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All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Testing the Delayed Gamma Capability in MCNP6

The mission of the Domestic Nuclear Detection Office is to quickly and reliably detect unauthorized attempts to import or transport special nuclear material for use against the United States. Developing detection equipment to meet this objective requires accurate simulation of both the detectable signature and detection mechanism. A delayed particle capability was initially added to MCNPX 2.6.A in 2005 to sample the radioactive fission product parents and emit decay particles resulting from the decay chain. To meet the objectives of detection scenario modeling, the capability was designed to sample a particular time for emitting particular multiplicity of a particular energy. Because the sampling process of selecting both time and energy is interdependent, to linearize the time and emission sampling, atom densities are computed at several discrete time steps, and the time-integrated production is computed by multiplying the atom density by the decay constant and time step size to produce a cumulative distribution function for sampling the emission time, energy, and multiplicity. The delayed particle capability was initially given a time-bin structure to help reasonably reproduce, from a qualitative sense, a fission benchmark by Beddingfield, which examined the delayed gamma emission. This original benchmark was only qualitative and did not contain the magnitudes of the actual measured data but did contain relative graphical representation of the spectra. A better benchmark with measured data was later provided by Hunt, Mozin, Reedy, Selpel, and Tobin at the Idaho Accelerator Center; however, because of the complexity of the benchmark setup, sizable systematic errors were expected in the modeling, and initial results compared to MCNPX 2.7.0 showed errors outside of statistical fluctuation. Presented in this paper is a more simplified approach to benchmarking, utilizing closed form analytic solutions to the granddaughter equations for particular sets of decay systems. We examine five different decay chains (two-stage decay to stable) and show the predictability of the MCNP6 delayed gamma feature. Results do show that while the default delayed gamma calculations available in the MCNP6 1.0 release can give accurate results for some isotopes (e.g., 137 Ba), the percent differences between the closed form analytic solutions and the MCNP6 calculations were often >40% ( 28 Mg, 28 Al, 42 K, 47 Ca, 47 Sc, 60 Co). With the MCNP6 1.1 Beta release, the tenth entry on the DBCN card allows improved calculation within <5% as compared to the closed form analytic solutions for immediate parent emissions and transient equilibrium systems. While the tenth entry on the DBCN card for MCNP6 1.1 gives much better results for transient equilibrium systems and parent emissions in general, it does little to improve daughter emissions of secular equilibrium systems. Finally, hypotheses were presented as to why daughter emissions of secular equilibrium systems might be mispredicted in some cases and not in others.

42 ENGINEERING↗
DOE OSTI2020

Fission Gas Monitoring System Efficiency Calibration Summary Report

The Fission Gas Monitoring System was designed to work in conjunction with the Fuel Accident Condition Simulator Furnace and is used to measure fission gas releases during post-irradiation fuel heating tests. A high-purity helium sweep gas is swept past the heated fuel sample in the furnace and routed to a fission gas monitoring system, which cryrogenically traps the krypton (Kr) and xenon (Xe) fission gases. As the radioactive species of the trapped gas decays, high-purity germanium detectors monitor the amount of fission gas in each trap. The primary fission product present in this test is 85Kr, which has a 10.76-year half-life. The presence of 85Kr indicates particle defects and iodine release. There is also the potential for re-irradiating the fuel compacts in the Neutron Radiography Reactor in the Hot Fuel Examination Facility basement. With re-irradiation, it is possible to have xenon fission gas present, specifically 133Xe, which has a 5.243-day half-life. Re-irradiation also produces 131I, which is important for design-basis accidents and regulatory licensing.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2020

Computational Tool for Cosmic Ray Flux and Cosmogenic Activation Production Rates

Silicon charge couple devices (CCDs) are used in direct detection dark matter searches. Silicon can be obtained with very high purity and negligible amounts of radioactive contaminants. However, silicon exposed to cosmic rays can be activated, leading to the buildup of radioactive isotopes such as tritium. The decay of tritium can produce signals that cannot be distinguished from the expected signals of dark matter interactions and tritium produced by cosmic rays is expected as one of the leading sources of background for next-generation experiments. The cosmic ray flux depends on variables such as geomagnetic latitude and longitude, atmospheric depth/altitude, solar activity, and surrounding environment for example. The goal of this work is to create a tool that will evaluate the total cosmic ray exposure and related tritium production rate for any given exposure history of a silicon detector. EXcel-based Program for calculation Atmospheric Cosmic-ray Spectrum (EXPACS) was used to obtain the cosmic ray fluxes. We have worked on creating a 3-dimensional gird that spans latitude, longitude, and altitude, and can be used to interpolate the cosmic ray flux at any given location. This computation tool additionally has use for work requiring knowledge of the cosmic ray flux at multiple locations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Investigating Helium Bubble Nucleation and Growth through Simultaneous In-Situ Cryogenic, Ion Implantation, and Environmental Transmission Electron Microscopy

