The hydrogen retention of B4C converted graphite was investigated by u
sing ECR ion irradiation apparatus. The retention properties were exam
ined by a technique of thermal desorption spectroscopy (TDS) after the
hydrogen ion irradiation. The H-2 desorption peaks appeared both at 3
50 and 700 degrees C. The former peak was regarded as the detrapping f
rom B-H bondings, and the latter from C-H bondings in the B4C layer. T
he CH4 desorption peaks appeared both at 250 and 700 degrees C. Compar
ed with the case of graphite, the hydrogen retention of B4C rapidly de
creased with the temperature, since the detrapping of B-H bondings occ
urred around at 300 degrees C. The total amount of trapped hydrogens i
n the B4C was 1.5 times larger than that of the graphite. The activati
on energies of H-2 and CH4 desorptions of the B4C were considerably sm
aller than those of the graphite. The hydrogen retention of the B4C wa
s largely reduced by the He+ ion bombardment after the hydrogen ion ir
radiation. In particular, the reduction ratio for the hydrogens trappe
d by boron was observed to be large.