Abstract: A direct dosimeter for measuring gamma radiation flux having dose rates in excess of 0.1 megarad/hr. The dosimeter includes a gamma heating material such as aluminum or lead positioned in an evacuated housing. A thermocouple measures the temperature of the material when subjected to high levels of gamma radiation. From the time rate of change of the temperature measurements, the absolute value of gamma radiation flux may be determined before the temperature of the material has reached a steady state value.