Nuclear Signatures Research Articles

Abstract 3553: Three-dimensional (3D) telomere signatures of sporadic pediatric papillary thyroid carcinoma (PTC)

Abstract The incidence of thyroid carcinoma has increased worldwide, including in pediatric patients. Papillary thyroid carcinoma (PTC) is the most common subtype. Previous studies have suggested that clinical presentation and outcome diverge between pediatric and adult PTC and that this difference is likely due to distinct genetic alterations. BRAF V600E point mutation is highly prevalent in adults, while genetic fusions (RET/PTC, AGK-BRAF, ETV6-NTRK3) are the most prevalent events in the pediatric population. As telomere loss or dysfunction results in aneuploidy and chromosomal rearrangements, which can promote carcinogenesis, we investigated the three-dimensional (3D) structure of the telomeres in the nuclei from 21 pediatric patients (≤18 y.o), representing 16 PTC cases (with paired normal and tumor tissues for five of them) and five normal thyroid tissues from patients undergoing thyroidectomy for reasons other than cancer. We performed quantitative fluorescence in situ hybridization (FISH), 3D imaging, and 3D telomere analysis using TeloView® software to examine telomere dysfunction. The parameters examined included total number of signals (numbers of telomeres), total number of telomere aggregates, a/c ratio (indicating the phase of the cell cycle), total intensity (telomere length) and nuclear volume. Thyroid cancer cells showed lower average intensity of signals (p<0.0001) and lower intensity signals (p<0.0001), as well as higher nuclear volume (p<0.0001), compared to normal thyroid cells. In addition, tumour cells showed a higher a/c ratio (p<0.0001), indicating that they are more actively dividing than normal cells, which correlates with the high proliferation rate of cancer cells. We did not observe any alterations related to the total number of telomere signals and total number of aggregates, which suggests no significant aneuploidies occurring with these samples. The 3D nuclear telomere signature was able to detect differences in telomere architecture in tumours, compared to normal. Further analysis is necessary to define whether nuclear telomere architecture and specific genetic alterations observed in pediatric thyroid cancer are associated. Citation Format: Luiza Sisdelli, Maria Isabel Cordioli, Fernanda Vaisman, Osmar Monte, Carlos Longui, Adriano N. Cury, Monique O. Freitas, Aline Rangel-Pozzo, Sabine Mai, Janete Cerutti. Three-dimensional (3D) telomere signatures of sporadic pediatric papillary thyroid carcinoma (PTC) [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3553.

Samarium isotope compositions of uranium ore concentrates: A novel nuclear forensic signature

Uranium ore is mined and milled to produce uranium ore concentrate (UOC), a regulated product of the nuclear fuel cycle. Diversion of UOC from the fuel cycle into possible weapons production is a key concern in global nonproliferation efforts. As such, the ability to trace the origin of seized nuclear materials is imperative to law enforcement efforts. Although isotopic signatures of UOCs have proven fruitful to pinpoint sample provenance, new isotopic signatures are needed because most existing isotopic signatures are not indicative of the original ore body from which the U is derived. In this work, we developed a new method to separate samarium (Sm) from a U-rich sample matrix and report the first Sm isotope compositions of 32 UOCs derived from a variety of worldwide uranium mines. Relative to terrestrial standards, approximately half the UOCs have resolved and anticorrelated 149Sm-150Sm isotope compositions, consistent with the capture of thermal neutrons by 149Sm in the ore body. The UOCs with anomalous Sm isotope compositions tend to derive from older (~>1.5Ga) and higher-grade ore bodies, although other factors, such as the presence of neutron moderators like water, also play a role. Nonetheless, the Sm isotope compositions of UOCs directly reflects the neutron fluence over the history of the original ore body and can be used to discern different geologic conditions associated with that ore body. As such, this work demonstrates the potential use of Sm isotopes as a novel nuclear forensics signature for origin assessment of UOCs.

