  We show that interactions of fast particles with the boundary shell of the
local hot bubble could make an important contribution to the 0.5-1 keV diffuse
X-ray background observed with ROSAT. The bulk of these nonthermal X-rays are
due to line emission from fast O ions of energies around 1 MeV/nucleon. This is
the typical energy per particle in the ejecta of the supernova which is thought
to have energized the bubble. We find that there is sufficient total energy in
the ejecta to produce X-rays of the required intensity, subject to the details
of the evolution of the fast particle population since the supernova explosion
(about 3 10$^5$ years ago based on the age of the Geminga pulsar). The
unequivocal signature of lines from deexcitations in fast ions is their large
width ($\delta E/E$~0.1 for O lines), which will clearly distinguishes them
from X-ray lines produced in a hot plasma. If a small fraction of the total
ejecta energy is converted into accelerated particle kinetic energy (>~30
MeV/nucleon), the gamma-ray line emission produced in the boundary shell of the
local hot bubble could account for the recently reported COMPTEL observations
of nuclear gamma-ray lines from a broad region towards the Galactic center.
