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A prototype quasi-parasitic thermal neutron beam monitor based on isotropic neutron scattering from a thin natural vanadium foil and standard $^3$He proportional counters is conceptualized, designed, simulated, calibrated, and commissioned. The European Spallation Source designed to deliver the highest integrated neutron flux originating from a pulsed source is currently under construction in Lund, Sweden. The effort to investigate a vanadium-based neutron beam monitor was triggered by a list of requirements for Beam Monitors permanently placed in the ESS neutron beams in order to provide reliable monitoring at complex beamlines: low attenuation, linear response over a wide range of neutron fluxes, near to constant efficiency for neutron wavelengths in a range of 0.6-10 \r{A}, calibration stability and the possibility to place the system in vacuum are all desirable characteristics. The scattering-based prototype, employing a natural vanadium foil and standard $^3$He proportional counters, was investigated at the V17 and V20 neutron beamlines of the Helmholtz-Zentrum in Berlin, Germany, in several different geometrical configurations of the $^3$He proportional counters around the foil. Response linearity is successfully demonstrated for foil thicknesses ranging from 0.04 mm to 3.15 mm. Attenuation lower than 1% for thermal neutrons is demonstrated for the 0.04 mm and 0.125 mm foils. The geometries used for the experiment were simulated allowing for absolute flux calibration and establishing the possible range of efficiencies for various designs of the prototype. The operational flux limits for the beam monitor prototype were established as a dependency of the background radiation and prototype geometry. The herein demonstrated prototype monitors can be employed for neutron fluxes ranging from $10^3-10^{10}$ n/s/cm$^2$.

A thorough experimental characterization of a multiplexing backend with multiple energy analysis on a cold-neutron triple axis spectrometer (cTAS) is presented. The prototype employs two angular segments (2 theta-segments) each containing five vertically scattering analyzers (energy channels), which simultaneously probe an energy transfer range of 2 meV at the corresponding two scattering angles. The feasibility and strength of such a vertically scattering multiple energy analysis setup is clearly demonstrated. It is shown, that the energy resolution near the elastic line is comparable to the energy resolution of a standard cTAS. The dispersion relation of the antiferromagnetic excitations in MnF2 has been mapped out by performing constant energy transfer maps. These results show that the tested setup is virtually spurion free. In addition, focusing effects due to (mis)matching of the instrumental resolution ellipsoid to the excitation branch are clearly evident. (C) 2016 Elsevier B.V. All rights reserved.

The first experimental characterization of a multiple energy analysis wide angle backend for a cold triple-axis spectrometer is reported. The multi-analyzer module MultiFLEXX employs 155 detection channels which simultaneously probe an extensive range in wavevector and energy transfer. Successful mapping of magnetic excitations in MnF2 and Ho demonstrate order of magnitude gains in data collection efficiency using this novel type backend. MultiFLEXX is competitive to standard triple-axis spectroscopy in terms of energy resolution and signal-to-noise ratio. A minority of the detector channels is affected by spurious signals inherent to this multiplexing concept. The characteristic signature of these spurious signals easily allows for their discrimination. The instrument concept focuses on detection efficiency in the horizontal scattering plane which makes it an ideal technique for fast mapping and parametric studies including extreme sample environment.

Although already in use for more than 70 years, boron trifluoride (BF3)-filled detectors are still the ‘black sheep’ of the neutron detector family. Reasons include the lower achievable efficiency ...

Energy dependent neutron transmission imaging has recently gained attention for the potential to spatially resolve texture, crystallographic phase and lattice strain. Especially promising is the time-of-flight (TOF) approach that takes maximum advantage of the new generation of pulsed spallation neutron sources, such as SNS, JSNS and ESS. In this paper, the authors demonstrate the feasibility to efficiently apply the TOF approach at a continuous source in order to spatially resolve and quantify the (lattice) strain distribution in a flat steel sample under tensile loading. Although transmission-based TOF imaging for strain mapping at a pulsed source is well published, this work is the first attempt to demonstrate such measurement using choppers at a continuous neutron source. A critical component for spatially resolved TOF imaging is the availability of a high spatial resolution imaging detector, capable of the required time resolution. For the herein presented work, a conventional 2D position-sensitive 3 He detector with a spatial resolution of 2×3 mm 2 has been used for proof-of-principle measurements. The results are compared to conventional lattice strain measurements obtained at an engineering neutron diffractometer, where the same mechanical loading system was utilized. The efficiency of the time-of-flight transmission method is discussed with respect to other methods, at continuous as well as at pulsed sources.

