Experience with monitoring mixed radiation fields in nuclear reactors is described. Dose rates were measured by the radiation-produced heat in simple calorimeters constructed for this purpose. Principles of construction are reviewed for two types of instruments. Accuracies of about 10 per cent are estimated.
One type of calorimeter measured the total reactor radiation. This device embodied a graphite radiation absorber suspended within a hollow cylinder. Heat flowed radially to the wall of the cylinder. Four units of this type were operated in the Materials Testing Reactor.
The other type of instrument measured only the gamma portion of the reactor radiation. Neutron sensitivity was minimized by using lead as the absorber. Heat flowed axially along the lead rod to a heat sink. Three versions were built in evolving the final model which was used to determine gamma heat in the Brookhaven graphite reactor.