Identification of short-lived fission products in delayed gamma-ray spectra for nuclear material signature verifications

Short-lived Fission Products (FPs) of both uranium (U) and plutonium (Pu) isotopes were identified in neutron irradiated nuclear material (NM) standards in the high-energy gamma-rays range in the perspective of the utilisation of the Delayed Gamma-ray Spectrometry (DGS) technique for nuclear material signature verifications. DGS is a promising active Non-Destructive Assay (NDA) technique that found applications not only in nuclear safeguards but also in nuclear security.This paper presents results of measurement campaigns that include the development of experimental set-up, sample irradiation, gamma-ray spectra acquisitions and qualitative analysis of the obtained gamma-spectra. The experimental setup-up is based on an HPGe planar detector of high-energy resolution and an irradiation chamber made of high-density polyethylene (HDPE) that accommodates a sealed 252Cf source of 50 MBq activity. The delayed gamma-ray spectra of standard samples of U and Pu neutron interrogated samples are successfully acquired using the cyclic neutron irradiation method. 35 and 24 FPs with half-lives ranging from dozens seconds to minutes were identified in the irradiated U and Pu samples, respectively. In the energy range 2–4.9 MeV of the acquired DGS gamma-ray spectra; we have successfully identified 72 gamma-ray peaks of 21 FPs in U and Pu standard samples. This large number of identified FPs is auspicious to the full development of DGS as new active NDA technique for nuclear signature verifications.

Effects of natural zeolites on field-scale geologic noble gas transport

Improving predictive models for noble gas transport through natural materials at the field-scale is an essential component of improving US nuclear monitoring capabilities. Several field-scale experiments with a gas transport component have been conducted at the Nevada National Security Site (Non-Proliferation Experiment, Underground Nuclear Explosion Signatures Experiment). However, the models associated with these experiments have not treated zeolite minerals as gas adsorbing phases. This is significant as zeolites are a common alteration mineral with a high abundance at these field sites and are shown here to significantly fractionate noble gases during field-scale transport. This fractionation and associated retardation can complicate gas transport predictions by reducing the signal-to-noise ratio to the detector (e.g. mass spectrometers or radiation detectors) enough to mask the signal or make the data difficult to interpret. Omitting adsorption-related retardation data of noble gases in predictive gas transport models therefore results in systematic errors in model predictions where zeolites are present.Herein is presented noble gas adsorption data collected on zeolitized and non-zeolitized tuff. Experimental results were obtained using a unique piezometric adsorption system designed and built for this study. Data collected were then related to pure-phase mineral analyses conducted on clinoptilolite, mordenite, and quartz. These results quantify the adsorption capacity of materials present in field-scale systems, enabling the modeling of low-permeability rocks as significant sorption reservoirs vital to bulk transport predictions.

Ionized gas outflow signatures in SDSS-IV MaNGA active galactic nuclei

ABSTRACT The prevalence of outflow and feedback signatures in active galactic nuclei (AGNs is a major unresolved question which large integral field unit (IFU) surveys now allow to address. In this paper, we present a kinematic analysis of the ionized gas in 2778 galaxies at z ∼ 0.05 observed by Sloan Digital Sky Survey-IV (SDSS-IV) Mapping Nearby Galaxies at Apache Point Observatory (MaNGA). Specifically, we measure the kinematics of the [O iii] λ5007 Å emission line in each spatial element and fit multiple Gaussian components to account for possible non-gravitational motions of gas. Comparing the kinematics of the ionized gas between 308 MaNGA-selected AGNs that have been previously identified through emission-line diagnostics and sources not classified as AGN, we find that while 25 per cent of MaNGA-selected AGN show [O iii] components with emission-line widths of >500 km s−1 in more than 10 per cent of their spaxels, only 7 per cent of MaNGA non-AGNs show a similar signature. Even the AGNs that do not show nuclear AGN photoionization signatures and that were only identified as AGN based on their larger scale photoionization signatures show similar kinematic characteristics. In addition to obscuration, another possibility is that outflow and mechanical feedback signatures are longer lived than the AGN itself. Our measurements demonstrate that high velocity gas is more prevalent in AGN compared to non-AGN and that outflow and feedback signatures in low-luminosity, low-redshift AGN may so far have been underestimated. We show that higher luminosity MaNGA-selected AGNs are able to drive larger scale outflows than lower luminosity AGN. But estimates of the kinetic coupling efficiencies are ≪1 per cent and suggest that the feedback signatures probed in this paper are unlikely to have a significant impact on the AGN host galaxies. However, continuous energy injection may still heat a fraction of the cool gas and delay or suppress star formation in individual galaxies even when the AGN is weak.

