Measurements of recombination along the tracks of 2‐MeV alpha particles and 0.7‐MeV protons in thermally grown silicon dioxide are presented. The results agree quite well with the columnar recombination model at applied fields above about 1 MV/cm if one assumes an initial Gaussian column radiusb=3.5 nm. The agreement between theory and experiment at high fields is accomplished even if the excess carriers are assumed to reach instantaneous thermal equilibrium with the lattice. At fields below 1 MV/cm, the agreement between the columnar model and the experiment is improved if one assumes that the carriers remain hot for a finite time before reaching thermal equilibrium with the lattice. The discussion of the details of the thermalization process is intended to be only rough and qualitative because the process is very difficult to model. However, the model and the experiment agree fairly well at low fields if one assumes that the carriers have an energy on the order of 1 eV for a time on the order of 10−13s. The sensitivity of the model calculations to these assumptions is discussed in some detail.