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Background: Theoretical calculations have shown that the energy and angular correlations in the three-body decay of the two-neutron unbound 260 can provide information on the ground-state wave function, which has been predicted to have a dineutron configuration and 2n halo structure. Purpose: To use the experimentally measured three-body correlations to gain insight into the properties of 260, including the decay mechanism and ground-state resonance energy. Method: 26O was produced in a one-proton knockout reaction from 27F and the 24O + n + n decay products were measured using the MoNA-Sweeper setup. The three-body correlations from the 26O ground-state resonance decay were extracted. The experimental results were compared to Monte Carlo simulations in which the resonance energy and decay mechanism were varied. Results: The measured three-body correlations were well reproduced by the Monte Carlo simulations but were not sensitive to the decay mechanism due to the experimental resolutions. However, the three-body correlations were found to be sensitive to the resonance energy of 26O. A 1σ upper limit of 53 keV was extracted for the ground-state resonance energy of 26O. Conclusions: Future attempts to measure the three-body correlations from the ground-state decay of 26O will be very challenging due to the need for a precise measurement of the 24O momentum at the reaction point in the target. [ABSTRACT FROM AUTHOR]

The neutron decay of an unbound resonance in 12Be has been measured at 1243 ± 21 keV decay energy with a width of 634 ± 60 keV. This state was populated with a one-proton removal reaction from a 71 MeV/u 13B beam incident upon a beryllium target. The invariant mass reconstruction of the resonance was achieved by measuring the daughter fragment in coincidence with neutrons. Despite being above the 2n separation energy, the state decays predominantly by the emission of one neutron to 1 'Be, setting an upper limit on the branching ratio for the two-neutron decay channel to 10Be of less than 5%. From the characteristics of the population and decay of the resonance, it is concluded that this state cannot correspond to the previously observed state at 4580 ± 5 keV. [ABSTRACT FROM AUTHOR]

The article reports on the observation of neutron decay of a low-lying unbound state in Beryllium isotopes and preliminary limits on its branching ratios. Topics discussed include conduct of the study at the U.S. National Superconducting Cyclotron Laboratory, use of two cathode-readout drift chambers (CRDCs) to measure position of the particles, interpretation of data performed with the Monte Carlo simulation.

The article offers information on a study to determine the neutron decay of a low-lying unbound state in 12Beryllium and preliminary limits on its branching ratios. Topics discussed include determination of resonance energy of beryllium isotopes, neutron decay in two bound states in 11beryllium, and calculation of momentum vectors of the neutrons. Other topic discussed include use of invariant mass method to determine the energy released in the decay of a nucleus.

The article offers information on a study related to the measurement of neutron decay of an unbound resonance in Beryllium (Be) 12Be conducted at the National Superconducting Cyclotron Laboratory in U.S. Topics discussed include interpretation of data with Monte Carlo simulation, the use of charged particle detector to measure position, angle and energy loss and the role of the sweeper dipole magnet to introduce angular correlations.

The article discusses the Low-lying neutron unbound states in Beryllium. It mentions that neutron decay of an unbound resonance in Be has been measured with decay energy along with a width of 634 ± 60 kilo electron volt (keV). It presents that experiment were being carried out at the National Superconducting Cyclotron Laboratory.

The article presents brief information on low-lying neutron unbound states in beryllium isotope. It states that neutron decay of an unbound resonance in beryllium isotope has been measured at particular decay energy. It further mentions that energy, the state decays predominantly by the emission of one neutron to beryllium isotope. Information related to continuum shell mode is also discussed.

The ground state two-proton decay lifetime of l9Mg, populated by the one-neutron knockout of an intermediateenergy 20Mg radioactive beam, was measured utilizing a new experimental technique. A thin silicon detector positioned at varying distances (0.0-1.0 mm) downstream of the reaction target measured the energy loss of l9Mg and the two-proton decay product 17Ne. The lifetime was deduced from fits to the measured energy-loss line shapes and depended upon the contribution of prompt reaction processes to the yield of l7Ne. For relative l7Ne prompt contributions from 82% to 92%, the extracted lifetimes ranged from 1.75+0.43-0.42 to 6.4+2.4-2.7 ps. The results are consistent with the previously reported l9Mg lifetime measurement and serve as both an important complementary study and a validation of this new technique, which can provide lifetime information for short-lived states beyond the proton drip line. [ABSTRACT FROM AUTHOR]