Detecting Light Dark Matter via Inelastic Cosmic Ray Collisions.

Direct detection experiments relying on nuclear recoil signatures lose sensitivity to sub-GeV dark matter for typical galactic velocities. This sensitivity is recovered if there exists another source of flux with higher momenta. Such an energetic flux of light dark matter could originate from the decay of mesons produced in inelastic cosmic ray collisions. We compute this novel production mechanism-a cosmic beam dump experiment-and estimate the resulting limits from XENON1T and LZ. We find that the dark matter flux from inelastic cosmic rays colliding with atmospheric nuclei can dominate over the flux from elastic collisions with relic dark matter. The limits that we obtain for hadrophilic scalar mediator models are competitive with those from MiniBoone for light MeV-scale mediator masses.

Mitohormesis, UPRmt, and the Complexity of Mitochondrial DNA Landscapes in Cancer.

The discovery of the Warburg effect, the preference of cancer cells to generate ATP via glycolysis rather than oxidative phosphorylation, has fostered the misconception that cancer cells become independent of the electron transport chain (ETC) for survival. This is inconsistent with the need of ETC function for the generation of pyrimidines. Along with this misconception, a large body of literature has reported numerous mutations in mitochondrial DNA (mtDNA), further fueling the notion of nonfunctional ETC in cancer cells. More recent findings, however, suggest that cancers maintain oxidative phosphorylation capacity and that the role of mtDNA mutations in cancer is likely far more nuanced in light of the remarkable complexity of mitochondrial genetics. This review aims at describing the various model systems that were developed to dissect the role of mtDNA in cancer, including cybrids, and more recently mitochondrial-nuclear exchange and conplastic mice. Furthermore, we put forward the notion of mtDNA landscapes, where the surrounding nonsynonymous mutations and variants can enhance or repress the biological effect of specific mtDNA mutations. Notably, we review recent studies describing the ability of some mtDNA landscapes to activate the mitochondrial unfolded protein response (UPRmt) but not others. Furthermore, the role of the UPRmt in maintaining cancer cells in the mitohormetic zone to provide selective adaptation to stress is discussed. Among the genes activated by the UPRmt, we suggest that the dismutases SOD2 and SOD1 may play key roles in the establishment of the mitohormetic zone. Finally, we propose that using a UPRmt nuclear gene expression signature may be a more reliable readout than mtDNA landscapes, given their diversity and complexity.

Development and validation of a novel and robust blood small nuclear RNA signature in diagnosing autism spectrum disorder.

Reliable molecular signatures are needed to improve the early and accurate diagnosis of autism spectrum disorder (ASD), and indicate physicians to provide timely intervention. This study aimed to identify a robust blood small nuclear RNA (snRNA) signature in diagnosing ASD. 186 blood samples in the microarray dataset were randomly divided into the training set (n = 112) and validation set (n = 72). Then, the microarray probe expression profiles were re-annotated into the expression profiles of 1253 snRNAs though probe sequence mapping. In the training set, least absolute shrinkage and selection operator (LASSO) penalized generalized linear model was adopted to identify the 9-snRNA signature (RNU1-16P, RNU6-1031P, RNU6-258P, RNU6-335P, RNU6-485P, RNU6-549P, RNU6-98P, RNU6ATAC26P, and RNVU1-15), and a diagnostic score was calculated for each sample according to the snRNA expression levels and the model coefficients. The score demonstrated a good diagnostic ability for ASD in the training set (area under receiver operating characteristic curve (AUC) = 0.90), validation set (AUC = 0.87), and the overall (AUC = 0.88). Moreover, the blood samples of 23 ASD patients and 23 age- and gender-matched controls were collected as the external validation set, in which the signature also showed a good diagnostic ability for ASD (AUC = 0.88). In subgroup analysis, the signature was robust when considering the confounders of gender, age, and disease subtypes, and displayed a significantly better performance among the female and younger cases (P = .039; P = .002). In comparison with a 55-gene signature deriving from the same dataset, the snRNA signature showed a better diagnostic ability (AUC: 0.88 vs 0.80, P = .049). In conclusion, this study identified a novel and robust blood snRNA signature in diagnosing ASD, which might help improve the diagnostic accuracy for ASD in clinical practice. Nevertheless, a large-scale prospective study was needed to validate our results.

