Effective Capture Cross Section of Pa-233 for Thermal Reactor Neutrons

Thorium metal was irradiated in the thermal neutron flux of the Low Intensity Test Reactor and of a graphite reactor. From mass spectrographic analysis of the U²³⁴ content and assumption of an effective capture cross section (including epithermal as well as thermal neutron capture) of 8.0 barns for Th²³², the effective neutron capture cross section of Pa²³³ for thermal reactor neutrons was determined to be 140 ± 20 barns.