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This paper reports on the first cross section measurement of the 72Ge(p,y)73As reaction. The proton capture reaction on 72Ge is relevant to the astrophysical p-process and was identified in a sensitivity study as one of the important reactions required to estimate the abundances of the light p nuclei. The γ-summing technique was employed using the summing Nal(Tl) detector (SuN) from the National Superconducting Cyclotron Laboratory. The experiment was performed at the University of Notre Dame using a 1.8-3.6 MeV proton beam. In order to test the predictive power of different theoretical calculations in the region, experimental values were compared to the results given by the nuclear reaction code TALYS1.6. The theoretical uncertainties in the cross section arising from different combinations of nuclear level densities, γ-ray strength functions, and optical model potentials were reduced to 10-18% by the experimental data. The recommended reaction rates from the standard astrophysical libraries, BRUSL1B and REACLIB, are found to be in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

Neutron-capture cross sections in the energy range of 0.01-10 MeV for 146,148,150,152Sm nuclei were calculated using the γ-ray strength and level density functions extracted from the Oslo-type experiments. The uncertainties in the cross-section values were determined using a Monte Carlo method. For the 148,150,152Sm isotopes, the calculated cross sections are in a good agreement with the existing experimental data and for the 146Sm nucleus, an experimental (n,γ) cross section is reported for the first time. The results are compared with the ENDF, EAF, and TENDL evaluations. Maxwellian-averaged cross sections were also calculated using the same input γSF and LD functions. [ABSTRACT FROM AUTHOR]

The γ-strength functions and level densities in the quasicontinuum of 147,149Sm isotopes have been extracted from particle-γ coincidences using the Oslo method. The nuclei of interest were populated via (p,d) reactions on pure 148,150Sm targets and the reaction products were recorded by the Hyperion array. An upbend in the low-energy region of the γSF has been observed. The systematic analysis of the γSF for a range of Sm isotopes highlights the interplay between scissors mode and the upbend. Shell-model calculations show reasonable agreement with the experimental γSFs and confirm the correspondence between the upbend and scissors mode. [ABSTRACT FROM AUTHOR]

β-decay half-lives of neutron-rich nuclides in the A=100-110 mass region have been measured using an implantation station installed inside of the Summing NaI(Tl) (SuN) detector at the National Superconducting Cyclotron Laboratory. Accurate half-lives for these nuclides are important for nuclear astrophysics, nuclear structure, and nuclear technology. The half-lives from the present work are compared with previous measurements, showing overall good agreement. [ABSTRACT FROM AUTHOR]

he β-decay intensity of 70Co was measured for the first time using the technique of total absorption spectroscopy. The large β-decay Q value [12.3(3) MeV] offers a rare opportunity to study β-decay properties in a broad energy range. Two surprising features were observed in the experimental results, namely, the large fragmentation of the β intensity at high energies, as well as the strong competition between ? rays and neutrons, up to more than 2 MeV above the neutron-separation energy. The data are compared to two theoretical calculations: the shell model and the quasiparticle random phase approximation (QRPA). Both models seem to be missing a significant strength at high excitation energies. Possible interpretations of this discrepancy are discussed. The shell model is used for a detailed nuclear structure interpretation and helps to explain the observed γ-neutron competition. The comparison to the QRPA calculations is done as a means to test a model that provides global β-decay properties for astrophysical calculations. Our work demonstrates the importance of performing detailed comparisons to experimental results, beyond the simple half-life comparisons. A realistic and robust description of the β-decay intensity is crucial for our understanding of nuclear structure as well as of r-process nucleosynthesis. [ABSTRACT FROM AUTHOR]

