Krypton Isotopes Research Articles

Reabsorption‐Free Scintillating Hetero‐Ligand MOF Crystals Activated by Ultrafast Energy Transfer

AbstractFast photoluminescence and scintillation with a Stokes shift larger than 1 eV is achieved in hetero‐ligand metal–organic framework (MOF) crystals comprising inorganic linking nodes and fluorescent conjugated ligands. By finely engineering the MOF composition with the use of ligands with strictly complementary emission and absorption properties and highly delocalized molecular electronic orbitals, the singlet excitons diffusion is enhanced through the ligand framework, fully exploiting both Förster and Dexter energy transfer mechanisms. This allows for the sensitization of energy acceptor ligand fluorescence by ultrafast non‐radiative energy transfer with a rate up to the THz range. This efficient antenna effect instantly activates the MOF scintillation with a Stokes shift as large as 1.3 eV in the blue spectral range, matching the highest sensitivity spectral window of the best photodetector available. This is obtained using a minimal doping level of the energy acceptor species, with a consequent elimination of emission re‐absorption that allows the achievement of a 500% increment of the MOFs scintillation efficiency and the detection of the radioactive krypton isotope 85Kr from the gas phase with an improved sensitivity compared with the reference material.

Accurate prediction of gaseous isotopes Xe and Kr concentrations from the burnup of nuclear fuel using simple regression algorithm.

Mathematical techniques for modeling and simulating dangerous or complex systems, such as nuclear technology systems, often require high-performance computing to process and analyze available data. In this paper, simple and quick method to support studies and research related to nuclear fuel is presented. This reasonably simple method helps to predict different concentrations of actinides and fission products in nuclear fuels without the need for expensive specialized programs and highly-trained researchers. The great importance of this approach is the speed of predicting the components of nuclear fuel concentrations, which in turn leads to quick decision-making, such as the possibility of operating fuel at higher burnup values, predicting the amount of gases resulting from nuclear fission (which may accumulate and cause problems in nuclear fuel such as volume swells), and other important decisions in nuclear fuel technology. The predicted equations have been generalized for higher values of burnup and compared with comparable results from MCNP codes. The equations deduced in calculating the different concentrations of xenon and krypton isotopes resulting from fission in burnup of nuclear fuel showed very precise results with discrepancies (magnitude of an error between the data points and the corresponding predicted ones) less than 2%. The suggested method offers a great advantage for researchers, which are the use one of any simple or common computational programs available to most researchers and do not need much experience to deal with, such as MATLAB, Excel that are easy to use for regression analyses. In this paper, the advantages of the proposed method are explained along with the limitations of its use.

Simulation of radioactive fission gas release from defective PWR fuel rod using the MFPR/R mechanistic code

A software package was elaborated by coupling the mechanistic code MFPR/R with a recently developed advanced model of mass exchange in defective fuel rods, to simulate the release of radioactive gaseous fission products into the coolant during operation of a thermal reactor. To simulate the oxidation of UO2 fuel, the processes of steam dissociation and radiolysis in the rod free volume were additionally considered. The package was validated by calculating the release of krypton, iodine and xenon isotopes into the coolant from defective rods under irradiation in the pressurized light water loop of the NRX reactor at Chalk River Nuclear Laboratories. It is shown that a reasonable overall agreement between calculations and experiment for noble gas isotopes can be obtained by introducing a single fitting parameter that takes into account uncertainties in the rod geometry and the rate of hydrogen production in the rod free volume.

Efficient radioactive gas detection by scintillating porous metal–organic frameworks

Natural and anthropogenic gas radionuclides such as radon, xenon, hydrogen and krypton isotopes must be monitored to be managed as pathogenic agents, radioactive diagnostic agents or nuclear activity indicators. State-of-the-art detectors based on liquid scintillators suffer from laborious preparation and limited solubility for gases, which affect the accuracy of the measurements. The actual challenge is to find solid scintillating materials simultaneously capable of concentrating radioactive gases and efficiently producing visible light revealed with high sensitivity. The high porosity, combined with the use of scintillating building blocks in metal–organic frameworks (MOFs), offers the possibility to satisfy these requisites. We demonstrate the capability of a hafnium-based MOF incorporating dicarboxy-9,10-diphenylanthracene as a scintillating conjugated ligand to detect gas radionuclides. Metal–organic frameworks show fast scintillation, a fluorescence yield of ∼40%, and accessible porosity suitable for hosting noble gas atoms and ions. Adsorption and detection of 85Kr, 222Rn and 3H radionuclides are explored through a newly developed device that is based on a time coincidence technique. Metal–organic framework crystalline powder demonstrated an improved sensitivity, showing a linear response down to a radioactivity value below 1 kBq m−3 for 85Kr, which outperforms commercial devices. These results support the possible use of scintillating porous MOFs to fabricate sensitive detectors of natural and anthropogenic radionuclides.

