Neutron Transmission Research Articles

Temperature distribution during welding measured by neutron imaging

This study was carried out to investigate the neutron transmission signal as a function of sample temperature during a welding process. A theoretical description that includes the Debye-Waller factor was used to describe the temperature influence on the neutron cross-sections. Neutron imaging using a monochromatic beam helps to observe transmission variations related to the material temperature. In-situ neutron imaging of welding experiments show the distribution of the temperature in bulk steel samples. The performed finite element modelling of expected temperature distributions shows good agreement with the obtained experimental data.

A multimodal neutron-based technique for the elemental analysis of materials in bulk

Neutrons and gamma rays are effective probes for the elemental characterisation of bulk samples. Neutrons interactions with matter are characteristic of the nature of the target nucleus, and the incident neutron energy. Most nuclides exhibit distinctive structure in their total and differential cross sections, thus elements can be differentiated via their total, elastic and inelastic scattering cross sections, and the energies of prompt gamma rays produced in inelastic collisions. In this work we report on the use of the fast neutron transmission analysis technique for the analysis of 12C in graphite. We also present results of prompt gamma ray neutron activation analysis of graphite using 14 MeV neutrons, which was explored for the purpose of developing a multimodal neutron-based technique for elemental analysis of materials in bulk.

A high-temperature and high-pressure cell for in situ visualization of reaction processes by neutron imaging

This study developed a high-temperature and high-pressure (HTHP) cell for in situ neutron imaging of hydrothermal reactions. The cell’s maximum temperature and pressure were 500 °C and 50 MPa, respectively, and its vessel for observing reactions comprised SUS316 stainless steel. Neutron transmission images were obtained to observe the behavior of sub- and supercritical water and the decomposition of two plastics (polypropylene and polyethylene) at HTHP. The images showed that water’s density and phase changed with temperature and pressure, affecting neutron transmission (and thus image brightness). The plastics began to melt and change shape at 150–200 °C, and they decomposed at 500 °C and 20 MPa. This study provides a basis for future research using the HTHP cell to examine various reactions such as the decomposition of biomass samples, the reforming of heavy oil, and the synthesis of nano-materials using sub- and supercritical water.

Radiation synthesis of boronic acid modified graphene oxide for enhance the neutron shielding property of silicone rubber

In this study, poly(3-acrylaminophenylboronic acid) modified graphene oxide (GO-PAAPBA) has been prepared by polymerization of 3-acrylaminophenylboronic acid (AAPBA) on the surface of GO. The –O· free radical was formed by γ-ray radiation, which initiated the polymerization of AAPBA. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and Raman spectroscopy were employed to characterize the structure of GO-PAAPBA. The grafting density of poly(3-acrylaminophenylboronic acid) is increased with increasing of the absorbed dose. The GO-PAAPBA was added into vinyl-terminated polydimethylsiloxane (Vi-PDMS) to prepare room temperature cured silicon rubber composites (SR/GO-PAAPBA). The GO-PAAPBA exhibits better dispersion performance than pure GO, which is contribute to improve thermal conductivity and mechanical properties. Significantly, with grafting density of PAAPBA increasing, the comprehensive performances of SR/GO-PAAPBA are more remarkable. SR/GO-PAAPBA-1.88 with outstanding thermal and mechanical abilities exhibits beat neutron shielding property. The neutron transmission of SR/GO-PAAPBA-1.88 is 10% lower than that of SR. The SR nanocomposite with efficient thermal conductivity and neutron shielding ability has a promising prospect to be applied as advanced flexible shielding material.

Versatile pressure and temperature controlled cell for neutron reflectometry and small-angle neutron scattering

We have designed and realized a temperature and pressure controlled cell for Neutron Reflectometry (NR) and Small Angle Neutron Scattering (SANS) that is compatible with simultaneous optical transmission and resistivity measurements. The cell can accommodate samples up to 102 mm (4 inch) in diameter, can be pressurized from vacuum up to 10 bar gas pressure and the sample temperature can be controlled up to 350°C. The four single crystal quartz windows ensure both a good neutron and optical transmission and hence can be used in combination with in-situ optical transmission measurements. We present the cell and illustrate its performance with a series of neutron reflectometry experiments performed on Ta based thin films under a hydrogen containing atmosphere.