Background: The Doppler broadening of γ-ray peaks due to nuclear recoil from β-delayed nucleon emission can be used to measure the energies of the nucleons. This method has never been tested using β-delayed proton emission or applied to a recoil heavier than A = 10. Purpose: To test and apply this Doppler broadening method using γ-ray peaks from the 26P(βpγ)25 Al decay sequence. Methods: A fast beam of 26P was implanted into a planar Ge detector, which was used as a 26P β-decay trigger. The SeGA array of high-purity Ge detectors was used to detect γ rays from the 26P(βpγ)25 Al decay sequence. Results: Radiative Doppler broadening in β-delayed proton-γ decay was observed for the first time. The Doppler broadening analysis method was verified using the 1613-keV γ-ray line for which the proton energies were previously known. The 1776-keV γ ray de-exciting the 2720 keV 25Al level was observed in 26P(βpγ)25 Al decay for the first time and used to determine that the center-of-mass energy of the proton emission feeding the 2720-keV level is 5.1 ± 1.0 (stat.) ± 0.6 (syst.) MeV, corresponding to a 26Si excitation energy of 13.3 ± 1.0 (stat.) ± 0.6 (syst.) MeV for the proton-emitting level. Conclusions: The Doppler broadening method has been demonstrated to provide practical measurements of the energies for β-delayed nucleon emissions populating excited states of nuclear recoils at least as heavy as A = 25. [ABSTRACT FROM AUTHOR]

Classical novae are expected to contribute to the 1809-keV Galactic γ-ray emission by producing its precursor 26Al, but the yield depends on the thermonuclear rate of the unmeasured 25Al(p, γ)26Si reaction. Using the β decay of 26P to populate the key Jπ = 3+ resonance in this reaction, we report the first evidence for the observation of its exit channel via a 1741.6 ± 0.6(stat) ± 0.3(syst) keV primary γ ray, where the uncertainties are statistical and systematic, respectively. By combining the measured γ-ray energy and intensity with other experimental data on 26Si, we find the center-of-mass energy and strength of the resonance to be Er = 414.9 ± 0.6(stat) ± 0.3(syst) ± 0.6(lit) keV and ωγ = 23 ± 6(stat)+11-10(lit.) meV, respectively, where the last uncertainties are from adopted literature data. We use hydrodynamic nova simulations to model 26Al production showing that these measurements effectively eliminate the dominant experimental nuclear-physics uncertainty and we estimate that novae may contribute up to 30% of the Galactic 26Al. [ABSTRACT FROM AUTHOR]

Neutron-rich silver isotopes were populated in the fragmentation of a 136Xe beam and the relativistic fission of 238U. The fragments were mass analyzed with the GSI Fragment Separator and subsequently implanted into a passive stopper. Isomeric transitions were detected by 105 high-purity germanium detectors. Eight isomeric states were observed in 122-126Ag nuclei. The level schemes of 122,123,125Ag were revised and extended with isomeric transitions being observed for the first time. The excited states in the odd-mass silver isotopes are interpreted as core-coupled states. The isomeric states in the even-mass silver isotopes are discussed in the framework of the proton-neutron split multiplets. The results of shell-model calculations, performed for the most neutron-rich silver nuclei are compared to the experimental data. [ABSTRACT FROM AUTHOR]

The interpretation of observations of cooling neutron star crusts in quasipersistent x-ray transients is affected by predictions of the strength of neutrino cooling via crust Urca processes. The strength of crust Urca neutrino cooling depends sensitively on the electron-capture and β-decay ground-state-to-ground-state transition strengths of neutron-rich rare isotopes. Nuclei with a mass number of A=61 are predicted to be among the most abundant in accreted crusts, and the last remaining experimentally undetermined ground-state-to-ground-state transition strength was the β decay of 61V. This Letter reports the first experimental determination of this transition strength, a ground-state branching of 8.1-3.1+4.0%, corresponding to a log ft value of 5.5-0.2+0.2. This result was achieved through the measurement of the β-delayed γ rays using the total absorption spectrometer SuN and the measurement of the β-delayed neutron branch using the neutron long counter system NERO at the National Superconducting Cyclotron Laboratory at Michigan State University. This method helps to mitigate the impact of the pandemonium effect in extremely neutron-rich nuclei on experimental results. The result implies that A=61 nuclei do not provide the strongest cooling in accreted neutron star crusts as expected by some predictions, but that their cooling is still larger compared to most other mass numbers. Only nuclei with mass numbers 31, 33, and 55 are predicted to be cooling more strongly. However, the theoretical predictions for the transition strengths of these nuclei are not consistently accurate enough to draw conclusions on crust cooling. With the experimental approach developed in this work, all relevant transitions are within reach to be studied in the future. [ABSTRACT FROM AUTHOR]

