Defects in single-walled carbon nanotubes introduced by low-energy electron irradiation at 8 K were sensitively detected by cryogenic thermal desorption of hydrogen molecules H-2 in the temperature range of 10-40 K. The thermal desorption spectrum was found to change significantly with sample annealing at temperatures as low as 40-70 K. Experimental results suggest that the H-2 physisorption sites responsible for the 'defect' peak at 28 K are interstitial channel space between nanotubes closely packed in bundles which becomes more easily accessible on damage. It is also suggested that the disordering provides groove sites for H-2 physisorption with smaller binding energy causing the damage-induced spectral component around 16 K, slightly lower than the desorption peak at 20 K that is observed in undamaged samples. The spectral change at 40-70 K could be interpreted by migration of adatoms at the low temperatures. (C) 2009 Elsevier B. V. All rights reserved.