Nuclear Ground State Research Articles

Neutrino-pair emission from nuclear de-excitation in core-collapse supernova simulations

We study the impact of neutrino-pair production from the de-excitation of highly excited heavy nuclei on core-collapse supernova simulations, following the evolution up to several 100 ms after core bounce. Our study is based on the AGILE-Boltztran supernova code, which features general relativistic radiation hydrodynamics and accurate three-flavor Boltzmann neutrino transport in spherical symmetry. In our simulations the nuclear de-excitation process is described in two different ways. At first we follow the approach proposed by Fuller and Meyer [Astrophys. J. 376,701 (1991)], which is based on strength functions derived in the framework of the nuclear Fermi-gas model of non-interacting nucleons. Secondly, we parametrize the allowed and forbidden strength distributions in accordance with measurements for selected nuclear ground states. We determine the de-excitation strength by applying the Brink hypothesis and detailed balance. For both approaches, we find that nuclear de-excitation has no effect on the supernova dynamics. However, we find that nuclear de-excitation is the leading source for the production of electron antineutrinos as well as heavy-lepton flavor (anti)neutrinos during the collapse phase. At sufficiently high densities, the associated neutrino spectra are influenced by interactions with the surrounding matter, making proper simulations of neutrino transport important for the determination of the neutrino-energy loss rate. We find that even including nuclear de-excitations, the energy loss during the collapse phase is overwhelmingly dominated by electron neutrinos produced by electron captures.

First Use of High-Frequency Intensity Modulation of Narrow-Linewidth Laser Light and Its Application in Determination ofFr206,205,204Ground-State Properties

Collinear laser spectroscopy was performed on the nuclear ground states of the neutron-deficient isotopes (206,205,204)Fr. A new technique was developed to suppress hyperfine pumping in collinear laser spectroscopy of atoms. This involved high-frequency intensity modulation of narrow-linewidth laser light using fast-switching electro-optical modulators. The nuclear ground-state spins of (206,205,204)Fr were determined to be 3, 9/2, and 3, respectively. Both the changes in mean-squared charge radii and nuclear magnetic dipole moments indicate a departure from single-particle estimates.

Precision experiments and fundamental physics at low energies – Part I

Precision experiments and fundamental physics at low energies – Part I

Structure of the phonon vacuum state

The action of the long-range residual force on the expectation value of observables in the nuclear ground states is evaluated by finding optimal values for the coefficients of the canonical transformation which connects the phonon vacuum state with the (quasi)particle ground state. After estimating the improvements over the predictions of the independent-particle approximation we compare the ground-state wave functions, obtained using the presented approach, with those obtained using the conventional random phase approximation (RPA) and its extended version. The problem with overbinding of the nuclear ground state calculated using the RPA is shown to be removed if one sticks to the prescriptions of the present approach. The reason being that the latter conforms to the original variational formulation. Calculations are performed within the two-level Lipkin-Meshkov-Glick model in which we present results for the ground and first excited state energies as well as for the ground-state particle occupation numbers.

Systematics of nuclear ground-state properties of Sr isotopes by covariant density functional theory

The hyperfine structure and isotope shifts of Sr isotopes, both even-even and odd-even nuclei, are studied in the covariant density functional theory with the new parameter set DD-PC1. Pairing correlation is treated using the Bogoliubov model with a separable form of the pairing interaction. Spin parity, charge radii, two-neutron separation energies, and pairing energies of ground states are calculated and compared with experimental data. We find a shape transition at $N\ensuremath{\approx}60$ in charge radii and spin parity, which are consistent with each other and generally agree with experiments. Although the nuclear masses are not very sensitive to these shape changes, odd-even mass differences and pairing effects are very important for study of the shape transition and shape coexistence phenomena in Sr isotopes.

