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Within the scope of our ongoing project we have demonstrated success measuring the decay products of various radioactive materials using these microcalorimeter detectors.
The discovery of a binary neutron star merger (NSM) through both its gravitational wave and electromagnetic emission has revealed these events to be key sites of $r$-process nucleosynthesis. Here, we evaluate the prospects of finding the remnants of Galactic NSMs by detecting the gamma-ray decay lines from their radioactive $r$-process ejecta. We find that 126 Sn, which has several lines in the energy range 415-695 keV and resides close to the second $r$-process peak, is the most promising isotope, because of its half-life $t_{1/2}$ = 2:30(14) 10 5 yr being comparable to the ages of recent NSMs. Using a Monte Carlo procedure, we predict that multiple remnants are detectable as individual sources by next-generation $\gamma$-ray telescopes which achieve sub-MeV line sensitivities of ~18 -8 -10 -6 $\gamma$ cm -2 s -1 . However, given the unknown locations of the remnants, the most promising search strategy is a systematic survey of the Galactic plane and bulge extending to high Galactic latitudes. Individual known supernova remnants which may be mis-classi ed NSM remnants could also be targeted, especially those located outside the Galactic plane. Detection of a moderate sample of Galactic NSM remnants would provide important clues to unresolved issues such as the production of actinides in NSMs, properties of merging NS binaries, and even help distinguish them from rare supernovae as current Galactic $r-$process sources. We also investigate the diffuse flux from longer-lived nuclei (e.g. 182 Hf) that could in principle trace the Galactic spatial distribution of NSMs over longer timescales, but find that the detection of the diffuse flux appears challenging even with next-generation telescopes.
Returned Surveyor 3 camera visor examined for alpha radioactive deposit formed by decay of radon isotopes diffusing out of lunar surface
The detection and measurement of the cosmic ray charge spectrum for nuclei heavier than iron (Fe, Z = 26) are discussed. These trans-iron nuclei are of great interest for several reasons. They promise to be one of the more sensitive clocks for use in determining the age of cosmic rays. The discovery of radioactive nuclides and their decay products in the primary flux, will allow an estimation of the elapsed time since these cosmic rays were synthesized. In addition, the relatively short interaction length of the very heavy trans-iron particles makes their relative abundance a source of information regarding the amount of interstellar matter that they had to traverse to reach the earth. A study of the trans-iron cosmic rays may provide clues as to the very processes of nucleosyntheses by which the bulk of the trans-iron nuclei in the universe are produced. This in turn may shed light on the mechanics of the supernova, which is postulated to be the major source of all cosmic rays. Finally, trans-iron cosmic ray experiments may demonstrate the existence of the recently postulated super-heavy nuclei.
The distribution of radioactive polonium-210, a decay product of radon-222, shows enhanced concentrations at the edges of lunar maria. Enhancements are seen at the edges of Mare Fecunditatis, Mare Crisium, Mare Smythii, Mare Tranquillitatis, Mare Nubium, Mare Cognitum, and Oceanus Procellarum. The observation is indicative of the transient emission of radon gas from the perimeters of lunar maria.
Some CFF-Xe (Chemically Fractionated Fission Xenon), whose isotopic composition is established by simultaneous decay and migration of radioactive fission products, is probably present in the Earth's lithosphere, a conclusion based on available Xe data from various crustal and mantle rocks . Our recent isotopic analysis of Xe in alumophosphate from zone 13 of Okelobondo (southern extension of Oklo), along with the independent estimation of the isotopic composition of atmospheric fission Xe , supports the hypothesis that CFF-Xe was produced on a planetary scale. Additional information is contained in the original extended abstract.
