Harald Conrad

Structural properties of native and sonicated cinerean, a β-(1 → 3)(1 → 6)-d-glucan produced by Botrytis cinerea

Cinerean, the extracellular beta-(1-->3) (1-->6)-D-glucan of the fungus Botrytis cinerea was studied. Electron micrographs of the native polysaccharide revealed quasi-endless fibrils with an estimated diameter of ca. 1.5 nm. A particle mass of 10(9)-10(10) daltons was determined from dilute solutions by low-angle laser light scattering. Sonication of increasing duration led to fragmentation of the native polymer with an approximately exponential decrease of mass in the range of average molecular masses between 250,000 and 50,000 daltons. Shadowed by platinum, cinerean fibril fragments with a weight-average molecular mass of 172,000 +/- 3000 daltons could be characterized from electron micrographs as a distribution of rods of most probable length of 45 nm and an average length of 72 nm. Small-angle X-ray scattering confirmed the fibrillar structure of the native cinerean and the rodlike structure of sonicated cinerean. A rod diameter of 1.9 +/- 0.2 nm and a mass per unit length of 2250 +/- 490 daltons/nm were found. The latter is in agreement with the value of 1830 daltons/nm calculated from the length distribution determined from the electron micrographs. These data-especially the mass per unit length-suggest a quaternary structure for the polysaccharide. Such a structure would explain the rigidity of the rods which, in turn, is responsible for the characteristic phase separation behaviour in aqueous solutions observed by nephelometry and viscometry.

Research Activities on Neutrorics under ASTE Collaboration at AGS/BNL

A series of experiments on a mercury spallation target using high-peak-power GeV proton-beam from the Alternating Gradient Synchrotron (AGS) of Brookhaven National Laboratory (BNL) has been performed under an international collaboration among the laboratories in Japan, U.S. and Europe, namely the ASTE (AGS Spallation Target Experiment) collaboration. This paper reviews the current status of the experiments on neutronic performance of the mercury target.

POWTEX – the high-intensity time-of-flight diffractometer at FRM II for structure analysis of polycrystalline materials

In order to provide the large chemistry and materials science as well as the geosciences communities with a powerful tool for rapid data acquisition, a time-of-flight powder diffractometer to be installed at the new Munich reactor has been designed. The time-of-flight technique is expected to outperform a monochromator instrument by at least an order of magnitude in data acquisition time, particularly on small samples of less than a cubic centimetre. The construction of this innovative type of diffractometer utilizes modern components such as focusing super-mirror neutron guides, a four-unit high-speed disk chopper system and linear position-sensitive detectors covering a solid angle of about 2π steradian. The diffractometer design enables an easy enlargement of the focal spot size and is therefore equally well suited for the texture analysis of large geological and archaeological samples.

Experimental Source Performances: Consequences for Proton Pulse Durations and Rep Rates

Abstract Experimental results on neutron currents and storage times of both ambient temperature H2O and liquid H2 cryogenic moderators in various target and reflector environments are presented. These results are compared with measured neutron currents from both a representative thermal beam and the new horizontal cold D2 source at the ILL with respect to expected performances of pulsed sources. The results of the spallation experiments are compared with Monte Carlo calculations from Los Alamos. Based on the measured moderator storage times r the consequences of different proton pulse characteristics on the performance of neutron scattering instruments are discussed in general for both ambient temperature and cryogenic moderators. The possible gain of pulsed operation for time-of-flight and continuous source applications is outlined. In particular, small angle neutron scattering (SANS), a classical technique at a continuous source is taken as an example to show the pros and cons of different source concep...

Experiments on Neutron Leakage Currents and Moderator Storage Times of Various Spallation Target–Moderator–Reflector Assemblies

Results from spallation neutron source mock-up experiments on neutron leakage currents and storage times of ambient temperature as well as cryogenic moderators are presented. The experiments were carried out in support of high power sources like the German SNQ and the European ESS. The vast amount of work performed elsewhere will not be treated in this review. Lead, tungsten and depleted uranium targets were bombarded with protons and deuterons with energies between 400 MeV and 1.1 GeV. Beryllium, graphite, lead and D2O reflectors, as well as polyethylene and H2O pre-moderators around the liquid hydrogen moderators, were employed. The results for the time average leakage currents from both ambient and cold moderators are compared to those from the high flux reactor at the ILL in Grenoble. From the results on moderator storage times, the peak neutron leakage currents for pulsed operation of various target/moderator/reflector assemblies as a function of the proton pulse duration have been deduced.