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As part of a larger study to investigate atomic-diffusion behavior in both elemental boron and refractory transition-metal borides, neutron reflectometry was used to examine the temperature-induced self-diffusion of isotopically enriched thin films of amorphous $^{11}\mathrm{B}$ on $^{10}\mathrm{B}$ deposited by electron-beam evaporation. The reflectometry studies were performed and model boron density profiles for samples annealed at various times and temperatures of 360 and 400 \ifmmode^\circ\else\textdegree\fi{}C were fit to the reflectivity data. Although the $^{10}\mathrm{/}^{11}$B interface did not move relative to the air/boron interface upon annealing, the expected standard Fickian diffusion for the annealed samples was not observed. A pinned Fickian diffusion model, which imposes the boundary conditions of a fixed composition of $^{10}\mathrm{B}$ to $^{11}\mathrm{B}$ at the interface, fit the reflectivity data accurately and consistently. A typical equilibrium diffusion constant was determined to be \ensuremath{\sim}${10}^{\mathrm{\ensuremath{-}}17}$ ${\mathrm{cm}}^{2}$ ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$, measured at an annealing temperature of 360 \ifmmode^\circ\else\textdegree\fi{}C. The measured diffusion constants are inconsistent with the high melting temperature of elemental boron, but are consistent with measured boron diffusion constants in other amorphous thin films. The presence of clusters in the boron film is proposed to explain the observed results.

The critical current density {ital J}{sub {ital c}} in Y{sub 0.9}Gd{sub 0.1}Ba{sub 2}Cu{sub 3}O{sub 7{minus}{ital x}} was found to increase relative to the unirradiated value following neutron irradiations in a mixed-spectrum reactor (total neutron fluences ranged between 1{times}10{sup 17} and 2{times}10{sup 18} {ital n}/cm{sup 2}). Additional neutron irradiations of structurally similar GdBa{sub 2}Cu{sub 3}O{sub 7{minus}{ital x}} were carried out in either a highly thermalized or a pure fast-neutron environment (in the same reactor). This was done to determine whether enhancements in {ital J}{sub {ital c}} are to be attributed to defects arising from interactions with thermal neutrons ({ital E}{sub {ital n}}{similar to}0.025 eV) or with fast neutrons ({ital E}{sub {ital n}}{gt}0.1 MeV). Magnetic-hysteresis measurements on these samples indicate that flux pinning (and thereby {ital J}{sub {ital c}}) is enhanced by fast-neutron irradition, but not by thermal-neutron irradiation. On the other hand, the critical temperature {ital T}{sub {ital c}} is significantly altered by exposure both to thermal and fast neutrons. It is proposed that thermal neutrons induce the formation of Frenkel pair defects on the rare-earth sublattice, but that these point defects do not serve as effective flux-pinning centers.