An IGISOL portrait

This issue of Hyperfine Interactions consists of 21 articles describing scientific work related to the research at the on-line isotope separator facility IGISOL at the University of Jyvaskyla, Finland. Ten contributions containing a significant amount of original results, earlier unpublished, have been presented as a Topical Collection in the European Physical Journal (EPJA 48 issue No 4, 2012). In the early 1980s, the Ion Guide Isotope Separator On-Line (IGISOL) concept was realized at the 20 MeV proton cyclotron of the Physics Department at the University of Jyvaskyla (JYFL). For the first time, the technique allowed the production of high quality ISOL beams from nuclear reaction products with millisecond delay times without chemical restrictions. By providing access to short-lived isotopes of refractory elements it opened up new regions in the nuclear chart for nuclear decayand ground-state spectroscopy. During the 1980s, the main research activity at IGISOL was decay spectroscopy, and in particular, of fission products produced in proton-induced fission of natural uranium. Approximately 40 new isotopes and isomers were discovered and studied employing beta-, gamma-, and conversion electron spectroscopy. These experiments covered a broad range of neutron-rich nuclei from yttrium (Z = 39) to cadmium (Z = 48) and revealed how their structure was developing between highly deformed zirconium through triaxial ruthenium isotopes to weakly deformed vibrational cadmium isotopes. The original IGISOL facility was shut down in October 1991 and was reinstalled as IGISOL-2 at the science campus housing the laboratory for the K = 130 MeV heavy ion cyclotron. A new window of opportunity for extending research to neutrondeficient nuclei far from stability was opened and was going to have a strong impact

About the existence of a Poincaré transition in rotating nuclei

The Poincaré instability of nuclear shapes with respect to reflection asymmetric distortions is investigated in the framework of the Lublin–Strasbourg drop model and the modified Funny-Hills shape parametrization. It turn out that such an instability can, indeed, be observed, in particular in light nuclei, when exploring the whole nuclear deformation-energy landscape, but neither for nuclear ground-state nor saddle-point deformations.

Impact of Precision Mass Measurements on Nuclear Physics and Astrophysics

Among all nuclear ground-state properties, atomic masses are highly specific for each particular combination of neutron and proton number, N and Z, respectively. The data obtained through mass measurements provide details of the nuclear interaction and thus apply to a variety of physics topics. Some of the most crucial questions to be addressed by mass spectrometry of unstable radionuclides are, on the one hand, nuclear forces and structure, describing phenomena such as the so-called neutron-halos or the evolution of magic numbers when moving towards the borders of nuclear existence. On the other hand, the understanding of the processes of element formation in the Universe poses a challenge and requires an accurate knowledge of nuclear astrophysics. Here, precision atomic mass values of a large number of exotic nuclei participating in nucleosynthesis processes are among the key input data in large-scale reaction network calculations.

Towards a direct transition energy measurement of the lowest nuclear excitation in 229Th

The isomeric first excited state of the isotope 229Th exhibits the lowest nuclear excitation energy in the whole landscape of known atomic nuclei. For a long time this energy was reported in the literature as 3.5(5) eV, however, a new experiment corrected this energy to 7.6(5) eV, corresponding to a UV transition wavelength of 163(11) nm. The expected isomeric lifetime is τ = 3-5 hours, leading to an extremely sharp relative linewidth of ΔE/E ≈ 10−20, 5-6 orders of magnitude smaller than typical atomic relative linewidths. For an adequately chosen electronic state, the frequency of the nuclear ground-state transition will be independent frominfluences of external fields in the framework of the linear Zeeman andquadratic Stark effect, rendering 229mTh a candidate for a reference of anoptical clock with very high accuracy [1].Moreover, in the literature speculations about a potentially enhanced sensitivity of the ground-state transition of 229mTh for eventual time-dependentvariations of fundamental constants (e.g. fine structure constant α)can be found [3,4].We report on our experimental activities that aim at a direct identification of the UV fluorescence of the ground-state transition energy of 229mTh. A further goal is to improve the accuracy of theground-state transition energy as a prerequisite for a laser-based opticalcontrol of this nuclear excited state, allowing to build a bridge between atomic and nuclear physics and open new perspectives for metrological as wellas fundamental studies.

