We identify a redundancy between two- and three-nucleon contact interactions at the fourth and fifth orders of the chiral expansion, respectively. In particular, we show that tensor-type and spin-orbit three-nucleon contact interactions effectively account for that part of the two-nucleon interaction which depends on the total center-of-mass momentum and is unconstrained by relativity. This might give the chiral effective field theory enough flexibility to successfully address $A=3$ scattering observables already at N3LO.

The total kinetic energy (TKE) release in the fast neutron-induced fission of ${}^{237}\mathrm{Np}$ was measured for neutron energies from $E_n=2.6–100\mathrm{MeV}$ at the Los Alamos Neutron Science Center at the Weapons Neutron Research facility. The post-TKE release decreases nonlinearly with increasing incident neutron energy and can be represented as $\mathrm{TKE}\left(\mathrm{MeV}\right)=(174.38\pm 0.72)–(5.11\pm 0.5821){\log }_{10}{E}_n$ for $E_n>1\mathrm{MeV}$. Analysis of the fragment mass distributions indicates that the decrease in TKE with increasing $E_n$ is a consequence of the fading out of shell effects at high excitation energies (resulting in an increase of symmetric fission) and the decrease of the total kinetic energy associated with asymmetric fission with increasing $E_n$.

Higher moments of distributions of net charge and baryon number in heavy-ion collisions have been proposed as signals of fundamental QCD phase transitions. In order to better understand background processes for these observables, models are presented which enable one to gauge the effects of local charge conservation, decays of resonances and clusters, Bose symmetrization, and volume fluctuations. Monte Carlo methods for generating samplings of particles consistent with local charge conservation are presented and are followed by a review of simple analytic models involving a single type of charge with a constant experimental efficiency. The main model consists of thermal emission superimposed onto a simple parametrization of collective flow, known as a blast wave, with emission being consistent with individual canonical ensembles. The spatial extent of local charge conservation is parameterized by the size and extent over which charge is conserved. The sensitivity of third- and fourth-order moments, skewness and kurtosis, to these parameters, and to beam energy and baryon density is explored. Comparisons with STAR data show that a significant part of the observed non-Poissonian fluctuations in net-proton fluctuations are explained by charge and baryon-number conservation, but that measurements of the STAR collaboration for fluctuations of net electric charge significantly differ from expectations of the models presented here.

The information of the event-by-event fluctuations are extracted from flow harmonic distributions and cumulants, which can be done experimentally. In this work, I employ the standard method of Gram-Charlier series with normal kernel to find such distribution, which is the generalization of recently introduced flow distributions for the studies of the event-by-event fluctuations. In this path, I find the shifted cumulants $j_n\left\{2k\right\}$ which are consist of the collision geometry information. The experimental data imply that not only all of the information about the event-by-event fluctuations of collision zone properties and different stages of heavy-ion process are not encoded in the radial flow distribution $p\left(v_n\right)$, but also the observables describing harmonic flows can generally be given by the joint distribution $\mathcal{P}(v_1,v_2,\cdots )$. In such way, I first introduce a set of joint cumulants ${\mathcal{K}}_{nm}$, and then I find the flow joint distribution using these joint cumulants. Finally, I show that the symmetric cumulants $\mathrm{SC}(2,3)$ and $\mathrm{SC}(2,4)$ obtained from ALICE data are explained by the combinations ${\mathcal{K}}_{22}+\frac{1}{2}{\mathcal{K}}_{04}-{\mathcal{K}}_{31}$ and ${\mathcal{K}}_{22}+4{\mathcal{K}}_{11}^2$.

An extended investigation of the low-spin structure of the ${}^{65}\mathrm{Ni}$ nucleus was performed at the Institut Laue-Langevin, Grenoble, France, via the neutron capture reaction ${}^{64}\mathrm{Ni}(n,\gamma ){}^{65}\mathrm{Ni}$, using the Fission Product Prompt Gamma-Ray Spectrometer High-Purity Ge array. The level scheme of ${}^{65}\mathrm{Ni}$ was significantly expanded, with two new levels and 87 newly found transitions. Angular correlation analyses were also performed, allowing us to assign spins and parities for a number of states and to determine multipolarity mixing ratios for selected $\gamma$ transitions. The low-energy part of the experimental level scheme (up to about 1.4 MeV) was compared with Monte Carlo shell-model calculations, which predict spherical shapes for all states, apart from the $9/2^{+}$ and the second excited $1/2^{-}$ states of oblate deformation.

