860 research outputs found
Beta-decay properties of neutron-rich Ca, Ti, and Cr isotopes
Beta-decay properties of neutron-rich Ca, Ti, and Cr isotopes are studied
within a deformed proton-neutron quasiparticle random-phase approximation. The
underlying mean field is described self-consistently from deformed Skyrme
Hartree-Fock calculations with pairing correlations. Residual spin-isospin
interactions in the particle-hole and particle-particle channels are also
included in the formalism. The energy distributions of the Gamow-Teller
strength, the beta-decay feedings, the beta-decay half-lives, and the
beta-delayed neutron emission probabilities are discussed and compared with
other theoretical results, as well as with the available experimental
information. The evolution of these nuclear beta-decay properties is
investigated in isotopic chains in a search for structural changes. A reliable
estimate of the beta-decay properties in this mass region is a valuable
information for evaluating decay rates in astrophysical scenarios.Comment: 11 pages, 12 figure
Approaching the precursor nuclei of the third r-process peak with RIBs
The rapid neutron nucleosynthesis process involves an enormous amount of very exotic neutron-rich nuclei, which represent a theoretical and experimental challenge. Two of the
main decay properties that affect the final abundance distribution the most are half-lives and neutron branching ratios. Using fragmentation of a primary 238U beam at GSI we were able to measure such properties for several neutron-rich nuclei from 208Hg to 218Pb. This contribution provides a short update on the status of the data analysis of this experiment, together with a compilation of the latest results published in this mass region, both experimental and theoretical.
The impact of the uncertainties connected with the eta-decay rates and with beta-delayed neutron emission is illustrated on the basis of r-process network calculations. In order to
obtain a reasonable reproduction of the third r-process peak, it is expected that both half-lives and neutron branching ratios are substantially smaller, than those based on FRDM+QRPA,
commonly used in r-process model calculations. Further measurements around N 126 are required for a reliable modelling of the underlying nuclear structure, and for performing more realistic r-process abundance calculations.Postprint (published version
β-decay half-lives and β-delayed neutron emission probabilities for several isotopes of Au, Hg, Tl, Pb, and Bi, beyond N = 126
Background: There have been measurements on roughly 230 nuclei that are β-delayed neutron emitters. They
range from 8
He up to 150La. Apart from 210Tl, with a branching ratio of only 0.007%, no other neutron emitter
has been measured beyond A = 150. Therefore, new data are needed, particularly in the region of heavy nuclei
around N = 126, in order to guide theoretical models and help understand the formation of the third r-process
peak at A ∼ 195.
Purpose: To measure both β-decay half-lives and neutron branching ratios of several neutron-rich Au, Hg, Tl,
Pb, and Bi isotopes beyond N = 126.
Method: Ions of interest were produced by fragmentation of a 238U beam, selected and identified via the GSI-FRS
fragment separator. A stack of segmented silicon detectors (SIMBA) was used to measure ion implants and β
decays. An array of 30 3
He tubes embedded in a polyethylene matrix (BELEN) was used to detect neutrons with
high efficiency and selectivity. A self-triggered digital system is employed to acquire data and to enable time
correlations. The latter were analyzed with an analytical model and results for the half-lives and neutron-branching
ratios were derived by using the binned maximum-likelihood method.
Results: Twenty new β-decay half-lives are reported for 204−206Au, 208–211Hg,
211–216Tl,
215–218Pb, and 218–220Bi,
nine of them for the first time. Neutron emission probabilities are reported for 210,211Hg and 211–216Tl.
