Background: Shape coexistence in the $Z\approx 82$ region has been established in mercury, lead, and polonium isotopes. For even-even mercury isotopes with $100\le N\le 106$ multiple fingerprints of this phenomenon are observed, which seems to be no longer present for $N\ge 110$. According to a number of theoretical calculations, shape coexistence is predicted in the ${}^{188}\mathrm{Hg}$ isotope.

Purpose: The aim of this work was to measure lifetimes of excited states in ${}^{188}\mathrm{Hg}$ to infer their collective properties, such as the deformation. Extending the investigation to higher-spin states, which are expected to be less affected by band-mixing effects, can provide additional information on the coexisting structures.

Methods: The ${}^{188}\mathrm{Hg}$ nucleus was populated using two different fusion-evaporation reactions with two targets, ${}^{158}\mathrm{Gd}$ and ${}^{160}\mathrm{Gd}$, and a beam of ${}^{34}\mathrm{S}$ provided by the Tandem-ALPI accelerator complex at the Laboratori Nazionali di Legnaro. The channels of interest were selected using the information from the Neutron Wall array, while the $\gamma$ rays were detected using the GALILEO $\gamma$-ray spectrometer. Lifetimes of excited states were determined using the recoil-distance Doppler-shift method, employing the dedicated GALILEO plunger device.

Results: Lifetimes of the states up to spin $16\hslash$ were measured and the corresponding reduced transition probabilities were calculated. Assuming two-band mixing and adopting, as done commonly, the rotational model, the mixing strengths and the deformation parameters of the unperturbed structures were obtained from the experimental results. In order to shed light on the nature of the observed configurations in the ${}^{188}\mathrm{Hg}$ nucleus, the extracted transition strengths were compared with those resulting from state-of-the-art beyond-mean-field calculations using the symmetry-conserving configuration-mixing approach, limited to axial shapes, and the five-dimensional collective Hamiltonian, including the triaxial degree of freedom.

Conclusions: The first lifetime measurement for states with spin $\ge 6$ suggested the presence of an almost spherical structure above the ${12}_1^{+}$ isomer and allowed elucidating the structure of the intruder band. The comparison of the extracted $B\left(E2\right)$ strengths with the two-band mixing model allowed the determination of the ground-state band deformation. Both beyond-mean-field calculations predict coexistence of a weakly deformed band with a strongly prolate-deformed one, characterized by elongation parameters similar to those obtained experimentally, but the calculated relative position of the bands and their mixing strongly differ.

The fusion-evaporation reaction ${}^{32}\mathrm{S}+{}^{28}\mathrm{Si}$ at 125 MeV beam energy was used to populate high-spin states in the semimagic $N=28$ nuclei ${}^{53}\mathrm{Mn}$ and ${}^{54}\mathrm{Fe}$. With a combination of the Gammasphere spectrometer and ancillary devices including the Microball CsI(Tl) array, extensive high-spin level schemes are derived. They exhibit rotational-like collective structures and competing single-particle excitations. The experimental results are compared with predictions from shell-model calculations, for which the inclusion of isopin-symmetry-breaking terms is found to improve the description. An interpretation of the high-spin states is put forward using cranked Nilsson-Strutinsky calculations, indicative of contributions from collective excitations beyond some 8-MeV excitation energy and highlighting the importance of the $g_{9/2}$ intruder orbital in this energy range.

Background: The term Pygmy Dipole Resonance (PDR) denotes an accumulation of electric dipole excitations below and around the neutron separation threshold. It may be important, e.g., for the nucleosynthesis of heavy nuclei or the symmetry energy in the Equation of State (EoS). For a deeper understanding of the PDR, systematic studies are essential.

Purpose: The tin isotopic chain is a well-suited candidate to investigate the systematics of the PDR, and the ($\gamma ,{\gamma }^{\prime }$) reactions on ${}^{112,116,120,124}\mathrm{Sn}$ have already been measured in experiments using bremsstrahlung. It was claimed that the extracted electric dipole transition strengths of these isotopes increase with increasing neutron-to-proton ratio with the exception of ${}^{120}\mathrm{Sn}$. Furthermore, previous results from elastic photon scattering experiments on ${}^{120}\mathrm{Sn}$ are in disagreement with corresponding $(p,p^{\prime })$ Coulomb excitation data. To examine this discrepancy an additional high-sensitivity bremsstrahlung experiment on ${}^{120}\mathrm{Sn}$ was performed.

