Shield for Gamma spectroscopy - Blenheim

Hello, let me introduce my experimental Gamma spectroscopy shield that I have build in order to lower the background radiation. It is just a concept but it seems to work fine.

For the manufacturing I've used the following materials:
- an aluminium tube (205mm o.d. x h.135mm) closed from one side by an aluminium flange.
- about 40kg of lead pellets 0.8mm o.d.
- one plastic bottle (80mm o.d.)

I've poured the lead inside the aluminium tube to form an flat and uniform layer 30mm thick. Then I've cut the plastic bottle and I placed it inside the aluminium tube, resting on the bottome lead layer. At this point I've poured the remaining lead pellets filling the hollow space up to the top edge of the aluminium tube. The surronding lead volume is more than 50mm and the shielding is effective.

Some numbers:
With my GS-2812 I have a background reading of about 150CPS that reduces to 25CPS inside the shielding.

Further improvements:
Since the prototype seems to work fine, I'm thinking to improve it as follow:
- the probe will be inserted from below and will enter the shielding at least for the lenght of the scintillation crystal
- different layer of shielding materials other then lead will be added in order to reduce secondary radiations (bremsstrahlung) due to the strong deceleration of the beta particles hitting the lead of the shield. According to some articles about shielding techniques, layer of different materials would slow down the beta particles reducing the amount of energy released in form of X-rays. Among these material I would mention PVC, aluminium and copper.
- the sample will be introduced inside from the top and will rest on the tip of the gamma scintillator
- a lead cap will seal the top opening for a complete shielding

I've made a short video on Youtube showing the effectiveness and the benefits given by the shielding.

Thanks for reading,




Re: Shield for Gamma spectroscopy

Post: 715 - Steven Sesselmann
March 14th, 2014 03:03:22am

Thanks for sharing, I really like the idea of using lead shot, actually I have been rthinking of designing a spectrometry shield made from plastic, which can easily be shipped to anyone in the world, and filled up locally with lead shot.

Well done...


Re: Shield for Gamma spectroscopy

Post: 725 - Mike Collalto
March 17th, 2014 09:03:16am
Gday Emanuele.

I was discussing the use of Lead shot with a fellow amateur enthusiast colleague who frequents the Gamma Spectacular forum, saying that although the idea is excellent, the idea that there is a vast increase in the amount of surface area of Lead in contact with the air/chemicals in the air versus solid Pb castle design is a huge consideration with respect to Lead dust etc. I guess a good analogy is to alveoli in the lungs which increase surface area or how turning water into droplet form increases surface area.

Since we just thought of it, perhaps a solution to this is to use thinners to water down some suitable paint that you could use to pour over the Lead shot and perhaps this will stop the paint from gluing the small Lead shot together. Then after the thin coating has dried, it might be possible to apply a second coat and repeat the process ?

During our brief recent talk, he related how he was obtaining a spectrum from a Thoriated gas mantle in a plastic bag in his Lead castle, and that it was seemingly impossible to remove a particle of it that must have been on the outside of the bag the thoriated gas mantle came in. In the end, he discarded the inner copper liner of his Lead castle because he could not get rid of the contamination.

I must say i do immobilize all my samples these days, especially the Thorium mantle and other check sources with epoxy resin or acrylic so i can handle the check sources without fear of particles coming loose. This includes mineral samples and makes life a lot easier/safer.

Hope you are well prepared for any eventualities, and lastly, 'may the force be with you' :-)


Re: Shield for Gamma spectroscopy

Post: 748 - Emanuele C.
March 24th, 2014 07:03:45pm
Dear Steven, thanks for your comment. I'm quite convinced that lead shots are a good compromise and hope this can inspire you in the design of your new product.
I'm about to finish the 3D CAD design of my new shield; I will post drawing and cutaways of the project soon.
Emanuele :)

Re: Shield for Gamma spectroscopy

Post: 749 - Emanuele C.
March 24th, 2014 07:03:51pm
Hi Michele, nice to meet you. :)
I thought this solution basically for two reason:
1) In order to melt lead you should have fournaces and special equipment such as mold, protections, fume extracors, etc. Trying to do it yourself at home is quite risky and raises some concerns about health (.. end eventualy your family will be concerned about your "mental" health Yes, shots avoid lead to be molten into into mold, even if some precautions should be taken due to the fine dust that may escape during the pouring operations.
2) It is easier to transport the shielding encasing and the lead in case of portable equipment.

I don't know if is more effective compared to a solid lead shielding, but it is for sure lighter ;)

Thanks for your comments.

Re: Shield for Gamma spectroscopy

Post: 754 - Boris
March 25th, 2014 07:03:01am
Hi Emanuele,

To eliminate all the risks, if you are going to use lead shot, with is a very sound plan,
you could order it plated, so the balls are encapsulated, copper would be ideal, but there are a number of materials used.

years ago, I used this as weights for diving, because it is more comfortable then the hard blocks.
but then I needed only 8 Kg, so there is a financial problem associated with this...

Cheers, Boris.

Re: Shield for Gamma spectroscopy

Post: 1177 - Stanford
June 18th, 2014 05:06:49pm
Mike, is there a technical consideration for not wanting lead dust or is that a health concern?

Boris, does copper plated lead shot eliminate or mitigate the xray problem?

Emanuele, thanks for this discussion. You brought your 150cps down to 25cps inside the shielding... what is considered low enough?


Re: Shield for Gamma spectroscopy

Post: 1179 - Markus
June 18th, 2014 07:06:13pm
Some good lowlevel shieldings have a 1.5mm layer tin and a layer 1.0 mm copper inside.
The lead have thickness from 50 to 100mm and more...this lead have a low own background.

The crazyest shielding i read about was a monster of 1x1x1 meter!!!
with all around geigertubes to sort out the radioactivity where came from outside the shielding^^

Re: Shield for Gamma spectroscopy

Post: 1181 - Boris
June 18th, 2014 09:06:53pm
Hey Stanford,
Nope the copper plated layer is very thin, wont help a bit is my guestimation.

I would recommend thin copper sheet, rolled up it´s easy to adjust to the desired diameter.
and in this case more is better.

Tin and zinc are also very usable.
Bronze is an alloy of copper and tin. (used as bearings on heavy machinery)
Brass is copper and zinc.

euro coins are a nice alloy to (10-20-50 cents only)

This gives some ideas to what materials can be used.

Cheers, Boris.

Re: Shield for Gamma spectroscopy

Post: 1183 - Vital1 (Peter Daley)
June 19th, 2014 07:06:09am
I designed, and use a non conventional test chamber design.

I purchase enough painted plumbers lead on rolls, to create a 15mm thick lead
wall chamber.

I then lined the inner wall with 4mm of rolled copper sheeting.

Covered it all inside and out with Aluminum you can purchase as rolls from a
hardware store.

It is down to around 7 to 8 cps inside the sealed chamber, using a 50mm scintillator.

I use this designed because I wanted to test large and small items. This design makes it easier to position different sized items around the crystal.

Items like shoes, clothing, marinelli beakers, and check sources can all be placed in this test chamber design. Small samples are placed on plastic stands next to the scintillator.

It is easier to move, because the base and lid are separate from the body. Each
part can be lifted separately by one person.

The attached photo shows this test chamber design with a marinelle beaker full of coconut sugar ready for testing. There are four small rubber feet that the lid sits on. This is to stop metal to metal contact.

I just posted a soil test, using this design in the spectrum section of this forum


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