[en] The angular and energy distributions of neutrons scattered from room temperature samples of Dowtherm ''A'' have been measured using a few different initial neutron energies in the range from 10-2 to 10-1eV. The experiment has been performed with a rotating crystal spectrometer as pulsed monoenergetic beam source and a 16x256 - channel time analyser for timing of the scattered neutrons. With this arrangement data for several angles have been taken simultaneously. Results are represented in the form of differential cross-sections and also in the ''Scattering Law'' form. Physical interpretation with the aid of the space-time correlation iunction of Van Hove is discussed. (author)
[fr]
L'auteur a mesure la distribution angulaire et le spectre d'energie de neutrons diffuses par des echantillons de Dowtherm ''A'' a la temperature ambiante, en employant des neutrons dont l'energie incidente variait de 10-2 a 10-1 eV. L'experience a ete faite a l'aide d'un spectrometre a cristal tournant, employe comme source monoenergetique puisee, et d'un analyseur en temps de 16 X 256 canaux. Ce dispositif a permis de recueillir simultanement des donnees pour differents angles. Les resultats sont presentes sous la forme de sections efficaces differentielles et aussi sous la forme d'une loi de diffusion. L'auteur discute l'interpretation physique de ces resultats a l'aide de la fonction de correlation spatiotemporelle de Van Hove. (author)[es]
El autor ha medido la distribucion angular y energetica de neutrones dispersados por muestras de Dowtherm ''A '' a temperatura am-; biente, para una serie de energias iniciales de los neutrones comprendidas entre 1 0-2 y 10-1 eV. El experimento se ha realizado con un espectrometro de cristal rotativo, que se ha utilizado como fuente pulsada de haz monoenergetico, y un analizador de tiempo de 16x 256 canales para el cronometraje de los neutrones dispersados. Con este dispositivo, se han obtenido simultaneamente datos correspondientes a diferentes angulos. El autor expone los resultados en forma de secciones encaces diferenciales y tambien en forma de ''ley de dispersion''. Estudia la interpretacion fisica del fenomeno con ayuda de la funcion de correlacion espacio- tiempo de Van Hove. (author)Source
International Atomic Energy Agency, Vienna (Austria); United Nations Educational, Scientific and Cultural Organization (France); 486 p; Jan 1963; p. 307-315; Symposium on Inelastic Scattering of Neutrons in Solids and Liquids; Chalk River (Canada); 10-14 Sep 1962; ISSN 0074-1884; 
; Abstract also available in Russian; figs., 6 refs.
; Abstract also available in Russian; figs., 6 refs.
[en] The method of pseudo-statistical pulsing has been applied only to reactor-kinetic measurements so far. Ohanian, Perez and Uhrig proposed this method for time-of-flight measurements with pulsed accelerators. Comparative studies have shown, however, that it is not possible to give general arguments in favour of either the pseudostatistical or the conventional time-of-flight method. Which of the two methods may be preferred depends on the kind of experiment. Pseudo-statistical pulsing may be especially advantageous for scattering experiments with thermal neutrons. This paper is intended to give a description of a 'statistical' chopper and the method of measurement with this instrument. The different influences on the accuracy of the measurements are discussed and compared to those in a conventional time-of-flight experiment. A few examples of pseudo-statistical experiments have been simulated on a computer. It is shown that a statistical chopper is advantageous for time-of-flight spectra consisting of a number of peaks which are of main interest and have amplitudes greater than the average amplitudes of the spectra. Further, the method is advantageous in all cases where the background is very high. A preliminary experimental arrangement is described. (author)
Source
International Atomic Energy Agency, Vienna (Austria); 476 p; Sep 1968; p. 417-428; 4. IAEA Symposium on Neutron Inelastic Scattering; Copenhagen (Denmark); 20-25 May 1968; IAEA-SM--104/67; ISSN 0074-1884; ; 2 refs., 7 figs.
; 2 refs., 7 figs.
[en] The low-temperature irradiation facility, Tieftemperatur-Bestrahlungsanlage (TTB), at the 4-MW Munich Research Reactor (Forschungsreaktor Munchen-FRM) makes it possible to perform neutron irradiations at liquid helium temperature. Two irradiation positions exhibiting different neutron spectra are available. The possible integration of suitable measuring or transfer cryostats into the liquid helium circuit of the TTB allows the use of this facility for the study of a large variety of neutron irradiation effects in basic research as well as in materials sciences. In this paper, besides a description of the general experimental setup, some topics of current TTB research are briefly summarized
Journal
[en] For certain classes of neutron scattering experiments it is desirable to increase the neutron intensity at energies above the Maxwellian peak of a reactor spectrum considerably. This can be done by installing a piece of moderator having a high temperature, a so-called hot source, at the tip of the beam tube. In our experiments we used graphite as material for the hot source. The possible gain in neutron intensity attainable with a hot source was studied in a mock-up experiment for various sizes and temperatures of the graphite block using the pulsed neutron technique. The agreement of the measurements with calculations of the rethermalization properties of the graphite block based on transport theory was quite satisfactory. A plug carrying a graphite cylinder, 18 cm in diameter and 18 cm in height, was installed at the FR2 reactor. With proper thermal isolation a graphite temperature of about 1700°K was reached by nuclear heating only. Spectrum measurements at this temperature and systematic studies of the properties of the hot source are under way. An increase in neutron intensity of about a factor of 7 is expected at a neutron energy of 0.3 eV. The source will be first used for phonon dispersion measurements. (author)
Source
International Atomic Energy Agency, Vienna (Austria); 476 p; Sep 1968; p. 331-339; 4. IAEA Symposium on Neutron Inelastic Scattering; Copenhagen (Denmark); 20-25 May 1968; IAEA-SM--104/69; ISSN 0074-1884; ; 2 refs., 5 figs.
; 2 refs., 5 figs.
[en] A model system for the Lorentz gas can be made [Eder, Chen, and Egelstaff, Proc. Phys. Soc. London 89, 833 (1966); McPherson and Egelstaff, Can. J. Phys. 58, 289 (1980)] by mixing small quantities of hydrogen with an argon host. For neutron-scattering experiments the large H-to-Ar cross section ratio (∼200) makes the argon relatively invisible. Dynamic-structure-factor [S(Q,ω) for H2] measurements at room temperature have been made on this system using the IN4 spectrometer at the Institute Laue Langevin, Grenoble, France. Argon densities between 1.9 and 10.5 atoms/nm3 were used for 0.4< Q<5 A-1. Additional measurements were made with a He gas host at densities of 4 and 10.5 atoms/nm3; helium is relatively invisible also compared to hydrogen. These experiments are described, and some examples of the results are presented to show the qualitative effects observed. The principle observation is a pronounced narrowing of S(Q,ω) as a function of ω as the argon density is increased. This effect is large at low Q and decreases with increasing Q, and also decreases substantially when helium is used in place of argon. In addition, the shape of S(Q,ω) is more complex than can be accommodated within a simple model, but slightly less complicated than a computer simulation so showing the significance of multiple-collision processes
Journal