Neutron instrumentation development. — Members of the group accomplished the development of an energy-selective neutron imaging set-up for the investigation of the cold neutron moderator and beam extraction optics of the Budapest Research Reactor in the frame of the BrightnESS Horizon2020 project. This implied removal of a guide section, development of a dedicated chopper, detector and enforcement of shielding. The experience thus gained is employed in the design of a similar test beamline at ESS. In the frame of the same project, a multiblade solid boron converter neutron detector has been developed at ESS and thoroughly tested for efficiency and resolution on a cold neutron beamline at BNC.
The researchers of the Neutron Spectroscopy Department take part in the design of the neutron guide system of the macromolecular time-of-flight neutron diffractometer (NMX) going to be built at the European Spallation Source (ESS) in Lund, Sweden. The NMX will be the first TOF protein neutron diffractometer in the world. The source-sample distance is 157.5 m, the maximal beam size is 5 mm and the maximal needed divergence is 0.4 degree. The original guide system of NMX was simple, it had a short curved part and a straight section till the sample. Due to the decrease of the source size, this guide did not provide enough neutrons at the sample. The main difficulties of the design are the robustness of the guide system against floor movement, alignment accuracy and waviness of the mirrors, the need for decreasing the shielding cost, i.e., decreasing the number of neutrons within the guide while the intensity at the sample does not decrease, and that the neutron guide shall go out of line of sight within the first 24.5 m to avoid the fast neutrons going through the wall of the biological shielding. To solve these problems, we developed new methods for calculation of the robustness. We designed a new kind of guide system which produces a wide beam with low divergency within a short length meanwhile it goes out of the line of sight. The beam at the bunker wall has 0.1 degree divergence and its size is 4.5 cm in each direction. This beam is transported by a straight guide until the focusing part. We chose a parabolic focusing which focus the parallel beam to the sample which is also not used in the case of neutrons. This focusing solution increases the guide robustness against angular misalignment and waviness. The new solution increased the number of neutrons reaching the sample both because of the increased robustness and due to the better optimization possibilities meanwhile the total intensity in the guide decreased by one and a half order of magnitude, thus the needed shielding size decreased by a factor of two. The final decision on the guide system and also the publication of the results will be in 2017.
Neutron holography. — Research on the methodology and applications of atomic resolution neutron holography has been continued. The local structure of a Sn single crystal with Cd impurities was reconstructed and the distortions of the crystal structure around the impurity atom was discussed. It was found that the effect of the different interatomic potentials around the impurity atoms has to be included beside the Friedel oscillation of the conduction electrons to fit the model to the measured distortions. For the first time, 3D displacements of atoms were measured showing the tendency of the local structure changing to the white-tin phase stable at lower temperatures
Structural investigation of hybrid silica gels. — Alkyl- and aryl-substituted silica gels were synthesized and characterized using complementary physicochemical methods. The silica host materials are designed to be proper host materials, for biomolecules or organic dyes, especially enzymes or porphyrins. The influence of the type and quantity of organic moiety upon the silica support physicochemical properties were studied and correlated with the optical emission property of the in situ entrapped metalloporphyrin. In every case, the samples with substituted silica support yielded higher optical emission of the porphyrin, compared to the unsubstituted case.