Measurements of cross sections for the 209Bi(n, 4n) reaction by using high energy neutrons with continuous energy spectra

We measured 209 Bi(n, 4n) cross sections at neutron energies E n = 29.8 ± 1.8 MeV and E n = 34.8 ± 1.8 MeV. Bismuth oxide samples were irradiated with the neutrons produced by impinging 30, 35 and 40 MeV proton beams on a 1.05 cm thick beryllium target, where the proton beams were from the MC-50 Cyclotron of Korea Institute of Radiological Medical Sciences (KIRAMS). The neutron flux for each proton beam energy E p , Φ E p ( E n ), has a broad spectrum with respect to E n . By taking the difference in the neutron fluxes, the difference spectra, Φ 40 ( E n ) −Φ 35 ( E n ) and Φ 35 ( E n ) −Φ 30 ( E n ), are obatined and found to be peaked at E n = 29.8 and 34.8 MeV, respectively, with a width of about 3.6 MeV. By making use of this observation and employing the TENDL-2009 library we could extract the 209 Bi(n, 4n) 206 Bi cross sections at the aforementioned neutron energies.