Characterization of Fast Neutron Transmission Through an Iron Shield

In this paper we give an analysis of the neutron transmission through an iron sphere using Monte Carlo and transport theory methods based on ENDF/B-VII.1 general purpose library. The motivation for this investigation comes from a well-known deficiency in the iron inelastic data from the older library evaluation (ENDF/B-V), giving a concern for a fast neutron flux underestimation within the reactor pressure vessels. In order to benchmark the next-generation ENDF/B-VI iron data, the U.S. Nuclear Regulatory Commission and the former Czechoslovakian National Research Institute have jointly preformed several experiments in 1990s, addressing neutron leakage spectra obtained for a 252Cf fission source in a centre of an iron sphere. It was shown that the ENDF/B-VI iron cross section, containing several improvements over previous evaluations, will not entirely resolve the neutron spectrum discrepancies observed at high neutron energies. Since safety analyses of reactor pressure vessel embrittlement are often based on neutron transport calculations using specific multigroup cross section libraries, simulation of this benchmark was performed using a hybrid shielding methodology of ADVANTG3.0.3 and MCNP6.1.1b codes. Comparison of calculated and referenced dosimeter activation rates are presented for several "standard" nuclear reactions, often used in reactor pressure vessel dosimetry. For that purpose, the new IRDFF-II special library from the IAEA Nuclear Data Services was used as a reference source of dosimetry cross sections. The MCNP6.1.1b code was used for calculation of reaction rates, which were also compared with previous IRDFF-1.05 special library and general purpose ENDF/B-VII.1 library.

Orientation mapping of YbSn3 single crystals based on Bragg-dip analysis using a delay-line superconducting sensor

Recent progress in high-power pulsed neutron sources has stimulated the development of the Bragg-dip and Bragg-edge analysis methods using a two-dimensional neutron detector with high temporal resolution to resolve the neutron energy by the time-of-flight method. A delay-line current-biased kinetic inductance detector (CB-KID) is a two-dimensional superconducting sensor with a high temporal resolution and multi-hit capability. Here, it is demonstrated that a delay-line CB-KID with a 10B neutron conversion layer can be applied to high-spatial-resolution neutron transmission imaging and spectroscopy up to 100 eV. Dip structures are observed in the transmission spectra of YbSn3 single crystals, induced by Bragg diffraction and nuclear resonance absorption. The orientation mapping of YbSn3 crystals is successfully performed via the analysis of observed Bragg-dip positions in the transmission spectra.

Physical design and performance research of two counter-rotating T0 choppers for the multi-physics neutron diffractometer at China Spallation Neutron Source

The T0 chopper has the ability to remove the fast neutrons and high-energy gamma rays emitted at time zero of each pulse cycle. The multi-physics instrument of the China Spallation Neutron Source requires high epithermal neutron flux to obtain large momentum transfer, and the traditional single T0 chopper is a disadvantage for the transmission of epithermal neutrons in the long focusing guide. To solve this problem, the two counter-rotating T0 chopper design is proposed that can greatly improve the transmission efficiency of epithermal neutrons. The results of the beam experiment show that compared with the single T0 chopper operating at 50 Hz, the two counter-rotating T0 choppers at the same speed significantly improves the transmission efficiency of epithermal neutrons (especially the shorter wavelength neutrons). For example, when the two blades partially overlap, the transmission efficiencies of 0.05 Å, 0.1 Å, and 0.2 Å wavelength neutrons are increased by 9.4, 4.7, and 4.6 times, respectively, which fully proves that the two counter-rotating T0 chopper design is reasonable, and the experimental results are in line with expectations. The design and application of two counter-rotating T0 choppers at the China Spallation Neutron Source is the first example of this in the world and can be applied to neutron spectrometers with high epithermal neutron flux requirements, and can also be extended to fields such as the energy selection of high-energy particles.

