With its variety of radioactive sources, available facilities, and wealth of in-house technical expertise, the RSEL provides an ideal environment for testing of methods, materials, and instruments. The high intensity neutron generator and radioisotopes in the RSEL can be utilized for research, development, and testing of detectors, new detector development, unique material studies, assessments in gamma and/or neutron radiation fields, and a wealth of related applications ranging from instrument calibrations to biotechnology.
An Approach Towards Plastic Scintillators From Thermally Activated Delayed Fluorescent Dyes and Cross-Linkable Bismuth Compounds
S. Abraham, C. Fuentes-Hernandez, S. Mukhopadhyay, K. Singh
Cross-linked polyvinyltoluene (PVT) based plastic scintillators loaded with dyes exhibiting thermally activated delayed fluorescence (TADF) and various amounts of (caproate)di-(methacrylate) bismuth (CMB) were developed. The co-polymerization of vinyl toluene monomer loaded with different weight ratios of CMB and 1 wt% of TADF dye yielded highly transparent cross-linked plastic scintillators with intense green photoluminescence. The thermal and mechanical properties of the scintillators were investigated using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and micro indentation techniques. Their performance for radiation detection was assessed by performing gamma spectroscopy using a Cs-137 source and benchmarked to commercial plastic scintillators. The loading of CMB was guided by Monte Carlo N-Particle (MCNP) simulations. The results of this study show that the cross-linking approach and the use of TADF dyes yield scintillators with good mechanical properties with a uniaxial yield strength up to B66 MPa for compositions loaded with 40 wt% of CMB and high optical quality. However, the light yield in gamma spectroscopy experiments is found to be reduced with the addition of CMB, suggesting a trade-off between mechanical yield strength and light yield in gamma spectroscopy.
Applications of Neutron Generators: Fusion in a Practical Sense
C. Washburn, S. Mukhopadhyay
One of the more practical applications of nuclear fusion is the generation of neutrons using compact accelerator-based neutron sources (CANS). More specifically, one of the most widespread devices for generating neutrons is the appropriately named neutron generator (NG). Due to the great variety of applications in which neutrons can be used, many companies utilize their industrial capacity
to produce these fusion-oriented generators which can be supplied to research and industrial institutions. Advancements in neutron generation via nuclear fusion, widespread usage of neutrons in industry, and the implementation of NGs into research labs in United States universities demonstrates how nuclear fusion is a practical subject of nuclear science and warrants further experimentation.
Neutron Generator Radiography
L. Arnold, S. Soundararajan, M. White, C. Tran
Neutron Radiography is a form of non-destructive imaging that can provide insight about the type of material and internal components of an object. It can be used for investigating objects that cannot be imaged using X-rays. The DD Neutron Generator in RSEL can be used for fast neutron imaging, but the current image quality is poor. A neutron collimator to the system can redirect the neutron beam towards the object and improve image quality. A divergent collimator made from HDPE was designed in order to improve fast neutron imaging in the RSEL.. Neutron radiography was performed with and without the collimator present to determine the impact of the collimator on image quality.
Vertically Well-Aligned ZnO Nanoscintillator Arrays with Improved Photoluminescence and Scintillation Properties
M. Kurudirek, S. Kurudirek, N. Hertel, A. Erickson
ZnO nanoarrays were grown via a low-temperature hydrothermal method. Solutions, each with different additive combinations, were prepared and evaluated. The effects of the additives involved in the growth procedure, i.e., ammonium hydroxide and sodium citrate, were studied in terms of the morphological, optical and scintillation properties of the ZnO nanostructures. Measurement of the nanorod (NR) length, corresponding photoluminescence (PL) and scintillation spectra and their dependence on the additives present in the solution are discussed. ZnO NRs grown on a silica substrate, whose UV transmission was found to be better than glass, showed high-quality structural and optical properties. It was found that the addition of sodium citrate significantly reduced defects and correspondingly increased the intrinsic near-band-edge (NBE) UV emission intensity at ~380 nm.
To obtain high-quality nanostructures, samples were annealed in a 10% H2 + 90% N2 atmosphere. The anneal in the forming gas atmosphere enhanced the emission of the UV peak by reducing defects in the nanostructure. NRs are highly tapered towards the end of the structure. The tapering process was monitored using time growth studies, and its effect on PL and reflectance spectra are discussed. A good alpha particle response was obtained for the grown ZnO NRs, confirming its potential to be used as an alpha particle scintillator. After optimizing the reaction parameters, it was concluded that when ammonium hydroxide and sodium citrate were used, vertically well-aligned and long ZnO nanoarrays with highly improved optical and scintillation properties were obtained.
Assessing a Neutron Generator for Replication of the Galactic Cosmic Radiation Linear Energy Transfer Spectrum
L. Arnold, S. Mukhopadhyay, R. Aranda, N. Hertel
Galactic cosmic radiation (GCR) originates from outside of the solar system and poses a concern for the health of individuals who are exposed to it, such as astronauts. To systematically study relevant space radiation environments and select potential medical countermeasures, the linear energy transfer (LET) spectrum of GCR needs to be replicated. While recreating the environment can be accomplished with accelerator-based ion beams, the use of GT’s neutron generator in combination with available gamma sources has significant cost and schedule advantages. To ensure the neutron generator can be used to adequately replicate the LET spectrum, the properties of the emitted neutrons need to be quantified. By combining measurement data from Bonner Spheres and a CLLBC scintillator with MCNP6.2 simulations, one can determine the energy and direction of the generated neutrons with the aim of reproducing the GCR’s LET spectrum and developing countermeasures that can protect astronauts from GCR’s harmful effects.
Compact Portable Sources of High-LET Radiation: Validation and Potential Application for Galactic Cosmic Radiation Countermeasure Discovery
N. Hertel, S. Biegalski, V. Nelson, W. Nelson
Implementation of a systematic program for galactic cosmic radiation (GCR) countermeasure discovery will require convenient access to ground-based space radiation analogs. The current gold standard approach for GCR simulation is to use a particle accelerator for sequential irradiation with ion beams representing different GCR components. This has limitations, particularly for studies of non-acute responses, strategies that require robotic instrumentation, or implementation of complex in vitro models that are emerging as alternatives to animal experimentation. Here we explore theoretical and practical issues relating to a different approach to provide a high-LET radiation field for space radiation countermeasure discovery, based on use of compact portable sources to generate neutron-induced charged particles.
We present modeling studies showing that DD and DT neutron generators, as well as an AmBe radionuclide-based source, generate charged particles with a linear energy transfer (LET) distribution that, within a range of biological interest extending from about 10 to 200 keV/μm, resembles the LET distribution of reference GCR radiation fields experienced in a spacecraft or on the lunar surface. We also demonstrate the feasibility of using DD neutrons to induce 53BP1 DNA double-strand break repair foci in the HBEC3-KT line of human bronchial epithelial cells, which are widely used for studies of lung carcinogenesis. The neutron-induced foci are larger and more persistent than X ray-induced foci, consistent with the induction of complex, difficult-to-repair DNA damage characteristic of exposure to high-LET (>10 keV/μm) radiation. We discuss limitations of the neutron approach, including low fluence in the low LET range (<10 keV/ μm) and the absence of certain long-range features of high charge and energy particle tracks. We present a concept for integration of a compact portable source with a multiplex microfluidic in vitro culture system, and we discuss a pathway for further validation of the use of compact portable sources for countermeasure discovery.