Separate boundary and orthohydrogen-impurity scattering in solid hydrogen

Determine the crystallite boundary mean free path in solid parahydrogen by performing thermal-conductivity measurements near 1 K that reduce orthohydrogen impurity scattering sufficiently to distinguish the boundary-scattering contribution from the impurity-scattering contribution.

Background

The paper compares its full phonon Boltzmann transport calculations with thermal-conductivity measurements on polycrystalline solid parahydrogen containing 0.5% orthohydrogen. The phenomenological extrinsic mean free path used in the calculations combines crystallite-boundary scattering and orthohydrogen-impurity scattering, so the fitted value cannot by itself identify the intrinsic boundary mean free path.

The cited experimental analysis suggested that measurements at approximately 1 K could suppress the relative contribution of orthohydrogen impurities and thereby determine whether the observed low-temperature thermal resistance is dominated by crystallite boundaries. The paper notes that this distinction had not been established from the existing data.