The connection between fundamental nucleon-nucleon forces and the observed many-body structure of nuclei is a main question of modern nuclear physics. Evolution of the mean field, inversion of ...traditional shell structures, and structure of high spin states in nuclei with extreme proton-to-neutron ratios are at the center of numerous recent experimental investigations targeting the matrix elements of the effective nuclear Hamiltonian that is responsible for these phenomena. The FSU spsdfp cross-shell interaction for the shell model was successfully fitted to a wide range of mostly intruder negative parity states of the sd shell nuclei. In this paper, we explore the evolution of nuclear structure in and around the island of inversion (IoI), where low-lying states involve cross-shell particle-hole excitations. We apply the FSU interaction to systematically trace out the relative positions of the effective single-particle energies of the 0f_{7/2} and 1p_{3/2} orbitals forming the N=20 and 28 shell gaps. We find that above a proton number of about 13, the 0f_{7/2} neutron orbital lies below that of 1p_{3/2}, which is considered normal ordering but, systematically, for more exotic nuclei with lower Z=12 and 10 the order of orbitals reversed. The crossing of the neutron orbitals happens right near the neutron separation threshold. Our Hamiltonian reproduces remarkably well the absolute binding energies for a broad range of nuclei and the inversion in the configurations of nuclei inside the IoI. The effective interaction accounts well for the energies and variations with mass number A of aligned high-spin states that involve nucleon pairs prompted across the shell gap. This paper puts forward an empirically determined effective Hamiltonian where data from many recent experiments allowed us to significantly improve our knowledge about cross-shell nuclear interaction matrix elements. The quality with which this Hamiltonian describes the two-particle, two-hole cross-shell excitations, binding energies, and the physics of aligned states that were not a part of the fit, is remarkable, making the FSU interaction an important tool for the future exploration of exotic nuclei.
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Beta-decay spectroscopy experiments are limited by the detection efficiency of ions and electrons in the experimental setup. While there is a variety of different experimental setups in use for ...beta-decay spectroscopy, one popular choice is silicon double-sided strip detectors (DSSD). The higher Z of Ge and greater availability of thicker detectors as compared to Si potentially offer dramatic increases in the detection efficiency for beta-decay electrons. In this work, a planar GeDSSD has been commissioned for use in beta-decay spectroscopy experiments at the National Superconducting Cyclotron Laboratory (NSCL). The implantation response of the detector and its beta-decay detection efficiency is discussed.
•A planar Ge double-sided strip detector is implemented for decay spectroscopy.•Dual range preamplifiers provide sensitivity to both heavy ions and beta-decay electrons.•Beta-decay electron detection efficiencies greater than 50% are demonstrated.•Based on comparisons with simulation, an efficiency of roughly 90% is expected.
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The neutron unbound ground state of (25)O (Z=8, N=17) was observed for the first time in a proton knockout reaction from a (26)F beam. A single resonance was found in the invariant mass spectrum ...corresponding to a neutron decay energy of 770_+20(-10) keV with a total width of 172(30) keV. The N=16 shell gap was established to be 4.86(13) MeV by the energy difference between the nu1s(1/2) and nu0d(3/2) orbitals. The neutron separation energies for (25)O agree with the calculations of the universal sd shell model interaction. This interaction incorrectly predicts an (26)O ground state that is bound to two-neutron decay by 1 MeV, leading to a discrepancy between the theoretical calculations and experiment as to the particle stability of (26)O. The observed decay width was found to be on the order of a factor of 2 larger than the calculated single-particle width using a Woods-Saxon potential.
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9.
New evidence for a subshell gap at N=32 Prisciandaro, J.I.; Mantica, P.F.; Brown, B.A. ...
Physics letters. B,
06/2001, Volume:
510, Issue:
1
Journal Article
Peer reviewed
Open access
An 879.9(2) keV
γ-ray transition has been identified following the
β decay of
58V and assigned as the 2
+
1→0
+
1 transition in
58Cr
34. A peak in the energies of the first excited 2
+ states for the ...even–even chromium isotopes is now evident at
56Cr
32, providing empirical evidence for a significant subshell gap at
N=32. The appearance of this neutron subshell closure for neutron-rich nuclides may be attributed to the diminished
π1
f
7/2–
ν1
f
5/2 monopole proton–neutron interaction as protons are removed from the 1
f
7/2 single-particle orbital.
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The design and performance of a new Compton-suppressed HPGe and charged-particle array, CLARION2-TRINITY, are described. The TRINITY charged-particle array is comprised of 64 Cerium-doped Gadolinium ...Aluminum Gallium Garnet (GAGG:Ce) crystals configured into five rings spanning 7–54 degrees, and two annular silicon detectors that can shadow or extend the angular coverage to backward angles with minimal $\gamma$-ray attenuation. GAGG:Ce is a non-hygroscopic, bright, and relatively fast scintillator with a light distribution well matched to SiPMs. Count rates up to 40 kHz per crystal are sustainable. Fundamental characteristics of GAGG:Ce are measured and presented, including light- and heavy-ion particle identification (PID) capability, pulse-height defects, radiation hardness, and emission spectra. The CLARION2 array consists of up to 16 Compton-suppressed HPGe Clover detectors (efficiency at 1 MeV) configured into four rings (eight HPGe crystal rings) using a non-Archimedean geometry that suppresses back-to-back coincident 511-keV gamma rays. The entire array is instrumented with 100- and 500-MHz (14 bit) waveform digitizers which enable triggerless operation, pulse-shape discrimination, fast timing, and pileup correction. Lastly, two examples of experimental data taken during the commissioning of the CLARION2-TRINITY system are given: a PID spectrum from 16O + 18O fusion-evaporation, and PID and Doppler-corrected -ray spectra from 48Ti + 12C Coulomb excitation.
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