The Status and Future of Direct Nuclear Reaction Measurements for Stellar Burning

The study of stellar burning began just over 100 years ago. Nonetheless, we do not yet have a detailed picture of the nucleosynthesis within stars and how nucleosynthesis impacts stellar structure and the remnants of stellar evolution. Achieving this understanding will require precise direct measurements of the nuclear reactions involved. This report summarizes the status of direct measurements for stellar burning, focusing on developments of the last couple of decades, and offering a prospectus of near-future developments.Comment: Accepted to Journal of Physics G as a Major Report. Corresponding author: Zach Meisel ([email protected]

Catching Element Formation In The Act

Gamma-ray astronomy explores the most energetic photons in nature to address some of the most pressing puzzles in contemporary astrophysics. It encompasses a wide range of objects and phenomena: stars, supernovae, novae, neutron stars, stellar-mass black holes, nucleosynthesis, the interstellar medium, cosmic rays and relativistic-particle acceleration, and the evolution of galaxies. MeV gamma-rays provide a unique probe of nuclear processes in astronomy, directly measuring radioactive decay, nuclear de-excitation, and positron annihilation. The substantial information carried by gamma-ray photons allows us to see deeper into these objects, the bulk of the power is often emitted at gamma-ray energies, and radioactivity provides a natural physical clock that adds unique information. New science will be driven by time-domain population studies at gamma-ray energies. This science is enabled by next-generation gamma-ray instruments with one to two orders of magnitude better sensitivity, larger sky coverage, and faster cadence than all previous gamma-ray instruments. This transformative capability permits: (a) the accurate identification of the gamma-ray emitting objects and correlations with observations taken at other wavelengths and with other messengers; (b) construction of new gamma-ray maps of the Milky Way and other nearby galaxies where extended regions are distinguished from point sources; and (c) considerable serendipitous science of scarce events -- nearby neutron star mergers, for example. Advances in technology push the performance of new gamma-ray instruments to address a wide set of astrophysical questions.Comment: 14 pages including 3 figure

In-trap decay spectroscopy on highly-charged radioactive ions towards measurements on intermediate nuclei in beta beta decay

Diese Arbeit beschreibt die Entwicklung und Inbetriebnahme einer neuen Zerfallsspektroskopieanlage mit dem Ziel die schwachen Elektroneneinfangs-Verzweigungsverhältnisse der uu-Zwischenkerne im doppelten Betazerfall zu bestimmen. Die experimentell gewonnenen Daten sind von Bedeutung für theoretische Schalenmodellrechnungen, zur Bestimmung der Kernmatrixelemente des doppelten Betazerfalls. Hauptbestandteil der neuartigen Anlage ist eine Elektronenstrahl-Ionenfalle des TITAN (TRIUMF's Ion Trap for Atomic and Nuclear science) Experiments am TRIUMF in Vancouver, Kanada, mit welcher radioaktive Ionen durch eine Kombination aus elektrischen und magnetischen Felder und ohne Implantierung auf einem Trägermaterial gespeichert werden können. Neben der effektiven Reduzierung des Untergrunds, bietet die Verwendung der EBIT den Vorteil einer nahezu verlustfreien Speicherung von hochgeladenen Ionen, wodurch eine präzise Messung von Halbwertszeiten ermöglicht wird.This thesis presents the development and commissioning of a novel experimental setup to perform in-trap decay spectroscopy on highly-charged radioactive ions. The primary objective for such a device is the measurement of the weak electron-capture branching ratios of the odd-odd intermediate nuclei in double-beta decay. Those ratios will provide experimental input to benchmark theoretical shell-model calculations for the nuclear matrix elements in double-beta decay. The setup is part of the TITAN (TRIUMF's Ion Trap for Atomic and Nuclear science) facility at TRIUMF in Vancouver, Canada. The apparatus employs an open-access electron-beam ion trap to provide a low-background environment as well as backing-free ion storage, and is surrounded radially by seven low-energy planar silicon-lithium drifted photon detectors. Employing an electron beam for charge breeding optimizes the ion-cloud confinement and increases the ion storage time in the trap, thereby allowing half-life measurements

