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The effect of the isovector imaginary optical potential has been studied experimentally by using the particle-evaporation technique for the $^{11}\mathrm{B}+^{48}\mathrm{Ca}$ reaction with a 21.8 MeV $^{11}\mathrm{B}$ beam. Spectra of neutron, proton, and $\ensuremath{\alpha}$ particles emitted from the neutron-rich compound nucleus $^{59}\mathrm{Mn}$ have been measured and analyzed with traditional optical model potentials with their original parametrizations as well as with adjusted isovector imaginary components. It is shown that the isovector component of the imaginary potential is indispensable in the reproduction of proton and $\ensuremath{\alpha}$-particle yields from this reaction and even needs to be enhanced compared with the suggestions of the original model parametrizations. This can lead to important consequences for astrophysical reaction-rate calculations.

$\ensuremath{\gamma}$-ray emission from $^{12}\mathrm{C}$ and $^{13}\mathrm{C}$ samples irradiated with deuterium-tritium fusion neutrons was experimentally measured at the Omega Laser Facility and at the Ohio University Edwards Accelerator Laboratory. The intent of these measurements was to determine the feasibility of using $^{13}\mathrm{C}$-based plastic ablators with embedded $^{12}\mathrm{C}$ layers for ``dark mix'' diagnosis of inertial confinement fusion implosions. Spectrally resolved measurements at Ohio University identified significant 4.44-MeV $\ensuremath{\gamma}$-ray emission from the $^{13}\mathrm{C}(n,2n\ensuremath{\gamma})^{12}\mathrm{C}$-L1 reaction channel. The recorded 4.44-MeV $^{13}\mathrm{C}$ signal was compared against emission from an identically irradiated $^{12}\mathrm{C}$ target with known $^{12}\mathrm{C}$($n,{n}^{\ensuremath{'}}\ensuremath{\gamma})^{12}\mathrm{C}$-L1 cross section, which resulted in an average $^{13}\mathrm{C}(n,2n\ensuremath{\gamma})^{12}\mathrm{C}$-L1 cross section of 117 $\ifmmode\pm\else\textpm\fi{}$ 17 mb over the incident neutron energy distribution range from 14.4 to 15.8 MeV. Integrated $^{13}\mathrm{C}$ $\ensuremath{\gamma}$-ray signals above 2.9 MeV recorded with the Gas Cherenkov Detector at Omega exceeded MCNP6.1 predictions by a factor of 3. The additional signal was attributed to 4.44-MeV $\ensuremath{\gamma}\mathrm{s}$ resulting in an inferred $^{13}\mathrm{C}(n,2n\ensuremath{\gamma})^{12}\mathrm{C}$-L1 cross section of $95\ifmmode\pm\else\textpm\fi{}11$ mb at 14.1-MeV average incident neutron energy. As a result, the $^{13}\mathrm{C}$-based ``dark mix'' diagnostic concept was deemed infeasible.

Nuclear reactions of interest for astrophysics and applications often rely on statistical model calculations for nuclear reaction rates, particularly for nuclei far from $\beta$-stability. However, statistical model parameters are often poorly constrained, where experimental constraints are particularly sparse for exotic nuclides. For example, our understanding of the breakout from the NiCu cycle in the astrophysical rp-process is currently limited by uncertainties in the statistical properties of the proton-rich nucleus $^{60}$Zn. We have determined the nuclear level density of $^{60}$Zn using neutron evaporation spectra from $^{58}$Ni($^3$He, n) measured at the Edwards Accelerator Laboratory. We compare our results to a number of theoretical predictions, including phenomenological, microscopic, and shell model based approaches. Notably, we find the $^{60}$Zn level density is somewhat lower than expected for excitation energies populated in the $^{59}$Cu(p,$\gamma$)$^{60}$Zn reaction under rp-process conditions. This includes a level density plateau from roughly 5-6 MeV excitation energy, which is counter to the usual expectation of exponential growth and all theoretical predictions that we explore. A determination of the spin-distribution at the relevant excitation energies in $^{60}$Zn is needed to confirm that the Hauser-Feshbach formalism is appropriate for the $^{59}$Cu(p,$\gamma$)$^{60}$Zn reaction rate at X-ray burst temperatures., Comment: 10 pages, 8 figures

