Lifetimes of excited states in ${}^{211}\mathrm{At}$ were measured using the electronic $\gamma -\gamma$ fast timing technique. The nucleus of interest was populated in a ${}^{208}\mathrm{Pb}({}^6\mathrm{Li},3n){}^{211}\mathrm{At}$ fusion-evaporation reaction at the FN Tandem accelerator of the Institute for Nuclear Physics, University of Cologne. The lifetimes of the $17/2_1^{-}$ and $23/2_1^{-}$ states were determined, together with an upper limit for the $13/2_1^{-}$ state. The experimental results are compared to two shell-model calculations, one using a semiempirical interaction for three particles in a single $j=9/2$ shell and the other using the modified Kuo-Herling interaction in a multi-$j$ model space.

High-purity germanium (HPGe) detectors were used to make a precise measurement of the $\gamma$-ray spectrum produced following ordinary (nonradiative) capture of negative muons by natural Se, Kr, Cd, and Sm. The measurement was repeated for isotopically enriched ${}^{48}\mathrm{Ti}, {}^{76}\mathrm{Se}, {}^{82}\mathrm{Kr}, {}^{106}\mathrm{Cd}$, and ${}^{150}\mathrm{Sm}$ targets. By investigating energy and time distributions, the lifetime of negative muons in the different isotopes was deduced. A detailed analysis of the intensity of the $\gamma$ lines enabled the extraction of the relative yields of several daughter nuclei. The partial rates of $({\mu }^{-},\nu )$ capture to numerous excited levels of the ${}^{48}\mathrm{Sc}, {}^{76}\mathrm{As}, {}^{82}\mathrm{Br}, {}^{106}\mathrm{Ag}$, and ${}^{150}\mathrm{Tc}$ isotopes (considered to be virtual states of the intermediate odd-odd nuclei in the $\beta \beta$ decay of ${}^{48}\mathrm{Ca}, {}^{76}\mathrm{Ge}, {}^{82}\mathrm{Se}, {}^{106}\mathrm{Cd}$, and ${}^{150}\mathrm{Nd}$, respectively) were also extracted. These rates are important as an experimental input for the theoretical calculation of the nuclear matrix elements in $\beta \beta$ decay.

We determine a net-baryon multiplicity distribution which reproduces all cumulants measured so far by lattice QCD. We present the dependence on the volume and temperature of this distribution. We find that for temperatures and volumes encountered in heavy-ion reactions, the multiplicity distribution is very close to the Skellam distribution, making the experimental determination of it rather challenging. We further provide estimates for the statistics required to measure cumulants of the net-baryon and net-proton distributions.

We investigate the possibility of probing the hot and dense nuclear matter—created in relativistic heavy-ion collisions (HICs)—with strange vector mesons ($K^{*},{\overline{K}}^{*}$). Our analysis is based on the nonequilibrium parton-hadron-string dynamics (PHSD) transport approach which incorporates partonic and hadronic degrees of freedom and describes the full dynamics of HIC on a microscopic level—starting from the primary nucleon-nucleon collisions to the formation of the strongly interacting quark gluon plasma (QGP), followed by dynamical hadronization of (anti)quarks as well as final hadronic elastic and inelastic interactions. This allows us to study the $K^{*}$ and ${\overline{K}}^{*}$ meson formation from the QGP as well as the in-medium effects related to the modification of their spectral properties during the propagation through the dense and hot hadronic environment in the expansion phase. We employ relativistic Breit-Wigner spectral functions for the $K^{*},{\overline{K}}^{*}$ mesons with self-energies obtained from a self-consistent coupled-channel $G$-matrix approach to study the role of in-medium effects on the $K^{*}$ and ${\overline{K}}^{*}$ meson dynamics in heavy-ion collisions from FAIR/NICA to LHC energies. According to our analysis most of the final $K^{*}/{\overline{K}}^{*}$'s, that can be observed experimentally by reconstruction of the invariant mass of $\pi +K\left(\overline{K}\right)$ pairs, are produced during the late hadronic phase and originate dominantly from the $K\left(\overline{K}\right)+\pi \to K^{*}\left({\overline{K}}^{*}\right)$ formation channel. The amount of $K^{*}/{\overline{K}}^{*}$'s originating from the QGP channel is comparatively small even at LHC energies and those $K^{*}/{\overline{K}}^{*}$'s can hardly be reconstructed experimentally due to the rescattering of final pions and (anti)kaons. This mirrors the results from our previous study on the strange vector-meson production in heavy-ion collisions at RHIC energies. We demonstrate that $K^{*}/{\overline{K}}^{*}$ in-medium effects should be visible at FAIR/NICA and BES RHIC energies, where the production of $K^{*}/{\overline{K}}^{*}$'s occurs at larger net-baryon densities. Finally, we present the experimental procedures to extract the information on the resonance masses and widths by fitting the final mass spectra at LHC energies.

