Abstract
X‐irradiation for KBr crystals at helium temperature produces the well known α‐absorption at 6.14 eV (anion vacancies) and an absorption band at 5.4 eV. The generation and annealing properties of this band are the same as those of the anomalous thermal resistivity found after X‐irradiation. It is concluded that Br interstitial ions, which are known to cause the excess thermal resistivity, are also responsible for the 5.4 eV band.