Interplay between superconductivity and charge-density wave (CDW) in 2H-NbSe2 single crystals irradiated by 3 MeV protons is studied. Both Tc and TCDW are found to decrease monotonically with the increase in irradiation dose. This behavior is different from electron-irradiated NbSe2, where TCDW is suppressed monotonically with the increase in dose, while Tc shows an initial enhancement before it starts to decrease. We attempt to explain this difference based on the negative pressure effect which has been reported in our previous study on NbSe2 irradiated by heavy ions.
