Proton Single-particle Research Articles

Generation of 1.6 GeV single-particle proton beams

We present a scattering slow extraction method employing a rotating foil in the Rapid Cycling Synchrotron (RCS) to produce a stable 1.6 GeV single-particle proton beam at CSNS. The foil scatters particles on the beam’s edge over multiple turns, with those at large scattering angles being separated and extracted through a Lambertson magnet. By adjusting the scatter foil’s rotational speed and position, we can precisely control the intensity and repetition rate of the extracted beam. This approach enables the efficient extraction of extremely low-intensity proton beams from CSNS-II/RCS. By setting single-particle collimators in the downstream beamline, a single-particle proton beam is achieved. Using 4y, we simulated the scattering slow extraction process in detail, confirming that a stable 1.6 GeV single-particle proton beam can be extracted, the beam energy can be adjusted from 0.8 to 1.6 GeV using the degrader, the time interval between adjacent single protons can be adjusted from hundreds of nanoseconds to tens of microseconds, to meet the needs of different experiments. Both the beam loss and the residual radiation doses are kept at low levels. Published by the American Physical Society 2024

Fission valleys and favored isotopes emitted from 310\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{310}$$\\end{document}126

The decay channels for the superheavy nucleus 310\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{310}$$\\end{document}126 are studied under the binary macroscopic–microscopic method. The macroscopic part is calculated as the heavy-light interacting charged liquid drops, linked through the finite range Yukawa-plus-exponential force. The microscopic energy is calculated based on the spheroidally deformed two-center shell model. The proton and neutron single-particle levels are introduced in the binary Strutinsky procedure. The resulting shell corrections are added to the macroscopic part to obtain the fission barriers. The dynamical part follows by introducing the Werner–Wheeler inertia. The final lifetimes are calculated for all possible isotopic channels around the most favored heavy-light fragment pairs.

Ab initio valence-space in-medium similarity renormalization group calculations for neutron-rich P, Cl, and K isotopes* *Supported by the National Key R&D Program of China (2023YFA1606403), the National Natural Science Foundation of China (12205340, 12175281, 12347106, 12121005), the Natural Science Foundation of Gansu Province, China (22JR5RA123, 23JRRA614), the Strategic Priority Research Program of Chinese Academy of Sciences (XDB34000000), the Key Research

Neutron-rich P, Cl, and K isotopes, particularly those with neutron numbers of approximately , have attracted extensive experimental and theoretical interest. We utilize the ab initio valence-space in-medium similarity renormalization group approach, based on chiral nucleon-nucleon and three-nucleon forces, to investigate the exotic properties of these isotopes. Systematic calculations of the low-lying spectra are performed. A key finding is the level inversion between and states in odd-A isotopes, attributed to the inversion of and single-particle states. The ab initio calculations, which incorporate the three-nucleon forces, correlate closely with existing experimental data. Further calculations of effective proton single-particle energies provide deeper insights into the shell evolution for and sub-shells. Our results indicate that the three-body force plays important roles in the shell evolution for and sub-shells with neutron numbers ranging from 20 to 28. Additionally, systematic ab initio calculations are conducted for the low-lying spectra of odd-odd nuclei. The results correspond with experimental data and provide new insights for future research into these isotopes up to and beyond the drip line.

Analysis and identification of degradation products in gas, particle, and liquid phases of polypropylene and polyethyleneterephthalate microplastics aging through non-thermal plasma simulation.

Plastic aging can cause alterations in the physical and chemical characteristics of plastics, as well as their behavior in the environment. Due to the extremely slow natural aging process, laboratory simulated aging methods have to be used. In this study, non-thermal plasma (NTP) was adopted to investigate the aging process of polypropylene (PP) and polyethylene terephthalate (PET) microplastics. Various analytical instruments, including proton transfer reaction mass spectrometry and single-particle aerosol mass spectrometry, were employed to examine and identify the organic constituents of the gas, liquid, and particle phase degradation products, as well as to monitor the degradation process. The results showed that after 90min of aging, both PP and PET surfaces showed yellowing, and the carbonyl index of PP increased while that of PET decreased, with an increase in crystallinity. The organic components of reaction products, such as ketones, esters, acids, and alcohols, increased with longer aging times. Gas products mainly contain aromatic hydrocarbons, while particles from aged PET contain compounds with benzene rings and metal elements. Liquid products from aged PP show a significant presence of branched alkanes. Based on this analysis, degradation mechanisms of PP and PET by NTP were proposed. This investigation represents the initial systematically exploration of the release of organic substances during the degradation of microplastics mediated by NTP. It provides significant insights into the detrimental organic compounds emitted during this process, thereby offering valuable information for understanding the environmental and human health implications of natural microplastic degradation. Furthermore, it addressed the requirements for increased attention to the potential environmental risks associated with these harmful components.

