A polyethylene composite of 5% boron is widely used in neutron shielding applications because of its excellent nuclear and physical characteristics. Type 201 is lightweight and easily moved for temporary shielding. It is especially useful in shielding against low and intermediate neutron flux levels where excessive temperatures will not be encountered - recommended limit is 180° F (82° C).
Because of its high boron content, type 201 shows excellent attenuation of thermal neutrons and significant reduction of capture-gamma dose. Fast neutrons are shielded by the very high concentration of hydrogen (96% that of water).
Another important advantage of type 201 is its low cost. Type 201 is available with a variety of shapes,
including sheets, bricks, and rods. It is easily shaped and cut using ordinary woodworking tools.
For special applications, it may be desirable to use boron loadings other than 5%. Shieldwerx can
custom manufacture boron-polyethylene in concentrations from 0.5% to 7%. Please contact
one of our shielding experts for further information on these special order materials.
To better serve the marketplace, our 5% Borated Poly was expanded to include a high density version of 201. This material has all the properties of the 201, but the added density contributes to better gamma shielding.
As an alternative to shaping the material in your own shops, our experienced staff can supply the material to your specifications. We have furnished everything from collimators to large cylinders fabricated from type 201HD in our machine shop. Standard shapes include sheets, bricks, rods, and pellets.
This borated polyethylene material has been used around research and test reactors to shield personnel and equipment for neutron radiography and other specialized experiments. It has also been used for shielding of large neutron beam line applications. It has also been frequently used in activation analysis, in the vicinity of research accelerators, and in hot cells and glove boxes that contain neutron sources.
Self-Extinguishing borated polyethylene has slightly more hydrogen content than type 201, and is used for similar applications when flame resistance is a major consideration. It is also a high density shielding material.
For example, self-extinguishing materials are highly desirable in power reactor environments where there is concern about materials that might add to the general level of combustible materials (fire loading). ASTM Test D-635, Flammability of Self-Supporting Plastics, shows the material to be self-extinguishing. ASTM Test D-2863 gives a Limiting Oxygen Index of 30.2. In addition to fire resistance, type 207 produces only negligible amounts of smoke when expose to flame.
Type 207HD contains almost the same amount of hydrogen as that found in water - this gives the material good characteristics for the attenuation of fast neutrons. In addition, it contains boron for thermal neutron capture and capture-gamma suppression. Its density of 1.6 g/cc (100 lbs./cu ft), relatively high for polyethylene based material, contributes to gamma shielding.
Our self-extinguishing line was expanded to include a 5% version of 207HD. This material has all the properties of the 207HD with the added increase in boron content to meet newer safety standards.
Type 207HD5 is used in nuclear power plants for shielding hatches, ducts, sumps, and stairwells and/or other applications where fire safety is a concern.
Control of criticality is of the utmost importance during all phases of power reactor fuel handling, including reprocessing. In order to assure neutron isolation during these stages, materials containing very high concentrations of boron are frequently used.
Type 210 consists of polyethylene loaded with 30% natural boron. It contains 1.87 x 10²² boron atoms per cc and is a very effective thermal neutron poison. It also has significant hydrogen content which is often desirable in criticality control. Type 210 is available in sheets, bricks, and rods. It can also be manufactured with other Boron loadings.
Pure polyethylene (HDPE) is frequently used as a moderator where it is desired to slow fast neutrons down to thermal energies for experimentations. In these applications it is highly desirable to maximize the hydrogen content and minimize any impurities - especially those that might absorb neutrons.
We can supply high purity virgin polyethylene for this application in a variety of shapes and sizes including sheets, bricks, rods, and pellets for filling irregular spaces. Pure polyethylene can be readily machined into complete shapes for applications involving reactor physics, activation analysis, isotopic neutron sources and specially fabricated neutron casks.
Gamma-sensitive radiation detectors used in the vicinity of reactors or other neutron sources must be shielded from capture-gamma rays. These gammas arise from capture of thermal neutrons by surrounding materials or by the detecting crystal itself. Use of borated polyethylene as a shield can attenuate the neutron flux, but the neutrons captured by the boron will result in a 0.42 MeV gamma ray and will therefore not completely eliminate the gamma background.
7.5% Lithium-Polyethylene is very effective in reducing gammas because it produces no capture gammas. Thus, when used to shield a gamma detector from neutrons, it eliminates the usual capture-gamma background. It should be note that due to its lower capture cross-section, lithium is less effective than boron for capturing thermal neutrons and therefore requires a greater thickness than borated polyethylene.
This material can be supplied as cylinders, or as sheets or bricks for building up your own detector shield. All lithium compounds used in our shielding contain the natural isotopic distribution of lithium. Shields using customer-supplied enriched lithium-6 have been manufactured for special applications.
SWX-217 Poly-Biz is an effective alternative to lead-based shielding products. It is comprised of a solid suspension of high density bismuth powder in a polyethylene matrix. Poly-Biz is a non-hazardous gamma shield with an additional benefit as a neutron moderator.
1-inch of Poly-Biz is roughly equivalent to 1/4-inch of lead for gamma shielding applications. Poly-Biz is typically provided as slabs or bricks, but is readily machined into custom shapes, like the cylinder of the shielding cask pictured with handles.
Polyethylene based rods are supplied in standard lengths of 12" (305mm). Nominal diameters are available in 1" (25mm) increments from 4" to 10" (102mm to 254mm). Rods are typically supplied 0.25" (6.4mm) oversize to permit machining to the exact size required. Rod lengths or diameters other than our standard sizes are available on special order. These cylinders are routinely machined to produce small neutron source casks.
Radiation shielding supplied in the form of small pellets has some unique advantages. They can be used to fill irregular volumes as well as spaces that may normally be inaccessible. In addition, the pellets can be poured in place or can be readily transported by means of air pressure or vacuum. They can be removed at a later time if desired. This provides a simple means for filling and emptying shield spaces.
These shielding pellets are available in type 201HD and 213. The pellets vary somewhat in size, but generally are on the order of 1/8" - 1/4" chunks for type 201HD and 1/16" - 3/16" round pellets for type 213. Type 201HD is available with the crusher fines, dry screened or wet washed. It should be pointed out that the packing density of pellets of any kind would be approximately one-half the density of solid material. This, of course, is because of the packing space between the pellets, and this must be considered in estimating the shielding effectiveness.
Size Chart - Inches
Size Chart - Centimeters
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