By using a deformed Broglia-Winther nuclear interaction potential in the framework of the WKB method, the near- and above-barrier heavy-ion-fusion cross sections of ${}^{16}\mathrm{O}$ with some lanthanides and actinides have been calculated. The effect of deformed surface diffuseness on the nuclear interaction potential, the effective interaction potential at distinct angle, barrier position, barrier height, cross section at each angles, and fusion cross sections of ${}^{16}\mathrm{O}+{}^{147}\mathrm{Sm},{}^{150}\mathrm{Nd},{}^{154}\mathrm{Sm}$, and ${}^{166}\mathrm{Er}$ and ${}^{16}\mathrm{O}+{}^{232}\mathrm{Th},{}^{238}\mathrm{U},{}^{237}\mathrm{Np}$, and ${}^{248}\mathrm{Cm}$ have been studied. The differences between the results obtained by using deformed surface diffuseness and those obtained by using constant surface diffuseness were noticeable. Good agreement between experimental data and theoretical calculation with deformed surface diffuseness were observed for ${}^{16}\mathrm{O}+{}^{147}\mathrm{Sm},{}^{154}\mathrm{Sm},{}^{166}\mathrm{Er},{}^{238}\mathrm{U},{}^{237}\mathrm{Np}$, and ${}^{248}\mathrm{Cm}$ reactions. It has been observed that deformed surface diffuseness plays a significant role in heavy-ion-fusion studies.

Solar neutrinos interact within double-beta decay ($\beta \beta$) detectors and contribute to backgrounds for $\beta \beta$ experiments. Background contributions due to solar neutrino interactions with $\beta \beta$ nuclei of ${}^{82}\mathrm{Se}, {}^{100}\mathrm{Mo}$, and ${}^{150}\mathrm{Nd}$ are evaluated. They are shown to be significant for future high-sensitivity $\beta \beta$ experiments that may search for Majorana neutrino masses in the inverted-hierarchy mass region. The impact of solar neutrino backgrounds and their reduction are discussed for future $\beta \beta$ experiments.

Using the Coulomb modified correlation expansion for the Glauber model $S$ matrix, we calculate the interaction cross sections of oxygen isotopes (${}^{16–26}\mathrm{O}$) on ${}^{12}\mathrm{C}$ at 1.0 GeV/nucleon. The densities of ${}^{16–26}\mathrm{O}$ are obtained using (i) the Slater determinants consisting of the harmonic oscillator single-particle wave functions (SDHO) and (ii) the relativistic mean-field approach (RMF). Retaining up to the two-body density term in the correlation expansion, the calculations are performed employing the free as well as the in-medium nucleon-nucleon ($NN$) scattering amplitude. The in-medium $NN$ amplitude considers the effects arising due to phase variation, higher momentum transfer components, and Pauli blocking. Our main focus in this work is to reveal how could one make the best use of SDHO densities with reference to the RMF one. The results demonstrate that the SDHO densities, along with the in-medium $NN$ amplitude, are able to provide satisfactory explanation of the experimental data. It is found that, except for ${}^{23,24}\mathrm{O}$, the predicted SDHO matter rms radii of oxygen isotopes closely agree with those obtained using the RMF densities. However, for ${}^{23,24}\mathrm{O}$, our results require reasonably larger SDHO matter rms radii than the RMF values, thereby predicting thicker neutron skins in ${}^{23}\mathrm{O}$ and ${}^{24}\mathrm{O}$ as compared to RMF ones. In conclusion, the results of the present analysis establish the utility of SDHO densities in predicting fairly reliable estimates of the matter rms radii of neutron-rich nuclei.

To compare theoretical calculations of thermal fluctuations of conserved quantities, such as charge susceptibilities or specific heat, to experimentally measured correlations and fluctuations in heavy ion collisions, one must confront the reality of changing conditions within the collision environment and transport of conserved quantities within the finite duration of the expansion and dissolution of the reaction. In previous work, fluctuations of conserved charges from lattice calculations, where charge is allowed to fluctuate within the designated volume consistent with the grand canonical ensemble, was linked to correlations in heavy ion collisions, which accounted for the finite time with which to transport absolutely conserved quantities. In this case details of the correlations were related to the evolution of the susceptibility. In this work, this paradigm is extended to compare fluctuations of momentum or energy to transverse energy correlations that can be measured in heavy ion collisions. The sensitivity of these correlations to the equation of state, viscosity, and diffusion is illustrated by considering simple models without transverse expansion. Only correlations in relative spatial rapidity are discussed here, but the prospects for extending these ideas to realistic calculations and for making realistic connections with experiment are discussed.

