Abstrakt
The Fe-56(n,gamma) thermal neutron capture cross section and the Fe-57 level scheme populated by this reaction have been investigated in this work. Singles gamma-ray spectra were measured with an isotopically enriched Fe-56 target using the guided cold neutron beam at the Budapest Reactor, and gamma gamma-coincidence data were measured with a natural Fe target at the LWR-15 research reactor in Rez, Czech Republic.
A detailed level scheme consisting of 448 gamma rays populating/depopulating 97 levels and the capture state in Fe-57 has been constructed, and approximate to 99% of the total transition intensity has been placed. The transition probability of the 352-keV gamma ray was determined to be P-gamma(352) = 11.90 +/- 0.07 per 100 neutron captures.
The Fe-57 level scheme is substantially revised from earlier work and approximate to 33 previously assigned levels could not be confirmed while a comparable number of new levels were added. The Fe-57 gamma-ray cross sections were internally calibrated with respect to H-1 and S-32 gamma-ray cross section standards using iron(III) acetylacetonate (C15H21FeO6) and iron pyrite (FeS2) targets.
The thermal neutron cross section for production of the 352-keV gamma-ray cross section was determined to be sigma(gamma)(352) = 0.2849 +/- 0.015 b. The total Fe-56(n,gamma) thermal radiative neutron cross section is derived from the 352-keV gamma-ray cross section and transition probability as sigma(0) = 2.394 +/- 0.019 b.
A least-squares fit of the gamma rays to the level scheme gives the Fe-57 neutron separation energy S-n = 7646.183 +/- 0.018 keV.