Crystalline Orientation of CaF2 window determined by Neutron Transmission Imaging using a Delay Line Current-Biased Kinetic-Inductance Detector

The combination of a high speed two-dimensional neutron detector and an intensive pulsed neutron source provides not only neutron transmission imaging but also information on crystal structures, orientations and constituent elements by analyzing neutron transmission spectra. The delay-line current-biased kinetic-inductance detector (CB-KID) is a two-dimensional superconducting neutron detector with high spatial and temporal resolutions, and multi-hit tolerance. We demonstrated that the delay-line CB-KID with a 10B neutron conversion layer can be applied for neutron transmission measurements up to 100 keV. We observed two-different dip structures in the transmission spectra in a CaF2 single crystal, i.e., one is from the Bragg diffraction and the other is from nuclear resonance absorption. We consider that some duplicated structures in resonance absorption dips are originating from a double-bunch structure of proton pulses for producing pulsed neutrons in the accelerator.

Monte Carlo simulation of a high-efficacy composite material: feasibility for neutron and gamma ray shielding of Small Modular Reactor (SMR) facilities

Secondary neutrons with energy distribution similar to that of a Small Modular Reactor (SMR) was generated by bombarding a water target with 10 MeV proton beam from a Cyclotron and analyzed using Monte Carlo (MC) technique. Transmission of neutrons (SMR-Analogue) through a batch of spheres (r = 20 cm) made of a composite of Lead (PB), Boron Carbide (BC) and Polyethylene (PL) granules of varying volume concentrations was investigated. An optimized blend of 50%(vol) PB, 2%(vol) BC and 48%(vol) PL: (50PB2BC48PL) giving the lowest neutron transmission factor was evaluated. The tenth value layer thickness (TVLT) relevant to SMR neutrons in the optimized composite and in ordinary concrete was calculated to be 5.6 cm and 25.4 cm respectively. The high (50% vol) Lead content guaranteed a high attenuation of gamma rays co-produced by neutron activation of reactor cooling water. Feasibility of the high-efficacy optimized compact composite in radiological shielding of SMR is envisaged.

Higher order correction and spectral deconvolution of wavelength-resolved neutron transmission imaging at the CONRAD-2 instrument

This paper uses a Fourier self-deconvolution method for improving the wavelength resolution in transmission experiments at continuous neutron sources utilizing a double-crystal monochromator device to probe as well as correct the generation of higher-order neutron scattering in a monochromatic neutron beam. The cold neutron radiography CONRAD-2 equipment has been utilized to resolve the steel transmission spectra of changing BCC phase and FCC phase fractions. Therefore, both low and high-spectral resolution instruments with equivalent wavelength resolution have been proposed. The primary benefit of Fourier self-deconvolution is its ability to precisely narrow individual bands without modifying their relative position or the total band area. Thus, the resolution of the transmission spectrum has been improved by a factor of 3.16, and the info that the sample material comprises two crystallographic phases has been determined by the wavelength resolution improvement employing the deconvolution approach. Additionally, the slight variation in Bragg edge position for different phase fractions and the locations of the double phase Bragg edges have also been obtained using the ray-tracing simulation tool McStas. The high resolution neutron wavelength selection experiment with the ESS test_beamline (V20) instrument employing the neutron time-of-flight detection demonstrates the precision of the resolving steel Bragg edge.

