Water shielding

[ZeeCaptain]

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).


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]

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

[luuk]

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

[iRad]

Luuk
Great information to know and make a copy of, thanks for the table.
Tom

[luuk]

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

[Sparky]

A couple of years ago I experimented with a 34 gallon (129 l) trash bin as a water shield using both tap and rain water. It was much less effective than I thought it would be. I learned that water requires a very large “build-up” correction factor because of the large scattering distance and that the tap water contained some detectable NORM as well. The common attenuation formulas are for narrow beam conditions. With about 10 inches (25 cm) of water thickness the shield reduced counts about 28% with the tap water and more with the rain water (I can’t find my data for the rainwater test).

I recently moved to a different house and the city was kind enough to provide a nice clean recycling bin of about 80 gallon (303 l) capacity. I still had the test hardware so I repeated the test with tap water. The water thickness was about 13 inches (33 cm) on the sides and about 20 inches (50 cm) above and below.
The results were similar to the last test. Using a one inch NaI probe and a Ludlum model 2, I saw a reduction of a little more than 50% in gross counts. I took brief spectrums of background (shielded and unshielded) using a 38 mm NaI probe after calibrating with Radium. The water did have slightly reduced relative counts on the low energy end. The only background radionuclides I think I could ID was Pb214 and Bi214 (U238 chain) in both Spectrums. I believe rainwater might further reduce counts to 60-75% but it will take a very wet day to find that out.

The idea is only practical if you have very large volumes of very clean water. I watered the lawn with my “shielding” afterward.