126 research outputs found
Probing the single-particle character of rotational states in F using a short-lived isomeric beam
A beam containing a substantial component of both the ,
ns isomeric state of F and its , 109.77-min ground
state has been utilized to study members of the ground-state rotational band in
F through the neutron transfer reaction , in inverse kinematics.
The resulting spectroscopic strengths confirm the single-particle nature of the
13/2 band-terminating state. The agreement between shell-model
calculations, using an interaction constructed within the shell, and our
experimental results reinforces the idea of a single-particle/collective
duality in the descriptions of the structure of atomic nuclei
Probing elastic and inelastic breakup contributions to intermediate-energy two-proton removal reactions
The two-proton removal reaction from 28Mg projectiles has been studied at 93
MeV/u at the NSCL. First coincidence measurements of the heavy 26Ne projectile
residues, the removed protons and other light charged particles enabled the
relative cross sections from each of the three possible elastic and inelastic
proton removal mechanisms to be determined. These more final-state-exclusive
measurements are key for further interrogation of these reaction mechanisms and
use of the reaction channel for quantitative spectroscopy of very neutron-rich
nuclei. The relative and absolute yields of the three contributing mechanisms
are compared to reaction model expectations - based on the use of eikonal
dynamics and sd-shell-model structure amplitudes.Comment: Accepted for publication in Physical Review C (Rapid Communication
Elastic breakup cross sections of well-bound nucleons
The 9Be(28Mg,27Na) one-proton removal reaction with a large proton separation
energy of Sp(28Mg)=16.79 MeV is studied at intermediate beam energy.
Coincidences of the bound 27Na residues with protons and other light charged
particles are measured. These data are analyzed to determine the percentage
contributions to the proton removal cross section from the elastic and
inelastic nucleon removal mechanisms. These deduced contributions are compared
with the eikonal reaction model predictions and with the previously measured
data for reactions involving the re- moval of more weakly-bound protons from
lighter nuclei. The role of transitions of the proton between different bound
single-particle configurations upon the elastic breakup cross section is also
quantified in this well-bound case. The measured and calculated elastic breakup
fractions are found to be in good agreement.Comment: Phys. Rev. C 2014 (accepted
Correlations in intermediate-energy two-proton removal reactions
We report final-state-exclusive measurements of the light charged fragments
in coincidence with 26Ne residual nuclei following the direct two-proton
removal from a neutron-rich 28Mg secondary beam. A Dalitz-plot analysis and
comparisons with simulations show that a majority of the triple- coincidence
events with two protons display phase-space correlations consistent with the
(two-body) kinematics of a spatially-correlated pair-removal mechanism. The
fraction of such correlated events, 56(12) %, is consistent with the fraction
of the calculated cross section, 64 %, arising from spin S = 0 two-proton
configurations in the entrance-channel (shell-model) 28Mg ground state wave
function. This result promises access to an additional and more specific probe
of the spin and spatial correlations of valence nucleon pairs in exotic nuclei
produced as fast secondary beams.Comment: accepted for publication in Physical Review Letter
Investigations of three, four, and five-particle exit channels of levels in light nuclei created using a 9C beam
The interactions of a E/A=70-MeV 9C beam with a Be target was used to
populate levels in Be, B, and C isotopes which undergo decay into many-particle
exit channels. The decay products were detected in the HiRA array and the level
energies were identified from their invariant mass. Correlations between the
decay products were examined to deduce the nature of the decays, specifically
to what extent all the fragments were created in one prompt step or whether the
disintegration proceeded in a sequential fashion through long-lived
intermediate states. In the latter case, information on the spin of the level
was also obtained. Of particular interest is the 5-body decay of the 8C ground
state which was found to disintegrate in two steps of two-proton decay passing
through the 6Beg.s. intermediate state. The isobaric analog of 8Cg.s. in 8B was
also found to undergo two-proton decay to the isobaric analog of 6Beg.s. in
6Li. A 9.69-MeV state in 10C was found to undergo prompt 4-body decay to the
2p+2alpha exit channel. The two protons were found to have a strong
enhancementin the diproton region and the relative energies of all four p-alpha
pairs were consistent with the 5Lig.s. resonance
On Determining Dead Layer and Detector Thicknesses for a Position-Sensitive Silicon Detector
In this work, two particular properties of the position-sensitive, thick
silicon detectors (known as the "E" detectors) in the High Resolution Array
(HiRA) are investigated: the thickness of the dead layer on the front of the
detector, and the overall thickness of the detector itself. The dead layer
thickness for each E detector in HiRA is extracted using a measurement of alpha
particles emitted from a Pb pin source placed close to the detector
surface. This procedure also allows for energy calibrations of the E detectors,
which are otherwise inaccessible for alpha source calibration as each one is
sandwiched between two other detectors. The E detector thickness is obtained
from a combination of elastically scattered protons and an energy-loss
calculation method. Results from these analyses agree with values provided by
the manufacturer.Comment: Accepted for publication in Nuclear Instruments and Methods in
Physics Researc
The observation of long-range three-body Coloumb effects in the decay of 16Ne
The interaction of an =57.6-MeV Ne beam with a Be target was used
to populate levels in Ne following neutron knockout reactions. The decay
of Ne states into the three-body O++ continuum was observed
in the High Resolution Array (HiRA). For the first time for a 2p emitter,
correlations between the momenta of the three decay products were measured with
sufficient resolution and statistics to allow for an unambiguous demonstration
of their dependence on the long-range nature of the Coulomb interaction.
Contrary to previous experiments, the intrinsic decay width of the Ne
ground state was found to be narrow (~keV), consistent with
theoretical estimates.Comment: 6 pages, 5 figure
Time-of-flight mass measurements of neutron-rich chromium isotopes up to N = 40 and implications for the accreted neutron star crust
We present the mass excesses of 59-64Cr, obtained from recent time-of-flight
nuclear mass measurements at the National Superconducting Cyclotron Laboratory
at Michigan State University. The mass of 64Cr is determined for the first
time, with an atomic mass excess of -33.48(44) MeV. We find a significantly
different two-neutron separation energy S2n trend for neutron-rich isotopes of
chromium, removing the previously observed enhancement in binding at N=38.
Additionally, we extend the S2n trend for chromium to N=40, revealing behavior
consistent with the previously identified island of inversion in this region.
We compare our results to state-of-the-art shell-model calculations performed
with a modified Lenzi-Nowacki-Poves-Sieja interaction in the fp shell,
including the g9/2 and d5/2 orbits for the neutron valence space. We employ our
result for the mass of 64Cr in accreted neutron star crust network calculations
and find a reduction in the strength and depth of electron-capture heating from
the A=64 isobaric chain, resulting in a cooler than expected accreted neutron
star crust. This reduced heating is found to be due to the >1-MeV reduction in
binding for 64Cr with respect to values from commonly used global mass models.Comment: Accepted to Physical Review
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