Background: Incomplete fusion (ICF) in reactions involving weakly bound projectiles is understood to play an important role in enhancing the ratio of asymmetric to symmetric fission at $E\le V_b$, widening the fission fragment folding angle distribution at $E\le V_b$ and suppressing the complete fusion (CF) cross section at $E>V_b$. Experimental cross sections for individual ICF channels are necessary to obtain quantitative estimates of the above effects.

Purpose: Measurement of the cross sections for individual transfer-induced or ICF-fission channels in ${}^{6,7}\mathrm{Li}+{}^{238}\mathrm{U}$ reactions to explain quantitatively the difference in the ratio of asymmetric to symmetric fission for total fission and CF fission.

Methods: Triple coincidence measurement of two fission fragments and one light charged projectilelike fragment (PLF) is carried out using two multiwire proportional counter (MWPC) detectors and an array of CSI(Tl) scintillation detectors at energies near the Coulomb barrier. By calculating the efficiency of the detectors by Monte Carlo simulation and fission probability by GEF code, the angle-integrated ICF cross sections corresponding to p, d, t, and $\alpha$ emission are obtained. Mass distributions for total fission are calculated by adding the distributions for CF fission and all ICF fissions with weight factors proportional to the measured cross sections.

Results: ICF cross sections corresponding to $\alpha$ emission are found to be the highest in both the reactions. The relative contribution of ICF to total fusion at the lowest measured energy is found to be $\approx 70\%$ and it decreases with increasing projectile energy, consistent with the systematics of several reactions involving the same weakly bound projectiles. The simulated mass distributions for total fission are found to reproduce the experimental mass distributions.

Conclusions: Deuteron (triton) capture is observed to be the major ICF channel in the reaction involving ${}^6\mathrm{Li}\left({}^7\mathrm{Li}\right)$ projectile. The ratio of the sum of ICF to total fusion cross section for the present systems are consistent with the systematics. The difference in the ratio of asymmetric to symmetric fission between total fission and CF fission is explained quantitatively.

A recent article [D. A. Brown, G. P. A. Nobre, and M. W. Herman, Phys. Rev. C 98, 024616 (2018)] proposed a modification of the cross section formula used in practical calculations of compound nucleus reactions. We discuss the main concepts and approximations of statistical reaction theory and conclude that the standard practical implementations of the cross section formula remain the preferred choice.

We installed a source for ultracold neutrons at a new, dedicated spallation target at TRIUMF. The source was originally developed in Japan and uses a superfluid-helium converter cooled to $0.9\mathrm{K}$. During an extensive test campaign in November 2017, we extracted up to $325000$ ultracold neutrons after a one-minute irradiation of the target, over three times more than previously achieved with this source. The corresponding ultracold-neutron density in the whole production and guide volume is $5.3{\mathrm{cm}}^{-3}$. The storage lifetime of ultracold neutrons in the source was initially 37 s and dropped to 24 s during the 18 days of operation. During continuous irradiation of the spallation target, we were able to detect a sustained ultracold-neutron rate of up to $1500{\mathrm{s}}^{-1}$. Simulations of UCN production, UCN transport, temperature-dependent UCN yield, and temperature-dependent storage lifetime show excellent agreement with the experimental data and confirm that the ultracold-neutron-upscattering rate in superfluid helium is proportional to $T^7$.

The level structure of ${}^{31}\mathrm{Mg}$, which is located close to the region of the $N$ = 20 “island of inversion” in the nuclear chart, has been studied by $\beta \text{−}\gamma$ spectroscopy with spin-polarized ${}^{31}\mathrm{Na}$. In ${}^{31}\mathrm{Mg}$, shape coexistence is expected as a result of subtle competition between the spherical mean field and the nuclear correlation which favors deformed configurations. In the present work, our unique method utilizing the anisotropic $\beta$ decay of spin-polarized ${}^{31}\mathrm{Na}$ enables us to firmly assign the spins of all positive-parity excited levels in ${}^{31}\mathrm{Mg}$ below the neutron separation energy at 2.3 MeV. Furthermore, by constructing a very detailed decay scheme, including two newly found levels, the spins of negative-parity levels are restricted. The examination of the spectroscopic information shows that the deformed rotational bands with $K^{\pi }=1/2^{+}$ and $1/2^{-}$, which have very similar structures to those observed in a higher excitation energy region of ${}^{25}\mathrm{Mg}$, appear as the ground-state and low-lying bands, respectively, in ${}^{31}\mathrm{Mg}$. The experimental levels of ${}^{31}\mathrm{Mg}$ are compared, on the level-by-level basis, with two types of theoretical calculations. These are, first, the antisymmetrized molecular dynamics (AMD) plus generator coordinate method (GCM) and, second, the shell model with the EEdf1 interaction, which is microscopically derived from chiral effective field theory. It is understood that 8 levels among the experimental 11 levels are the members of four types of largely deformed rotational bands and 2 levels are of spherical nature. The $1/2^{+}$ 2.244-MeV level is successfully reproduced by the shell-model calculation with a dominant 4p4h configuration. The present work clearly demonstrates that various structures coexist in a low excitation energy region of ${}^{31}\mathrm{Mg}$.

