Borated Polyethylene (10% B)

(CH₂)ₙ + B

Shielding

Density: 1 g/cm³

Atom density: 0.119303 atoms/b·cm

Polyethylene loaded with 10 wt% natural boron: hydrogen slows the neutrons down and B-10 absorbs them, in one material.

Where these numbers come from

PNNL-15870 Rev. 2, "Polyethylene, Borated" (id polyethylene-borated): density and full isotopic composition are taken from the compendium unchanged.

Open the compendium entry for the isotope-by-isotope table and the compendium's own notes.

Material compositions from PNNL-15870 Rev. 2 (April 2021), R.S. Detwiler, R.J. McConn Jr., T.F. Grimes, S.A. Upton, and E.J. Engel, Compendium of Material Composition Data for Radiation Transport Modeling, Pacific Northwest National Laboratory. Full report (DOI 10.2172/1782721)

Composition

Nuclide (ZAID)	Weight fraction	Atom fraction	Atom density (atoms/b·cm)
H-1 (1001)	1.2532e-1	6.2768e-1	7.4885e-2
H-2 (1002)	2.8805e-5	7.2192e-5	8.6127e-6
B-10 (5010)	1.8427e-2	9.2894e-3	1.1083e-3
B-11 (5011)	8.1550e-2	3.7391e-2	4.4608e-3
C-12 (6012)	7.6568e-1	3.2208e-1	3.8425e-2
C-13 (6013)	8.9738e-3	3.4835e-3	4.1560e-4

This is the material as formulated. The cards below carry weight fractions, written negative, which is what MCNP and Serpent read as a mass basis.

Bound scattering

ENDF/B-VII.1 has a thermal scattering law for this material as formulated, so the cards attach poly.20t. Free-gas scattering would misplace the thermal spectrum here.

Generated material cards

MCNP

c Borated Polyethylene (10% B)
c PNNL-15870 Rev. 2, "Polyethylene, Borated" -
c reactormc.net/nrdp/material/borated-poly; rho = 1 g/cm3 (use -1 on the cell
c card)
m30    1001.80c  -0.125322  $ H1
       1002.80c  -2.8805e-5  $ H2
       5010.80c  -0.018427  $ B10
       5011.80c  -0.081550  $ B11
       6000.80c  -0.774645  $ C
mt30   poly.20t

MCNP and Serpent cards use .80c (ENDF/B-VII.1 at 293.6 K) — renumber m1 and change the suffix to match your deck. SCONE compositions are atom densities in atoms/barn-cm with the .03 suffix matching temp 300. See the library reference before changing a suffix: the mapping is not portable between vendors.

Notes

The compendium formulation is 10 wt% boron as B₄C in polyethylene, at 1.00 g/cm³. The old entry described a 5 wt% product at 0.95 g/cm³, which matched neither the compendium nor the 5% products on the market (~1.02 g/cm³) — commercial sheet runs from about 1% to 30% boron, so check the datasheet for the material you actually have. Boron capture is what suppresses the 2.2 MeV capture gamma that plain polyethylene produces.

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