We use the superfluid tunneling model (STM) to calculate the half-lives of α decays of odd-$A$ and odd-odd superheavy nuclei (SHN) with $Z\ge 100$ and $A\ge 250$. The experimental data are reproduced to accuracies comparable to other contemporary models of the α decay of the SHN. We then apply the STM to examine the influence of the quasiparticle structure on the properties of the chains of α decays arising from odd-$A$ SHN. Using representative calculations of the one-quasi-particle structure of odd-$Z$ and odd-$N$ SHN, we illustrate the important role played by high-Ω orbitals in defining the observed characteristics of the α-decay chains. We point out sources of possible ambiguity that may arise due to the quasiparticle structure when assigning α-decay chains to specific SHN.

The ${}^{18}\mathrm{F}(p,\alpha ){}^{15}\mathrm{O}$ reaction is key to determining the ${}^{18}\mathrm{F}$ abundance in classical novae. However, the cross section for this reaction has large uncertainties at low energies largely caused by interference effects. Here, we resolve a longstanding issue with unknown spin-parities of subthreshold states in ${}^{19}\mathrm{Ne}$ that reduces these uncertainties. The ${}^{20}\mathrm{Ne}({}^3\mathrm{He},{}^4\mathrm{He}){}^{19}\mathrm{Ne}$ neutron pick-up reaction was used to populate ${}^{19}\mathrm{Ne}$ excited states, focusing on the energy region of astrophysical interest $(\approx 6–7 \mathrm{MeV})$. The experiment was performed at the Triangle Universities Nuclear Laboratory using the high resolution Enge split-pole magnetic spectrograph. Spins and parities were found for states in the astrophysical energy range. In particular, the state at 6.133 MeV $(E_r^{\text{c.m.}}=-277 \mathrm{keV})$ was found to have spin and parity of $3/2^{+}$ and we confirm the existence of an unresolved doublet close to 6.288 MeV $(E_r^{\text{c.m.}}=-120 \mathrm{keV})$ with $J^{\pi }=1/2^{+}$ and a high-spin state. Using these results, we demonstrate a significant factor of two decrease in the reaction rate uncertainties at nova temperatures.

The ${\beta }^{+}$ decay of ${}^8\mathrm{B}$ provides the dominant source of solar neutrinos above 2 MeV. Consequently, experiments that detect neutrinos from the sun require an accurate determination of the ${}^8\mathrm{B}$ neutrino energy spectrum. In this work, the $\beta$-decay Paul trap surrounded by double-sided silicon strip detectors was utilized to precisely measure the decay products of trapped ${}^8\mathrm{B}$ ions. The results were used to determine the ${}^8\mathrm{Be}$ final-state distribution and to reconstruct the neutrino energy spectrum. This measurement using trapped ions is the first of its kind and puts the neutrino energy spectrum on much firmer footing by discriminating between recently reported values for the maximum of the final-state distribution.

We present local, position-space chiral $NN$ potentials through four orders of chiral effective field theory ranging from leading order (LO) to next-to-next-to-next-to-leading order (${\mathrm{N}}^3\mathrm{LO}$, fourth order) of the $\mathrm{\Delta }$-less version of the theory. The long-range parts of these potentials are fixed by the very accurate $\pi N$ low-energy constants (LECs) as determined in the Roy-Steiner equations analysis. At the highest order (${\mathrm{N}}^3\mathrm{LO}$), the $NN$ data below 190 MeV laboratory energy are reproduced with the respectable ${\chi }^2/\mathrm{datum}$ of 1.45. A comparison of the ${\mathrm{N}}^3\mathrm{LO}$ potential with the phenomenological Argonne $v_{18}$ (AV18) potential reveals substantial agreement between the two potentials in the intermediate range ruled by chiral symmetry, thus providing a chiral underpinning for the phenomenological AV18 potential. Our chiral $NN$ potentials may serve as a solid basis for systematic ab initio calculations of nuclear structure and reactions that allow for a comprehensive error analysis. In particular, the order-by-order development of the potentials will make possible a reliable determination of the truncation error at each order. Our new family of local position-space potentials differs from existing potentials of this kind by a weaker tensor force as reflected in relatively low $D$-state probabilities of the deuteron ($P_D\lesssim 4.0$% for our ${\mathrm{N}}^3\mathrm{LO}$ potentials) and predictions for the triton binding energy above 8.00 MeV (from two-body forces alone). As a consequence, our potentials may lead to different predictions when applied to light and intermediate-mass nuclei in ab initio calculations and, potentially, help solve some of the outstanding problems in microscopic nuclear structure.

