Energy Neutron Source Research Articles

Detecting energy dependent neutron capture distributions in a liquid scintillator

A novel technique is being developed to estimate the effective dose of a neutron field based on the distribution of neutron captures in a scintillator. Using Monte Carlo techniques, a number of monoenergetic neutron source energies and locations were modelled and their neutron capture response was recorded. Using back propagation Artificial Neural Networks (ANN) the energy and incident direction of the neutron field was predicted from the distribution of neutron captures within a 6Li-loaded liquid scintillator. Using this proposed technique, the effective dose of 252Cf, 241AmBe and 241AmLi neutron fields was estimated to within 30% for four perpendicular angles in the horizontal plane. Initial theoretical investigations show that this technique holds some promise for real-time estimation of the effective dose of a neutron field.

Baseline design of a low energy neutron source at ESS-Bilbao

This article briefly describes the basic design of the ESS-Bilbao neutron target station as well as its expected neutronic performance. The baseline engineering design, associated ancillary systems, and plant layout for the facility is now complete. A rotating target composed of twenty beryllium plates has been selected as the best choice in terms of both neutron yield and engineering complexity. It will provide neutron beams with a source term of 1015 n s−1 resulting from the direct 9Be(p, xn) reaction using a 75 mA proton beam at 50 MeV. The design envisages a target station equipped with two fully optimized moderators capable of withstanding a proton-beam power of 112 kW. This design is flexible enough to accommodate future upgrades in final proton energy. The envisaged neutron-beam brightness will enable several applications, including the use of cold and thermal neutrons for condensed matter research as well as fast-neutron irradiation studies. We close by discussing the role that this facility may play once the European Spallation Source becomes operational in Lund, Sweden.

Low-Flux Neutron Radiation Detection Technology with High Sensitivity

Boron-containing plastic scintillator detectors have a high detection efficiency for low-intensity thermal neutrons and fast neutrons which is currently the preferred types of neutron detector. This article is based on Monte Carlo method, studied boron-containing plastic scintillator for neutron detection performance, and analysis the energy deposition flux characteristics and detection efficiency when low intensity fission neutron incident to the boron plastic scintillator. We obtain the low-flux neutron detector performance in a variety of neutron source energy, boron-containing plastic scintillator diameter and length. Results showed that, when the boron-containing plastic scintillator lengths increase, the energy deposition flux will increase. When the length and diameter is constant, increasing source strength can increase the energy deposition flux brought by the recoil proton to a certain extent. When the source intensity over after thermal neutrons, due to the decrease of the cross section, the energy deposition fluxes brought by the react of neutrons and will decrease. The results provide help for low intensity fission neutron radiation detection technology with high sensitivity.

Optimization of a solid state polarizing bender for cold neutrons

We have designed a solid state bender to polarize cold neutrons for the Spin Echo Scattering Angle Measurement (SESAME) instrument at the Low Energy Neutron Source (LENS) at Indiana University. The design attempts to achieve high neutron polarization across a wide range of neutron wavelengths and divergence angles by optimizing the supermirror coating materials. The transmission and polarizing efficiency of the bender were modeled using the VITESS software, then measured at both continuous-wave and pulsed neutron sources. While the measured peak neutron transmission and polarization agree reasonably well with simulations, neither quantity has been successfully modeled for long wavelength neutrons. These results imply an insufficient understanding of the magnetic microstructure of the supermirror coatings used.

Neutron spin manipulation devices using YBCO films

The Meissner effect in a thin-film superconductor can be used to create a sharp boundary between regions of different magnetic field and hence can be used as a component of neutron spin manipulation devices. We have developed two cryogenic neutron spin manipulation devices using single-crystal, high-Tc, YBCO films, which can be cooled without using liquid cryogens and eliminate small angle scattering associated with polycrystalline films.The devices are a spin flipper and a spin precession device both of which use 350-nm-thick YBCO films covered with gold on a 0.5 mm thick sapphire substrate. The spin flipper consists of one such film mounted on an oxygen-free copper frame and connected to a closed-cycle He refrigerator. The flipper is capable of working with a maximum neutron beam size of 42 x 42 mm2 and can be used with both vertical and horizontal guide fields.The spin precession device was constructed by mounting two of the YBCO films parallel to one another with an H-magnet between them. By changing the current through the H – magnet, the precession of the neutron polarisation between the films can be controlled. Tests at the Low Energy Neutron Source (LENS) show that this device is capable of generating controlled spin precession for a neutron beam up to 20 x 20 mm2 in cross section.

