Making it out of lead! How?

[WobblyHand]

We have considered the sources facing forward, so easier to make geometry. It is wasteful of radiation we need just getting absorbed in shielding. The angled irradiation increases the number of hits. This is a back-scatter scheme. The higher energy gamma rays enters the sample, and some of then get lucky and hit an atom of sample. That hit makes it "glow x-rays". Of the X-rays generated, going all over the place, some fraction are in the direction of the detector.

Multiple use? We do hope so! If we get it really low cost, and it works, some HM members might want to get one together. If they can machine their own somehow, all we need distribute is the drawing.

Surprisingly - I made it all the way though your epic xrf thread. It was continues to be interesting, so keep it up!

As for multiple use, I was merely thinking that lost wax is destructive of the positive. So a better idea would be to make a silicone rubber mold of the wax item that you laboriously machined. Once you get the mold one can make as many positives as one wants. The mold could be aluminum with some minor changes.

My comment on the pockets for the sources is to have them come in a plane, rather than normal to the concave surface. That way the mold can be removed without damaging the wax. Actually, if the pockets are normal to the planar back surface, you could forgo lost wax and just machine a mold straight from aluminum. That would be the way to make a lot of them.

 

[graham-xrf]

Yep, cast it. We make special profile lead gaskets all the time at the railway using two piece steel molds. Or you can make silicone molds quite effectively that will cast lead with surprising precision. Great candidate for 3D printed pattern.

OK - this is experience we value.
I have not done it before, but I can maybe provide the G-Code, or at the very least, a STEP .stp model file, which is universally transportable between various CAD softwares.
So - who has a 3D printer, for a tryout?

We can maybe figure out a version that can use a 3D printed assembly, still shielded, by carefully setting a lead shield "little bucket-without-a-lid" into the plastic, for each source. Up to now, a one-piece, uncompromising lead shield seemed the answer

Then also, add a shield lead ring set into a groove trench around the detector.

There also needs to be a flat square lead sheet under the detector, arranged as two thin sheets, the one nearest the detector having a couple of holes for fine wires, and the second cover turned 180° to cover the holes.

For @RJSakowski OK, we can't see the glue elements. I had been conditioned by previous best practice. The thing about anchoring stuff like radioactive sources, like diamonds in a setting, is never to trust glue of any kind, but go back to fundamental materials and foolproof shapes. Years ago, the anti-static ionizing bars over the clean room tables had to be recalled because the radioactives were in tiny glass balls, laid into some kind of plastic, probably epoxy. They started to come out as "glass balls dust". I think the glue might have stood up to it, were it not being deteriorated by the very radioactives they were supposed to contain! I think it was Polonium-210. Think Alexander Litvinenko.

 

[graham-xrf]

Surprisingly - I made it all the way though your epic xrf thread. It was continues to be interesting, so keep it up!

As for multiple use, I was merely thinking that lost wax is destructive of the positive. So a better idea would be to make a silicone rubber mold of the wax item that you laboriously machined. Once you get the mold one can make as many positives as one wants. The mold could be aluminum with some minor changes.

My comment on the pockets for the sources is to have them come in a plane, rather than normal to the concave surface. That way the mold can be removed without damaging the wax. Actually, if the pockets are normal to the planar back surface, you could forgo lost wax and just machine a mold straight from aluminum. That would be the way to make a lot of them.

If we 3D print it in plastic, with a sprue, and a drain.
Then dunk in gypsum plaster, enough times to goo it all over, drying in between.
Then warm up slow, until baked at a bit more than 100C, to lose all water.
Then fire it. Oven, torch, whatever.

Would we not turn the plastic 3D thing into carbon, and then to CO2, and end up with a mold we can pour lead into?

[Edit: Maybe not such a good idea. A 3D printed part takes a long time to make, and is not a "cheap" thing. The re-usable rubber, and the wax seems better]

 

[WobblyHand]

If we 3D print it in plastic, with a sprue, and a drain.
Then dunk in gypsum plaster, enough times to goo it all over, drying in between.
Then warm up slow, until baked at a bit more than 100C, to lose all water.
Then fire it. Oven, torch, whatever.

Would we not turn the plastic 3D thing into carbon, and then to CO2, and end up with a mold we can pour lead into?

Don't know how well the PLA or whatever will bake out, but that's the idea. The waxes sold for this purpose (investment casting) will bake out properly. Have to say the 3D investment casting is worth a try! You will have to work on the surface quality of the print - because that surface will be replicated in the final part.