The neutron capture detector (NCD) is introduced as a novel detection scheme for thermal and epithermal neutrons that could provide large-area neutron counters by using common detector materials and proven technologies. The NCD is based on the fact that neutron captures are usually followed by prompt gamma cascades, where the sum energy of the gammas equals to the total excitation energy of typically 6–9 MeV. This large sum energy is measured in a calorimetric approach and taken as the signature of a neutron capture event. An NCD consists of a neutron converter, comprising of constituents with large elemental neutron capture cross-section like cadmium or gadolinium, which is embedded in common scintillator material. The scintillator must be large and dense enough to absorb with reasonable probability a portion of the sum energy that exceeds the energy of gammas emitted by common (natural, medical, industrial) radiation sources. An energy window, advantageously complemented with a multiplicity filter, then discriminates neutron capture signals against background. The paper presents experimental results obtained at the cold-neutron beam of the BER II research reactor, Helmholtz-Zentrum Berlin, and at other neutron sources with a prototype NCD, consisting of four BGO crystals with embedded cadmium sheets, and with a benchmark configuration consisting of two separate NaI(Tl) detectors. The detector responses are in excellent agreement with predictions of a simulation model developed for optimizing NCD configurations. NCDs could be deployed as neutron detectors in radiation portal monitors (RPMs). Advanced modular scintillation detector systems could even combine neutron and gamma sensitivity with excellent background suppression at minimum overall expense.

Energy resolved imaging has recently gained attention for the potential of spatially resolved texture, crystallographic phase and strain investigations. Especially a time-of-flight (TOF) approach that takes maximum advantage of the new generation of pulsed spallation neutron sources is currently in the focus of investigations. Here, we present results of corresponding TOF measurements recorded at the continuous source of Helmholtz Center Berlin. The critical component for TOF imaging is however the availability of a high resolution imaging detector capable of the required time resolution. Here, a gated time-integrating detector without the corresponding continuous time resolution has been used and the measurements therefore have to be interpreted as proof-of-principle experiments as will be discussed. Measurements of different series of samples revealing structural differences related to their crystalline structure will be presented as well as a strain measurement on a dieless drawn wire.

The construction of new neutron facilities in Europe, Japan and the United States signals the need for many kinds of neutron detectors. In order to address a portion of this need, we are developing low-cost, reliable, medium-resolution (1–2.5 cm), single-wire-per-tube neutron gaseous detectors for moderate counting rates of about 10 6 counts/m 2 /s that are capable of being used in a vacuum environment. The detectors are fabricated with square tubes in order to avoid the efficiency problems of round tubes. Components used on the interior of the detector are chosen to have low outgassing rates. The detectors are baked while attached to a vacuum pumping station in order to assure a long lifetime without changing the gas.

The Extreme Environment Diffractometer (EXED) is a new neutron time-of-flight instrument at the BER II research reactor at the Helmholtz-Zentrum Berlin, Germany. Although EXED is a special-purpose instrument, its early construction made it available for users as a general-purpose diffractometer. In this respect, EXED became one of the rare examples, where the performance of a time-of-flight diffractometer at a continuous source can be characterized. In this paper, we report on the design and performance of EXED with an emphasis on the unique instrument capabilities. The latter comprise variable wavelength resolution and wavelength band, control of the incoming beam divergence, the possibility to change the angular positions of detectors and their distance to the sample, and use of event recording and offline histogramming. These features combined make EXED easily tunable to the requirements of a particular problem, from conventional diffraction to small angle neutron scattering. The instrument performance is demonstrated by several reference measurements and user experiments.

A large distance between the reactor core and the monochromator together with a take-off angle of 90° leads to low flux but high angular resolution of the diffractometer around 90° scattering angle. The sample-table consists of two goniometers for heavy loads. An x-y-z table for heavy loads can be mounted, as well as different eulerian cradles, a mirror furnace or a tensile rig. The detector is a 20x20cm2 position sensitive delay-line detector made by EMBL. A sophisticated primary and secondary slit system together with the recently installed high-resolution camera system allows the application of the high precision instrument alignment and calibration system recently developed at HMI. Here some special features of the instrument are presented and the consequences are outlined.

The energy determination of thermal and cold neutrons could revolutionize the field of neutron scattering science and transform the instrument design for future facilities. This contribution evaluates the feasibility and potential of a statistical determination of the neutron energy in the new generation of neutron detectors. In particular, the novel technology of multi-layer 10B thin film detectors present a unique opportunity of exploiting this possibility by using the various neutron penetration depths to extract energy information. A statistical mathematical model for doing so is being developed. To this end, measurements of absorption profiles on boron carbide have been performed at the Institutt for Energiteknikk, Norway and the Helmholtz Zentrum Berlin, Germany. The results of the data analysis allow for a preliminary estimate on the feasibility and the potential of this method.

