The Physics of Spallation Processes

Introduction 32.5 GeV incident proton energy will be subject. As for example the systematics of neutronproduction cross sections and neutron energy spectra as a function of incident protonenergy, target material, and target geometry are not well known or documented in theliterature.The NESSI and the former PS208 collaboration at CERN have—in order to fill thesegaps systematically—performed a series of proton- and antiproton induced experiments[Egi00, Enke99, Fil01, Fil01b, Fil99, Gol01, Gol00, Gol00b, Gol99b, Gol99d, Gol99e,Gol99f, Gol98b, Gol96, Gol96b, Her01, Hil01, Hil98, Hil96b, Hil95b, Hil95c, Jah01, Jah99,Jah96, Jah95, Jah95b, Let00, Lot01, Lot99, Lot98, Lot97, Pie00, Pie99, Pie97, Sch97] usinga highly efficient 4π sr gadolinium loaded scintillator neutron detector [Gal94, Gal01]partly in combination with a 4π sr silicon detector [Boh92, Fig95, Pau92] for chargedparticles. These measurements covered a large range of incident hadron (p, p, π ± , K andd) energies, as well as a variety of target materials and geometries. In contrast to theolder measurements of typically only average neutron multiplicities [Fra65, Rus80, Arm84,Vas90, Nik90, Tak97, Ara99], the NESSI experiments have provided also event-by-eventinformation on these multiplicities.PISA effectively considered as successor of or supplement to NESSI is an experimentcurrently under construction at the internal ring COSY. Recent test-measurements providedfirst data currently being analyzed and briefly presented here.JESSICA is a 1:1 ESS Hg target-reflector-moderator mockup which aims at studyingsub-thermal neutrons using advanced moderators. Time-dependent neutron spectra areinvestigated by Bragg reflection and ’time-of-flight’ (TOF)-methods.The extensive set of benchmark data obtained in the NESSI, PISA and JESSICAexperiments imposes strong constraints on the theoretical modeling of the occurring interactions[Enke99, Gol01, Gol00, Gol00b, Gol99b, Gol99e, Her01, Hil01], and allows oneto calibrate and improve widely-used high-energy transport codes [Fil00, Fil96, Ste98].The accuracy of such codes is critical for the design of high-power target stations, sincethe optimization of geometrically expanded high power target stations will finally rely ongeneral Monte-Carlo particle transport codes having maximum predictive power.In particular above 1 GeV so far only limited data [Fil97, Hsi97, Shu97] were availablefor light charged particles, intermediate mass and fission fragments. Calculated datadeviate as much as a factor of 5-10. With NESSI, H and He production cross sectionswhich are of particular interest for studying radiation damage in target and structurematerials have been measured. Kinetic energy and angular distributions of H- and Heisotopesas a function of thermal excitation energy E ∗ have been deduced [Enke99, Gol96b,Her00, Pie00]–following a procedure described in detail in ref. [Gol96b, Pie00].Unfortunately the experimental setup of NESSI [Enke99, Gol96, Gol96b, Let00] is notsuited for measuring the kinetic energy or angular distribution of neutrons as for examplereported for 800 MeV proton-induced reactions on heavy thick targets in ref. [Rus80] orthick tungsten targets [Tak97]. These spectra would be of particular interest for shieldingrequirements of spallation neutron sources. Published data for 800 MeV p+Pb vary, for instance,by a factor of two at neutron energies above 50 MeV [Rus80, Ami92, Sta93, Mar97].Energy spectra and angular distributions of neutrons have recently been measured at variousincident projectile energies [Ler01, Egi00, Led99, Tit00, Ish97, Mei99]. Isotopic distributionsand kinetic energies of residual nuclides have recently been studied by exploiting