 

[graham-xrf]

Most of the stuff I cast is much smaller than what you have in mind. 1-1/2 inch is pretty big for what I do. That said, most of my work is cast simply because lead is difficult to machine. Even with a hardener, Antimony, alloyed in it's a PITA. On other parts, I need multiples and machining once to make a dozen pieces is obvious.

I use aluminium for molds because lead doesn't bond at the temperatures where I cast. There are fishing gear and bullet molds that differ, some steel some carbide(?). But for what I do, aluminium gives good results. And easy to work.

I often must put a lot more thought into making the mold than I would for making the part itself. But it does pay off in the long run. And the mold goes on a shelf for future use.(?) The part pictured above would be a fairly simple mold to make. Likely a little deburring, but with lead no big deal.

.

Also for @WobblyHand
To avoid mold release problems, it may be OK to cast it without the recess holes for the sources, and drill them out afterwards.

If the mold is aluminum, does it just "let go" from the lead easily?
Do you let it cool slow? Do you dunk it in water?
Should we put a couple of degrees slope into the sides, to help it come out?

 

[graham-xrf]

Get a copper plumbing end-cap. Pre-heat the copper and flux the inside of it. Then pour your lead in it. The copper will act to give the whole assembly more rigidity, and make it less likely to bend in the chuck. It will act as a foundation.

Copper and lead solder together real fine, making a join layer of harder amalgam, Try wire wool on a de-soldered and wiped heating pipe joint to know this! If the flux is boric acid, we are still OK. Boron is only atomic number 5. It glows feeble at 183.3eV

This idea is great for holding it together in a chuck.
Just maybe, we could leave the copper in place. Copper has atomic number 6 [Edit: 29]. The X-ray that it produces is only a feeble a loud 8.04keV and 8.90keV very visible to the detector. [Edited].

This opens the possibility of a design in copper, with source pockets filled with lead, and then drilled out to fit the sources.
We note: Tin-lead solders, brass, bronze, are all verboten. We have to keep the elements pure.

 

[WobblyHand]

Also for @WobblyHand
To avoid mold release problems, it may be OK to cast it without the recess holes for the sources, and drill them out afterwards.

If the mold is aluminum, does it just "let go" from the lead easily?
Do you let it cool slow? Do you dunk it in water?
Should we put a couple of degrees slope into the sides, to help it come out?

If the holes go in normal to the back plane that would be ok, not sure that pad angle is that important. Less handling to cast it.

Aluminum is fine for a lead mold. Guys cast bullets with aluminum molds all the time. In my experience casting, at worst, one gives the mold a rap with a wooden stick and the piece will pop out. I'd let the mold cool slowly rather than shocking it with water. It won't take long for the lead to solidify. Actually, it would be worth preheating the mold the first time, to prevent wrinkles, but after a couple of casts, that mold will be good and hot!

It's always good to make the mold release easier, so sloping the sides will help a bit.

 

[DAT510]

Reading this post and the use of Americium, reminds me of the story about the "Radio Active Boy Scout" and the smallest EPA Superfund Site.

The Radioactive Boy Scout, by Ken Silverstein

When a teenager attempts to build a breeder reactor

harpers.org

 

[WobblyHand]

Since I don't have a model, with exact sizes, I don't know the exact weight, but I'm estimating the lead ring will weigh around 1kg. (1135 gm) This is based on 40mm diameter, 20mm high cylinder of lead. Based on experience casting bullets with a hand mold, I'd say that a full mold will be hard to hold up for long! Especially since you want long mold handles to stay away from the heat/splashing lead.

 

[graham-xrf]

Since I don't have a model, with exact sizes, I don't know the exact weight, but I'm estimating the lead ring will weigh around 1kg. (1135 gm) This is based on 40mm diameter, 20mm high cylinder of lead. Based on experience casting bullets with a hand mold, I'd say that a full mold will be hard to hold up for long! Especially since you want long mold handles to stay away from the heat/splashing lead.

Thanks for the input, and indeed thanks to all who have replied.

It has triggered some alternative ideas. Also, I am trying to confine the lead to where it is actually needed. If that piece weighs a whole kilogram, I am imagining the whole gadget may become a bit unwieldy. Where we do use lead, it takes at least 2mm to stop the gamma.