I am going through the literature to gather information about the densities of vacancies and interstitials in group IV materials. Literature seems to suggest that vacancies and interstitials are created using separate methods. For instance, vacancies could be created by heating the crystal and then by rapidly cooling it down, whereas the interstitials are created by irradiation. My naive intuition says whenever a vacancy is created, an interstitial must be created as well; am I wrong? Can someone please clarify?

Thanks!