Method: The Nuclear Resonance Fluorescence (NRF) method is used, which is based on the scattering of real photons. The bremsstrahlung experiment presented in this work was performed with a maximum energy of $E_{\gamma ,\max }=9.5\mathrm{MeV}$ at the $\gamma \mathrm{ELBE}$ facility at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR). Besides a state-to-state analysis, the quasicontinuum was investigated as well.

Results: Above $E_x=4$ MeV 228 dipole transitions were clearly identified; 163 were observed for the first time. Assuming that all identified dipole transitions have electric dipole character the summed electric dipole strength equals $\sum B\left(E1\right)\uparrow =369\left(49\right)\times {10}^{-3}{e}^2{\text{fm}}^2$ [which amounts to 0.58(8)% of the Thomas-Reiche-Kuhn sum rule] for transitions from 4 MeV to $S_n=9.1$ MeV. This is an enhancement of a factor 2.3 compared to the previously published ${}^{120}\mathrm{Sn}(\gamma ,{\gamma }^{\prime })$ results. This increase can be explained by the contribution of many weak, previously not included transitions in the state-to-state analysis. The photoabsorption cross sections deduced from the quasicontinuum analysis exceed those of the $(p,p^{\prime })$ experiment in average by about $50\%$ between 5.9 and 8.7 MeV.

Conclusion: The newly extracted summed $B\left(E1\right)$ value of the state-to-state analysis is larger than those of ${}^{112,116}\mathrm{Sn}$ and smaller than that of ${}^{124}\mathrm{Sn}$. The difference between the electric dipole transition strengths deduced from isolated peaks of the present ($\gamma ,{\gamma }^{\prime }$) data and those from the inelastic proton scattering experiment above 6.3 MeV is still striking. The analysis of the photoabsorption cross section including the quasicontinuum of levels overcomes this problem and the results are in the order of magnitude of the $(p,p^{\prime })$ data and continue the $(\gamma ,n)$ cross sections at the neutron separation threshold.

Background: Nuclear waste management is considered amongst the major challenges in the field of nuclear energy. A possible means of addressing this issue is waste transmutation in advanced nuclear systems, whose operation requires a fast neutron spectrum. In this regard, the accurate knowledge of neutron-induced reaction cross sections of several (minor) actinide isotopes is essential for design optimization and improvement of safety margins of such systems. One such case is ${}^{240}\mathrm{Pu}$, due to its accumulation in spent nuclear fuel of thermal reactors and its usage in fast reactor fuel. The measurement of the ${}^{240}\mathrm{Pu}(n,f)$ cross section was previously attempted at the CERN n_TOF facility EAR1 measuring station using the time-of-flight technique. Due to the low amount of available material and the given flux at EAR1, the measurement had to last several months to achieve a sufficient statistical accuracy. This long duration led to detector deterioration due to the prolonged exposure to the high $\alpha$ activity of the fission foils, therefore the measurement could not be successfully completed.

Purpose: It is aimed to determine whether it is feasible to study neutron-induced fission at n_TOF/EAR2 and provide data on the ${}^{240}\mathrm{Pu}(n,f)$ reaction in energy regions requested for applications.

Methods: The study of the ${}^{240}\mathrm{Pu}(n,f)$ reaction was made at a new experimental area (EAR2) with a shorter flight path which delivered on average 30 times higher flux at fast neutron energies. This enabled the measurement to be performed much faster, thus limiting the exposure of the detectors to the intrinsic activity of the fission foils. The experimental setup was based on microbulk Micromegas detectors and the time-of-flight data were analyzed with an optimized pulse-shape analysis algorithm. Special attention was dedicated to the estimation of the non-negligible counting loss corrections with the development of a new methodology, and other corrections were estimated via Monte Carlo simulations of the experimental setup.

Results: This new measurement of the ${}^{240}\mathrm{Pu}(n,f)$ cross section yielded data from $9\mathrm{meV}$ up to $6\mathrm{MeV}$ incident neutron energy and fission resonance kernels were extracted up to $10\mathrm{keV}$.

Conclusions: Neutron-induced fission of high activity samples can be successfully studied at the n_TOF/EAR2 facility at CERN covering a wide range of neutron energies, from thermal to a few MeV.

