Aluminum foils of 99.99% purity were charged with hydrogen using a gas plas
ma method with a voltage in the range of 1.0-1.2 keV and current densities
ranging from 0.66 to 0.81 mA cm(-2), resulting in the introduction of a lar
ge amount of hydrogen. X-ray diffraction measurements indicated that within
experimental error there was a zero change in lattice parameter after plas
ma charging. This result is contradictory to almost all other FCC materials
, which exhibit a lattice expansion when the hydrogen enters the lattice in
terstitially. It is hypothesised that the hydrogen does not enter the latti
ce interstitially, but instead forms a II-vacancy complex at the surface wh
ich diffuses into the volume and then clusters to form H-2 bubbles. The nat
ure and agglomeration of the bubbles were studied with a variety of techniq
ues, such as small angle, ultra small angle and inelastic neutron scatterin
g (SANS, USANS and INS), transmission and scanning electron microscopy (TEM
and SEM), precision density measurements (PDM) and X-ray diffraction. The
USANS and SANS results indicated scattering from a wide range of bubble siz
es from <10 Angstrom up to micron size bubbles. Subsequent SEM and TEM meas
urements revealed the existence of bubbles on the surface, as well as in th
e bulk and INS experiments show that hydrogen is in the bulk in the form of
H-2 molecules. In this paper we calculate the radial distribution function
of the bubbles from the SANS and USANS results using methods based on the
models derived by Brill et al., Fedorova et al. and Mulato et al. The scatt
ering is assumed to be from independent spherical bubbles. Mulato et al. mo
del is modified by incorporating smearing effects, which consider the instr
umental resolution of the 30 m SANS spectrometer at NIST. The distribution
functions calculated from the two methods are compared, and these distribut
ions are then compared with the range of particle sizes found from TEM and
SEM techniques. (C) 1999 Elsevier Science S.A. All rights reserved.