Mass Measurements of Neutron-Deficient Yb Isotopes and Nuclear Structure at the Extreme Proton-Rich Side of the N=82 Shell

International audienceHigh-accuracy mass measurements of neutron-deficient Yb isotopes have been performed at TRIUMF using TITAN’s multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS). For the first time, an MR-TOF-MS was used on line simultaneously as an isobar separator and as a mass spectrometer, extending the measurements to two isotopes further away from stability than otherwise possible. The ground state masses of Yb150,153 and the excitation energy of Ybm151 were measured for the first time. As a result, the persistence of the N=82 shell with almost unmodified shell gap energies is established up to the proton drip line. Furthermore, the puzzling systematics of the h11/2-excited isomeric states of the N=81 isotones are unraveled using state-of-the-art mean field calculation

Approche stochastique du problème du pouvoir prédictif dans la modélisation du champ moyen

Results of our study of the theoretical modelling capacities focussing on the nuclear phenomenological mean-field approaches are presented. It is expected that a realistic theory should be capable of predicting satisfactorily the results of the experiments to come, i.e., having what is called a good predictive power. To study the predictive power of a theoretical model, we had to take into account not only the errors of the experimental data but also the uncertainties originating from approximations of the theoretical formalism and the existence of parametric correlations. One of the central techniques in the parameter adjustment is the solution of what is called the Inverse Problem. Parametric correlations usually induce ill-posedness of the inverse problem; they need to be studied and the model regularised. We have tested two types of realistic phenomenological Hamiltonians showing how to eliminate the parametric correlations theoretically and in practice. We calculate the level confidence intervals, the uncertainty distributions of model predictions and have shown how to improve theory’s prediction capacities and stability.Les résultats de notre étude des capacités de modélisation théorique axées sur les approches phénoménologiques nucléaires dans le cadre de la théorie du champ-moyen sont présentés. On s’attend à ce qu’une théorie réaliste soit capable de prédire de manière satisfaisante les résultats des expériences à venir, c’est-à-dire avoir ce qu’on appelle un bon pouvoir prédictif. Pour étudier le pouvoir prédictif d’un modèle théorique, nous avons dû tenir compte non seulement des erreurs des données expérimentales, mais aussi des incertitudes issues des approximations du formalisme théorique et de l’existence de corrélations paramétriques. L’une des techniques centrales dans l’ajustement des paramètres est la solution de ce qu’on appelle le Problème Inverse. Les corrélations paramétriques induisent généralement un problème inverse mal-posé; elles doivent être étudiées et le modèle doit être régularisé. Nous avons testé deux types de hamiltoniens phénoménologiques réalistes montrant comment éliminer théoriquement et en pratique les corrélations paramétriques.Nous calculons les intervalles de confiance de niveau, les distributions d’incertitude des prédictions des modèles et nous avons montré comment améliorer les capacités de prédiction et la stabilité de la théorie

From exotic mean-field symmetries to new classes of isomers in atomic nuclei

International audienceIn this article, we address the occurrence and properties of exotic point-group symmetries in nuclei. We focus on the relations between the specific gap openings in the single-nucleon spectra, which represent a measure of nuclear stability studied with the help of the nuclear mean-field theory and accompanying octupole shape properties manifesting the link between the particular stability configurations (magic octupole gaps) and resulting exotic geometrical forms. We employ a realistic phenomenological realisation of the nuclear mean-field theory with the so-called universal Woods–Saxon Hamiltonian and the group representation theory to formulate the experimental identification criteria of the addressed symmetries. We use the newest parameterisations of the Hamiltonian obtained employing the inverse problem theory. To stabilise the modelling predictions, we detect and eliminate parametric correlations. Following earlier articles introducing the octupole “fourfold magic numbers” and “universal magic numbers”, $N=136 {\text{ and }} 198$, examined in the heavy and super-heavy nuclei, we generalise these concepts for the whole mass table for the octupole magic chain $N=32, 40, 56, 64, 70, 90, 112, 136, 198$. They bring in the so-called high-rank tetrahedral and octahedral point groups strengthening the specific shell effects and gap openings and implying the unique hindrance factors: at the exact tetrahedral symmetry limit, the collective electric quadrupole and dipole reduced transition probabilities vanish provoking new isomerism. Under these circumstances, many rotational states which in other nuclei manifest strong decay probabilities, in the high-rank symmetry case become isomeric—forming a new class of nuclear high-rank symmetry isomers. The consequences for the future experimental studies of those isomers are discussed especially in the domain of exotic nuclei