First spectroscopic study of odd-odd Cu78

Nuclei in the vicinity of Ni78 are important benchmarks for nuclear structure, which can reveal changes in the shell structure far from stability. Spectroscopy of the odd-odd isotope Cu78 was performed for the first time in an experiment with the EURICA setup at the Radioactive Isotope Beam Factory at RIKEN Nishina Center. Excited states in the neutron-rich isotope were populated following the β decay of Ni78 produced by in-flight fission and separated by the BigRIPS separator. A level scheme based on the analysis of γ−γ coincidences is presented. Tentative spin and parity assignments were made when possible based on the β-decay feeding intensities and γ-decay properties of the excited states. Time correlations between β and γ decay show clear indications of an isomeric state with a half-life of 3.8(4) ms. Large-scale Monte Carlo shell-model calculations were performed using the A3DA-m interaction and a valence space comprising the full fp shell and the 1g9/2 and 2d5/2 orbitals for both protons and neutrons. The comparison of the experimental results with the shell-model calculations allows interpreting the excited states in terms of spin multiplets arising from the proton-neutron interaction. The results provide further insight into the evolution of the proton single-particle orbitals as a function of neutron number, and quantitative information about the proton-neutron interaction outside the doubly magic Ni78 core.Received 6 October 2022Revised 3 January 2023Accepted 9 January 2023DOI:https://doi.org/10.1103/PhysRevC.107.044301©2023 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasBeta decayEnergy levels & level densitiesIsomer decaysNuclear spin & parityNuclear structure & decaysNucleon-nucleon interactionsShell modelProperties59 ≤ A ≤ 89Nuclear Physics

Proton single-particle energy gaps in Sc isotopes

Variation in the proton single-particle energy gaps is investigated within the framework of nuclear shell model. The change is identified to originate mainly from the central force of the proton-neutron interaction. The relationship between the nuclear state and the single-particle energy gap is discussed. The first 3/2− state of 55Sc reveals the fragile character of N = 34 semi-magic shell gap.

Relativistic and nonrelativistic mean field analysis of the shell evolution in 44−52Ar isotopes

The systematic search of axial ground state and the emergence of new gaps in neutron-rich [Formula: see text]Ar isotopes are the challenging of current calculations of relativistic and nonrelativistic mean field models. For this purpose, we have employed the model based on Relativistic Hartree–Bogoliubov (RHB) with the density-dependent effective interaction of point coupling DD-PCX type. However, the nonrelativistic mean field calculations based on Hartree-Fock model were carried out with Skyrme SV-min parametrization. All the present calculations were performed within axial symmetries. The results provide that most of isotopes show an oblate-deformed ground state. In particular, [Formula: see text]Ar and [Formula: see text]Ar display a spherical shape in their ground states with SV-Min calculations. There is a notable signature of the sub-shell closure at neutron number [Formula: see text], whereas [Formula: see text] is expected to be nearly quenched in the spherical ground. Furthermore, coexistence features are predicted in the neutron-rich [Formula: see text]Ar isotope. We have also studied the neutron axial densities and its central depletion in the well-deformed grounds for the first time. In addition to these, the proton single-particle evolution and bubble-like structure at [Formula: see text]Ar are very well reproduced with DD-PCX calculations.

Bubble nuclei with shape coexistence in even-even isotopes of Hf to Hg

The shape of a nucleus is one of the fundamental nuclear properties. We perform a systematic investigation of bubble nuclei that also exhibit shape coexistence in Hf, W, Os, Pt, and Hg even-even isotopes using the deformed relativistic Hartree-Bogoliubov theory in continuum. For a systematic study, we first consider nuclear bubble structures and shape coexistence separately. We confirm that deformations and pairing correlations hinder bubble structures by comparing our results with those from relativistic continuum Hartree-Bogoliubov theory that assumes spherical symmetry in nuclei. We then predict candidate isotopes with both bubble structure and shape coexistence. We observe that the depletion fraction factor that characterizes bubble structure is mostly smaller in oblate deformation than in prolate, while some isotopes such as $^{206}\mathrm{Os}$ have bubble structures both in oblate and prolate deformations. We compare the proton single-particle energy levels for the candidates of shape coexistence both with only prolate bubble structure and with prolate and oblate bubble structures.

