The radiative branching ratio of the Hoyle state is crucial to estimate the triple-α reaction rate in stellar environments at medium temperatures of T=0.1 to 2 GK. Knowledge of the γ-decay channel is critical as this is the dominant radiative decay channel for the Hoyle state. A recent study by Kibédi et al. [Phys. Rev. Lett. 125, 182701 (2020)] has challenged our understanding of this astrophysically significant branching ratio and its constraints. The main purpose was to perform a new measurement of the γ-decay branching ratio of the Hoyle state to deduce the radiative branching ratio of the Hoyle state, an additional objective was to independently verify aspects of the measurement conducted by Kibédi et al. For the primary experiment of this work the Hoyle state was populated by the ^12C(p,p') reaction at 10.8 MeV at the Oslo Cyclotron Laboratory. The γ-decay branching ratio was deduced through triple-coincidence events between a proton populating the Hoyle state and the subsequent γ-ray cascade. An independent analysis of the 2014 data published by Kibédi et al. has been carried out. From the main experiment of this work, a γ-decay branching ratio of the Hoyle state was determined as Γ_γ^7.65/Γ^7.65=4.0(3)× 10^-4, yielding a radiative branching ratio of Γ_rad/Γ=4.1(4) × 10^-4. The reanalysis of the 2014 experiment in this work yielded Γ_γ^7.65/Γ^7.65=4.5(6)× 10^-4, with a radiative branching ratio of Γ_rad/Γ=4.6(6) × 10^-4. The measurements of the radiative branching ratio of the Hoyle state in this work is in excellent agreement with several recent studies, as well as the previously adopted ENSDF average of Γ_rad/Γ=4.16(11)× 10^-4.

The $\ensuremath{\gamma}$-strength function and the nuclear level density for the odd-odd, rare-earth nucleus $^{166}\mathrm{Ho}$ have been extracted from $^{163}\mathrm{Dy}(\ensuremath{\alpha},p\ensuremath{\gamma})^{166}\mathrm{Ho}$ data using the Oslo method. A structure at $\ensuremath{\approx}3$ MeV in the $\ensuremath{\gamma}$-strength function is interpreted as the $M1$ scissors resonance. By employing three different methods we find that its strength depends rather strongly on the modeling of the $E1$ strength, while its centroid does not. The $^{166}\mathrm{Ho}$ scissors resonance parameters are consistent with previous results on other rare-earth nuclei.

We report on a study of the alpha-decay fine structure and the associated E alpha-E gamma correlations in the decays of 171,172Os and 171,172,174Ir. In total, 13 new alpha-decay energy lines have been resolved, and three new gamma-ray transitions have been observed following the new decay branches to 168Re and 167W. The weak alpha-decay branch from the bandhead of the nu i13/2 band in 171Os observed in this work highlights an unusual competition between alpha, beta, and electromagnetic decays from this isomeric state. The nucleus 171Os is therefore one of few nuclei observed to exhibit three different decay modes from the same excited state. The nuclei of interest were produced in 92Mo(83Kr, xpyn) fusion-evaporation reactions at the Accelerator Laboratory of the University of Jyvaskyla, Finland. The fusion products were selected using the gas-filled ion separator RITU and their decays were characterized using an array of detectors for charged particles and electromagnetic radiation known as GREAT. Prompt gamma-ray transitions were detected and correlated with the decays using the JUROGAM II germanium detector array surrounding the target position. Results obtained from total Routhian surface (TRS) calculations suggest that alpha-decay fine structure and the associated hindrance factors may be a sensitive probe of even relatively small shape changes between the final states in the daughter nucleus.