ABOUT COMPETITION BETWEEN TETRAHEDRAL AND OCTAHEDRAL SYMMETRIES IN ATOMIC NUCLEI *

International audienceFollowing a recent discovery of the simultaneous signs of the octahedral and tetrahedral symmetries in 152 Sm, we discuss the issue of a competition between the two symmetries in atomic nuclei together with the identification criteria. Illustrations using selected rare-earth and zirconium nuclei as examples are presented

Shortening the Way to Experimental Evidence for High-rank Symmetries in Atomic Nuclei: Researcher Instructions

International audienceWe discuss criteria for experimental identification of the nuclear tetrahedral and octahedral so-called high-rank symmetries based on the meanfield and group representation theories. We examine the possibly largestsearch zones on the (Z;N)-plane: in addition to traditionally discussed areas of even–even nuclei with proton and neutron numbers surrounding the tetrahedral magic ones (Zt0 ;Nt 0 = 32, 40, 56, 64, 70, 90, 112, 136), we discuss also the odd–even and even–odd nuclei for which the identification criteria non-trivially differ from those for the even–even ones. We also propose the appropriately chosen particle–hole excited states to profit from the deformation driving mechanism contributed by combinations of certain orbitals. The discussion is summarised in the form of a series of‘user’ instructions

Systematic Search For Evidence of Tetrahedral and Octahedral Symmetries in Subatomic Physics: Follow-up of the First Identification Case in 152Sm

In a recent article [1] group-theory representation-methods have been combined with the realistic mean-field calculation results to elaborate new, specifically designed methods of experimental identification of the tetrahedral/octahedral symmetries in atomic nuclei. The authors demonstrated that experimental data on 152 Sm existing in the literature are fully compatible with the extremely restrictive group-theory criteria of simultaneous presence of tetrahedral and octahedral symmetries, thus identifying these symmetries in subatomic physics for the first time. We discuss theory predictions related to the systematic presence of these symmetries as well as their manifestations throughout the Periodic Table in the form of islands centred around the doublymagic tetrahedral-symmetry nuclei. The corresponding theory predictions are discussed in the context of the planned new experiments, which would employ the advanced mass-spectrometry methods [2], in view of the new experimental search criteria [1]. The addressed field of symmetry-research presents particularly promising potentialities in the domain of exotic nuclei studies. Indeed, as it can be demonstrated, in the exact tetrahedral and/or octahedral symmetry limits the corresponding nuclei emit neither E2 nor E1 radiation generating isomeric states with lifetimes which can become much longer than those of the related ground states. This is expected to open the new research strategies for the whole domain of the exotic nuclei studies throughout the Periodic Table

Systematic Search For Evidence of Tetrahedral and Octahedral Symmetries in Subatomic Physics: Follow-up of the First Identification Case in 152^{152}Sm

International audienceIn a recent article [1] group-theory representation-methods have been combined with the realistic mean-field calculation results to elaborate new, specifically designed methods of experimental identification of the tetrahedral/octahedral symmetries in atomic nuclei. The authors demonstrated that experimental data on 152 Sm existing in the literature are fully compatible with the extremely restrictive group-theory criteria of simultaneous presence of tetrahedral and octahedral symmetries, thus identifying these symmetries in subatomic physics for the first time. We discuss theory predictions related to the systematic presence of these symmetries as well as their manifestations throughout the Periodic Table in the form of islands centred around the doublymagic tetrahedral-symmetry nuclei.The corresponding theory predictions are discussed in the context of the planned new experiments, which would employ the advanced mass-spectrometry methods [2], in view of the new experimental search criteria [1]. The addressed field of symmetry-research presents particularly promising potentialities in the domain of exotic nuclei studies. Indeed, as it can be demonstrated, in the exact tetrahedral and/or octahedral symmetry limits the corresponding nuclei emit neither E2 nor E1 radiation generating isomeric states with lifetimes which can become much longer than those of the related ground states. This is expected to open the new research strategies for the whole domain of the exotic nuclei studies throughout the Periodic Table.Key words: Nuclear structure / Nuclear Platonic symmetries / Exotic nuclei / Shape isomer