Investigation of the nuclear properties of 181Ta and 182, 183, 184, 186W structural materials

In this paper, the nuclear ground states properties such as binding energies per particle, charge, neutron and proton rms radii, and charge, neutron and proton density distributions of 181Ta and 182, 183, 184, 186W structural materials for acceleration driven subcritical reactor system have been investigated. Calculations have been performed using Skyrme force parameters, which are based on the nuclear saturation properties, in the Hartree–Fock method. The obtained results have been discussed and compared with the results of experimental and relativistic mean field theory.

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

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.

Nuclear prolate-shape dominance with the Woods-Saxon potential

We study the prolate-shape predominance of the nuclear ground-state deformation by calculating the masses of more than two thousand even-even nuclei using the Strutinsky method, modified by Kruppa, and improved by us. The influences of the surface thickness of the single-particle potentials, the strength of the spin-orbit potential, and the pairing correlations are investigated by varying the parameters of the Woods-Saxon potential and the pairing interaction. The strong interference between the effects of the surface thickness and the spin-orbit potential is confirmed to persist for six sets of the Woods-Saxon potential parameters. The observed behavior of the ratios of prolate, oblate, and spherical nuclei versus potential parameters are rather different in different mass regions. It is also found that the ratio of spherical nuclei increases for weakly bound unstable nuclei. Differences of the results from the calculations with the Nilsson potential are described in detail.

Systematic study of decay properties of heaviest elements

Decay properties and stability of heaviest nuclei with Z ≤ 132 are studied within the macro-microscopical approach for nuclear ground-state masses. We use phenomenological relations for the half-lives with respect to α-decay, β-decay and spontaneous fission. Our calculations demonstrate that the β-stable isotopes 291Cn and 293Cn with a half-life of about 100 years are the longest-living superheavy nuclei located on the first island of stability. We found the second island of stability of superheavy nuclei in the region of Z ≈ 124 and N ≈ 198. It is separated from the “continent” by the “gulf” of short-living nuclei with half-lives shorted than 1 μs.

The isospin mixing and the superallowed Fermi beta decay

In the present work, the isospin admixtures in the nuclear ground states of the parent nuclei and isospin structure of the isobar analog resonance (IAR) states have been investigated by studying the 0 + →0 + superallowed Fermi β decays using Pyatov’s restoration method. Within the random phase approximation (RPA), in this method, the effect of isospin breaking due to the Coulomb forces has been evaluated, taking into account the effect of pairing correlations between nucleons.

Nuclear hyperfine level pattern and hyperfine specific heat of frustrated Gd-pyrochlores Gd2 M 2O7 (M = Ti, Sn, Hf, Zr)

The nuclear contribution to the specific heat originates from the combination of a nuclear electric quadrupole interaction and a nuclear magnetic hyperfine interaction of the magnetic atoms embedded in the crystalline lattice structure. We have estimated the nuclear hyperfine level patterns of the nuclear ground state \(I_{g} = 3/2^{-}\) and the first excited state \(I_{ex} = 5/2^{+}\) at 86.5 keV of Mossbauer-active Gd155 nucleus of Gd-based pyrochlores Gd2M2O7 (M = Ti, Sn, Hf, Zr). The nuclear quadrupole and hyperfine interactions are scaled in accordance with the ratios of quadrupole and magnetic moments of \(I_{g} = 3/2^{-}\) state of Gd155 and Gd157 nuclei to get the contribution from Gd157 nucleus of Gd2M2O7 to the hyperfine specific heat Chf appropriate to its relative isotopic abundance. It is found that Chf(T) shows a Schottky hump around 6–8 mK for these pyrochlores. At temperatures much higher than the hyperfine level splitting, Chf behaves as AT − 2 with A ∼ 1–2 × 10 − 4 JK/mole-Gd which is consistent with experimental results.

