Scuba soft lead for shielding?

[RobertD]

Has anyone ever tried using so called "soft lead" pouches (ballast bags for scuba diving) for shielding purposes? They are sometimes available at low prices at scuba diving outfits and I believe they are filled with simple lead shot, although some manufacturers are claiming to harden the lead with antimony.

Any thoughts?

[Sesselmann]

Robert,

Can't see why it wouldn't work. I suggest getting a small sample of it first and running a gamma spectrum on it. It is not uncommon for recycled lead to have radioactive contaminants. Lead is not the only metal you can use for a shield, other heavy metals like Tungsten and Bismuth can also make great shields without the toxicity of lead, but lead is cheaper.

Steven

[RobertD]

Thanks Steven.
Will give it a shot and report back.

[RobertD]

Allright, quick update on the subject.
I went to the scuba shop with my Radiacode and had a "look" at the soft lead. I did not see any significant contamination so I went ahead and purchased a few bags.
My "lead castle" now consists of a 0.4 liter tin can inside a 0.8 liter tin can and the space in between is filled with the lead shot. Another soft lead bag is used to cover the opening on top.
With this setup, the background count rate of my Capesym CsI(Tl) detector went down from 30 cps to 3 cps.
Here is a one hour spectrum of a few pieces of a Thorium welding electrode. Calibration is a little bit off, I know.

welding.PNG (83.56 KiB) Viewed 1051 times

welding_log.PNG (96.15 KiB) Viewed 1051 times

[Rob Tayloe]

Some years back I was developing a nuclear engineering lab class. I wanted to fabricate some detector shields. I visited several places that sold and mounted tires on cars and trucks. These places saved the old wheel weights, which were mostly lead. I obtained a small lead melter (such as used by gun enthusiasts to make their own bullets) and proceeded to make molds from aluminum.

Lead fumes are very toxic, so I did the lead melting outdoors and kept upwind of the fumes. Small batches (couple of kg) of lead weights were placed in the melter. As the lead melted the steel parts would "float" to the top. The steel and slag were scooped off the top of the melt and the molten lead was poured into the mold form. I found it necessary to use several propane torches to keep the molds hot while casting the lead. After the lead solidified the molds were disassembled and the lead shield extracted. I painted the lead shield to reduce the lead contamination potential to users. Students were strongly advised to wash hands following labs. No eating allowed in the labs.

Since retiring, I have purchased several hundred pounds of lead shot and lead bricks. The lead bricks (5 cm x 10 cm x 20 cm or 2"x4"x8") were wrapped in a thin plastic coating (think something a bit thicker than saran wrap).

The lead shot was purchased in 25 lb (~11 kg) bags. Typically the bags were sewn burlap. I then placed these intact bags in larger plastic bags (e.g. large freezer bags). I can stack the lead bricks and bags of shot to make ad hoc temporary shields about various detector - source configurations.

I have found best prices for lead shot (in the USA) at places that supply reloaders (for shotgun shells). A few links are provided -

https://www.ballisticproducts.com/Magnu ... oducts/68/

https://www.rotometals.com/ballast-weig ... e-freight/

https://www.sportsmans.com/shooting-gea ... t/p/p51929

[Phouly]

You can absolutely use soft lead for Shielding as far as I can Tell, Ive purchased around 400 lbs from my local scrap yard for $1/lb in the form of Lead Roof Flashing, and have cast it into blocks , and I've seen about a 98% reduction in background for anything lower than 300kev and then it tapers to almost no reduction past 1600kev.

[Sesselmann]

Hi Guys,

If you can find some at a reasonable cost, Bismuth is a nice alternative for shielding. I found a local supplier who has quite a bit. Of course one cant compare the price to scrap lead, but for smaller shields it is a nice alternative. The melting point is 271 C˚ and it can be cast just like lead without being as toxic.

https://billingmetals.com.au/bismuth-99 ... ules-1-kg/

PS, his advertised price is in AUD.

Steven