Background: $^{40}\mathrm{K}$ plays a significant role in the radiogenic heating of Earth-like exoplanets, which can affect the development of a habitable environment on their surfaces. The initial amount of $^{40}\mathrm{K}$ in the interior of these planets depends on the composition of the interstellar clouds from which they formed. Within this context, nuclear reactions that regulate the production of $^{40}\mathrm{K}$ during stellar evolution can play a critical role.Purpose: In this study, we constrain for the first time the astrophysical reaction rate of $^{40}\mathrm{K}(n,p)^{40}\mathrm{Ar}$, which is responsible for the destruction of $^{40}\mathrm{K}$ during stellar nucleosynthesis. We provide to the nuclear physics community high-resolution data on the cross section and angular distribution of the $^{40}\mathrm{Ar}(p,n)^{40}\mathrm{K}$ reaction. These are important to various applications involving $^{40}\mathrm{Ar}$. The associated reaction rate of the $^{40}\mathrm{Ar}(p,n)^{40}\mathrm{K}$ process addresses a reaction rate gap in the Joint Institute for Nuclear Astrophysics REACLIB database in the region of intermediate-mass isotopes.Methods: We performed differential cross-section measurements on the $^{40}\mathrm{Ar}(p,n)^{40}\mathrm{K}$ reaction, for six energies in the center-of-mass system between 3.2 and 4.0 MeV and various angles between ${0}^{\ensuremath{\circ}}$ and ${135}^{\ensuremath{\circ}}$. The experiment took place at the Edwards Accelerator Laboratory at Ohio University using the beam swinger target location and a standard neutron time-of-flight technique. We extracted total and partial cross sections by integrating the double differential cross sections we measured.Results: The total and partial cross sections varied with energy due to the contribution from isobaric analog states and Ericson type fluctuations. The energy-averaged neutron angular distributions were symmetrical relative to ${90}^{\ensuremath{\circ}}$. Based on the experimental data, local transmission coefficients were extracted and were used to calculate the astrophysical reaction rates of $^{40}\mathrm{Ar}(p,n)^{40}\mathrm{K}$ and $^{40}\mathrm{K}(n,p)^{40}\mathrm{Ar}$ reactions. The new rates were found to vary significantly from the theoretical rates in the REACLIB library. We implemented the new rates in network calculations to study nucleosynthesis via the slow neutron capture process, and we found that the produced abundance of $^{40}\mathrm{K}$ is reduced by up to 10% compared to calculations with the library rates. At the same time, the above result removes a significant portion of the previous theoretical uncertainty on the $^{40}\mathrm{K}$ yields from stellar evolution calculations.Conclusions: Our results support a destruction rate of $^{40}\mathrm{K}$ in massive stars via the $^{40}\mathrm{K}(n,p)^{40}\mathrm{Ar}$ reaction that is larger compared to previous estimates. The rate of $^{40}\mathrm{K}$ destruction via the $^{40}\mathrm{K}(n,p)^{40}\mathrm{Ar}$ reaction now has a dramatically reduced uncertainty based on our measurement. This result directly affects the predicted stellar yields of $^{40}\mathrm{K}$ from nucleosynthesis, which is a critical input parameter for the galactic chemical evolution models that are currently employed for the study of significant properties of exoplanets.

Background: Reaction rates of radiative capture reactions can play a crucial role in the nucleosynthesis of heavy nuclei in explosive stellar environments. These reaction rates depend strongly on $\ensuremath{\gamma}$-ray decay widths in the reaction products, which are, for nonresonant capture reactions at high excitation energies, derived from the $\ensuremath{\gamma}$-ray strength function and the nuclear level density. Recently, the ratio method was applied to primary $\ensuremath{\gamma}$ rays observed from ($d,p$) reactions and nuclear resonance fluorescence measurements to extract the dipole strength in atomic nuclei and to test the generalized Brink-Axel hypothesis.Purpose: The purpose of this work is to apply the ratio method to primary $\ensuremath{\gamma}$-ray intensities of the $^{63,65}\mathrm{Cu}(p,\ensuremath{\gamma})$ reactions to extract $\ensuremath{\gamma}$-ray strength information on the nuclei $^{64,66}\mathrm{Zn}$. The impact of spin distribution, total $\ensuremath{\gamma}$-ray decay widths, level densities, and width fluctuations on the application of the ratio method will be discussed. Additionally, by comparing the relative $\ensuremath{\gamma}$-ray strength at different excitation energies, conclusions on the validity of the generalized Brink-Axel hypothesis can be made.Method: The radiative proton capture reaction measurements have been performed at the HORUS $\ensuremath{\gamma}$-ray spectrometer of the University of Cologne at one excitation energy for each reaction. Primary $\ensuremath{\gamma}$-ray intensities have been determined by normalizing secondary $\ensuremath{\gamma}$-ray transitions in two-step cascades using their absolute branching ratio. The ratio method was applied to the measured primary $\ensuremath{\gamma}$-ray intensities as well as to previous measurements by Erlandsson $et$ $al.$ at different excitation energies.Results: The relative strength function curve for $^{64}\mathrm{Zn}$ from our measurement shows no significant deviation from the previous measurement at a different excitation energy. The same is true for $^{66}\mathrm{Zn}$ where both measurements were at almost the same excitation energy. Absolute $\ensuremath{\gamma}$-strength function values have been obtained by normalizing the relative curves to quasiparticle random phase approximation calculations because of the absence of experimental data in the respective energy region.Conclusion: The generalized Brink-Axel hypothesis, i.e., the independence of the strength function on the excitation energy, seems to hold in the studied energy region and nuclei. The method to obtain primary $\ensuremath{\gamma}$-ray intensities from two-step cascade spectra was shown to be a valuable and sensitive tool although its uncertainties are connected to the knowledge of the low-energy level scheme of the investigated nucleus. The scaling in the ratio method should be taken with care, because the relative strength is not a simple sum of ${f}_{E1}$ and ${f}_{M1}$ but a somewhat complex linear combination dependent on the excitation energy of the nucleus.