Nuclear calcium signatures are associated with root development

In plants, nuclear Ca2+ releases are essential to the establishment of nitrogen-fixing and phosphate-delivering arbuscular mycorrhizal endosymbioses. In the legume Medicago truncatula, these nuclear Ca2+ signals are generated by a complex of nuclear membrane-localised ion channels including the DOES NOT MAKE INFECTIONS 1 (DMI1) and the cyclic nucleotide-gated channels (CNGC) 15s. DMI1 and CNCG15s are conserved among land plants, suggesting roles for nuclear Ca2+ signalling that extend beyond symbioses. Here we show that nuclear Ca2+ signalling initiates in the nucleus of Arabidopsis root cells and that these signals are correlated with primary root development, including meristem development and auxin homeostasis. In addition, we demonstrate that altering genetically AtDMI1 is sufficient to modulate the nuclear Ca2+ signatures, and primary root development. This finding supports the postulate that stimulus-specific information can be encoded in the frequency and duration of a Ca2+ signal and thereby regulate cellular function.

Nuclear morphometrics and chromatin condensation patterns as disease biomarkers using a mobile microscope.

Current cancer diagnosis involves the use of nuclear morphology and chromatin condensation signatures for accurate advanced stage classification. While such diagnostic approaches rely on high resolution imaging of the cell nucleus using expensive microscopy systems, developing portable mobile microscopes to visualize nuclear and chromatin condensation patterns is desirable at clinical settings with limited infrastructure. In this study, we develop a portable fluorescent mobile microscope capable of acquiring high resolution images of the nucleus and chromatin. Using this we extracted nuclear morphometric and chromatin texture based features and were able to discriminate between normal and cancer cells with similar accuracy as wide-field fluorescence microscopy. We were also able to detect subtle changes in nuclear and chromatin features in cells subjected to compressive forces, cytoskeletal perturbations and cytokine stimulation, thereby highlighting the sensitivity of the portable microscope. Taken together, we present a versatile platform to exploit nuclear morphometrics and chromatin condensation features as physical biomarkers for point-of-care diagnostic solutions.

Molybdenum isotope compositions of uranium ore concentrates by double spike MC-ICP-MS

The molybdenum (Mo) isotope composition of uranium ore concentrate (UOC) has been proposed as a nuclear forensic signature due to the ubiquitous presence of Mo in the nuclear fuel cycle and to the possibility that different UOC production pathways lead to characteristic Mo isotope fractionation. Furthermore, Mo forms a volatile hexafluoride which leads to the retainment of Mo in the nuclear fuel cycle through U enrichment and reactor operation processes. As a result, it is possible that the nuclear fuel cycle generates a rich array of Mo isotope signatures. The first step in interpreting Mo isotope signatures generated during the nuclear fuel cycle is to characterize the Mo isotope composition of starting materials. In this study, a suite of UOC samples were analyzed for their Mo isotope composition in order to constrain the range of Mo isotope compositions entering the front end of the nuclear fuel cycle. Analytical protocols were developed to purify Mo from a U rich matrix prior to Mo isotope analysis by double spike MC-ICP-MS. A >3‰ variation in the 98Mo/95Mo ratio was observed in the suite of UOC samples with δ98Mo ranging from −1.15 to +1.96‰ relative to the NIST 3134 Mo standard reference material. The δ98Mo range observed in the UOC samples is very similar to the δ98Mo range observed in crustal igneous rocks and Mo-bearing minerals, suggesting that Mo isotope variability in UOC is driven by variability in the parent U ores. However, Mo isotope fractionation during UOC production is evident with one of the UOC samples being isotopically heavy relative to its parent U ore by 0.75‰, suggesting that different UOC production processes also contribute to the total Mo isotope variability observed. Overall, it is expected that the Mo isotope signatures generated during enrichment and reactor process will be clearly discernible from those generated during UOC production.