Amplitude- and truncated partial-wave analyses are combined into a single-channel method for extracting multipoles directly from measured data. In practice, we have created a two-step procedure which is fit to the same database: in the first step we perform an energy-independent amplitude analysis where continuity is achieved by constraining the amplitude phase, and the result of this first step is then taken as a constraint for the second step where a constrained, energy-independent, truncated partial-wave analysis is done. The method is tested on the world collection of data for $\eta$ photoproduction, and the obtained fit results are very good. The sensitivity to different possible choices of amplitude phase is investigated and it is demonstrated that the present database is insensitive to notable phase changes due to an incomplete database. New measurements are recommended to remedy the problem.

Background: The sharing of excitation energy between the fission fragments is one of the key issues in studying nuclear fission. One way to address this is by studying prompt-fission neutron multiplicities as a function of other fission observables such as the mass, $\overline{\nu }\left(A\right)$. These are vital benchmark data for both fission and nuclear deexcitation models, putting constrains on the fragment excitation energy and hence on the competing prompt neutron/$\gamma$-ray emission. Despite numerous detailed studies, recent measurements done at JRC-Geel with the SCINTIA array in the epithermal region show surprisingly strong discrepancies to earlier thermal fission data and the Wahl systematics.

Purpose: The purpose was to perform measurements of the prompt-fission neutron multiplicity, as a function of fragment mass and total kinetic energy (TKE), in ${}^{235}\mathrm{U}\left({\text{n}}_{\text{th}},\text{f}\right)$ and ${}^{252}\mathrm{Cf}\left(\text{sf}\right)$, to verify and extend the SCINTIA results. Another goal was to validate the analysis methods, and prepare for planned investigations at excitation energies up to 5.5 MeV.

Methods: The experiments were conducted at the former 7 MV Van de Graaff facility in JRC-Geel, using a Twin Frisch-Grid Ionization Chamber and two liquid scintillation detectors. A neutron beam with an average energy of 0.5 MeV was produced via the ${}^7\mathrm{Li}$(p,n) reaction. The neutrons were thermalized by a 12 cm thick block of paraffin. Digital data acquisition systems were utilized. Comprehensive simulations were performed to verify the methodology and to investigate the role of the mass and energy resolution on measured $\overline{\nu }\left(A\right)$ and $\overline{\nu }\left(\text{TKE}\right)$ values. The simulation results also revealed that the $\partial \overline{\nu }\left(A\right)/\partial A$ and $\partial \overline{\text{TKE}}/\partial \overline{\nu }$ are affected by the mass and energy resolution. However, the effect is small for the estimated resolutions of this work. Detailed Fluka simulations were performed to calculate the fraction of thermal neutron-induced fission, which was estimated to be about $98\%$.

Results: The experimental results on $\overline{\nu }\left(A\right)$ are in good agreement with earlier data for ${}^{252}\mathrm{Cf}\left(\text{sf}\right)$. For ${}^{235}\mathrm{U}\left({\text{n}}_{\text{th}},\text{f}\right)$, the $\overline{\nu }\left(A\right)$ data is very similar to the data obtained with SCINTIA, and therefore we verify these disclosed discrepancies to earlier thermal data and to the Wahl evaluation. The experimental results on $\overline{\nu }\left(\text{TKE}\right)$ are also in agreement with the data at epithermal energies. For ${}^{252}\mathrm{Cf}\left(\text{sf}\right)$ a slope value of $\partial \overline{\text{TKE}}/\partial \overline{\nu }=\left(-12.9\pm 0.2\right)\mathrm{MeV}/\mathrm{n}$ was obtained. For ${}^{235}\mathrm{U}\left({\text{n}}_{\text{th}},\text{f}\right)$ the value is $\left(-12.0\pm 0.1\right)\mathrm{MeV}/\mathrm{n}$. Finally, the neutron spectrum in the center-of-mass system was derived and plotted as a function of fragment mass.

Conclusions: This work clearly proves the lack of accurate correlation between fission fragment and neutron data even in the best-studied reactions. The new results highlight the need of a new evaluation of the prompt-fission multiplicity for ${}^{235}\mathrm{U}\left({\text{n}}_{\text{th}},\text{f}\right)$.

