Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 20 (1987), S. 419-424 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The effect of Soller collimation on the resolution characteristics of small-angle scattering spectrometers for which there is a limitation to the total length, as in the case of a pulsed source instrument, is examined. Any finite distance between the exit of the collimation and the sample position causes the resolution of the instrument to deteriorate. This results from a correlation in angle and position for points at the sample producing an extra (cross-correlation) term in the resolution function. Expressions for this general case are derived. They are similar to those when the incident beam is defined at the sample position, except that both the source and the sample contributions have an extra term which is proportional to the finite distance between the end of the incident collimation and the sample.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 2
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 589-601 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Small-angle neutron scattering instruments can be built to use either steady-state or time-of-flight techniques, although only the latter are practical at pulsed neutron sources. The techniques used to provide beams of suitable quality, wavelength range and angular collimation are considered in detail for steady-state and time-of-flight instruments at reactor neutron sources, and for time-of-flight instruments at pulsed neutron sources. For both instrument types a cold neutron source provides a definite advantage. Most, but not all, steady-state instruments use long flight paths, which can be shown to provide conditions which are optimum in many ways. However, frame overlap considerations force the use of a short flight path for time-of-flight instruments, and this in turn forces these instruments to use different collimation and beam-quality techniques from those that are usually used for steady-state instruments. Although adequate techniques now exist for building short-flight-path small-angle neutron scattering instruments, some of these short-path techniques are still developing, and can be expected to improve in the future. At present the time-of-flight instruments are more difficult to build and use, but for many experiments this difficulty is more than compensated by the large wave-vector range covered in a single measurement with such instruments.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 3
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The design, development and performance of the time-of-flight (TOF) small-angle diffractometer (SAD) at the Intense Pulsed Neutron Source (IPNS) at Argonne National Laboratory are described. Similar TOF-SANS instruments are in operation at the pulsed neutron sources at Los Alamos National Laboratory, USA, at Rutherford Appleton Laboratory, England, and at KEK, Japan. These instruments have an advantage by comparison with their steady-state counterparts in that a relatively wide range of momentum transfer (q) can be monitored in a single experiment without the need to alter the collimation or the sample-to-detector distance. This feature makes SANS experiments easy and very effective for studying systems such as those undergoing phase transitions under different conditions, samples that cannot be easily reproduced for repetitive experiments, and systems under high temperature, pressure or shear. Three standard samples are used to demonstrate that the quality of the SANS data from SAD is comparable with those from other established steady-state SANS facilities. Two examples are given to illustrate that the wide q region accessible in a single measurement at SAD is very effective for following the time-dependent phase transitions in paraffins and temperature- and pressure-dependent phase transitions in model biomembranes.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 4
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 311-319 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The resolution of a time-of-flight small-angle scattering spectrometer is complicated because many wavelengths contribute to the intensity for a particular scattering vector. The resolution function varies according to the wavelength distribution as well as with collimation. A rigorous calculation of the instrumental resolution requires averaging the resolution function weighted by the wavelength spectrum within the band of wavelengths used in a given measurement. For each scattering vector an effective wavelength is defined which, after substitution into the resolution expression developed for fixed wavelength, gives the resolution of the time-of-flight measurement. Alternatively, the resolution may be established by Monte Carlo methods. In order to check the calculated resolution function and the overall instrument resolution, measurements have been made on biological samples (myelin and collagen) which give sharp Bragg peaks at small values of scattering vector. The analysis of these results provides a direct comparison with calculations and with a similar measurement on a steady-source instrument.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 5
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Two time-of-flight powder diffractometers have operated at the Intense Pulsed Neutron Source (IPNS) since August 1981. These instruments use dedicated microcomputers to focus time-of-flight events so that data from different detectors can be summed into a single histogram. Thus, large multidetector arrays can be employed at any scattering angle from 12 to 157°. This design permits data to be collected over a uniquely wide range of d spacings while maintaining high resolution and count rates. The performance of the two instruments is evaluated by analyzing data from a standard Al2O3 sample by the Rietveld method. These instruments provide the capability for moderate- to high-resolution measurements with the duration of a typical run being a few hours.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 6
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 7
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 8
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 9
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An inelastic electronic excitation has been observed in CeB6 near 47 meV (545 K) by means of neutron and Raman spectroscopy. This excitation has been identified as the Γ8→Γ7 crystalline-electric-field (CEF) transition. From the anomalous energy shift of this excitation at low temperatures, detectable due to the high resolution of Raman spectroscopy (±5 K), we deduce a Γ8 ground-state split by about 30 K. With this new CEF level scheme the first consistent interpretation of so far seemingly unrelated thermal, elastic, and magnetic data is achieved. In spite of the large body of thermal, magnetic, and elastic data of CeB6 accumulated over the past years, various diverging proposals for the CEF level scheme have been reported. In all schemes a Γ7 ground state was assumed, but the CEF splittings ranged from 10 K6 to more than 400 K. The absence of CEF excitations in direct spectroscopic measurements up to 400 K has been puzzling, and pointed to the necessity of high-energy neutron experiments. We have performed inelastic magnetic neutron scattering experiments using high-energy incident neutrons up to 185 meV from the Intense Pulsed Neutron Source at Argonne National Laboratory. An inelastic peak at 46 meV (530 K) is clearly identified as magnetic scattering by its Q dependence. The absolute intensity corresponds to the value of a Γ8→Γ7 transition. In addition, we have carried out Raman measurements on (100) faces of CeB6. At room temperature we found an inelastic excitation at 372 cm−1 (530 K). It is absent in the reference compound LaB6. From the polarization analysis we found that the transition has Γ3+ and Γ5+ symmetry. Both facts characterize this excitation as the Γ8→Γ7 CEF transition, which is the first CEF excitation seen in a metal by means of Raman spectroscopy. The high resolution of Raman spectroscopy enabled us to detect a 10-cm−1 shift of the Γ8→Γ7 transition energy to 382 cm−1 for temperatures below 20 K. This can only be explained by assuming a Γ8 ground state, which is split by 30 K. From the spectroscopic data we can establish a completely new CEF level scheme for CeB6 with a Γ8 ground state, split by about 30 K and a Γ7 state 545 K above. This allows a straightforward interpretation of various other experimental data, such as magnetic entropy, static magnetic susceptibility, high-field magnetization, magnetic form factor,8 temperature, and magnetic-field-dependent elastic constants and the antiferroquadrupolar ordering below TQ =3.3 K. A recent theoretical investigation of magnetic ordering of a periodic Anderson Hamiltonian with orbital degeneracy has been applied to CeB6. On the basis of entropy and magnetization data it was assumed that the quartet Γ8 is the ground state. Hence it was predicted that the low-temperature phase II (2.1 K〈T〈3.3 K) is due to an orbital antiferromagnetic ordered state, contrary to the conclusions of an antiferroquadrupolar ordering. This work was in part supported by Deutsche Forschungsgemeinschaft, SFB 125 and SFB 126.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...