One consequence of a high altitude nuclear explosion (HANE) is the creation of an artificial radiation belt that can have severe consequences for space-based infrastructure in low Earth orbit (LEO). A HANE-generated radiation belt is produced when radioactive debris ions beta decay to produce an intense population of magnetically-trapped, high-energy electrons that can affect satellites through increased total dose rates and/or internal charging. Recent results from NASA's Van Allen Probes mission has shown how electromagnetic waves can scatter radiation belt electrons decreasing their intensity and effects. Radiation Belt Remediation (RBR) seeks to exploit those processes to rapidly deplete the intensity of either natural or HANE-produced radiation belts by artificially injecting waves to enhance electron scattering and loss rates. One promising option for producing the required waves is to use modulated medium energy electron beams as a type of 'wireless transmitter'. (author)
We present measurements of bulk radiocontaminants in the high-resistivity silicon CCDs from the DAMIC experiment at SNOLAB. We utilize the exquisite spatial resolution of CCDs to discriminate between α and β decays, and to search with high efficiency for the spatially-correlated decays of various radioisotope sequences. Using spatially-correlated β decays, we measure a bulk radioactive contamination of 32 Si in the CCDs of 140 ± 30 μBq/kg, and place an upper limit on bulk 210 Pb of < 160 μBq/kg. Using similar analyses of spatially-correlated α and β decays, we set upper limits of < 11 μBq/kg (0.9 ppt) on 238 U and < 7.3 μBq/kg (1.8 ppt) on 232 Th in the bulk silicon. The ability of DAMIC CCDs to identify and reject spatially-coincident backgrounds, particularly from 32 Si, has significant implications for the next generation of silicon-based dark matter experiments, where β's from 32 Si decay will likely be a dominant background.
We investigate the potential of decay storage of low and intermediate radioactive waste for release procedures. We present the Safetec software tool HL3 and its application to data from the German nuclear power plant at the site in Stade. In general, during the dismantling process of nuclear power plants, waste of slightly contaminated and/or activated systems is produced in large amounts. These are in particular demolition rubble from concrete structures and ingots from the melting process of metals. If, at the time of disposal, the nuclear inventory is near or slightly above federal clearance limits, the material cannot be released as conventional waste. However, due to the decline of the nuclear inventory over time, a significant amount of that waste could qualify for the release procedure in the future. Although this concept of decay storage is well known, specific predictions of the mass flow to be released is non-trivial. The mass flow over time depends on the composition of known and assumed nuclides (nuclide vector), as well as on the underlying threshold values for release. To handle the waste stream as a function of time, the nuclide composition and specific threshold values, Safetec developed a bespoke software tool named HL3. Its primary function is to visualize and to test/analyze various nuclide vectors and its decompositions over time. For the application within German law, threshold values according to the different disposal routes can be considered. Using the batch interface in the software tool HL3, large amounts of data can be automatically analyzed in a traceable and quick way. To test both, the tool and the benefit for the concept of decay storage, we have applied our code HL3 to material from the dismantling of the pressurized-water reactor at the site in Stade, Germany. We set the focus on concrete debris and metal ingots, which in principle are best suited for decay storage over years. The assignment and the packaging of that waste from Stade were based on application documents for decommissioning of the Year 2000 and according to the state of art conditioning technique at that time. Based on the data of that waste and the appropriate disposal routes, we calculate and discuss the amount of waste releasable after decay storage. As for the situation in Germany, we find that only a negligible amount would be releasable, mainly due to other reasons. These are the deterioration of detectability of radionuclides with time, and other regulatory conditions. However, on an international scale, a different assessment can be drawn. Our results thus motivate to reconsider the option of interim decay storage to reduce radioactive waste in large amounts. (authors)