A Platform for Investigating Nuclear Organization and its Changes During Human iPSC Differentiation

The Allen Institute for Cell Science is developing a state space of stem cell structural signatures to understand the principles by which cells reorganize during the cell cycle and differentiation. We have developed a pipeline to generate high-replicate, dynamic image data on cell organization and activities using endogenous fluorescently tagged human induced pluripotent stem cells (hiPSCs) (the Allen Cell Collection at www.allencell.org). Each of the ∼25 lines express a monoallelic EGFP-tagged protein representing a cellular structure. For each structure, we take advantage of thousands of replicate high-resolution 3D images to develop quantitative image-based assays, segmentations, analyses, and computational models. We are initiating an analogous study of the nucleus, with a goal of creating a “state space of nuclear signatures.” We are endogenously tagging an initial set of eight key nuclear landmark proteins with EGFP and analyzing their sub-nuclear localization as the cells progress through the cell cycle and differentiate into cardiomyocytes. These landmarks include the nucleolus, nuclear lamina, nuclear pores, cohesin, CTCF, histones, and heterochromatin. We are also developing methods to quantify the change in localization patterns for these nuclear landmark proteins in the undifferentiated hiPSCs vs. cardiomyocytes derived from them. Preliminary image analyses, for example, reveal that H2B in cardiomyocytes displays less variation in both signal intensity and local spatial structure, generating a “smoother” protein distribution pattern within the nucleus and suggesting that our analysis approaches can detect changes in localization patterns of nuclear landmark proteins. We are also using single-cell RNAseq, FISH, and single-cell activity assays to conjoin gene expression with organization and phenotype. These cell lines and our analyses will further be integrated with genome-wide assays of chromatin architecture together with the 4D Nucleome Project and once fully characterized will be distributed publicly.

A reference material for evaluation of 137 Cs radiochronometric measurements.

A new nuclear forensic reference material has been characterized as a standard for radiochronometric determination of the model purification date for 137Cs sources. The purification date of a radioactive source is a potentially diagnostic nuclear forensic signature for determining the provenance of a radioactive material. Reference values have been measured for the attributes needed to use the 137Cs/137Ba chronometer: the molality (reported here as nmol g-1) of 137Cs and of the radiogenic portion of 137Ba in the material (hereafter referred to as 137Ba*). All measurement results were decay-corrected to represent the composition of the material on the reference date of July 7, 2011. The molality of 137Cs is (0.7915 ± 0.0073) nmol g-1; this value was calculated from the massic activity of 137Cs, (348.4 ± 3.0) kBq g-1, as measured in the NIST 4π-γ secondary standard ionization chamber (previously calibrated by 4π-(e+x)-γ-coincidence efficiency extrapolation counting) and the evaluated half-life of 137Cs, (30.05 ± 0.08) years. The molality of 137Ba*, (1.546 ± 0.024) nmol g-1, was measured by isotope dilution mass spectrometry using the measured relative proportion of 138Ba in the material to apply a correction for the 137Ba contribution from natural Ba. A model age of (47.04 ± 0.56) years, corresponding to a model purification date of June 22, 1964 with an expanded uncertainty of 200 days is calculated from the reference material values. This age is consistent with the date engraved on the capsule that contained the 137Cs starting material and with a prior independent determination of the model purification date. A full discussion of the uncertainties of the reference material values is included.

What’s that yellow powder? A nuclear forensic case study

In this paper the utilization of three analytical chemistry techniques including gamma spectrometry, XRF, and ICP-MS/OES is described for performing nuclear forensic analyses on an unknown powder. We have demonstrated that each method was unique in providing specific material characteristics, yet they were also complementary for extracting useful nuclear forensic signatures. It is the integral effort of all three analytical chemistry tools in the nuclear forensic tool box that ultimately allowed us to reveal the identity of the unknown nuclear material as Nb2O5 mixed with ~ 9% HEU.

