A High Resolution Spallation Driven Facility at the CERN-PS to Measure Neutron Cross Sections in the Interval from 1 eV to 250 MeV: a Relative Performance Assessment

In the proposed facility with 24 GeV PS beam on a Lead target, the number of produced neutrons exceeds 760 per proton. In comparison, with a LINAC (GELINA) one currently obtains only about 0.05 neutrons per electron of about 100 MeV. An additional factor of 2.5 for the CERN facility is due to the strong, forward peaking of the neutron flux, arising from the high proton energy and corresponding longitudinal boost. This huge factor in neutron yield per incident particle, namely 2.5 x 760/0.05 = 3.8 x 10^4, is only partially off-set by the higher, time averaged current of the LINAC e.g. 100 mA vs . 2 mA of the CERN-PS. Therefore the useful, initial neutron rate at the CERN facility is about three orders of magnitude larger than in the most performing electron LINAC’s, GELINA in Belgium and ORELLA in the US. The time duration of the PS pulse is presently Deltat|_r.m.s.=13.5 ns and we believe it could be reduced to Deltat|_r.m.s.= 6.75 ns. The electron LINAC has much shorter pulses Deltat| _r.m.s.= 1 ns, to which however the resolution of the counters has to be added. But for neutron energy 1 MeV, is not affecting the actual TOF energy resolution, dominated by the fluctuations of moderation. Since these time fluctuations are largely independent of the chosen mechanism to produce the initial neutrons, the initial flux difference between the two methods, e.g. electrons vs. protons, reflects directly in the counting rate for a given TOF resolution at the measuring station. Furthermore the CERN PS (< 1/2.4 sec^-1) has a much smaller repetition rate than the LINAC (1 /800 sec-1) and it presents no problems of time overlaps at the measuring station due to successive bunches. The accidental background due to radio-active targets is also much better suppressed. Finally the gamma-prompt flash is considerably smaller for a proton machine than in the case of an electron LINAC and no gamma-filters are required.