Water shielding

How to build the perfect shield for your measurements? Discuss it here!
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ZeeCaptain
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Water shielding

Post by ZeeCaptain » 30 May 2017, 22:45

Hi,

i ordered 14 kg lead-balls a short time ago and now i am planning on creating my shielding.

While doing this i thought: Why take lead if you can take water?

Is there any mayor downside using water beside the size and that it is maybe is not the best idea working with very expensive toys near/in so much water?

Here is my (poorly drawn draft).
Image

The outer and inner shell would be PVC or some other plastic. The lead in side the inner shell is to counter the lift from the air inside the water. The inner container can be pulled out of the inner shell to work on the detector, change samples and so on.

What do you think of this idea?
Do i need to add some Copper in the inner container against fluorescence from the shielding?
How worse does water compared to lead shield against gamma rays?

greetings

Felix

miree
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Re: Water shielding

Post by miree » 01 Jun 2017, 05:15

Hi!

Gamma-ray interaction probability is proportional to Z^2 ( Z is the atomic number of the shield material ). The reason for taking lead is the large Z=82. Water would be a pretty weak shield: hydogen (Z=1) and oxygen (Z=8). To get the same shielding as lead you would need a very large volume of water.

Water is good to slow down neutrons because the mass of hydrogen nuclei is almost equal to the mass of a neutron. That maximizes the momentum transfer in collisions between neutron and hydrogen nuclei.

Best regards,
Michael
Michael Reese
Darmstadt Germany

luuk
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Re: Water shielding

Post by luuk » 02 Jun 2017, 07:08

Hi Felix,

Water can be used as a shielding although the Z is indeed relative low compared to Lead, it will be good for shielding against low energies and because a large part of the “natural” background are manly low energies they can be easy reduced with water special energies <500KeV.
There are also some advantages: it is cheap and it is every were available (but you will need a lot of it), and if not in use you can drain it and don’t have a big heavy shielding standing in the way!
If you have a water tank like used for rainwater it is easy >200liter/Kg it can work as a nice shield worth to try it out.

Luuk

P.s. I found this table it might be usefull.

Absorber 100KeV 200KeV 500KeV

Water 4.1 cm 5.1 cm 7.1 cm
Aluminium 1.6 cm 2.2 cm 3.5 cm
Iron 0.3 cm 0.6 cm 1.1 cm
Copper 0.2 cm 0.5 cm 1.0 cm
Lead 0.01 cm 0.07 cm 0.4 cm

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iRad
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Re: Water shielding

Post by iRad » 02 Jun 2017, 07:23

Luuk
Great information to know and make a copy of, thanks for the table.
Tom
Please check out my eBay Store: http://stores.ebay.com/The-Rad-Lab
Cheers, Tom Hall

luuk
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Re: Water shielding

Post by luuk » 02 Jun 2017, 14:49

Oops an errror!
I forgot to mention that the table gives the half value, so the radiation is reduced by 50%.
Luuk

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