The observed thermal relaxation of transiently accreting neutron stars during quiescence periods in low-mass x-ray binaries suggests the existence of unknown heat sources in the shallow layers of neutron-star crust. Making use of existing experimental nuclear data, we estimate the maximum possible amount of heat that can be deposited in the outer crust of an accreting neutron star due to electron captures and pycnonuclear fusion reactions triggered by the burial of x-ray burst ashes.

The tidal deformability probability distribution extracted from GW170817 alone, or including multimessenger information, is confronted by additional constraints from astrophysical and nuclear physics within a semiagnostic approach for the dense matter equation of state. We use Bayesian statistics to combine together low-density nuclear physics data, such as the ab initio predictions based on chiral effective field theory interactions or the isoscalar giant monopole resonance, and astrophysical constraints from neutron stars, such as the maximum mass of neutron stars or the probability distribution function of the tidal deformability $\tilde{\mathrm{\Lambda }}$ obtained from the GW170817 event. The so-called posterior probability distribution functions are marginalized over several nuclear empirical parameters ($L_{\text{sym}},K_{\text{sym}},Q_{\text{sat}}$, and $Q_{\text{sym}}$), as well as over observational quantities such as the $1.4M_{\odot }$ radius $R_{1.4}$ and the pressure at twice the saturation density $P\left(2n_{\text{sat}}\right)$. The correlations between $L_{\text{sym}}$ and $K_{\text{sym}}$ and between $K_{\text{sat}}$ and $Q_{\text{sat}}$ are also further analyzed. Tension is found between the posteriors: The first one is localized in the tidal deformability probability distribution itself, depending whether multimessenger analysis is included, and the second one is between the observational data and the nuclear physics inputs. These tensions impact the predictions for $L_{\text{sym}},K_{\text{sym}}$, and $R_{1.4}$ with centroids which differ by 2–$3\sigma$. Implications for the nuclear equation of state are also discussed.

Background: Resonance scattering has been extensively used to study the structure of exotic, neutron-deficient nuclei. Extension of the resonance scattering technique to neutron-rich nuclei was suggested more than 20 years ago. This development is based on the isospin conservation law. In spite of broad field of the application, it has never gained a wide-spread acceptance.

Purpose: To benchmark the experimental approach to study the structure of exotic neutron-rich nuclei through resonance scattering on a proton target.

Method: The excitation function for $p+{}^8\mathrm{Li}$ resonance scattering is measured using a thick target by recording coincidence between light and heavy recoils, populating $T=3/2$ isobaric analog states (IAS) in ${}^9\mathrm{Be}$.

Results: A good fit of the ${}^8\mathrm{Li}(p,p){}^8\mathrm{Li}$ resonance elastic scattering excitation function was obtained using previously tentatively known $5/2^{-}T=3/2$ state at 18.65 MeV in ${}^9\mathrm{Be}$ and a new broad $T=3/2s$-wave state—the $5/2^{+}$ at 18.5 MeV. These results fit the expected isomirror properties for the $T=3/2A=9$ isoquartet.

Conclusions: Our analysis confirmed isospin as a good quantum number for the investigated highly excited $T=3/2$ states and demonstrated that studying the structure of neutron-rich exotic nuclei through IAS is a promising approach.

We present the neutron elastic scattering amplitude for an arbitrarily polarized target in an irreducible spherical-tensor representation. The general approach for the description of neutron spin dynamics for propagation through the medium with an arbitrary polarization is discussed in relation to the search for a time-reversal invariance violation in neutron scattering.

We develop a formalism to calculate electromagnetic (EM) transition rates for rotational-vibrational models of nuclei. The formalism is applied to recently proposed models of ${}^{12}\mathrm{C}$ and ${}^{16}\mathrm{O}$ which are inspired by nuclear dynamics in the Skyrme model. We compare the results to experimental data as well as other nuclear models. The results for ${}^{12}\mathrm{C}$ are in good agreement with the data across all models, making it difficult to differentiate the models. More experimental data is needed to do this, and we suggest which transitions would be most interesting to measure. The models of ${}^{16}\mathrm{O}$ are less successful in describing the data, and we suggest some possible improvements to our approximations which may help.