Dry storage systems are characterized by passive and inherent safety systems ensuring safety even in case of severe incidents or accidents. After the events of Fukushima, the advantages of such passively and inherently safe dry storage systems have become more and more obvious. As with the storage of all radioactive materials, the storage of spent nuclear fuel (SF) and high-level radioactive waste (HLW) must conform to safety requirements. Following safety aspects must be achieved throughout the storage period: - safe enclosure of radioactive materials, - safe removal of decay heat, - securing nuclear criticality safety, - avoidance of unnecessary radiation exposure. The implementation of these safety requirements can be achieved by dry storage of SF and HLW in casks as well as in other systems such as dry vault storage systems or spent fuel pools, where the latter is neither a dry nor a passive system. Furthermore, transport capability must be guaranteed during and after storage as well as limitation and control of radiation exposure. The safe enclosure of radioactive materials in dry storage casks can be achieved by a double-lid sealing system with surveillance of the sealing system. The safe removal of decay heat must be ensured by the design of the storage containers and the storage facility. The safe confinement of radioactive inventory has to be ensured by mechanical integrity of fuel assembly structures. This is guaranteed, e.g. by maintaining the mechanical integrity of the fuel rods or by additional safety measures for defective fuel rods. In order to ensure nuclear critically safety, possible effects of accidents have also to be taken into consideration. In case of dry storage it might be necessary to exclude the re-positioning of fissile material inside the container and/or neutron moderator exclusion might be taken into account. Unnecessary radiation exposure can be avoided by the cask or canister vault system itself. In Germany dry storage of SF in casks fulfills both transport and storage requirements. Mostly, storage facilities are designed as concrete buildings above the ground, but due to regional constraints, one storage facility has also been built as a rock tunnel. The decay heat is always removed by natural air flow; further technical equipment is not needed. The removal of decay heat and shielding had been modeled and calculated by state-of-the-art computer codes before such a facility has been built. TueV and BAM present their long experience in the licensing process for sites and casks and inform about spent nuclear fuel management and issues concerning dry storage of spent nuclear fuel. Different storage systems and facilities in Germany, Europe and world-wide are compared with respect to the safety aspects mentioned above. Initial points are the safety issues of wet storage of SF, and it is shown how dry storage systems can ensure the compliance with the mentioned safety criteria over a long storage period. The German storage concept for dry storage of SF and HLW is presented and discussed. Exemplarily, the process of licensing, erection and operation of selected German dry storage facilities is presented. (authors)
The 253.3–keV excited state located in {sup 93}Rb was studied at the Holifield Radioactive Ion Beam Facility in Oak Ridge. This state, described as isomeric in databases, was populated in the decay of {sup 93}Kr produced by proton–induced fission of {sup 238}U and isolated using the isotope separation on–line technique. We report that the 253.3–keV level does not reveal isomerism and the upper limit of the half-life from our measurement is 4 ns. Our findings are supported by previously reported results that were not taken into account in the latest nuclear databases.
The probability that a nucleus will absorb a neutron, described in units of area as the neutron-capture cross section, is important to many areas of nuclear science including stellar nucleosynthesis, reactor performance, nuclear medicine, and defense applications. Although neutron-capture cross-sections have been directly measured for most stable nuclei, fewer results exist for radioactive isotopes and predictions typically have large uncertainties. There are almost no nuclear data for neutron-induced reactions on the radioactive nucleus 88 Zr, despite its significance for nuclear-security missions. By exposing 88 Zr to the intense neutron flux of a nuclear reactor, it was determined that 88 Zr has a thermal neutron capture cross section of (861,000 ± 69,000) b, which is the second-largest ever measured, despite being predicted to be only 10 b. The only other nuclei known to have thermal neutron capture cross sections greater than 1x10 5 b are 135 Xe and 157 Gd (2.6x10 6 b and 2.5x10 5 b, respectively) and no other cross section of comparable size has been discovered in the past 70 years (Fig. 1). The measurement of the 135 Xe cross section followed the determination that a fission product was poisoning the early reactors.7 The applications for 157 Gd were not immediately appreciated, but now the isotope has been developed into a detector material, burnable reactor poison, and potential medical neutron capture therapy (NCT) agent. In the case of 88 Zr, a unique aspect of the neutron-capture reaction is that both the target and the product 89 Zr nuclei are radioactive and give intense γ-ray emissions upon decay. This result suggests that as additional measurements with radioactive isotopes become feasible in the near future via access to new facilities for sample production and measurement, other cross-section surprises may be uncovered.
