Neutron Drip Research Articles

Mass measurements of Ga60–63 reduce x-ray burst model uncertainties and extend the evaluated T=1 isobaric multiplet mass equation

We report precision mass measurements of neutron-deficient gallium isotopes approaching the proton drip line. The measurements of Ga60–63 performed with the TITAN multiple-reflection time-of-flight mass spectrometer provide a more than threefold improvement over the current literature mass uncertainty of Ga61 and mark the first direct mass measurement of Ga60. The improved precision of the Ga61 mass has important implications for the astrophysical rp process, as it constrains essential reaction Q values near the Zn60 waiting point. Based on calculations with a one-zone model, we demonstrate the impact of the improved mass data on prediction uncertainties of x-ray burst models. The first-time measurement of the Ga60 ground-state mass establishes the proton-bound nature of this nuclide, thus constraining the location of the proton drip line along this isotopic chain. Including the measured mass of Ga60 further enables us to extend the evaluated T=1 isobaric multiplet mass equation up to A=60.Received 14 August 2021Revised 22 October 2021Accepted 16 November 2021DOI:https://doi.org/10.1103/PhysRevC.104.065803©2021 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasBinding energy & massesCoulomb energies & analogue statesModels based on symmetriesNuclear astrophysicsNuclear physics of explosive environmentsNuclear reactionsNucleosynthesis in explosive environmentsShell modelProperties59 ≤ A ≤ 89MassTechniquesMass spectrometryTime-of-flight mass spectrometryNuclear Physics

Surface properties for Ne, Na, Mg, Al, and Si isotopes in the coherent density fluctuation model using the relativistic mean-field densities

We have systematically studied the surface properties, such as symmetry energy, neutron pressure, and symmetry energy curvature coefficient for Ne, Na, Mg, Al, and Si nuclei from the proton to neutron drip lines. The coherent density fluctuation model (CDFM) is used to estimate these quantities taking the relativistic mean-field densities as inputs. The Brückner energy density functional is taken for the nuclear matter binding energy and local density approximation is applied for its conversion to coordinate space. The symmetry energy again decomposed to the volume and surface components within the liquid drop model formalism to the volume and surface parts separately. Before calculating the surface properties of finite nuclei, the calculated bulk properties are compared with the experimental data, whenever available. The NL3* parameter set with the Bardeen–Cooper–Schrieffer (BCS) pairing approach in an axially deformed framework is used to take care of the pairing correlation when needed. The deformed density is converted to its spherical equivalent with a two-Gaussian fitting, which is used as an input for the calculation of weight function in the CDFM approximation. With the help of the symmetry energy, the isotopes 29F, 28Ne, 29,30Na, and 31,35,36Mg are considered to be within the island of inversion (Han et al. Phys. Lett. B, 772, 529 (2017). doi:10.1016/j.physletb.2017.07.007). Although we get large symmetry energies corresponding to a few neutron numbers for this isotopic chain as expected, an irregular trend appears for all these considered nuclei. The possible reason behind this abnormal behavior of symmetry energy for these lighter mass nuclei is also included in the discussion, which gives a direction for future analysis.

Ground State Properties and Shape Transition of Even-Even 76Os, 78Pt, 80Hg and 82Pb Isotopes in the Framework of Skyrme Hartree-Fock-Bogoliubov Theory

The Hartree-Fock-Bogolyubov (HFB) theory is a good theoretical approximation for describing the nuclear structure of neutron-rich deformed nuclei, it is generalized the HF theory with BCS pairing theory. In this work, ground-state properties of even-even 76Os, 78Pt, 80Hg and 82Pb isotopes from proton drip-line to neutron drip-line have been studied in the framework of the axially deformed Hartree-Fock-Bogoliubov (HFB) method with two Skyrme nucleon-nucleon force HFB9 and UNE1. The numerically calculated results of binding energy, two neutron separation energy, two neutron shell gap, quadrupole deformation, neutron pairing gap and charge radius are discussed and compared with the available values of the experiment, Finite Range Droplet Model (FRDM), Relativistic Mean-Field (RMF) and Hartree-Fock-Bogoliubov based on D1S Gognay force. The energy surface curves are plotted for some isotones of the investigated nuclei, the transition in the shapes was clear with the change in the number of neutrinos. Our calculations show good agreements in comparison with other data and results.