First application of the dispersive optical model to (p,2p) reaction analysis within the distorted-wave impulse approximation framework

Both ($e$,$e'p$) and ($p$,$2p$) reactions have been performed to study the proton single-particle character of nuclear states with its related spectroscopic factor. Recently, the dispersive optical model (DOM) was applied to the ($e$,$e'p$) analysis revealing that the traditional treatment of the single-particle overlap function, distorted waves, and nonlocality must be further improved to achieve quantitative nuclear spectroscopy. We apply the DOM wave functions to the traditional ($p$,$2p$) analysis and investigate the consistency of the DOM spectroscopic factor that describes the ($e$,$e'p$) cross section with the result of the ($p$,$2p$) analysis. Additionally, we make a comparison with a phenomenological single-particle wave function and optical potential. Uncertainty arising from a choice of $p$-$p$ interaction is also investigated. We implement the DOM wave functions to the distorted wave impulse approximation (DWIA) framework for ($p$,$2p$) reactions. DOM + DWIA analysis on $^{40}$Ca($p$,$2p$)$^{39}$K data generates a proton $0d_{3/2}$ spectroscopic factor of 0.560, which is meaningfully smaller than the DOM value of 0.71 shown to be consistent with the ($e$,$e'p$) analysis. Uncertainties arising from choices of single-particle wave function, optical potential, and $p$-$p$ interaction do not explain this inconsistency. The inconsistency in the spectroscopic factor suggests there is urgent need for improving the description of $p$-$p$ scattering in a nucleus and the resulting in-medium interaction with corresponding implications for the analysis of this reaction in inverse kinematics.

Reexamination of the N=50 and Z=28 shell closure

Recent experiments performed in neutron-rich copper isotopes have revealed a crossing in the nucleus $^{75}\mathrm{Cu}$ between the $3/{2}^{\ensuremath{-}}$ and $5/{2}^{\ensuremath{-}}$ levels, which correspond to the ground state and the first excited state in isotopes with mass number below $A=75$. Due to the strong single-particle character of these states, this scenario can be investigated through the analysis of the proton spectrum provided by mean-field models in nickel isotopes with neutron numbers between $N=40$ and $N=50$. In this work, we show that the aforementioned crossing is mainly driven by the mean field provided by the effective nucleon-nucleon and spin-orbit interactions. We also analyze the impact of the tensor interaction and find that in some mean-field models it is essential to reproduce the crossing of the $2{p}_{3/2}$ and $1{f}_{5/2}$ proton single-particle levels, as in the case of the SAMi-T Skyrme force and the D1M Gogny interaction, whereas in other cases, as for example the SLy5 Skyrme force, a reasonable tensor force appears to be unable to modify the mean-field enough to reproduce this level crossing. Finally, in the calculations performed with the so-called simple effective interaction (SEI), it is shown that the experimental data in nickel and copper isotopes considered in this work can be explained satisfactorily without any explicit consideration of the tensor interaction.

Evolution of proton single-particle states in neutron-rich Sb isotopes beyond N=82

The β decay of the semimagic Sn isotopes Sn136,137,138 has been studied at the Radioactive Isotope Beam Factory at the RIKEN Nishina Center. The first experimental information on excited states was obtained for Sb137 while, in the case of Sb136, the established excitation scheme could be extended by ten previously unidentified levels. In the decay of the most-neutron-rich isotope Sn138, two γ rays were observed for the first time. The new experimental results, in combination with state-of-the-art shell-model calculations, provide the first information with respect to the evolution of the 0g7/2 and 1d5/2 proton single-particle states with increasing neutron number beyond N=84.

Charge Radii of Tin Isotopes and Their Proton-Density Distributions within the Dispersive Optical Model

Proton single-particle properties of even–even tin isotopes in the mass number range between 100 and 132 were calculated on the basis of the dispersive optical model. The possibility of describing data on the charge radius $$r_{\mathrm{ch}}$$ was studied. A decrease in the rate of growth of $$r_{\mathrm{ch}}$$ with increasing $$N$$ in the region of $$N>76$$ was obtained via increasing the energy interval in the vicinity of $$E_{\mathrm{F}}$$ where the imaginary part of the potential used is close to zero. The predictive power of the dispersive optical model for the density distribution in nuclei far from the beta-stability valley was demonstrated.