Two-neutron transfer reactions are studied within the interacting boson model based on the nuclear energy density functional theory. Constrained self-consistent mean-field calculations with the Skyrme energy density functional are performed to provide microscopic input to completely determine the Hamiltonian of the IBM. Spectroscopic properties are calculated only from the nucleonic degrees of freedom. This method is applied to study the $(t,p)$ and $(p,t)$ transfer reactions in the assorted set of rare-earth nuclei ${}^{146-158}\mathrm{Sm}$, ${}^{148-160}\mathrm{Gd}$, and ${}^{150-162}\mathrm{Dy}$, where spherical-to-axially deformed shape phase transition is suggested to occur at the neutron number $N\approx 90$. The results are compared with those from the purely phenomenological IBM calculations, as well as with the available experimental data. The calculated $(t,p)$ and $(p,t)$ transfer reaction intensities, from both the microscopic and phenomenological IBM frameworks, signal the rapid nuclear structural change at particular nucleon numbers.

${}^{56,54}\mathrm{Fe}(n,\alpha ){}^{53,51}\mathrm{Cr}$ cross sections were measured in the neutron energy region of 5–11 MeV using three neutron sources based on accelerators, a twin gridded ionization chamber, and highly enriched ${}^{56}\mathrm{Fe}$ and ${}^{54}\mathrm{Fe}$ foil samples. The ${}^{238}\mathrm{U}(n,f)$ reaction was used to monitor the neutron fluence, and the interferences from the low-energy neutrons were corrected according to the neutron energy spectra obtained through unfolding the pulse height spectra measured by a liquid scintillator. Both the measured cross sections show a “shoulder” structure in the 8–11 MeV region which may be caused by the level structure of the residual nuclei. The present paper aims to improve constraint of the ${}^{56,54}\mathrm{Fe}(n,\alpha ){}^{53,51}\mathrm{Cr}$ excitation functions in the MeV region where their neutron energy dependences are significant, while related measurements are nonexistent or scarce and the deviations among existing measurements and evaluations are significant. To obtain more precise excitation functions of the ${}^{56,54}\mathrm{Fe}(n,\alpha ){}^{53,51}\mathrm{Cr}$ reactions, further measurements and improved evaluations are required.

In this work we study the low energy kaon-hyperon interaction, considering effective chiral Lagrangians that include kaons, $\sigma$ mesons, hyperons, and the corresponding resonances. We calculate the scattering amplitudes, and then the total cross sections, angular distributions, polarizations, and the $S$ and $P$ phase shifts.

We adopt a covariant version of the naive dimensional analysis and construct the two-nucleon contact Lagrangian constrained by Lorentz, parity, charge conjugation, and Hermitian conjugation symmetries. We show that at $\mathcal{O}\left(q^0\right)$, $\mathcal{O}\left(q^2\right)$, and $\mathcal{O}\left(q^4\right)$, where $q$ denotes a generic small momentum, there are 4, 13, and 23 terms, respectively. We find that by performing $1/m_N$ expansions, the covariant Lagrangian reduces to the conventional nonrelativistic one, which includes 2, 7, and 15 terms at each corresponding order.

A major barrier in the study of neutron-induced nuclear reactions is the impossibility of direct measurements with short-lived radioactive isotopes. For these exotic nuclei, theoretical inputs such as the photon strength function (PSF) are poorly constrained. At Los Alamos National Laboratory, the Detector for Advanced Neutron Capture Experiments (DANCE) provides direct measurements of $\gamma$-ray cascades following neutron capture reactions on stable or long-lived radioactive nuclei. While Hauser-Feshbach calculations can provide reasonable predictions for neutron capture on heavy nuclei, their application to neutron-rich light nuclei with low nuclear level densities and low neutron separation energies is questionable. In this paper, we report on the $\gamma$-ray spectra from individual neutron resonances from the ${}^{96}\mathrm{Zr}(n,\gamma )$ reaction, with an emphasis on the sensitivity of of the $\gamma$-ray spectra to different PSF models. The comparison of the measured $\gamma$-ray spectra with predicted spectra does not support the addition of a low-energy enhancement of the size reported in many charged-particle reaction measurements, but the sensitivity of the $\gamma$-ray spectra to different PSF models is weak.

