  Appreciable hard X-ray (HXR) and gamma-ray emissions in the 0.04 to 150 MeV
energy range associated with the 2003 October 29 solar flare (X10/3B) were
observed at 20:38 to 20:58 UT by the SONG instrument onboard the CORONAS-F
mission. To restore flare gamma-ray spectra we fitted the SONG energy loss
spectra with a three-component model of the incident spectrum: (1) a power law
in energy, assumed to be due to electron bremsstrahlung; (2) a broad continuum
produced by prompt nuclear de-excitation gamma-lines; and (3) a broad
gamma-line generated from pion decay. We also restored spectra from the RHESSI
data, compared them with the SONG spectra and found a reasonable agreement
between these spectra in the 0.1 to 10 MeV energy range. The pion-decay
emission was observed from 20:44:20 UT and had its maximum at 20:48 to 20:51
UT. The power-law spectral index of accelerated protons estimated from the
ratio between intensities of different components of gamma rays changed with
time. The hardest spectrum with a power-law index S = - 3.5 to - 3.6 was
observed at 20:48 to 20:51 UT. Time histories of the pion-decay emission and
proton spectrum were compared with changes of the locations of flare energy
release as shown by RHESSI hard X-ray images and remote H alpha brightening. An
apparent temporal correlation between processes of particle acceleration and
restructuring of flare magnetic field was found. In particular, the protons
were accelerated to sub-relativistic energies after radical change of the
character of footpoint motion from a converging motion to a separation motion.
