162 research outputs found
Is the structure of 42Si understood?
A more detailed test of the implementation of nuclear forces that drive shell
evolution in the pivotal nucleus \nuc{42}{Si} -- going beyond earlier
comparisons of excited-state energies -- is important. The two leading
shell-model effective interactions, SDPF-MU and SDPF-U-Si, both of which
reproduce the low-lying \nuc{42}{Si}() energy, but whose predictions for
other observables differ significantly, are interrogated by the population of
states in neutron-rich \nuc{42}{Si} with a one-proton removal reaction from
\nuc{43}{P} projectiles at 81~MeV/nucleon. The measured cross sections to the
individual \nuc{42}{Si} final states are compared to calculations that combine
eikonal reaction dynamics with these shell-model nuclear structure overlaps.
The differences in the two shell-model descriptions are examined and linked to
predicted low-lying excited states and shape coexistence. Based on the
present data, which are in better agreement with the SDPF-MU calculations, the
state observed at 2150(13)~keV in \nuc{42}{Si} is proposed to be the ()
level.Comment: accepted in Physical Review Letter
Two-neutron knockout as a probe of the composition of states in Mg, Al, and Si
Simpson and Tostevin proposed that the width and shape of exclusive parallel
momentum distributions of the A-2 residue in direct two-nucleon knockout
reactions carry a measurable sensitivity to the nucleon single-particle
configurations and their couplings within the wave functions of exotic nuclei.
We report here on the first benchmarks and use of this new spectroscopic tool.
Exclusive parallel momentum distributions for states in the neutron-deficient
nuclei Mg, Al, and Si populated in such direct two-neutron
removal reactions were extracted and compared to predictions combining eikonal
reaction theory and shell-model calculations. For the well-known Mg and
Al nuclei, measurements and calculations were found to agree, supporting
the dependence of the parallel momentum distribution width on the angular
momentum composition of the shell-model two-neutron amplitudes. In Si, a
level at 3439(9) keV, of relevance for the important
Al(p,)Si astrophysical reaction rate, was confirmed to be
the state, while the state, expected to be strongly populated
in two-neutron knockout, was not observed. This puzzle is resolved by
theoretical considerations of the Thomas-Ehrman shift, which also suggest that
a previously reported 3471-keV state in Si is in fact the ()
level with one of the largest experimental mirror-energy shifts ever observed.Comment: Accepted for publication in Phys. Rev. C as a Rapid Communicatio
The Uptake of Methyl Vinyl Ketone, Methacrolein, and 2-Methyl-3-butene-2-ol onto Sulfuric Acid Solutions
Experimental Study of the S Excited Level Scheme
Information on the S level scheme was expanded through experimental
work utilizing a fusion-evaporation reaction and in-beam -ray
spectroscopy. Prompt -ray transitions were detected by the Gamma-Ray
Energy Tracking Array (GRETINA) and recoiling S residues were selected
by the Fragment Mass Analayzer (FMA). Tools based on machine-learning
techniques were developed and deployed for the first time in order to enhance
the unique selection of S residues and identify any associated
-ray transitions. The new level information, including the extension of
the even-spin yrast sequence through , was interpreted in
terms of a basic single-particle picture as well shell-model calculations which
incorporated the empirically derived FSU interaction. A comparison between the
properties of the yrast states in the even- isotones from to
, and for Si-S in particular, was also presented with an
emphasis on the role and influence of the neutron orbital on the
structure in the region
Spectroscopy of proton-rich 79Zr : Mirror energy differences in the highly-deformed fpg shell
Energy differences between isobaric analogue states have been extracted for the A=79, 79Zr/79Y mirror pair following their population via nucleon-knockout reactions from intermediate-energy rare-isotope beams. These are the heaviest nuclei where such measurements have been made to date. The deduced mirror energy differences (MED) are compared with predictions from a new density-functional based approach, incorporating isospin-breaking effects of both Coulomb and nuclear charge-symmetry breaking and configuration mixing
Electromagnetic properties of 21O for benchmarking nuclear Hamiltonians
The structure of exotic nuclei provides valuable tests for state-of-the-art
nuclear theory. In particular electromagnetic transition rates are more
sensitive to aspects of nuclear forces and many-body physics than excitation
energies alone. We report the first lifetime measurement of excited states in
O, finding
\,ps. This
result together with the deduced level scheme and branching ratio of several
-ray decays are compared to both phenomenological shell-model and ab
initio calculations based on two- and three-nucleon forces derived from chiral
effective field theory. We find that the electric quadrupole reduced transition
probability of $\rm B(E2;1/2^+ \rightarrow 5/2^+_{g.s.}) = 0.71^{+0.07\
+0.02}_{-0.06\ -0.06}^2^41/2^+$
state, is smaller than the phenomenological result where standard effective
charges are employed, suggesting the need for modifications of the latter in
neutron-rich oxygen isotopes. We compare this result to both large-space and
valence-space ab initio calculations, and by using multiple input interactions
we explore the sensitivity of this observable to underlying details of nuclear
forces.Comment: 23 pages, 3 figure
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