TREFF: Reflectometer and instrument component test beamline at MLZ

TREFF is a high resolution polarized neutron reflectometer and instrument component test beamline resulting in a highly modular instrument providing a flexible beam line for various applications

Performance Measurement of a 2D Position Sensitive Neutron Scintillation Detector based on Silicon Photomultipliers

In recent years, the price increase of 3He has triggered the search for alternative neutron detectors. One of the viable options is a scintillation based neutron detector. Usually, Photomultiplier tubes (PMTs) are used in these detectors for photodetection. However, with increase in performance requirements, such as operability in magnetic field and spatial resolution, a need for an advanced neutron detector arises. Therefore, we developed a detector prototype with an active area of 13 cm × 13 cm using Silicon photomultipliers (SiPM). As compared to PMTs, SiPMs offer more compactness, more robustness and lower sensitivity to magnetic field. The final detector is aimed to be used in the future at the TREFF instrument of the Heinz Maier-Leibnitz Zentrum (MLZ) in Garching, Germany for neutron reflectometry (NR). First measurements were carried out at TREFF and at the dedicated detector test instrument V17 at BER-II of HZB in Berlin, Germany. In this work, we report the results for detection efficiency, gamma discrimination, two dimensional position resolution, count rate and detection linearity

The new versions 3.5 and 4.0 of the instrument simulation program VITESS

The new VITESS versions 3.5 and 4.0 have recently been finished. VITESS 4 is designed to be used for virtual experiments, e.g. at MLZ. The instruments are stored as yaml files, which enables changing the instrument parameters from NICOS (as in a real experiment). For maintenance and performance reasons, the new GUI is written in Qt and the monitor output will be visualized using the FZJ program GR. Version 4.0 will not have the complete set of modules, but only those found in many instruments, altogether 36 out of 58. Additionally, the use of parameters from files is reduced. It is under test now for virtual experiments at the neutron reflectometer MARIA at MLZ in Garching. As it will take time to get VITESS 4 complete and faultless, version 3 will still be needed for some time. VITESS 3.5 contains several new features that are needed for instrument simulations for the HBS, e.g. a source module for HBS and a rotating monochromator. It also contains already many improvements realized for the virtual experiments like additional features for the reflectometer sample and monitor update during the run. The HBS source is also available in McStas. Next year, version 3.6 will be written with the main new feature to save instruments, stored under version 3, in the new format using yaml files. Then, all missing modules will be added to version 4 and released as version 4.1. We will present the main new features of version 3.5 and 4.0 and also show how to simulate the HBS source, both in VITESS and in McStas

Thermal moderator-reflector design of the 24Hz target station for the High Brilliance Neutron Source

The High Brilliance Neutron Source (HBS) is expected to be the next-generation neutron facility, which uses low proton energy (70MeV) to achieve high neutron brilliance. As the moderator-reflector unit is correlated to the neutron moderation, reflection, and transportation, designing a suitable moderator-reflector unit is one of the important issues for achieving the “high brilliance” of the thermal neutron cloud. In this research, the optimization of the thermal moderator-reflector of the 24Hz target station will be conducted to optimize pulse shape and intensity. The Monte Carlo simulation is applied to the design. PHITS and Diffmod are used. In this presentation, at first, the proof-of-principle simulation to reduce the absorption of hydrogenous moderator material is introduced. The time and energy characteristic of candidate material and structure are simulated and analyzed. Then, according to the neutron transportation simulation of different moderator-reflector unit, the specific design is presented. And we will show the result of thermal behavior and neutronic characteristics of this moderator-reflector unit.This work is part of the collaboration within ELENA and LENS on the development of HiCANS

Investigation of Pancake-like Moderator-Reflector Structure for the High Brilliance Neutron Source (HBS)

