2,042 research outputs found
Three-body correlations in the ground-state decay of 26O
Background: Theoretical calculations have shown that the energy and angular
correlations in the three-body decay of the two-neutron unbound O26 can provide
information on the ground-state wave function, which has been predicted to have
a dineutron configuration and 2n halo structure.
Purpose: To use the experimentally measured three-body correlations to gain
insight into the properties of O26, including the decay mechanism and
ground-state resonance energy.
Method: O26 was produced in a one-proton knockout reaction from F27 and the
O24+n+n decay products were measured using the MoNA-Sweeper setup. The
three-body correlations from the O26 ground-state resonance decay were
extracted. The experimental results were compared to Monte Carlo simulations in
which the resonance energy and decay mechanism were varied.
Results: The measured three-body correlations were well reproduced by the
Monte Carlo simulations but were not sensitive to the decay mechanism due to
the experimental resolutions. However, the three-body correlations were found
to be sensitive to the resonance energy of O26. A 1{\sigma} upper limit of 53
keV was extracted for the ground-state resonance energy of O26.
Conclusions: Future attempts to measure the three-body correlations from the
ground-state decay of O26 will be very challenging due to the need for a
precise measurement of the O24 momentum at the reaction point in the target
Population of 13Be in a Nucleon Exchange Reaction
The neutron-unbound nucleus 13Be was populated with a nucleon-exchange
reaction from a 71 MeV/u secondary 13B beam. The decay energy spectrum was
reconstructed using invariant mass spectroscopy based on 12Be fragments in
coincidence with neutrons. The data could be described with an s-wave resonance
at E = 0.73(9) MeV with a width of Gamma = 1.98(34) MeV and a d-wave resonance
at E = 2.56(13) MeV with a width of Gamma = 2.29(73) MeV. The observed spectral
shape is consistent with previous one-proton removal reaction measurements from
14B.Comment: Published in Phys. Rev.
First Observation of 15Be
The neutron-unbound nucleus 15Be was observed for the first time. It was populated using neutron transfer from a deuterated polyethylene target with a 59 MeV/u 14Be beam. Neutrons were measured in coincidence with outgoing 14Be particles and the reconstructed decay energy spectrum exhibits a resonance at 1.8(1) MeV. This corresponds to 15Be being unbound by 0.45 MeV more then 16Be thus significantly hindering the sequential two-neutron decay of 16Be to 14Be through this state
Spectroscopy of neutron-unbound F
The ground state of F has been observed as an unbound resonance
keV above the ground state of F. Comparison of this
result with USDA/USDB shell model predictions leads to the conclusion that the
F ground state is primarily dominated by -shell configurations. Here
we present a detailed report on the experiment in which the ground state
resonance of F was first observed. Additionally, we report the first
observation of a neutron-unbound excited state in F at an excitation
energy of keV.Comment: 10 pages, 11 figures, Accepted for publication in Phys. Rev.
Observation of a low-lying neutron-unbound state in 19C
Proton removal reactions from a secondary 22N beam were utilized to populate
unbound states in neutron-rich carbon isotopes. Neutrons were measured with the
Modular Neutron Array (MoNA) in coincidence with carbon fragments. A resonance
with a decay energy of 76(14) keV was observed in the system 18C+n
corresponding to a state in 19C at an excitation energy of 653(95)keV. This
resonance could correspond to the first 5/2+ state which was recently
speculated to be unbound in order to describe 1n and 2n removal cross section
measurements from 20C.Comment: accepted for publication in Nucl. Phys.
Energy distributions from three-body decaying many-body resonances
We compute energy distributions of three particles emerging from decaying
many-body resonances. We reproduce the measured energy distributions from
decays of two archetypal states chosen as the lowest and
-resonances in C populated in -decays. These states are
dominated by sequential, through the Be ground state, and direct decays,
respectively. These decay mechanisms are reflected in the ``dynamic'' evolution
from small, cluster or shell-model states, to large distances, where the
coordinate or momentum space continuum wavefunctions are accurately computed.Comment: 4 pages, 4 figures. Accepted for publication in Physical Review
Letter
Population of neutron unbound states via two-proton knockout reactions
The two-proton knockout reaction 9Be(26Ne,O2p) was used to explore excited
unbound states of 23O and 24O. In 23O a state at an excitation energy of
2.79(13) MeV was observed. There was no conclusive evidence for the population
of excited states in 24O.Comment: 6 pages, 3 figures, Proc. 9th Int. Spring Seminar on Nucl. Phys.
Changing Facets of Nuclear Structure, May 20-34, 200
Neutron knockout of 12Be populating neutron-unbound states in 11Be
Neutron-unbound resonant states of 11Be were populated in neutron knock-out
reactions from 12Be and identified by 10Be-n coincidence measurements. A
resonance in the decay-energy spectrum at 80(2) keV was attributed to a highly
excited unbound state in 11Be at 3.949(2) MeV decaying to the 2+ excited state
in 10Be. A knockout cross section of 15(3) mb was inferred for this 3.949(2)
MeV state suggesting a spectroscopic factor near unity for this 0p3/2- level,
consistent with the detailed shell model calculations.Comment: 5 pages, 2 figures \pacs{29.38.Db, 29.30.Hs, 24.50.+g, 21.10.Pc,
21.10.Hw, 27.20.+n} \keywords{neutron decay spectroscopy, neutron-unbound
states in 11Be
Reversing gene erosion: reconstructing ancestral bacterial genomes from gene-content and gene-order data
- …