Performance characteristics of a polyethylene collimator with an EJ-426 detector in neutron source localisation

In this paper, characteristics of neutron source localisation using an EJ-426 detector with a polyethylene collimator are presented. The detector is placed inside of the polyethylene collimator, where the collimator has a constant internal diameter and external diameter gradually increases towards the back end. The combined detector-collimator unit was mounted onto an equatorial mount and, data were collected from an ultra-fast mixed-field analyser. Neutron images have been produced to characterise the area investigated in real-time. Radiation images are fundamentally related to the detector efficiency and to the collimator geometry. In order to characterise the neutron source localisation capability of the polyethylene collimator, with an EJ-426 detector, experiments have been carried out using three different neutron sources. Results indicate that the existing design of the polyethylene collimator is suitable for localisation of low energy neutron sources. The measurements were performed in the low-scatter facility of the Neutron Metrology, National Physical Laboratory, Teddington, UK.

Three-dimensional (3D) Fast Neutron Tomography at the Low Energy Neutron Source (LENS)

We have constructed a neutron imaging station at the Low Energy Neutron Source (LENS), located within the Center for the Exploration of Energy and Matter at Indiana University. In contrast to many existing neutron imaging stations, we utilize a broad range of neutron energies, extending into the fast neutron regime, to take advantage of the higher fluxes and larger penetrating power of these high-energy neutrons. The imaging station consists of a collimator to define the beam, a rotating sample stage, and a cooled charge-coupled device camera (Alta U6) using a scintillator. A LiF + ZnS screen is used to produce scintillation light. Typical image collection times are a few seconds for a aperture to sample distance ratio of 100, yielding a spatial resolution of 0.2 × 0.2 mm2. Examples of the scanned and calculated image are presented.

New Neutron Radiation Effects Capabilities at the Low Energy Neutron Source (LENS)

The Low Energy Neutron Source (LENS) is a novel, university-based pulsed neutron source located within the Center for Explo- ration of Energy and Matter (CEEM) at Indiana University. The source utilizes a low energy p-n reaction in Beryllium coupled with a high-current, variable-pulse-width proton accelerator to produce either short or long neutron pulses. One of the target stations has been optimized for neutron radiation effects studies of device and board level electronics testing with quasi monochromatic high flux neutron beams (∼ 1 MeV equivalent silicon). The total neutron flux at the device under test (DUT) is approximately 2 · 1010 (n/cm2/sec) with low gamma contamination, 1 · 109 (n/cm2/sec). The neutron spectrum at the DUT position has been calculated using MCNP-X and has been characterized using foil activation measurements. In this paper we will describe the physical arrange-ment of the Device Test Area and indicate the unique features that have been incorporated to enhance testing effectiveness. We will also present the results of MCNP-X calculations with various adsorbed reflector arrangements that modify the spectrum incident on the device. Validation of the MCNP-X calculations using foil activation measurements will also be presented.

LENS: 2013 Facility Overview

The Low Energy Neutron Source at Indiana University began construction in the fall of 2003, and the facility has now been producing cold neutrons for approximately 8 years. LENS now has three instruments in operation on its cold target station as well as a facility for investigating neutron radiation effects on a second target station. Instrumentation development continues to represent a significant fraction of the activity at LENS, with the current activities focused primarily on neutron spin manipulation and moderator development. Research into the effects of confinement on simple and complex fluids has dominated our materials investigations. In this paper, we summarize recent activities in these areas using each of the instruments and provide an update on our operational experience over the last few years.

Baseline Design of a Low Energy Neutron Source at ESS-Bilbao

This article briefly describes the basic design of the ESS-Bilbao neutron target station as well as its expected neutronic performance. The baseline engineering design, associated ancillary systems, and plant layout for the facility is now complete. A rotating target composed of twenty beryllium plates has been selected as the best choice in terms of both neutron yield and engineering complexity. It will provide neutron beams with a source term of 1015n s−1 resulting from the direct 9 Be(p, xn) reaction using a 75mA proton beam at 50 MeV. The design envisages a target station equipped with two fully optimized moderators capable of withstanding a proton-beam power of 112kW. This design is flexible enough to accommodate future upgrades in final proton energy. The envisaged neutron-beam brightness will enable several applications, including the use of cold and thermal neutrons for condensed matter research as well as fast-neutron irradiation studies. We close by discussing the role that this facility may play once the European Spallation Source becomes operational in Lund, Sweden.

