ORNL is managed by UT-Battelle LLC for the US Department of Energy Presented to DENIM 2019 Matthew Stone ORNL Neutron Scattering Directorate Bethesda, MD September 17, 2019 Good neutron absorbers make good beamline neighbors Victor Fanelli Lowell Crow Jennifer Niedziela
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Good neutron absorbers make good beamline neighbors
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ORNL is managed by UT-Battelle LLC for the US Department of Energy
Presented to DENIM 2019
Matthew StoneORNLNeutron Scattering Directorate
Bethesda, MDSeptember 17, 2019
Good neutron absorbers make good beamline neighbors
Victor FanelliLowell CrowJennifer Niedziela
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Outline
• Scope & Introduction
• Materials characterized
• Measurements
• Conclusions
“He only says, ‘Good fences make good neighbors.’”R. Frost Mending Wall (1914)
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Scope• Not biological shielding
• Shielding in the vicinity of the neutron beam– Apertures– Masks– Shielding sample environments and samples– Shielding inside of instruments
• Hippocratic oath of neutron shielding– “First, do no harm”– Some shielding adds to the background
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Boron Carbide (ZHIP)
Cadmium
Sample
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• Total cross section is sum of two parts– Scattering cross section PLUS Absorption cross section
𝐸𝐸 (meV) =81.81 (Å)2
Σ𝑇𝑇= Σ𝑠𝑠 + Σ𝑎𝑎 = Σ𝑐𝑐 + Σ𝑖𝑖 + Σ𝑎𝑎• Absorption varies with energy
– Faster neutrons (higher energy, shorter wave-lengths) are more difficult to absorb
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How much material do you need to stop a neutron?
E=3.5 meVλ=4.8 Å
E=14.7 meVλ=2.4 Å
E=81.81 meVλ=1 Å
Compound Z (mm) Z (mm) Z (mm) Melting Point (K)Al 1600 3300 7800 933Cu 70 140 340 1358