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arXiv · 2609.37087

Trace isotopes set the neutron horizon of liquid argon

Yasser Maghrbi
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Abstract

Near 57 keV, destructive interference makes argon-40 almost transparent to neutrons. The 0.4% of argon-36 and argon-38 in natural argon then supply over 90% of its opacity, amplified 230-fold. Published transmission data rule out the argon-36 evaluation FLUKA uses by default, even with every other isotope made transparent, and bound its cross section in the window to 2-11 b. In a DUNE-scale detector, switching to the data-consistent evaluations moves the fiducial fraction of argon-41 calibration captures by 9-13% while the total yield changes by only 2%: the effect is on where captures occur, not how many.

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Yasser Maghrbi. 2026-09-29. Trace isotopes set the neutron horizon of liquid argon. https://arxiv.org/abs/2609.37087

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