Measurement of the M1 radiative strength function in Fe resonances by using the shift of the primary gamma line emitted upon the capture of intermediate-energy neutrons

A procedure is proposed for studying the partial cross sections for radiati ve neutron capture in the energy region around a few keV. This procedure is based on measuring, by means of a Ge gamma spectrometer, the shift of prim ary gamma transitions induced by neutrons with energies in the range 5 less than or equal to E-n less than or equal to 200 keV with respect to transit ions following thermal-neutron capture. By the way of illustration, the fir st results are presented that have been obtained by measuring the partial c ross sections for radiative-neutron capture in Fe-56 resonances that is fol lowed by gamma transitions to the ground state and the first excited state of the daughter nucleus Fe-57. Two runs of measurements have been performed with neutrons from the reaction Li-7(p, n) implemented at a Van de Graaf a ccelerator, the ring and central geometries of sample arrangement being use d alternatively in these measurements. Owing to this, neutron capture has b een studied independently in the neutron-energy ranges 10-60 keV and 25-80 keV covered in the former and the latter experimental setting, respectively .