We report on a study of the α-decay fine structure and the associated Eα−Eγ correlations in the decays of Os171,172 and Ir171,172,174. In total, 13 new α-decay energy lines have been resolved, and three new γ-ray transitions have been observed following the new decay branches to Re168 and W167. The weak α-decay branch from the bandhead of the νi13/2 band in Os171 observed in this work highlights an unusual competition between α, β, and electromagnetic decays from this isomeric state. The nucleus Os171 is therefore one of few nuclei observed to exhibit three different decay modes from the same excited state. The nuclei of interest were produced in Mo92(Kr83,xpyn) fusion-evaporation reactions at the Accelerator Laboratory of the University of Jyväskylä, Finland. The fusion products were selected using the gas-filled ion separator RITU and their decays were characterized using an array of detectors for charged particles and electromagnetic radiation known as GREAT. Prompt γ-ray transitions were detected and correlated with the decays using the JUROGAM II germanium detector array surrounding the target position. Results obtained from total Routhian surface (TRS) calculations suggest that α-decay fine structure and the associated hindrance factors may be a sensitive probe of even relatively small shape changes between the final states in the daughter nucleus.5 MoreReceived 13 October 2022Accepted 11 January 2023DOI:https://doi.org/10.1103/PhysRevC.107.014308Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by Bibsam.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasAlpha decayLow & intermediate energy heavy-ion reactionsNuclear structure & decaysProperties150 ≤ A ≤ 189Nuclear Physics

Nuclei in the vicinity of 78Ni are important benchmarks for nuclear structure, which can reveal changes in the shell structure far from stability. Spectroscopy of the odd-odd isotope 78Cu was performed for the first time in an experiment with the EURICA setup at the Radioactive Isotope Beam Factory at RIKEN Nishina Center. Excited states in the neutron-rich isotope were populated following the beta decay of 78Ni produced by in-flight fission and

The Zirconium (Z = 40) isotopic chain has attracted interest for more than four decades. The abrupt lowering of the energy of the first 2^+ state and the increase in the transition strength B(E2; 2^+_1→ 0^+_1) going from ^98 Zr to ^100 Zr has been the first example of “quantum phase transition” in nuclear shapes, which has few equivalents in the nuclear chart. Although a multitude of experiments have been performed to measure nuclear properties related to nuclear shapes and collectivity in the region, none of the measured lifetimes were obtained using the Recoil Distance Doppler Shift method in the γγ -coincidence mode where a gate on the direct feeding transition of the state of interest allows a strict control of systematical errors. This work reports the results of lifetime measurements for the first yrast excited states in ^98-104 Zr carried out to extract reduced transition probabilities. The new lifetime values in γγ -coincidence and γ -single mode are compared with the results of former experiments. Recent predictions of the Interacting Boson Model with Configuration Mixing, the Symmetry Conserving Configuration Mixing model based on the Hartree–Fock–Bogoliubov approach and the Monte Carlo Shell Model are presented and compared with the experimental data.

Excited states in Cu-78 were observed for the first time following the ss decay of Ni-78 created by in-flight fission of U-238. Based on the coincidence relationships between the observed gamma-ray transitions, it was possible to construct a level scheme comprising eight excited states with tentative spin assignments for 5 of them. In addition to the gamma-decaying states, an isomeric state with a lifetime of 3.8(4) ms was found to decay by internal conversion.

The proton inelastic scattering on 68,70,72 Ni isotopes was measured at the NSCL at MSU, employing the S800 spectrometer coupled to the GRETINA γ-ray array. The aim of the experiment was to determine the degree of collectivity in these neutron-rich Z = 28 isotopes. The use of a hadronic probe allows to complement previous Coulomb excitation measurements of the reduced transition probability B(E2; 0 + → 2 + ) and deduce the neutron-to-proton transition matrix elements ratio. The high resolution in γ-ray energy achievable with GRETINA gives large control on feeding transitions, thus reducing possible systematics errors in the determination of transition strengths.

The gamma-strength function and the nuclear level density for the odd-odd, rare-earth nucleus 166Ho have been extracted from 163Dy(alpha, p gamma )166Ho data using the Oslo method. A structure at P-'3 MeV in the gamma-strength function is interpreted as the M1 scissors resonance. By employing three different methods we find that its strength depends rather strongly on the modeling of the E1 strength, while its centroid does not. The 166Ho scissors resonance parameters are consistent with previous results on other rare-earth nuclei.

