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In this work we estimate the production rates for the three-body radiative capture processes α + n + n → He + γ and α + α + n → Be + γ, as well as the four-body recombination reactions α + α + n + n → He + α, + n + n + n → He + n, α + α + n + n → Be + n and α + α + α + n → Be + α. These processes compete as a source of He and Be. The hyperspherical adiabatic expansion method is used. With this method no assumption is made about the capture mechanism. Both sequential and direct capture are included. The production rates for the radiative and the four-body recombination processes are found to be comparable for a mass density of about 10g/cm ( ∼ 10 neutrons/cm) and temperatures of a few GK. [ABSTRACT FROM AUTHOR]

Three-body continuum problems are investigated for light nuclei of astrophysical relevance. We focus on three-body decays of resonances or recombination via resonances or the continuum background. The concepts of widths, decay mechanisms and dynamic evolution are discussed. We also discuss results for the triple α decay in connection with 2 resonances and density and temperature dependence rates of recombination into light nuclei from α-particles and neutrons. [ABSTRACT FROM AUTHOR]

Mean-square charge radii and magnetic moments have been measured for the neutron deficient lead isotopes, 182–190Pb. The measurement was performed at the ISOLDE online mass separator, using the in-source resonance ionization spectroscopy technique. The wavelength of the first excitation step for the resonance ionization laser ion source (RILIS) was scanned over the resonance(s) whilst the α- and γ-ray spectra from the decay of the Pb isotopes were recorded as a function of the wavelength. The isotope shift and, in the case of odd- A isotopes, the hyperfine splitting were deduced. The rms-charge radii of the very neutron deficient Pb isotopes follow the smooth trend of the heavier isotopes. This finding indicates a spherical shape for the lead ground states at the neutron mid-shell ( N = 104), where the excitation energy of the oblate 0+ state in the even isotopes reaches its minimum. [ABSTRACT FROM AUTHOR]

The laser ion source has been used for the study of the isotope shifts of neutron-deficient Eu isotopes. The extension of the region of applicability of the method by using the- and-radiation detection is reported. We have measured the isotope shifts of the europium optical line 576.520 nm for. To increase the laser ion source efficiency an axial magnetic field (350 gauss) was applied. Nearly a twofold rise of the ionization efficiency for Eu was observed. By using the effect of optical ion bunching an increase of the selectivity was obtained. The isotope shift data forare in agreement with the previously measured isotope shifts for these nuclides. The new data forand refined data forpoint to a gradual increase of the deformation for these isotopes. Comparisons with microscopic-macroscopic calculations and calculations in the framework of the Hartree-Fock model were performed. [ABSTRACT FROM AUTHOR]

In the frame of the R&D program for the SPES project of the Legnaro Laboratories, the production yields of Rb, In and Cs isotopes have bean measured at the synchrocyclotron of the Petersburg Nuclear Physics Institute (PNPI) of Gatchina (Russia). Production yields for direct proton fission and neutron-induced fission on a high-density UC2 powder target are compared. The overall efficiencies as a function of the target temperature have been measured. [ABSTRACT FROM AUTHOR]

We assume an environment of neutrons and α-particles of given density and temperature where nuclear syntheses into He, Be, and C are possible. The resulting relative abundance as a function of density and temperature is investigated. [ABSTRACT FROM AUTHOR]

In-source laser spectroscopy experiments for bismuth isotopes at the 306.77-nm atomic transition has been carried out at the Investigation of Radioactive Isotopes on Synchrocyclotron facility of Petersburg Nuclear Physics Institute. New data on isotope shifts and hyperfine structure for Bi ground states and isomers (189,190 m1,190m2,191,192,192m,194,194m,198mBi) have been obtained. The changes in the mean-square charge radii δ ⟨r²⟩ and magnetic-moment values have been deduced. For Bi nuclei a marked deviation from the isotopic trend of δ⟨r²⟩ in lead and thallium isotopic chains has been demonstrated at N < 111. This has been interpreted as an indication of the onset of quadrupole deformation. Analysis of the magnetic moments for odd-odd Bi isotopes also points to the possible increase in deformation at N < 111. [ABSTRACT FROM AUTHOR]

