The limits of the nuclear landscape explored by the relativistic continuum Hartree–Bogoliubov theory

The Insight -Hard X-ray Modulation Telescope ( Insight -HXMT) is a broadband X-ray and γ-ray (1-3000 keV) astronomy satellite. One of its three main telescopes is the High Energy X-ray telescope (HE). The main detector plane of HE comprises 18 NaI(Tl)/CsI(Na) phoswich detectors, where NaI(Tl) is used as the primary detector to measure ~ 20-250 keV photons incident from the field of view (FOV) defined by collimators, and CsI(Na) is used as the active shielding detector to NaI(Tl) by pulse shape discrimination. Additionally, CsI(Na) is used as an omnidirectional γ-ray monitor. The HE collimators have a diverse FOV, i.e. 1.1°×5.7° (15 units), 5.7°×5.7° (2 units), and blocked (1 unit). Therefore, the combined FOV of HE is approximately 5.7°×5.7°. Each HE detector has a diameter of 190 mm resulting in a total geometrical area of approximately 5100 cm2, and the energy resolution is ~15% at 60 keV. For each recorded X-ray event by HE, the timing accuracy is less than 10 μs and the dead-time is less than 10 μs. HE is used for observing spectra and temporal variability of X-ray sources in the 20-250 keV band either by pointing observations for known sources or scanning observations to unveil new sources. Additionally, HE is used for monitoring the γ-ray burst in 0.2-3 MeV band. This paper not only presents the design and performance of HE instruments but also reports results of the on-ground calibration experiments.

The Low Energy X-ray telescope (LE) onboard the Insight-HXMT astronomy satellite

Magnetic rotation and antimagnetic rotation are exotic rotational phenomena observed in weakly deformed or near-spherical nuclei, which are respectively interpreted in terms of the shears mechanism and two shearslike mechanism. Since their observations, magnetic rotation and antimagnetic rotation phenomena have been mainly investigated in the framework of tilted axis cranking based on the pairing plus quadrupole model. For the last decades, the covariant density functional theory and its extension have been proved to be successful in describing series of nuclear ground-states and excited states properties, including the binding energies, radii, single-particle spectra, resonance states, halo phenomena, magnetic moments, magnetic rotation, low-lying excitations, shape phase transitions, collective rotation and vibrations, etc. This review will mainly focus on the tilted axis cranking covariant density functional theory and its application for the magnetic rotation and antimagnetic rotation phenomena.

Progress on tilted axis cranking covariant density functional theory for nuclear magnetic and antimagnetic rotation

The Insight-Hard X-ray Modulation Telescope (Insight-HXMT) is a broad band X-ray and gamma-ray (1-3000 keV) astronomy satellite. The High Energy X-ray telescope (HE) is one of its three main telescopes. The main detector plane of HE is composed of 18 NaI(Tl)/CsI(Na) phoswich detectors, where NaI(Tl) serves as primary detector to measure ~ 20-250 keV photons incident from the field of view (FOV) defined by the collimators, and CsI(Na) is used as an active shield detector to NaI(Tl) by pulse shape discrimination. CsI(Na) is also used as an omnidirectional gamma-ray monitor. The HE collimators have a diverse FOV: 1.1{\deg}x 5.7{\deg} (15 units), 5.7{\deg}x 5.7{\deg} (2 units) and blocked (1 unit), thus the combined FOV of HE is about 5.7{\deg}x 5.7{\deg}. Each HE detector has a diameter of 190 mm, resulting in the total geometrical area of about 5100 cm_2. The energy resolution is ~15% at 60 keV. The timing accuracy is better than 10 {\mu}s and dead-time for each detector is less than 10 {\mu}s. HE is devoted to observe the spectra and temporal variability of X-ray sources in the 20-250 keV band either by pointing observations for known sources or scanning observations to unveil new sources, and to monitor the gamma-ray sky in 0.2-3 MeV. This paper presents the design and performance of the HE instruments. Results of the on-ground calibration experiments are also reported.

The High Energy X-ray telescope (HE) onboard the Insight-HXMT astronomy satellite

The ground-state properties of nuclei with 8 $\le$ Z $\le$ 120 from the proton drip line to the neutron drip line have been investigated using the relativistic continuum Hartree-Bogoliubov (RCHB) theory with the relativistic density functional PC-PK1. With the effects of the continuum included, there are totally 9035 nuclei predicted to be bound, which largely extends the existing nuclear landscapes predicted with other methods. The calculated binding energies, separation energies, neutron and proton Fermi surfaces, root-mean-square (rms) radii of neutron, proton, matter, and charge distributions, ground-state spins and parities are tabulated. The extension of the nuclear landscape obtained with RCHB is discussed in detail, in particular for the neutron-rich side, in comparison with the relativistic mean field calculations without pairing correlations and also other predicted landscapes. It is found that the coupling between the bound states and the continuum due to the pairing correlations plays an essential role in extending the nuclear landscape. The systematics of the separation energies, radii, densities, potentials and pairing energies of the RCHB calculations are also discussed. In addition, the alpha-decay energies and proton emitters based on the RCHB calculations are investigated.