Ultrahigh-precision noble gas isotope analyses reveal pervasive subsurface fractionation in hydrothermal systems.

Mantle-derived noble gases in volcanic gases are powerful tracers of terrestrial volatile evolution, as they contain mixtures of both primordial (from Earth's accretion) and secondary (e.g., radiogenic) isotope signals that characterize the composition of deep Earth. However, volcanic gases emitted through subaerial hydrothermal systems also contain contributions from shallow reservoirs (groundwater, crust, atmosphere). Deconvolving deep and shallow source signals is critical for robust interpretations of mantle-derived signals. Here, we use a novel dynamic mass spectrometry technique to measure argon, krypton, and xenon isotopes in volcanic gas with ultrahigh precision. Data from Iceland, Germany, United States (Yellowstone, Salton Sea), Costa Rica, and Chile show that subsurface isotope fractionation within hydrothermal systems is a globally pervasive and previously unrecognized process causing substantial nonradiogenic Ar-Kr-Xe isotope variations. Quantitatively accounting for this process is vital for accurately interpreting mantle-derived volatile (e.g., noble gas and nitrogen) signals, with profound implications for our understanding of terrestrial volatile evolution.

Thiophene-based conjugated ultra-micropore rigid polymers for selective xenon capture

Radioactive isotopes of krypton (Kr) and xenon (Xe) are produced from the fission reaction of nuclear reactors. The separation of Xe/Kr from the nuclear off-gas is important for the spent fuel reprocessing. Compared with the industrial method of cryogenic distillation, physical adsorption is a simple and energy-saving method for Xe/Kr separation. Here, three rigid conjugated micropore polymers, including thiophene containing CMP-PY-BTP, TBTP and fluorine-containing CMP-PY-TFB, were prepared in high yield through direct CH arylation reaction, and their structure–function relationship with Xe/Kr separation was described. CMP-PY-TFB, BTP, and TBTP all possessed rigid micropores with Brunauer-Emmett-Teller specific surface areas of 786.25, 141.64 and 488.30 m2/g, respectively. Among three polymers, CMP-PY-TBTP exhibited the highest Xe/Kr selectivity (11.9 for ideal adsorption solution theory selectivity and 9.3 for Henry selectivity), owing to the combined effect of stronger polarization of its thiophene structural unit and micropore confinement (5.4 Å). The density functional theory (DFT) calculation revealed that Xe was more strongly adsorbed in thiophene-containing units than that of fluorine-containing unit which verified the stronger interaction caused by thiophene group’s polarization. Though having weaker polarization to Xe, fluorine-containing CMP-PY-TFB exhibited the highest Xe uptake of 43.59 cm3 g−1 due to its largest specific surface area (786.25 m2/g).

Signatures of shape phase transitions in krypton isotopes based on relativistic energy density functionals

Spectroscopic properties that characterize the shape phase transitions in krypton isotopes with the mass $A\approx80$ region are investigated within the framework of the nuclear density functional theory. Triaxial quadrupole constrained self-consistent mean-field calculations that employ relativistic energy density functionals and a pairing interaction are carried out for the even-even nuclei $^{76-86}$Kr. The spectroscopic properties are computed by solving the triaxial quadrupole collective Hamiltonian, with the ingredients, i.e., the deformation-dependent moments of inertia and mass parameters, and the collective potential, determined by using the SCMF solutions as microscopic inputs. Systematic behaviors of the SCMF potential energy surfaces, the corresponding low-energy spectra, electric quadrupole and monopole transition probabilities, and the fluctuations in the triaxial quadrupole deformations indicate evolution of the underlying nuclear structure as functions of the neutron number, that is characterized by a considerable degree of shape mixing. A special attention is paid to the transitional nucleus $^{82}$Kr, which has been recently identified experimentally as an empirical realization of the E(5) critical-point symmetry.

Krypton in the Chassigny meteorite shows Mars accreted chondritic volatiles before nebular gases.

Volatile elements are thought to have been delivered to Solar System terrestrial planets late in their formation through accretion of chondritic meteorites. Mars can provide information on inner Solar System volatile delivery during the earliest planet formation stages. We measured krypton isotopes in the martian meteorite Chassigny, representative of the planet's interior. We found chondritic krypton isotope ratios, which imply early incorporation of chondritic volatiles. The atmosphere of Mars has different (solar-type) krypton isotope ratios, indicating that it is not a product of magma ocean outgassing or fractionation of interior volatiles. Atmospheric krypton instead originates from accretion of solar nebula gas after formation of the mantle but before nebular dissipation. Our observations contradict the common hypothesis that during planet formation, chondritic volatile delivery occurred after solar gas acquisition.

