Journal of Imaging

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15 pages, 6039 KiB

Open AccessArticle

Improved Acquisition and Reconstruction for Wavelength-Resolved Neutron Tomography

by Singanallur Venkatakrishnan, Yuxuan Zhang, Luc Dessieux, Christina Hoffmann, Philip Bingham and Hassina Bilheux

J. Imaging 2021, 7(1), 10; https://doi.org/10.3390/jimaging7010010 - 15 Jan 2021

Cited by 4 | Viewed by 3445

Abstract

Wavelength-resolved neutron tomography (WRNT) is an emerging technique for characterizing samples relevant to the materials sciences in 3D. WRNT studies can be carried out at beam lines in spallation neutron or reactor-based user facilities. Because of the limited availability of experimental time, potential [...] Read more.

Wavelength-resolved neutron tomography (WRNT) is an emerging technique for characterizing samples relevant to the materials sciences in 3D. WRNT studies can be carried out at beam lines in spallation neutron or reactor-based user facilities. Because of the limited availability of experimental time, potential imperfections in the neutron source, or constraints placed on the acquisition time by the type of sample, the data can be extremely noisy resulting in tomographic reconstructions with significant artifacts when standard reconstruction algorithms are used. Furthermore, making a full tomographic measurement even with a low signal-to-noise ratio can take several days, resulting in a long wait time before the user can receive feedback from the experiment when traditional acquisition protocols are used. In this paper, we propose an interlaced scanning technique and combine it with a model-based image reconstruction algorithm to produce high-quality WRNT reconstructions concurrent with the measurements being made. The interlaced scan is designed to acquire data so that successive measurements are more diverse in contrast to typical sequential scanning protocols. The model-based reconstruction algorithm combines a data-fidelity term with a regularization term to formulate the wavelength-resolved reconstruction as minimizing a high-dimensional cost-function. Using an experimental dataset of a magnetite sample acquired over a span of about two days, we demonstrate that our technique can produce high-quality reconstructions even during the experiment compared to traditional acquisition and reconstruction techniques. In summary, the combination of the proposed acquisition strategy with an advanced reconstruction algorithm provides a novel guideline for designing WRNT systems at user facilities. Full article

(This article belongs to the Special Issue Neutron Imaging)

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9 pages, 2257 KiB

Open AccessArticle

Neutron Imaging Using a Fine-Grained Nuclear Emulsion

by Katsuya Hirota, Tomoko Ariga, Masahiro Hino, Go Ichikawa, Shinsuke Kawasaki, Masaaki Kitaguchi, Kenji Mishima, Naoto Muto, Naotaka Naganawa and Hirohiko M. Shimizu

J. Imaging 2021, 7(1), 4; https://doi.org/10.3390/jimaging7010004 - 5 Jan 2021

Cited by 4 | Viewed by 3069

Abstract

A neutron detector using a fine-grained nuclear emulsion has a sub-micron spatial resolution and thus has potential to be applied as high-resolution neutron imaging. In this paper, we present two approaches to applying the emulsion detectors for neutron imaging. One is using a [...] Read more.

A neutron detector using a fine-grained nuclear emulsion has a sub-micron spatial resolution and thus has potential to be applied as high-resolution neutron imaging. In this paper, we present two approaches to applying the emulsion detectors for neutron imaging. One is using a track analysis to derive the reaction points for high resolution. From an image obtained with a 9 μm pitch Gd grating with cold neutrons, periodic peak with a standard deviation of

1.3

μm was observed. The other is an approach without a track analysis for high-density irradiation. An internal structure of a crystal oscillator chip, with a scale of approximately 30 μm, was able to be observed after an image analysis. Full article

(This article belongs to the Special Issue Neutron Imaging)

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12 pages, 7119 KiB

Open AccessArticle

Comparison of Thermal Neutron and Hard X-ray Dark-Field Tomography

by Alex Gustschin, Tobias Neuwirth, Alexander Backs, Manuel Viermetz, Nikolai Gustschin, Michael Schulz and Franz Pfeiffer

J. Imaging 2021, 7(1), 1; https://doi.org/10.3390/jimaging7010001 - 23 Dec 2020

Cited by 1 | Viewed by 2932

Abstract

High visibility (0.56) neutron-based multi-modal imaging with a Talbot–Lau interferometer at a wavelength of

1.6

Å is reported. A tomography scan of a strongly absorbing quartz geode sample was performed with both the neutron and an X-ray grating interferometer (70 kVp) for a [...] Read more.

