Resonance Absorption Imaging Research Articles

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.

Direct calibration of laser intensity via Ramsey interferometry for cold atom imaging.

A majority of ultracold atom experiments utilize resonant absorption imaging techniques to obtain the atomic density. To make well-controlled quantitative measurements, the optical intensity of the probe beam must be precisely calibrated in units of the atomic saturation intensity Isat. In quantum gas experiments, the atomic sample is enclosed in an ultra-high vacuum system that introduces loss and limits optical access; this precludes a direct determination of the intensity. Here, we use quantum coherence to create a robust technique for measuring the probe beam intensity in units of Isat via Ramsey interferometry. Our technique characterizes the ac Stark shift of the atomic levels due to an off-resonant probe beam. Furthermore, this technique gives access to the spatial variation of the probe intensity at the location of the atomic cloud. By directly measuring the probe intensity just before the imaging sensor our method in addition yields a direct calibration of imaging system losses as well as the quantum efficiency of the sensor.

Laser-driven neutron source and nuclear resonance absorption imaging at ILE, Osaka University: review.

Here, we present an overview on the recent progress in the development of the laser-driven neutron source (LDNS) and nuclear resonance absorption (NRA) imaging at the Institute of Laser Engineering (ILE), Osaka University. The LDNS is unique because the number of neutrons per micro pulse is very large, and the source size and the pulse width are small. Consequently, extensive research and development of LDNSs is going on around the world. In this paper, a typical neutron generation process by the laser-driven ion beam, called the pitcher-catcher scheme, is described. The characteristics of the LDNS are compared with those of the accelerator-driven neutron source (ADNS), and unique application of the LDNS, such as NRA imaging, is presented. In the LDNS, NRA imaging is possible with a relatively short beam line in comparison with that of the ADNS since the neutron pulse width and the source size of the LDNS are small. Future prospects in research and development of NRA imaging with the LDNS at ILE Osaka University are also described.

Energy-resolved neutron imaging with glass gas electron multiplier and dynamic time-over-threshold method

Energy-resolved neutron imaging with pulsed neutron source provides quantitative neutron imaging techniques such as Bragg-edge imaging, resonance absorption imaging, and polarized neutron imaging. Micro-pattern gaseous detectors (MPGDs) such as gas electron multipliers (GEMs) are widely used in neutron detection. In this research, we will report on the first demonstration of energy-resolved neutron imaging with a glass gas electron multiplier (G-GEM) and the dynamic time-over-threshold (dToT) signal processing method. We successfully performed energy-resolved neutron imaging at J-PARC MLF by measuring incident position and the Time-of-Flight (TOF) of each neutron simultaneously.

The energy-resolved neutron imaging system, RADEN

The energy-resolved neutron imaging system, RADEN, has been installed at the pulsed neutron source in the Materials and Life Science Experimental Facility of the Japan Proton Accelerator Research Complex. In addition to conventional neutron radiography and tomography, RADEN, the world's first imaging beam-line at a pulsed neutron source, provides three main options for new, quantitative neutron imaging techniques: Bragg-edge imaging to visualize the spatial distribution of crystallographic information, resonance absorption imaging for elemental composition and temperature information, and polarized neutron imaging for magnetic field information. This paper describes the results of characterization studies of the neutronic performance and installed devices at RADEN and shows the results of several demonstration studies for pulsed neutron imaging.

Characteristics of the 2012 model lithium-6 time-analyzer neutron detector (LiTA12) system as a high efficiency detector for resonance absorption imaging

Neutron resonance absorption imaging, being used to visualize a spatial distribution of elements and/or temperature within a sample, is one of the important applications of an intense short-pulse neutron source. Two-dimensional time-analyzer neutron detectors are indispensable to perform neutron energy dependent imaging by means of the time-of-flight technique. Some state-of-the-art time-analyzer neutron detectors have been developed for thermal or cold neutrons. However the detection efficiencies of such neutron detectors are not sufficient for neutron resonance absorption imaging which utilizes neutrons in the energy region from eV to keV.The 2012 model lithium-6 time-analyzer neutron detector (LiTA12) system, based on a lithium glass scintillator and multi-anode photomultiplier tube, has the highest neutron efficiency among the detectors for pulsed neutron imaging together with the flexibility to tune the efficiency by changing the thickness of the lithium glass. The authors estimated performances of the detector at resonance neutron energies finding that 0.7 mm width line pairs made by 3 μm thick gold could be resolved at 4.9 eV and the maximum count rate of 8 Mcps was achieved at 1 keV.