A Large Area Picosecond Photodetector for Neutron Transmission Measurements at DICER at LANSCE

A Large Area Picosecond Photodetector for Neutron Transmission Measurements at DICER at LANSCE

Superconducting neutron transmission imaging for investigating a sequential change in phase separations of low-melting Wood’s metal

We built a new cryostat system for a current-biased kinetic inductance detector (CB-KID) to be able to place a sample at room temperature for conducting the neutron transmission imaging experiments with pulsed neutrons. A Wood’s metal alloy sample (Bi 50wt.%, Pb 25wt.%, Sn 12.5wt.%, Cd 12.5wt.%) of melting temperature 75.2°C was used to check a practical test by observing fine microstructures under beam power of 812 kW at beamline BL10 of J-PARC (MLF). The Wood’s metal is composed of four phases, of which one is a Cd-rich needle-like phase of an average width of 25 µm and length of 5 mm. Since Cd is a strong neutron absorber, it is suitable for observing the fine mosaic structure contrastingly in neutron transmission imaging. After neutron-transmission imaging with the Wood’s metal in the initial state, we subsequently melted the Wood’s metal sample and solidified it again by slow cooling during the same beam time. We were successful in observing an impressive change in morphology of the phases by neutron-transmission imaging. Room-temperature sample imaging is very convenient for possible users, and is expected to be very useful for applying our CB-KID system to versatile different materials of interests.

Study of the effective temperatures of two neutron moderating materials: Ethane and triphenylmethane

We studied the effective temperatures of hydrogen and carbon in solid ethane at 80 K and triphenylmethane at 22 K at the VESUVIO spectrometer (ISIS Neutron and Muon Source, Rutherford Appleton Laboratory, UK), using the Deep Inelastic Neutron Scattering (DINS) and Neutron Transmission techniques. The systems are of potential application as moderators for the design of cold neutron sources. We discuss in detail the process of data analysis and parameter fitting, in which we introduced improved algorithms. The results were compared with density functional theory calculations, which yield compatible results. The importance of these determinations for their applications to Nuclear Engineering calculations is highlighted. The results of the effective temperatures obtained are supported by comparisons with the total cross sections measured simultaneously with DINS in this experiment.

Neutron resonance absorption imaging of simulated high-level radioactive waste in borosilicate glass

We performed a preliminary study of neutron resonance absorption imaging to investigate the spatial distribution of constituent elements in borosilicate glasses containing simulated high-level radioactive waste, in which elemental inhomogeneities affect the physical and chemical stabilities of the glass. Dips generated by the resonance absorptions of Rh, Pd, Na, Gd, Cs, and Sm were observed in the neutron transmission spectra of the glass samples. The spatial distributions of these elements were obtained from the neutron transmission images at the resonance energies. The distributions of Rh and Pd visualized the sedimentation of these platinum group elements. In contrast, the lanthanides (Gd and Sm) and Cs were uniformly dispersed. These results show that neutron resonance absorption imaging is a promising tool for characterizing borosilicate glasses and investigating the vitrification mechanism of high-level radioactive waste.

Boron-containing plastic composites as neutron shielding material for additive manufacturing processes

A study of samples of shielding materials which exploit plastic as the basis of neutron absorbing composite with 25%–37% weight boron-containing powder has been provided. Composite samples were prepared by fused filament fabrication (FFF). Acrylonitrile butadiene styrene (ABS) and polyethylene terephthalate glycol (PETG) plastics were used as the polymer matrix material, while boron nitride powder and amorphous boron powder were used as boron-containing fillers.According to measurements of the neutron transmission on the monochromatic beam of the IR-8 reactor (main monochromatic neutron beam line - 2.4 Å), the use of boron as a filler in the plastic provides a decrease in the penetration depth of neutrons by 56%–78%: from 3.0 mm for a sample of plastic without filler to 0.65 mm for a sample with amorphous boron powder.Tensile and bending mechanical tests showed that the addition of boron-containing powder leads to development of brittleness of composite materials. The boron-containing samples experienced a 40%–55% of strength decrease and the failure of samples occurred without plastic deformation, while in ABS and PETG samples the plastic deformation takes up a significant portion of the test diagram.