High visibility (0.56) neutron-based multi-modal imaging with a Talbot–Lau interferometer at a wavelength of

1.6

Å is reported. A tomography scan of a strongly absorbing quartz geode sample was performed with both the neutron and an X-ray grating interferometer (70 kVp) for a quantitative comparison. Small scattering structures embedded in the absorbing silica matrix were well resolved in neutron dark-field CT slices with a spatial resolution of about 300 μ

m

. Beneficial effects, such as monochromaticity and stronger penetration power of the used neutron radiation, helped to avoid the beam hardening-related artificial dark-field signal which was present in the X-ray data. Both dark-field modalities show mostly the same structures; however, some scattering features appear only in the neutron domain. Potential applications of combined X-ray and neutron multi-modal CT enabling one to probe both the nuclear and the electron density-related structural properties are discussed. strongly absorbing samples are now accessible for the dark-field modality by the use of thermal neutrons. Full article

(This article belongs to the Special Issue Neutron Imaging)

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16 pages, 3957 KiB

Open AccessFeature PaperArticle

4D Bragg Edge Tomography of Directional Ice Templated Graphite Electrodes

by Ralf F. Ziesche, Anton S. Tremsin, Chun Huang, Chun Tan, Patrick S. Grant, Malte Storm, Dan J. L. Brett, Paul R. Shearing and Winfried Kockelmann

J. Imaging 2020, 6(12), 136; https://doi.org/10.3390/jimaging6120136 - 11 Dec 2020

Cited by 10 | Viewed by 3509

Abstract

Bragg edge tomography was carried out on novel, ultra-thick, directional ice templated graphite electrodes for Li-ion battery cells to visualise the distribution of graphite and stable lithiation phases, namely LiC₁₂ and LiC₆. The four-dimensional Bragg edge, wavelength-resolved neutron tomography technique [...] Read more.

Bragg edge tomography was carried out on novel, ultra-thick, directional ice templated graphite electrodes for Li-ion battery cells to visualise the distribution of graphite and stable lithiation phases, namely LiC₁₂ and LiC₆. The four-dimensional Bragg edge, wavelength-resolved neutron tomography technique allowed the investigation of the crystallographic lithiation states and comparison with the electrode state of charge. The tomographic imaging technique provided insight into the crystallographic changes during de-/lithiation over the electrode thickness by mapping the attenuation curves and Bragg edge parameters with a spatial resolution of approximately 300 µm. This feasibility study was performed on the IMAT beamline at the ISIS pulsed neutron spallation source, UK, and was the first time the 4D Bragg edge tomography method was applied to Li-ion battery electrodes. The utility of the technique was further enhanced by correlation with corresponding X-ray tomography data obtained at the Diamond Light Source, UK. Full article

(This article belongs to the Special Issue Neutron Imaging)

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12 pages, 659 KiB

Open AccessArticle

Light Yield Response of Neutron Scintillation Screens to Sudden Flux Changes

by Tobias Neuwirth, Bernhard Walfort, Simon Sebold and Michael Schulz

J. Imaging 2020, 6(12), 134; https://doi.org/10.3390/jimaging6120134 - 5 Dec 2020

Cited by 3 | Viewed by 2861

Abstract

We performed a study of the initial and long term light yield of different scintillation screen mixtures for neutron imaging during constant neutron irradiation. We evaluated the light yield during different neutron flux levels as well as at different temperatures. As high frame [...] Read more.