Krypton isotopes tell the early story of Earth’s life-giving elements

Since its infancy, our planet has accumulated volatiles from more than one source.

Krypton isotopes tell the early story of Earth’s life-giving elements

Krypton isotopes tell the early story of Earth’s life-giving elements

Harvesting krypton isotopes from the off-gas of an irradiated water target to generate 76Br and 77Br

A flowing-water target was irradiated with a 150 MeV/nucleon beam of 78Kr at the National Superconducting Cyclotron Laboratory to produce 77Kr and 76Kr. Real-time gamma-imaging measurements revealed the mass transport of the krypton radioisotopes through the target-water processing, or “isotope harvesting”, system. The production rates were determined to be 2.7(1) × 10–4 nuclei of 76Kr and 1.18(6) × 10–2 nuclei of 77Kr formed per incident 78Kr ion. Utilizing an off-gas processing line as part of the isotope harvesting system, a total of 7.2(1) MBq of 76Kr and 19.1(6) MBq of 77Kr were collected in cold traps. Through the decay, the daughter radionuclides 76Br and 77Br were generated and removed from the traps with an average efficiency of 77 ± 12%. Due to the differences in half-lives of 76Kr and 77Kr, it was possible to isolate a pure sample of 76Br with 99.9% radionuclidic purity. The successful collection of krypton radioisotopes to generate 76Br and 77Br demonstrates the feasibility of gas-phase isotope harvesting from irradiated accelerator cooling-water. Larger-scale collections are planned for collecting by-product radionuclides from the Facility for Rare Isotope Beams.

Noble gases in Dome C micrometeorites - An attempt to disentangle asteroidal and cometary sources

We have performed a comprehensive noble gas study, including the isotopes of krypton and xenon, on a set of micrometeorites (MMs) collected from surface snow at Dome C (DC) on the Antarctic plateau. He and Ne are generally dominated by a solar component, with lower 4He concentrations and 4He/20Ne ratios in crystalline (Xtal) compared to fine-grained carbonaceous (FgC) MMs. Concentrations of (surface-correlated) solar wind (SW) He and Ne in FgC MMs are at the high end of what has been seen in earlier work, whereas the abundances of (volume-correlated) Kr and Xe are similar to what has been found in previous studies of MMs. In most samples, isotopic ratios for Kr and Xe are in the usual range of Q-Kr and -Xe (the Q component is the dominating component in primitive macroscopic meteorites) and air. When quantifiable, cosmic ray exposure (CRE) ages based on cosmogenic 21Ne and 3He, in combination with the Poynting-Robertson effect, are broadly consistent with an origin of the MMs from the asteroid belt. An exception is an Xtal MM, which exhibits a cosmogenic 21Ne concentration in agreement with an origin from beyond Saturn, consistent with a possible cometary origin. In addition, data for trapped noble gases in three (out of ten analyzed) DC MMs provide hints that these may be related to a cometary source. One sample, a fragment of a FgC MM, is of particular interest. This fragment exhibits a Xe composition, although with large analytical uncertainties, deficient in the heavy isotopes 134Xe and 136Xe. This is similar to the Xe isotopic pattern, probably related to cometary ice, measured by Rosetta in the coma of comet 67P/Churyumov-Gerasimenko. The same MM also has an unusually high 36Ar/38Ar ratio, consistent with Rosetta's Ar measurement (in this case the latter having a large uncertainty). The other hints are for two MMs, of crystalline (Xtal) type, that show Ne similar to that found in laboratory analysis of refractory grains captured from comet 81P/Wild 2 by the Stardust mission. Additionally, a FgC/Xtal MM may contain excess 3He, similar to what has been seen in some cluster interplanetary dust particles (cluster IDPs).

Deep-mantle krypton reveals Earth's early accretion of carbonaceous matter.

