usually for the purpose of biological protection using multi-layer composition.

For example some submarines are sequential layers of water and iron. In the later submarines using liquid metal coolant is used instead of lead and iron. Everything is determined by the characteristics of the reactor. The combined use of light and heavy materials needed for protection from both the gamma and neutron radiation by

Following shielding materials are used in submarines;

1) High atomic number materials are required to stop gammas. Lead is the preferred choice.

2) For Capture Gammas. Boronated Polythene is used to reduce this effect.

3) Dense hydrogenous materials are the most efficient neutron shields. Polythene is used extensively.

The ppt attached explains shielding and its calculations

Thanks a lot Dr. Ahmad

Dr Ahmad,

Thank you for a very detailed and informative response. However, just a question about bullet point # 2 in your response regarding Captured Gammas: isn't Boronated Polyethylene primarily used for capturing neutrons because of the high neutron cross section of Boron, and the low Z for carbon  and hydrogen in Polyethylene to thermalize the neutrons?

It would seem that for slowing down Gamma Rays one needs a high Z element.

you are right.

Secondary Gamma Rays are created by the capture of thermal neutrons by hydrogen. These captured gamma rays can be minimized by adding boron, resulting in a significantly reduced energy dosage of only .42 MeV.

please see attached document on boronated plastic shield.

Thank you for the clarification. What you actually meant in your response, and I did deduct is: The proposed Boronated polyethylene is to "PREVENT" the creation of the "Capture Gamma Rays" through the (n,Gamma) reaction. Whereas the implication in the original response was that Boronated Polyethylene was used as a shield.

Thank you for the clarification.