We demonstrate that the valence energy-loss function of hexagonal boron nitride (hBN) displays a strong anisotropy in shape, excitation energy and dispersion for momentum transfer q parallel or perpendicular to the hBN layers. This is manifested by e.g. an energy shift of 0.7 eV that cannot be captured by single-particle approaches and is a demonstration of a strong anisotropy in the two-body electron-hole interaction. Furthermore, for in-plane directions of q we observe a splitting of the π-plasmon in the ΓM direction that is absent in the ΓK direction and this can be traced back to band-structure effects.

We investigate the highly anisotropic behavior of the in-plane and out-of-plane infraredactive phonons of h-BN by means of infrared reflectivity and absorption measurements under high pressure. Infrared reflectivity spectra at normal incidence on high quality single crystals show strict fulfillment of selection rules and an unusually long E 1u (TO) phonon lifetime. Accurate values of the dielectric constants at ambient pressure ε ⊥ 0 = 6.96, ε ⊥ ∞ = 4.95, ε ∥ 0 = 3.37, and ε ∥ ∞ = 2.84 have been determined from fits to the reflectivity spectra. The outof-plane A 2u phonon reflectivity band is revealed in measurements on an inclined facet, and absorption measurements at an incidence angle of 30 • allow us to observe both the A 2uTO and LO modes. Pressure coefficients and Grüneisen parameters for all infrared-active modes are determined and compared with ab-initio calculations. While Grüneisen parameters are generally small in this layered crystal, the A 2u (TO) displays an exceptionally large and negative Grüneisen parameter that results in a widening of the type I hyperbolic region with increasing pressure. The softening of the A 2u (TO) mode is induced by a dynamical buckling of the flat honeycomb layers.

This paper describes the high-field studies on accelerator structures conducted at the X-band Test Facility, XTF, which was commissioned at KEK in 2004. A 60cm-long structure built at KEK has been processed in 2004-2005, with an accumulated operation time with the RF turned on of ~1000 hours. The RF breakdown rate of this structure at 65MV/m with 400nsec flat pulses was initially measured to be ~once per 0.2×10 6 pulses, and decreased to ~once per 0.7×10 6 pulses with the processing. This latter breakdown rate satisfies the stability requirement for use of such accelerator structures at the linear collider. The high-power performance of two more 60cm structures will be measured in 2005. These studies are expected to provide benchmark performance data of accelerator structures in both high-gradient and mediumgradient operations, such as those envisaged in applications to compact X-band accelerators.

The influence of a dipole magnetic field in the extractor on the beamlet deflection has been investigated using a JAERI 400 keV H− ion source. The beam deflection angle decreased from 10.2 to 7.0 mrad when the integrated value of the magnetic field was changed from 2530 to 910 G cm. The measured deflection angle was larger than the estimated value from the ion trajectory considering the magnetic field. To understand the dominant factor that enhances the beam deflection angle, three-dimensional trajectory simulation was performed. It was confirmed that the axis of the beamlet deflected by the magnetic field in the extractor is displaced from the center of the aperture at the grounded grid (GRG). This displacement enhances the beam deflection angle due to the effect of the electrostatic lens at the GRG. This phenomenon is similar to the beam deflection by aperture displacement of the GRG.

Novel fast neutron imaging concept with statistical reconstruction for analysis of recoiled proton tracks in nuclear emulsion is proposed. For each recoiled proton track event, incident neutron direction can be constrained on a cone with axis of a recoiled proton track and an opening angle derived from both an estimated neutron energy and a recoiled proton energy. As in the Compton imaging method, a position of fast neutron source can be identified by intersection of event cones if appropriate information of the incident neutron energy is given. In reconstructed image obtained by this method for a 252 Cf source, single peak was appeared with the estimated neutron energy of lower than 1.5 MeV.