Cross-Shell Excitation in F and Ne Isotopes around N = 20

Within the framework of the configuration–interaction shell model, the present work applies three effective interactions to investigate the effects of the cross-shell excitation on F and Ne isotopes around N = 20, which are significantly proton–neutron asymmetric, and have different properties compared with the proton–neutron symmetric nuclei. It is shown that cross-shell excitation is necessary in order to reproduce separation energies, neutron drip lines, and low-energy levels of these isotopes. Furthermore, the cross-shell excitation of (0–5)ħω is suggested to be important in the description of 29F and 30Ne. However, the three interactions are insufficient in describing the bound structure of 29,31Ne, and provide inconsistent shell structures and evolutions in the target nuclei. Their cross-shell interactions are suggested to be improved.

Proton radioactivity and α-decay of neutron-deficient nuclei

Proton radioactivity and α-decay half-lives of neutron-deficient nuclei have been systematically studied. The proton-nucleus interaction potential is developed by single folding the density distribution of the daughter nuclei with the effective M3Y-Paris nucleon-nucleon (NN) interaction. The penetrability is calculated with the Wentzel-Kramers-Brillouin approximation. The applicability of the universal decay law on the proton decay half-lives has been examined and a new set of parameters has been identified. The competition between α-decay and proton radioactivity of neutron-deficient nuclei has been investigated. The proton radioactivity is found to be the dominant mode of decay for nuclides located very close to the proton drip-line. The effect of using different microscopic proton and neutron density distributions on the half-lives for these two decay modes is studied. It is found that the calculated half-lives with the microscopic densities that obtained from the self-consistent Hartree–Fock-Bogoliubov method successfully reproduce the experimental data. The impact of nuclear deformation on the half-lives is investigated for these two decay modes. The influence of nonlocality through the finite-range exchange part of the NN interaction on the α-decay process is elucidated. Our theoretical calculations have been confirmed experimentally and satisfactory agreement has been achieved.

Rich band structure and multiple long-lived isomers in the odd-odd Cs118 nucleus

One of the largest sets of collective excitations built on two-quasiparticle configurations in odd-odd nuclei of the proton-rich A≈120 mass region is reported in Cs118. Several new rotational bands and long-lived isomers have been identified. The 8+ bandhead of the πh11/2⊗νh11/2 band is a short-lived isomer with a half-life in the nanosecond range, while the 7+ state below it is a long-lived isomer with a half-life of T1/2=0.55(6)μs. Two other long-lived isomers have been identified: a 66-keV transition detected at the MARA focal plane depopulates one of them, indicating a half-life in the microsecond range, while no depopulating transitions have been identified for the other, indicating a much longer half-life. Extensive particle number conserving cranked shell model calculations and alignment analysis have been employed to investigate the rich band structure of Cs118, which exhibits one of the most complete sets of two-quasiparticle configurations in nuclei close to the proton drip line.11 MoreReceived 12 May 2021Accepted 8 October 2021DOI:https://doi.org/10.1103/PhysRevC.104.044325©2021 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasCollective levelsCollective modelsElectromagnetic transitionsIsomer decaysLifetimes & widthsNuclear spin & parityNuclear structure & decaysProperties90 ≤ A ≤ 149Nuclear Physics

β -delayed neutron-emission and fission calculations within relativistic quasiparticle random-phase approximation and a statistical model