Precise helicity-dependent cross sections and the double-polarization observable $E$ were measured for $\eta$ photoproduction from quasifree protons and neutrons bound in the deuteron. The $\eta \to 2\gamma$ and $\eta \to 3{\pi }^0\to 6\gamma$ decay modes were used to optimize the statistical quality of the data and to estimate systematic uncertainties. The measurement used the A2 detector setup at the tagged photon beam of the electron accelerator MAMI in Mainz. A longitudinally polarized deuterated butanol target was used in combination with a circularly polarized photon beam from bremsstrahlung of a longitudinally polarized electron beam. The reaction products were detected with the electromagnetic calorimeters Crystal Ball and TAPS, which covered 98% of the full solid angle. The results show that the narrow structure observed earlier in the unpolarized excitation function of $\eta$ photoproduction off the neutron appears only in reactions with antiparallel photon and nucleon spin (${\sigma }_{1/2}$). It is absent for reactions with parallel spin orientation (${\sigma }_{3/2}$) and thus very probably related to partial waves with total spin 1/2. The behavior of the angular distributions of the helicity-dependent cross sections was analyzed by fitting them withLegendre polynomials. The results are in good agreement with a model from the Bonn-Gatchina group, which uses an interference of $P_{11}$ and $S_{11}$ partial waves to explain the narrow structure.

In-source laser spectroscopy experiments for bismuth isotopes at the 306.77-nm atomic transition has been carried out at the Investigation of Radioactive Isotopes on Synchrocyclotron facility of Petersburg Nuclear Physics Institute. New data on isotope shifts and hyperfine structure for Bi ground states and isomers $\left({}^{189,190\mathrm{m}1,190\mathrm{m}2,191,192,192\mathrm{m},194,194\mathrm{m},198\mathrm{m}}\mathrm{Bi}\right)$ have been obtained. The changes in the mean-square charge radii $\delta \langle r^2\rangle$ and magnetic-moment values have been deduced. For Bi nuclei a marked deviation from the isotopic trend of $\delta \langle r^2\rangle$ in lead and thallium isotopic chains has been demonstrated at $N<111$. This has been interpreted as an indication of the onset of quadrupole deformation. Analysis of the magnetic moments for odd-odd Bi isotopes also points to the possible increase in deformation at $N<111$.

An upper limit to the mass of the three-proton unbound nucleus ${}^{17}\mathrm{Na}$ was measured to be $\mathrm{\Delta }M\le 34.72\left(6\right)$ MeV. The excitation energies, widths, and decay modes for one- and two-proton decaying states of ${}^8\mathrm{B}, {}^9\mathrm{B}, {}^9\mathrm{C}, {}^{16}\mathrm{F}$, and ${}^{17}\mathrm{Ne}$ were also measured. The energy-angular decay correlations in the $2p$ decay of ${}^{17}\mathrm{Ne}$ are presented.

Background: Two-nucleon ($2N$) short-range correlations (SRC) in nuclei have been recently thoroughly investigated, both theoretically and experimentally and the study of three-nucleon ($3N$) SRC, which could provide important information on short-range hadronic structure, is underway. Novel theoretical ideas concerning $2N$ and $3N$ SRC are put forward in the present paper.

Purpose: The general features of a microscopic one-nucleon spectral function which includes the effects of both $2N$ and $3N$ SRC and its comparison with ab initio spectral functions of the three-nucleon systems are illustrated.

Methods: A microscopic and parameter-free one-nucleon spectral function expressed in terms of a convolution integral involving ab initio relative and center-of-mass (c.m.) momentum distributions of a $2N$ pair and aimed at describing two- and three-nucleon short-range correlations, is obtained by using: (i) the two-nucleon momentum distributions obtained within ab initio approaches based upon nucleon-nucleon interactions of the Argonne family; (ii) the exact relation between one- and two-nucleon momentum distributions; (iii) the fundamental property of factorization of the nuclear wave function at short internucleon ranges.

Results: The comparison between the ab initio spectral function of ${}^3\mathrm{He}$ and the one based upon the convolution integral shows that when the latter contains only two-nucleon short-range correlations the removal energy location of the peaks and the region around them exhibited by the ab initio spectral function are correctly predicted, unlike the case of the high and low removal energy tails; the inclusion of the effects of three-nucleon correlations brings the convolution model spectral function in much better agreement with the ab initio one; it is also found that whereas the three-nucleon short-range correlations dominate the high energy removal energy tail of the spectral function, their effects on the one-nucleon momentum distribution are almost one order of magnitude less than the effect of two-nucleon short-range correlations.