Radiation detector systems for homeland security applications have been usually equipped with 3He tubes to detect the distinguished neutron signature of Special Nuclear Materials (SNMs). The serious shortage of 3He gas, however, recently initiated substantial efforts to develop alternative neutron detectors, particularly for large-area Radiation Portal Monitors (RPMs). Most activities are currently directed to detectors comprising 6Li or 10B — beyond doubt with remarkable success. Nevertheless, their broad deployment poses an economic challenge. Our contribution presents a different technique — the detection of neutron capture gammas. In contrast to other attempts we do not focus on characteristic gammas or conversion electrons in the low-energy range, or on the detection of single high-energy capture gammas. Rather we propose to measure the sum energy of multiple gammas released after neutron capture reactions in a semi-calorimetric approach. This method allows simultaneous measurements of neutron and gamma radiation with a single detector (even including spectroscopic information for nuclide identification). A first prototype of such a Neutron Capture Detector (NCD) was developed based on proven standard detector materials and technologies. It consists of thin Cadmium sheets surrounded by four BGO scintillation crystals. The detector response was studied in measurements with cold neutrons extracted at the BER II reactor, and with fission neutrons from 252Cf. The NCD performance is discussed in comparison with those of a 3He tube. Simulation calculations have been performed to estimate the detection efficiency as a function of the detector size. A complete database to model the multiple-gamma emission from excited 114Cd nuclei was composed by a semi-empirical approach which combines the gamma energies and yields of well resolved transitions with information from integral measurements. The simulation results are validated experimentally and allow optimizing more complex NCD systems for RPM applications.

A small shift of an angular distribution of prompt γ‐rays relative to the fission axis of 236U* 235U(n,γf) process is presented. This effect has been observed in the experiment at BER‐II reactor of BENSC/HMI (Berlin). The sign of the shift depends on the direction of the incident neutron beam polarization. This phenomena can be explained by the rotation of fissile nucleus 236U*, like the effect that has been observed recently at ILL in ternary fission of 235U by cold polarized neutrons. The main surprise of this result is the detection of scission gamma‐rays radiated by a fissile nucleus during the time interval of the order of 10−21 s before or after the moment of the neck rupture. Detailed measurements of trigger γ‐rays energy dependence are in progress at the neutron beam “MEPHISTO” of FRM‐II reactor (Garching).

In the Joint Research Activity DETNI (DETectors for Neutron Instrumentation) of the FP6 EU Integrated Infrastructure Initiative for Neutron Scattering and Muon Spectroscopy (NMI3) prototypes of three novel modular thermal neutron area detector types, based on thin solid neutron converters, were built and tested, which were developed for time- and wavelength resolved neutron detection with 2-D spatial and time resolutions of 50–1000 µm (FWHM) and of up to 2 ns, respectively, and for counting rates in the 107 – 108 cps range, i.e. for coping with the highest resolution and rate requirements at pulsed spallation neutron sources with MW average proton beam power like ESS. The detector types are (i) four-fold segmented modules of Silicon microstrip detectors (Si-MSD) with 157Gd converter layer between two double-sided Si sensors with 80 ¼m strip pitch, (ii) hybrid low-pressure microstrip gas chamber (MSGC) detectors with three-stage gas amplification and 2-D position-sensitive MSGC plates either side of a composite 157Gd/CsI converter, (iii) CASCADE detectors with cascaded 10B-coated GEM (Gas Electron Multiplier) foils either side of a 2-D position-sensitive readout electrode. For readout in DETNI prototypes of two novel, channel-wise self-triggered high-rate ASICs, of ADC-FPGA boards with Gigabit glass fiber readout and of the necessary data acquisition firmware and software have been developed. The ASICs, i.e. the 128-channel n-XYTER ASIC, optimized for the Si-MSD and strip hit rates of 200 khits/s, and the 32-channel MSGCROC ASIC for the MSGC with variable amplification and strip rates of 900 khits/s, deliver for each strip spatial and 4 (2) ns time stamp resolution, respectively, the latter e.g. for correlating x and y strips unambiguously, as well as analog amplitude resolution for center-of-gravity interpolation and gating. In this paper the current status of prototyping will be reported.

A two-dimensional (2D) position sensitive detector for neutron scattering applications based on low-pressure gas amplification and micro-strip technology was built and tested with an innovative readout electronics and data acquisition system. This detector contains a thin solid neutron converter and was developed for time- and thus wavelength-resolved neutron detection in single-event counting mode, which improves the image contrast in comparison with integrating detectors. The prototype detector of a Micro-Strip Gas Chamber (MSGC) was built with a solid natGd/CsI thermal neutron converter for spatial resolutions of about 100 μm and counting rates up to 107 neutrons/s. For attaining very high spatial resolutions and counting rates via micro-strip readout with centre-of-gravity evaluation of the signal amplitude distributions, a fast, channel-wise, self-triggering ASIC was developed. The front-end chips (MSGCROCs), which are very first signal processing components, are read out into powerful ADC-FPGA boards for on-line data processing and thereafter via Gigabit Ethernet link into the data receiving PC. The workstation PC is controlled by a modular, high performance dedicated software suite. Such a fast and accurate system is crucial for efficient radiography/tomography, diffraction or imaging applications based on high flux thermal neutron beam. In this paper a brief description of the detector concept with its operation principles, readout electronics requirements and design together with the signals processing stages performed in hardware and software are presented. In more detail the neutron test beam conditions and measurement results are reported. The focus of this paper is on the system integration, two dimensional spatial resolution, the time resolution of the readout system and the imaging capabilities of the overall setup. The detection efficiency of the detector prototype is estimated as well.