We performed a study of the initial and long term light yield of different scintillation screen mixtures for neutron imaging during constant neutron irradiation. We evaluated the light yield during different neutron flux levels as well as at different temperatures. As high frame rate imaging is a topic of interest in the neutron imaging community, the decay characteristics of scintillation screens are of interest as well. Hence, we also present and discuss the decay behavior of the different scintillation screen mixtures on a time scale of seconds. We have found that the decay time of ZnS:Cu/⁶LiF excited with a high neutron flux is potentially much longer than typically stated. While most of the tested scintillation screens do not provide a significant improvement over currently used scintillation screen materials, Zn(Cd)S:Ag/⁶LiF seems to be a good candidate for high frame rate imaging due to its high light yield, long-term stability as well as fast decay compared to the other evaluated scintillation screens. Full article

(This article belongs to the Special Issue Neutron Imaging)

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11 pages, 5704 KiB

Open AccessArticle

A Fast Neutron Radiography System Using a High Yield Portable DT Neutron Source

by David L. Williams, Craig M. Brown, David Tong, Alexander Sulyman and Charles K. Gary

J. Imaging 2020, 6(12), 128; https://doi.org/10.3390/jimaging6120128 - 26 Nov 2020

Cited by 12 | Viewed by 3120

Abstract

Resolution measurements were made using 14.1 MeV neutrons from a high-yield, portable DT neutron generator and a neutron camera based on a scintillation screen viewed by a digital camera. Resolution measurements were made using a custom-built, plastic, USAF-1951 resolution chart, of dimensions 125 [...] Read more.

Resolution measurements were made using 14.1 MeV neutrons from a high-yield, portable DT neutron generator and a neutron camera based on a scintillation screen viewed by a digital camera. Resolution measurements were made using a custom-built, plastic, USAF-1951 resolution chart, of dimensions 125 × 98 × 25.4 mm³, and by calculating the modulation transfer function from the edge-spread function from edges of plastic and steel objects. A portable neutron generator with a yield of 3 × 10⁹ n/s (DT) and a spot size of 1.5 mm was used to irradiate the object with neutrons for 10 min. The neutron camera, based on a ⁶LiF/ZnS:Cu-doped polypropylene scintillation screen and digital camera was placed at a distance of 140 cm, and produced an image with a spatial resolution of 0.35 cycles per millimeter. Full article

(This article belongs to the Special Issue Neutron Imaging)

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22 pages, 7311 KiB

Open AccessFeature PaperArticle

Boron-Based Neutron Scintillator Screens for Neutron Imaging

by William Chuirazzi, Aaron Craft, Burkhard Schillinger, Steven Cool and Alessandro Tengattini

J. Imaging 2020, 6(11), 124; https://doi.org/10.3390/jimaging6110124 - 19 Nov 2020

Cited by 15 | Viewed by 3902

Abstract

In digital neutron imaging, the neutron scintillator screen is a limiting factor of spatial resolution and neutron capture efficiency and must be improved to enhance the capabilities of digital neutron imaging systems. Commonly used neutron scintillators are based on ⁶LiF and gadolinium [...] Read more.

In digital neutron imaging, the neutron scintillator screen is a limiting factor of spatial resolution and neutron capture efficiency and must be improved to enhance the capabilities of digital neutron imaging systems. Commonly used neutron scintillators are based on ⁶LiF and gadolinium oxysulfide neutron converters. This work explores boron-based neutron scintillators because ¹⁰B has a neutron absorption cross-section four times greater than ⁶Li, less energetic daughter products than Gd and ⁶Li, and lower γ-ray sensitivity than Gd. These factors all suggest that, although borated neutron scintillators may not produce as much light as ⁶Li-based screens, they may offer improved neutron statistics and spatial resolution. This work conducts a parametric study to determine the effects of various boron neutron converters, scintillator and converter particle sizes, converter-to-scintillator mix ratio, substrate materials, and sensor construction on image quality. The best performing boron-based scintillator screens demonstrated an improvement in neutron detection efficiency when compared with a common ⁶LiF/ZnS scintillator, with a 125% increase in thermal neutron detection efficiency and 67% increase in epithermal neutron detection efficiency. The spatial resolution of high-resolution borated scintillators was measured, and the neutron tomography of a test object was successfully performed using some of the boron-based screens that exhibited the highest spatial resolution. For some applications, boron-based scintillators can be utilized to increase the performance of a digital neutron imaging system by reducing acquisition times and improving neutron statistics. Full article

(This article belongs to the Special Issue Neutron Imaging)

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11 pages, 7950 KiB

Open AccessArticle

Neutron Radiography and Tomography of the Drying Process of Screed Samples

by Lorenz Kapral, Michael Zawisky and Hartmut Abele

J. Imaging 2020, 6(11), 118; https://doi.org/10.3390/jimaging6110118 - 5 Nov 2020

Cited by 1 | Viewed by 2281

Abstract

The moisture content of screed samples is an essential parameter in the construction industry, since the screed must dry to a certain level of moisture content to be ready for covering. This paper introduces neutron radiography (NR) and neutron tomography (NT) as new, [...] Read more.

