Background study for ( n , γ ) cross section measurements with C 6 D 6 detectors at CSNS Back-n

The Back-n beam line of the China Spallation Neutron Source is the first white neutron facility in China. One of its goals is to perform radiative neutron capture cross-section (${\sigma }_{\mathrm{n\gamma }}$) measurements. To study the experimental backgrounds of this new facility, a measurement of the ${\sigma }_{\mathrm{n\gamma }}$ of ¹⁹⁷Au was carried out with a C₆D₆ detector system at Back-n. Time-dependent backgrounds induced by the scattered neutrons and in-beam gamma-rays were measured and analyzed with ${}^{\mathrm{nat}}$C and ${}^{\mathrm{nat}}$Pb samples. The black resonance filter technique was employed to evaluate the shape of the backgrounds and perform the normalization. Besides, Monte Carlo simulations of these backgrounds were carried out with the Geant4 toolkit. The simulated results were compared with the experimental ones and the good agreement found allowed us to validate the background evaluation method.