The neutron-unbound nucleus 15Be was observed for the first time. It was populated using neutron transfer from a deuterated polyethylene target with a 59 MeV/u 14Be beam. Neutrons were measured in coincidence with outgoing 14Be particles and the reconstructed decay energy spectrum exhibits a resonance at 1.8(1) MeV. This corresponds to 15Be being unbound by 0.45 MeV more then 16Be thus significantly hindering the sequential two-neutron decay of 16Be to 14Be through this state. [ABSTRACT FROM AUTHOR]

Neutron-unbound resonant states of 11Be were populated in neutron knockout reactions from 12Be and identified by 10Be-n coincidence measurements. A resonance in the decay-energy spectrum at 80(2) keV was attributed to a highly excited unbound state in 11Be at 3.949(2) MeV decaying to the 2+ excited state in 10Be. A knockout cross section of 15(3) mb was inferred for this 3.949(2) MeV state, suggesting a spectroscopic factor near unity for this 0p3/2- level, consistent with the detailed shell model calculations. [ABSTRACT FROM AUTHOR]

A new resonance having a relative decay energy of ~0.6 MeV has been observed above the two-neutron separation energy in 24O at an excitation energy of ~7.5 MeV. The new level was found to directly feed the first excited state in 23O, an E=0.045(2)-MeV resonance, through the measurement of neutron-neutron correlations. Energy level comparisons with 23O suggest that this new level in 24O is dominated by an unpaired neutron in the ?0d3/2 single-particle orbital coupled to a single hole in the ?0d5/2 single-particle orbital. Establishment of this two-neutron discrimination technique provides a means for investigating high-lying excited states in neutron-rich nuclei. [ABSTRACT FROM AUTHOR]

In the preceding Comment, Fortune argues that, in our original paper [Peters et al., Phys. Rev. C 83, 057304 (2011)], we did not or could not separate the two neutron-unbound states in 11Be near 4 MeV. However, including the suggested contribution of the 3.887-MeV state decaying via 18 keV to the 2+ State in 10Be does not fit the data; neither do any other attempts incorporating any contribution of this decay channel. The best fit was achieved with a single resonance of decay energy 80(2) keV. [ABSTRACT FROM AUTHOR]

A two-neutron unbound excited state of 24O was populated through a (d,d') reaction at 83.4 MeV/nucleon. A state at E = 715 ± 110 (stat) ± 45 (sys) keV with a width of T < 2 MeV was observed above the two-neutron separation energy placing it at 7.65 ± 0.2 MeV with respect to the ground state. Three-body correlations for the decay of 24O -» 22 O + 2n show clear evidence of a sequential decay through an intermediate state in 23O. Neither a di-neutron nor phase-space model for the three-body breakup were able to describe these correlations. [ABSTRACT FROM AUTHOR]

A previously published measurement of the reaction of a 59 MeV/nucleon 14Be beam on a deuterated polyethylene target was further analyzed to search for 12He as well as initial state effects in the population of the 10He ground state. No evidence for either was found. A lower limit of about 1 MeV was determined for a possible resonance in 12He. In addition, the three-body decay energy spectrum of l0He could not be described by a reaction mechanism calculation based on the halo structure of the initial 14Be assuming a direct a-particle removal reaction. [ABSTRACT FROM AUTHOR]

The Modular Neutron .Array (MONA) and 4 Tm Sweeper magnet were used to measure the free neutrons and heavy charged particles from the radioactive ion beam induced 32Mg + 9Be reaction. The fragmentation reaction was simulated with the consü'ained molecular dynamics model (CoMD), which demonstrated that the (N/Z) of the heavy fragments and free neutron multiplicities were observables sensitive to the density dependence of the symmetry energy at subsaturation densities. Through comparison of these simulations with the experimental data, constraints on the density dependence of the symmetry energy were extracted. The advantage of radioactive ion beams as a probe of the symmetry' energy is demonstrated through examination of CoMD calculations for stable and radioactive-beam-induCed reactions. [ABSTRACT FROM AUTHOR]

A two-proton knockout reaction from a 17C beam at 55 MeV/u was used to produce the unbound nucleus 15Be. No significant number of events were observed for the decay of 15Be into a neutron and a 14Be fragment. An upper limit for the 14Be production cross section of 0.079 ± 0.038 mb was extracted, which is more than an order of magnitude smaller than the predicted two-proton knockout reaction cross section. Based on these results we conclude that any populated states in 15Be decay through three sequential neutron decays into 12Be, via the unbound first excited state of 14Be. Therefore, these states in 15Be must be neutron unbound by more than 1.54 MeV, which is the location of the first excited 2+ state in 14Be. [ABSTRACT FROM AUTHOR]

