Ionizing radiation and sweeping modify the defects present in quartz. According to relaxation theory the modification should produce a fractional frequency offset, &Dgr;f/f, equal to the negative of the sum of the changes in strength of the acoustic loss peaks with peak temperatures below the turnover. We have measured the acoustic loss and frequency versus temperature curves as functions of radiation dose, and alkali and hydrogen sweeping for AT‐cut cultured quartz crystals with widely varying aluminum concentrations. The largest offsets were observed for the Na‐swept crystals and the smallest for the H‐swept samples. In addition, the smallest radiation‐induced offsets were found in swept crystals with the lowest Al content. The magnitude of &Dgr;f/fwas different from that predicted by relaxation theory. Instead, the observed &Dgr;f/fat the turnover consisted of: (1) the expected relaxation component, (2) a &Dgr;f/fat low temperatures in all samples studied, and (3) a change in the overallf(T) curve which appears only in Na‐swept crystals. The lowToffset is caused byT‐independent changes in the elastic modulus. These must be due to the modifications of the interatomic forces brought about by the radiation‐induced defect changes. Our general findings support the use of swept low‐aluminum quartz in radiation environments.