Proton-neutron force and proton single-particle strength in Sc, F, and Li isotopes

In the present work, the effect of proton-neutron interaction and its different components, i.e., central, spin-orbit, and tensor force, on proton shell-structure of odd-$A$ Sc, F, and Li isotopes is studied within the nuclear shell model framework. It has been observed that the central force possesses strong-orbital node $(nl)$ and weak-spin $(j)$ dependency, and plays a key role in producing changes in proton shell-structure. The integrated effect of proton shell-structure and proton single-particle strength in building the level structure of $^{49,53,55}\mathrm{Sc}$, $^{23,25}\mathrm{F}$, and $^{9}\mathrm{Li}$ isotopes are also discussed. Proton single-particle strength in the level structure of above-mentioned nuclei is studied using proton-transfer spectroscopic factors. It has been particularly discerned that the low energy of the ${\frac{3}{2}}_{1}^{\ensuremath{-}}$ state of $^{55}\mathrm{Sc}$ is caused by the weakening of the $N=34$ semimagic gap, the high energy of the ${\frac{1}{2}}_{1}^{+}$ state of $^{23}\mathrm{F}$ is originated from an increase in the energy gap between orbitals $\ensuremath{\pi}1{s}_{1/2}$ and $\ensuremath{\pi}0{d}_{5/2}$ at $N=14$, and the high energy of the ${\frac{1}{2}}_{1}^{\ensuremath{-}}$ state of $^{9}\mathrm{Li}$ is originated from the large energy gap between $\ensuremath{\pi}0{p}_{1/2}$ and $\ensuremath{\pi}0{p}_{3/2}$ orbitals which remained nearly constant from $^{5}\mathrm{Li}$ to $^{9}\mathrm{Li}$.

Analysis of nuclear structure in the nuclear chart and improvement to the gross theory of β decay

The gross theory, a global method for the calculation of nuclear $\ensuremath{\beta}$ decay, is improved using single-particle treatment. We analyzed the $\ensuremath{\beta}$-decay channel for the entire region of nuclides and found that the allowed transition is suppressed systematically in the neighborhood of heavier doubly magic nuclei. This is mainly due to the shift of neutron and proton single-particle levels in one major shell, which leads to a change in the spin and parity between parent and daughter nuclei. Under this consideration, the nuclear matrix elements for the allowed transition in the gross theory are suppressed in the above condition. In the vicinity of the doubly magic numbers of neutron-rich nuclides, such as nuclei with $Z=50$ and 82, the calculated half-lives are longer than those reported in previous work, where only parity mismatch was considered. In superheavy neutron-rich nuclei with $N=184$, the half-lives are predicted to be longer due to the same mechanism.

Pseudospin Symmetry and Microscopic Origin of Shape Coexistence in the ^{78}Ni Region: A Hint from Lifetime Measurements.

Lifetime measurements of excited states of the light N=52 isotones ^{88}Kr, ^{86}Se, and ^{84}Ge have been performed, using the recoil distance Doppler shift method and VAMOS and AGATA spectrometers for particle identification and gamma spectroscopy, respectively. The reduced electric quadrupole transition probabilities B(E2;2^{+}→0^{+}) and B(E2;4^{+}→2^{+}) were obtained for the first time for the hard-to-reach ^{84}Ge. While the B(E2;2^{+}→0^{+}) values of ^{88}Kr, ^{86}Se saturate the maximum quadrupole collectivity offered by the natural valence (3s, 2d, 1g_{7/2}, 1h_{11/2}) space of an inert ^{78}Ni core, the value obtained for ^{84}Ge largely exceeds it, suggesting that shape coexistence phenomena, previously reported at N≲49, extend beyond N=50. The onset of collectivity at Z=32 is understood as due to a pseudo-SU(3) organization of the proton single-particle sequence reflecting a clear manifestation of pseudospin symmetry. It is realized that the latter provides actually reliable guidance for understanding the observed proton and neutron single particle structure in the whole medium-mass region, from Ni to Sn, pointing towards the important role of the isovector-vector ρ field in shell-structure evolution.

