Neutron imaging is a powerful tool in the field of non-destructive testing that utilizes unique attenuation properties of neutrons allowing through-images of some high-density objects. The Radiation Science and Engineering Center (RSEC) has had a neutron imaging facility for the last several decades. With the installation of a new core moderator assembly and new beam ports at the RSEC -- the Penn State Breazeale Reactor (PSBR) in 2018, a dedicated neutron beam port became available for a new neutron imaging facility at RSEC (RSEC -- NIF). The initial design of the beam port designated for the RSEC -- NIF was of divergent type that needed to be upgraded by means of collimator components and filters. After a thorough investigation of existing neutron imaging facilities around the world, it has been decided to collimate the beam port with convergent and divergent collimators and to filter the gamma and neutron content with the single crystal bismuth and sapphire filters. A set of system characterization experiments were conducted at the RSEC -- NIF that confirmed the system's correspondence to a Category I facility by ASTM standards. In addition to that, the collimation ratio of the new system was measured following the procedures given in the ASTM protocols and resulted in the effective L/D ratio value between 107 and 115. The thermal flux across the exit surface from the beam port at the biological shield was measured to be equal to 5.4E+06 n/cm^2-s at 1MWth reactor power. The application of the RSEC -- NIF's capabilities in neutron radiography (NR) and tomography (NT) techniques were demonstrated imaging different types of environmental samples for the presence and visualization of microplastic particles. Preliminary results of NT experiments conducted at the RSEC -- NIF have shown that this technique can be used as an intermediary step to visualize the content and spatial distribution of microplastics in the sand columns. Additionally, the NR capabilities of the RSEC -- NIF were utilized to visualize the microplastic particles in the sediment samples and used water filters. All obtained results and the continuation of research in this direction can potentially shed some light in the general research of microplastic transport mechanisms in different terrestrial and aquatic ecosystems.

There is a need for fast, nondestructive techniques to monitor nuclear materials and associated manufacturing processes throughout the traditional nuclear fuel cycle. Accurately analyzing unique elemental and isotopic signatures can enhance the ability to monitor and verify nuclear-material related activities. Epithermal neutron activation analysis (ENAA) allows for additional information to be extracted when compared to thermal or typical nuclear reactor spectrum neutron activation analysis. Many isotopes of many elements have similar radiative capture cross-sections at thermal neutron energies, whereas cross-sections among isotopes in the epithermal energy regime can span orders of magnitude at resonant energies. It is therefore desirable to have a nearly monochromatic, tunable source of neutrons to preferentially activate isotopes of interest at their resonant energies, thereby enhancing the experimental signal to noise ratio. A comprehensive review of the nuclear fuel cycle was performed to analyze elemental and isotopic compositions of samples throughout the traditional fuel cycle. To complement the existing nuclear forensics science, industrial processing variability was investigated in an attempt to identify unique signatures that are indicative of specific industrial processing techniques or materials utilized. Variations in techniques, industrial equipment, and processing of nuclear material have been investigated for the front end of the nuclear fuel cycle, namely: mining, milling, conversion, enrichment, and fuel fabrication. A holistic review of the nuclear fuel cycle was used to make inferences regarding relevant criteria for a nondestructive assay technique to monitor nuclear material processing. Time correlated prompt gamma activation analysis (PGAA) was selected as the nondestructive assay technique, and the advantages, methodologies, and instrumentation required for these measurements were investigated. PGAA will be used as a fast interrogation technique to verify nuclear material manufacturing processes. To utilize PGAA, a series of mechanical neutron choppers to be used as both a time-of-flight (TOF) and velocity selection system have been developed for use at the Penn State Breazeal Reactor (PSBR). The design goals of this system were intended to effectively pulse epithermal neutrons in the energy range of 0.5 - 40 eV with 2% or better neutron energy resolution, and a neutron transmission of 1E-6 or better. The operating energy range and resolution for the mechanical neutron chopper system were determined after evaluating characteristics of many isotopic resonances of interest. Specifically, it was observed that many resonances in the energy range of 0.5 - 40 eV have a full width half maximum (FWHM) of 1 eV or less. Four different chopper geometries have been evaluated for their utility as mechanical neutron choppers for the proposed chopper system. In particular, Fermi, ring, piston, and disc choppers have been assessed for their potential neutronics performance and mechanical durability and constructability. In addition, simulations were performed to quantitatively assess different neutron absorbing materials. A series of high-speed disc choppers was selected for the final design, and optimization work was performed to maximize the neutron pulse intensity. Analytical calculations regarding the neutron transmission and time structure of the pulse were verified with Monte Carlo simulations. It has been estimated that the optimized system will produce an epithermal neutron intensity of 2.2E4 n/MW*s where the simulated energy bounds are 0.5 and 43.1 eV. These energy bounds correspond to the simulated energy bin from MCNP6.2 at the upper limit of the operating range of the mechanical neutron chopper. This facility can also be operated in a TOF configuration such that the neutrons arriving at the source have a white (continuous energy) spectrum. This can be accomplished by holding the second stage of choppers stationary (or removing it from the beam completely). The unique source of epithermal neutrons capable of being produced by this facility will have applications in both prompt and delayed ENAA, as well as neutron resonance transmission analysis (NRTA) and fundamental nuclear data measurements. A data tool has also been created to estimate the material response for time correlated PGAA measurements. The creation of this tool serves three main purposes. The first is to evaluate sample sensitivity to the mechanical neutron chopper system. Second, the data tool is used to identify unique signatures relevant for nuclear forensics. Lastly, the data tool complements the design of the mechanical neutron chopper to provide a sample dependent set of optimal set of operating parameters based on the sensitivity and unique signature analysis. To do this, all isotopic cross-sections contained in a release of MCNP6.2 were evaluated for resonance structure. A hypothetical reference sample library is under development based on inductively coupled plasms mass spectrometry (ICP-MS) data found in literature and ASTM standards. The elemental composition, natural abundances, and microscopic cross-section data are used to construct complex macroscopic cross-sections of samples as a function of neutron energy between the operating energy range of the chopper system. The macroscopic cross-sections were analyzed for unique signature identification and isotopic sensitivity based on concentration. This analysis presented is used to provide an optimal set of operating parameters for the neutron chopper instrument. The review of variability within nuclear fuel cycle industrial processing as well as the data analysis tool provides a novel, systematic approach to identify unique, observable signatures relevant to nuclear forensic science.