The origin of the mid-infrared nuclear polarization of active galactic nuclei

We combine new (NGC 1275, NGC 4151, and NGC 5506) and previously published (Cygnus A, Mrk 231, and NGC 1068) sub-arcsecond resolution mid-infrared (MIR; 8-13 $\mu$m) imaging- and spectro-polarimetric observations of six Seyfert galaxies using CanariCam on the 10.4-m Gran Telescopio CANARIAS. These observations reveal a diverse set of physical processes responsible for the nuclear polarization, and permit characterization of the origin of the MIR nuclear polarimetric signature of active galactic nuclei (AGN). For all radio quiet objects, we found that the nuclear polarization is low (<1 per cent), and the degree of polarization is often a few per cent over extended regions of the host galaxy where we have sensitivity to detect such extended emission (i.e., NGC 1068 and NGC 4151). We suggest that the higher degree of polarization previously found in lower resolution data arises only on the larger-than-nuclear scales. Only the radio-loud Cygnus A exhibits significant nuclear polarization ($\sim$11 per cent), attributable to synchrotron emission from the pc-scale jet close to the core. We present polarization models that suggest that the MIR nuclear polarization for highly obscured objects arises from a self-absorbed MIR polarized clumpy torus and/or dichroism from the host galaxy, while for unabsorbed cores, MIR polarization arises from dust scattering in the torus and/or surrounding nuclear dust.

Evolutionary and demographic processes shaping geographic patterns of genetic diversity in a keystone species, the African forest elephant (Loxodonta cyclotis).

The past processes that have shaped geographic patterns of genetic diversity may be difficult to infer from current patterns. However, in species with sex differences in dispersal, differing phylogeographic patterns between mitochondrial (mt) and nuclear (nu) DNA may provide contrasting insights into past events. Forest elephants (Loxodonta cyclotis) were impacted by climate and habitat change during the Pleistocene, which likely shaped phylogeographic patterns in mitochondrial (mt) DNA that have persisted due to limited female dispersal. By contrast, the nuclear (nu) DNA phylogeography of forest elephants in Central Africa has not been determined. We therefore examined the population structure of Central African forest elephants by genotyping 94 individuals from six localities at 21 microsatellite loci. Between forest elephants in western and eastern Congolian forests, there was only modest genetic differentiation, a pattern highly discordant with that of mtDNA. Nuclear genetic patterns are consistent with isolation by distance. Alternatively, male‐mediated gene flow may have reduced the previous regional differentiation in Central Africa suggested by mtDNA patterns, which likely reflect forest fragmentation during the Pleistocene. In species like elephants, male‐mediated gene flow erases the nuclear genetic signatures of past climate and habitat changes, but these continue to persist as patterns in mtDNA because females do not disperse. Conservation implications of these results are discussed.

PGE2 mediates EGFR internalization and nuclear translocation via caveolin endocytosis promoting its transcriptional activity and proliferation in human NSCLC cells.

Prostaglandin E2 (PGE2) contributes to tumor progression by promoting cancer cell growth, invasion and by creating a favorable pro-tumor microenvironment. PGE2 has been reported to transactivate and internalize into the nucleus receptor tyrosine kinases such as Epidermal growth factor receptor (EGFR), thereby supporting tumor progression. Here we demonstrate that in non-small cell lung carcinoma (NSCLC) cells, PGE2 induces EGFR nuclear translocation via different dynamin-dependent endocytic pathways, promotes the formation of an EGFR-STAT3 complex, affects nuclear EGFR target gene expression and mediates tumor cell proliferation. Indeed, we find that PGE2 induces EGFR internalization and consequent nuclear import through Clathrin- and Caveolin-mediated endocytosis and through the interaction of EGFR with Importin β1. Within the nucleus, EGFR forms a complex with STAT3, an event blocked by ablation of Clathrin Heavy Chain or Caveolin-1. The combination of EGF and PGE2 prolongs nuclear EGFR transcriptional activity manifested by the upregulation of CCND1, PTGS2, MYC and NOS2 mRNA levels and potentiates nuclear EGFR-induced NSCLC cell proliferation. Additionally, NSCLC patients with high expression of a nuclear EGFR gene signature display shorter survival times than those with low expression, thus showing a putative correlation between nuclear EGFR and poor prognosis in NSCLC. Together, our findings indicate a complex mechanism underlying PGE2-induced EGF/EGFR signaling and transcriptional control, which plays a key role in cancer progression.