Conclusions: The convolution model of the spectral function of the three-nucleon systems featuring both two- and three-nucleon short-range correlations and correctly depending upon the ab initio two-nucleon relative and center-of-mass momentum distributions provides in the correlation region a satisfactory approximation of the spectral function in a wide range of momentum and removal energy. The extension of the model to complex nuclei is expected to provide a realistic microscopic parameter-free model of the spectral function, whose properties are therefore governed by the features of realistic two-nucleon interactions and the momentum distributions in a given nucleus.

Background: Various cluster states of astrophysical interest are expected to exist in the excited states of ${}^{28}\mathrm{Si}$. However, they have not been identified firmly, because of the experimental and theoretical difficulties.

Purpose: To establish the ${}^{24}\mathrm{Mg}+\alpha ,{}^{16}\mathrm{O}+{}^{12}\mathrm{C}$, and ${}^{20}\mathrm{Ne}+2\alpha$ cluster bands, we theoretically search for the negative-parity cluster bands that are paired with the positive-parity bands to constitute the inversion doublets. We also offer the isoscalar monopole and dipole transitions as a promising probe for the clustering. We numerically show that these transition strengths from the ground state to the cluster states are very much enhanced.

Method: The antisymmetrized molecular dynamics with Gogny D1S effective interaction is employed to calculate the excited states of ${}^{28}\mathrm{Si}$. The isoscalar monopole and dipole transition strengths are directly evaluated from wave functions of the ground and excited states.

Results: Negative-parity bands having ${}^{24}\mathrm{Mg}+\alpha$ and ${}^{16}\mathrm{O}+{}^{12}\mathrm{C}$ cluster configurations are obtained in addition to the newly calculated ${}^{20}\mathrm{Ne}+2\alpha$ cluster bands. All of them are paired with the corresponding positive-parity bands to constitute the inversion doublets with various cluster configurations. The calculation shows that the bandheads of the ${}^{24}\mathrm{Mg}+\alpha$ and ${}^{20}\mathrm{Ne}+2\alpha$ cluster bands are strongly excited by the isoscalar monopole and dipole transitions.

Conclusions: The present calculation suggests the existence of inversion doublets with the ${}^{24}\mathrm{Mg}+\alpha ,{}^{16}\mathrm{O}+{}^{12}\mathrm{C}$, and ${}^{20}\mathrm{Ne}+2\alpha$ configurations. Because of the enhanced transition strengths, we offer the isoscalar monopole and dipole transitions as good probe for the ${}^{24}\mathrm{Mg}+\alpha$ and ${}^{20}\mathrm{Ne}+2\alpha$ cluster bands.

Ultracold neutrons (UCNs) are key for precision studies of fundamental parameters of the neutron and in searches for new charge-parity-violating processes or exotic interactions beyond the Standard Model of particle physics. The most prominent example is the search for a permanent electric-dipole moment of the neutron (nEDM). We have performed an experimental comparison of the leading UCN sources currently operating. We have used a “standard” UCN storage bottle with a volume of 32 liters, comparable in size to nEDM experiments, which allows us to compare the UCN density available at a given beam port.

Of particular interest in astrophysics is the ${}^{34}\mathrm{S}(p,\gamma ){}^{35}\mathrm{Cl}$ reaction, which serves as a stepping stone in thermonuclear runaway reaction chains during a nova explosion. Though the isotopes involved are all stable, the reaction rate of this significant step is not well known, due to a lack of experimental spectroscopic information on states within the Gamow window above the proton separation threshold of ${}^{35}\mathrm{Cl}$. Measurements of level spins and parities provide input for the calculation of resonance strengths, which ultimately determine the astrophysical reaction rate of the ${}^{34}\mathrm{S}(p,\gamma ){}^{35}\mathrm{Cl}$ proton capture reaction. By performing the ${}^{37}\mathrm{Cl}(p,t){}^{35}\mathrm{Cl}$ reaction in normal kinematics at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory, we have conducted a study of the region of astrophysical interest in ${}^{35}\mathrm{Cl}$, and have made the first-ever constraint on the spin and parity assignment for a level at $6677\pm 15$ keV $(E_r=306$ keV), inside the Gamow window for novae.

