The nuclear shell structure, which originates in the nearly independent motion of nucleons in an average potential, provides an important guide for our understanding of nuclear structure and the ...underlying nuclear forces. Its most remarkable fingerprint is the existence of the so-called magic numbers of protons and neutrons associated with extra stability. Although the introduction of a phenomenological spin-orbit (SO) coupling force in 1949 helped in explaining the magic numbers, its origins are still open questions. Here, we present experimental evidence for the smallest SO-originated magic number (subshell closure) at the proton number six in
C obtained from systematic analysis of point-proton distribution radii, electromagnetic transition rates and atomic masses of light nuclei. Performing ab initio calculations on
C, we show that the observed proton distribution radii and subshell closure can be explained by the state-of-the-art nuclear theory with chiral nucleon-nucleon and three-nucleon forces, which are rooted in the quantum chromodynamics.
The Rare-RI Ring (R3) is a recently commissioned cyclotronlike storage ring mass spectrometer dedicated to mass measurements of exotic nuclei far from stability at Radioactive Isotope Beam Factory ...(RIBF) in RIKEN. The first application of mass measurement using the R3 mass spectrometer at RIBF is reported. Rare isotopes produced at RIBF-^{127}Sn, ^{126}In, ^{125}Cd, ^{124}Ag, ^{123}Pd-were injected in R3. Masses of ^{126}In, ^{125}Cd, and ^{123}Pd were measured whereby the mass uncertainty of ^{123}Pd was improved. This is the first reported measurement with a new storage ring mass spectrometry technique realized at a heavy-ion cyclotron and employing individual injection of the preidentified rare nuclei. The latter is essential for the future mass measurements of the rarest isotopes produced at RIBF. The impact of the new ^{123}Pd result on the solar r-process abundances in a neutron star merger event is investigated by performing reaction network calculations of 20 trajectories with varying electron fraction Y_{e}. It is found that the neutron capture cross section on ^{123}Pd increases by a factor of 2.2 and β-delayed neutron emission probability, P_{1 n}, of ^{123}Rh increases by 14%. The neutron capture cross section on ^{122}Pd decreases by a factor of 2.6 leading to pileup of material at A=122, thus reproducing the trend of the solar r-process abundances. The trend of the two-neutron separation energies (S_{2n}) was investigated for the Pd isotopic chain. The new mass measurement with improved uncertainty excludes large changes of the S_{2n} value at N=77. Such large increase of the S_{2n} values before N=82 was proposed as an alternative to the quenching of the N=82 shell gap to reproduce r-process abundances in the mass region of A=112-124.
An electrostatic time-of-flight detector named E-MCP has been developed for quick diagnostics of circulating beam and timing measurement in mass spectrometry at the Rare-RI Ring in RIKEN. The E-MCP ...detector consists of a conversion foil, potential grids, and a microchannel plate. Secondary electrons are released from the surface of the foil when a heavy ion hits it. The electrons are accelerated and deflected by 90∘ toward the microchannel plate by electrostatic potentials. A thin carbon foil and a thin aluminum-coated mylar foil were used as conversion foils. We obtained time resolutions of 69(1) ps and 43(1) ps (standard deviation) for a 84Kr beam at an energy of 170 MeV/u when using the carbon and the aluminum-coated mylar foils, respectively. A detection efficiency of approximately 90% was obtained for both foils. The E-MCP detector equipped with the carbon foil was installed inside the Rare-RI Ring to confirm particle circulation within a demonstration experiment on mass measurements of nuclei around 78Ge produced by in-flight fission of uranium beam at the RI Beam Factory in RIKEN. Periodic time signals from circulating ions were clearly observed. Revolution times for 78Ge, 77Ga, and 76Zn were obtained. The results confirmed successful circulation of the short-lived nuclei inside the Rare-RI Ring.
γ emission probabilities from unbound states in 78,80Se, populated by a neutron-transfer reaction (d,p) on 77,79Se nuclei in inverse kinematics, were measured by directly detecting reaction residues. ...Assuming the spin distribution at the respective excitation energy of the unbound state, the cross-sections of the 79Se(n,γ)80Se reaction were evaluated using the γ emission probabilities. The surrogate-ratio method with the experimental γ emission probabilities of 78,80Se was also employed to deduce the cross-sections of 79Se(n,γ) reaction by incorporating the theoretical evaluations of the neutron-capture reaction on the isomeric state in 77Se. Our two cross-sections are in good agreement with existing nuclear data compilations for the neutron-capture reaction on 79Se. The presented method contributes to the body of existing knowledge by providing approaches for determining the neutron capture cross-sections of radioactive nuclei at various neutron energies.