The interconnection between the resonances and virtual states of a three-body system and the resonances and virtual states in its two-body subsystems is investigated using the Borromean halo nucleus 11Li as a realistic example. The three-body core + neutron + neutron model is used, where the neutron-core interaction is fixed to reproduce a given s-wave virtual state and a p-wave resonance. The neutron-neutron interaction is then multiplied by a factor which is progressively changed from 0 to 1 and the resulting trajectories of the three-body states in the complex energy plane are investigated. [ABSTRACT FROM AUTHOR]

In-source laser spectroscopy experiments for neutron-deficient thallium isotopes at the 276.9-nm atomic transition have been carried out at the Investigation of Radioactive Isotopes on Synchrocyclotron facility of Petersburg Nuclear Physics Institute. New data on isotope shifts and the hyperfine structure for I183-207T1 isotopes and isomers are presented. The changes in the mean-square charge radii and magnetic-moment values are deduced. It is shown that nuclear properties of Tl isotopes and isomers smoothly change at the neutron midshell and beyond without development of strong deformation in contrast to the adjacent Hg nuclei. A rather great isomer shift between I = 1/2 and I = 9/2 states for odd 186Tl isotopes is preserved for both sides of the previously investigated mass range. For the first time, a similar isomer shift is found for the odd-odd isotope I86T1. The close resemblance of the charge radii isotopic behavior for the Tl and Pb ground states is demonstrated. [ABSTRACT FROM AUTHOR]

We compute the three-body structure of the lowest resonances of 12Be considered as two neutrons around an inert 10Be core. This is an extension of the bound-state calculations of 12Be into the continuum spectrum. We investigate the lowest resonances of angular momenta and parities, 0±, 1-, and 2+. Surprisingly enough, they all are naturally occurring in the three-body model. We calculate bulk structure dominated by small-distance properties as well as decays determined by the asymptotic large-distance structure. Both 0+ and 2+ have two-body 10Be-neutron d-wave structure, while 1- has an even mixture of p and d waves. The corresponding relative neutron-neutron partial waves are distributed among s, p, and d waves. The branching ratios show different mixtures of one-neutron emission, three-body direct, and sequential decays. We argue for spin and parities 0+, 1-, and 2+ for the resonances at 0.89, 2.03, and 5.13, respectively. The computed structures are in agreement with existing reaction measurements. [ABSTRACT FROM AUTHOR]

We suggested that the two resonances at 0.89 and 2.03 MeV above the two-neutron separation threshold have spins and parities of 0+ and 1-. In the Comment, Fortune claims that these states almost unambiguously must be 3- and 4+ states. We work in three-body cluster models with Jπ = 0+,1-,2+ where all three-body continuum structures are included. Fortune bases his assignments on the bound-state shell-model and (t,p) calculations. Our conclusions are from three-body structure results including widths. Assignments as 0+ and 1- (or, perhaps, 3-) resonances are the most natural within the three-body cluster model. [ABSTRACT FROM AUTHOR]

Decay spectroscopy of 184Tl has been performed at the CERN Isotope Separator On-Line (ISOLDE) facility. An excitation energy of 506.1(1) keV and a half-life of 47.1(7) ms of the intruder based (10-) state have been extracted. The internal decay characteristics of this state are determined and discussed, extending the systematics of such states in the even-mass thallium nuclei below neutron midshell at N = 104. The retardation factors of the isomeric M2 and E3 transitions are deduced and compared with retardation factors in neighboring odd-mass and even-mass thallium isotopes. The new information is combined with a review of hindered and unhindered a-decay data of Bi187-192 populating levels in daughter nuclei 183-188Tl and supports the interpretation of the intruder character of the (10-) state in 184Tl. [ABSTRACT FROM AUTHOR]

Low-energy β-delayed fission of 194,196At and 200,202Fr was studied in detail at the mass separator ISOLDE at CERN. The fission-fragment mass distributions of daughter nuclei 194,196Po and 202Rn indicate a triple-humped structure, marking the transition between asymmetric fission of 178,180Hg and symmetric fission in the light Ra-Rn nuclei. Comparison with the macroscopic-microscopic finite-range liquid-drop model and the self-consistent approach employing the Gogny D1S energy density functional yields discrepancies. This demonstrates once more the need for dynamical fission calculations, because for both models the potential-energy surfaces lack pronounced structures, in contrast to those for the actinide region. [ABSTRACT FROM AUTHOR]