The neutron-unbound nucleus 13Be was populated with a nucleon exchange reaction from a 71 MeV/u secondary 13B beam. The decay-energy spectrum was reconstructed using invariant mass spectroscopy based on 12Be fragments in coincidence with neutrons. The data could be described with an s-wave resonance at Er = 0.73(9) MeV with a width of ⌈, = 1.98(34) MeV and a d-wave resonance at Er = 2.56(13) MeV with a width of ⌈, = 2.29(73) MeV. The observed spectral shape is consistent with previous one-proton removal reaction measurements from 14B. [ABSTRACT FROM AUTHOR]

Two low-lying neutron-unbound excited states of 24O, populated by proton-knockout reactions on 26F, have been measured using the MoNA and LISA arrays in combination with the Sweeper Magnet at the Coupled Cyclotron Facility at the NSCL using invariant mass spectroscopy. The current measurement confirms the separate identity of two states with decay energies 0.51(5) MeV and 1.20(7) MeV, and provides support for theoretical model calculations, which predict a 2+ first excited state and a 1+ higher-energy state. The measured excitation energies for these states, 4.70(15) MeV for the 2+ level and 5.39(16) MeV for the 1+ level, are consistent with previous lower-resolution measurements, and are compared with five recent model predictions. [ABSTRACT FROM AUTHOR]

Background: In neutron-rich nuclei around N=40 rapid changes in nuclear structure can be observed. While Ni68 exhibits signatures of a doubly magic nucleus, experimental data along the isotopic chains in even more exotic Fe and Cr isotopes-such as excitation energies and transition strengths-suggest a sudden rise in collectivity toward N=40. Purpose: Reduced quadrupole transition strengths for low-lying transitions in neutron-rich 58,60,62Cr are investigated. This gives quantitative new insights into the evolution of quadrupole collectivity in the neutron-rich region close to N=40. Method: The recoil distance Doppler-shift (RDDS) technique was applied to measure lifetimes of low-lying states in Cr58,60,62Cr. The experiment was carried out at the National Superconducting Cyclotron Laboratory (NSCL) with the SeGA array in a plunger configuration coupled to the S800 magnetic spectrograph. The states of interest were populated by means of one-proton knockout reactions. Results: Data reveal a rapid increase in quadrupole collectivity for 58,60,62Cr toward N=40 and point to stronger quadrupole deformations compared to neighboring Fe isotopes. The experimental B(E2) values are reproduced well with state-of-the-art shell-model calculations using the LNPS effective interaction. A consideration of intrinsic quadrupole moments and B42 ratios suggest an evolution toward a rotational nature of the collective structures in 60,62Cr. Compared to 58Cr, experimental B42 and B62 values for 60Cr are in better agreement with the E(5) limit. Conclusion: Our results indicate that collective excitations in neutron-rich Cr isotopes saturate at N=38, which is in agreement with theoretical predictions. More detailed experimental data of excited structures and interband transitions are needed for a comprehensive understanding of quadrupole collectivity close to N=40. This calls for additional measurements in neutron-rich Cr and neighboring Ti and Fe nuclei. [ABSTRACT FROM AUTHOR]

In an experiment at the A1900 spectrometer of the National Superconducting Cyclotron Laboratory at Michigan State University the new isotope 59Ge was identified and the cross section for production of the most neutrondeficient 59-62Ge isotopes in the fragmentation of a78Kr beam at 150 MeV/nucleon measured. This experimental information is relevant for the hunt of new two-proton emitters in the region above the doubly-magic 48Ni. [ABSTRACT FROM AUTHOR]

Background: Be15 is expected to have low-lying 3/2+ and 5/2+ states. A first search did not find the 3/2+ [A. Spyrou et al., Phys. Rev. C 84, 044309 (2011)]; however, a resonance in 15Be was populated in a second attempt and determined to be unbound with respect to 14Be by 1.8(1) MeV with a tentative spin-parity assignment of 5/2+ [J. Snyder et al., Phys. Rev. C 88, 031303(R) (2013)]. Purpose: Search for the predicted 15Be3/2+ state in the three-neutron decay channel. Method: A two-proton removal reaction from a 55 MeV/u 17C beam was used to populate neutron-unbound states in 15Be. The two-, three-, and four-body decay energies of the 12Be+ neutron(s) detected in coincidence were reconstructed using invariant mass spectroscopy. Monte Carlo simulations were performed to extract the resonance and decay properties from the observed spectra. Results: The low-energy regions of the decay energy spectra can be described with the first excited unbound state of 14Be (Ex=1.54 MeV, Er=0.28 MeV). Including a state in 15Be that decays through the first excited 14Be state slightly improves the fit at higher energies though the cross section is small. Conclusions: A 15Be component is not needed to describe the data. If the 3/2+ state in 15Be is populated, the decay by three-neutron emission through 14Be is weak, =11% up to 4 MeV. In the best fit, 15Be is unbound with respect to 12Be by 1.4 MeV (unbound with respect to 14Be by 2.66 MeV) with a strength of 7%. [ABSTRACT FROM AUTHOR]

