This paper describes a method for measuring neutron-absorption cross sections based on the following principle: Introduction of a neutron-absorbing substance into a pile decreases the reactivity and in order to keep the power level constant the control rods must be displaced. By proper calibration this displacement may be used as a precision measure of the absorption cross section.

• Received 14 March 1947

DOI:https://doi.org/10.1103/PhysRev.72.16