The size of a ΔK=0 M1 excitation strength has been determined for the first time in a predominantly axially deformed even-even nucleus. It has been obtained from the observation of a rare K-mixing situation between two close-lying Jπ=1+ states of the nucleus 164Dy with components characterized by intrinsic projection quantum numbers K=0 and K=1. Nuclear resonance fluorescence induced by quasimonochromatic linearly polarized γ-ray beams provided evidence for K mixing of the 1+ states at 3159.1(3) and 3173.6(3) keV in excitation energy from their γ-decay branching ratios into the ground-state band. The ΔK=0 transition strength of B(M1;0+1→1+K=0)=0.008(1)μ²N was inferred from a mixing analysis of their M1 transition rates into the ground-state band. It is in agreement with predictions from the quasiparticle phonon nuclear model. This determination represents first experimental information on the M1 excitation strength of a nuclear quantum state with a negative R-symmetry quantum number. [ABSTRACT FROM AUTHOR]

Background: The rapid neutron capture process is one of the main nucleosynthesis processes of elements heavier than Fe. Uncertainties in nuclear properties, such as masses, half-lives, and β-delayed neutron probabilities can cause orders of magnitude of variation within astrophysical r-process simulations. Presently, theoretical models are used to make global predictions of various nuclear properties for the thousands of nuclei required for these simulations, and measurements are required to benchmark these models, especially far from stability. Purpose: β-decay strength distributions can be used to not only inform astrophysical r-process simulations, but also to provide a stringent test for theoretical calculations. The aim of this work is to provide accurate strength distributions for 69,71Coβ decay. Method: The technique of total absorption spectroscopy was used to measure the β decay of 69,71Co for the first time at the National Superconducting Cyclotron Laboratory. The ions were implanted in a double-sided silicon strip detector at the center of the Summing NaI(Tl) detector and identified using standard particle identification methods. The response of the detection system to the β-decay electron and subsequent γ-ray radiation was fit to the observed experimental data using a χ²-minimization technique. Results: β-feeding intensities and Gamow-Teller strength distributions were extracted from the fits of the experimental data. The β-decay intensities show that there is a large percentage of feeding to levels above 2 MeV, which have not been observed in previous studies. The resultant β-feeding intensities and Gamow-Teller strength distributions were compared to shell model and quasiparticle random phase approximation (QRPA) calculations. Conclusions: Comparing experimentally determined β-decay strength distributions provides a test of models, which are commonly used for global β-decay properties for astrophysical calculations. This work highlights the importance of performing detailed comparisons of models to experimental data, particularly far from stability and as close to the r-process path as possible. [ABSTRACT FROM AUTHOR]

Background: The recent observation of a neutron-star merger finally confirmed one astrophysical location of the rapid neutron-capture process (r-process). Evidence of the production of A < 140 nuclei was seen, but there is still little detailed information about how those lighter elements are produced in such an environment. Many of the questions surrounding the A ≈ 80 nuclei are likely to be answered only when the nuclear physics involved in the production of r-process nuclei is well understood. Neutron-capture reactions are an important component of the r-process, and neutron-capture cross sections of r-process nuclei, which are very neutron rich, have large uncertainties. Purpose: Indirectly determine the neutron-capture cross section and reaction rate of 73 Zn (n, γ) 74 Zn. Methods: The nuclear level density (NLD) and γ -ray strength function (γ SF) of 74 Zn were determined following a total absorption spectroscopy (TAS) experiment focused on the ß decay of 74 Cu into 74 Zn performed at the National Superconducting Cyclotron Laboratory. The NLD and γ SF were used as inputs in a Hauser-Feshbach statistical model to calculate the neutron-capture cross section and reaction rate. Results: The NLD and γ SF of 74 Zn were experimentally constrained for the first time using ß -delayed γ rays measured with TAS and the ß -Oslo method. The NLD and γ SF were then used to constrain the neutron-capture cross section and reaction rate for the 73 Zn (n, γ) 74 Zn reaction. Conclusions: The uncertainty in the neutron-capture cross section and reaction rate of 73 Zn (n, γ) 74 Zn calculated in TALYS was reduced to under a factor of 2 from a factor of 5 in the cross section and a factor of 11 in the reaction rate using the experimentally obtained NLD and γ SF. [ABSTRACT FROM AUTHOR]