By using a phenomenologically successful Woods-Saxon potential, I study the shape and shell structure of (A) neutron drip line nuclei with $10\le N\le 60$, (B) neutron-rich nuclei related to the $r$ process with $40\le N\le 90$, and (C) one-particle spectra in the potential provided by the nucleus ${}^{70}\mathrm{Fe}$ as a representative of so-called $N=40$ “island of inversion” (IoI) nuclei. First, the shell structure that is unique in very weakly bound neutrons is systematically studied, and the approximate neutron number of odd-$N$ nuclei at which spherical (or deformed) halos can be found is pinned down. Second, the difference of the shell structure in $r$-process nuclei from that in stable nuclei is examined. Third, the similarity and the difference between the shell structure of $N=20$ IoI nuclei and that of $N=40$ IoI nuclei are analyzed. As a result, it is concluded that in Fe and Cr isotopes the deformation called “$N=40$ IoI” continuing up to $N=50$ is unlikely.

Background: Ratios of cross sections for mirror reactions sometimes deviate from the values expected on the basis of charge symmetry. These deviations are attributed to smoothly varying charge-dependent effects (proton charge, different $Q$ values) and to the effects of isospin mixed states in the compound nucleus. The effects are large and well known for certain positive-parity states in ${}^8\mathrm{Be}$, but information is lacking for negative-parity states.

Purpose: We measure the excitation functions of angle integrated cross sections for two pairs of reactions that involve ${}^8\mathrm{Be}$ as an intermediate state: (1) ${}^6\mathrm{Li}$ ($d,p^{\prime }){}^7\mathrm{Li}$ (0.478 MeV) and ${}^6\mathrm{Li}$ ($d,n^{\prime }$) ${}^7\mathrm{Be}$ (0.429 MeV) and (2) ${}^7\mathrm{Li}$ ($p,p^{\prime }){}^7\mathrm{Li}$ (0.478 MeV) and ${}^7\mathrm{Li}$ ($p,n^{\prime }$) ${}^7\mathrm{Be}$ (0.429 MeV), measure the ratios of the neutron-emitting and proton-emitting reactions, and examine the implications for the structure of ${}^8\mathrm{Be}$.

Method: The ratios were determined by observing the isotropically emitted $\gamma$ rays from the decay of ${}^7\mathrm{Li}$ (0.478 MeV) and ${}^7\mathrm{Be}$ (0.429 MeV). Shell model calculations were performed for both positive- and negative-parity states. Results were compared to existing information.

Results: Ratios, usually with an accuracy of $\pm 2\%$, were obtained for deuteron energies from 0.15 to 7.2 MeV and proton energies from 3.0 to 10.0 MeV. There were relatively strong deviations from expectations based on charge symmetry at the lowest deuteron energies and smaller deviations between $E_d=$ 2 and 4 MeV. There were very strong deviations for proton energies near 3 and 5.5 MeV, with strong neutron strength near 3 MeV and strong proton strength near 5 MeV. The shell model calculations were generally in good agreement for the positive-parity states and, with some exceptions, for negative-parity states. There is reasonable evidence for the lowest lying $2^{-}T=1$ state at $E_x=20.2$ MeV and for two new isospin mixed pairs, one for $2^{+}$ states near 22 MeV and another for $2^{-}$ states near 24 MeV.

Conclusions: The results will constrain future calculations for isospin mixed states in ${}^8\mathrm{Be}$.

The low-energy structure of ${}^{65}\mathrm{Co}$ was studied by means of $\gamma$- and fast-timing spectroscopy at the ISOLDE/CERN facility. The known level scheme of ${}^{65}\mathrm{Co}$ populated following the ${\beta }^{-}$ decay of ${}^{65}\mathrm{Fe}$ was expanded. The experimental results were compared with large-scale shell-model calculations. The measured long lifetime of the $(1/2_1^{-})$ level confirms its nature as a highly collective state with proton excitations across the $Z=28$ gap and neutrons across the $N=40$ subshell.

