We have found that a Raman scattering (RS) peak around 1870 cm(-1) was produced by the annealing of the X-ray irradiated film of single-walled carbon nanotubes (SWNTs) at 450 degrees C. The intensity of 1870-cm(-1) peak showed a maximum at the probe energy of 2.3 eV for the RS spectroscopy with various probe lasers. Both the peak position and the probe-energy dependence were almost identical to those of the one-dimensional carbon chains previously reported in multi-walled carbon nanotubes. Consequently, we concluded that the 1870-cm(-1) peak found in the present study is attributed to carbon chains. The formation of carbon chains by the annealing at temperature lower than 500 degrees C is firstly reported by the present study. The carbon chains would be formed by aggregation of the interstitial carbons, which are formed as a counterpart of carbon vacancies by X-ray irradiation diffused on SWNT walls. The result indicates that the combination of X-ray irradiation and subsequent thermal annealing is a feasible tool for generating new nanostructures in SWNT. (C) 2016 Author(s).