Results of decay spectroscopy on nuclei in the vicinity of the doubly magic 48Ni are presented. The measurements were performed with a time projection chamber with optical readout which records tracks of ions and protons in the gaseous volume. Six decays of 48Ni, including four events of two-proton ground-state radioactivity, were recorded. An advanced reconstruction procedure yielded the 2p decay energy for 48Ni of Q2p = 1.29(4) MeV. In addition, the energy spectra of β-delayed protons emitted in the decays of 44Cr and 46Fe, as well as half-lives and branching ratios, were determined. The results were found to be consistent with the previous measurements made with Si detectors. A new proton line in the decay of 44Cr corresponding to the decay energy of 760 keV is reported. The first evidence for the β2p decay of 46Fe, based on one clear event, is shown. [ABSTRACT FROM AUTHOR]

The applicability of Coulomb dissociation reactions to determine the cross section for the inverse neutron capture reaction was explored using the reaction 8Li(γ,n)7Li. A 69.5 MeV/nucleon 8Li beam was incident on a Pb target, and the outgoing neutron and 7Li nucleus were measured in coincidence. The deduced (n,y) excitation function is consistent with data for the direct capture reaction 7Li(n,γ)8Li and with low-energy effective field theory calculations. [ABSTRACT FROM AUTHOR]

Production cross sections for neutron-rich nuclei from the fragmentation of a 82Se beam at 139 MeV/u were measured. The longitudinal momentum distributions of 126 neutron-rich isotopes of elements 11 ≼ Z ≼ 32 were scanned using an experimental approach of varying the target thickness. Production cross sections with beryllium and tungsten targets were determined for a large number of nuclei including several isotopes first observed in this work. These are the most neutron-rich nuclides of the elements 22 ≼ Z ≼ 25 (64Ti, 67V, 69Cr, and 72Mn). One event was registered consistent with 70Cr and another one with 75Fe. The production cross sections are correlated with Qg systematics to reveal trends in the data. The results presented here confirm our previous results from a similar measurement using a 76Ge beam and can be explained with a shell model that predicts a subshell closure at N = 34 around Z = 20. This is demonstrated by systematic trends and calculations with the abrasion-ablation model that are sensitive to separation energies. [ABSTRACT FROM AUTHOR]

The ground state of neutron-rich unbound 13Li was observed for the first time in a one-proton removal reaction from 14Be at a beam energy of 53.6 MeV/u. The 13Li ground state was reconstructed from "Li and two neutrons giving a resonance energy of 120-80+60 keV. All events involving single- and double-neutron interactions in the Modular Neutron Array (MoNA) were analyzed, simulated, and fitted self-consistently. The three-body ("Li + n + n) correlations within Jacobi coordinates showed strong dineutron characteristics. The decay energy spectrum of the intermediate 12Li system (11Li + n) was described with an s-wave scattering length of greater than --4 fm, which is a smaller absolute value than reported in a previous measurement. [ABSTRACT FROM AUTHOR]

β-delayed proton emission from nuclides in the neighborhood of 100Sn was studied at the National Superconducting Cyclotron Laboratory (NSCL). The nuclei were produced by fragmentation of a 120 MeV/nucleon 112Sn primary beam on a Be target. Beam purification was provided by the A1900 Fragment Separator and the Radio Frequency Fragment Separator. The fragments of interest were identified and their decay was studied with the NSCL Beta Counting System in conjunction with the Segmented Germanium Array. The nuclei 96Cd, 98Ing, 98Inm, and 99In were identified as β-delayed proton emitters, with branching ratios bβp = 5.5(40)%, 5.5-2+3%, 19(2)%, and 0.9(4)%, respectively. The branching ratios for 89Ru, 91.92Rh, 93Pd, and 95Ag were deduced for the first time with bβp = 3-1.7+1.9%, 1.3(5)%, 1.9(1)%, 7.5(5)%, and 2.5(3)%, respectively. The bβp = 22(1)% value for 101Sn was deduced with higher precision than previously reported. The impact of the newly measured bβp values on the composition of the type I x-ray burst ashes was studied. [ABSTRACT FROM AUTHOR]

The article presents the study which examined the β-delayed proton emission from nuclides in the neighborhood of 100tin (Sn). The study was conducted at the National Superconducting Cyclotron Laboratory (NSCL) in Michigan. The NSCL Beta Counting System and the Segmented Germanium Array were used to study the decay of the nuclides.

