An Improved Experimental Set-Up for (N,xn) Reactions Studies

Abstract

The (n,xn) reactions play an important role in many nuclear applications like accelerator-driven systems, fast neutron reactors or nuclear medicine. Their experimental study is necessary to improve and validate simulation models especially between about 10 MeV and 200 MeV where the pre-equilibrium process becomes significant and data are scarce. A new experimental set-up has been built near the Tandem 7MV of Bruyères-le-Châtel (France) in order to perform new (n,xn) double-differential cross section measurements. It is composed of a 4π neutron detector and a low background neutron beam line. The detector, called CARMEN, is a tank containing 1 m 3 of Gd-loaded liquid scintillator. It is intended to neutron multiplicity distributions measurements event by event with a very high efficiency (85% to fission neutrons). Due to its high sensitivity, CARMEN requires a well collimated neutron beam line as well as a low background. The neutrons are produced by nuclear reactions between proton or deuteron primary beams and tritium or deuterium targets surrounded by a heavy concrete shielding through which a channel was made defining the neutron beam. Neutron beams between 4 and 25 MeV are thus available. The entire set-up (detector and neutron production) and original experiments will be presented.The energy spectra of tagged (n,2n) reactions have been measured in the 8.3 -13.3 MeV range on several targets. The results are compared with the predictions of the nuclear reaction code TALYS.