The Savannah River Site (SRS) is an 802 square-kilometer (310 square-miles) United States Department of Energy (US DOE) nuclear facility located along the Savannah River near Aiken, South Carolina. Nuclear weapons material production began in the early 1950's, utilizing five (5) production reactors. In the early 1990's all SRS production reactor operations were terminated. The first reactor closure end-state declaration was documented in a Comprehensive Environmental Response and Compensation and Liability Act (CERCLA) Early Action Record of Decision. The decision for the final closure of the 29,543 square-meter (318,000 square-feet) 105-P Reactor was determined to be in situ decommissioning (ISD). ISD is an acceptable and cost-effective alternative to off-site disposal for the reactor building, which will allow for consolidation of remedial action wastes generated from other cleanup activities within the P Area. ISD is considered protective by the regulators, U.S. Environmental Protection Agency (USEPA) and the South Carolina Department of Health and Environmental Control (SCDHEC), public and stakeholders as waste materials are stabilized / immobilized, and radioactivity is allowed to naturally decay, thus preventing future exposure to the environment. Stakeholder buy-in was critical in the up-front planning in order to achieve this monumental final decision. Numerous public meetings and workshops were held in two different states (covering a 321 kilometer (200-mile) radius) with stakeholder and SRS Citizens Advisory Board (CAB) participation. These meetings were conducted over an eight- month period as the end-state decision making progressed. Information provided to the public evolved from workshop to workshop as data became available and public input from the public meetings were gathered. ISD is being considered for the balance of the four (4) SRS reactors and other hardened facilities such as the chemical Separation Facilities (canyons). Closure of the SRS P Reactor Area was precedent setting and sets the stage for closure of other reactors and hardened facilities. The DOE, USEPA, and SCDHEC engaged in active, up-front, and timely involvement with the SRS. The SRS CAB, elected officials, and citizens of South Carolina and Georgia met to discuss the P reactor area closure and associated risks. Early public involvement gave SRS and the regulators assurance that the selected decision was valid and would not be overturned. Public input improved the process and ensured that the important decision on the final end-state of the reactor facilities was not made in isolation. ISD of P Reactor will provide adequate protection of human health and the environment and the lowest cost since short-term risk is minimized to remedial workers from exposure to contaminated equipment and facilities by leaving the reactor vessel in place allowing for radiological decay over time. (authors)
A recent remarkable discovery by Katharina Lodders showed that the abundances of extinct radioactivities (relative to reference nuclei) in chondrites, achondrites, and irons are proportional to the squares of their mean lives, whereas no such abundance-mean life relationship is apparent for the data of calcium-aluminum rich inclusions (CAIs) and a variety of other inclusion types. In this talk I shall interpret these results in terms of galactic and solar nebula processes. The first step in organizing the data for interpretation is to require that both the abundance of the extinct radioactivity (as measured by its decay product abundance) and that of the reference nuclide should have the same nucleosynthesis history, or else that a correction to the ratio be made to compensate for the ratio of the two different production processes. The striking feature of this diagram is that the lower edge of the data (the Lodders Line) is remarkably straight; most of the data are derived from chondrites; and its slope on the log-log diagram is two. So the extinct radioactivities are present in proportion to the square of their mean lives. All the other data lie above the Lodders line in this diagram; the sources of that data are in general somewhat larger particles than those that have contributed to the Lodders Line. A straight relationship between abundances of extinct radioactivities
β-decay spectroscopy of 173,174 Ho (Z = 67, N = 106,107) was conducted at Radioactive Isotope Beam Factory at RIKEN by using in-flight fission of a 345-MeV/u 238 U primary beam. A previously unreported isomeric state at 405 keV with half-life of 3.7(12) μs and a spin and parity of (3/2 + ) is identified in 173 Ho. Moreover, a new state with a spin and parity of 9 - was discovered in 174 Er. The experimental log ft values of 5.84(20) and 5.25(18) suggest an allowed-hindered β decay from the ground state of 174 Ho to the K π = 8 - isomeric state in 174 Er. Configuration-constrained potential energy surface (PES) calculations were performed and the predictions are in reasonable agreement with the experimental results.
