Soft Report - Dipartimento di Fisica - Sapienza

Activity at Large Scale FacilitiesThese activities are mainly devoted to neutron and x-ray applications at ILL and ESRFfacilities in Grenoble (France). There are several projects concerning instrumentconstruction and improvement as well as development of new devices. Long term projectsare AXES (ESRF), BRISP (ILL), ID16 (ESRF), IN13 (ILL) and the participation to the NMI3initiative of the EU under FP6. The research groups are very active in both scientific andtechnical activities as it is evident also from their participation to the life and conduction ofthe facilities.Participation to various bodies related to the facilities conductionF. Barocchi (NMI3, SAC)L. Braicovich (ESRF Chairman of the Scientific Advisory Committee, SAC, 2002-2005)C. Petrillo (ILL Steering Committee, ESFRI neutron expert group, ESRF SAC member)G. Ruocco (ESRF SAC member, 1997-2005, ESRF President Selection Panel, ESFRI softX-ray expert group, ESRF Council member)F. Sacchetti (ILL Instrument subcommittee)Development of the neutron Brillouin Spectrometer BRISPDuring the last two years the BRISP spectrometer has been completed and tested. BRISP is the onlyreactor-based neutron instrument in the world dedicated to the study of small momentum inelasticscattering. This instrument has a conventional general layout, but it is the only small-angle scatteringspectrometer using thermal neutrons (incident energies above 20 meV). In addition, the primaryspectrometer exploits an innovatory design based on a long converging honeycomb collimator, whichis the first ever employed in the world. This special collimator is a substantial improvement over otherpossible solutions and increases the performances in terms of intensity by about a factor ten. Theoverall BRISP layout is reported in Fig. 1 and the actual situation at the beginning of 2005 is shown inFig. 2.The instrument has successfully passed all the complex safety constraints regarding the radiologicalshielding and conventional structures at a reactor source. The spectrometer has been tested duringthe last 2005 reactor cycle. The tests confirmed the predicted performances in terms of energyresolution, momentum transfer, energy range and intensity. The instrument configuration used duringthis test phase was essentially the final one, except for the detector outer shielding which was notinstalled. The effectiveness of different configurations was verified and led to the definition of anexecutive design of the permanent shielding structure at the detector vacuum tank.Finally, a test experiment has been performed at the end of the last reactor cycle in 2005. Themeasurements were devoted to the study of the dynamic structure factor of liquid Pb at the meltingpoint, and were carried out with a limited and provisional shielding of the detector chamber. Thebackground present in the first measurements is expected to be strongly reduced in the finalconfiguration with complete shielding, which will be available in 2006. This test experimentdemonstrated that the instrument, even in its first configuration, is already competitive in terms ofintensity with the most efficient three axis spectrometer IN8 of ILL.Considering the possible improvements attainable by the construction of a new Fermi chopper, we canalready state that the BRISP spectrometer provides the best performance in the world, when theoverall capabilities in terms of intensity, energy resolution and dynamic range are examined at thesame time and compared with the general performances of other instruments.Few technical details:- available incident energies: 20.1 and 80.3 meV (PG monochromator), 51.9 meV with Cu monochromator- two-dimensional neutron detection between 0.5° and 15° scattering angle- Q el values as low as 0.03 Å -1 @ 20 meV can be reached- peak flux density after neutron monochromatization: 1.5 10 7 n cm -2 s -1- accessible dynamical range: ~ 0.2 < E < 100 meV and ~ 0.03 < Q < 8 Å -1- space and time accessible domains: ~ 0.05 < t < 20 ps and ~ 1 < r < 200 Å(further details can be found at http://www.ill.fr/YellowBook/BRISP and http://infmweb.fi.infn.it/BRISP)31SOFT Scientific Report 2004-06