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Shielding Effects > Solution Details

Shielding Materials

Solution entered: 2/6/2008    Solution updated: **********

Most radiation fields at Hanford are combinations of different kinds of radiation. Normally, temporary shielding is installed to reduce dose rates from fast neutrons, thermal neutrons, beta, and gamma radiation. Fast neutrons are attenuated by materials containing large amounts of hydrogen. The interaction of the fast neutrons with hydrogen slows the neutron to thermal energies where they are more easily attenuated. Dense metals, such as lead, will also slow fast neutrons by inelastic scattering at higher energy levels. Shielding materials commonly used are water and polyethylene. Thermal neutrons are slowed by water/polyethylene and can be virtually eliminated by the presence of high thermal neutron cross-section materials such as boron, lithium, or cadmium. Beta radiation is best shielded using materials with few protons and neutrons in the nuclei so that bremsstrahlung, a secondary radiation similar to gamma, is not created. Plastics, rubber, concrete, and light metals like aluminum make good beta shielding. Rule-of-Thumb: Range of beta particles in air is ~12 feet/Mev of energy.


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