Improving my shielding

[ZeeCaptain]

Hi,

at the moment i use 15 40x10x3cm 10kg Steelplated lead plates as my shielding. (so i get about 6cm shielding in allmost any direction)
The normal background with my detector is around 105 cps and in the shielding, about 2.2cps, but on the side the cables come out, there is no plate but a bucket filled with about 10kg of lead balls. I will take care of the "upper" end later.

Now i want to improve the shielding by lining it, because the fluorescence is fairly visible. I am not really into the lining of shieldings so i would love to hear if my lining is appropriate.

I am considering a 2mm lining of Sn99.9% or Sn95Sb4Cu1 (I think the Sn95Sb4Cu1 could be better to work on and more durable, what do you think?)
And 0.7mm of copper.

The dimensioning of the lining is nearly like the wraith_oz's new shield.

What do you think of it?


greetings

Felix

[MaxGaspa]

ZeeCaptain,

For my shield (picture atteched) made by lead with 3.5 thickness minimum the shielding factor (defined as the ratio of counts with energy grater than 20 kev) is about 20 and I tested the effect (known and reported in several textbook ) of the copper lining. In the picture you can find three spectrum of a 0.9 +/- 20% uCi Of Cs137 (Spectrum Techniques) using three different condition

Green line = lead only

Pale blue = a cylinder of plastic 4 mm thick

Brown = an additional cylinder (most internal) was added made of pure copper 1mm thickness and two disk of pure copper same thickness one attached at the top (with an hole for the cable) and bottom of the cylinder.

As you can see the X-ray fluorescence peak (at the red vertical line) is decreased adding copper but the additional material will increase the back scattering peak. You should choose whether is better to have more X-ray or more back-scattering.

I never tested a sheet of tin because pure tin is very soft and is quite difficult to get it (at least in Italy) at a reasonable cost.

Hope this helps

Max

[sgt_bear]

Hi
you could use pure tin, at 2mm it will be quite flexible, but not super soft. Probably would be best to mount it on the lead plates with flexible glue! I did use pure tin in my shield, and i bought it from pewtersheet.co.uk, they deliver to anywhere in europe. For the inner part of CU you could use multiple layers of copper sheed used in roofing, which should be available in a materials store near your or at a roofing company. Use two layers of 0.5mm or one layer of 1mm, 0.7mm as you desire might be difficult to get...or construct.

I used 2mm of Tin, and 2.3mm of Copper (given from pipe, not choosen that dimension) in my shield: viewtopic.php?f=10&t=292

[ZeeCaptain]

Thanks for your answers!
I think i am going with the Sn95Sb4Cu1 for some extra durability. Also i don't really want to glue it to the single elements so i am a bit more flexible with the setup. Instead i think i am going to glue it onto a magnetic film so i can attach it to different plates and remove it when needed.
Beside from that: The paint on the plates is really old and it is starting to rust so i have to repaint it.
Does someone have a industrial shielding and can tell me if they are coated with normal paint like 2K or are they coated with plastic? I talked to a few paint shops that say, whatever paint i use, it will rub off when slipping the plates onto each other and i don't think i could prevent that when moving the shield or putting samples in it so i might go for a plastic lining.

[Alain]

Hi,

I think puting magnetic stuff into a shield (close to PMT in the detector) is not a good idea. PMT's are extremely sensitive to magnetic field (even Earth natural field) and even with good magnetic shield you should avoid to put anithing magnetic inside the shield. In other case you might expect some troubles with spectrum-shifting.

Regards,
Alain