Palladium can readily dissociate molecular hydrogen at its surface, and rapidly accept it onto the octahedral sites of its face-centered cubic crystal structure. This can include radioactive tritium. As tritium β-decays with a half-life of 12.3 years, He-3 is generated in the metal lattice, causing significant degradation of the material. Helium bubble evolution at high concentrations can result in blister formation or exfoliation and must therefore be well understood to predict the longevity of materials that absorb tritium. A hydrogen over-pressure must be applied to palladium hydride to prevent hydrogen from desorbing from the metal, making it difficult to study tritium in palladium by methods that involve vacuum, such as electron microscopy. Recent improvements in in-situ ion implantation Transmission Electron Microscopy (TEM) allow for the direct observation of He bubble nucleation and growth in materials. In this work, we present results from preliminary experiments using the new ion implantation Environmental TEM (ETEM) at the University of Huddersfield to observe He bubble nucleation and growth, in-situ, in palladium at cryogenic temperatures in a hydrogen environment. After the initial nucleation phase, bubble diameter remained constant throughout the implantation, but bubble density increased with implantation time. β-phase palladium hydride was not observed to form during the experiments, likely indicating that the cryogenic implantation temperature played a dominating role in the bubble nucleation and growth behavior.

36 MATERIALS SCIENCE↗
NASA NTRS1989

Instrumental and atmospheric background lines observed by the SMM gamma-ray spectrometer

Preliminary identifications of instrumental and atmospheric background lines detected by the gamma-ray spectrometer on NASA's Solar Maximum Mission satellite (SMM) are presented. The long-term and stable operation of this experiment has provided data of high quality for use in this analysis. Methods are described for identifying radioactive isotopes which use their different decay times. Temporal evolution of the features are revealed by spectral comparisons, subtractions, and fits. An understanding of these temporal variations has enabled the data to be used for detecting celestial gamma-ray sources.

Share, G. H.↗
NASA NTRS1995

The isotopic composition of iron-group galactic cosmic rays

Results from studies of the isotopic composition of iron group elements in the galactic cosmic radiation are reviewed, emphasizing recently reported measurements from the ISEE-3 spacecraft. The observed isotope distributions for the elements Ti through Mn are in good agreement with those expected for a propagated solar-like source composition, with the possible exception of an enhanced abundance of Ti-50. It is found that a significant fraction of the radioactive secondary nuclide Mn-54 has decayed, indicating a confinement time of iron group cosmic rays in the galaxy of at least 2 Myr. The source ratio Fe-54/Fe-56 is found to be consistent with the solar value, but the ratio Ni-60/Ni-58 is greater than solar by a factor of 2.8+/-1.0. The measured abundance of Co-59 is significantly greater than the calculated secondary contribution, suggesting that this nuclide has been produced in the source regions by the electron capture decay of Ni-59 and implying a time delay between nucleosynthesis and acceleration approximately greater than 10(exp 5) yr.

Wiedenbeck, M. E.↗
DOE OSTI2018

Superallowed α Decay to Doubly Magic Sn 100

In this paper, we report the first observation of the 108 Xe → 104 Te → 100 Sn α-decay chain. The α emitters, 108 Xe [E α = 4.4(2) MeV, T 1/2 = 58 +106 -23 μs] and 104 Te[E α = 4.9(2) MeV, T 1/2 < 18 ns], decaying into doubly magic 100 Sn were produced using a fusion-evaporation reaction 54 Fe( 58 Ni, 4n) 108 Xe, and identified with a recoil mass separator and an implantation-decay correlation technique. This is the first time alpha radioactivity has been observed to a heavy self-conjugate nucleus. A previous benchmark for study of this fundamental decay mode has been the decay of 212 Po into doubly magic 208 Pb. Enhanced proton-neutron interactions in the N = Z parent nuclei may result in superallowed α decays with reduced α-decay widths significantly greater than that for 212 Po. Finally, from the decay chain, we deduce that the α-reduced width for 108 Xe or 104 Te is more than a factor of 5 larger than that for 212 Po.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2026