LWR spent fuel transmutation with fusion-fission hybrid reactors

In this paper the transmutation of light water reactors (LWR) spent fuel is analyzed. The system used for this study is the fusion-fission transmutation system (FFTS). It uses a high energy neutron source produced with deuterium-tritium fusion reactions, located in the center of the system, which is surrounded by a fission region composed of nuclear fuel where the fissions take place. In this study, the fuel of the fission region is obtained from the recycling of LWR spent fuel. The MCNPX Monte Carlo code was used to setup a model of the FFTS. Two fuel types were analyzed for the fissile region: the mixed oxide fuel (MOX), and the inert matrix fuel (IMF). Results show that in the case of the MOX fuel, an important Pu-239 breeding is achieved, which can be interesting from the point of view of maximal uranium utilization. On the contrary, in the case of the IMF fuel, high consumption of Pu-239 and Pu-241 is observed, which can be interesting from the point of view of non-proliferation issues. A combination of MOX and IMF fuels was also studied, which shows that the equilibrium of actinides production and consumption can be achieved. These results demonstrate the versatility of the fusion-fission hybrid systems for the transmutation of LWR spent fuel.

Target Performance at the Low Energy Neutron Source

The Indiana University Low Energy Neutron Source (LENS) production target was recently upgraded to handle the high power 13 MeV proton pulsed beam. The target, a 2 inch diameter beryllium disk, is 1.2 millimeters thick allowing the 13 MeV protons to pass completely through the target and stop in the cooling water eliminating the buildup of protons inside the beryllium. This change along with upgrading the cooling water system has produced the most reliable target to date for LENS operations. Details about the failure modes will be presented.

Neutron Moderator Development Research at the Low Energy Neutron Source

The Low Energy Neutron Source at Indiana University completed its construction phase roughly three years ago, and one of the more active research thrusts at the facility since that time has been our attempts to advance the state of the art in neutron moderation. This research program includes basic materials characterization, especially total neutron cross section measurements, as well as in-situ testing of the performance of various prototype moderators. This paper reviews a number of the more noteworthy results we have uncovered and describes the goals of the moderator development program at LENS.

Moderators at LENS: Performance and Development Research

The Target/Moderator/Reflector (TMR) system at the Low Energy Neutron Source has a flexible design in order to accommodate research into the performance of neutron moderators in general and small-scale accelerator-driven neutron sources in particular. Since producing its first cold neutron beam in April of 2005, the LENS TMR has undergone a number of design changes, and has been used to investigate a number of novel moderator ideas. In this paper we summarize the impact of some of these design changes on moderator performance as well as some recent results from a novel inhomogeneous moderator design that combines traditional moderating material (polyethylene) with single crystals of silicon.

LENS Operating Experience

Indiana University is operating a Low Energy Neutron Source which provides cold neutrons for material research and neutron physics and MeV energy for the neutron radiation effects studies. Neutrons are being produced by a 13 MeV proton beam incident on a Beryllium target. The LENS Proton Delivery System (PDS) is routinely operating at 13 MeV and 25 mA at 1.8% duty factor. The RF system, consisting of three Litton 5773 klystron RF tubes at 425 MHz and 1 MW each, power the AccSys Technology PL-13 LINAC. The proton beam delivers up to 6 kilowatts of power to the Beryllium target. Details of the beam spreading system, target cooling system, and accelerator operations will be discussed.

Development of a light-weight portable neutron survey meter

A light-weight portable neutron survey meter was developed using a mixed organic gas counter for dose management at nuclear power plants and accelerator facilities. This survey meter, NSN31041, is ~2 kg in weight and W160×H250×L300 mm(3) in size, which is capable of measuring neutron ambient dose equivalent rate from thermal to 15 MeV neutrons. The neutron energy response of the survey meter is evaluated using continuous energy neutron sources of (252)Cf, (241)Am-Be, thermal neutrons generated from a graphite pile loading a (252)Cf source, concrete-moderated neutrons of (241)Am-Be source and D(2)O-moderated neutrons of (252)Cf source. The measured response data show very good agreement with neutron ambient dose equivalent within a 50 % deviation.