Neutron-rich ${}^{88,90,92,94}\mathrm{Se}$ isotopes were studied via in-beam $\gamma$-ray spectroscopy after nucleon removal reactions at intermediate energies at the Radioactive Isotope Beam Factory. Based on $\gamma -\gamma$ coincidence analysis, low-lying excitation level schemes are proposed for these nuclei, including the $2_1^{+}, 4_1^{+}$ states and $2_2^{+}$ states at remarkably low energies. The low-lying $2_2^{+}$ states, along with other features, indicate triaxiality in these nuclei. The experimental results are in good overall agreement with self-consistent beyond-mean-field calculations based on the Gogny D1S interaction, which suggests both triaxial degree of freedom and shape coexistence playing important roles in the description of intrinsic deformations in neutron-rich Se isotopes.

We derive the charged current absorption rate of electron and antielectron neutrinos in dense matter using a fully relativistic approach valid at arbitrary matter degeneracy. We include mean field energy shifts due to nuclear interactions and the corrections due to weak magnetism. The rates are derived both from the familiar Fermi's golden rule and from the techniques of finite temperature field theory, and are shown to be equivalent. In various limits, these results can also be used to calculate neutral current opacities. We find that some pieces of the response have been left out in previous derivations and their contribution at high density can be significant. Useful formulas and detailed derivations are presented and we provide a new open-source implementation of these opacities for use in radiation hydrodynamic simulations of core-collapse supernovae and neutron star mergers.

The even-$Z$ odd-$N$ neutron-halo nuclei, which are the lightest neutron-halo nuclei heavier than ${}^{37}\mathrm{Mg}$, are explored by studying the shell structure unique in weakly bound neutrons for spherical or deformed shapes. It is pointed out that due to the narrowed $N=50$ spherical energy gap and a few resulting close-lying neutron one-particle levels, $1g_{9/2}, 3s_{1/2}$, and $2d_{5/2}$, for spherical shape, nuclei with some weakly bound neutrons filling in those levels may be deformed and have a good chance to show deformed $s$-wave halos. Promising candidates are ${}_{24}{}^{71}\mathrm{Cr}_{47}, {}_{24}{}^{73}\mathrm{Cr}_{49}, {}_{24}{}^{75}\mathrm{Cr}_{51}$, and ${}_{26}{}^{77}\mathrm{Fe}_{51}$ in the case that those nuclei lie inside the neutron drip line. An interesting possibility of the deformed $p$-wave or $s$-wave halos is suggested also for the nucleus ${}_{18}{}^{53}\mathrm{Ar}_{35}$.

Pion energy spectra are presented for central collisions of neutron-rich ${}^{132}\mathrm{Sn}+{}^{124}\mathrm{Sn}$ and neutron-deficient ${}^{108}\mathrm{Sn}+{}^{112}\mathrm{Sn}$ systems using simulations with the Boltzmann-Uehling-Uhlenbeck transport model. These calculations, which incorporate isospin-dependent mean-field potentials for relevant baryons and mesons, display a sensitivity to the pion spectra that could allow significant constraints on the density dependence of the symmetry energy and its mean-field potential at suprasaturation densities. The predicted sensitivity increases with the isospin asymmetry of the total system and decreases with incident energy.

The angular distributions of differential cross sections of ${}^{12}\mathrm{C}+{}^{12}\mathrm{C}$ elastic and inelastic scattering populating the ground and excited states in ${}^{12}\mathrm{C}$ up to 15 MeV excitation energy are precisely measured for the first time at an incident energy of $100A$ MeV to study the effect of repulsive three-body forces. Using the high-resolution spectrometer Grand Raiden at the Research Center for Nuclear Physics (RCNP), Osaka University, we have obtained the differential cross sections for the ground state ($0_1^{+}$) and 4.44 MeV ($2_1^{+}$) excited state, as well as the summed differential cross sections for the states between 4.44 and 15 MeV in the angular range of $1.0^{\circ }–7.5^{\circ }$. The results are compared with microscopic coupled-channel calculations. The potential between the colliding nuclei is determined by the double folding method with three different complex $G$-matrix interactions, the ESC, CEG07b, and MPa interactions. The CEG07b and MPa interactions, which include repulsive three-body forces, describe the data well, whereas the ESC interaction, which does not include repulsive three-body forces, fails to reproduce the data. The results provide evidence of repulsive three-body forces in ${}^{12}\mathrm{C}$ and demonstrate the possible sensitivity of elastic scattering to three-body forces.

Background: The ${}^{11}\mathrm{B}{(p,2\alpha )}^4\mathrm{He}$ reaction is being discussed as a prime candidate for advanced aneutronic fusion fuel systems. Particular interest in this reaction has recently emerged for laser driven plasma systems for energy generation and jet-propulsion systems. The lack of long-lived radioactive reaction products has been suggested as the main advantage of proton-boron fusion fuel. However, 19% of natural boron is ${}^{10}\mathrm{B}$, with the ${}^{10}\mathrm{B}(p,\alpha ){}^7\mathrm{Be}$ fusion reaction producing long-lived ${}^7\mathrm{Be}$ as a side product.