In this work, we present new data on the $^{182,183,184}$W($\gamma,n$) cross sections, utilizing a quasi-monochromatic photon beam produced at the NewSUBARU synchrotron radiation facility. Further, we have extracted the nuclear level density and $\gamma$-ray strength function of $^{186}$W from data on the $^{186}$W($\alpha,\alpha^\prime\gamma$)$^{186}$W reaction measured at the Oslo Cyclotron Laboratory. Combining previous measurements on the $^{186}$W($\gamma,n$) cross section with our new $^{182,183,184}$W($\gamma,n$) and ($\alpha,\alpha^\prime\gamma$)$^{186}$W data sets, we have deduced the $^{186}$W $\gamma$-ray strength function in the range of $1<E_\gamma<6$ MeV and $7<E_\gamma<14$ MeV. Our data are used to extract the level density and $\gamma$-ray strength functions needed as input to the nuclear-reaction code \textsf{TALYS}, providing an indirect, experimental constraint for the $^{185}$W($n,\gamma$)$^{186}$W cross section and reaction rate. Compared to the recommended Maxwellian-averaged cross section (MACS) in the KADoNiS-1.0 data base, our results are on average lower for the relevant energy range $k_B T \in [5,100]$ keV, and we provide a smaller uncertainty for the MACS. The theoretical values of Bao \textit{et al.} and the cross section experimentally constrained on photoneutron data of Sonnabend \textit{et al.} are significantly higher than our result. The lower value by Mohr \textit{et al.} is in very good agreement with our deduced MACS. Our new results could have implications for the $s$-process and in particular the predicted $s$-process production of $^{186,187}$Os nuclei.

The electromagnetic transition probabilities of the yrast 2^+ states in the midshell Te isotopes, two protons above the closed shell at Sn, are of great importance for the understanding of nuclear collectivity in these isotopes and the role played by the neutron-proton interactions and cross-shell excitations. However, the large uncertainty of the experimental data for the midshell nucleus 118 Te and the missing data for 116 Te make it difficult to pin down the general trend of the evolution of transition probabilities as a function of the neutron number. In this work, the lifetime of the yrast 2^+ state in 118 Te was measured, with the aim of reducing the uncertainty of the previous measurement. The result is τ _2+=7.46(19) ps. In addition, the lifetime of the 4^+ state was measured to be τ _4+ = 4.25(23) ps. The experimental transition rates are extracted from the measured lifetimes and compared with systematic large-scale shell-model calculations. The trend of the B(E2;0^+→ 2^+) values in the midshell area is in good agreement with the calculations and the calculated B_4/2 ratio provide evidence for 118 Te as a near perfect harmonic vibrator.

