Determination of the parameters of the 1.15 keV resonance in 56Fe by prompt gamma-ray detection

Time-of-flight measurements of the capture cross-section of iron have been made on the Harwell electron linac HELIOS with a gamma-ray detector using the pulse amplitude weighting technique. The work is in support of the Task Force which was set up by the NEANDC to resolve the large discrepancies between capture and transmission measurements of the 1.15 keV resonance parameters. Two series of measurements were made. In the first, relative capture yields from a 2 mm thick natural iron sample were measured. These data allow the 1.15 keV parameters to be determined relative to the parameters of other resonances in iron. In the second series a thin laminated sample of iron and gold was used, allowing absolute resonance parameters to be obtained by normalizing the capture yield at the 'saturated resonance' in gold at 4.9 eV. Results are presented based on recent calculations of the weighting function using a sophisticated electron transport code. (author)