Experimental determination of the U-236(n(th), f) cross section

The U-236(n(th),f) cross section was measured for the first time at the hig h-flux reactor of the Institut Laue-Langevin in Grenoble, yielding a value of (0.3 +/- 1.0) mb. This means that sigma (f) less than or equal to 1.3 mb , which is about two orders of magnitude lower than previously adopted. Thi s result was obtained by combining a highly enriched U-236 Sample with a ve ry clean neutron beam and assuming that the Westcott factor g(f) = I for U- 236(n, f) With cold neutrons. The new value is compatible with the latest f ission resonance data and with the subthreshold character of the thermal ne utron induced fission of U-236.