The method of neutron transmutation doping (NTD) was used to modify the composition of the tantalum pentoxide (Ta2O5) dielectric of commercial solid tantalum electrolytic capacitors. The dielectric properties of these isotopically engineered capacitors were measured in the temperature range 90-300 K. Neutron irradiation periods of 30 and 120 days resulted in shifts in the capacitance-temperature and dielectric loss-temperature profiles with increasing irradiation dose. The 10 muF 35 V rated tantalum capacitors showed a good radiation hardness. (C) 2002 Elsevier Science B.V. All rights reserved.