Experimental Study of the Phenomenology of Spallation Neutrons in a Large Lead Block

%PS211 %title \\ \\The purpose of PS211 is to determine how neutrons, produced by spallation inside a large Lead volume are slowed down by undergoing a very large number of scatterings, losing each time a small fraction ($\sim$ 1\%) of their kinetic energy. The focus is in determining the probability for a spallation neutron produced at an energy of several MeV or more, to survive capture on Lead resonances and to reach resonance energies of materials to be transmuted, such as 5.6 eV for $^{99}$Tc. This process, of Adiabatic Resonance Crossing, involves a subtle interplay between the capture resonances of the Lead medium and of selected impurities. This phenomenology of spallation neutrons in a large Lead volume, is the physics foundation of the Fast Energy Amplifier proposed by C. Rubbia, and could open up new possibilities in the incineration of long-lived nuclear waste such as Actinides or Fission Fragments (e.g. $^{99}$Tc, $^{129}$I, etc.).\\ \\334 tons of high purity Lead, installed in t7, are exposed to a primary proton beam of 3.5~GeV/c or 2.5~GeV/c (10$^{7}$ to 10$^{10}$ protons per PS shot) in the fast extraction mode, and 2.5 to 0.6 GeV/c in the slow extraction mode (10$^{3}$ protons per PS shot). Neutron energy spectra are measured with various techniques over an energy dynamic range of 8 orders of magnitudes. Both prompt and delayed $\gamma$ measurements are performed to study the capture rates in various elements of interest. The correlation between neutron capture time and energy is determined. A pneumatic system ("rabbit") allows to perform delayed $\gamma$ measurements of short-lived daughters activity, during the 14.4 seconds available between two consecutive PS shots. In addition, various types of standard activation measurements are performed.\\ \\Data taking started in April 1996 and was completed by July 1997. The Collaboration is now mainly engaged in a large analysis effort. \\ \\