch(es) to press the lead into the complex piece.

This is getting exciting enough to spin a board. @homebrewed what's your front end (analog circuitry) look like again?

To minimize the effects of power supply noise you could run off a small 6V battery. I have a lead acid gel battery for this purpose. Did this for my radar chronometer. 50/60 Hz noise would be greatly diminished. The output voltage is about 6.4V. I ran it through an LDO regulator to get 5V, and a second 3.3V regulator for my analog circuitry. If I recall correctly, I'm using very low noise op amps similar to what @graham-xrf chose.

 

[RJSakowski]

I'll ask a question that may have been discussed before. Is your detector shielded from the source? Xrays travel in a straight line so facing the aperture toward the sample and away from the detector should eliminate any primary radiation. As to making your lead shielding. I would use a variation on the lost wax method of casting. A pattern could be machined from machinist's wax and used to make a mold, The wax us burned out and the metal poured to make the part. Jewelers have used this technique to make complex castings in gold and silver and large bronzes have been cast using this method. With the much lower melting point of lead, it should be fairly easy. IIRC, plaster of Paris can be used for the mold. Another possibility is making a reusable mold from silicone with a plaster of Paris shell. If plaster of Paris won;t work, the mold could be made from potter's clay and fired. Rather than wax, it may be possible to 3D print the master and burn it out. The clay may be required for that. Is there a low melting point filament available? Thinking children's 3D printer here.

 

[graham-xrf]

Another possibility for positioning the sources might be to 3d print the complex shape and use lead inserts. For a single use one could print the punch(es) to press the lead into the complex piece.

3D-Printed?
That you suggest this makes me think you might have access to a 3D-printer.
Looking back to post #530 on page 53, there is a whole bunch of geometry and pictures. For convenience, I put one of them here again.
This would be machined entirely out of lead, like Mr Pete has shown can be done.
Alternatively, using lead bucket inserts, and the rest is out of aluminium or 3D-printed plastic


Now suppose I enlarge the holes to accept a lead bucket pressed or glued into them.
If the "walls" are 1.6mm thick, then 99% X-rays are stopped.
If the walls are 1.8mm thick, then it's 99.9%
If the walls are 2mm thick, then go with more "9s"

Now suppose I add the models of the lead source shielding mugs, and also, alter the body to have a lead shield cylinder stuck in there around the PIN diode. The rest of the body now becomes aluminium or 3D-printed plastic. There is still to be a aluminium barrier foil or disc behind the plastic (not shown), and come to that, possibly also aluminium foil or graphite over the aperture to the PIN diode.
However this goes together, all those low noise electronics are in a Faraday enclosure, also with some effort to design against magnetic field ingress.

Now suppose you get a STEP file of the shape, or the FreeCAD model. I have not yet tried generating G-Code, or suchlike.
(Is that only for CNC machining)? There may be strategies, like printing first a thin base layer to have it stick down to the platform, and "supports".
Whatever it be, if you have a re-worked model STEP, or CAD from FreeCAD, do you have a printer to make one?

For @RJSakowski , Hi there. We have today been looking at your posts.
With the geometry I had in mind, there is not any path for source photons to hit anything except the test target. Photons may travel to the end of the universe, but they can't go around corners! The original geometry could do with some improving, but..



If the 3D-printing route is taken, one has the advantage that just about any shape can be made, and @WobblyHand might want to try.

For those without 3D printers ,to make the holes in a turned metal blank, one needs a rotary or index-able something under the drill. It may be that a much simpler shape, with all the sources facing forward, not tipped at any angle, would work just as well. I think Mark @homebrewed has already shown that it seems to work OK

I am at present enmeshed in electronics, and giving consideration to switched gain range amplifiers, but if the STEP file is desired, I can try modifications to the CAD model now.

 

[graham-xrf]

People's preferences?
Just to ask - are we wanting 6 or 8 sources?
Also - might putting the board up the middle of some ferrite toroids, or SMPSU transformer cores be a cheap alternative to mu-metal?
Also, do we all like having the PIN diode soldered planar to the amplifier board, instead of on a right-angled plug-on? The little computer could then come off the back on the right angled header?

 

[RJSakowski]

I seem to recall that model now. I'll confess that I haven't followed your progress through all the posts.

I don't have a 3D printer myself. As to a low melting point filament, this is what I found. https://filaments.ca/collections/3d-filaments/products/pcl-low-temperature-filament-yellow-2-85mm At a melting point of 60ºC, it could be melted of of a mold with hot water. It would be a simple way to make complex geometry.

As to the design, my assumption is that the sources are essentially isotropic radiators so the orientation of the source is of little consequence.
I would want the sample to be a close to the detector as possible, consistent with proper shielding of the source. I would also want as much lead between the source and the detector as possible. To that end, on your model, I would fill the air space below the detector in the drawing with lead and extend the lead behind the source. More shielding around the detector too.