This work theoretically explores the role of neutron transfer channels and/or collective inelastic surface excitations in the fusion of ${}^{28}\mathrm{Si}$ with ${}^{90,92,94,96}\mathrm{Zr}$ targets by using the coupled channel theory and the energy dependent Woods-Saxon potential (EDWSP) model. The series of ${}^{90,92,94,96}\mathrm{Zr}$ targets is quite interesting due to the fact that the possibilities of neutron transfer channels with positive ground state $Q$ values increase with the increase of isotopic mass. For ${}^{28}\mathrm{Si}+{}^{90}\mathrm{Zr}$ reaction, the influences of inelastic surface excitations turned out to be important and coupling of such channels to their relative motion reproduced the experimental data. In the case of ${}^{28}\mathrm{Si}+{}^{92}\mathrm{Zr}$ reaction, in addition to consideration of low lying states such as $2^{+}$ and $3^{-}$ vibrational states of colliding nuclei, the coupling to two neutron pickup channels is necessarily required to address the sub-barrier fusion anomalies. For ${}^{28}\mathrm{Si}+{}^{94,96}\mathrm{Zr}$ reactions, the inclusions of multiphonon states of type $2^{+}$ and $3^{-}$ of colliding nuclei were not able to reproduce the fusion enhancement particularly at below barrier energies. In this case, neutron transfer channels with positive ground state $Q$ value play a crucial role in the enhancement of fusion cross-section data at sub-barrier energies and therefore must be included in the coupled channel description. In distinction, in the EDWSP model, the energy dependence in the nucleus-nucleus potential causes barrier modification effects and subsequently induces a barrier lowering phenomenon. In this way, the EDWSP based outcomes reasonably address the sub-barrier fusion anomalies of ${}^{28}\mathrm{Si}+{}^{90,92,94,96}\mathrm{Zr}$ reactions and thus impacts of dominant intrinsic channels are intrinsically included due to the dynamical nature of the energy dependent interaction potential. For studied systems, the EDWSP outcomes are able to achieve an agreement with the portion of above barrier fusion data within 10% with a probability greater than 90%. Within this model, 33 fusion data points out of 38 fusion data points lie within 5%. Only five fusion data points lie within 10% and thereby the EDWSP model adequately addresses the fusion anomalies of the chosen reactions. The smaller values of ${\chi }^2$ analysis for the EDWSP calculations, which range from 2.82 to 3.14, indicate that the model predictions appropriately describe the observed fusion dynamics of the studied reactions.

Background: In the fission of actinides, the nearly back-to-back motion of the fission fragments has a strong effect on the kinematics of fission neutrons. This leads to a favoring of opening angles near $0^{\circ }$ and ${180}^{\circ }$ in the neutron-neutron $\left(n\text{−}n\right)$ opening angle distribution of correlated neutron pairs from the same fission event.

Purpose: To measure the $n\text{−}n$ opening angle and energy correlations in the photofission of ${}^{238}\mathrm{U}$. As of this writing, measurements of correlated $n\text{−}n$ opening angle distributions have been reported only for the spontaneous and neutron-induced fission of actinides. This work is the first to report such a measurement using photofission and will provide useful experimental input for photofission models used in codes such as Monte Carlo N-Particle (MCNP) and the Fission Reaction Event Yield Algorithm (FREYA).

Methods: Fission is induced using bremsstrahlung photons produced via a low-duty-factor, pulsed, linear electron accelerator. The bremsstrahlung photon beam impinges on a ${}^{238}\mathrm{U}$ target that is surrounded by a large neutron scintillation detection system capable of measuring particle position and time of flight, from which the $n\text{−}n$ opening angle and energy are measured. Neutron-neutron angular correlations are determined by taking the ratio between a correlated $n\text{−}n$ distribution and an uncorrelated $n\text{−}n$ distribution formed by the pairing of neutrons produced during different beam pulses. This analysis technique greatly diminishes effects due to detector efficiencies, acceptance, and experimental drifts.

Results: The angular correlation of neutrons from the photofission of ${}^{238}\mathrm{U}$ shows a high dependence on neutron energy as well as a dependence on the angle of the emitted neutrons with respect to the incoming photon beam. Angular correlations were also measured using neutrons from the spontaneous fission of ${}^{252}\mathrm{Cf}$, showing good agreement with past measurements.

Conclusions: The measured angular correlations reflect the underlying back-to-back nature of the fission fragments. An anomalous decline in $n\text{−}n$ yield was observed for opening angles near ${180}^{\circ }$ for ${}^{238}\mathrm{U}$.