Constraints on key O 17 (α,γ) Ne 21 resonances and impact on the weak s process

The efficiency of the slow neutron-capture process in massive stars is strongly influenced by neutron-capture reactions on light elements. At low metallicity, O16 is an important neutron absorber, but the effectiveness of O16 as a light-element neutron poison is modified by competition between subsequent O17(α,n)Ne20 and O17(α,γ)Ne21 reactions. The strengths of key O17(α,γ)Ne21 resonances within the Gamow window for core helium burning in massive stars are not well constrained by experiment. This work presents more precise measurements of resonances in the energy range Ec.m.=612-1319 keV. We extract resonance strengths of ωγ638=4.85±0.79μeV, ωγ721=13.1-2.4+3.2μeV, ωγ814=7.72±0.55meV, and ωγ1318=136±13meV, for resonances at Ec.m.=638, 721, 814, and 1318 keV, respectively. We also report an upper limit for the 612 keV resonance of ωγ<140 neV (95% c.l.), which effectively rules out any significant contribution from this resonance to the reaction rate. From this work, a new O17(α,γ)Ne21 thermonuclear reaction rate is calculated and compared to the literature. The effect of present uncertainties in the O17(α,γ)Ne21 reaction rate on weak s-process yields are then explored using postprocessing calculations based on a rotating 20M⊙ low-metallicity massive star. The resulting O17(α,γ)Ne21 reaction rate is lower with respect to the preexisting literature and found to enhance weak s-process yields in rotating massive star models.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Measurement of the

The r-process has been shown to be robust in reproducing the abundance distributions of heavy elements, such as europium, seen in ultra-metal poor stars. In contrast, observations of elements 26 < Z < 47 display overabundances relative to r-process model predictions. A proposed additional source of early nucleosynthesis is the weak r-process in neutrino-driven winds of core-collapse supernovae. It has been shown that in this site (α,n) reactions are both crucial to nucleosynthesis and the main source of uncertainty in model-based abundance predictions. Aiming to improve the certainty of nucleosynthesis predictions, the cross section of the important reaction 86Kr(α,n)89Sr has been measured at an energy relevant to the weak r-process. This experiment was conducted in inverse kinematics at TRIUMF with the EMMA recoil mass spectrometer and the TIGRESS gamma-ray spectrometer. A novel type of solid helium target was used

Direct Experimental Constraints on the Spatial Extent of a Neutrino Wavepacket

International audienceDespite their high relative abundance in our Universe, neutrinos are the least understood fundamental particles of nature. They also provide a unique system to study quantum coherence in fundamental systems due to their extremely weak interaction probabilities. The quantum properties of neutrinos emitted in experimentally relevant sources are virtually unknown and theoretical predictions for the spatial width of neutrino wavepackets vary by many orders of magnitude. In weak nuclear decay, the size of a neutrino wavepacket, $\sigma_{\nu,x}$, is related to the spatial wavefunction of its parent at production. Here, we present the first direct limits of this quantity through a new experimental concept to extract the energy width, $\sigma_{\textrm{N},E}$, of the recoil daughter nucleus emitted in the nuclear electron capture (EC) decay of $^7$Be. The final state in the EC decay process contains a recoiling $^7$Li nucleus and an electron neutrino ($\nu_e$) which are entangled at their creation. The $^7$Li energy spectrum is measured to high precision by directly embedding $^7$Be radioisotopes into a high resolution superconducting tunnel junction that is operated as a cryogenic charge sensitive detector. The lower limit on the spatial coherence of the recoil daughter was found to be $\sigma_{\textrm{N}, x} \geq 6.2$ pm, which implies the system remains in a spatially coherent state much larger than the nuclear scale. Further, this implies a lower limit on the size of a neutrino wavepacket, $\sigma_{\nu,x} \geq 35$ nm, which is more than five orders of magnitude more stringent than the limits from all combined reactor oscillation experiments. These results have wide-reaching implications in several areas including quantum coherence, the nature of spatial localization at sub-atomic scales, interpretation of neutrino physics data, and the potential reach of future large-scale experiments