Background: $\ensuremath{\beta}$-delayed neutron emission and fission are essential in $r$-process nucleosynthesis. Although the number of experimental studies covering $r$-process nuclei has recently increased, the uncertainties of $\ensuremath{\beta}$-delayed neutron emission and fission are still large for $r$-process simulations.Purpose: Our aim is to introduce a theoretical framework for the description of $\ensuremath{\beta}$-delayed neutron-emission and fission rates based on relativistic nuclear energy density-functional and statistical models and investigate their properties throughout the nuclide map.Methods: To obtain $\ensuremath{\beta}$ strength functions, the relativistic proton-neutron quasiparticle random-phase approximation is employed. Particle evaporations and fission from highly excited nuclear states are estimated by the Hauser-Feshbach statistical model. $\ensuremath{\beta}$-delayed neutron branching ratios ${P}_{n}$ are calculated and compared with experimental data, and the $\ensuremath{\beta}$-delayed fission branching ratio ${P}_{f}$ are also assessed by using different fission barrier data.Results: Calculated ${P}_{n}$ are in a good agreement with the experimental data and the root mean square deviation is comparable to results of preceding works. It is found that energy withdrawal by $\ensuremath{\beta}$-delayed neutron-emission sensitivity varies ${P}_{n}$, especially for nuclei near the neutron drip line. ${P}_{f}$ depend sensitively on fission barrier data. It is found that not only the barrier height but also the number of barrier humps is important to evaluate ${P}_{f}$.Conclusions: The framework introduced in this work provides an improved theoretical description of the $\ensuremath{\beta}$-delayed neutron emission and fission. Since ${P}_{f}$ as well as ${P}_{n}$ depend strongly on fission barrier information, four kinds of fission barrier data are used in this work to allow further sensitivity studies of the $r$-process nucleosynthesis on the nuclear fission. More studies on fission barrier are highly requested to assess the role of $\ensuremath{\beta}$-delayed fission in the $r$-process study. A complete set of calculated data for $\ensuremath{\beta}$-delayed neutron emission and fission are summarized as a table in supplemental material for its use in $r$-process studies as well as to complement a part of nuclear data in which no experimental data are available.

Collapse of N = 28 magicity in exotic 40Mg—probe of deformed halo and 2n-radioactivity at Mg neutron drip-line

The exotic phenomenon of two-neutron halos and 2n-radioactivity are explored in the neutron-rich 40,42,44Mg by employing various variants of the relativistic mean-field approach. The extended tail of spatial density distributions including the enhanced neutron radii and skin thickness, pairing correlations, single-particle spectrum and wave functions predict 40,42,44Mg to be strong candidates for deformed neutron halos. Weakening of magicity at N = 28 plays a significant role in the existence of a weakly bound halo in 40Mg which is currently the heaviest isotope of Mg accessible experimentally. Large deformation, mixing of f–p shell Nilsson orbitals and the valence neutron occupancy of p-states leads to a reduced centrifugal barrier and broader spatial density distributions that favour 2n-radioactivity in 42,44Mg.

Proton inelastic scattering reveals deformation in 8He

A measurement of proton inelastic scattering of 8He at 8.25A MeV at TRIUMF shows a resonance at 3.54(6) MeV with a width of 0.89(11) MeV. The energy of the state is in good agreement with coupled cluster and no-core shell model with continuum calculations, with the latter successfully describing the measured resonance width as well. Its differential cross section analyzed with phenomenological collective excitation form factor and microscopic coupled reaction channels framework consistently reveals a large deformation parameter β2 = 0.40(3), consistent with no-core shell model predictions of a large neutron deformation. This deformed double-closed shell at the neutron drip-line opens a new paradigm.

Systematical studies of theE1photon strength functions combining the Skyrme-Hartree-Fock-Bogoliubov plus quasiparticle random-phase approximation model and experimental giant dipole resonance properties