The limits of the nuclear landscape explored by the relativistic continuum Hatree-Bogoliubov theory

High-spin states of $^{138}\mathrm{Pm}$ have been populated using the $^{124}\mathrm{Te}(^{19}\mathrm{F},\phantom{\rule{0.28em}{0ex}}5\mathrm{n})^{138}\mathrm{Pm}$ reaction at a beam energy of 105 MeV. A new positive-parity side band with the same $\ensuremath{\pi}{h}_{11/2}\ensuremath{\bigotimes}\ensuremath{\nu}{h}_{11/2}$ configuration as that of the yrast band is observed in $^{138}\mathrm{Pm}$. The properties of the two positive-parity bands show general agreement with the fingerprints of chiral rotation and thus these two bands are suggested to be candidates for near degenerate chiral doublet bands. Besides, odd-even spin staggering of the $\ensuremath{\pi}{h}_{11/2}\ensuremath{\bigotimes}\ensuremath{\nu}{h}_{11/2}$ bands is studied systematically in odd-odd Cs, La, Pr, and Pm isotopes. As a result of this study we suggest that the spin value of lowest observed state of the yrast band be reassigned as 9 in $^{138}\mathrm{Pm}$. This new spin assignment is also supported by the argument of alignment additivity.

Candidate chiral doublet bands in Pm 138

The candidate chiral doublet bands in ${}^{128}$La have been searched for through the ${}^{118}$Sn(${}^{14}$N, 4n)${}^{128}$La reaction at a beam energy of 69 MeV. A positive-parity sideband with the same configuration as that of the yrast band has been identified. The positive-parity and spins of the sideband have been assigned based on the $\ensuremath{\Delta}I=1$ mixed $M1/E2$ and $E2$ characters of the linking transitions between the sideband and the yrast band. The properties of the sideband and the yrast band are discussed. The newly identified sideband and the yrast band are suggested to form the candidate of the near degenerate chiral doublet bands.

Candidate chiral doublet bands in 128 La

Level structures of 113In have been studied through the fusion-evaporation reaction 110Pd (7Li ,4n113In at a beam energy of 50MeV. More than 40 new $ \gamma$ transitions have been observed in 113In . Two new dipole bands are established and one of them is proposed as a magnetic rotation band with the configuration of $\ensuremath \pi g_{9/2}^{-1}\otimes\nu h_{11/2}^{2} g_{7/2}^{2}$ . Self-consistent tilted axis cranking relativistic mean field calculations have been performed to interpret the rotational structure. Several decay paths of the $\ensuremath \pi h_{11/2}$ intruder band have been established, by which the level energies and spins of the $\ensuremath \pi h_{11/2}$ intruder band are determined.

Level structures of 113In

Based on recent experimental data, the band structure of the odd-odd nucleus ${}^{86}$Y has been studied. The positive-parity yrast band built on the configuration $\ensuremath{\pi}{g}_{9/2}\ensuremath{\bigotimes}\ensuremath{\nu}{g}_{9/2}^{\ensuremath{-}1}$ shows a large signature splitting, and a signature inversion occurs at $I\ensuremath{\sim}13\ensuremath{\hbar}$. The signature inversion is interpreted by the competition between single-particle and collective excitations in this nucleus. The negative-parity dipole band, which is probably connected with magnetic rotation, is assigned to the configurations $\ensuremath{\pi}{g}_{9/2}^{2}{({p}_{3/2}/{f}_{5/2})}^{\ensuremath{-}1}\ensuremath{\bigotimes}\ensuremath{\nu}{g}_{9/2}^{\ensuremath{-}1}$ before and to $\ensuremath{\pi}{g}_{9/2}^{2}{({p}_{3/2}/{f}_{5/2})}^{\ensuremath{-}1}\ensuremath{\bigotimes}\ensuremath{\nu}{g}_{9/2}^{\ensuremath{-}3}$ after the alignment. Self-consistent titled axis cranking calculations based on relativistic mean-field theory are performed to interpret the rotational structure. Characteristic features of magnetic rotation are found for the negative-parity band.

Signature splitting and magnetic rotation in 86 Y

High-spin states of $^{113}\mathrm{In}$ have been populated using the $^{110}\mathrm{Pd}(^{7}\mathrm{Li},4n)^{113}\mathrm{In}$ reaction at beam energies of 38 and 50 MeV. More than 50 new $\ensuremath{\gamma}$ transitions are observed in $^{113}\mathrm{In}$. Three previously observed magnetic dipole bands are extended to higher spin states, and several new $E2$ crossover transitions within the bands are observed in two of the dipole bands. A new positive-parity $▵I=2$ band built on the $\ensuremath{\pi}{d}_{5/2}$ configuration is established. The known $▵I=2$ band is extended to $51/{2}^{+}$ state, and a gentle up-bend associated to the alignment of neutrons in the normal-parity $\ensuremath{\nu}{g}_{7/2}/{d}_{5/2}$ orbitals is found. The properties of this band are discussed based on the self-consistent tilted axis cranking relativistic mean-field model calculations. The predicted $B(E2)$, deformation parameters ${\ensuremath{\beta}}_{2}$ and $\ensuremath{\gamma}$, and ${J}^{(2)}/B(E2)$ ratios indicate that the $▵I=2$ band based on the $\ensuremath{\pi}{g}_{9/2}^{\ensuremath{-}2}{g}_{7/2}\ensuremath{\bigotimes}\ensuremath{\nu}{({h}_{11/2})}^{2}$ and $\ensuremath{\pi}{g}_{9/2}^{\ensuremath{-}2}{g}_{7/2}\ensuremath{\bigotimes}\ensuremath{\nu}{({h}_{11/2})}^{2}{({g}_{7/2}/{d}_{5/2})}^{2}$ configurations, has the characteristics of antimagnetic rotation. Furthermore, the two-shears-like mechanism for the possible antimagnetic rotational bands is examined by investigating the orientation of the angular momenta.

Ke-Yan Ma

Papers

Candidate chiral doublet bands in Pm 138

Candidate chiral doublet bands in 128 La

Level structures of 113In

Signature splitting and magnetic rotation in 86 Y

Possible antimagnetic rotational band and neutron alignment in In 113