Neutron-capture reactions on very neutron-rich nuclei are essential for heavy-element nucleosynthesis through the rapid neutron-capture process, now shown to take place in neutron-star merger events. For these exotic nuclei, radiative neutron capture is extremely sensitive to their γ-emission probability at very low γ energies. In this work, we present measurements of the γ-decay strength of 70Ni over the wide range 1.3≤Eγ≤8 MeV. A significant enhancement is found in the γ-decay strength for transitions with Eγ<3 MeV. At present, this is the most neutron-rich nucleus displaying this feature, proving that this phenomenon is not restricted to stable nuclei. We have performed E1-strength calculations within the quasiparticle time-blocking approximation, which describe our data above Eγ≃5 MeV very well. Moreover, large-scale shell-model calculations indicate an M1 nature of the low-energy γ strength. This turns out to be remarkably robust with respect to the choice of interaction, truncation, and model space, and we predict its presence in the whole isotopic chain, in particular the neutron-rich 72,74,76Ni. [ABSTRACT FROM AUTHOR]

We report the independent experimental confirmation of an isomeric state in the proton drip-line nucleus 26P. The γ-ray energy and half-life determined are 164.4 ± 0.3 (sys) ± 0.2 (stat) keV and 104 ± 14 ns, respectively, which are in agreement with the previously reported values. These values are used to set a semiempirical limit on the proton separation energy of 26 P, with the conclusion that it can be bound or unbound. [ABSTRACT FROM AUTHOR]

One of the greatest questions for modern physics to address is how elements heavier than iron are created in extreme astrophysical environments. A particularly challenging part of that question is the creation of the so-called p-nuclei, which are believed to be mainly produced in some types of supernovae. The lack of needed nuclear data presents an obstacle in nailing down the precise site and astrophysical conditions. In this work, we present for the first time measurements on the nuclear level density and average γ strength function of 92Mo. State-of-the-art p-process calculations systematically underestimate the observed solar abundance of this isotope. Our data provide stringent constraints on the 91Nb(p,γ)92Mo reaction rate, which is the last unmeasured reaction in the nucleosynthesis puzzle of 92Mo. Based on our results, we conclude that the 92Mo abundance anomaly is not due to the nuclear physics input to astrophysical model calculations. [ABSTRACT FROM AUTHOR]

Nuclear reactions where an exotic nucleus captures a neutron are critical for a wide variety of applications, from energy production and national security, to astrophysical processes, and nucleosynthesis. Neutron capture rates are well constrained near stable isotopes where experimental data are available; however, moving far from the valley of stability, uncertainties grow by orders of magnitude. This is due to the complete lack of experimental constraints, as the direct measurement of a neutron-capture reaction on a short-lived nucleus is extremely challenging. Here, we report on the first experimental extraction of a neutron capture reaction rate on 69Ni, a nucleus that is five neutrons away from the last stable isotope of Ni. The implications of this measurement on nucleosynthesis around mass 70 are discussed, and the impact of similar future measurements on the understanding of the origin of the heavy elements in the cosmos is presented. [ABSTRACT FROM AUTHOR]

Background: Measurements of β decay provide important nuclear structure information that can be used to probe isospin asymmetries and inform nuclear astrophysics studies. Purpose: To measure the β-delayed γ decay of 26P and compare the results with previous experimental results and shell-model calculations. Method: A 26P fast beam produced using nuclear fragmentation was implanted into a planar germanium detector. Its β-delayed γ-ray emission was measured with an array of 16 high-purity germanium detectors. Positrons emitted in the decay were detected in coincidence to reduce the background. Results: The absolute intensities of 26Pβ-delayed γ rays were determined. A total of six new β-decay branches and 15 new γ-ray lines have been observed for the first time in 26Pβ decay. A complete β-decay scheme was built for the allowed transitions to bound excited states of 26Si. ft values and Gamow-Teller strengths were also determined for these transitions and compared with shell-model calculations and the mirror β decay of 26Na, revealing significant mirror asymmetries. [ABSTRACT FROM AUTHOR]

