Investigation of the Hoyle state in 12C and the related triple alpha reaction rate

The fusion of three alpha particles to form the excited Hoyle state in ¹²C, and subsequent electromagnetic decay to the ground state, is the only known pathway to synthesis of stable carbon in the Universe. This process takes place in red giant stars, in which the helium density and temperature are su ciently high for three α particles to fuse. The Hoyle state is located energetically above the ⁸Be + α and 3α energies, which makes it a resonance for the triple-α process, and thus greatly enhances the production of carbon. This also means that the Hoyle state is unstable to α breakup, and consequently, the probability that the Hoyle state decays electromagnetically to a stable con guration of ¹²C is very small, only about 0.04%. After over 60 years of research, the electromagnetic branching ratio is only known with 10% accuracy, and the adopted value mainly relies on measurements from the 1960-70s. The rate of the triple-α process depends directly on the tiny radiative decay branch of the Hoyle state, and it is imperative for astrophysical modeling to reduce its uncertainty. The present work focuses on a series of pair conversion measurements of transitions from the two first excited states in ¹²C, populated by the (p; p') reaction at 10.5 MeV beam energy. The measurements were carried out with the Super-e spectrometer at the Australian National University, where the beam was delivered by the 14UD tandem accelerator. The experiments were conducted with aim to deduce an accurate value on the radiative width of the Hoyle state, by a novel method. Another goal was to deduce a new, improved value on the partial E0 decay branching ratio. Two new values on the radiative width, based on new and averaged measurements, are discussed, and a new value on the E0 branching ratio is recommended. The values are Γrad = 2:29(24) meV, Γrad = 3:27(57) meV, and Γ(E0)/Γ = 7:19(37)*10⁶, respectively. In order to have confidence in the measurements, a great deal of work was put into characterization of the spectrometer transmission and detection efficiency. A part of this characterization involved the analysis of conversion electron and internal pair spectra of transitions in ⁵⁴Fe, which has a clean energy spectrum that includes a strong E0 transition. Besides being a test case, the experiment is also part of a campaign to obtain high precision spectroscopy data on excited 0+ states and E0 transitions in the N ≈ Z ≈ 28 region of the nuclear chart. Shape co-existence and collective vibrations in the vicinity of the Z = N = 28 closed shells are continuously challenging our basic understanding of the nuclear structure, and experimental data are essential. As physics results emerged from the data, a more comprehensive analysis became a part of this thesis. Two deformed band structures, built on the 0+2 and 2+2 levels, were identfi ed, and properties of the 0+3 state were deduced

African migrant christianities - Delocalization or relocalization of identities? Kap. 11

I: Lauterbach, K., & Vähäkangas, M. (Eds.). (2020). Faith in African Lived Christianity: Bridging Anthropological and Theological Perspectives.African migrant Christianity is a field that has been attracting increased academic interest in recent decades. Numerous studies within anthropology and theology have discussed the topic in general and activities connected with it in different countries in particular. In addition, the theme has been studied as a transnational field where the relationship between the soil of the ancestors and the new homeland has been brought to the fore. This chapter highlights two particular aspects of epistemological and ontological interest in order to address the question of how anthropology and theology can come into dialogue: firstly, through analysis of how technology influences human behavior, permits simultaneity, and affects Christian discursive practices in transnational and transcultural relations; secondly, by looking at how migration and the new media affect identity construction for the individual believer. The chapter will start by highlighting some of the globalizing processes that have influenced the development of various African Christianities and, in particular, the activities of the Nigerian-based Redeemed Christian Church of God (rccg) in Norway. Of special interest is how technological media and new forms of communication – in particular through the Internet and social media – generate simultaneity in religious practices and facilitate the development of congregations across long distances. The second section of the chapter deals with the relationship between migration, identity construction, and religion, focusing in particular on theories of identity construction linked to religious practices in diaspora churches. Towards the end of the chapter recent developments among African transnational churches are discussed within the framework of technology and forms of identity-making. How do technological innovations influence the individual, and how do questions of technology and migration affect theology, understood as religious discursive practices? Does the intensified use of the Internet and social media favor theories of delocalized identities, or could it be argued that it leads to a relocalization of identities through transnational Pentecostal networks?publishedVersio

Improvisert samvirke. Den Norske Redningstjeneste og Forsvaret

Masteroppgave i samfunnssikkerhet og kriseledelse - Universitetet i Nordland, 201

Pygmy resonance and low-energy enhancement in the γ\gamma-ray strength functions of Pd~isotopes

An unexpected enhancement in the $\gamma$-ray strength function, as compared to the low energy tail of the Giant Dipole Resonance (GDR), has been observed for Sc, Ti, V, Fe and Mo isotopes for $E_\gamma<4$ MeV. This enhancement was not observed in subsequent analyses on Sn isotopes, but a Pygmy Dipole Resonance (PDR) centered at $E_\gamma\approx8$ MeV was however detected. The $\gamma$-ray strength functions measured for Cd isotopes exhibit both features over the range of isotopes, with the low-energy enhancement decreasing- and PDR strength increasing as a function of neutron number. This suggests a transitional region for the onset of low-energy enhancement, and also that the PDR strength depends on the number of neutrons. The $\gamma$-ray strength functions of $^{105-108}$Pd have been measured in order to further explore the proposed transitional region. Experimental data were obtained at the Oslo Cyclotron Laboratory by using the charged particle reactions ($^{3}$He, $^{3}$He$^{\prime}\gamma$) and ($^{3}$He, $\alpha$$\gamma$) on $^{106,108}$Pd target foils. Particle$-\gamma$ coincidence measurements provided information on initial excitation energies and the corresponding $\gamma$-ray spectra, which were used to extract the level densities and $\gamma$-ray strength functions according to the Oslo method. The $\gamma$-ray strength functions indicate a sudden increase in magnitude for $E_{\gamma}>4$ MeV, which is interpreted as a PDR centered at $E_{\gamma}\approx8$ MeV. An enhanced $\gamma$-ray strength at low energies is also observed for $^{105}$Pd, which is the lightest isotope measured in this work. Further, the results correspond and agree very well with the observations from the Cd isotopes, and support the suggested transitional region for the onset of low-energy enhancement with decreasing mass number. The neutron number dependency of the PDR strength is also evident