This paper describes the design and characterization of a fast neutron irradiation facility (FNI) at the Penn State Breazeale Reactor. The facility was designed to provide a hard neutron spectrum with a minimum of contamination by thermal neutrons and gamma rays, and to accommodate semiconductor wafers of up to 8 inches (~20 cm) in diameter. The design was effected through two-step Monte Carlo simulations that included (i) core criticality simulations, and (ii) FNI shielding analysis. A rectangular FNI shape was selected to improve the neutronic coupling between the FNI and the core. Analysis was performed to determine an optimum combination of materials and their dimensions. The FNI was constructed and it has been in use for about two years now. A set of activation foils was irradiated to obtain the FNI neutron spectrum andevaluate spatial flux distribution. The neutron spectrum was unfolded using the SAND-II code. Good agreement was observed between the calculated and measured data.

Neutron radiography represents a powerful non-destructive testing technique that is still very much in development. The book reveals the amazing diversity of scientific and industrial applications of this technique, the advancements of the state-of-art neutron facilities, the latest method developments, and the expected future of neutron imaging.

Abstract: The objective of this research was to bring a thermal neutron beam facility to the Ohio State University Nuclear Reactor Laboratory for the purposes of neutron-based research. The neutron beam is extracted from the reactor core through a neutron collimator emplaced in Beam Port #2, the radial beam port facing the core at a 30° angle. The collimator is an aluminum tube containing components designed to filter and shape the neutron beam. The filters are poly-crystalline bismuth (10.16 cm thickness, 12.7 cm diameter) for significantly reducing gamma ray content and single-crystal sapphire (12.7 cm thickness, 10.16 cm diameter) for preferentially passing thermal neutrons while scattering more energetic neutrons out of the beam. The thermal neutron beam is defined by multiple 3.0 cm diameter apertures in borated aluminum. Apertures in polyethylene-based disks and in Pb disks provide shielding for fast neutrons and gamma rays, respectively, in the neutron collimator. Characterization of the beam was performed using foil activation analysis to find the neutron flux and a low-cost digital neutron imaging apparatus to "see" the beam profile. The neutron collimator delivers the filtered thermal neutron beam with a 3.5 cm diameter umbra and a thermal neutron equivalent flux of (8.55 +̲ 0.19) x 106 cm−2s−1 at 450 kW reactor power (90% of rated limit) to the sample location. The beam is highly thermalized with a cadmium ratio of 266 +̲ 13. The facility was designed for neutron depth profiling, a nondestructive analytical technique for finding the concentration versus depth in the near surface (tens of microns) for isotopes that undergo charged particle emitting reactions, such as 10B(n, 4He)7Li, 6Li (n, 3H)4He, and 3He (n, 1H)3H, to name a few.

"This publication is a compilation of the main results and findings of an IAEA coordinated research project (CRP) on development, characterization and testing of materials of relevance to nuclear energy sector using neutron beams. The document contains joint research results from nineteen institutions, which can be grouped into the main six technical areas: investigation of oxide dispersion-strengthened steels, research on zirconium based materials (including hydrogen uptake), investigations of welded structures and objects, results with irradiated materials, optimization of instruments for residual strain/stress measurements, and efforts towards standardization of neutron imaging. Particular emphasis was placed on variable environments during material characterization and testing as required by some applications such as intensive irradiation load, high temperature and high pressure conditions, and the presence of strong magnetic fields. The publication also includes some additional materials supplied by the international experts along with nineteen individual contributions describing the current status of use of diverse neutron beam techniques for materials research targeting the nuclear energy sector. These nineteen individual reports are available on CD-ROM attached to this publication. The publication will be of interest to physicists and engineers in the area of materials research, neutron beam scientists and personnel responsible for instruments, managers of neutron beam facilities, nuclear reactor designers and nuclear industry representatives."--Publisher's description.

For this Workshop, the organizers have attempted to invite experts from all known centers which are engaged in neutron beam development for neutron capture therapy. The Workshop was designed around a series of nineteen invited papers which dealt with neutron source design and development and beam characterization and performance. Emphasis was placed on epithermal beams because they offer clinical advantages and are more challenging to implement than thermal beams. Fission reactor sources were the basis for the majority of the papers; however three papers dealt with accelerator neutron sources. An additional three invited papers provided a summary of clinical results of Ncr therapy in Japan between 1968 and 1989 and overviews of clinical considerations for neutron capture therapy and of the status of tumor targeting chemical agents for Ncr. Five contributed poster papers dealing with NCT beam design and performance were also presented. A rapporteurs' paper was prepared after the Workshop to attempt to summarize the major aspects, issues, and conclusions which resulted from this Workshop. Many people contributed to both the smooth functioning of the Workshop and to the preparation of these proceedings. Special thanks are reserved for Ms. Dorothy K.