Borated Polyethylene – How It Works

Plasti-Shield® is an effective shielding material with 5% boron by weight to meet all relevant applications in healthcare such as cancer treatment, diagnostic, and hospital facilities. Other applications include linear accelerators, nuclear/radiation shielding, industrial uses, nuclear power plants, seaport, airport, and border security and other applications requiring attenuation of thermal neutrons. Prime vendors to the U.S. government certify Plasti-Shield® as Grade II, with 1% boron, and Grade 111, with 2% boron, neutron-shielding material on nuclear submarines and naval warships. Our process, materials, quality programs, sampling, testing, tracing and packaging all meet or exceed military specifications including MIL-P-23536A.

Yet how does borated polyethylene act a shield?

The best materials for shielding neutrons must do three things: moderate or slow down neutrons, absorb slow neutrons, and shield against any resulting radiation.

Moderating or slowing down neutrons. Materials containing light atoms such as hydrogen atoms found in polyethylene accomplish this. The nucleus of a hydrogen atom contains only one proton. Since a proton and a neutron have almost identical masses, a neutron travelling from a fission reaction colliding with a hydrogen nucleus gives up most, if not all, its energy to the proton after one collision. This is similar to billiards when a cue ball hits another ball of identical mass, the cue ball can stop and the other ball starts moving with the same velocity. On the other hand, if a cue ball hits a bowling ball (neutron vs. heavy nucleus), the cue ball bounces off with very little change in velocity, only a change in direction. Therefore, a material such as lead is ineffective for blocking neutron radiation. To clarify, lead is very effective at stopping gamma rays and x-rays which differ from neutron radiation.

Technically, a hydrogen (H-1) atom has a moderating cross-section of 20 and a capture cross-section of 0.2.

Absorbing slow neutrons. Materials with high neutron capture cross-sections like boron easily absorb slow, or thermal, neutrons. Boron’s neutron capture cross-section is 2000 times more than hydrogen.

Technically, a boron (B-10) atom has a moderating cross-section of 2 and a capture cross-section of 200.

Shielding against any resulting radiation. In the case certain absorber materials such as cadmium a strong emission of gamma (v) rays accompany the absorption of neutrons requiring additional shielding to weaken the

effect of the gamma (v) rays. This phenomenon is much less important for boron as a neutron absorption material and results in a significantly reduced energy dosage of only 0.42 MeV.

Borated polyethylene is lightweight and workable making it the perfect choice for neutron shielding.

For more information contact MarShield Radiation Protection Products- 1-800-381-5335.