The present PREX-II and CREX experiments are measuring the rms radius of the weak charge density of ${}^{208}\mathrm{Pb}$ and ${}^{48}\mathrm{Ca}$. We discuss the feasibility of a new parity violating electron scattering experiment to measure the surface thickness of the weak charge density of a heavy nucleus. Once PREX-II and CREX have constrained weak radii, an additional parity violating measurement at a momentum transfer near $0.76{\mathrm{fm}}^{-1}$ for ${}^{208}\mathrm{Pb}$ or $1.28{\mathrm{fm}}^{-1}$ for ${}^{48}\mathrm{Ca}$ can determine the surface thickness.

Recently, the $E1$ photoneutron cross sections were measured consistently using quasimonochromatic laser Compton-scattering $\gamma$-ray beams at NewSUBARU (Japan) for a set of ten odd-even nuclei, spherical as well as deformed, covering relatively widely light to heavy species and at energies ranging between the neutron threshold and 40 MeV. This consistent set of experimental photoneutron cross sections allow us to estimate the total $E1$ photoabsorption cross sections, through validated theoretical models, by excluding the quasideuteron component and by including the missing low-energy and charged-particle emission contributions. In turn, the total $E1$ photoabsorption cross sections are used to derive the three main moments of the $E1$ distributions, namely the integrated cross section, the centroid energy, and the polarizability. These so-called model-dependent experimental moments follow a rather smooth trend with atomic mass, as theoretically expected, except for the specific case of ${}^{209}\mathrm{Bi}$ which presents a surprising 10% increase of both the integrated strength and the polarizability with respect to its even-even spherical neighbor ${}^{208}\mathrm{Pb}$. A rather consistent value for the enhancement factor of the $E1$ energy-weighted sum rule could be extracted from the present experimental data. The experimentally derived moments are compared for the ten odd-even systems with calculations based on the mean-field plus quasiparticle random phase approximation (QRPA). Spherical as well as axially deformed predictions based on the Skyrme and Gogny interactions are considered to discuss the results. Special attention is also paid to the approximate treatment of odd systems of nucleons in this context. It is found that in general theoretical predictions can rather well describe the data for the full set of nuclei, except for ${}^{209}\mathrm{Bi}$ presenting a kink in all the three main $E1$ moments with respect to the well-studied ${}^{208}\mathrm{Pb}$ case. Such an experimental determination cannot be explained by mean-field plus QRPA calculations. New measurements of photoabsorption cross section on ${}^{208}\mathrm{Pb}$ and ${}^{209}\mathrm{Bi}$ in the 14–19 MeV range as well as future theoretical calculations, in particular of odd-even systems, may help to solve such a mystery. The present data are also used to reinvestigate the correlation between the nuclear matter symmetry energy and its slope at saturation density. The analysis based on both Skyrme and Gogny Hartree-Fock-Bogolyubov (HFB) plus QRPA calculations confirm previous results, though quantitatively larger variations of the correlation parameters are found.

Background: The measured subbarrier fusion cross sections in heavy-ion reactions are found to be significantly large as compared with those expected from the one-dimensional barrier penetration model (1d-BPM). Although attempts have been made to comprehend the enhancement in terms of different intrinsic degrees of freedom of the colliding nuclei, a clear understanding of the same is yet to come.

Purpose: The objectives of this study is to understand the interplay of the channel coupling effect on fusion excitation function and explore the decay dynamics of the excited compound nucleus in the sub-and-near barrier region.

Method: Fusion excitation function has been measured at energies from 7% below to 38% above the Bass barrier using a recoil mass spectrometer. Furthermore, cross sections of the different evaporation residues, such as 98, 99, 100, and 101 u, have been extracted.

Results: The observed enhancement in the subbarrier fusion cross sections over the 1d-BPM predictions has been explained by considering the low-lying inelastic excitations among the interacting partners using ccfull code and by the barrier modification using the dynamical cluster-decay model (DCM). The cross sections of individual residual mass fractions (98, 99, 100, and 101 u) have been compared with the Hauser-Feshbach model.

Conclusion: Coupled-channel calculations and DCM have successfully explained the total fusion cross sections data. The measured total fusion cross section ${\sigma }_{\mathrm{fus}}$ was found to be approximately equal to the sum of various residual mass fractions ($\mathrm{\Sigma }{\sigma }_{\mathrm{ER}}$) at energies above the Bass barrier. One-dimensional barrier height and radius parameters extracted from the measured data are in good agreement with the Bass model and DCM parameters.