Establishing when, and from where, carbon, nitrogen and water were delivered to Earth is a fundamental objective in understanding the origin of habitable planets such as Earth. Yet, volatile delivery to Earth remains controversial1-5. Krypton isotopes provide insights on volatile delivery owing to their substantial isotopic variations among sources6-10, although pervasive atmospheric contamination has hampered analytical efforts. Here we present the full suite of krypton isotopes from the deep mantle of the Galápagos and Iceland plumes, which have the most primitive helium, neon and tungsten isotopic compositions11-16. Except for 86Kr, the krypton isotopic compositions are similar to a mixture of chondritic and atmospheric krypton. These results suggest early accretion of carbonaceous material by proto-Earth and rule out any combination of hydrodynamic loss with outgassing of the deep or shallow mantle to explain atmospheric noble gases. Unexpectedly, the deep-mantle sources have a deficit in the neutron-rich 86Kr relative to the average composition of carbonaceous meteorites, which suggests a nucleosynthetic anomaly. Although the relative depletion of neutron-rich isotopes on Earth compared with carbonaceous meteorites has been documented for a range of refractory elements1,17,18, our observations suggest such a depletion for a volatile element. This finding indicates that accretion of volatile and refractory elements occurred simultaneously, with krypton recording concomitant accretion of non-solar volatiles from more than one type of material, possibly including outer Solar System planetesimals.

Coulomb excitation of Kr80,82 and a change in structure approaching N=Z=40

Background: Nuclei approaching N=Z=40 are known to exhibit strongly deformed structures and are thought to be candidates for shape coexistence. In the krypton isotopes, Kr80,82 are poorly characterized, preventing an understanding of evolving deformation approaching N=40. Purpose: The present work aims to determine electric quadrupole transition strengths and quadrupole moments of Kr80,82 in order to better characterize their deformation. Methods: Sub-barrier Coulomb excitation was employed, impinging the isotopes of krypton on Pt196 and Pb208 targets. Utilizing a semiclassical description of the safe Coulomb-excitation process E2 matrix elements could then be determined. Results: Eleven new or improved matrix elements are determined in Kr80 and seven in Kr82. The new B(E2;01+→21+) value in Kr82 disagrees with the evaluated value by 3σ, which can be explained in terms of deficiencies in a previous Coulomb-excitation analysis. Conclusions: Comparison of measured Qs(21+) and B(E2;01+→21+) values indicates that neutron-deficient (N≤42) isotopes of krypton are closer to axial deformation than other isotopic chains in the mass region. A continuation of this trend to higher Z may result in Sr and Zr isotopes exhibiting near-axial prolate deformation.1 MoreReceived 19 July 2021Revised 1 September 2021Accepted 28 September 2021DOI:https://doi.org/10.1103/PhysRevC.104.044313©2021 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasCollective levelsElectromagnetic transitionsSpectroscopic factors & electromagnetic momentsProperties59 ≤ A ≤ 89Nuclear Physics

Stellar s -process neutron capture cross sections on Kr78,80,84,86 determined via activation, atom trap trace analysis, and decay counting

Understanding stellar $s$-process nucleosynthesis requires knowledge of neutron capture cross sections. In this work krypton gas is activated by an intense neutron beam at stellar energies. Applying for the first time atom-trap trace analysis (ATTA), long-lived reaction products are individually trapped and counted via fluorescence using cycling atomic transitions excited by precisely tuned lasers. Absolute isotope production is determined by comparison with reference samples. Improved capture cross sections are determined for four krypton isotopes, and the effect of the new values on relative $s$-process abundances in medium- and high-mass stars is investigated.

Structure of Krypton Isotopes using the Generalised Bohr Hamiltonian Method

We investigate the properties of the excited spectra of the even-even isotopes of krypton using a Generalised Bohr Hamiltonian with three different Skyrme functionals. In particular, we investigate the evolution of the low-lying and states and their associated electromagnetic transitions. The model reproduces quite nicely the energy trends apart from 88Kr, where none of the interactions used here are able to grasp a sudden change in the energy spectrum. Additionally, we explore the neutron deficient region 72–76Kr which is a proposed region for shape coexistence. We observe that the model can reproduce the structure of the experimental spectrum of 72Kr exceedingly well.

Tracing the Origins of the Ice Giants Through Noble Gas Isotopic Composition

The current composition of giant planet atmospheres provides information on how such planets formed, and on the origin of the solid building blocks that contributed to their formation. Noble gas abundances and their isotope ratios are among the most valuable pieces of evidence for tracing the origin of the materials from which the giant planets formed. In this review we first outline the current state of knowledge for heavy element abundances in the giant planets and explain what is currently understood about the reservoirs of icy building blocks that could have contributed to the formation of the Ice Giants. We then outline how noble gas isotope ratios have provided details on the original sources of noble gases in various materials throughout the solar system. We follow this with a discussion on how noble gases are trapped in ice and rock that later became the building blocks for the giant planets and how the heavy element abundances could have been locally enriched in the protosolar nebula. We then provide a review of the current state of knowledge of noble gas abundances and isotope ratios in various solar system reservoirs, and discuss measurements needed to understand the origin of the ice giants. Finally, we outline how formation and interior evolution will influence the noble gas abundances and isotope ratios observed in the ice giants today. Measurements that a future atmospheric probe will need to make include (1) the 3He/4He isotope ratio to help constrain the protosolar D/H and 3He/4He; (2) the 20Ne/22Ne and 21Ne/22Ne to separate primordial noble gas reservoirs similar to the approach used in studying meteorites; (3) the Kr/Ar and Xe/Ar to determine if the building blocks were Jupiter-like or similar to 67P/C-G and Chondrites; (4) the krypton isotope ratios for the first giant planet observations of these isotopes; and (5) the xenon isotopes for comparison with the wide range of values represented by solar system reservoirs.