Feasibility of F-FDG Dose Reductions in Breast Cancer PET/MRI

The goal of this study was to determine the level of clinically acceptable F-fluoro-2-deoxy-D-glucose (F-FDG) dose reduction in time of flight (TOF) - positron emission tomography/magnetic resonance imaging (PET/MRI) in patients with breast cancer. Twenty-six consecutive female patients with histologically proven breast cancer were analyzed (median age, 51 years; range, 34 - 83 years). Simulated dose-reduced PET images were generated by un-listing the list mode data on PET/MRI. The acquired 20 minutes PET frame was reconstructed in 5 ways: a reconstruction of the first 2 minutes with 3 iterations and 28 subsets for reference, and reconstructions simulating 100%, 20%, 10%, 5% of the original dose. General image quality and artifacts (GIQ+A), image sharpness (IS), noise (N), and lesion detectability (LD) were analyzed using a four-point scale. Qualitative parameters were compared by using the non-parametric Friedman test for multiple samples and the Wilcoxon signed-rank test for paired samples. Comparison of different groups of independent samples was performed using the Mann-Whitney-U-Test. Overall, 355 lesions (71 lesions with five different reconstructions each) were evaluted. The 20 minutes reconstruction with 100% injected dose showed the best results in all categories. In GIQ+A, IS and N the reconstructions with a simulated dose of 20% and 10% were significantly better than the 2 minutes reconstructions (p<=0.001). Furthermore, 20%, 10%, and 5% reconstructions did not yield different results compared to the 2 minutes reconstruction in LD of the primary lesion. Using 10% of the injected dose a calculated mean dose of 22.6 +/- 5.5 MBq (range 17.9 - 36.9 MBq) would have been applied, resulting in an estimated whole-body radiation burden of 0.5 +/- 0.1 mSv (range 0.4 - 0.7 mSv). 10% of the standard dose of F-FDG (reduction of up to 90%) results in clinically acceptable PET-image quality in TOF PET/MRI. The calculated radiation exposure would be comparable to the effective dose of a single digital mammography. A reduction of radiation burden to this level might justify partial-body examinations with PET/MRI for dedicated indications

Isomer studies in the vicinity of the doubly-magic nucleus Sn-100: Observation of a new low-lying isomeric state in Ag-97

Long-lived isomeric states in Ag-97 and In101-109 were investigated with the FRS Ion Catcher at GSI. In the isotope Ag-97, a long-lived (1/2(-)) isomeric state was discovered, and its excitation energy was determined to be 618(38) keV. This is simultaneously the first discovery of a nuclear isomeric state by multiple-reflection time-of-flight mass spectrometry. The measured excitation energies were compared to large-scale shell-model calculations, which indicated the importance of core excitation around Sn-100. Furthermore, advanced mean-field calculations for the Ag-97 nucleus and relevant neighboring nuclei were performed, which have contributed to a better understanding of the repetitive appearance of certain isomeric structures in neighboring nuclei, and which have supported the discovery of the isomeric state in Ag-97 in a global shell-evolution scheme. (C) 2020 The Author(s). Published by Elsevier B.V

Ethical considerations in global HIV phylogenetic research

Phylogenetic analysis of pathogens is an increasingly powerful way to reduce the spread of epidemics, including HIV. As a result, phylogenetic approaches are becoming embedded in public health and research programmes, as well as outbreak responses, presenting unique ethical, legal, and social issues that are not adequately addressed by existing bioethics literature. We formed a multidisciplinary working group to explore the ethical issues arising from the design of, conduct in, and use of results from HIV phylogenetic studies, and to propose recommendations to minimise the associated risks to both individuals and groups. We identified eight key ethical domains, within which we highlighted factors that make HIV phylogenetic research unique. In this Review, we endeavoured to provide a framework to assist researchers, public health practitioners, and funding institutions to ensure that HIV phylogenetic studies are designed, done, and disseminated in an ethical manner. Our conclusions also have broader relevance for pathogen phylogenetics