For ultracold neutrons with a kinetic energy below 10 neV, strong scattering, characterized by $2pi l_{c} / lambdaleq 1$, can be obtained in metamaterials of C and $^7$Li. Here $l_{c}$ and $lambda$ are the coherent scattering mean free path and the neutron wavelength, respectively. UCN interferometry and high-resolution spectroscopy (nano-electronvolt to pico-electronvolt resolution) in parallel waveguide arrays of neutronic metamaterials are given as examples of new experimental possibilities.
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