A detailed nuclear-decay spectroscopy study of the neutron-deficient isotope 178T1 has been performed using the highly selective Resonance Ionization Laser Ion Source and ISOLDE mass separator (CERN), which allowed a unique isobarically pure beam of 178T1 to be produced. The first identification of the ß-delayed fission of this isotope was made and its probability PßDf(I78T1) = 0.15(6)% was determined. An asymmetric fission fragment mass distribution of the daughter isotope l78Hg (populated by the ß decay of 178T1) was deduced based on the measured fission fragment energies. The fine-structure a-decay pattern of I78T1 allowed the low-energy states in the daughter nucleus 174Au to be studied. [ABSTRACT FROM AUTHOR]

This Brief Report reports on the first observation of the β--delayed γ decay of 215Pb, feeding states in 215Bi. The 215Pb beam was produced using resonant laser ionization and mass separated at the ISOLDE-CERN on-line mass separator. This ensured clean identification of the γ rays as belonging to the decay of 215Pb or its γ-decay daughters. A half-life of 147(12) s was measured for the 215Pb β decay and a level scheme for the daughter nucleus 215Bi is proposed, resulting in an extended systematics of the excited states of the neutron-rich Bi isotopes. [ABSTRACT FROM AUTHOR]

Post-accelerated isomerically purified radioactive beams, available at the CERN On-Line Isotope Mass Separator facility using the resonant ionization laser technique, have been used to study the Coulomb excitation of the I&pi; = 3- state in 70Cu (Z = 29, N = 41). While first results using a Iπ =6- beam were reported previously, the present complementary experiment allows us to complete the study of the multiplet of states (3-, 4- ,5-,6-) arising from the π2p3νlg9/2 configuration. Besides the known γ-ray transition deexciting the 4- state, a ground-state γ ray of 511(3) keV was observed for the first time and was unambiguously associated with the 5- state deexcitation. This observation fixes the energy, spin, and parity of this state, completing the low-energy level scheme of 70Cu. B(E2) values for all possible E2 transitions within the multiplet were determined. A comparison with large-scale shell model calculations using different interactions and valence spaces shows the importance of proton excitation across the Z = 28 shell gap and the role of the 2d5/2 neutron orbital. [ABSTRACT FROM AUTHOR]

Background: Shell evolution can impact the structure of the nuclei and lead to effects such as shape coexistence. The nuclei around 68Ni represent an excellent study case, however, spectroscopic information of the neutron-rich, Z<28 nuclei is limited. Purpose: The goal is to measure γ-ray transitions in 66Fe,66Co, and 66Ni populated in the β- decay of 66Mn to determine absolute β feedings and relative γ-decay probabilities and to compare the results with Monte Carlo shell model calculations in order to study the influence of the relevant single neutron and proton orbital occupancies around Z=28 and N=40. Method: The low-energy structures of 65,66Fe,66Co, and 66Ni were studied in the β- decay of 66Mn produced at ISOLDE, CERN. The beam was purified by means of laser resonance ionization and mass separation. The β and γ events detected by three plastic scintillators and two MiniBall cluster germanium detectors, respectively, were correlated in time to build the low-energy excitation schemes and to determine the β-decay half-lives of the nuclei. Results: The relative small β-decay ground state feeding of 66Fe obtained in this work is at variant to the earlier studies. Spin and parity 1+ was assigned to the 66Co ground state based on the strong ground-state feeding in the decay of 66Fe as well as in the decay of 66Co. Experimental log(ft) values, γ-ray de-excitation patterns, and energies of excited states were compared to Monte Carlo shell model calculations. Based on this comparison, spin and parity assignments for the selected number of low-lying states in the 66Mn to 66Ni chain were proposed. Conclusions: The β-decay chain starting 66Mn toward 66Ni, crossing N=40, evolves from deformed nuclei to sphericity. The β-decay population of a selected number of 0+ and 2+ states in 66Ni, which is understood within shape coexistence framework of Monte Carlo shell model calculations, reveals the crucial role of the neutron 0g9/2 shell and proton excitations across the Z=28 gap. [ABSTRACT FROM AUTHOR]