Direct Experimental Constraints on the Spatial Extent of a Neutrino Wavepacket

International audienceDespite their high relative abundance in our Universe, neutrinos are the least understood fundamental particles of nature. They also provide a unique system to study quantum coherence in fundamental systems due to their extremely weak interaction probabilities. The quantum properties of neutrinos emitted in experimentally relevant sources are virtually unknown and theoretical predictions for the spatial width of neutrino wavepackets vary by many orders of magnitude. In weak nuclear decay, the size of a neutrino wavepacket, $\sigma_{\nu,x}$, is related to the spatial wavefunction of its parent at production. Here, we present the first direct limits of this quantity through a new experimental concept to extract the energy width, $\sigma_{\textrm{N},E}$, of the recoil daughter nucleus emitted in the nuclear electron capture (EC) decay of $^7$Be. The final state in the EC decay process contains a recoiling $^7$Li nucleus and an electron neutrino ($\nu_e$) which are entangled at their creation. The $^7$Li energy spectrum is measured to high precision by directly embedding $^7$Be radioisotopes into a high resolution superconducting tunnel junction that is operated as a cryogenic charge sensitive detector. The lower limit on the spatial coherence of the recoil daughter was found to be $\sigma_{\textrm{N}, x} \geq 6.2$ pm, which implies the system remains in a spatially coherent state much larger than the nuclear scale. Further, this implies a lower limit on the size of a neutrino wavepacket, $\sigma_{\nu,x} \geq 35$ nm, which is more than five orders of magnitude more stringent than the limits from all combined reactor oscillation experiments. These results have wide-reaching implications in several areas including quantum coherence, the nature of spatial localization at sub-atomic scales, interpretation of neutrino physics data, and the potential reach of future large-scale experiments

Direct Experimental Constraints on the Spatial Extent of a Neutrino Wavepacket

International audienceDespite their high relative abundance in our Universe, neutrinos are the least understood fundamental particles of nature. They also provide a unique system to study quantum coherence in fundamental systems due to their extremely weak interaction probabilities. The quantum properties of neutrinos emitted in experimentally relevant sources are virtually unknown and theoretical predictions for the spatial width of neutrino wavepackets vary by many orders of magnitude. In weak nuclear decay, the size of a neutrino wavepacket, $\sigma_{\nu,x}$, is related to the spatial wavefunction of its parent at production. Here, we present the first direct limits of this quantity through a new experimental concept to extract the energy width, $\sigma_{\textrm{N},E}$, of the recoil daughter nucleus emitted in the nuclear electron capture (EC) decay of $^7$Be. The final state in the EC decay process contains a recoiling $^7$Li nucleus and an electron neutrino ($\nu_e$) which are entangled at their creation. The $^7$Li energy spectrum is measured to high precision by directly embedding $^7$Be radioisotopes into a high resolution superconducting tunnel junction that is operated as a cryogenic charge sensitive detector. The lower limit on the spatial coherence of the recoil daughter was found to be $\sigma_{\textrm{N}, x} \geq 6.2$ pm, which implies the system remains in a spatially coherent state much larger than the nuclear scale. Further, this implies a lower limit on the size of a neutrino wavepacket, $\sigma_{\nu,x} \geq 35$ nm, which is more than five orders of magnitude more stringent than the limits from all combined reactor oscillation experiments. These results have wide-reaching implications in several areas including quantum coherence, the nature of spatial localization at sub-atomic scales, interpretation of neutrino physics data, and the potential reach of future large-scale experiments