In the evaluation of the half-life of the neutrinoless double-$\beta$ decay ($0\nu \beta \beta$) of a doubly closed-subshell nucleus ${}^{96}\mathrm{Zr}$, the structure of the nucleus ${}^{96}\mathrm{Mo}$ is essentially important. The $\alpha$-clustering aspects of ${}^{96}\mathrm{Mo}$ are investigated for the first time. By studying the nuclear rainbows in $\alpha$ scattering from ${}^{92}\mathrm{Zr}$ at high energies and the characteristic structure of the excitation functions at the extreme backward angle at the low-energy region, the interaction potential between the $\alpha$ particle and the ${}^{92}\mathrm{Zr}$ nucleus is determined well in the double folding model. The validity of the double folding model was reinforced by studying $\alpha$ scattering from neighboring nuclei ${}^{90}\mathrm{Zr}, {}^{91}\mathrm{Zr}$, and ${}^{94}\mathrm{Zr}$. The double-folding-model calculations reproduced well all the observed angular distributions over a wide range of incident energies and the characteristic excitation functions. By using the obtained potential the $\alpha +{}^{92}\mathrm{Zr}$ cluster structure of ${}^{96}\mathrm{Mo}$ is investigated in the spirit of a unified description of scattering and structure. The existence of the second-higher nodal band states with the $\alpha +{}^{92}\mathrm{Zr}$ cluster structure, in which two more nodes are excited in the relative motion compared with the ground band, is demonstrated. The calculation reproduces well the ground-band states of ${}^{96}\mathrm{Mo}$ in agreement with experiment. The experimental $B\left(E2\right)$ value of the transition in the ground band is also reproduced well. The effect of $\alpha$ clustering in ${}^{96}\mathrm{Mo}$ on the the half-life of the $0\nu \beta \beta$ double-$\beta$ decay of ${}^{96}\mathrm{Zr}$ is discussed.

We study the excited states of zero seniority for various like-particle systems interacting by pairing forces and by general two-body interactions. We consider two types of excitations, generated from a ground state described by a pair condensate. One type is obtained by breaking a pair from the ground-state condensate and replacing it by “excited” collective pairs built on time-reversed single-particle orbits. The second type of zero-seniority excited states is described by a condensate of identical excited pairs. The structure of these excited states is analyzed for the picket fence model and for the valence neutrons of ${}^{108}\mathrm{Sn}$. For a state-depending pairing interaction, the first type of excited states agree well with the $J=0$ states which are known in ${}^{108}\mathrm{Sn}$. At the same time, these states can be also associated unambiguously with those exact states which are the closest in energy to the experimental levels. The states corresponding to the excited pair condensate (EPC) appear at low energies, around the energy of the second-excited state of the first type, and they do not have a simple correspondence with exact eigenstates. However, at a much higher excitation energy there is an exact state which is similar in structure to an EPC state. It is shown that this EPC state has the features of a giant pairing vibration.

Electron-positron pairs can be produced via the Schwinger mechanism in the presence of strong electric fields. In particular, the fields involved in $\alpha$ decay and nuclear fission are strong enough to produce them. The energy of the $e^{+}{e}^{-}$ pair is related to the relative distance and velocity of the daughter nuclei. Thus, the energy distribution of the produced pairs can give information about the dynamics of the fission and $\alpha$-decay processes. A neck model of nuclear fission is used to illustrate how the pairs can be used as a probe of the dynamics.

We consider nucleon-nucleon scattering using the formulation of chiral effective field theory which is claimed to be renormalization group invariant. The cornerstone of this framework is the existence of a well-defined infinite-cutoff limit for the scattering amplitude at each order of the expansion, which should not depend on a particular regulator form. Focusing on the ${}^3{P}_0$ partial wave as a representative example, we show that this requirement can in general not be fulfilled beyond the leading order, in spite of the perturbative treatment of subleading contributions to the amplitude. Several previous studies along these lines, including the next-to-leading order calculation by B. Long and C. J. Yang [Phys. Rev. C 84, 057001 (2011)] and a toy model example with singular long-range potentials by B. Long and U. van Kolck [Ann. Phys. 323, 1304 (2008)], are critically reviewed and scrutinized in detail.