Seasonal Variability of Xe‐133 Global Atmospheric Background: Characterization and Implications for the International Monitoring System of the Comprehensive Nuclear‐Test‐Ban Treaty

AbstractGlobal simulations of the atmospheric dispersion of worldwide industrial Xe‐133 releases have revealed a large spatial and day‐to‐day variability of the resulting so‐called Xe‐133 atmospheric background. Most stations of the International Monitoring System (IMS) of the Comprehensive nuclear‐Test‐Ban Treaty Organization actually detect Xe‐133 regularly. Measured levels are explained by a varying combination of local and distant industrial sources and can interfere with discrimination of nuclear test signatures. Therefore, a better understanding of the Xe‐133 atmospheric background is needed. In this study, a validated 2 year simulation data set and a 4 year measurement data set of Xe‐133 activity concentrations have been analyzed in order to characterize possible seasonal variations of the Xe‐133 atmospheric background due to atmospheric circulation, with a focus on (i) global distributions, (ii) occurrences of detections by the IMS network, and (iii) time series of monthly averages at IMS stations. Results show a larger spatial extent of the atmospheric background during winter months, which translates into a larger number of detections on the IMS network during winter months for both hemispheres. Some IMS stations present a significant seasonal variability in terms of levels, or both in terms of levels and origins. However, not all IMS stations are subject to seasonal variations, given their location with respect to sources and large‐scale atmospheric circulation. In addition, a first set of predicted information about expected levels of atmospheric background at IMS stations not yet operational is provided, given the current knowledge of sources.

Development of a tagged source of Pb-206 nuclei

There is a particular class of unavoidable backgrounds that plague low-background experiments and rare event searches, particularly those searching for nuclear recoil event signatures: decaying daughters of the 238U nuclear decay chain, which result from radon plate-out on detector materials. One such daughter isotope, 210Po, undergoes α-decay and produces a recoiling 103 keV 206Pb nucleus. To characterize this important background in the context of noble element detectors, we have implemented a triggered source for these 206Pb recoils in a dual-phase xenon time projection chamber (Xe TPC) within the Davis Xenon R&D testbed system (DAX). By adhering 210Po to the surface of a PIN diode and electrically floating the diode on the cathode of the TPC, we tag the α signals produced in the PIN diode and trigger on the correlated nuclear recoils in the liquid xenon (LXe). We discuss our methods for 210Po deposition, electronic readout of the PIN diode signals at high voltage, and analysis methods for event selection.

Identification of the maze in the conformational landscape of fenchol.

The rotational spectrum of the bicyclic molecule fenchol (C10H18O, 1,3,3-trimethylbicyclo[2.2.1]heptan-2-ol) - a biogenic volatile organic compound - was recorded in the gas phase using an impulse Fourier transform microwave spectrometer coupled to a supersonic jet expansion over the 2-20 GHz range. Quantum chemical calculations were performed to characterize the conformational landscape of the two diastereoisomers, endo-fenchol and exo-fenchol, with respect to the orientation of the hydroxyl group. The three most stable structures for each diastereoisomer were optimized at the MP2/6-311++G(2df,p) level of theory. Two of them were found to be very close in energy. Molecular parameters obtained from the analysis of observed signals led to the observation of one conformer per diastereoisomer. For the endo-fenchol molecule the rs geometry associated with the hydroxyl group was obtained, from the observation and analysis of the rotational spectra associated with the deuterated hydroxyl group. The nuclear quadrupolar hyperfine signature was identified. The hydroxyl group was found to be oriented into the direction of the methyl groups attached to C3, for the more stable conformer of endo-fenchol. For exo-fenchol, it is oriented into the methyl group attached to C1.