The properties of exotic nuclei on the verge of existence play a fundamental part in our understanding of nuclear interactions. Exceedingly neutron-rich nuclei become sensitive to new aspects of ...nuclear forces. Calcium, with its doubly magic isotopes (40)Ca and (48)Ca, is an ideal test for nuclear shell evolution, from the valley of stability to the limits of existence. With a closed proton shell, the calcium isotopes mark the frontier for calculations with three-nucleon forces from chiral effective field theory. Whereas predictions for the masses of (51)Ca and (52)Ca have been validated by direct measurements, it is an open question as to how nuclear masses evolve for heavier calcium isotopes. Here we report the mass determination of the exotic calcium isotopes (53)Ca and (54)Ca, using the multi-reflection time-of-flight mass spectrometer of ISOLTRAP at CERN. The measured masses unambiguously establish a prominent shell closure at neutron number N = 32, in excellent agreement with our theoretical calculations. These results increase our understanding of neutron-rich matter and pin down the subtle components of nuclear forces that are at the forefront of theoretical developments constrained by quantum chromodynamics.
A new approach (called COBRA) for investigating double beta decay using CdTe semiconductor detectors is proposed. This will allow simultaneous measurements of 5β−β−- and 4β+β+-emitters at once. ...Half-life limits for neutrinoless double beta decay of 116Cd and 130Te can be improved by more than one order of magnitude and sensitivities on the effective Majorana neutrino mass of less than 1 eV can be obtained. Furthermore, for the first time a realistic chance of observing double electron capture processes exists. Additional searches for rare processes like the 4-fold forbidden 113Cd β-decay, the electron capture of 123Te and dark matter detection can be performed. The achievable limits are evaluated for 10 kg of such detectors and can be scaled accordingly towards higher masses because of the modular design of the proposed experiment.
When Kai Zuber’s pioneering text on neutrinos was published in 2003, the author correctly predicted that the field would see tremendous growth in the immediate future. In that book, Professor Zuber ...provided a comprehensive self-contained examination of neutrinos, covering their research history and theory, as well as their application to particle physics, astrophysics, nuclear physics, and the broad reach of cosmology; but now to be truly comprehensive and accurate, the field’s seminal reference needs to be revised and expanded to include the latest research, conclusions, and implications. Revised as needed to be equal to the research of today, Neutrino Physics, Third Edition delves into neutrino cross-sections, mass measurements, double beta decay, solar neutrinos, neutrinos from supernovae, and high-energy neutrinos, as well as entirely new experimental results in the context of theoretical models. Written to be accessible to graduate students and readers from diverse backgrounds, this edition, like the first, provides both an introduction to the field as well as the information needed by those looking to make their own contributions to it. And like the second edition, it whets the researcher’s appetite, going beyond certainty to pose those questions that still need answers. Features Presents the only single-author comprehensive text on neutrino physics Includes experimental and theoretical particle physics and examines solar neutrinos and astroparticle implications Offers details on new developments and recent experiments
Large-scale shell-model calculations were carried out for the half-lives and branching ratios of the 2νββ decay of 76Ge to the ground state and the lowest three excited states 21+, 02+ and 22+ in ...76Se. In total, the wave functions of more than 10,000 intermediate 1+ states in 76As were calculated in a three-step procedure allowing an efficient use of the available computer resources. In the first step, 250 lowest states, below some 5 MeV of excitation energy, were calculated without truncations within a full major shell 0f5/2−1p−0g9/2 for both protons and neutrons. The wave functions of the rest of the states, up to some 30 MeV, were computed in two more steps by introducing two consecutive stages of truncation. The computed magnitudes of the 2νββ nuclear matrix elements (including the value of the axial-vector coupling gA), |M2ν|gA2, converged to the values 0.168gA2, 1.2×10−3gA2, 0.121gA2, and 3.1×10−3gA2 for the 0g.s.+, 21+, 02+, and 22+ states, respectively. Using up-to-date phase-space integrals, the corresponding branching ratios were derived to be 99.926%, 4.4×10−5%, 0.074% and 2.5×10−7%. The experimental half-life (1.926±0.094)×1021 yr of the ground-state transition was used to derive the value gA=0.80±0.01 for the axial-vector coupling, which is consistent with other shell-model calculations suggesting a quenched value of gA. Using this value of gA, predictions for the transition half-lives were derived.
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•Multi-reflection time-of-flight mass separator for purification of radioactive ion beams.•Enhanced ion beam purification by stacking of multiple cleaned ion samples in an ...intermediate ion trap to increase the signal intensity of Penning trap mass measurements.•Multi-reflection time-of-flight mass spectrometer for high-precision mass measurements of short-lived species.•Multi-reflection time-of-flight mass analyzer for target and ion-source development of exotic beams.
