40 research outputs found
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
Competing particleāhole excitations in Ā³ā°Na: Constraining state-of-the-art effective interactions
The oddāodd nucleus Ā³ā°Na is studied via a one-proton, one-protonāone-neutron and one-neutron removal reaction using an intermediate-energy Ā³Ā¹Mg, Ā³Ā²Mg and Ā³Ā¹Na radioactive ion beam, respectively. Combining high-resolution Ī³-ray spectroscopy with the selectivity of the three reaction mechanisms, we are able to distinguish multiple particleāhole configurations. Negative-parity states in Ā³ā°Na are observed for the first time, providing an important measure of the excitation of the 1p1h/3p3h configuration and hence the sdāpf shell gap. The extracted band structures and level energies serve as invaluable input for the theoretical refinement of the effective interactions used in this region