A cryostat is described for irradiations with electrons at liquid helium temperatures and subsequent photoconductivity and infrared absorption studies in the range from 20 to 400 K. Heat is removed from the sample by conduction through a copper tail touching the bottom of the liquid helium container. A mechanical ``switch'' enables the thermal separation of the sample assembly from the helium bath during the annealing studies. A rotatable outer‐tail piece permits irradiation with electrons through aluminum windows avoiding damage to the optical NaCl windows. The beam dosimetry and monitoring equipment are described in detail.