# Calculation of gamma ray shielding value in liquids?

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1. Nov 5, 2014

### Qw_freak

Hi folks

Please bear with me, I'm new here and this may not be the correct forum to ask this question. If this is the case, I'll of course remove my question and ask it the appropriate place instead.

However, here it goes:

I need to be able to calculate how much a given intensity of gamma radiation will penetrate a given column of liquid at different densities.

I hope this makes sense.

2. Nov 5, 2014

### mathman

Gamma ray transport is a complicated process. The penetrating radiation will consist of an unscattered component which is attenuated exponentially with distance and a scattered component which is a function of the source energy, material, etc.

Getting precise results usually requires Monte Carlo calculations.

3. Nov 5, 2014

### Astronuc

Staff Emeritus
As mathman indicated, one has to use a Monte Carlo approach. To do that, one needs to know the macroscopic cross sections for the photon-electron interactions based on the elements (and electron density) comprising the liquid. These are usually tabulated. Basically one has to follow a photon as it's energy is degraded, and also track it's progression through the liquid. There is Compton scattering, but also photoelectric effect in which the gamma is absorbed and an electron absorbs the energy. Also, of the gamma energy is above 1.0221 MeV, then pair-production may occur, which then will produce two 0.511 MeV gammas upon annihilation of the positron with an electron.

4. Nov 6, 2014

### Qw_freak

Thank you both for taking your time to reply to my question.

I may not need a very precise result rather than a good picture of how different densities will effect the amount of radiation I will be able to detect with a scintillator.
Is there an approximated approach which I can use to calculate the unscattered component?

Edit:
My radioactive sources strength's vary from 12Mbq to 12 Gbq

Last edited: Nov 6, 2014
5. Nov 6, 2014

### e.bar.goum

The value you care about is the energy of the radioactive sources, not their activity. The energy is relevant to what Astronuc is talking about.

Are you talking about a liquid scintillator detector? If so, I think that Glen F. Knolls Radiation Detection and Measurement has a treatment of them. Apologies, I don't have my copy with me, else I'd check. He definitely goes over gamma ray attenuation though.

To first order, the Beer-Lambert law does what you want. http://en.wikipedia.org/wiki/Beer–Lambert_law You will need to look up the scattering cross section for whatever liquid you are using, but that is tabulated, and unless you're looking at something exotic, you should be able to find them.