Core-electron distributions in beryllium

Abstract

X-ray diffraction and Compton profile measurements have been extended to larger scattering vectors and electron momenta than used previously in order to check the claims of an expansion of the core electrons in beryllium metal from the free-atom configuration. The absolute reflection powers of the h0.1 reflections with 0.74 < sin θ/λ < 1·40 Å⁻¹ were measured from a single-crystal wafer in the symmetrical Laue geometry. Close agreement with the theoretical scattering factors of the free atom is obtained with the thermal parameters B₁₁= 0·460 ± 0·01 Ų and B₃₃ = 0·415 ± 0·01 Ų, which are almost identical with the neutron results. The Compton profile measurement was made on a thin polycrystalline foil of Be using an annular ²⁴¹Am source and a high purity Ge detector. The measurements were corrected for the instrumental factors and for multiple Compton scattering. The results agree completely with the free-atom values for momentum values above p≳2a.u., which substantiates the conclusion of the diffraction measurement, namely that the free-atom calculation gives an adequate description of the Is core also in solid Be.