Valuable theoretical predictions of nuclear dipole excitations in the whole nuclear chart are of great interest for different applications, including in particular nuclear astrophysics. We present here the systematic study of the electric-dipole $(E1)$ photon strength functions combining the microscopic Hartree-Fock-Bogoliubov plus quasiparticle random-phase approximation (HFB $+$ QRPA) model and the parametrizations constrained by the available experimental giant dipole resonance (GDR) data. For about 10 000 nuclei with $8\ensuremath{\le}\mathrm{Z}\ensuremath{\le}124$ lying between the proton and the neutron drip-lines on nuclear chart, the particle-hole (ph) strength distributions are computed using the HFB + QRPA model under the assumption of spherical symmetry and making use of the BSk27 Skyrme effective interaction derived from the most accurate HFB mass model (HFB-27) so far achieved. Large-scale calculations of the BSk27 + QRPA $E1$ photon strength functions are performed in the framework of a specific folding procedure describing the damping of nuclear collective motion empirically. In particular, three phenomenological improvements are considered in this folding procedure. First, two interference factors are introduced and adjusted to reproduce at best the available experimental GDR data. Second, an empirical expression accounting for the deformation effect is applied to describe the peak splitting of the strength function. Third, the width of the strength function is corrected by a temperature-dependent term, which effectively increases the deexcitation photon strength function at low energy. The theoretical $E1$ photon strength functions as well as the extracted GDR peaks and widths are comprehensively compared with available experimental data. A relatively good agreement with data indicates the reliability of the present calculations. Eventually, the astrophysical rates of $(n,\ensuremath{\gamma})$ reactions for all the 10 000 nuclei with $8\ensuremath{\le}Z\ensuremath{\le}124$ lying between the proton and the neutron drip lines are estimated using the present $E1$ photon strength functions. The resulting reaction rates are compared with the previous BSk7 + QRPA results as well as the Gogny-HFB + QRPA predictions based on the D1M interaction.

Signature of magic numbers in light exotic nuclei

The advent of technology widened the study of shell closure for nuclei lying far away from the stability line. The classic shell closures are observed to be valid for nuclei near the stability line. The light exotic nuclei exhibit unique behavior compared to those of stable ones. The objective of this work is to study the shell closure in light nuclei near the neutron drip-line to the proton drip-line region. The systematics of two nucleon separation energy difference ([Formula: see text]) between calculated and experimental data are taken as a tool to study the shell closure of light nuclei. Nucleon separation energy is determined using the liquid drop model (LDM) expression with modified asymmetry and pairing energy terms. The light mass numbered isotopes and isotones as a function of even neutron and even proton numbers were considered for this work. The shell structure predicted by [Formula: see text] systematics is compared with the first excitation energy [Formula: see text]. The modified LDM is successful in identifying the shell structure properties of light nuclei in exotic region. The study supports the emergence of new shell closure and the disappearance of existing classic shell closure for both neutron and proton numbers. The shell structure predicted by [Formula: see text] systematics for isotopes (isotones) of magic nucleon number [Formula: see text] was in agreement with the results of [Formula: see text] analysis.

Mass Measurements of Neutron-Deficient Yb Isotopes and Nuclear Structure at the Extreme Proton-Rich Side of the N=82 Shell.

High-accuracy mass measurements of neutron-deficient Yb isotopes have been performed at TRIUMF using TITAN's multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS). For the first time, an MR-TOF-MS was used on line simultaneously as an isobar separator and as a mass spectrometer, extending the measurements to two isotopes further away from stability than otherwise possible. The ground state masses of ^{150,153}Yb and the excitation energy of ^{151}Yb^{m} were measured for the first time. As a result, the persistence of the N=82 shell with almost unmodified shell gap energies is established up to the proton drip line. Furthermore, the puzzling systematics of the h_{11/2}-excited isomeric states of the N=81 isotones are unraveled using state-of-the-art mean field calculations.