The β decay of 76Ga was studied using the technique of total absorption spectroscopy for the first time. The experiment was performed at the National Superconducting Cyclotron Laboratory using the Summing NaI(Tl) detector. The extracted β-decay feeding intensity distribution and Gamow-Teller transition strength distribution are compared to shell-model calculations to help constrain nuclear matrix elements relevant to the neutrinoless double-β decay of 76Ge. [ABSTRACT FROM AUTHOR]

The known I^{π}=8&#95;{1}^{+}, E&#95;{x}=2129-keV isomer in the semimagic nucleus ^{130}Cd&#95;{82} was populated in the projectile fission of a ^{238}U beam at the Radioactive Isotope Beam Factory at RIKEN. The high counting statistics of the accumulated data allowed us to determine the excitation energy, E&#95;{x}=2001.2(7)  keV, and half-life, T&#95;{1/2}=57(3)  ns, of the I^{π}=6&#95;{1}^{+} state based on γγ coincidence information. Furthermore, the half-life of the 8&#95;{1}^{+} state, T&#95;{1/2}=224(4)  ns, was remeasured with high precision. The new experimental information, combined with available data for ^{134}Sn and large-scale shell model calculations, allowed us to extract proton and neutron effective charges for ^{132}Sn, a doubly magic nucleus far-off stability. A comparison to analogous information for ^{100}Sn provides first reliable information regarding the isospin dependence of the isoscalar and isovector effective charges in heavy nuclei.

The interpretation of observations of cooling neutron star crusts in quasipersistent x-ray transients is affected by predictions of the strength of neutrino cooling via crust Urca processes. The strength of crust Urca neutrino cooling depends sensitively on the electron-capture and β-decay ground-state-to-ground-state transition strengths of neutron-rich rare isotopes. Nuclei with a mass number of A=61 are predicted to be among the most abundant in accreted crusts, and the last remaining experimentally undetermined ground-state-to-ground-state transition strength was the β decay of ^{61}V. This Letter reports the first experimental determination of this transition strength, a ground-state branching of 8.1&#95;{-3.1}^{+4.0}%, corresponding to a log ft value of 5.5&#95;{-0.2}^{+0.2}. This result was achieved through the measurement of the β-delayed γ rays using the total absorption spectrometer SuN and the measurement of the β-delayed neutron branch using the neutron long counter system NERO at the National Superconducting Cyclotron Laboratory at Michigan State University. This method helps to mitigate the impact of the pandemonium effect in extremely neutron-rich nuclei on experimental results. The result implies that A=61 nuclei do not provide the strongest cooling in accreted neutron star crusts as expected by some predictions, but that their cooling is still larger compared to most other mass numbers. Only nuclei with mass numbers 31, 33, and 55 are predicted to be cooling more strongly. However, the theoretical predictions for the transition strengths of these nuclei are not consistently accurate enough to draw conclusions on crust cooling. With the experimental approach developed in this work, all relevant transitions are within reach to be studied in the future.

The size of a ΔK=0 M1 excitation strength has been determined for the first time in a predominantly axially deformed even-even nucleus. It has been obtained from the observation of a rare K-mixing situation between two close-lying J^{π}=1^{+} states of the nucleus ^{164}Dy with components characterized by intrinsic projection quantum numbers K=0 and K=1. Nuclear resonance fluorescence induced by quasimonochromatic linearly polarized γ-ray beams provided evidence for K mixing of the 1^{+} states at 3159.1(3) and 3173.6(3) keV in excitation energy from their γ-decay branching ratios into the ground-state band. The ΔK=0 transition strength of B(M1;0&#95;{1}^{+}→1&#95;{K=0}^{+})=0.008(1)μ&#95;{N}^{2} was inferred from a mixing analysis of their M1 transition rates into the ground-state band. It is in agreement with predictions from the quasiparticle phonon nuclear model. This determination represents first experimental information on the M1 excitation strength of a nuclear quantum state with a negative R-symmetry quantum number.