Conclusions: The new β-decay half-lives are in good agreement with previous measurements on nuclei in this
region. The measured neutron emission probabilities are comparable to or smaller than values predicted by global
models such as relativistic Hartree Bogoliubov plus the relativistic quasi-particle random phase approximation
(RHB + RQRPA).Spanish Ministerio de Economía y Competitividad-FPA2011- 28770-C03-03, FPA2008-04972-C03-3, AIC-D2011-0705, FPA2011-24553, FPA2008-6419, FPA2010-17142, FPA2014-52823-C2-1-P, FPA2014- 52823-C2-2-P, and CPAN CSD-2007-00042 (Ingenio2010)Program Severo Ochoa-SEV-2014-0398German Helmholtz Association (Young Investigators)-VH-NG 627 (LISA-Lifetime Spectroscopy for Astrophysics)Nuclear Astrophysics Virtual Institute-VH-VI-417German Bundesministerium für Bildung und Forschung-06MT7178 / 05P12WOFNFSpanish Nuclear Security Council (CSN)-Catedra ArgosUK Science & Technology Facilities Council (STFC)-ST/F012012/
The BRIKEN Project: extensive measurements of ß-delayed neutron emitters for the astrophysical r process
An ambitious program to measure decay properties, primarily ß-delayed neutron emission probabilities and half-lives, for a significant number of nuclei near or on the path of the rapid neutron capture process, has been launched at the RIKEN Nishina Center. We give here an overview of the status of the project.Postprint (published version
Performance analysis of AlGaAs/GaAs tunnel junctions for ultra-high concentration photovoltaics
An n(++)-GaAs/p(++)-AlGaAs tunnel junction with a peak current density of 10 100Acm(-2) is developed. This device is a tunnel junction for multijunction solar cells, grown lattice-matched on standard GaAs or Ge substrates, with the highest peak current density ever reported. The voltage drop for a current density equivalent to the operation of the multijunction solar cell up to 10 000 suns is below 5 mV. Trap-assisted tunnelling is proposed to be behind this performance, which cannot be justified by simple band-to-band tunnelling. The metal-organic vapour-phase epitaxy growth conditions, which are in the limits of the transport-limited regime, and the heavy tellurium doping levels are the proposed origins of the defects enabling trap-assisted tunnelling. The hypothesis of trap-assisted tunnelling is supported by the observed annealing behaviour of the tunnel junctions, which cannot be explained in terms of dopant diffusion or passivation. For the integration of these tunnel junctions into a triple-junction solar cell, AlGaAs barrier layers are introduced to suppress the formation of parasitic junctions, but this is found to significantly degrade the performance of the tunnel junctions. However, the annealed tunnel junctions with barrier layers still exhibit a peak current density higher than 2500Acm(-2) and a voltage drop at 10 000 suns of around 20 mV, which are excellent properties for tunnel junctions and mean they can serve as low-loss interconnections in multijunction solar cells working at ultra-high concentrations
Experimental study of Tc 100 β decay with total absorption γ -ray spectroscopy
The β decay of Tc100 has been studied by using the total absorption γ-ray spectroscopy technique at the Ion Guide Isotope Separator On-Line facility in Jyväskylä. In this work the new Decay Total Absorption γ-ray Spectrometer in coincidence with a cylindrical plastic β detector has been employed. The β intensity to the ground state obtained from the analysis is in good agreement with previous high-resolution measurements. However, differences in the feeding to the first-excited state as well as weak feeding to a new level at high excitation energy have been deduced from this experiment. Theoretical calculations performed in the quasiparticle random-phase approximation framework are also reported. Comparison of these calculations with our measurement serves as a benchmark for calculations of the double β decay of Mo100. © 2017 American Physical Society
New antineutrino energy spectra predictions from the summation of beta decay branches of the fission products
In this paper, we study the impact of the inclusion of the recently measured
beta decay properties of the Tc, Mo, and
Nb nuclei in an updated calculation of the antineutrino energy spectra
of the four fissible isotopes U, and Pu. These
actinides are the main contributors to the fission processes in Pressurized
Water Reactors. The beta feeding probabilities of the above-mentioned Tc, Mo
and Nb isotopes have been found to play a major role in the component
of the decay heat of Pu, solving a large part of the
discrepancy in the 4 to 3000\,s range. They have been measured using the Total
Absorption Technique (TAS), avoiding the Pandemonium effect. The calculations
are performed using the information available nowadays in the nuclear
databases, summing all the contributions of the beta decay branches of the
fission products. Our results provide a new prediction of the antineutrino
energy spectra of U, Pu and in particular of U for
which no measurement has been published yet. We conclude that new TAS
measurements are mandatory to improve the reliability of the predicted spectra.Comment: 10 pages, 2 figure
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