Hyperspherical three-body model calculation for the bound and resonant states of the neutron dripline nuclei 42,44Mg using isospectral potential

In this paper, an effective theoretical scheme is presented to investigate ground and resonant levels of weakly bound nuclei near the neutron-dripline. The hyperspherical harmonics expansion method is employed for the bound state while supersymmetric quantum mechanics (SSQM) is used for the resonant state. The three-body Schrödinger equation is solved for the lowest bound state with chosen set of two-body potentials to obtain the energy and normalized wavefunction. The three-body effective potential has a very shallow well following a low-wide barrier giving a broad resonance due to far extended wavefunction in the asymptotic region. Numerical computation of such broad resonance is very challenging due to large computational errors. Hence, a one-parameter family of isospectral potential is constructed with the ground state energy and wavefunction, by the use of the algebra of SSQM. This enhanced potential facilitates a more accurate computation of the resonance energy and width. Effectiveness of the scheme has been checked for the J=π0+ bound and resonant states of neutron-rich nuclei 42,44Mg in the coreNN three-body cluster model where core=40,42Mg. In the present calculation, two-neutron separation energies obtained with very large number of partial waves for the J=π0+ bound states of neutron-rich nuclei 42,44Mg are found to be 0.41433 MeV and 0.44975 MeV respectively. Results of the calculation have been compared with those found in the literature.

Possible existence of bound nuclei beyond neutron drip lines driven by deformation * *Supported by the National Natural Science Foundation of China (U2032138, 11775112, 12075085, 11935003, 12047568, 11790323, 11790325) and the State Key Laboratory of Nuclear Physics and Technology, Peking University (NPT2020ZZ01)

Based on the relativistic calculations of the nuclear masses in the transfermium region from No to Ds using the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc), the possible existence of bound nuclei beyond the neutron drip lines is studied. The two-neutron and multi-neutron emission bound nuclei beyond the primary neutron drip line of are predicted in , and isotopes. A detailed microscopic mechanism investigation reveals that nuclear deformation plays a vital role in the existence of bound nuclei beyond the drip line. Furthermore, not only the quadrupole deformation but also the higher orders of deformation are indispensable in the reliable description of the phenomenon of reentrant binding.

Systematic study of two-proton radioactivity with a screened electrostatic barrier * *Supported in part by the National Natural Science Foundation of China (11205083, 11505100, 11705055), the Construct Program of the Key Discipline in Hunan Province, the Research Foundation of Education Bureau of Hunan Province, China (18A237), the Natural Science Foundation of Hunan Province, China (2018JJ3324), the Innovation Group of Nuclear

In this study, a phenomenological model is proposed based on Wentzel-Kramers-Brillouin (WKB) theory and applied to investigate the two-proton ( ) radioactive half-lives of nuclei near or beyond the proton drip line. The total diproton-daughter nucleus interaction potential is composed of the Hulthen-type electrostatic term and the centrifugal term. The calculated radioactive half-lives can accurately reproduce the existing 10 experimental datasets of five true radioactive nuclei with σ = 0.736. In addition, we extend this model to predict the half-lives of possible radioactive nuclei whose radioactivity is energetically allowed or observed but not yet quantified in NUBASE2016. The predicted results are in agreement with those obtained using the Gamow-like model, generalized liquid drop model, Sreeja formula, and Liu formula.

Astrophysical reaction rates of [formula omitted]-induced reactions for nuclei with [formula omitted] from the new Atomki-V2 [formula omitted]-nucleus potential

The new Atomki-V2 α-nucleus potential is applied to calculate astrophysical reaction rates NA〈σv〉 of intermediate mass and heavy target nuclei from iron (Z=26) up to bismuth (Z=83). Overall, reaction rates of α-induced reactions are provided for 4359 target nuclei, covering as well neutron-deficient as extremely neutron-rich target nuclei from the proton to the neutron dripline. Contrary to previous rate compilations, these new calculations include all relevant exit channels with the dominating (α, xn) reactions for neutron-rich target nuclei.