The High Brilliance Neutron Source (HBS) project is developing a high-current accelerator-driven neutron source (HiCANS) to maintain a healthy neutron landscape in Europe. Despite the lower primary neutron yield of the nuclear reactions compared to reactor or spallation neutron sources, HiCANS achieve a competitive neutron brightness by a compact moderator and reflector design, which makes a large fraction of the primary neutron spectrum available for applications. The spectral and temporal, i.e. frequency and pulse length, characteristics of the neutron pulse are tailored to the instruments hosted at a target station.Based on the ‘pancake’ and ‘butterfly’ moderator geometries developed for the European Spallation Source (ESS), we investigate a pancake-like structure by means of Monte Carlo simulations involving multi-parameter optimization routines. By increasing the interface area, we try to improve the coupling between thermal and cryogenic moderator. The extraction surfaces of the applied pancake-like geometry achieve a cold neutron flux of 85%-87% of a cylindrical para H2 moderator (length= 10 cm, diameter = 2.4 cm) with ideal coupling. The flux through the thermal extraction surfaces reaches 70%-79% in comparison to an ideal case with just a single extraction channel looking at the thermal flux maximum in the center of the thermal moderator. The optimized structure with up to six extraction channels looks therefore very promising for target stations that serve a large number of thermal and cold instruments. At this conference, we will present the results of our study of this moderator-reflector assembly. [1] X. Y. Author, Neutron News, 22, 7 (2011

Thermal moderator-reflector design of the 24 Hz target station for the High Brilliance Neutron Source

The High Brilliance Neutron Source (HBS) project develops a high current accelerator driven neutron source (HiCANS), aiming to substitute existing neutron research reactors, that reach the end of life. This study focuses on the thermal neutron moderator design for a low frequency, long pulse target station of HBS. We investigate the neutronic characteristics of the D2O+H2O mixture moderator material using the Monte Carlo particle transport code PHITS. Our findings show that, compared to D2O with lower neutron absorption, confinement of H2O is the dominant factor in achieving a high neutron flux within the moderator and thus a high neutron brightness. We find that surrounding the central thermal water moderator with a D2O+H2O mixture can achieve a better balance between confinement and absorption. However, because of multiple angles of reflecting neutron, this design will also increase the divergence of the neutron beam

Prompt gamma rays from fast neutron inelastic scattering on aluminum, titanium and copper

Prompt gamma rays induced by inelastic scattering of fast neutrons on aluminum, titanium and copper were measured at an angle of 90o between fast neutron beam and detector of the instrument FaNGaS, operated by Jülich Centre of Neutron Science at Heinz-Maier-Leibnitz Zentrum in Garching. The fast neutron flux was 1.40 108 cm−2 s−1 with the average energy of 2.30 MeV. Intensities and neutron spectrum averaged isotopic partial cross section for production of 214 gamma lines (22 for aluminum, 72 for titanium and 120 for copper) are presented. The results are consistent with the literature data. However, the new sets of gamma lines are recommended to replace the old datasets from fast neutrons reactors with several new lines also recognizing a few false identifications. Additionally, the detection limits of aluminum, titanium, copper, iron and indium were determined as 1.0, 0.4, 0.9, 0.5 and 1.3 mg, respectively, for a counting time of 12 h

Thermal moderator-reflector assembly for HBS

The thermal moderator is the key component in a research neutron source to convert the primary neutrons which typically have energies in the MeV regime into useful neutrons for investigations that shall have energies well below 1 eV. In the case of a HiCANS as HBS, the thermal moderator has to be optimized according to the compact target size and to the proton pulse lengths at the different target stations. Extraction channels in the thermal moderator are used to either place cold sources feeding instruments that need a cold neutron spectrum or to extract thermal neutron beams from the volume of highest thermal neutron flux density. Requirements of restricted space, neutron transparency of the main structural materials, the technically demanding flowing liquid thermal moderator material, the complex nature of intense thermal and induced mechanical loading, industry-standard requirements for operational safety, etc. impose important boundary conditions on the design of the thermal moderator.Here, we present the details of a thermal moderator design serving up to 12 instruments at a target station operated at 96 Hz. The thermal moderator consists of a combined welded complex-profiled Al vessel containing 12 thin-walled cast extraction channels arranged in 2 levels. The vessel is filled with H2O as moderator material which is pumped for cooling purposes. The entire system is surrounded by a lead reflector and arranged on top of the compact Ta target. We show the results of simulations concerning the neutronics and the thermal behaviour of this thermal moderator-reflector assembly.This work is part of the collaboration within ELENA and LENS on the development of HiCANS