In this work, we present new data on the $^{182,183,184}\mathrm{W}(\ensuremath{\gamma},n$) cross sections, utilizing a quasi-monochromatic photon beam produced at the NewSUBARU synchrotron radiation facility. Further, we have extracted the nuclear level density and $\ensuremath{\gamma}$-ray strength function of $^{186}\mathrm{W}$ from data on the $^{186}\mathrm{W}(\ensuremath{\alpha},{\ensuremath{\alpha}}^{\ensuremath{'}}\ensuremath{\gamma})^{186}\mathrm{W}$ reaction measured at the Oslo Cyclotron Laboratory. Combining previous measurements on the $^{186}\mathrm{W}(\ensuremath{\gamma},n$) cross section with our new $^{182,183,184}\mathrm{W}(\ensuremath{\gamma},n$) and ($\ensuremath{\alpha},{\ensuremath{\alpha}}^{\ensuremath{'}}\ensuremath{\gamma})^{186}\mathrm{W}$ data sets, we have deduced the $^{186}\mathrm{W}\phantom{\rule{4pt}{0ex}}\ensuremath{\gamma}$-ray strength function in the range of $1<{E}_{\ensuremath{\gamma}}<6$ MeV and $7<{E}_{\ensuremath{\gamma}}<14$ MeV. Our data are used to extract the level density and $\ensuremath{\gamma}$-ray strength functions needed as input to the nuclear-reaction code talys, providing an indirect, experimental constraint for the $^{185}\mathrm{W}(n,\ensuremath{\gamma})^{186}\mathrm{W}$ cross section and reaction rate. Compared to the recommended Maxwellian-averaged cross section (MACS) in the KADoNiS-1.0 database, our results are on average lower for the relevant energy range ${k}_{B}T\ensuremath{\in}[5,100]$ keV, and we provide a smaller uncertainty for the MACS. The theoretical values of Bao et al. [At. Data Nucl. Data Tables 76, 70 (2000)] and the cross section experimentally constrained on photoneutron data of Sonnabend et al. [Astrophys. J. 583, 506 (2003)] are significantly higher than our result. The lower value by Mohr et al. [Phys. Rev. C 69, 032801(R) (2004)] is in very good agreement with our deduced MACS. Our new results provide an improved uncertainty estimate for the ($n,\ensuremath{\gamma})^{186}\mathrm{W}$ reaction rate, which is one important ingredient in simulations for investigating the neutron density and the $^{186,187}\mathrm{Os}$ production in the $s$ process.

In this work, we present new data on the 182,183,184W(& gamma; , n) cross sections, utilizing a quasi-monochromatic photon beam produced at the NewSUBARU synchrotron radiation facility. Further, we have extracted the nuclear level density and & gamma; -ray strength function of 186W from data on the 186W(& alpha;, & alpha;'& gamma; ) 186W reaction measured at the Oslo Cyclotron Laboratory. Combining previous measurements on the 186W(& gamma; , n) cross section with our new 182,183,184W(& gamma; , n) and (& alpha;, & alpha;'& gamma; ) 186W data sets, we have deduced the 186W & gamma; -ray strength function in the range of 1 < E & gamma; < 6 MeV and 7 < E & gamma; < 14 MeV. Our data are used to extract the level density and & gamma; -ray strength functions needed as input to the nuclear-reaction code TALYS, providing an indirect, experimental constraint for the 185W(n, & gamma; ) 186W cross section and reaction rate. Compared to the recommended Maxwellian-averaged cross section (MACS) in the KADoNiS-1.0 database, our results are on average lower for the relevant energy range kBT & ISIN; [5, 100] keV, and we provide a smaller uncertainty for the MACS. The theoretical values of Bao et al. [At. Data Nucl. Data Tables 76, 70 (2000)] and the cross section experimentally constrained on photoneutron data of Sonnabend et al. [Astrophys. J. 583, 506 (2003)] are significantly higher than our result. The lower value ingredient in simulations for investigating the neutron density and the 186,187Os production in the s process.

We present the first experimental evidence of the scissors mode in the superheavy nucleus 254 No produced in the 208 Pb( 48 Ca, 2 n γ )) 254 No reaction. The spectrum of γ rays emitted by the excited 254 No nuclei shows an enhanced γ -ray yield for transition energies of ≈ 2 . 5 MeV. By measuring the linear polarization properties of the emitted γ rays, we confirm that the transitions in the enhancement region are predominantly of magnetic-dipole character, characteristic for the scissors mode. To further characterize the enhanced γ -ray yield, simulations of the electromagnetic decay of 254 No were performed. The observed enhancement is reproduced by including an M 1 component in the γ strength function with total strength B ( M 1 ↑ ) = 11 . 8 ( 19 ) μ 2 N . This is in good agreement with the integrated M 1 strength from sum-rule estimates and new calculations within the quasi-particle random-phase approximation presented here. Our results provide a stringent test of phenomenological formulae for the scissors mode currently used in stellar nucleosynthesis calculations. We find that those formulae are not satisfactory, and we recommend using sum-rule estimates assuming a rigid-body moment of inertia instead for describing the scissors mode in superheavy nuclei.