Proton single particle energies next to 78Ni: Spectroscopy of 77Cu via single proton knock-out reaction

Excited states of 77Cu have been investigated by use of single proton knock-out reaction at the Radioactive Isotope Beam Factory in RIKEN in order to reveal the main components of the proton single-particle states. Three excited states were observed at 271, 902 and 2068 keV in 77Cu. The lowest-energy excited state follows the trend predicted for the crossing of the 3/21− and 5/21− states. Comparing the excitation energies of the 3/2−, 5/2− and 7/2− levels from 69Cu to 77Cu one can see that the Z=28 shell gap between the p3/2 and f7/2 states is rather stable, while the f5/2−f7/2 spin–orbit splitting decreases by ∼1.5 MeV in agreement with shell model calculations using the tensor force.

Radial overlap correction to superallowed 0+→0+ β decay reexamined

Within the nuclear shell model, we investigate the correction $\delta_{RO}$ to the Fermi matrix element due to a mismatch between proton and neutron single-particle radial wave functions. Eight superallowed $0^+ \to 0^+$ $\beta$ decays in the $sd$-shell, comprised of $^{22}$Mg, $^{26m}$Al, $^{26}$Si, $^{30}$S, $^{34}$Cl, $^{34}$Ar, $^{38m}$K and $^{38}$Ca are re-examined. The radial wave functions are obtained from a spherical Woods-Saxon potential whose parametrizations are optimized in a consistent adjustment of the depth and the length parameter to relevant experimental observables, such as nucleon separation energies and charge radii, respectively. The chosen fit strategy eliminates the strong dependence of the radial mismatch correction to a specific parametrization, except for calculations with an additional surface-peaked term. As an improvement, our model proposes a new way to calculate the charge radii, based on a parentage expansion which accounts for correlations beyond the extreme independent-particle model. Apart from the calculations with a surface-peak term and the cases where we used a different model space, the new sets of $\delta_{RO}$ are in general agreement with the earlier result of Towner and Hardy [1]. Small differences of the corrected average $\overline{\mathcal{F}t}$ value are observed.

Widths of P26(1+) and mass of P26(g.s.)

For the ${1}^{+}$ first-excited state of $^{26}\mathrm{P}$, the lifetime and the upper limit on the proton width have been combined with shell-model spectroscopic factors to place an upper limit on the proton single-particle (sp) width. With a potential model, this limit on sp width allows an upper limit on the ${1}^{+}$ resonance energy of ${E}_{\mathrm{r}}<124\phantom{\rule{0.16em}{0ex}}\mathrm{keV}$. Combining with the known ${1}^{+}$ excitation energy provides a limit on the proton separation energy of $^{26}\mathrm{P}(\mathrm{g}.\mathrm{s}.)$ of ${S}_{\mathrm{p}}>40\phantom{\rule{0.16em}{0ex}}\mathrm{keV}$, considerably better than a recent result of ${S}_{\mathrm{p}}>\ensuremath{-}135\phantom{\rule{0.16em}{0ex}}\mathrm{keV}$ from a similar procedure that used $R$-matrix sp widths.

Two-proton radioactivity with 2p halo in light mass nuclei A = 18–34

Two-proton radioactivity with 2p halo is reported theoretically in light mass nuclei A=18–34. We predict 19Mg, 22Si, 26S, 30Ar and 34Ca as promising candidates of ground state 2p-radioactivity with S2p<0 and Sp>0. Observation of extended tail of spatial charge density distribution, larger charge radius and study of proton single particle states, Fermi energy and the wave functions indicate 2p halo like structure which supports direct 2p emission. The Coulomb and centrifugal barriers in experimentally identified 2p unbound 22Si show a quasi-bound state that ensures enough life time for such experimental probes. Our predictions are in good accord with experimental and other theoretical data available so far.

Single-particle properties of N = 12 to N = 20 silicon isotopes within the dispersive optical model

Experimental neutron and proton single-particle energies in N = 12 to N = 20 silicon isotopes and data on neutron and proton scattering by nuclei of the isotope 28Si are analyzed on the basis of the dispersive optical model. Good agreement with available experimental data was attained. The occupation probabilities calculated for the single-particle states in question suggest a parallel-type filling of the 1d and 2s 1/2 neutron states in the isotopes 26,28,30,32,34Si. The single-particle spectra being considered are indicative of the closure of the Z = 14 proton subshell in the isotopes 30,32,34Si and the N = 20 neutron shell.