Two effects relevant for the study of astrophysical reaction rates: gamma transitions in capture reactions and Coulomb suppression of the stellar enhancement

Nucleosynthesis processes involve reactions on several thousand nuclei, both close to and far off stability. The preparation of reaction rates to be used in astrophysical investigations requires experimental and theoretical input. In this context, two interesting aspects are discussed: (i) the relevant gamma transition energies in astrophysical capture reactions, and (ii) the newly discovered Coulomb suppression of the stellar enhancement factor. The latter makes a number of reactions with negative Q value more favorable for experimental investigation than their inverse reactions, contrary to common belief.Comment: 5 pages, 5 figures, to appear in the proceedings of CGS 13 (Int. Conf. Capture Gamma Ray Spectroscopy and Related Topics

Symmetries at and Near Critical Points of Quantum Phase Transitions in Nuclei

We examine several types of symmetries which are relevant to quantum phase transitions in nuclei. These include: critical-point, quasidynamical, and partial dynamical symmetries.Comment: 5 pages, 4 figures, Proc. 13th Int. Conf. on "Capture Gamma-Ray Spectroscopy and Related Topics", August 25-29, 2008, Cologne, German

Quantum phase transitions in rotating nuclei

We extend the classical Landau theory for rotating nuclei and show that the backbending in 162Yb, that comes about as a result of the two-quasiparticle alignment, is identified with the second order phase transition. We found that the backbending in 156Dy, caused by the instability of $\gamma$-vibrations in the rotating frame, corresponds to the first order phase transition.Comment: 4 pages, 2 figure

Two non-destructive neutron inspection techniques: prompt gamma-ray activation analysis and cold neutron tomography

Deux techniques d’inspection non-destructives utilisant des faisceaux de neutrons froids ont été développées à la source de neutrons SINQ de l’Institut Paul Scherrer : (1) l’analyse par activation neutronique prompte (PGAA) et (2) la tomographie neutronique. L’analyse par PGA (Prompt Gamma-ray Activation) est une méthode nucléaire qui permet de déterminer la concentration d’éléments présents dans un échantillon. Cette technique consiste à détecter les rayons gamma prompts émis par l’échantillon suite à des réactions de captures neutroniques. L’installation PGA à SINQ a été conçue, construite et testée par le prof. J. Kern et la Dr. M. Crittin. Cette thèse propose une nouvelle approche analytique, nommée la standardisation du k0, qui permet d’obtenir une meilleure précision dans la détermination des concentrations. Cette méthode a été utilisée tout d’abord pour mesurer la quantité de bore dans des solutions aqueuses. Puis, la mesure de matériaux de référence a prouvé la validité de la méthode pour des analyses multiélémentaires. Finalement, divers échantillons provenant de domaines très variés tels que l’archéologie, la géologie, la médecine, l’industrie nucléaire et la science des matériaux, ont été étudiés avec cette technique. Le PGAA s’est révélé particulièrement important pour l’analyse de l’hydrogène et du bore qui sont difficilement mesurables avec d’autres techniques. En outre, une lentille à neutrons a permis de déterminer la distribution bidimensionnelle d’éléments dans un échantillon provenant d’un réacteur naturel. La première partie de cette thèse décrit la technique et les résultats de l’analyse par PGA. Une installation de tomographie utilisant des neutrons froids a été développée en collaboration avec l’Université de Gand (Belgique) sur la même ligne de faisceau que le système PGA, les deux instruments étant utilisés de façon alternée. La tomographie neutronique est semblable à la tomographie par rayons X, laquelle est couramment utilisée dans les sciences médicales et l’industrie. Comme celle-ci, elle fournit des informations tridimensionnelles sur la structure des échantillons. Cependant, comme les processus d’interaction des neutrons et des rayons X avec la matière sont différents, les informations fournies sont complémentaires. Contrairement aux rayons X, les neutrons pénètrent facilement la plupart des métaux, ce qui permet d’améliorer le contraste des éléments légers. Par ailleurs, les neutrons froids rendent possible l’étude de matériaux métalliques encore plus denses. L’installation comprenait une table de rotation et un détecteur, lequel était composé d’un scintillateur et d’une caméra CCD. La résolution, qui était limitée par la divergence du guide de neutrons (L/D = 70), était d’environ 0.24 mm dans des conditions optimales. En outre, un dispositif permettant de sélectionner la vitesse des neutrons a été utilisé pour des expériences de radiographie et de tomographie nécessitant des faisceaux monochromatiques. Finalement, différentes études ont porté sur des objets provenant de la géologie, l’archéologie, la médecine dentaire, l’industrie nucléaire et l’aérospatiale. Cette technique et ses résultats font l’objet de la deuxième partie de cette thèse.Two non-destructive inspection techniques employing both cold neutron beams have been developed at the Swiss spallation source SINQ of the Paul Scherrer Institute: (1) prompt gamma-ray activation analysis (PGAA) and (2) neutron tomography. PGAA is a nuclear analytical method for identifying and quantifying simultaneously the elements contained in a sample. The technique consists in detecting capture gamma rays emitted by the target material during neutron irradiation. The PGA facility at SINQ was designed, constructed, and tested by Prof. J. Kern and Dr. M. Crittin. In the present work, a new analytical approach, namely the k0- standardization, has been studied and applied to obtain higher accuracies in the determination of element concentrations. First, this method has been applied successfully for quantitative determination of boron in aqueous solutions. Then, standard reference materials were analyzed to assess the accuracy of the method for multielement determination. Finally, the technique was applied to various samples from archeology, geology, medicine, nuclear industry and material science. Of particular interest was the concentration determination of hydrogen and boron, two elements that are difficult to measure with other techniques. Besides, a neutron focusing capillary lens was used to measure element concentrations in two-dimensional array across the surface of a bulky sample from a natural reactor. A description of the PGAA technique and of some results is presented in the first part of this thesis. A new cold neutron tomography set-up was developed at SINQ in collaboration with the University of Ghent (Belgium) with the objective to complement the existing thermal neutron radiography station. The new device was set up at the same beam line as the PGA instrument so that the two facilities were employed alternately. Neutron tomography is similar to X-ray tomography, which is widely used in medicine and industry. It provides three-dimensional information on the inner structure of a sample. As a result of the differences between neutron and X-ray interaction mechanisms, complementary information is provided by the two techniques. Unlike X-rays, neutrons have the prominent ability to penetrate most metals easily while delivering a high contrast for many light elements. Besides, if cold neutrons are used, thicker sections of metallic materials can be inspected. The whole tomography system consisted of a rotation table and an imaging device, which was based on a scintillator converting the neutron beam to a light image viewed with a CCD camera. The achievable resolution was limited by the inherent divergence of the neutron guide (L/D = 70) and was about 0.24 mm under optimal conditions. Furthermore, a neutron velocity selector was used to perform radiography and tomography experiments with monochromatic neutron beams. Finally, examinations were performed on objects covering a broad range of application fields, such as geology, dentistry, archeology, nuclear industry and aerospatial industry. A detailed presentation of the cold neutron tomography set-up and some results obtained with this technique are given in the second part of this thesis