Measurements are reported for the angle-averaged double-differential cross section ${\ensuremath{\langle}{d}^{2}\ensuremath{\sigma}/\phantom{\ensuremath{\sigma}d{E}_{n}d{\mathrm{\ensuremath{\Omega}}}_{n}}\phantom{\rule{0.0pt}{0ex}}d{E}_{n}d{\mathrm{\ensuremath{\Omega}}}_{n}\ensuremath{\rangle}}_{{0}^{\ensuremath{\circ}}l\ensuremath{\theta}l7.{4}^{\ensuremath{\circ}}}$ for the breakup reaction $^{2}\mathrm{H}$($n,2n$)$^{1}\mathrm{H}$, induced by 14-MeV neutrons generated using an inertial confinement fusion platform. A bright neutron source, created on the OMEGA Laser System [Boehly et al., Opt. Commun. 133, 495 (1997)] with a luminosity of $L={10}^{24}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$, was used to irradiate deuterated targets. The absolute yields and energy spectra from the breakup neutrons emitted in a forward-angle geometry ($\ensuremath{\theta}={0}^{\ensuremath{\circ}}$ to 7.4\ifmmode^\circ\else\textdegree\fi{}) were detected with a sensitive, high-dynamic-range neutron time-of-flight spectrometer. The cross-section data, measured for neutron energy range from 0.5 to 10 MeV, is well reproduced by a theoretical calculation employing realistic nucleon--nucleon and three-nucleon forces.

The Oslo method has been applied to particle-$\ensuremath{\gamma}$ coincidences following the $^{239}\mathrm{Pu}(d,p)$ reaction to obtain the nuclear level density (NLD) and $\ensuremath{\gamma}$-ray strength function ($\ensuremath{\gamma}\mathrm{SF}$) of $^{240}\mathrm{Pu}$. The experiment was conducted with a 12 MeV deuteron beam at the Oslo Cyclotron Laboratory. The low spin transfer of this reaction leads to a spin-parity mismatch between populated and intrinsic levels. This is a challenge for the Oslo method as it can have a significant impact on the extracted NLD and $\ensuremath{\gamma}\mathrm{SF}$. We have developed an iterative approach to ensure consistent results even for cases with a large spin-parity mismatch, in which we couple Green's function transfer calculations of the spin-parity dependent population cross-section to the nuclear decay code rainier. The resulting $\ensuremath{\gamma}\mathrm{SF}$ shows a pronounced enhancement between 2--4 MeV that is consistent with the location of the low-energy orbital $M1$ scissors mode.

Bethe wrote a pivotal paper providing the formalism for the theory of nuclear level densities. At that time, there were no known deformed nuclei, so Bethe made the assumption that all nuclei are spherical. After deformed nuclei were discovered, theorists predicted that the level density for such nuclei should be substantially enhanced over the level density for neighboring spherical nuclei. Despite these results, two comprehensive level density compilations based on neutron resonances counting at low neutron energy failed to find significant enhancement in level density for deformed nuclei. A recent paper has concluded that the Bethe spin distribution for nuclear levels is not appropriate for deformed nuclei. When a more accurate spin distribution is used in resonance analysis, it is found that an enhancement of approximately the predicted magnitude is observed.