Non-contact measurement of partial gas pressure and distribution of elemental composition using energy-resolved neutron imaging

Neutron resonance absorption imaging is a non-destructive technique that can characterize the elemental composition of a sample by measuring nuclear resonances in the spectrum of a transmitted beam. Recent developments in pixelated time-of-flight imaging detectors coupled with pulsed neutron sources pose new opportunities for energy-resolved imaging. In this paper we demonstrate non-contact measurements of the partial pressure of xenon and krypton gases encapsulated in a steel pipe while simultaneously passing the neutron beam through high-Z materials. The configuration was chosen as a proof of principle demonstration of the potential to make non-destructive measurement of gas composition in nuclear fuel rods. The pressure measured from neutron transmission spectra (∼739 ± 98 kPa and ∼751 ± 154 kPa for two Xe resonances) is in relatively good agreement with the pressure value of ∼758 ± 21 kPa measured by a pressure gauge. This type of imaging has been performed previously for solids with a spatial resolution of ∼ 100 μm. In the present study it is demonstrated that the high penetration capability of epithermal neutrons enables quantitative mapping of gases encapsulate within high-Z materials such as steel, tungsten, urania and others. This technique may be beneficial for the non-destructive testing of bulk composition of objects (such as spent nuclear fuel assemblies and others) containing various elements opaque to other more conventional imaging techniques. The ability to image the gaseous substances concealed within solid materials also allows non-destructive leak testing of various containers and ultimately measurement of gas partial pressures with sub-mm spatial resolution.

Non-destructive shadowgraph imaging of ultra-cold atoms.

An imaging system is presented that is capable of far-detuned non-destructive imaging of a Bose-Einstein condensate with the signal proportional to the second spatial derivative of the density. Whilst demonstrated with application to Rb85, the technique generalizes to other atomic species and is shown to be capable of a signal-to-noise of ∼25 at 1 GHz detuning with 100 in-trap images showing no observable heating or atom loss. The technique is also applied to the observation of individual trajectories of stochastic dynamics inaccessible to single shot imaging. Coupled with a fast optical phase locked loop, the system is capable of dynamically switching to resonant absorption imaging during the experiment.

Optimally focused cold atom systems obtained using density-density correlations

Resonant absorption imaging is a common technique for detecting the two-dimensional column density of ultracold atom systems. In many cases, the system's thickness along the imaging direction greatly exceeds the imaging system's depth of field, making the identification of the optimally focused configuration difficult. Here we describe a systematic technique for bringing Bose-Einstein condensates (BEC) and other cold-atom systems into an optimal focus even when the ratio of the thickness to the depth of field is large: a factor of 8 in this demonstration with a BEC. This technique relies on defocus-induced artifacts in the Fourier-transformed density-density correlation function (the power spectral density, PSD). The spatial frequency at which these artifacts first appear in the PSD is maximized on focus; the focusing process therefore both identifies and maximizes the range of spatial frequencies over which the PSD is uncontaminated by finite-thickness effects.

Non-destructive studies of fuel pellets by neutron resonance absorption radiography and thermal neutron radiography

Many isotopes in nuclear materials exhibit strong peaks in neutron absorption cross sections in the epithermal energy range (1–1000eV). These peaks (often referred to as resonances) occur at energies specific to particular isotopes, providing a means of isotope identification and concentration measurements. The high penetration of epithermal neutrons through most materials is very useful for studies where samples consist of heavy-Z elements opaque to X-rays and sometimes to thermal neutrons as well. The characterization of nuclear fuel elements in their cladding can benefit from the development of high resolution neutron resonance absorption imaging (NRAI), enabled by recently developed spatially-resolved neutron time-of-flight detectors. In this technique the neutron transmission of the sample is measured as a function of spatial location and of neutron energy. In the region of the spectra that borders the resonance energy for a particular isotope, the reduction in transmission can be used to acquire an image revealing the 2-dimensional distribution of that isotope within the sample. Provided that the energy of each transmitted neutron is measured by the neutron detector used and the irradiated sample possesses neutron absorption resonances, then isotope-specific location maps can be acquired simultaneously for several isotopes. This can be done even in the case where samples are opaque or have very similar transmission for thermal neutrons and X-rays or where only low concentrations of particular isotopes are present (<0.1atom% in some cases). Ultimately, such radiographs of isotope location can be utilized to measure isotope concentration, and can even be combined to produce three-dimensional distributions using tomographic methods.In this paper we present the proof-of-principle of NRAI and transmission Bragg edge imaging performed at Flight Path 5 (FP5) at the LANSCE pulsed, moderated neutron source of Los Alamos National Laboratory. A set of urania mockup fuel assemblies with intentionally introduced defects was investigated. The maps of elemental composition of pellets containing urania and tungsten were obtained simultaneously by resonance absorption imaging with spatial resolution better than ∼200μm, while the voids and cracks were revealed by the transmission images obtained with thermal and cold neutrons. Our proof-of-principle experiments demonstrate that simultaneous acquisition of resonance and Bragg edge spectra enables concurrent mapping of isotope distributions, imaging of cracks and voids as well as measurements of some crystallographic parameters of fuel assemblies and their cladding. A detailed study of energy-dependent neutron statistics achievable at FP5 with our present detection system is also presented for a wide range of neutron energies.

