We report observations of one-dimensional neutron diffraction from highly oriented pyrolytic graphite (HOPG), where the scattering angle varies continuously with incident angle following classical grating-like behavior. The 2D polycrystalline structure of HOPG—with highly aligned layers along the $c$ axis but random in-plane rotations—creates planes of scattering intensity in reciprocal space at $Q_c=n(2\pi /d)$ where $d=3.35\AA$ is the interlayer spacing. As the Ewald sphere sweeps through reciprocal space during sample rotation, it continuously intersects these planes, producing the observed angular dispersion. We observe both first-order ($n=1$) and second-order ($n=2$) diffraction at conventional scattering angles (${25}^{\circ }–{70}^{\circ }$), with peak positions that remain temperature-independent between 10 K and 294 K and follow quantitative agreement with momentum conservation $Q_c=k[sin\psi -sin{\psi }_f]=n(2\pi /d)$. X-ray diffraction under similar conditions shows no comparable behavior, confirming that sharp nuclear-vacuum contrast is essential. While diffraction intensities are weak ($\sim {10}^{-6}$ of Bragg peaks), the observations demonstrate how the interplay of atomic-scale periodicity, nuclear contrast, and structural disorder enables observation of continuous diffraction curves at thermal neutron wavelengths, illustrating how HOPG's unique microstructure determines its scattering properties beyond conventional Bragg diffraction.

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• Crystal structure
• 2-dimensional systems
• Neutron diffraction
• Neutron scattering