SIAL{sup R} is a proven, safe, cost-effective and licensed waste solidification technology that has been used successfully for 20 years in Slovakia and the Czech Republic for processing of various problematic radioactive waste streams. This abstract presents and summarises the most interesting performance records of the SIAL{sup R} geopolymer solidification technology, the applied mobile devices as well as the characteristics of final products. Radioactive waste solidification into matrix SIAL{sup R} is based on polycondensation of inorganic aluminosilicate components with chemical composition similar to average cement. The main components of matrix SIAL{sup R} are natural inorganic raw materials containing SiO{sub 2}, Al{sub 2}O{sub 3}, CaO, MgO, Na{sub 2}O, K{sub 2}O, Fe{sub 2}O{sub 3}, and TiO{sub 2}. The treatment/solidification process is modified for individual radioactive streams with different compositions. To determine the most appropriate composition, the SIAL{sup R} application technology is laboratory tested on real samples of each individual waste stream identified for solidification. Then an appropriate mixture of aluminosilicate composition and other inorganic compounds is defined for a given solidification application. When determining the most appropriate mixture, other requirements are taken into consideration: maximum dose rate on the drum with solidified product, mass, volume, alpha radionuclide content in the final product, need for a waste's dewatering before solidification, dry matter content in the solidification product as well as other specific waste acceptance criteria (i.e., compressive strength, leachability, diffusion coefficients, radiation stability, biodegradability of matrix, distribution and partition coefficients, influence of frost and water presence to the product stability including long term physical stability in water, dustiness, flammability, time dependence of compression strength and water reduction, product homogeneity and also radiolytic G-value for hydrogen release, GH{sub 2}). The Amec Foster Wheeler baseline approach to implementing the SIAL{sup R} waste treatment process is structured on three steps - waste characterization, waste retrieval and pre-treatment and at last the solidification of pre-treated waste itself. The equipment used for the solidification process is relatively small, lightweight and designed for the specific application on site, directly 'in situ' or local to the tanks storing the sludge's/resins/other waste streams. This mitigates the problems normally experienced by transferring sticky, tight waste through long pipes. The equipment is normally 'tailor-made' to take into account the real space conditions and other existing facility requirements. At Bohunice and Dukovany sites, the facilities for encapsulation were designed to occupy existing areas of the plants in close proximity to the tanks where the waste was being stored. This allowed for the removal of the waste using Remote Operated Vehicles and for the waste to be immediately treated on site without the need for transportation thus saving both, time and resource. To date, SIAL{sup R} has been used successfully to immobilize approximately 2 x 10{sup 6} kg of waste which includes sludge, resin, crystalline borates and contaminated organic waste from Bohunice and Mochovce, Slovakia and approximately 300 m{sup 3} of spent ion exchange resins and sludge from tanks on site at the Dukovany NPP (Nuclear Power Plant) in the Czech Republic. The technology now has a track record of over 20 years which includes on-going research and development. The International missions WANO (the World Association of Nuclear Operators) and OSART (the Operational Safety Review Team) evaluated the SIAL{sup R} matrix technology at Dukovany NPP as an example of good practice. (authors)
As with the storage of all radioactive materials, the storage of spent nuclear fuel (SF) and high-level radioactive waste (HLW) must conform to safety requirements. Safety aspects like safe enclosure of radioactive materials, safe removal of decay heat, nuclear criticality safety and avoidance of unnecessary radiation exposure must be achieved throughout the storage period. The implementation of these safety requirements can be achieved by dry storage of SF and HLW in casks as well as in other systems such as dry vault storage systems or spent fuel pools, where the latter is neither a dry nor a passive system. After the events of Fukushima, the advantages of passively and inherently safe dry storage systems have become more obvious. TUV and BAM, who work as independent experts for the competent authorities, present the licensing process for sites and casks and inform about spent nuclear fuel management and issues concerning dry storage of spent nuclear fuel, based on their long experience in these fields. All safety relevant issues like safe enclosure, shielding, removal of the decay heat or behavior of cask and building under accident conditions are checked and validated with state-of-the-art methods and computer codes before the license approval. It is shown how dry storage systems can ensure the compliance with the mentioned safety criteria over a long storage period. Exemplarily, the process of licensing, erection and operation of selected German dry storage facilities is presented. (authors)
Beta-decay spectroscopy provides important information on nuclear structure and properties needed to understand topics as widely varied as fundamental nuclear astrophysics to applied nuclear reactor design. However, there are significant limitations of our knowledge due to an inability to experimentally measure everything. Therefore, it is often necessary to rely on theoretical calculations which need to be vetted with experimental results. The focus of this report will be results from experimental research performed by the Principal Investigator (PI) and his research group at Mississippi State University in which the group played the lead role in proposing, implementing, performing and analyzing the experiment. This research was carried out at both the National Superconduction Cyclotron Laboratory (NSCL) at Michigan State University and the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Laboratory. The primary emphasis of the research was the use of \bdec spectroscopy as a tool to understand the evolution of nuclear structure in neutron-rich nuclei which could then be applied to improve theory and to increase the overall knowledge of nuclear structure.