A measurement of ( n , xnγ ) cross sections for 208 Pb from threshold up to 20 MeV

Gamma production cross sections for neutron inelastic scattering, (n,2nγ ) and (n,3nγ ) reactions on 208Pb were measured at the Geel Electron Linear Accelerator (GELINA) from the respective thresholds up to at most 20 MeV. An unprecedented neutron energy resolution of 1.1 keV at 1 MeV (35 keV at 10 MeV) and a total uncertainty of about 5% was achieved for the integral gamma production cross section of the most intense transition in 208Pb. The gamma production cross section was measured for 29 transitions of the inelastic channel, 5 transitions of the (n,2nγ ) channel and one transition of the (n,3nγ ) channel. Based on the evaluated level scheme of 208Pb, the total neutron inelastic scattering cross section and the level cross sections were deduced. Four large volume HPGe (high purity germanium) detectors were used for the detection of the γ -rays. The 88.11% enriched 208Pb sample was placed at a flight path length of 198.551 m. The cross sections were measured relative to the 235U(n,f ) standard cross section by continuously monitoring the neutron flux with a fission chamber containing 235U. The results are compared with the existing experimental data from the literature and with model estimates obtained with the recent * Corresponding author. Tel.: +32 14 571 381. E-mail address: [email protected] (A.J.M. Plompen). 1 On leave of absence from “Horia Hulubei” National Institute for Physics and Nuclear Engineering, Bucharest,