The moisture content of screed samples is an essential parameter in the construction industry, since the screed must dry to a certain level of moisture content to be ready for covering. This paper introduces neutron radiography (NR) and neutron tomography (NT) as new, non-destructive techniques for analysing the drying characteristics of screed. Our NR analyses evaluate the results of the established methods while offering much higher spatial resolution of 200

μ

m, thereby facilitating a two- and three-dimensional understanding of screed’s drying behaviour. Because of NR’s exceptionally high sensitivity regarding the total cross section of hydrogen the precise moisture content of screed samples is obtainable, resulting in new observations. The current methods to measure moisture content comprise the ‘calcium carbide method’, the ‘Darr method’, and electrical sensor systems. Full article

(This article belongs to the Special Issue Neutron Imaging)

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17 pages, 3066 KiB

Open AccessArticle

Design of Neutron Microscopes Equipped with Wolter Mirror Condenser and Objective Optics for High-Fidelity Imaging and Beam Transport

by Muhammad Abir, Daniel S. Hussey and Boris Khaykovich

J. Imaging 2020, 6(10), 100; https://doi.org/10.3390/jimaging6100100 - 27 Sep 2020

Cited by 4 | Viewed by 3447

Abstract

We present and compare the designs of three types of neutron microscopes for high-resolution neutron imaging. Like optical microscopes, and unlike standard neutron imaging instruments, these microscopes have both condenser and image-forming objective optics. The optics are glancing-incidence axisymmetric mirrors and therefore suitable [...] Read more.

We present and compare the designs of three types of neutron microscopes for high-resolution neutron imaging. Like optical microscopes, and unlike standard neutron imaging instruments, these microscopes have both condenser and image-forming objective optics. The optics are glancing-incidence axisymmetric mirrors and therefore suitable for polychromatic neutron beams. The mirrors are designed to provide a magnification of 10 to achieve a spatial resolution of better than 10

μ

m. The resolution of the microscopes is determined by the mirrors rather than by the L/Dratio as in conventional pinhole imaging, leading to possible dramatic improvements in the signal rate. We predict the increase in the signal rate by at least two orders of magnitude for very high-resolution imaging, which is always flux limited. Furthermore, in contrast to pinhole imaging, in the microscope, the samples are placed far from the detector to allow for a bulky sample environment without sacrificing spatial resolution. Full article

(This article belongs to the Special Issue Neutron Imaging)

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14 pages, 3157 KiB

Open AccessArticle

Measuring Thickness-Dependent Relative Light Yield and Detection Efficiency of Scintillator Screens

by William C. Chuirazzi and Aaron E. Craft

J. Imaging 2020, 6(7), 56; https://doi.org/10.3390/jimaging6070056 - 29 Jun 2020

Cited by 10 | Viewed by 3641

Abstract

Digital camera-based neutron imaging systems consisting of a neutron scintillator screen optically coupled to a digital camera are the most common digital neutron imaging system used in the neutron imaging community and are available at any state-of-the-art imaging facility world-wide. Neutron scintillator screens [...] Read more.

Digital camera-based neutron imaging systems consisting of a neutron scintillator screen optically coupled to a digital camera are the most common digital neutron imaging system used in the neutron imaging community and are available at any state-of-the-art imaging facility world-wide. Neutron scintillator screens are the integral component of these imaging system that directly interacts with the neutron beam and dictates the neutron capture efficiency and image quality limitations of the imaging system. This work describes a novel approach for testing neutron scintillators that provides a simple and efficient way to measure relative light yield and detection efficiency over a range of scintillator thicknesses using a single scintillator screen and only a few radiographs. Additionally, two methods for correlating the screen thickness to the measured data were implemented and compared. An example ⁶LiF:ZnS scintillator screen with nominal thicknesses ranging from 0–300 μm was used to demonstrate this approach. The multi-thickness screen and image and data processing methods are not exclusive to neutron scintillator screens but could be applied to X-ray imaging as well. This approach has the potential to benefit the entire radiographic imaging community by offering an efficient path forward for manufacturers to develop higher-performance scintillators and for imaging facilities and service providers to determine the optimal screen parameters for their particular beam and imaging system. Full article