Neutron imaging for magnetization inside an operating inductor

Magnetic components are key parts of energy conversion systems, such as electric generators, motors, power electric devices, and magnetic refrigerators. Toroidal inductors with magnetic ring cores can be found inside such electric devices that are used daily. For such inductors, magnetization vector M is believed to circulate with/without distribution inside magnetic cores as electric power was used in the late nineteenth century. Nevertheless, notably, the distribution of M has never been directly verified. Herein, we measured a map of polarized neutron transmission spectra for a ferrite ring core assembled on a familiar inductor device. The results showed that M circulates inside the ring core with a ferrimagnetic spin order when power is supplied to the coil. In other words, this method enables the multiscale operando imaging of magnetic states, allowing us to evaluate the novel architectures of high-performance energy conversion systems using magnetic components with complex magnetic states.

Li2B4O7–Bi2O3–ZrO4–CaWO4 glass system for neutron protection in neutron applications

In this study, new glass samples with a chemical composition of 40Li2B4O7+xBi2O3+(55–x)ZrO4+5CaWO4 (x = 10, 20, 30, 40, and 50 wt%) were fabricated using the melt quenching-annealing technique. Important neutron shielding parameters, such as the effective neutron removal cross-section, half-value layer, and neutron transmission factor, of all the new glass samples were calculated using the GEANT4 Monte Carlo simulation code. In addition, neutron dose measurements were performed using an 241Am–Be fast neutron source with an activity of 74 GBq and an average neutron energy of 4.5 MeV and a BF3 gaseous neutron detector. The results were compared with those of conventional shielding materials to determine the neutron absorption capabilities of the new glass materials. All the new glass samples were found to have excellent neutron shielding abilities. In particular, the GB5 sample had a high absorption capacity compared to the other samples. These new glass samples may be used as shielding materials in various radiation applications, such as generation of nuclear energy, radiation medicine, and the transport and storage of radioactive wastes.

Hybrid improper ferroelectricity and phase transition behavior of Li2Nd2Ti3O10 ceramics with A-site ordered triple-layer Ruddlesden-Popper structure

Hybrid improper ferroelectricity has been extensively reported through theoretical prediction and experimental investigation in the oxides with Ruddlesden-Popper (R–P) structures. However, the experimentally reported ferroelectric materials based on triple-layer R–P structures are rare, and the weak ferroelectricity impedes its practical application. In the present work, the single-phase Li2Nd2Ti3O10 ceramics with A-site cation ordered triple-layer R–P structure was obtained by spark plasma sintering technique, and the crystal structure of P21ab symmetry was revealed by neutron powder diffraction and transmission electron microscope analysis. Furthermore, the switchable ferroelectricity in Li2Nd2Ti3O10 ceramics has been observed at room temperature, and the saturated polarization-electric field hysteresis loop was obtained with Pr = 0.4 μC/cm2 under the electric field of 250 kV/cm. The phase transition behavior of Li2Nd2Ti3O10 oxides was revealed by the temperature-dependence Raman and dielectric spectra combined with the piezoelectric property.

The application of graphene/h-BN metamaterial in medical linear accelerators for reducing neutron leakage in the treatment room.

Neutrons can be generated in medical linear accelerators (Linac) due to the interaction of high-energy photons (> 10MeV) with the components of the accelerator head. The generated photoneutrons may penetrate the treatment room if a suitable neutron shield is not used. This causes a biological risk to the patient and occupational workers. The use of appropriate materials in the barriers surrounding the bunker may be effective in preventing the transmission of neutrons from the treatment room to the outside. In addition, neutrons are present in the treatment room due to leakage in the Linac's head. This study aims to reduce the transmission of neutrons from the treatment room by using graphene/hexagonal boron nitride (h-BN) metamaterial as a neutron shielding material. MCNPX code was used to model three layers of graphene/h-BN metamaterial around the target and other components of the linac, and to investigate its effect on the photon spectrum and photoneutrons. Results indicate that the first layer of a graphene/h-BN metamaterial shield around the target improves photon spectrum quality at low energies, whereas the second and third layers have no significant effect. Regarding neutrons, three layers of the metamaterial results in a 50% reduction in the number of neutrons in the air within the treatment room.