The transparency of metal foils for ultracold neutrons (UCNs) plays an important role in the design of future high-density UCN sources, which will feed a number of fundamental physics experiments. In this work, we describe and discuss the measured transmission of a collimated beam of very slow neutrons (UCNs and very cold neutrons) through foils of Al, Cu, and Zr of various thicknesses at room temperature. Our goal was to separate scattering and absorption in the sample bulk from surface scattering, and to quantify the contribution of the surface. We were able to demonstrate that the surface roughness of these foils caused a significant fraction of UCN scattering. The surface roughness parameter $b$ extracted from UCN measurements was shown to be of the same order of magnitude as the surface parameter determined by atomic-force microscopy. They lie in the order of several hundreds of angstroms. Using the formalism developed here, transmission data from previous neutron-optical experiments were re-analyzed and their surface roughness parameter $b$ was extracted.

Excitation functions of ${}^3\mathrm{He}$-induced nuclear reactions on ${}^{\mathrm{nat}}\mathrm{Ta}$ were measured utilizing the MGC-20E cyclotron, stacked-foils activation technique, and high-resolution gamma-ray spectrometry. From their threshold energies up to 27 MeV, cross sections for ${}^{\mathrm{nat}}\mathrm{Ta}({}^3\mathrm{He},xn){}^{182}\mathrm{Re}^{\mathrm{m}}, {}^{182}\mathrm{Re}^{\mathrm{g}}, {}^{181}\mathrm{Re}$, and ${}^{\mathrm{nat}}\mathrm{Ta}({}^3\mathrm{He},\alpha xn){}^{178}\mathrm{Ta}^{\mathrm{A}}, {}^{180}\mathrm{Ta}^{\mathrm{g}}$ reactions were measured. The half-life of the radionuclide ${}^{181}\mathrm{Re}$ was checked experimentally. The intensity of the energy line 360.7 keV, in the radionuclide ${}^{181}\mathrm{Re}$ decay scheme, was revised experimentally. The new experimental intensity represents about half the reported value in the different nuclear structure databases. The nuclear reaction codes TALYS-1.9 and EMPIRE-3.2.3 were used to predict the formation of these products. The isomeric cross-section ratio for the ${}^{182}\mathrm{Re}^{\mathrm{m},\mathrm{g}}$ was also calculated. The ratio indicates that the pre-equilibrium mechanism is dominant at energies over 19 MeV. Various combinations of the models’ parameters implemented in EMPIRE such as nuclear level density models, optical model, and pre-equilibrium parameters were used to reproduce the experimental excitation functions. For TALYS calculations, the TENDL-2019 nuclear data library based on TALYS-1.9 was used. The present data were compared to theoretical results and the available experimental data. Integral yields for the produced radioisotopes were determined.

The isospin dependence of nuclear level density has been investigated by analyzing the spectra of evaporated neutrons from excited ${}^{116}\mathrm{Sn}$ and ${}^{116}\mathrm{Te}$ nuclei. These nuclei are populated via $p+{}^{115}\mathrm{In}$ and ${}^4\mathrm{He}+{}^{112}\mathrm{Sn}$ reactions in the excitation energy range of 18–26 MeV. Because of low excitation energy, the neutron spectra are predominantly contributed by the first-chance decay leading to the $\beta$-stable ${}^{115}\mathrm{Sn}$ and neutron-deficient ${}^{115}\mathrm{Te}$ as residues for the two cases. Theoretical analysis of the experimental spectra has been performed within the Hauser-Feshbach formalism by employing different models of the level-density parameter. It is observed that the data could only be explained by the level-density parameter that decreases monotonically when the proton number deviates from the $\beta$-stable value. This is also confirmed by performing a microscopic shell-model calculation with the Woods-Saxon mean field. The results have strong implications on the estimation of the level density of unstable nuclei and calculation of astrophysical reaction rates relevant to $r$ and $rp$ processes.

We calculate the lifetime of the hypertriton as a function of the $\mathrm{\Lambda }$ separation energy $B_{\mathrm{\Lambda }}$ in an effective field theory with $\mathrm{\Lambda }$ and deuteron degrees of freedom. We also consider the impact of new measurements of the weak decay parameter of the $\mathrm{\Lambda }$. While the sensitivity of the total width to $B_{\mathrm{\Lambda }}$ is small, the partial widths for decays into individual final states and the experimentally measured ratio $R={\mathrm{\Gamma }}_{{}^3\mathrm{He}}/\left({\mathrm{\Gamma }}_{{}^3\mathrm{He}}+{\mathrm{\Gamma }}_{pd}\right)$ show a strong dependence. For the standard value $B_{\mathrm{\Lambda }}=(0.13\pm 0.05)$ MeV, we find $R=0.37\pm 0.05$, which is in good agreement with past experimental studies and theoretical calculations. For the recent STAR value $B_{\mathrm{\Lambda }}=(0.41\pm 0.12\pm 0.11)$ MeV, we obtain $R=0.57\pm 0.11$.

