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[en] At the high flux reactor of the Institute Laue Langevin in Grenoble a new interferometer for very cold neutrons has been installed. The interferometer employs three diffraction gratings, mounted on precision rotation tables and translation stages which allow rotation around all three axis in space and a translation perpendicular to the incident beam and to the lines of the grating. They are arranged parallel to each other have a periodicity of 2μm and a grating area of about 10 cm2. At the first version of the interferometer the distance from the first to the third grating was 0.5 m. For intensity reasons it was decided to use phase gratings in transmission mode, where the stripes of the grating have rectangular cross-section. grating. In the process of our neutron diffraction measurments we saw that the ratio of the width of steps and gaps, the stripes height and the cross-section of the stripes of the latter gratings made of quartz-glass are better suited for a satisfactory performance than those of the first two series. We measured the intensities and the ratio of the intensities of the zero and first order diffraction and calculated the intensity of the exit beam of the interferometer, which depends on the above mentioned ratio. As a result of this one can see that the step height of the first and the third grating should produce a phase shift of π/2 and that of the second grating a phase shift of π to avoid zero order diffraction which is not used at the second grating. The velocity of neutrons having a wavelength of 100A is40m/s. This small value causes severe problems concerning background vibration, which disturbs the operation of the interferometer. Therefore it was necessary to mount the gratings on an optical table with dimensions 6 x 1.2 x 0.4m3 and a weight of 1.8 t, which is supported by pneumatic isolation legs. In addition an active vibration isolation system has been developed to isolate the table against vibrations with frequencies below two Herz. (Author, shortened by G.Q.)
[en] Neutron beta decay is described accurately within the standard model of particle physics using the first CKM-matrix element, Vud, and the ratio of vector and axial vector couplings, λ, as parameters. Angular correlations, spectra and the neutron lifetime are accessible experimentally, providing an excellent toolkit for investigating the structure of weak interaction. Measuring the Beta Asymmetry, A, is the most precise way of determining λ, which is an important standard model parameter and necessary for the determination of Vud from Neutron Decay. Moreover it allows to derive limits on non-standard model couplings by combining with measurements of other correlation coefficients. In this talk we present the most precise measurement of the Beta Asymmetry performed with the decay spectrometer Perkeo III carried out at the PF1B cold neutron beam facility at the Institut Laue-Langevin. We discuss the result and its implications.
[en] Pelican, a direct geometry multi-purpose cold neutron spectrometer, combines the state of the art monochromators and Fermi chopper systems to perform inelastic and quasi-elastic neutron scatterings on a variety of materials of powder, polycrystal, single crystal, glass and liquid, covering fields of physics, chemistry and biology. The provision of cryogenic vacuum from sample to detector intends to decrease background to a minimum level. Polarized incident beam will be realized by supermirror polarizer and polarization analysis will be achieved by He-3 polarization filter. The instrument is designed to accommodate various sample environments like high magnetic field, low and high temperatures, etc. The installation of the instrument has finished. The first neutron has been delivered to sample. Full scale testing and optimisation of the instrument are in progress. The preliminary test results will be presented together with the schedule for getting the instrument into user program.
[en] The authors report detailed experiments and comparison with first-principle theoretical calculation of the diffraction of cold neutrons (λ4A2 nm) at single- and double-slit assemblies of dimensions in the 20--100 μm range. Their experimental results show all predicted features of the diffraction patterns in great detail. Particularly, their double-slit diffraction experiment is its most precise realization hitherto for matter waves
[en] A system of two perfect silicon crystal plates (1.07 m apart) both placed in back reflection position ((1,1,1)-planes) has been constructed. This system can be used to capture highly monochromatic (6.27 A) neutrons. Thereby, the neutrons are reflected back and forth. To reduce the lateral losses, a neutron guide was placed between the crystal plates. A pulsed magnetic field (1.3 T at the site of the crystal plates) fills in and releases the neutrons. Storage times up to 30 ms have been achieved and computer simulations show that they could be extended up to more than 100 ms. During the measurement period, the losses of the neutrons have been reduced to 9% per back and forth reflection (3.4 ms) by alignment of the neutron guide. Computer simulations show that the achieved rate should be lowered significantly by further alignment. There is also a probability for the neutrons that they are captured without a magnetic pulse. These neutrons get lost after several back and forth reflections and are (partly) detected as equally spaced peaks in the time-of-flight spectrum. Due to the very low background at the IRIS facility (in between the direct neutron pulses), these neutrons showed up in the spectrum without magnetic pulsing. (Author)
[en] The cold neutron technique has been applied to the study of the scattering properties of light and heavy water. It is shown that with respect to neutron scattering water behaves much like a solid. It is estimated that a water molecule occupies a stationary position for a period of 2x10-12 seconds performing about 10 vibrations before it makes a diffusion jump of a length of at least 15 nm. The consequences of the observations for neutron thermalization problems are discussed briefly
[en] The working group meeting was chaired by Carpenter and Brun. This session was intended as a session to present ideas that had not yet been fully explored, as well as a place for discussion of topics that did not readily fit in any of the other workshop sessions. The first part of the session focused on moderator materials. During the course of the discussions of some novel potential moderator materials it became clear that there was not even agreement on what makes a good moderator for cold neutrons at short-pulse sources. There were two competing diametrically-opposed schools of thought.
[en] According to the authors, fusion reaction density will probably be much lower than projected by ongoing major fusion reactor design studies. A near term application in the energy sector will be more likely via fuel breeding as a fusion-fission (hybrid) reactor system, rather than a pure fusion reactor electricity production. This paper represents a preliminary hybrid reactor design concept driven by cold fusion neutrons, based on a recent presentation
[en] The scope of this project includes the development, design, procurement/fabrication, testing, and installation of all of the components necessary to produce a working cold source within an existing HFIR beam tube hole in the pressure vessel. All aspects of the cold source design will be based on demonstrated technology adapted to the HFIR design and operating conditions