The β-delayed γ-ray spectroscopy of neutron-rich ^{123,125}Ag isotopes is investigated at the Radioactive Isotope Beam Factory of RIKEN, and the long-predicted 1/2^{-} β-emitting isomers in ^{123,125}Ag are identified for the first time. With the new experimental results, the systematic trend of energy spacing between the lowest 9/2^{+} and 1/2^{-} levels is extended in Ag isotopes up to N=78, providing a clear signal for the reduction of the Z=40 subshell gap in Ag towards N=82. Shell-model calculations with the state-of-the-art V&#95;{MU} plus M3Y spin-orbit interaction give a satisfactory description of the low-lying states in ^{123,125}Ag. The tensor force is found to play a crucial role in the evolution of the size of the Z=40 subshell gap. The observed inversion of the single-particle levels around ^{123}Ag can be well interpreted in terms of the monopole shift of the π1g&#95;{9/2} orbitals mainly caused by the increasing occupation of ν1h&#95;{11/2} orbitals.

This corrects the article DOI: 10.1103/PhysRevLett.116.242502.

The level structure of the neutron-rich ^{77}Cu nucleus is investigated through β-delayed γ-ray spectroscopy at the Radioactive Isotope Beam Factory of the RIKEN Nishina Center. Ions of ^{77}Ni are produced by in-flight fission, separated and identified in the BigRIPS fragment separator, and implanted in the WAS3ABi silicon detector array, surrounded by Ge cluster detectors of the EURICA array. A large number of excited states in ^{77}Cu are identified for the first time by correlating γ rays with the β decay of ^{77}Ni, and a level scheme is constructed by utilizing their coincidence relationships. The good agreement between large-scale Monte Carlo shell model calculations and experimental results allows for the evaluation of the single-particle structure near ^{78}Ni and suggests a single-particle nature for both the 5/2&#95;{1}^{-} and 3/2&#95;{1}^{-} states in ^{77}Cu, leading to doubly magic ^{78}Ni.

The β-decay intensity of ^{70}Co was measured for the first time using the technique of total absorption spectroscopy. The large β-decay Q value [12.3(3) MeV] offers a rare opportunity to study β-decay properties in a broad energy range. Two surprising features were observed in the experimental results, namely, the large fragmentation of the β intensity at high energies, as well as the strong competition between γ rays and neutrons, up to more than 2 MeV above the neutron-separation energy. The data are compared to two theoretical calculations: the shell model and the quasiparticle random phase approximation (QRPA). Both models seem to be missing a significant strength at high excitation energies. Possible interpretations of this discrepancy are discussed. The shell model is used for a detailed nuclear structure interpretation and helps to explain the observed γ-neutron competition. The comparison to the QRPA calculations is done as a means to test a model that provides global β-decay properties for astrophysical calculations. Our work demonstrates the importance of performing detailed comparisons to experimental results, beyond the simple half-life comparisons. A realistic and robust description of the β-decay intensity is crucial for our understanding of nuclear structure as well as of r-process nucleosynthesis.

The β-decay half-lives of 110 neutron-rich isotopes of the elements from &#95;{37}Rb to &#95;{50}Sn were measured at the Radioactive Isotope Beam Factory. The 40 new half-lives follow robust systematics and highlight the persistence of shell effects. The new data have direct implications for r-process calculations and reinforce the notion that the second (A≈130) and the rare-earth-element (A≈160) abundance peaks may result from the freeze-out of an (n,γ)⇄(γ,n) equilibrium. In such an equilibrium, the new half-lives are important factors determining the abundance of rare-earth elements, and allow for a more reliable discussion of the r process universality. It is anticipated that universality may not extend to the elements Sn, Sb, I, and Cs, making the detection of these elements in metal-poor stars of the utmost importance to determine the exact conditions of individual r-process events.

A novel technique has been developed, which will open exciting new opportunities for studying the very neutron-rich nuclei involved in the r process. As a proof of principle, the γ spectra from the β decay of ^{76}Ga have been measured with the SuN detector at the National Superconducting Cyclotron Laboratory. The nuclear level density and γ-ray strength function are extracted and used as input to Hauser-Feshbach calculations. The present technique is shown to strongly constrain the ^{75}Ge(n,γ)^{76}Ge cross section and reaction rate.