In this paper we perform systematic calculations of $\beta$-decay half-lives for the $r$-process waiting-point isotones of $N=81$ and 82, in the framework of nucleon-pair approximation. A phenomenological form of the Hamiltonian, which includes single-particle energies, pairing plus quadrupole interactions, and Gamow-Teller interactions is assumed, and the theoretical $\beta$-decay energies are taken based on the Bayesian machine learning. A good agreement with experimental values of half-lives is achieved by using the nucleon-pair truncated model space in which the $S$-pair condensation dominates. Our calculated half-lives are found to be very sensitive to $\beta$-decay energies on the one hand, and are quite robust with respect to extension of the model space and variation of interaction parameters on the other hand.

Over the next decade new $\mu \to e$ conversion searches at Fermilab (Mu2e) and J-PARC (COMET, DeeMe) are expected to advance limits on charged lepton flavor violation (CLFV) by more than four orders of magnitude. By considering the consequence of $P$ and $CP$ on elastic $\mu \to e$ conversion and the structure of possible charge and current densities, we show that rates are governed by six nuclear responses and a single scale, $q/m_N$, where $q\approx m_{\mu }$ is the momentum transferred from the leptons to the nucleus. To relate this result to microscopic formulations of CLFV, we construct in nonrelativistic effective theory (NRET) the CLFV nucleon-level interaction, pointing out the relevance of the dimensionless scales $y={\left(\frac{qb}{2}\right)}^2>|{\vec{v}}_N|>|{\vec{v}}_{\mu }|>|{\vec{v}}_T|$, where $b$ is the nuclear size, ${\vec{v}}_N$ and ${\vec{v}}_{\mu }$ are the nucleon and muon intrinsic velocities, and ${\vec{v}}_T$ is the target recoil velocity. We discuss previous work, noting the lack of a systematic treatment of the various small parameters. Because the parameter $y$ is not small, a proper calculation of $\mu \to e$ conversion requires a full multipole expansion of the nuclear response functions, an apparently daunting task with Coulomb-distorted electron partial waves. We demonstrate that the multipole expansion can be carried out to high precision by introducing a simplifying local momentum $q_{\mathrm{eff}}$ for the electron. Previous work has been limited to simple charge or spin interactions, thereby treating the nucleus effectively as a point particle. We show that such formulations are not compatible with the general form of the $\mu \to e$ conversion rate, failing to generate three of the six allowed nuclear response functions. The inclusion of the nucleon velocity ${\vec{v}}_N$ yields an NRET with 16 operators and a rate of the general form. Consequently, in the current discovery era for CLFV, it provides the most sensible starting point for experimental analysis, defining what can and cannot be determined about CLFV from the highly exclusive process of $\mu \to e$ conversion. Finally, we expand the NRET operator basis to account for the effects of ${\vec{v}}_{\mu }$, associated with the muon's lower component, generating corrections to the CLFV coefficients of the point-nucleus response functions. Using advanced shell-model methods, we compute $\mu \to e$ conversion rates for a series of experimental targets, deriving bounds on the coefficients of the CLFV operators. These calculations are the first to include a general basis of CLFV operators, full evaluation of the associated nuclear response functions, and an accurate treatment of electron and muon Coulomb effects. We discuss target selection as an experimental “knob” that can be turned to probe the microscopic origins of CLFV. We describe two types of coherence that enhance certain CLFV operators and selection rules that blind elastic $\mu \to e$ conversion to others. We discuss the matching of the NRET onto higher level effective field theories, such as those constructed at the light quark level, noting opportunities to build on existing work in direct detection of dark matter. We discuss the relation of $\mu \to e$ conversion to $\mu \to e+\gamma$ and $\mu \to 3e$, showing how MEG II and Mu3e results will complement those of Mu2e and COMET. Finally we describe a accompanying script—in Mathematica and Python versions—that can be used to compute $\mu \to e$ conversion rates in various nuclear targets for the full set of NRET operators.

Recent observations of several massive pulsars, with masses near and above $2M_{\odot }$, point towards the existence of matter at very high densities, compared to normal matter that we are familiar with in our terrestrial world. This leads to the possibility of the appearance of exotic degrees of freedom other than nucleons inside the core of the neutrons stars (NSs). Another significant property of NSs is the presence of a high surface magnetic field, with the highest range of the order of $\approx {10}^{16}$ G. We study the properties of highly dense matter with the possibility of the appearance of heavier strange and nonstrange baryons, and kaons in the presence of a strong magnetic field. We find that the presence of a strong magnetic field stiffens the matter at high density, delaying the kaon appearance and, hence, increasing the maximum attainable mass of NS family.