Identification of chondritic krypton and xenon in Yellowstone gases and the timing of terrestrial volatile accretion

Identifying the origin of noble gases in Earth's mantle can provide crucial constraints on the source and timing of volatile (C, N, H2O, noble gases, etc.) delivery to Earth. It remains unclear whether the early Earth was able to directly capture and retain volatiles throughout accretion or whether it accreted anhydrously and subsequently acquired volatiles through later additions of chondritic material. Here, we report high-precision noble gas isotopic data from volcanic gases emanating from, in and around, the Yellowstone caldera (Wyoming, United States). We show that the He and Ne isotopic and elemental signatures of the Yellowstone gas requires an input from an undegassed mantle plume. Coupled with the distinct ratio of 129Xe to primordial Xe isotopes in Yellowstone compared with mid-ocean ridge basalt (MORB) samples, this confirms that the deep plume and shallow MORB mantles have remained distinct from one another for the majority of Earth's history. Krypton and xenon isotopes in the Yellowstone mantle plume are found to be chondritic in origin, similar to the MORB source mantle. This is in contrast with the origin of neon in the mantle, which exhibits an isotopic dichotomy between solar plume and chondritic MORB mantle sources. The co-occurrence of solar and chondritic noble gases in the deep mantle is thought to reflect the heterogeneous nature of Earth's volatile accretion during the lifetime of the protosolar nebula. It notably implies that the Earth was able to retain its chondritic volatiles since its earliest stages of accretion, and not only through late additions.

Analysis of fission product gas pressure and radioactivity in SAMOP reactor experimental facility

The fission-product gas pressure and radioactivity analysis of a subcritical assembly for 99Mo production (SAMOP) experimental facility have been done. SAMOP reactor is fueled with low enriched uranyl nitrate solution UO2(NO3)2 of 300 g U/L, the reactor core is in the form an annular tube surrounded by a ring of fuel tubes. The SAMOP system is designed to be operated at 100 to 120 hours periodic operation per batch. The analysis method is done by using ORIGEN2 computer code, at the condition of the maximum fuel temperature of 54 °C, 120 hours reactor operating time, and neutron flux varied from 1010 to 1012 n/cm2s. The result show that the inventory of the gaseous fission products is dominantly consisted of the xenon, radium, helium, and tritium isotopes with the total activity of 1.3775x1013 Bq (372.29 Ci) and total gas volume of 0.0986 cm3 or giving a total gas pressure of 5.78 kPa. The isotopes of xenon and krypton are the major contributors to the total gas pressure. The analysis result shows that the gas pressure of the fission products is very small, therefore the pressure monitoring in the SAMOP reactor core is not necessary.

Eighth-order virial equation of state and speed-of-sound measurements for krypton.

An eighth-order virial equation of state (VEOS) for krypton, valid for temperatures up to 5000 K, was developed using the accurate potential functions proposed by Jäger et al. [J. Chem. Phys. 144, 114304 (2016)] for the pair interactions and nonadditive three-body interactions between krypton atoms. While the second and third virial coefficients were already calculated by Jäger et al., the fourth- to eighth-order coefficients were determined in the present work. A simple analytical function was fitted individually to the calculated values of each virial coefficient to obtain the VEOS in an easy-to-use analytical form. To enable a stringent test of the quality of the new VEOS, we measured the speed of sound in krypton in the temperature range from 200 K to 420 K and at pressures up to 100 MPa with a very low uncertainty (at the 0.95 confidence level) of 0.005%-0.018% employing the pulse-echo technique. In order to verify that the isotopic composition of the krypton sample conforms to that of natural krypton in air, high-precision measurements of krypton isotope ratios using a high-sensitivity noble gas mass spectrometer were performed. The extensive comparison with the new speed-of-sound data as well as with experimental p-ρ-T and speed-of-sound data from the literature indicates that pressures and speeds of sound calculated using our new VEOS have uncertainties (at the 0.95 confidence level) of less than 0.1% at state points at which the VEOS is sufficiently converged.