The search for new decay chains of oganesson isotopes is presented. The experiment utilized the Dubna Gas Filled Recoil Separator and a highly segmented recoil-decay detection system. The signals from all detectors were analyzed in parallel by digital and analog data acquisition systems. For the first time, a target of mixed californium (51% Cf249, 13% Cf250, and 36% Cf251) recovered from decayed Cf252 sources was produced and irradiated with an intense Ca48 beam. The observation of a new decay chain of Og294 is reported. The prospects for reaching new isotopes Og295,296 are discussed.

Author(s): Jones, MD; MacChiavelli, AO; Wiedeking, M; Bernstein, LA; Crawford, HL; Campbell, CM; Clark, RM; Cromaz, M; Fallon, P; Lee, IY; Salathe, M; Wiens, A; Ayangeakaa, AD; Bleuel, DL; Bottoni, S; Carpenter, MP; Davids, HM; Elson, J; Gorgen, A; Guttormsen, M; Janssens, RVF; Kinnison, JE; Kirsch, L; Larsen, AC; Lauritsen, T; Reviol, W; Sarantites, DG; Siem, S; Voinov, AV; Zhu, S | Abstract: A model-independent technique was used to determine the γ-ray strength function (γSF) of Fe56 down to γ-ray energies less than 1 MeV for the first time with GRETINA using the (p,p′) reaction at 16 MeV. No difference was observed in the energy dependence of the γSF built on 2+ and 4+ final states, supporting the Brink hypothesis. In addition, angular distribution and polarization measurements were performed. The angular distributions are consistent with dipole radiation. The polarization results show a small bias towards magnetic character in the region of the enhancement.

Nuclear level densities (NLDs) and $\ensuremath{\gamma}$-ray strength functions ($\ensuremath{\gamma}\mathrm{SFs}$) have been extracted from particle-$\ensuremath{\gamma}$ coincidences of the $^{92}\mathrm{Zr}(p,{p}^{\ensuremath{'}}\ensuremath{\gamma})^{92}\mathrm{Zr}$ and $^{92}\mathrm{Zr}(p,d\ensuremath{\gamma})^{91}\mathrm{Zr}$ reactions using the Oslo method. The new $^{91,92}\mathrm{Zr}\phantom{\rule{4pt}{0ex}}\ensuremath{\gamma}\mathrm{SF}$ data, combined with photonuclear cross sections, cover the whole energy range from ${E}_{\ensuremath{\gamma}}\ensuremath{\approx}1.5\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}$ up to the giant dipole resonance at ${E}_{\ensuremath{\gamma}}\ensuremath{\approx}17$ MeV. The wide-range $\ensuremath{\gamma}\mathrm{SF}$ data display structures at ${E}_{\ensuremath{\gamma}}\ensuremath{\approx}9.5$ MeV, compatible with a superposition of the spin-flip $M1$ resonance and a pygmy $E1$ resonance. Furthermore, the $\ensuremath{\gamma}\mathrm{SF}$ shows a minimum at ${E}_{\ensuremath{\gamma}}\ensuremath{\approx}2--3\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}$ and an increase at lower $\ensuremath{\gamma}$-ray energies. The experimentally constrained NLDs and $\ensuremath{\gamma}\mathrm{SFs}$ are shown to reproduce known ($n,\ensuremath{\gamma}$) and Maxwellian-averaged cross sections for $^{91,92}\mathrm{Zr}$ using the talys reaction code, thus serving as a benchmark for this indirect method of estimating ($n,\ensuremath{\gamma}$) cross sections for Zr isotopes.

The spin cutoff parameter determining the nuclear level density spin distribution $\ensuremath{\rho}(J)$ is defined through the spin projection as ${\ensuremath{\langle}{J}_{z}^{2}\ensuremath{\rangle}}^{1/2}$ or equivalently for spherical nuclei, ${(\frac{\ensuremath{\langle}J(J+1)\ensuremath{\rangle}}{3})}^{1/2}$. It is needed to divide the total level density into levels as a function of $J$. To obtain the total level density at the neutron binding energy from the $s$-wave resonance count, the spin cutoff parameter is also needed. The spin cutoff parameter has been calculated as a function of excitation energy and mass with a super-conducting Hamiltonian. Calculations have been compared with two commonly used semiempirical formulas. A need for further measurements is also observed. Some complications for deformed nuclei are discussed. The quality of spin cut off parameter data derived from isomeric ratio measurement is examined.