Purpose: A detailed measurement of the ${}^{10}\mathrm{B}(p,\alpha ){}^7\mathrm{Be}$ reaction over the critical energy range of hot fusion plasma environments will help to determine the amount of ${}^7\mathrm{Be}$ radioactivity being produced. This information can be used in turn to monitor the actual fusion temperature by offline measurement of the extracted ${}^7\mathrm{Be}$ activity. The goal of the here presented experiment is to expand on the results of earlier experiments, covering a wider energy range of interest for aneutronic plasma fusion applications, including also both ${}^{10}\mathrm{B}(p,{\alpha }_0){}^7\mathrm{Be}$ and the ${}^{10}\mathrm{B}(p,{\alpha }_1){}^7\mathrm{Be}$ reaction channels.

Method: The reaction cross section was measured over a wide energy range from $E_p=400$ to 1000 keV using particle detection and from $E_p=80$ to 1440 keV using $\gamma$-ray spectroscopic techniques. Reaction $\alpha$ particles were measured at different angles to obtain angular distribution information. The results are discussed in terms of an $R$-matrix analysis.

Results: The cross section data cover a wider energy range than previously investigated and bridge a gap in the previously available data sets. The cross sections show good agreement with previous results in the low energy region and show that the ${}^{10}\mathrm{B}(p,{\alpha }_0){}^7\mathrm{Be}$ channel is considerably larger than that of the ${}^{10}\mathrm{B}(p,{\alpha }_1){}^7\mathrm{Be}$ channel up to $E_p\approx 1\mathrm{MeV}$.

Conclusions: The new reaction data provides important new information about the reaction cross section over the entire energy range of plasma fusion facilities. This data, when coupled with previous measurement of the competing ${}^{10}\mathrm{B}(p,\gamma ){}^{11}\mathrm{C}$ reaction, will provide the opportunity for an extensive $R$-matrix analysis of the rather complex level structure in the ${}^{11}\mathrm{C}$ compound nucleus system.

Explicit analytic expressions are derived for the effective-range function for the case when the interaction is represented by a sum of the short-range square-well and long-range Coulomb potentials. These expressions are then transformed into forms convenient for extrapolating to the negative-energy region and obtaining the information about bound-state properties. Alternative ways of extrapolation are discussed. Analytic properties of separate terms entering these expressions for the effective-range function and the partial-wave scattering amplitude are investigated.

We study for the first time the internal structure of ${}^{140}\mathrm{Te}$ through the $\beta$-delayed $\gamma$-ray spectroscopy of ${}^{140}\mathrm{Sb}$. The very neutron-rich ${}^{140}\mathrm{Sb}$ nuclei with $Z=51$ and $N=89$ were produced by the in-flight fission of ${}^{238}\mathrm{U}$ beams at the Radioactive Isotope Beam Factory, RIKEN. The half-life and spin-parity of ${}^{140}\mathrm{Sb}$ are reported as $173\pm 12$ ms and $3^{-}$, respectively. In addition to the excited states of ${}^{140}\mathrm{Te}$ produced by the $\beta$-decay branch, the $\beta$-delayed one-neutron and two-neutron emission branches were also established. By identifying the first $2^{+}$ and $4^{+}$ excited states of ${}^{140}\mathrm{Te}$, we found that Te isotopes persist in their vibrator character with $E\left(4^{+}\right)/E\left(2^{+}\right)=2$. We discuss the distinctive features manifest in this region revealed in pairs of isotopes with the same neutron holes and particles with respect to $N=82$.

Neutron unbound states in ${}^{23}\mathrm{N}$ were populated via proton knockout from an 83.4 MeV/nucleon ${}^{24}\mathrm{O}$ beam on a liquid deuterium target. The two-body decay energy displays two peaks at $E_1\sim 100\mathrm{keV}$ and $E_2\sim 1\mathrm{MeV}$ with respect to the neutron separation energy. The data are consistent with shell model calculations predicting resonances at excitation energies of $\sim 3.6\mathrm{MeV}$ and $\sim 4.5\mathrm{MeV}$. The selectivity of the reaction implies that these states correspond to the first and second $3/2^{-}$ states. The energy of the first state is about 1.3 MeV lower than the first excited $2^{+}$ in ${}^{24}\mathrm{O}$. This decrease is largely due to coupling with the $\pi p_{3/2}^{-1}$ hole along with a small reduction of the $N=16$ shell gap in ${}^{23}\mathrm{N}$.