Predictive power for superheavy nuclear mass and possible stability beyond the neutron drip line in deformed relativistic Hartree-Bogoliubov theory in continuum

The predictive power of the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc) for nuclear mass is examined in the superheavy region, $102\ensuremath{\le}Z\ensuremath{\le}120$. The accuracy of predicting the 10 (56) measured (measured and empirical) masses is 0.635 (0.642) MeV, in comparison with 0.515 (1.360) MeV by WS4 and 0.910 (2.831) MeV by FRDM. Possible stability against multineutron emission beyond the two-neutron drip line is explored by the DRHBc theory, which takes into account simultaneously the deformation effects, the pairing correlations, and the continuum effects. Nuclei stable against two- and multineutron emissions beyond the two-neutron drip line are predicted in $_{106}\mathrm{Sg}, _{108}\mathrm{Hs}, _{110}\mathrm{Ds}$, and $_{112}\mathrm{Cn}$ isotopic chains, forming a peninsula of stability adjacent to the nuclear mainland. This stability is mainly due to the deformation which significantly affects the shell structure around the Fermi surface. The pairing correlations and continuum influence the stability peninsula in a self-consistent way.

A Development of a 40-Gb/s Readout Interface STARE for the AGATA Project

The Advanced GAmma Tracking Array (AGATA) multidetector spectrometer will provide precise information for the study of the properties of the exotic nuclear matter (very unbalanced proton (Z) and neutron (N) numbers) along proton- and neutron-drip lines and of super-heavy nuclei. This is done using the latest technology of particle accelerators. The AGATA spectrometer consists of 180 high-purity germanium detectors. Each detector is segmented into 38 segments. The very harsh project requirements are to measure gamma-ray energies with very high resolution ( <; 1×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> ) at a high detector counting rate (50 K events/s/crystal). This results in a very high data transfer rate per crystal (5-8 Gb/s). The 38 segments are sampled at 100 MHz with 14 bits of resolution. The samples are continuously transferred to the control and processing (CAP) module, which reduces the data rate from 64 to 5 Gb/s. The CAP module also adds continuous monitoring data, which results in total outgoing data rate of 10 Gb/s. The serial transfer acquisition and readout over Ethernet (STARE) module is designed to fit between the CAP module and the computer farm. It will package the data from the CAP module and transmit it to the server farm using a 10-Gb/s user datagram protocol (UDP) connection with a delivery insurance mechanism implemented to ensure that all data are transferred.

Systematic study of two-proton radioactivity half-lives based on a modified Gamow-like model

In this work, we systematically study the two-proton ([Formula: see text]) radioactivity half-lives of nuclei close to the proton drip line within a modified Gamow-like model. Using this model, the calculated [Formula: see text] radioactivity half-lives can well reproduce the experimental data. Moreover, we blackuse this model to predict the [Formula: see text] radioactivity half-lives of 22 candidates blackwhose [Formula: see text] radioactivity is energetically allowed or observed but not yet quantized in evaluated nuclear properties table NUBASE2016. blackThe predicted results are in good agreement with the ones obtained by using Gamow-like model, effective liquid drop model (ELDM), generalized liquid drop model (GLDM) as well as a four-parameter formula.

Odd-even staggering for production cross sections ofnuclei near the neutron drip-line * *Supported by the National Natural Science Foundation of China (12005314) and the SYSU 100 Top Talents Program

In our previous studies [Phys. Rev. C 97, 044619 (2018); Phys. Rev. C 103, 044610 (2021)], a universal odd-even staggering (OES) has been observed in extensive cross sections of isotopes not far from stability, measured for different fragmentation and spallation reactions. Four OES relations have been proposed on the basis of this OES universality. However, it is still unclear whether this OES universality and OES relations are applicable to many isotopes near the drip-lines. Here, the OES in recent experimental cross sections of very neutron-rich nuclei approaching the drip-line (from Ge, Se+ Be) is quantitatively investigated, to further validate the OES universality and OES relations. The OES magnitudes in these experimental data approaching the neutron drip-line generally agree with those evaluated previously, mainly from experimental data near stability. New OES evaluations derived from these experimental data are also recommended for more exotic nuclei near the neutron drip-line, which extends the conclusions of our previous OES studies. In addition, the OES relation calculations are consistent with these experimental data of very neutron-rich nuclides according to their comparisons in this work. Finally, comparisons with additional experimental data (from U+ Be) also support that new OES evaluations and OES relation calculations can be applied for exotic nuclei near the neutron drip-line.