Perturbed angular distributions with LaBr3 detectors: The g factor of the first 10+ state in Cd 110 reexamined

The time differential perturbed angular distribution technique with LaBr3 detectors has been applied to the Iπ = 11-/2 isomeric state (Ex=846 keV, τ=107 ns) in 107Cd, which was populated and recoil-implanted into a gadolinium host following the 98Mo(^12C, 3n)^107Cd reaction. The static hyperfine field strength of Cd recoil implanted into gadolinium was thus measured, together with the fraction of nuclei implanted into field-free sites, under similar conditions as pertained for a previous implantation perturbed angular distribution g-factor measurement on the Iπ=10+ state in 110Cd. The 110Cdg(10+) value was thereby reevaluated, bringing it into agreement with the value expected for a seniority-two vh11/2 configuration.This research was supported in part by the Australian Research Council Grants No. DP120101417, No. DP130104176, No. DP140102986, No. DP140103317, No. DP170101673, No. LE150100064, and No. FT100100991, and by The Australian National University Major Equipment Committee Grant No. 15MEC14

137,138,139^{137,138,139}La(nn, γ\gamma) cross sections constrained with statistical decay properties of 138,139,140^{138,139,140}La nuclei

The nuclear level densities and $\gamma$-ray strength functions of $^{138,139,140}$La were measured using the $^{139}$La($^{3}$He, $\alpha$), $^{139}$La($^{3}$He, $^{3}$He$^\prime$) and $^{139}$La(d, p) reactions. The particle-$\gamma$ coincidences were recorded with the silicon particle telescope (SiRi) and NaI(Tl) (CACTUS) arrays. In the context of these experimental results, the low-energy enhancement in the A$\sim$140 region is discussed. The $^{137,138,139}$La($n, \gamma)$ cross sections were calculated at $s$- and $p$-process temperatures using the experimentally measured nuclear level densities and $\gamma$-ray strength functions. Good agreement is found between $^{139}$La($n, \gamma)$ calculated cross sections and previous measurements

Test of the generalized Brink-Axel hypothesis in ⁶⁴ ⁶⁵Ni

Previously published particle-γ coincidence data on the 64Ni(p,p′γ) 64Ni and 64Ni(dpγ)65Ni reactions were further analyzed to study the statistical properties of γ decay in64, 65Ni. To do so, the γ-decay to the quasicontinuum region and discrete low-lying states was investigated at γ -ray energies of 2.0–9.6 and 1.6–6.1 MeV in 64 Ni and 65 Ni, respectively. In particular, the dependence of the γ-strength function with initial and final excitation energy was studied to test the validity of the generalized Brink-Axel hypothesis. Finally, the role of fluctuations in transition strengths was estimated as a function of γ-ray and excitation energy. The γ-strength function is consistent with the hypothesis of the independence of initial excitation energy, in accordance with the generalized Brink-Axel hypothesis. The results show that the γdecay to low-lying levels displays large fluctuations for low initial excitation energies.We are also grateful for the financial support received from the Research Council of Norway (NFR). S.S. and G.M.T. acknowledge funding under NFR project Grants No. 210007 and No. 262952/F20. A.C.L. acknowledges financial support from the ERC-STG2014 under Grant No. 637686

Evidence for shape coexistence in 52Cr through conversion-electron and pairconversion spectroscopy

Electric monopole (E0) transitions are a highly sensitive probe of the charge distribution of an atomic nucleus. A large E0 transition strength (ρ2(E0)) is a clear indicator of nuclear shape coexistence. In the region between doubly magic 40Ca and 56Ni, E0 transitions have never been observed in the Ti or Cr isotopes, nor in the heavier iron isotopes (56,58Fe). We have performed the first measurements of the E0 transitions in 52Cr via conversion-electron and pair-conversion spectroscopy using the Super-e spectrometer at the Australian National University Heavy Ion Accelerator Facility. We present the first spectra obtained for 52Cr, including the first observation of the E0 transition from the first-excited 0+ state in 52Cr, in both electron-positron pairs and conversion-electron spectroscopy. The preliminary values for the E0 strength in the 1531keV 2+ → 2+ transition in 52Cr is ρ2(E0) � 103 = 470(190), and for the 1728-keV 23+ → 21+ transition, it is ρ2(E0) 103 = 1800(1200). The large E0 strengths observed are consistent with shape coexistence in this region. However, despite the relatively precise observation of the conversion-electron and electron-positron pair intensities, the E0 strengths have large uncertainties. More precise determinations of relevant spectroscopic quantities, such as the state lifetimes and transition mixing ratios for mixed M1 + E2 transitions, are needed to determine the E0 strength more precisely.This research was supported in part by the Australian Research Council grant numbers DP140102986 and DP170101673, and was partially supported by the International Joint Research Promotion Program of Osaka University and JSPS KAKENHI Grant Number JP17H02893. This work is also based on the research supported partly by National Research Foundation of South Africa (118645, 90741). J.T.H.D., A.A., B.J.C., M.S.M.G., T.J.G., B.P.M., and B.P.E.T. acknowledge support of the Australian Government Research Training Program. Support for the ANU Heavy Ion Accelerator Facility operations through the Australian National Collaborative Research Infrastructure Strategy program is acknowledged