Chiral thermodynamics of dense hadronic matter

We discuss phases of hot and dense hadronic matter using chiral Lagrangians. A two-flavored parity doublet model constrained by the nuclear matter ground state predicts chiral symmetry restoration. The model thermodynamics is shown within the mean-field approximation. A field-theoretical constraint on possible phases from the anomaly matching is also discussed.

Storage ring at HIE-ISOLDE

We propose to install a storage ring at an ISOL-type radioactive beam facility for the first time. Specifically, we intend to setup the heavy-ion, low-energy ring TSR at the HIE-ISOLDE facility in CERN, Geneva. Such a facility will provide a capability for experiments with stored secondary beams that is unique in the world. The envisaged physics programme is rich and varied, spanning from investigations of nuclear ground-state properties and reaction studies of astrophysical relevance, to investigations with highly-charged ions and pure isomeric beams. The TSR might also be employed for removal of isobaric contaminants from stored ion beams and for systematic studies within the neutrino beam programme. In addition to experiments performed using beams recirculating within the ring, cooled beams can also be extracted and exploited by external spectrometers for high-precision measurements. The existing TSR, which is presently in operation at the Max-Planck Institute for Nuclear Physics in Heidelberg, is well-suited and can be employed for this purpose. The physics cases as well as technical details of the existing ring facility and of the beam and infrastructure requirements at HIE-ISOLDE are discussed in the present technical design report.

Physics highlights from laser spectroscopy at the IGISOL

Laser spectroscopy provides model-independent access to a variety of radioactive nuclear ground state and isomeric state properties. These include the nuclear moments, changes in mean-square charge radii, and direct measurements of the nuclear spin. At the IGISOL laboratory, the collinear laser spectroscopy programme is able to access cases, such as refractory elements and short-lived states, not available at conventional facilities. A summary of physics highlights is presented here.

DECAY PROPERTIES AND STABILITY OF HEAVIEST ELEMENTS

Decay properties and stability of heaviest nuclei with Z≤132 are studied within the macro-microscopical approach for nuclear ground state masses and phenomenological relations for the half-lives with respect to α-decay, β-decay and spontaneous fission. We found that at existing experimental facilities the synthesis and detection of nuclei with Z>120 produced in fusion reactions may be difficult due to their short half-lives (shorter than 1 μs). The nearest (more neutron-rich) isotopes of superheavy elements with 111≤Z≤115 to those synthesized recently in Dubna in 48 Ca -induced fusion reactions are found to be β+-decaying. This fact may significantly complicate their experimental identification. However it gives a chance to synthesize in fusion reactions the most stable superheavy nuclei located at the center of the island of stability. Our calculations yield that the β-stable isotopes 291 Cn and 293 Cn with a half-life of about 100 years are the longest-living superheavy nuclei located at the island of stability.

Optical spectroscopy of an atomic nucleus: Progress toward direct observation of the 229Th isomer transition

The nucleus of the thorium-229 isotope possesses a first excited nuclear state (229mTh) at an exceptionally low energy of 7.8±0.5eV above the nuclear ground state (229gTh), as determined by earlier indirect measurements. This is the only nuclear excited state known that is within the range of optical spectroscopy. This paper reports progress toward detecting the 229mTh state directly by luminescence spectroscopy in the vacuum ultraviolet spectral region. The estimated natural linewidth of the 229gTh↔229mTh isomer transition of 2π×0.1 to 2π×10mHz is expected to broaden to ∼10kHz for 229Th4+ doped into a suitable crystal. The factors governing the choice of crystal system and the substantial challenges in acquiring a sufficiently large quantity of 229Th are discussed. We show that the 229gTh↔229mTh transition energy can be identified to within 0.1nm by luminescence excitation and luminescence spectroscopy using the Advanced Light Source (ALS) at Lawrence Berkeley National Laboratory. This would open the door for subsequent laser-based measurements of the isomer transition and future applications of 229Th in nuclear clocks. We also show that 233U-doped materials should produce an intrinsic, continuous, and sufficiently high rate of 229mTh→229gTh luminescence and could be a useful aid in the initial direct search of the isomer transition.