Characterization of the First Prototype of the L1K65n Differential-Output Charge-Sensitive Preamplifier ASIC for High-Performance, Low-Background HPGe Detector Readout

Next-generation neutrinoless double-beta (0νββ) decay searches require a large detector/isotope mass and very low radioactive backgrounds. The upcoming LEGEND-1000 experiment (Large Enriched Germanium Experiment for Neutrinoless double-beta Decay) constitute a ton-scale array of several hundred high-purity germanium (HPGe) detectors enriched in 76Ge, the isotope of interest. It aims to reach a sensitivity beyond 10 28 years on the 0νββ decay half-life of 76Ge, necessitating an order of magnitude reduction in background with respect to the state of the art. This will require the implementation of a dedicated application specific integrated circuit (ASIC) preamplifier that will significantly lower background contribution compared to the conventional low-mass front end (LMFE) employed in the Majorana Demonstrator and LEGEND-200 experiments while maintaining or improving energy resolution and other performance parameters. Features include a high (9 MeV) dynamic range with noise low enough to achieve a trigger threshold of <1 keV, a single power supply to reduce background-inducing cabling, and a differential output to maintain signal integrity over several meters of transmission line. The chip would be optimized to operate in liquid argon (87 K) and be able to do so reliably for ten years. Following on from an earlier 180-nm prototype, we have developed a differential-output charge-sensitive preamplifier ASIC fabricated in a 65-nm process, 1×2 mm in size, that addresses these needs. Here, we present recent results from the successful testing and characterization of the first version of this device.

ASIC↗
DOE OSTI2014

First Results from the Modular Total Absorption Spectrometer at the HRIBF

A Modular Total Absorption Spectrometer constructed at the Holifield Radioactive Ion Beam Facility has been applied to decay studies of over 20 {sup 238}U fission products. The measurements were focused on nuclei identified as important for decay heat analysis during a nuclear fuel cycle. Preliminary results on the average electromagnetic (EM) energy release in the β decay of {sup 89}Kr and {sup 139}Xe isotopes yielded values of 2446 keV and 1126 keV, respectively. It represents an increase of over 35% and 20%, respectively, when compared to the average EM energies deduced using the ENSDF database.

43 PARTICLE ACCELERATORS↗
DOE OSTI2019

Development of Waste Disposal Strategy for RH LLW Stored in the ATR Canal - 19453

The Advanced Test Reactor (ATR), located at Idaho National Laboratory (INL), is 250 megawatt research reactor designed and operated for the United States Department of Energy for irradiation testing of advanced nuclear fuels and material samples. The pressurized light-water moderated and cooled reactor achieved criticality in 1967. It is designed to allow high neutron flux irradiation of structural materials and nuclear fuels to replicate long-term exposure of materials in traditional lower-flux reactor cores. The ATR also produces rare isotopes for the use in the medical and other industries. The ATR is one of only four reactors in the world with this high-flux irradiation capability. Adjacent to the ATR is a water-filled canal which is used to handle casks, prepare experiments, perform irradiation experiments, and store irradiated components generated from reactor operations. The canal is used to store irradiated (activated) metals that are subsequently determined to be waste. In many instances, these items are too radioactive to remove from the canal and remain in temporary storage until a sufficient decay period has elapsed to where they can be safely removed. The more highly-radioactive remote-handled (RH) waste items requiring hundreds of years to decay have been in storage in the canal since the first ATR core internal changeout (CIC) which was conducted in the 1970's. The INL has recently completed construction and startup of a new Remote-Handled Low-Level Waste (RH LLW) Disposal Facility, which will serve as the final disposal capability for legacy RH (greater than 200 mR/hr on contact) metal waste currently stored in the canal. The ATR will need to develop a method for packaging, characterizing, removing, and shipping this material to the new disposal facility. Based on the configuration of the new disposal cells at the RH LLW Disposal Facility, the ATR must produce an entire new process for handing and packaging the legacy RH waste and preparing it for transport and final disposal. The ATR Canal RH LLW Cleanup Project scope is to develop the processes, tools, and equipment for safely sizing, packaging, and removing RH LLW from the canal. This paper presents highlights and challenges the project faces to develop and implement this capability: - Designing new tools, fabricating new equipment, and implementing new processes at an active Hazard Category-I nuclear facility. - Ensuring new equipment and tools are compatible with the existing equipment and processes at both the generator and the disposal facilities. - Sizing legacy waste under water using remote tools and equipment to minimize void space in waste disposal canisters while ensuring as low as reasonably achievable (ALARA) goals are met. - Loading waste containers underwater and preparing them to meet the liquid-free criteria of the disposal facility waste acceptance criteria (WAC). - Providing a new shielded transport container to transfer waste from ATR to the new on-site RH LLW Disposal Facility. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2015