The online precision mass spectrometer ISOLTRAP at ISOLDE/CERN was recently upgraded by adding a multi-reflection time-of-flight mass separator/spectrometer (MR-ToF MS) between the linear radio-frequency ion trap and the two Penning traps already in place. As a mass separator, the MR-ToF device has improved significantly ISOLTRAP's capability of purification of contaminated ion beams. In addition, the MR-ToF MS can be operated as a mass spectrometer, either to analyze the ISOLDE ion beam or for precision mass measurements of nuclides that are shorter-lived or that have lower yields than those accessible for Penning-trap mass spectrometry. The MR-ToF MS and corresponding components, its integration into ISOLTRAP, and its various operation modes are reviewed. Furthermore, a precision measurement of the 137Eu mass is presented, determined with the help of the MR-ToF device as a mass separator.
Intracranial stents for the treatment of aneurysms can be responsible for parent artery straightening, a phenomenon with potential consequences for aneurysmal occlusion. We aimed to evaluate parent ...artery straightening following flow-diverter stent placement in patients with intracranial aneurysms and explored the association between parent artery straightening and subsequent aneurysm occlusion.
All patients treated with flow-diverter stents for anterior circulation aneurysms located downstream from the carotid siphon between January 2009 and January 2018 were screened for inclusion. Parent artery straightening was defined as the difference (α-β) in the parent artery angle at the neck level before (α angle) and after flow-diverter stent deployment (β angle). We analyzed the procedural and imaging factors associated with parent artery straightening and the associations between parent artery straightening and aneurysmal occlusion.
Ninety-five patients met the inclusion criteria (
= 64/95 women, 67.4%; mean age, 54.1 SD, 11.2 years) with 97 flow-diverter stents deployed for 99 aneurysms. Aneurysms were predominantly located at the MCA bifurcation (
= 44/95, 44.4%). Parent artery straightening was found to be more pronounced in patients treated with cobalt chromium stents than with nitinol stents (
= .02). In multivariate analysis, parent artery straightening (
= .04) was independently associated with aneurysm occlusion after flow-diverter stent deployment.
The use of flow-diverter stents for distal aneurysms induces a measurable parent artery straightening, which is associated with higher occlusion rates. Parent artery straightening, in our sample, appeared to be more prominent with cobalt chromium stents than with nitinol stents. This work highlights the necessary trade-off between navigability and parent artery straightening and may help tailor the selection of flow-diverter stents to aneurysms and parent artery characteristics.
A multi-reflection time-of-flight (MR-ToF) mass analyzer has been integrated into ISOLTRAP, the precision mass spectrometer for on-line mass determinations of short-lived nuclides at ISOLDE/CERN. The ...new instrument improves ISOLTRAP by providing a fast separation of isobaric contaminant species as well as subsequent ion selection using the fast Bradbury–Nielsen gate. Suppression ratios of up to 104 and mass-resolving powers of over 105 have been reached in off-line experiments. Preliminary data from on-line applications illustrate the benefit and performance of the device and its potential in the context of the ISOLTRAP setup.
The potential real-time spectroscopy of solar pp-neutrinos using 150Nd as target is investigated. The threshold of 196 keV would be the lowest of all solar neutrino experiments running so far. ...Experimental rates and parameters are discussed, about 906 SNU can be expected from pp-neutrinos and another 574 SNU from 7Be. Furthermore, it is investigated whether charged current reactions might cause a new background component for future double beta decay experiments based on a large amount of 150Nd.
RfaH, a paralog of the universally conserved NusG, binds to RNA polymerases (RNAP) and ribosomes to activate expression of virulence genes. In free, autoinhibited RfaH, an α-helical KOW domain ...sequesters the RNAP-binding site. Upon recruitment to RNAP paused at an ops site, KOW is released and refolds into a β-barrel, which binds the ribosome. Here, we report structures of ops-paused transcription elongation complexes alone and bound to the autoinhibited and activated RfaH, which reveal swiveled, pre-translocated pause states stabilized by an ops hairpin in the non-template DNA. Autoinhibited RfaH binds and twists the ops hairpin, expanding the RNA:DNA hybrid to 11 base pairs and triggering the KOW release. Once activated, RfaH hyper-stabilizes the pause, which thus requires anti-backtracking factors for escape. Our results suggest that the entire RfaH cycle is solely determined by the ops and RfaH sequences and provide insights into mechanisms of recruitment and metamorphosis of NusG homologs across all life.
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