Irradiation can't guarantee bacteria-free food. The word irradiation conjures up different images for different people. And, in fact, irradiation can do many different things. It is irradiation, in the form of radio waves, which allows a trucker to listen to country music as he drives across the country. It is irradiation, as ultraviolet light, that gives a tan line at the beach.
Irradiation runs metal detectors in food processing facilities.
And irradiation can kill pathogenic bacteria. As with all technologies it is both, depending on how it is used. A simple view of irradiation is that it is simply energy in wave form. It can be very high energy and penetrating, such as x-rays, or relatively low energy and reflecting, such as radio waves. Irradiation can be generated by electrical energy, light energy, magnetic energy, chemical energy or atomic energy.