M. Guttormsen,1, ∗ K. O. Ay,2 M. Ozgur,2 E. Algin,2, 3 A. C. Larsen,1 F. L. Bello Garrote,1 H. C. Berg,1, † L. Crespo Campo,1 T. Dahl-Jacobsen,1 F. W. Furmyr,1 D. Gjestvang,1 A. Görgen,1 T. W. Hagen,1 V. W. Ingeberg,1 B. V. Kheswa,1, 4 I. K. B. Kullmann,5 M. Klintefjord,1 M. Markova,1 J. E. Midtbø,1 V. Modamio,1 W. Paulsen,1 L. G. Pedersen,1 T. Renstrøm,1 E. Sahin,1 S. Siem,1 G. M. Tveten,1 and M. Wiedeking6, 7 1Department of Physics, University of Oslo, N-0316 Oslo, Norway 2Department of Physics, Eskisehir Osmangazi University, Faculty of Science and Letters, TR-26040 Eskisehir, Turkey 3Department of Metallurgical and Materials Engineering, Pamukkale University, 20160 Denizli, Turkey 4Department of Physics, University of Johannesburg, P.O. Box 524, Auckland Park 2006, South Africa 5Institut d’Astronomie et d’Astrophysique, CP-226, Université Libre de Bruxelles, 1050 Brussels, Belgium 6SSC Laboratory, iThemba LABS, P.O. Box 722, Somerset West 7129, South Africa 7School of Physics, University of the Witwatersrand, Johannesburg 2050, South Africa (Dated: April 20, 2022)

Lifetimes or lifetime limits of a small number of excited states of the sulfur isotopes with mass numbers $A=35$, 36, 37, and 38 have been measured using the differential recoil-distance method. The isotopes of sulfur were populated in binary grazing reactions initiated by a beam of $^{36}\mathrm{S}$ ions of energy 225 MeV incident on a thin $^{208}\mathrm{Pb}$ target which was mounted in the Cologne plunger apparatus. The combination of the PRISMA magnetic spectrometer and an early implementation of the AGATA $\ensuremath{\gamma}$-ray tracking array was used to detect $\ensuremath{\gamma}$ rays in coincidence with projectile-like nuclear species. Lifetime measurements of populated states were measured within the range from about 1 to 100 ps. The number of states for which lifetime measurements or lifetime limits were possible was limited by statistics. For $^{35}\mathrm{S}$, the lifetime was determined for the first $1/{2}^{+}$ state at 1572 keV; the result is compared with a previous published lifetime value. The lifetime of the ${3}^{\ensuremath{-}}$ state of $^{36}\mathrm{S}$ at 4193 keV was determined and compared with earlier measurements. No previous lifetime information exists for the (${6}^{+}$) state at 6690 keV; a lifetime measurement with large associated error was made in the present work. For $^{37}\mathrm{S}$, the states for which lifetime limits were established were those at 646 keV with ${J}^{\ensuremath{\pi}}=3/{2}^{\ensuremath{-}}$ and at 2776 keV with ${J}^{\ensuremath{\pi}}=11/{2}^{\ensuremath{-}}$; there are no previously published lifetime values for excited states of $^{37}\mathrm{S}$. Finally, a lifetime limit was established for the ${J}^{\ensuremath{\pi}}=({6}^{+})$ state of $^{38}\mathrm{S}$ at 3675 keV; no lifetime information exists for this state in the literature. Measured lifetime values were compared with the results of state-of-the-art shell-model calculations based on the PSDPF, SDPF-U, and FSU effective interactions. In addition, nuclear magnetic-dipole and electric-quadrupole moments, branching ratios, mixing ratios, and electromagnetic transition rates, where available, have been compared with shell-model values. The current work suffers from poor statistics; nevertheless, lifetime values and limits have been possible, allowing a useful discussion of the ability of state-of-the-art shell-model calculations to reproduce the experimental results.