We have studied the compound nucleus probability, the survival probability, and the evaporation residue cross sections for 6645 projectile-target combinations to synthesize the superheavy nuclei with atomic numbers $Z=110$–126 in the light of the entrance channel effects such as mass asymmetry, charge asymmetry, isospin asymmetry, non-compound nuclear fission probability, and Businaro-Gallone mass asymmetry. The role of quasifission in every reaction has also been considered. Decay chains of various superheavy nuclei produced from the reactions are portrayed as well. The most striking results are that the measured evaporation residue cross sections are of the order of picobarns, whereas the proposed reactions can yield up to microbarn cross sections for the superheavy nuclei with $110\le Z\le 126$. We suggest future experiments may utilize these hot fusion reactions to synthesize new elements ($Z>118$) or to study the properties of the known superheavy nuclei in greater detail. In particular, a proposed reaction containing both projectiles and targets that are naturally abundant, for example, ${}_{36}{}^{82}\mathrm{Kr}+{}_{90}{}^{232}\mathrm{Th}\to {}^{314}126+0n$, yields evaporation residue cross sections as high as 31 nb. The presently available experimental setup can test the prediction with ease to make a dream come true by putting a footstep into the eighth row of the periodic table.

The three-body system inside the unitary window is studied for three equal bosons and three equal fermions having $1/2$ spin-isospin symmetry. We perform a Gaussian characterization of the window using a Gaussian potential to define trajectories for low-energy quantities as binding energies and phase shifts. On top of this trajectories experimental values are placed or, when not available, quantities calculated using realistic potentials that are known to reproduce experimental values. The intention is to show that the Gaussian characterization of the window, thought as a contact interaction plus range corrections, captures the main low-energy properties of real systems as for example three helium atoms or three nucleons. The mapping of real systems on the Gaussian trajectories is taken as indication of universal behavior. The trajectories continuously link the physical points to the unitary limit allowing for the explanation of strong correlations between observables appearing in real systems and which are known to exist in that limit. In the present study we focus on low-energy bound, scattering, and virtual states.

We propose a new two-dimensional (2D) plotting method of isoscalar-isovector (IS-IV) densities of ${}^{48}\mathrm{Ca}$ and ${}^{208}\mathrm{Pb}$ to extract not only empirical symmetry energy coefficients $J, L$, and $K_{\mathrm{sym}}$ but also the asymmetric isospin term $K_{\tau }$ in the nuclear incompressibility. We adopted several modern relativistic and nonrelativistic energy density functional (EDF) for the theoretical calculations of IS and IV densities to compare with experimental neutron and proton density distributions determined by recent proton elastic scatterings. We found very strong correlations between the trajectory of the 2D density at the density $\rho =0.1{\mathrm{fm}}^{-3}$ and the symmetry energy coefficients $J, L$, and also $K_{\tau }$. For $K_{\mathrm{sym}}$, the Skyrme EDF SAMi-J family shows a strong correlation in the trajectory of 2D density, while the RMF Lagrangian DDME-J family shows a peculiar quadratic curve and does not provide the experimental value. The symmetry energy term $K_{\tau }$ of nuclear incompressibility is also discussed in term of the slope of 2D trajectory.

The multinucleon transfer reaction is treated as a diffusion process by solving four-variable master equations within the dinuclear system (DNS) concept. The reaction systems ${}^{136}\mathrm{Xe}+{}^{208}\mathrm{Pb}$ and ${}^{136}\mathrm{Xe}+{}^{198}\mathrm{Pt}$ are investigated and compared to the experimental data. The calculated results correctly describe the magnitude and maxima of the observed transfer cross sections for a wide range of transfers. One finds that the neutron richness of the reaction products is strongly dependent on the projectile energy near the Coulomb barrier. By comparing the obtained results for the above two reaction systems, the absolute cross sections from the ${}^{208}\mathrm{Pb}$ target predict smaller production cross sections for neutron-deficient nuclei and moderately neutron-rich nuclei as compared to ${}^{198}\mathrm{Pt}$.