113 research outputs found
Clarification of the low-lying states of Be-9
5 pages, 1 table, 2 figures.-- Presented at the
International Conference on Finite Fermionic Systems: Nilsson Model 50 years (Lund University, Sweden, June 14–18, 2005).--
PACS nrs.: 23.40.Hc, 27.20.+n, 24.80.+y.A newly developed technique for dealing with three-body decays of broad isolated levels is extended to deal with the broad, overlapping levels found at 2-9 MeV excitation energy in Be-9. The levels are populated through beta-decay of Li-9. The method gives firm evidence for the existence of several levels. Angular correlation studies allow spin values to be assigned.Peer reviewe
Anatomy of three-body decay I. Schematic models
Sequential three-body decay proceeds via spatially confined quasi-stationary
two-body configurations. Direct three-body decay populates the three-body
continuum without intermediate steps. The relative importance of these decay
modes is discussed in a schematic model employing only Coulomb or centrifugal
barrier potentials. Decisive dimensionless charge, mass and energy ratios are
derived. Sequential decay is usually favored for charged particles. Small
charge and small mass of high energy is preferably emitted first. Without
Coulomb potential the sequential decay is favored except when both resonance
energy and intermediate two-body energy are large.Comment: To be published in Nuclear Physics
Three-body decays: structure, decay mechanism and fragment properties
We discuss the three-body decay mechanisms of many-body resonances. R-matrix
sequential description is compared with full Faddeev computation. The role of
the angular momentum and boson symmetries is also studied. As an illustration
we show the computed -particle energy distribution after the decay of
12C(1^+) resonance at 12.7 MeV.Comment: 4 pages, 3 figures. Proceedings of the workshop "Critical Stability
of Few-Body Quantum Systems" 200
Anatomy of three-body decay III. Energy distributions
We address the problem of calculating momentum distributions of particles
emerging from the three-body decay of a many-body resonance. We show that these
distributions are determined by the asymptotics of the coordinate-space
complex-energy wave-function of the resonance. We use the hyperspherical
adiabatic expansion method where all lengths are proportional to the
hyperradius. The structures of the resonances are related to different decay
mechanisms. For direct decay all inter-particle distances increase proportional
to the hyperradius at intermediate and large distances. Sequential three-body
decay proceeds via spatially confined quasi-stationary two-body configurations.
Then two particles remain close while the third moves away. The wave function
may contain mixtures which produce coherence effects at small distances, but
the energy distributions can still be added incoherently. Two-neutron halos are
discussed in details and illustrated by the resonance in He. The
dynamic evolution of the decay process is discussed.Comment: 30 pages, 8 figures, to be published in Nuclear Physics
Isospin mixing and energy distributions in three-body decay
The structure of the second 2 resonance in Li is investigated with
special emphasis on its isospin 0 components. The wave functions are computed
in a three-body model (++) using the hyperspherical adiabatic
expansion method combined with complex scaling. In the decay into three free
particles the symmetry conserving short-range interaction dominates at short
distance whereas the symmetry breaking Coulomb interaction dominates at
intermediate and large distances resulting in substantial isospin mixing. We
predict the mixing and the energy distributions of the fragments after decay.
Computations are consistent with available experiments. We conjecture that
nuclear three-body decays frequently produce such large isospin mixing at large
distance where the energy distributions. are determined.Comment: 5 pages, 4 figures, to be published in Physics Letters
Evidence of a new state in Be observed in the Li -decay
Coincidences between charged particles emitted in the -decay of
Li were observed using highly segmented detectors. The breakup channels
involving three particles were studied in full kinematics allowing for the
reconstruction of the excitation energy of the Be states participating
in the decay. In particular, the contribution of a previously unobserved state
at 16.3 MeV in Be has been identified selecting the +
He + He+n channel. The angular correlations between the
particle and the center of mass of the He+n system favors spin and
parity assignment of 3/2 for this state as well as for the previously known
state at 18 MeV.Comment: 13 pages, 6 figure
Few-body decay and recombination in nuclear astrophysics
Three-body continuum problems are investigated for light nuclei of
astrophysical relevance. We focus on three-body decays of resonances or
recombination via resonances or the continuum background. The concepts of
widths, decay mechanisms and dynamic evolution are discussed. We also discuss
results for the triple decay in connection with resonances and
density and temperature dependence rates of recombination into light nuclei
from -particles and neutrons.Comment: 9 pages, 8 figures. Proceedings of the 21st European Few Body
Conference held in Salamanca (Spain) in August-September 201
Beta-delayed proton emission from <sup>21</sup>Mg
16 pags.; 9 figs.; 6 tabs.© 2015, SIF, Springer-Verlag Berlin Heidelberg. Beta-delayed proton emission from 21Mg has been measured at ISOLDE, CERN, with a detection setup consisting of two charged-particle telescopes surrounding the decay point. Altogether 27 βp branches were measured with center-of-mass energies between 0.4–7.2 MeV. Seven new βp branches were observed. Beta-delayed protons were used to determine the half-life of 21Mg as 118.6 ± 0.5 ms. From a line shape fit of the βp branches we extract the widths, spins, and parities of the resonances of 21Na. An improved interpretation of the decay scheme in accordance with the results obtained in reaction studies is presented.This work has been supported by the European Commision
within the Seventh Framework Programme “European Nuclear
Science and Applications Research”, contract no. 262010
(ENSAR), and by the Spanish research agency under number
FPA2012-32443.Peer Reviewe
Study of beta-delayed 3-body and 5-body breakup channels observed in the decay of ^11Li
The beta-delayed charged particle emission from ^11Li has been studied with
emphasis on the three-body n+alpha+^6He and five-body 2alpha+3n channels from
the 10.59 and 18.15 MeV states in ^11Be. Monte Carlo simulations using an
R-matrix formalism lead to the conclusion that the ^AHe resonance states play a
significant role in the break-up of these states. The results exclude an
earlier assumption of a phase-space description of the break-up process of the
18.15 MeV state. Evidence for extra sequential decay paths is found for both
states.Comment: 16 pages, 9 figures. Submitted to Nuclear Physics
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