We measured the energy dependence of the total reaction cross sections (σR) for the proton-drip-line nucleus,17Ne, using a solid hydrogen target. We compared the experimental data with theoretical ...calculations using the Glauber model. We found that the theoretical cross sections overestimate the experimental ones in the low-energy region (∼100A MeV), whereas they significantly underestimate the experimental data in the intermediate-energy region (∼300-500A MeV). These trends are the same as those for σR for carbon-proton collisions, which were measured previously. We discuss several possibilities for resolving this discrepancy. This work demonstrates the necessity of additional careful investigations of the energy dependence of σR for various nuclei on proton targets in order to determine nuclear size properties precisely.
Abstract
The matter radius of the doubly magic
$$^{56}$$
56
Ni was extracted from a measurement of the differential cross section by employing, for the first time, elastic proton scattering in ...inverse kinematics with a radioactive beam at
$$E_{kin}=390.2$$
E
kin
=
390.2
MeV/nucleon circulating in a storage ring and passing an internal hydrogen gas-jet target with a revolution frequency of around 2 MHz. The novel experimental scheme is based on UHV-compatible Si detectors operated as active vacuum windows, which were implemented in the ESR storage ring at GSI. A matter radius
$$<r_{m}^{2}>^{1/2}=3.74^{+0.03}_{-0.06}$$
<
r
m
2
>
1
/
2
=
3
.
74
-
0.06
+
0.03
fm was extracted for the doubly-magic self-conjugate nucleus
$$^{56}$$
56
Ni.
An experiment addressing electron capture (EC) decay of hydrogen-like Pm60+142 ions has been conducted at the experimental storage ring (ESR) at GSI. The decay appears to be purely exponential and no ...modulations were observed. Decay times for about 9000 individual EC decays have been measured by applying the single-ion decay spectroscopy method. Both visually and automatically analysed data can be described by a single exponential decay with decay constants of 0.0126(7)s−1 for automatic analysis and 0.0141(7)s−1 for manual analysis. If a modulation superimposed on the exponential decay curve is assumed, the best fit gives a modulation amplitude of merely 0.019(15), which is compatible with zero and by 4.9 standard deviations smaller than in the original observation which had an amplitude of 0.23(4).
We measured the energy dependence of the total reaction cross sections (σR) for the proton drip-line nucleus of neon isotopes, 17Ne, with a solid hydrogen target. The σR on a proton target in the ...low- and intermediate-energy regions were provided, where only a few values are available for unstable nuclei. The new data were compared with theoretical calculations using the Glauber model. In the low-energy region (∼100A MeV), the theoretical cross sections overestimate the experimental ones, whereas the theoretical ones significantly underestimate the experimental data in the intermediate energy region (∼300-500A MeV). We discuss several possibilities for solving this discrepancy. This work suggests the necessity of more careful investigations of the energy dependence of σR for various nuclei on a proton target to determine the nuclear size properties precisely.
Performance of the OEDO beamline Hwang, J W; Michimasa, S; Yamada, K ...
Journal of physics. Conference series,
12/2020, Letnik:
1643, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The OEDO (Optimized Energy Degrading Optics for RI beam) beamline has been developed to obtain low-energy (10 - 50 MeV/u) RI beams by slowing down the secondary beams at RIBF, RIKEN. Such beams are ...useful probes to investigate nuclear structure by means of nucleon transfer and Coulomb excitation reactions. The beamline is designed to produce a well-focused beam of small energy spread with the help of the angle-tuneable wedge degrader and the radio-frequency deflector. The commissioning and first physics experiments using the OEDO beamline were carried out in 2017. OEDO successfully provided the energy-degraded beams of Se, Zr, and Pd. Its performance including the optics and transmission was evaluated using those experimental data and it functions properly as designed. We expect that our novel beamline shed a light on the experimental approaches involving nuclear reactions at several tens of MeV/u to expand our knowledge of nuclei far beyond the line of stability.
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