(This article belongs to the Special Issue Neutron Imaging)

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12 pages, 1311 KiB

Open AccessArticle

On a Method For Reconstructing Computed Tomography Datasets from an Unstable Source

by Nicholas Stull, Josh McCumber, Lawrence D'Aries, Michelle Espy, Cort Gautier and James Hunter

J. Imaging 2020, 6(5), 35; https://doi.org/10.3390/jimaging6050035 - 19 May 2020

Cited by 1 | Viewed by 3488

Abstract

As work continues in neutron computed tomography, at Los Alamos Neutron Science Center (LANSCE) and other locations, source reliability over the long imaging times is an issue of increasing importance. Moreover, given the time commitment involved in a single neutron image, it is [...] Read more.

As work continues in neutron computed tomography, at Los Alamos Neutron Science Center (LANSCE) and other locations, source reliability over the long imaging times is an issue of increasing importance. Moreover, given the time commitment involved in a single neutron image, it is impractical to simply discard a scan and restart in the event of beam instability. In order to mitigate the cost and time associated with these options, strategies are presented in the current work to produce a successful reconstruction of computed tomography data from an unstable source. The present work uses a high energy neutron tomography dataset from a simulated munition collected at LANSCE to demonstrate the method, which is general enough to be of use in conjunction with unstable X-ray computed tomography sources as well. Full article

(This article belongs to the Special Issue Neutron Imaging)

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10 pages, 2339 KiB

Open AccessArticle

On the Genesis of Artifacts in Neutron Transmission Imaging of Hydrogenous Steel Specimens

by Beate Pfretzschner, Thomas Schaupp, Andreas Hannemann, Michael Schulz and Axel Griesche

J. Imaging 2020, 6(4), 22; https://doi.org/10.3390/jimaging6040022 - 9 Apr 2020

Cited by 1 | Viewed by 4374

Abstract

Hydrogen-charged supermartensitic steel samples were used to systematically investigate imaging artifacts in neutron radiography. Cadmium stencils were placed around the samples to shield the scintillator from excessive neutron radiation and to investigate the influence of the backlight effect. The contribution of scattered neutrons [...] Read more.

Hydrogen-charged supermartensitic steel samples were used to systematically investigate imaging artifacts in neutron radiography. Cadmium stencils were placed around the samples to shield the scintillator from excessive neutron radiation and to investigate the influence of the backlight effect. The contribution of scattered neutrons to the total detected intensity was investigated by additionally varying the sample-detector distance and applying a functional correlation between distance and intensity. Furthermore, the influence of the surface roughness on the edge effect due to refraction was investigated. Full article

(This article belongs to the Special Issue Neutron Imaging)

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13 pages, 4000 KiB

Open AccessArticle

Energy Resolved Neutron Imaging for Strain Reconstruction Using the Finite Element Method

by Riya Aggarwal, Michael H. Meylan, Bishnu P. Lamichhane and Chris M. Wensrich

J. Imaging 2020, 6(3), 13; https://doi.org/10.3390/jimaging6030013 - 22 Mar 2020

Cited by 3 | Viewed by 4885

Abstract

A novel pulsed neutron imaging technique based on the finite element method is used to reconstruct the residual strain within a polycrystalline material from Bragg edge strain images. This technique offers the possibility of a nondestructive analysis of strain fields with a high [...] Read more.