High Resolution Neutron Resonance Absorption Imaging at a Pulsed Neutron Beamline

The existence of resonance peaks in neutron absorption spectra in the epithermal range of energies enables unique non-destructive testing techniques. The deep penetration of epithermal neutrons provides the opportunity to perform a compositional analysis of a sample which is opaque to X-rays and thermal neutrons. The neutron resonances in the transmission spectra constitute a characteristic pattern for many isotopes, which can be used to identify the isotope and to map the distribution of the isotope in a sample. The neutron transmission spectra can be measured with the time of flight (TOF) technique using a pulsed neutron source. Combining this method with a high resolution neutron counting detector enables substantial improvements of spatial resolution of neutron resonance transmission imaging. Such a detector has been developed to register neutrons with 55 µm spatial and 10–1000 ns temporal resolution Our proof-of-principle experiments at the ISIS pulsed neutron spallation source demonstrate that compositional analysis of multi-element samples can now be performed with ∼150 µm spatial resolution. Images of a test mask consisting of &#60;200 µm thick foils of Au, Ag, In and Gd were collected in the 1–100 eV energy range. The experimental results demonstrate the potential for compositional analysis via resonance absorption transmission with high spatial resolution. In-bulk temperature measurement through Doppler broadening analysis will also benefit from this technique.

High resolution neutron counting detectors with microchannel plates and their applications in neutron radiography, diffraction and resonance absorption imaging

The event counting detection technology based on signal amplification in microchannel plates (MCPs) was initially developed for the applications with relatively low fluxes of photons, electrons and...

First demonstration of neutron resonance absorption imaging using a high-speed video camera in J-PARC

Abstract The neutron resonance absorption imaging technique with a high-speed video camera was successfully demonstrated at the beam line NOBORU, J-PARC. Pulsed neutrons were observed through several kinds of metal foils as a function of neutron time-of-flight by utilizing a high-speed neutron radiography system. A set of time-dependent images was obtained for each neutron pulse, and more than a thousand sets of images were recorded in total. The images with the same time frame were summed after the measurement. Then the authors obtained a set of images having enhanced contrast of sample foils around the resonance absorption energies of cobalt (132 eV), cadmium (28 eV), tantalum (4.3 and 10 eV), gold (4.9 eV) and indium (1.5 eV).

Neutron Visual Sensing Techniques Using the High Intensity Neutron Sources

In this manuscript, the fundamentals and merits of neutron visual sensing techniques, high-speed consecutive visual sensing technique, high-speed-scanning dynamic 3D visualization technique, multi-beam 3D velocimetry technique and energy-selective neutron imaging technique are summarized. These techniques have been developed mainly for the R&D of the nuclear energy system using the high-flux research reactors, JRR-3 and JRR-4, and a high-intensity pulsed neutron source, J-PARC. Very unique visualization and measurement, e.g. dynamic 3D velosimetry in JRR-4 were successfully carried out by these neutron visual sensing techniques. An energy-selective neutron imaging, e.g. the neutron resonance absorption imaging in J-PARC is extremely unique and newly developed visualization and measurement technique. Analytical investigation for the feasibility of multiphase flow experiment in J-PARC was also reported using a Monte Carlo neutron simulation code. It was confirmed from the analytical work that the measurement error of the void fraction of two-phase flow can be reduced by the energy-selective neutron imaging technique.

Spatial interference from well-separated split condensates

We use magnetic levitation and a variable-separation dual optical plug to obtain clear spatial interference between two condensates axially separated by up to $0.25$ mm---the largest separation observed with this kind of interferometer. Clear planar fringes are observed using standard (i.e., nontomographic) resonant absorption imaging. The effect of a weak inverted parabola potential on fringe separation is observed and agrees well with theory.

中性子共鳴吸収イメージング法による核種の拡散の観察

中性子共鳴吸収イメージング法による核種の拡散の観察