We present the first experimental evidence of the scissors mode in the superheavy nucleus 254No produced in the 208Pb(48Ca, 2nγ))254No reaction. The spectrum of γ rays emitted by the excited 254No nuclei shows an enhanced γ-ray yield for transition energies of ≈2.5 MeV. By measuring the linear polarization properties of the emitted γ rays, we confirm that the transitions in the enhancement region are predominantly of magnetic-dipole character, characteristic for the scissors mode. To further characterize the enhanced γ-ray yield, simulations of the electromagnetic decay of 254No were performed. The observed enhancement is reproduced by including an M1 component in the γ strength function with total strength B(M1↑)=11.8(19)μN2. This is in good agreement with the integrated M1 strength from sum-rule estimates and new calculations within the quasi-particle random-phase approximation presented here. Our results provide a stringent test of phenomenological formulae for the scissors mode currently used in stellar nucleosynthesis calculations. We find that those formulae are not satisfactory, and we recommend using sum-rule estimates assuming a rigid-body moment of inertia instead for describing the scissors mode in superheavy nuclei.

Lifetimes or lifetime limits of a small number of excited states of the sulfur isotopes with mass numbers A = 35, 36, 37, and 38 have been measured using the differential recoil-distance method. The isotopes of sulfur were populated in binary grazing reactions initiated by a beam of S-36 ions of energy 225 MeV incident on a thin Pb-208 target which was mounted in the Cologne plunger apparatus. The combination of the PRISMA magnetic spectrometer and an early implementation of the AGATA gamma-ray tracking array was used to detect gamma rays in coincidence with projectile-like nuclear species. Lifetime measurements of populated states were measured within the range from about 1 to 100 ps. The number of states for which lifetime measurements or lifetime limits were possible was limited by statistics. For S-35, the lifetime was determined for the first 1/2(+) state at 1572 keV; the result is compared with a previous published lifetime value. The lifetime of the 3(-) state of S-36 at 4193 keV was determined and compared with earlier measurements. No previous lifetime information exists for the (6(+)) state at 6690 keV; a lifetime measurement with large associated error was made in the present work. For S-37, the states for which lifetime limits were established were those at 646 keV with J(pi)=3/2(-) and at 2776 keV with J(pi)=11/2(-); there are no previously published lifetime values for excited states of 37S. Finally, a lifetime limit was established for the J(pi )= (6(+)) state of S-38 at 3675 keV; no lifetime information exists for this state in the literature. Measured lifetime values were compared with the results of state-of-the-art shell-model calculations based on the PSDPF, SDPF-U, and FSU effective interactions. In addition, nuclear magnetic-dipole and electric-quadrupole moments, branching ratios, mixing ratios, and electromagnetic transition rates, where available, have been compared with shell-model values. The current work suffers from poor statistics; nevertheless, lifetime values and limits have been possible, allowing a useful discussion of the ability of state-of-the-art shell-model calculations to reproduce the experimental results.

The experimental gamma-ray strength functions (gamma-SFs) of 142,144-151Nd have been studied for gamma-ray energies up to the neutron separation energy. The results represent a unique set of gamma-SFs for an isotopic chain with increasing nuclear deformation. The data reveal how the low-energy enhancement, the scissors mode and the pygmy dipole resonance evolve with nuclear deformation and mass number. The data indicate that the mechanisms behind the low-energy enhancement and the scissors mode are decoupled from each other.

Mirror energy differences (MED) between excited states in the A = 31, T = 1/2 mirror pair S-31 and P-31 have been measured up to high spin yrast states of positive and negative parity. The mirror nuclei were populated in the Mg-24(C-12, an) and Mg-24(C-12, ap) reactions, respectively. For the first time the MED are described in the framework of the shell model in a valence space that includes three main shells. The theoretical MED values as a function of angular momentum indicate that the main contribution arises from the Coulomb interaction, however, the isospin symmetry breaking term is not at all negligible and needs to be considered to reproduce the experimental findings.