A novel pulsed neutron imaging technique based on the finite element method is used to reconstruct the residual strain within a polycrystalline material from Bragg edge strain images. This technique offers the possibility of a nondestructive analysis of strain fields with a high spatial resolution. The finite element approach used to reconstruct the strain uses the least square method constrained by the conditions of equilibrium. This inclusion of equilibrium makes the problem well-posed. The procedure is developed and verified by validating for a cantilevered beam problem. It is subsequently demonstrated by reconstructing the strain from experimental data for a ring-and-plug sample, measured at the spallation neutron source RADEN at J-PARC in Japan. The reconstruction is validated by comparison with conventional constant wavelength strain measurements on the KOWARI diffractometer at ANSTO in Australia. It is also shown that the addition of a Tikhonov regularisation scheme further improves the reconstruction. Full article

(This article belongs to the Special Issue Neutron Imaging)

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Review

Jump to: Research

12 pages, 4774 KiB

Open AccessReview

NEURAP—A Dedicated Neutron-Imaging Facility for Highly Radioactive Samples

by Eberhard Lehmann, Knud Thomsen, Markus Strobl, Pavel Trtik, Johannes Bertsch and Yong Dai

J. Imaging 2021, 7(3), 57; https://doi.org/10.3390/jimaging7030057 - 16 Mar 2021

Cited by 7 | Viewed by 2422

Abstract

NEURAP is a dedicated set-up at the Swiss neutron spallation source (SINQ) at the Paul Scherrer Institut (PSI), optionally implemented as a special configuration of the neutron-imaging station NEUTRA. It is one of very few instrumentations available worldwide enabling neutron-imaging of highly radioactive [...] Read more.

NEURAP is a dedicated set-up at the Swiss neutron spallation source (SINQ) at the Paul Scherrer Institut (PSI), optionally implemented as a special configuration of the neutron-imaging station NEUTRA. It is one of very few instrumentations available worldwide enabling neutron-imaging of highly radioactive samples to be performed routinely, with special precautions and following a specific procedure. Since the relevant objects are strong γ-sources, dedicated techniques are needed to handle the samples and to perform neutron-imaging despite the radiation background. Dysprosium (Dy)-loaded imaging plates, effectively made sensitive to neutrons only, are employed. Neutrons are captured by Dy during neutron irradiation. Then the imaging plate is erased removing gamma detections. A subsequent relatively long self-exposure by the radiation from the intrinsic neutron-activated Dy within the imaging plate yields the neutron-only radiograph that is finally read out. During more than 20 years of NEURAP operation, images have been obtained for two major applications: (a) highly radioactive SINQ target components were investigated after long-term operation life; and (b) spent fuel rods and their cladding from Swiss nuclear power plants were characterized. Quantitative analysis of the image data demonstrated the accumulation of spallation products in the lead filled “Cannelloni” Zircaloy tubes of the SINQ target and the aggregation of hydrogen at specific sites in used fuel pins of power plants and their cladding, respectively. These results continue to help understanding material degradation and optimizing the operational regimes, which might lead to extending the safe lifetimes of these components. Full article

(This article belongs to the Special Issue Neutron Imaging)

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15 pages, 5637 KiB

Open AccessReview

The Neutron Imaging Instrument CONRAD—Post-Operational Review

by Nikolay Kardjilov, Ingo Manke, André Hilger, Tobias Arlt, Robert Bradbury, Henning Markötter, Robin Woracek, Markus Strobl, Wolfgang Treimer and John Banhart

J. Imaging 2021, 7(1), 11; https://doi.org/10.3390/jimaging7010011 - 19 Jan 2021

Cited by 6 | Viewed by 3967

Abstract

The neutron imaging instrument CONRAD was operated as a part of the user program of the research reactor BER-II at Helmholtz-Zentrum Berlin (HZB) from 2005 to 2020. The instrument was designed to use the neutron flux from the cold source of the reactor, [...] Read more.

The neutron imaging instrument CONRAD was operated as a part of the user program of the research reactor BER-II at Helmholtz-Zentrum Berlin (HZB) from 2005 to 2020. The instrument was designed to use the neutron flux from the cold source of the reactor, transported by a curved neutron guide. The pure cold neutron spectrum provided a great advantage in the use of different neutron optical components such as focusing lenses and guides, solid-state polarizers, monochromators and phase gratings. The flexible setup of the instrument allowed for implementation of new methods including wavelength-selective, dark-field, phase-contrast and imaging with polarized neutrons. In summary, these developments helped to attract a large number of scientists and industrial customers, who were introduced to neutron imaging and subsequently contributed to the expansion of the neutron imaging community. Full article

(This article belongs to the Special Issue Neutron Imaging)

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