Exclusive cross sections and momentum distributions have been measured for quasifree one-neutron knockout reactions from a Ca-54 beam striking on a liquid hydrogen target at similar to 200 MeV/u. A ...significantly larger cross section to the p(3/2), state compared to the f(5/2) state observed in the excitation of Ca-53 provides direct evidence for the nature of the N = 34 shell closure. This finding corroborates the arising of a new shell closure in neutron-rich calcium isotopes. The distorted-wave impulse approximation reaction formalism with shell model calculations using the effective GXPF1Bs interaction and ab initio calculations concur our experimental findings. Obtained transverse and parallel momentum distributions demonstrate the sensitivity of quasifree one-neutron knockout in inverse kinematics on a thick liquid hydrogen target with the reaction vertex reconstructed to final state spin-parity assignments.
One of the important rotational resonances in nonaxisymmetric neoclassical transport has been experimentally validated in the KSTAR tokamak by applying highly nonresonant n=1 magnetic perturbations ...to rapidly rotating plasmas. These so-called bounce-harmonic resonances are expected to occur in the presence of magnetic braking perturbations when the toroidal rotation is fast enough to resonate with periodic parallel motions of trapped particles. The predicted and observed resonant peak along with the toroidal rotation implies that the toroidal rotation in tokamaks can be controlled naturally in favorable conditions to stability, using nonaxisymmetric magnetic perturbations.
We report on the first proton-induced single proton- and neutron-removal reactions from the neutron-deficient ^{14}O nucleus with large Fermi-surface asymmetry S_{n}-S_{p}=18.6 MeV at ∼100 ...MeV/nucleon, a widely used energy regime for rare-isotope studies. The measured inclusive cross sections and parallel momentum distributions of the ^{13}N and ^{13}O residues are compared to the state-of-the-art reaction models, with nuclear structure inputs from many-body shell-model calculations. Our results provide the first quantitative contributions of multiple reaction mechanisms including the quasifree knockout, inelastic scattering, and nucleon transfer processes. It is shown that the inelastic scattering and nucleon transfer, usually neglected at such energy regime, contribute about 50% and 30% to the loosely bound proton and deeply bound neutron removal, respectively. These multiple reaction mechanisms should be considered in analyses of inclusive one-nucleon removal cross sections measured at intermediate energies for quantitative investigation of single-particle strengths and correlations in atomic nuclei.
Direct proton-knockout reactions of Sc-55 at similar to 220 MeV/nucleon were studied at the RIKEN Radioactive Isotope Beam Factory. Populated states of Ca-54 were investigated through -ray and ...invariant-mass spectroscopy. Level energies were calculated from the nuclear shell model employing a phenomenological intemucleon interaction. Theoretical cross sections to states were calculated from distorted-wave impulse approximation estimates multiplied by the shell model spectroscopic factors, which describe the wave function overlap of the Sc-55 ground state with states in Ca-54. Despite the calculations showing a significant amplitude of excited neutron configurations in the ground-state of Sc-55, valence proton removals populated predominantly the ground state of Ca-54. This counterintuitive result is attributed to pairing effects leading to a dominance of the ground-state spectroscopic factor. Owing to the ubiquity of the pairing interaction, this argument should be generally applicable to direct knockout reactions from odd-even to even-even nuclei.
The first γ-ray spectroscopy of 52Ar, with the neutron number N = 34, was measured using the 53K(p, 2p) one-proton removal reaction at ~210 MeV/u at the RIBF facility. The 2+1 excitation energy is ...found at 1656(18) keV, the highest among the Ar isotopes with N > 20. This result is the first experimental signature of the persistence of the N = 34 subshell closure beyond 54Ca, i.e., below the magic proton number Z = 20. Shell-model calculations with phenomenological and chiral-effective-field-theory interactions both reproduce the measured 2+1 systematics of neutron-rich Ar isotopes, and support a N = 34 subshell closure in 52Ar.
The CUP array of germanium (CAGe) is an array of fourteen high-purity germanium (HPGe) detectors. The detection efficiency of full-energy-peak emitted from the various samples assayed on the CAGe was ...calculated using the Monte Carlo simulation toolkit GEANT4. If the dead layer on the surface of the crystal is treated in the simulation as a continuous part of the active crystal, then the detection efficiency will be overestimated. Thus, the detection efficiency of the CAGe was adjusted using multi-nuclide source data and Monte Carlo simulations. The gamma spectra of the known activity source were obtained for each HPGe detector of the CAGe. The detection efficiency measured by the multi-source data was smaller than that of simulation data if the simulation treated the whole volume of germanium crystals as active for gamma detection. By optimizing the dead layers’ thicknesses in the simulation, the detection efficiency calculated by the simulation could be matched to that of multi-source data.
•Detection efficiency of an array of fourteen HPGe detectors was adjusted using Monte Carlo simulation and multi-source data.•Eleven gamma energy peaks emitted from multi-source are used for the detection efficiency calibration.•Good agreement between simulation and measurement is found by dead layer thickness optimizing in GEANT4 simulation geometry.
Direct reaction experiments in inverse kinematics are one of the best experimental tools to study a wide range of nuclear properties, providing a great probe into the nuclear structure of exotic ...nuclei and enabling the measurement of reactions relevant to many astrophysical scenarios. In order to fully exploit the next generation of radioactive ion beam facilities, a large amount of effort was devoted to developing nuclear detectors specially designed for direct reaction experiments. An instrumental part of these detector devices is the Micron X6 position-sensitive double sided silicon strip detector. This custom-made detector is segmented in 4 strips on its ohmic side and 8 resistive charge-splitting strips on its junction side, providing excellent position measurement of charged particles with a much smaller number of signals than traditional DSSSD with similar position resolution.
Abstract
KoBRA of RAON has been prepared for various low energy nuclear physics studies such as nuclear structure, reactions, and astrophysics. An
α
-particle transport test was performed using a ...standard
α
-source of
241
Am so as to examine the design parameters. The position distribution of the
α
-particles was measured with a PPAC at the dispersive and achromatic focal planes, and compared with that of a
lise
++
Monte Carlo calculation. The results are consistent with each other, confirming a few design parameters. We report on the preliminary results of the
α
-particle transport test for KoBRA.
Nuclear physics research at CENS Ahn, S.; Ahn, D. S.; Kim, S. ...
Journal of the Korean Physical Society,
03/2023, Letnik:
82, Številka:
6
Journal Article
Recenzirano
Understanding fundamental interactions of elementary particles is a long sought goal of nuclear physics study. Nuclear theorists recently estimated about 4000 nuclei are still unknown and their ...structures and reaction mechanisms need to be studied by both experiment and theory. The nuclear properties are also important to find the origin of elements in the Universe. The Center for Exotic Nuclear Studies (CENS) at the Institute for Basic Science was founded to address such fundamental problems in astrophysics and nuclear physics. In this paper, the latest research activities at CENS is highlighted and the status of experimental device developments performed by the center is reported.
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