An ESR study has been made on the migration and reactions of H atoms in 1-alkyne (0.5-7.0 mol %)/n-CmH2m+2 (in 10-13) mixed crystals irradiated at 77 K in order to elucidate the alkane radiolysis. A vinyl type of radical (R(v); CH2=C-CH2-R) was efficiently formed (similar to 20%) in the orthorhombic mixed crystals having odd carbon numbers in but not in the triclinic crystals having even in. For pure n-alkanes, the terminal-type alkyl radical (R(I); CH2-CH2-CH2-) was efficiently formed (similar to 25%) only in the former crystals in addition to penultimate (R(II); CH3-CH-CH2-) and interior (R(III); -CH2-CH-CH2-) radicals. The yield of R(v) radical increases and the RI yield concomitantly decreases with increases in the solute concentration. The sum of their yields was almost constant, indicating the same precursor for both radicals. These results could be understood only by H atom reactions. The C-H bond dissociation of the excited molecules formed by hole-electron geminate recombination would occur more favorably for secondary -CH2- bonds than primary CH3- bonds having a large bond strength, resulting in R(II) and R(III) radical formation along with an equal amount of H atoms. The H atoms produced were usually converted to R(n) and R(m) radicals by H abstraction from the secondary -CH2- bonds, as was observed in triclinic alkanes, In orthorhombic alkanes, where the molecules are packed with a wider molecular layer boundary than triclinic alkanes, some part (about half) of H atoms can escape to the boundary region and can migrate. They can abstract H atoms only from CH3 bonds to form R(I), since only terminal CH3 groups are exposed to the regions in the orthorhombic alkanes. In 1-alkyne/orthorhombic alkane mixed crystals, the escaped H atoms can add only to the outer carbon atom of radicals (no formation of HC=CH-CH2-). The present results reveal an important role of the layer boundary regions in the migration and reactions of H atoms and provide clear evidence for the H atom reaction mechanism in alkane radiolysis. HC=C-CH2- triplet bond, which is exposed to the boundary region, to form H2C=C-CH2- vinyl-type radicals (no formation of HC=CH-CH2-). The present results reveal an important role of the layer boundary regions in the migration and reactions of H atoms and provide clear evidence for the H atom reaction mechanism in alkane radiolysis.