Isotopic Depletion and Decay Methods and Analysis Capabilities in SCALE

The calculation of fuel isotopic compositions is essential to support design, safety analysis, and licensing of many components of the nuclear fuel cycle—from reactor physics and severe accident analysis to back-end fuel cycle issues, including spent-fuel storage and transportation, reprocessing, and radioactive waste management. Versions of the ORIGEN code, developed by Oak Ridge National Laboratory, have been used worldwide for isotopic depletion and decay analysis for more than three decades. The supported version of ORIGEN, maintained as the depletion analysis module for SCALE 6, performs detailed time-dependent isotopic generation and depletion for 1946 nuclides for reactor fuel and activation analysis. Stand-alone ORIGEN calculations can be performed using cross-section libraries developed for a wide range of reactor types and fuel designs used worldwide, including light water reactors UO2 and MOX, CANDU, VVER 440 and 1000, RBMK, and graphite reactors. Alternatively, within SCALE 6, ORIGEN can be automatically coupled to two-dimensional discrete ordinates or three-dimensional Monte Carlo transport solvers that provide problem-dependent cross sections for use in the ORIGEN depletion calculation. The hybrid ability to function as either a stand-alone or coupled depletion code provides ORIGEN advanced capabilities to simulate a broad range of applications for various reactor systems. The nuclear data libraries in ORIGEN have been significantly improved recently, using modern ENDF/B nuclear data evaluations. The most recent developments in SCALE 6.1 include the addition of ENDF/B-VII decay data, energy-dependent fission yields, and fine-group ORIGEN neutron cross sections based on the JEFF-3.0/A special purpose activation files. Advanced methods and data for neutron and gamma source energy spectral analysis are also available in the current version of the code. The ORIGEN code and associated nuclear data libraries have been extensively validated against experimental data that include spent nuclear fuel isotopic assay data for actinides and fission products, radiation source spectra, and decay heat measurements.

Neutron moderator development research at the low energy neutron source

The Low Energy Neutron Source at Indiana University completed its construction phase roughly three years ago, and one of the more active research thrusts at the facility since that time has been our attempts to advance the state of the art in neutron moderation. This research program includes basic materials characterization, especially total neutron cross-section measurements, as well as in-situ testing of the performance of various prototype moderators. This paper reviews a number of the more noteworthy results we have uncovered and describes the goals of the moderator development program at LENS.

Theoretical Correlation of Broad Spectrum Neutron Sources for Accelerated Soft Error Testing

Several broad spectrum, high energy neutron source facilities exist throughout the world for accelerated soft error testing. However, none accurately replicate the terrestrial neutron spectra across the range of 1 MeV to 1 GeV. The objective of this study is to quantify the errors introduced in accelerated soft error measurements from these facilities using a range of theoretical soft error cross-sections for both high and low critical charge events.

Some recent results using spin echo resolved grazing incidence scattering (SERGIS)

The advantages of neutrons for probing bulk structures are well known: they provide statistically averaged correlation functions over a large range of length scales and they are sensitive to light atoms such as hydrogen. These same qualities are, in principle, useful in the study of surfaces and buried morphologies in thin films, especially when the films are polymeric or biological. However, because of the limited sample volume for such systems, the scattering is weak, especially if the neutron beam has to be severely collimated in order to resolve distances of interest (typically 10 to several 100nm parallel to the surface of the sample). SERGIS is a technique that can potentially overcome these limitations by allowing high resolution measurements of lateral surface structure without requiring tight beam collimation. In this paper we discuss recent progress towards implementing SERGIS both at the Low Energy Neutron Source at Indiana University and on the Asterix reflectometer at the Los Alamos Neutron Science Center (LANSCE). The architecture we use exploits a robust symmetry-related cancellation of Larmor phase aberrations. The spatial resolution it achieves closely mimics that of the ideal magnetic Wollaston prisms. To make progress in understanding SERGIS, we have applied it to the measurement of simple diffraction gratings and developed a dynamical theory that accounts quantitatively and without adjustable parameters for all of the data sets we have measured to date. We argue here that, if SERGIS is to be applied to the study of weakly scattering thin films, it will be necessary to develop the technique of dark-field spin echo scattering angle measurement.