Measurement of Radioactive Contamination in the High-Resistivity Silicon CCDs of the DAMIC Experiment

We present measurements of radioactive contamination in the high-resistivity silicon charge-coupled devices (CCDs) used by the DAMIC experiment to search for dark matter particles. Novel analysis methods, which exploit the unique spatial resolution of CCDs, were developed to identify α and β particles. Uranium and thorium contamination in the CCD bulk was measured through α spectroscopy, with an upper limit on the 238 U ( 232 Th) decay rate of 5 (15) kg -1 d -1 at 95% CL. We also searched for pairs of spatially correlated electron tracks separated in time by up to tens of days, as expected from 32 Si – 32 P or 210 Pb – 210 Bi sequences of b decays. The decay rate of 32Si was found to be 80 +110 -65 (95% CI). An upper limit of ~35 kg -1 d -1 (95% CL) on the 210 Pb decay rate was obtained independently by α spectroscopy and the β decay sequence search. Furthermore, these levels of radioactive contamination are sufficiently low for the successful operation of CCDs in the forthcoming 100 g DAMIC detector.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Double-beta decay investigation with highly pure enriched $^{82}$Se for the LUCIFER experiment

The LUCIFER project aims at deploying the first array of enriched scintillating bolometers for the investigation of neutrinoless double-beta decay of 82 Se. The matrix which embeds the source is an array of ZnSe crystals, where enriched 82 Se is used as decay isotope. The radiopurity of the initial components employed for manufacturing crystals, that can be operated as bolometers, is crucial for achieving a null background level in the region of interest for double-beta decay investigations. In this work, we evaluated the radioactive content in 2.5 kg of 96.3 % enriched 82 Se metal, measured with a high-purity germanium detector at the Gran Sasso deep underground laboratory. The limits on internal contaminations of primordial decay chain elements of 232 Th, 238 U and 235 U are respectively: <61, <110 and <74 μBq/kg at 90 % C.L. The extremely low-background conditions in which the measurement was carried out and the high radiopurity of the 82 Se allowed us to establish the most stringent lower limits on the half-lives of the double-beta decay of 82 Se to 0+1, 2+2 and 2+1 excited states of 82 Kr of 3.4•10 22 , 1.3•10 22 and 1.0•10 22 y, respectively, with a 90 % C.L.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2024

Development of selenium imaging detectors toward a definitive search for neutrinoless ββ decay

Imaging sensors made from an ionization target layer of amorphous selenium (aSe) coupled to a silicon complementary metal-oxide-semiconductor (CMOS) active pixel array for charge readout are a promising technology for neutrino physics. The high spatial resolution in a solid-state target provides unparalleled rejection of backgrounds from natural radioactivity in the search for the neutrinoless ββ decay of 82 Se. With this grant, we experimentally determined two crucial factors necessary for the realization of this novel technology: i) the intrinsic energy response of aSe to ionizing electrons, and ii) the feasibility to couple a target layer of aSe to a CMOS active pixel sensor to image electron tracks.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2017