Deuteron-triton (DT) fusion is the primary fusion reaction used in controlled fusion research, mainly for its relatively high reaction cross sections compared to other fusion options. Even so, to attain appreciable reaction probabilities very high temperatures (on the order of $10–100\times {10}^6\mathrm{K}$) are required, which are extremely challenging to achieve and maintain. Here, it is shown that intense low-frequency laser fields, such as those in the near-infrared regime for the majority of intense laser facilities around the world, are highly effective in transferring energy to the DT system and enhancing the fusion probabilities. The fusion probabilities are shown to be enhanced by, at least, an order of magnitude in 800-nm laser fields with intensities on the order of ${10}^{21}\mathrm{W}/{\mathrm{cm}}^2$. The demanding temperature requirement of controlled nuclear fusion may be relaxed if intense low-frequency lasers are exploited.

The experiment of the NA61/SHINE Collaboration at the CERN SPS is performing a unique study of the phase diagram of strongly interacting matter by varying collision energy and nuclear mass number of colliding nuclei. In central $\mathrm{Pb}+\mathrm{Pb}$ collisions, the experiment of the NA49 Collaboration found structures in the energy dependence of several observables in the energy range of the CERN SPS that had been predicted for the transition to a deconfined phase. New measurements of the NA61/SHINE Collaboration find intriguing similarities in $p+p$ interactions for which no deconfinement transition is expected at the energies of the SPS. Possible implications will be discussed.

The recently observed weakly bound ${}^{39}\mathrm{Na}$ provides a stringent theoretical constraint on the neutron drip line. We studied the properties of drip-line nuclei around ${}^{39}\mathrm{Na}$ with the Hartree-Fock-Bogoliubov method and various Skyrme interactions. We adopted the extended ${\mathrm{SkM}}_{\mathrm{ext}1}^{*}$ parametrization which can properly describe two-neutron separation energies of oxygen and fluorine isotopes and deformations at the center of “island of inversion.” Systematic calculations of drip lines of O, F, Ne, Na, Mg, and Al isotopes have been performed. We infer that ${}^{42}\mathrm{Mg}$ is weakly bound and ${}^{45}\mathrm{Al}$ is less weakly bound. ${}^{44}\mathrm{Mg}$ and ${}^{47}\mathrm{Al}$ could barely exist. We also demonstrated the deformed halo properties of ${}^{39}\mathrm{Na}$. Our studies could be valuable for experimental explorations of drip-line nuclei in the forthcoming Facility for Rare Isotope Beams (FRIB) and other rare-isotope beam facilities.

The fusion-evaporation reaction ${}^{28}\mathrm{Si}+{}^{40}\mathrm{Ca}$ at 122 MeV beam energy was used to populate high-spin states in the odd-odd $N=Z$ nucleus ${}^{62}\mathrm{Ga}$. With the combination of the Gammasphere spectrometer and the Microball CsI(Tl) charged-particle detector array the decay scheme of ${}^{62}\mathrm{Ga}$ was extended beyond 10 MeV excitation energy. The onset of band structures was observed. These high-spin rotational states are interpreted and classified by means of cranked Nilsson-Strutinsky calculations.

Barrier distributions for the ${}^{28}\mathrm{Si}+{}^{142,150}\mathrm{Nd}$ systems were extracted from large-angle quasielastic scattering measurements. The measurements were carried out over a wide range of incident beam energies around the Coulomb barriers. The experimental results were compared with the predictions from coupled-channels calculations carried out using different coupling schemes. Reasonable agreement between the experimental and theoretical results was obtained. The role of coupling effects of the various excitation modes of the projectile and target on the observed barrier distributions is discussed. The sensitivity of the quasielastic scattering process on the mode of projectile excitation is clearly been seen from the use of two different types of targets, ${}^{142}\mathrm{Nd}$ and ${}^{150}\mathrm{Nd}$, having spherical and deformed shapes at the ground state, respectively.

The time-evolution of the magnetic field in hot homogeneous nuclear matter has two qualitatively different stages separated by the sphaleron transition time ${\tau }_c$. At early times, when the chiral conductivity ${\sigma }_{\chi }$ is a slow function of time, the soft chiral modes $k<{\sigma }_{\chi }$ of the magnetic field grow exponentially with time, which is known as the chiral instability. At later times ${\sigma }_{\chi }$ fluctuates due to the sphaleron transitions and can be regarded as a random process. It is argued that the average magnetic field is exponentially damped at later times. The time-evolution of the average field energy is more complicated and depends on the electrical conductivity of the chiral matter but does not depend on chirality. It exhibits instability only if the matter is a poor electrical conductor, such as the quark-gluon plasma near the critical temperature. The precise conditions for the instability and the growth rate of the unstable modes are derived.