Lithium Polyethylene

JC215

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 noted 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 bricks or slabs for building up your own detector shield. All lithium compounds used in our shielding contain the natural isotopic distribution of lithium. Shields using enriched lithium-6 have been supplied for special applications. Please note the customer must supply Li-6 for these special applications.

  • Useful for shielding detectors in neutron fields as the thermal neutron poison utilised does not emit capture gamma
  • High hydrogen content with 7.5% lithium
  • Shields using enriched lithium 6
  • Pre-cast shapes and sizes on request
  • Other lithium concentrations on request
Composition Data JC215
Hydrogen atom density / cm3: 5.44 x 10²²
Hydrogen weight percent: 8.59%
Lithium atom density / cm3: 6.96 x 10²¹
Lithium natural isotope distribution: 92.6 % ⁷Li and 7.4 % ⁶Li
Weight percent of all isotopes of lithium: 7.56%
Total Density: 1.06g/cm³ (66.2 lbs./ft³)
Radiation Properties
Macroscopic thermal neutron cross section: 0.51 (cm⁻¹)
Gamma resistance: 5 x 10⁸ rad
Neutron resistance: 2.5 x 10¹⁷ n/ cm²
Physical Properties
State: Bricks, slabs, cylinders
Color: Off white / Yellow
Odor: No odor
Machinability: Excellent
Thermal Properties
Recommended Temperature Limit: 180 °F (82.2 °C)
Chemical Properties
Chemical Name & Synonyms: Lithium Polyethylene
Trade Name & Synonyms: JC215
Chemical Family: Polyolefin’s
Formula: Mixture (CH²)n, Li
Solubility in Water: Negligible
Reactive Acids: Incompatible w/concentrate acids, Releases CO₂
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