Precision Tests of the Electroweak Interaction using Trapped Atoms and Ions

The objective of the proposed research is to study fundamental aspects of the electroweak interaction via precision measurements in beta decay to test our current understanding of fundamental particles and forces as contained in the so-called "Standard Model" of particle physics. By comparing elegant experiments to rigorous theoretical predictions, we will either confirm the Standard Model to a higher degree and rule out models which seek to extend it, or find evidence of new physics and help guide theorists in developing the New Standard Model. The use of ion and neutral atom traps at radioactive ion beam facilities has opened up a new vista in precision low-energy nuclear physics experiments. Traps provide an ideal source of decaying atoms: they can be extremely cold (~1 mK); they are compact (~1 mm^3); and perhaps most importantly, the daughter particles escape with negligible distortions to their momenta in a scattering-free, open environment. The project is taking advantage of these technologies and applying them to precision beta-decay studies at radioactive beam facilities. The program consists of two complementary efforts: 1) Ion traps are an extremely versatile tool for purifying, cooling and bunching low-energy beams of short-lived nuclei. A large-bore (210~mm) superconducting 7-Tesla solenoid is at the heart of a Penning trap system for which there is a dedicated beamline at T-REX, the upgraded radioactive beam facility at the Cyclotron Institute, Texas A&M University. In addition to providing a general-purpose decay station, the flagship program for this system is measuring the ft-values and beta-neutrino correlation parameters from isospin T=2 superallowed beta-delayed proton decays, complimenting and expanding the already strong program in fundamental interactions at the Institute. 2) A magneto-optical trap is being used at the TRIUMF Neutral Atom Trap facility to observe the (un)polarized angular distribution parameters of isotopes of potassium. We are able to highly polarize laser-cooled atoms and observe their decay with unprecedented precision. The correlation of the daughter beta particle with the initial nuclear spin as well as other correlations are sensitive to physics beyond the Standard Model. Both of these cutting-edge and exciting research efforts will test our understanding of the fundamental symmetries underlying our current theory of electroweak interactions. Complementary to high-energy collider experiments, these low-energy nuclear physics "table-top" experiments will search for new particles and interactions which are not already described by the Standard Model of particle physics. The value of this research is recognized to be cross-disciplinary, exciting and potentially revolutionary in our understanding of nature's fundamental interactions. Accordingly, it has been endorsed by the recent (2007) Nuclear Science Advisory Committee's Long Range Plan as part of their recommendation for a "New Standard Model Initiative." In addition to the near-term benefits of scholarly publications and visibility through description of this work at international conferences, an important benefit of this research program is the training of new, young and enthusiastic nuclear physicists. Participants in this demanding and rewarding field develop a very strong background in physics with experience in a range of its subfields since we use atomic techniques and apply them to a nuclear physics experiment which in the end tests the theories of high-energy physics.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Cosmogenic backgrounds to $0νββ$ in EXO-200

As neutrinoless double-beta decay experiments become more sensitive and intrinsic radioactivity in detector materials is reduced, previously minor contributions to the background must be understood and eliminated. With this in mind, cosmogenic backgrounds have been studied with the EXO-200 experiment. Using the EXO-200 TPC, the muon flux (through a flat horizontal surface) underground at the Waste Isolation Pilot Plant (WIPP) has been measured to be $Φ$ = 4.07±0.14 (sys)±0.03 (stat)×10 -7 cm -2 s -1 , with a vertical intensity of $I_v$ = 2.97+0.14-0.13 (sys) ± 0.02 (stat) × 10 -7 cm -2 s -1 sr -1 . Simulations of muon-induced backgrounds identified several potential cosmogenic radionuclides, though only 137 Xe is a significant background for the 136 Xe $0νββ$ search with EXO-200. Muon-induced neutron backgrounds were measured using $γ$-rays from neutron capture on the detector materials. This provided a measurement of 137 Xe yield, and a test of the accuracy of the neutron production and transport simulations. The independently measured rates of 136 Xe neutron capture and of 137 Xe decay agree within uncertainties. Geant4 and FLUKA simulations were performed to estimate neutron capture rates, and these estimates agreed to within ~ 40% or better with measurements. The ability to identify 136 Xe($n,γ$) events will allow for rejection of 137 Xe backgrounds in future $0νββ$ analyses.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Combined effects of radiation damage and He accumulation on bubble nucleation in Gd2Ti2O7

Pyrochlores have long been considered as host phases for long-term immobilization of radioactive waste nuclides that would undergo ..alpha..-decay for hundreds of thousands of years. This work utilizes ion-beam irradiations to examine the combined effects of radiation damage and He accumulation on bubble formation in Gd2Ti2O7 over relevant waste-form timescales. Helium bubbles are not observed in pre-damaged Gd2Ti2O7 implanted with 2 x 1016 He/cm2, even after post-implantation irradiations with 7 MeV Au3+ at 300, 500, and 700 K. However, He bubbles with average diameters of 1.5 nm and 2.1 nm are observed in pre-damaged (amorphous) Gd2Ti2O7 and pristine Gd2Ti2O7, respectively, after implantation of 2 x 1017 He/cm2. The critical He concentration for bubble nucleation in Gd2Ti2O7 is estimated to be 6 at.% He.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