Background: Asymmetric fission in sublead nuclei, especially mercury and platinum isotopes, has generated keen interest in studying fission in $A<200$ mass region. The role of proton and neutron shells on asymmetric fission in these nuclei is still under test and requires more investigation.

Purpose: This paper presents measurements aimed at studying the fission modes of ${}^{192}\mathrm{Hg}$ formed in the reaction ${}^{32}\mathrm{S}+{}^{160}\mathrm{Gd}$ in the excitation energy range 54–74 MeV.

Method: Mass distributions have been determined from the fission fragments' (FF) time of flight (TOF). Two multiwire proportional chambers were placed symmetrically on opposite sides of the beam to cover the folding angle for symmetric fission. The measured TOF of the fission fragments was used to obtain their velocities, and after clean separation of compound nuclear fission events, the velocities were further used to obtain the fission fragment mass and total kinetic energy (TKE) distribution.

Results: The fission fragment mass distributions at all beam energies were found to be characteristically flat topped, which deviates significantly from a single Gaussian behavior. The distinctive features of mass and energy distributions happen to be explained by the presence of a symmetric fission mode and three asymmetric fission modes, manifested by different total kinetic energies in varying mass regions. These asymmetric fission modes are a consequence of the stabilization role of proton shells at $Z\approx$ 36, $Z\approx$ 46, and $Z$ = 28/50. The most probable mass of light and heavy fragments are found to be around 86 and 106 u, respectively. The symmetric yield is found to increase with the excitation energy.

Conclusions: The present study indicates a mixture of symmetric and asymmetric modes in the fission of ${}^{192}\mathrm{Hg}$ nuclei and points out the relevance of deformed proton shells at $Z\approx$ 36 and 46.

A spheroidal model of the expansion of hadronic matter produced in heavy-ion collisions in the few-GeV energy regime is proposed. It constitutes an extension of the spherically symmetric Siemens-Rasmussen blast-wave model used in our previous works. The spheroidal form of the expansion, combined with a single-freeze-out scenario, allows for a significantly improved description of both the transverse-mass and the rapidity distributions of the produced particles. With the model parameters determined by the hadronic abundances and spectra, we make further predictions of the pion Hanbury-Brown–Twiss correlation radii that turn out to be in a qualitative agreement with the measured ones. The overall successful description of the data supports the concept of spheroidal symmetry of the produced hadronic systems in this energy range.

The study of radioisotopes as well as of highly charged ions is a very active and dynamic field. In both cases, the most sensitive probes involve species trapped in Penning or Paul traps after a series of production and separation steps that limit the types and lifetimes of species that can be investigated. We propose a novel production scheme that forms fully (or almost fully) stripped radionuclei in the form of highly charged ions (HCIs) directly in the trapping environment. The method extends the range of species, among them radioisotopes such as ${}^{21}\mathrm{F}, {}^{100}\mathrm{Sn}$, or ${}^{229}\mathrm{Th}$, that can be readily produced and investigated and is complementary to existing techniques.

The variation of collective vibrational spectra with varying $N$ displayed by the $Z=52$ Te isotopes, for less than $N=82$ closed shell, are of special interest. The spectral features of the ground band and the two and three phonon excited multiplets in ${}^{118–128}\mathrm{Te}$, are studied here empirically. The state energy $E\left(2_1{}^{+}\right)$ increases, and the energy ratio $R_{4/2}$ decreases with increasing neutron number $N$. Also the $0_2{}^{+}$ state rises up sharply, and the $0_3{}^{+}$ state follows it, unlike their relation in the E(5) symmetry. It is shown that ${}^{120}\mathrm{Te}$ isotope displays the weakly deformed status, and the heavier isotopes move towards the spherical harmonic vibrator status. The interacting boson model (IBM-1) is used to reproduce these spectral features of ${}^{118–124}\mathrm{Te}$, with use of slight variation of boson energy ε and of the quadrupole interaction strength. In the microscopic approach, the dynamic pairing plus quadrupole model of Kumar and Baranger also reproduces these basic spectral features.