Neutron multiplicity excitation function has been measured for the ${}^{30}\mathrm{Si}+{}^{197}\mathrm{Au}$ reaction populating the ${}^{227}\mathrm{Np}$ compound nucleus at excitation energies in the range 44.1–78.8 MeV using the National Array of Neutron Detector facility of Inter University Accelerator Centre, New Delhi. Measured pre-scission neutron multiplicity values are analyzed using a statistical model incorporating Krammer's fission width due to the dissipative drag in nuclear fission, shell corrections in fission barrier and level density, collective enhancement of level density, and $K$-orientation effect. The present work demonstrates that a strong fission hindrance is essential to reproduce the experimental pre-scission neutrons, whereas the temperature dependent dissipation coefficient as observed in a few recent measurements is not required to reproduce the experimental ${\nu }_{\mathrm{pre}}$ data. No substantial effect of collective enhancement of nuclear level density and tilting away effect of compound nucleus spin on neutron emission prior to the scission configuration was observed unlike fission of preactinides.

Mean lifetimes of yrast states of the isotopes ${}^{174,176,178,180}\mathrm{Hf}$ have been measured using fast-electronic scintillation timing. Excited states of ${}^{174,176,178}\mathrm{Hf}$ were populated via $\beta$ decay, while ${}^{180}\mathrm{Hf}$ was populated via Coulomb excitation. The lifetimes of the $2_1^{+}$ and $4_1^{+}$ states of all isotopes and the lifetimes of the $6_1^{+}$ states of ${}^{174,178}\mathrm{Hf}$ were measured, using the slope and the centroid shift methods. The mean lifetime, $\tau \left(4_1^{+}\right)=85\left(13\right)\mathrm{ps}$, of ${}^{178}\mathrm{Hf}$ has been determined for the first time. In addition, the mean lifetimes of the $2_1^{-}$ and the $3_1^{-}$ states of ${}^{176}\mathrm{Hf}$ have been determined. Systematic uncertainties on the evolution of data as a function of neutron number were reduced by using the same setup for all the isotopes of interest. The data are in agreement with other recent lifetime measurements where available and shows a shift of the maximum of collectivity for the Hf isotopic chain from neutron midshell at $N=104$ to $N=100$.

The antimagnetic rotation band $\nu h_{11/2}$ in ${}^{101}\mathrm{Pd}$ is investigated using cranking covariant density functional theory with a shell-model-like approach to treating the pairing correlations, in which the particle number is conserved strictly and the blocking effects are taken into account exactly. Four sets of pairing strength are adopted in the present calculations. The tendencies of the experimental moments of inertia, $B\left(E2\right)$ values, and spins are well reproduced with suitable pairing strengths. The up-bending mechanism of the antimagnetic rotation (AMR) band $\nu h_{11/2}$ in ${}^{101}\mathrm{Pd}$ is studied in terms of the component of the total angular momentum alignment and the occupation numbers around the Fermi surface. It can be found that the up-bending is mainly triggered by the proton $1g_{9/2}$ orbital. Moreover, the proton angular momentum alignment, which mainly comes from the rearrangement of proton occupations in $1g_{9/2}$ orbitals and the increasing components of $1g_{9/2}$, plays an important role in the two-shears-like mechanism.

In the present work, 22 fission-like residues with mass number $67\le A\le 156$ produced via complete fusion-fission and/or incomplete fusion-fission have been identified and their production cross sections measured at three projectile energies, viz., $92.0\pm 1.8$, $102.5\pm 1.5$, and $105.4\pm 1.6$ MeV in the ${}^{19}\mathrm{F}+{}^{169}\mathrm{Tm}$ system. The absolute cross section of each fission-like residue is measured by recoil-catcher activation technique using off-line $\gamma$-ray spectroscopy. The data have been analyzed to deduce the parameters for isotopic yield and isobaric charge distributions. The deduced isotopic yields for indium (${}^{107,108,109,110m}\mathrm{In}$) and neodymium (${}^{134,135,137,139}\mathrm{Nd}$) isotopes are reproduced by Gaussian distribution and their variance is in good agreement with that reported in literature. The mass distributions of fission-like residues at three energies are also found to be Gaussian peaked, which confirms their production via deexcitation of a compound nucleus through complete fusion-fission and/or incomplete fusion-fission processes. It has been observed that, the mass variance (${\sigma }_M^2$) values of fission fragments for two different systems, ${}^{12}\mathrm{C}+{}^{169}\mathrm{Tm}$ and ${}^{19}\mathrm{F}+{}^{169}\mathrm{Tm}$, at nearly the same excitation energy and angular momentum are distinctly different, indicating the importance of the entrance channel effect in fission reaction dynamics. The theoretically calculated isobaric charge dispersion parameters for these residues are found to be in good agreement with those obtained from the experimental data.