The Physics of Spallation Processes

2.2. RESEARCH REACTORS OR PULSED SPALLATION SOURCES? 11Table 2.1: Compilation of of European and Russian reactors and spallation sources.Country facility power n-flux [n cm −2 s −1 ]Czech Republic a LVR-15 Prague 10 MW 1 × 10 14France a ILL Grenoble 52 MW 1.2 × 10 15a LLB-Orphee Saclay 14 MW 3 × 10 14Germany a FRJ-II Jülich 23 MW 2 × 10 14a BER-II Berlin 10 MW 2 × 10 14a FRG-1 Geesthacht 5 MW 8 × 10 13a,b FRM-II Munich 20 MW 7 × 10 14Hungary a BRR 10 MW 1.6 × 10 14Netherlands a HCR Delft 2 MW 2 × 10 13Norway a JEEP2 2 MW 2.2 × 10 13Russia c IBR-2 2 MW 1 × 10 16Sweden a NFL R2 50 MW 1 × 10 14Switzerland d SINQ Villingen 1 MW 2 × 10 14UK e ISIS Abington 156 kW 2 − 10 × 10 15a research reactorb under constructionc pulsed reactord continuous spallation sourcee pulsed spallation source, neutron flux given as peak value, second target station is planned.higher peak fluxes shall be built. As for example the ESS will have a thermal neutron peakflux of up to 2 x 10 17 n cm −2 s −1 . Since the early 50ties the intensity of neutron sources hasincreased just by a factor of four. In contrast the ESS will yield in a tremendous progress.Its intensity increase by two orders of magnitude will revolutionize the neutron science.To convey an impression of the potential power of the ESS, today’s most powerful pulsedneutron spallation source, ISIS (UK) [Isi99], produces short pulses of an even higherpeak flux than those provided by the world’s strongest research reactor at the InstitutLaue-Langevin. But ISIS’ peak-intensity is only 1/30 of that projected for ESS.The need for both reactor based (normally steady-state or continuous) and acceleratorbased (pulsed) neutron sources has long been realized by the neutron science community.Due to the dramatic improvements in accelerator technology in recent years, generallyneutron pulses can be produced with much higher intensity than that available fromcontinuous sources. Furthermore, unlike the situation at a continuous neutron source,pulsed sources allow the determination of the kinetic energy of individual neutrons using“time-of-flight” methods and making “movies” of molecules in motion. Like a flashingstrobe light providing high speed illumination of an object the ESS as for example willproduce pulses of neutrons every 20 ms with 30 times more neutrons than are producedat the most powerful pulsed neutron sources currently available.Urgent need for new generation intense neutron sources is also clearly demonstratedwhen comparing the number of active researchers in the neutron scattering community