Background: Nuclear structure plays a significant role on the rapid neutron capture process (r process) since shapes evolve with the emergence of shells and subshells. There was some indication in neighboring nuclei that we might find examples of a new N = 56 subshell, which may give rise to a doubly magic 9034Se56 nucleus. Purpose: β-decay half-lives of nuclei around 90Se have been measured to determine if this nucleus has in fact a doubly magic character. Method: The fragmentation of a 136Xe beam at the National Superconducting Cyclotron Laboratory at Michigan State University was used to create a cocktail of nuclei in the A = 90 region. Results: We have measured the half-lives of 22 nuclei near the r-process path in the A = 90 region. The half-lives of 88As and 90Se have been measured for the first time. The values were compared with theoretical predictions in the search for nuclear-deformation signatures of a N = 56 subshell, and its possible role in the emergence of a potential doubly magic 90Se. The impact of such hypothesis on the synthesis of heavy nuclei, particularly in the production of Sr, Y, and Zr elements was investigated with a weak r-process network. Conclusions: The new half-lives agree with results obtained from a standard global QRPA model used in r-process calculations, indicating that 90Se has a quadrupole shape incompatible with a closed N = 56 subshell in this region. The impact of the measured 90Se half-life in comparison with a former theoretical predication associated with a spherical half-life on the weak r process is shown to be strong. [ABSTRACT FROM AUTHOR]

The ground state of 28F has been observed as an unbound resonance 220 keV above the ground state of 27F. A comparison of this result with USDA/USDB shell model predictions leads to the conclusion that the 28F ground state is primarily dominated by W-shell configurations. Here we present a detailed report on the experiment in which the ground state resonance of 28F was first observed. Additionally, we report the first observation of a neutron-unbound excited state in 27F at an excitation energy of 2500(220) keV. [ABSTRACT FROM AUTHOR]

Low-energy excited states in 71,73Ni populated via the β decay of 71,73Co were investigated in an experiment performed at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University (MSU). Detailed analysis led to the construction of level schemes of 71,73Ni, which are interpreted using systematics and analyzed using shell-model calculations. The 5/2- states attributed to the the f5/2 orbital and positive-parity 5/2+ and 7/2+ states from the g9/2 orbital have been identified in both 71,73Ni. In 71Ni the location of a 1/2- β-decaying isomer is proposed, and limits are suggested as to the location of the isomer in 73Ni. The location of positive-parity cluster states are also identified in 71,73Ni. Beta-delayed neutron branching ratios obtained from this data are given for both 71,73Co. [ABSTRACT FROM AUTHOR]

The isomeric and β decays of the N = Z + 2 nucleus 96Ag were investigated at the National Superconducting Cyclotron Laboratory. A cascade of γ-ray transitions originating from the deexcitation of a microsecond isomer was observed for the first time and was found in coincidence with two previously known transitions with energies of 470 and 667 keV. The isomeric half-life was determined as 1.45(7) μs, more precise than previously reported. The existence of a second, longer-lived microsecond isomer, associated with a 743-keV γ transition, is also proposed here. Shell model results within the (P3/2P1/2f5/2g9/2) model space, using the jj44b interaction, reproduced level energies and isomeric decay half-lives reasonably well. [ABSTRACT FROM AUTHOR]

The decay of the extremely neutron-deficient 48Ni was studied by means of an imaging time-projection chamber, which allowed the recording of tracks of charged particles. The decays of six atoms were observed. Four of them clearly correspond to two-proton radioactivity, providing the first direct evidence for this decay mode in 48Ni. Two decays represent β-delayed proton emission. The half-life of 48Ni is determined to be T1/2 = 2.1-0.4+1.4 ms. [ABSTRACT FROM AUTHOR]

Neutron-unbound states in 25F and 26F were populated via the reactions 9Be(26Ne, 24F+n) and 9Be(26Ne, 25F + n), respectively. A resonance close to the neutron separation energy in 25F was identified with a decay energy of 28 ± 4 keV. This resonance corresponds to an excited state in 25F at 4249 ± 116 keV assuming it decays to the ground state of 25F. Guided by shell-model calculations, a spin and parity of 1/2- can be assigned to this state. In the spectrum of 26F, which was produced in a nucleon-exchange reaction, there are indications for an excited state with a decay energy of ~270 keV. [ABSTRACT FROM AUTHOR]