The 85$Rb(p,n)85Sr reaction and the modified proton optical potential

The cross sections of the astrophysically relevant 85$Rb(p,n)85Srg,m reaction have been measured between Ec.m. = 2.16 and 3.96 MeV. The cross sections have been derived by measuring the gamma radiation following the beta decay of the reaction products. A comparison with the predictions of Hauser-Feshbach calculations using the NON-SMOKER code confirms a recently derived modification of the global optical proton potential.Comment: CGS XIII conferenc

Evolution of spectral properties along the O(6)-U(5) transition in the interacting boson model. I. Level dynamics

We investigate the evolution of quantal spectra and the corresponding wave functions along the [O(6)-U(5)]$\supset$O(5) transition of the interacting boson model. The model is integrable in this regime and its ground state passes through a second-order structural phase transition. We show that the whole spectrum as a function of the Hamiltonian control parameter, as well as structures of all excited states, exhibit rather organized and correlated behaviors, that provide deeper insight into the nature of this transitional path.Comment: 10 pages, 8 figure

New supersymmetric quartet of nuclei: 192Os, 193Os, 193Ir, 194Ir

We present evidence of the existence of a new supersymmetric quartet of nuclei in the A=190 mass region. The analysis is based on new experimental information on the odd-odd nucleus 194Ir from transfer and capture reactions. The new data allow the identification of a new supersymmetric quartet, consisting of the 192,193Os and 193,194Ir nuclei. We make explicit predictions fo r193Os, and suggest that its spectroscopic properties be measured in dedicated experiments. Finally, we study correlations between different transfer reactions.Comment: 5 pages, 2 figures, invited talk at CGS 13, Cologne, Germany, to be published in AIP Conference Proceeding

Patient Perspectives of the Doctor-at-Home Service

Introduction. Home health care has been established as an effective model for reducing mortality in the elderly. The Doctor-at-Home Service at the Community Health Centers of Burlington (CHCB) has offered home health care to Burlington residents since January 2015. Dr. Karen Sokol, MD, alone provides care to 176 patients at their homes, including at-home palliative care. CHCB hope to expand this program by hiring more providers. Objective. To understand the impact of the Doctor-at-Home Service from the pa- tients’ perspective. Methods. A survey was administered to a cohort of eighteen patients over an 8- week period and addressed topics such as barriers to healthcare, benefits, and costs associated with doctor-at-home programs. A theme analysis on the responses was then conducted to reflect patient opinions. Available summary data describing the pa- tient population was also analyzed. Results. The Doctor- at- Home program serves patients ranging from 26 to 100 years old, with the majority of the patient population comprised of senior citizens. Prior to at home care, patients faced barriers such as lack of transportation, negative past experi- ences, anxiety, and distance from relatives. Four main themes from patient responses were physician-patient relationship, convenience, quality of care, and environment of care. Discussion. Evidence is compelling that there is a desire and need for an exten- sion of the Doctor-at-Home program to reach additional patients. Doctor-at-Home pro- grams could eliminate identified barriers and provide quality care to patients, especially those with specific barriers to access.https://scholarworks.uvm.edu/comphp_gallery/1256/thumbnail.jp

Evolution of spectral properties along the O(6)-U(5) transition in the interacting boson model. II. Classical trajectories

This article continues our previous study of level dynamics in the [O(6)-U(5)]$\supset$O(5) transition of the interacting boson model [nucl-th/0504016] using the semiclassical theory of spectral fluctuations. We find classical monodromy, related to a singular bundle of orbits with infinite period at energy E=0, and bifurcations of numerous periodic orbits for E>0. The spectrum of allowed ratios of periods associated with beta- and gamma-vibrations exhibits an abrupt change around zero energy. These findings explain anomalous bunching of quantum states in the E$\approx$0 region, which is responsible for the redistribution of levels between O(6) and U(5) multiplets.Comment: 11 pages, 7 figures; continuation of nucl-th/050401