Structure of nuclei near100Sn and theπg 9/2 →vg 7/2 Gamow-Teller beta decays

Selected properties of the Gamow-Teller beta decay of even nuclei near¹⁰⁰Sn have been studied. Two theoretical models were used: a self-consistent Hartree-Fock-Bogolyubov approach with the Skyrme interaction and a shell-correction model with a Woods-Saxon average field and monopole pairing residual interaction. Calculations reproduce fairly well both theQ _EC values and the average energies of theI ^π=1⁺ states fed directly in the decay. It is shown that the observed energy splitting between the 1⁺ states cannot be associated with a stable deformation of a final doubly-odd nucleus. The calculated pairing factors are used to estimate the 0⁺ → 1⁺ GT transition strength in the neighbourhood of doubly-magic ₅₀ ¹⁰⁰ Sn₅₀.     

Proton emission, gamma deformation, and the spin of the isomeric state of Ho

The nonadiabatic quasiparticle model for triaxial shapes is used to perform calculations for decay of ¹⁴¹Ho, the only known odd-Z even-N deformed nucleus for which fine structure in proton emission from both ground and isomeric states was observed. All experimental data corresponding to this unique case namely, the rotational spectra of parent and daughter nuclei, decay widths and branching ratios for ground and isomeric states, could be well explained with a strong triaxial deformation γ20°. The recent experimental observation of fine structure decay from the isomeric state, can be explained only with an assignment of I=3/2⁺ as the decaying state, in contradiction with the previous assignment, of I=1/2⁺, based on adiabatic calculations. This study reveals that proton emission measurements could be a precise tool to probe triaxial deformations and other structural properties of exotic nuclei beyond the proton drip-line.     

Exploring the core deformation properties of 29F halo nucleus using T- and Y-configurations

²⁹F nucleus is a two-neutron halo nucleus with the core (²⁷F) + n + n three-body system. We studied the Jacobi coordinates dependant T-and Y-configurations properties due to the core deformation of this nucleus. For this deformation of the core, the separation energy (S_2n) and the root mean square (RMS) matter radius of this halo nucleus were calculated. This theoretical calculation for investigating T-and Y-configuration properties was accomplished through the MATLAB computational software. A positive core deformation was found, which indicates a prolate shaped halo nucleus. We found an excellent agreement for S_2n and 96.4% and 96% accuracies for the T- and Y-configurations respectively.     

Correlation investigations of the low-energy 10He spectrum

The spectrum of low-lying states in the ¹⁰He nucleus is investigated for the two-neutron transfer reaction ³H(⁸He, p)¹⁰He. The secondary beam of ⁸He nuclei with the energy 21.5 MeV/nucleon and a cryogenic tritium target are used in the experiment. The ¹⁰He ground state is observed in the missing mass spectrum at the energy of 2.1 MeV (Γ ～ 2 MeV) above the decay threshold. Analysis of the angular correlations of the ¹⁰He decay products yields the spin and parity of two excited ¹⁰He states, J ^π = 1^? in the energy range from 4 to 6 MeV and J ^π = 2⁺ at energies above 6 MeV.     

On the Possibility of Delayed Fission of Nuclei in the Region of Superheavy Transuranium Elements

Delayed fission of atomic nuclei was discovered in 1966. It is observed primarily in odd–odd nuclei for which the energy released in beta decay (K capture) is commensurate with the fission barrier in the nucleus formed after this process. Delayed fission was found in four nuclide regions: neutrondeficient isotopes in the Pb region, neutron-deficient isotopes in the Ac and Pa regions, and neutrondeficient and neutron-rich isotopes of transuranium elements. In the wake of investigations into the properties of isotopes of superheavy transuranium elements, numerous calculations were performed in order to determine the masses of new nuclei and to predict their decay properties. Explored and predicted properties of superheavy-element nuclides, where, for some odd–odd nuclei of transuranium elements, the K-capture energy is commensurate with the fission barriers in the corresponding daughter nuclei formed after K capture, are analyzed. Estimates of the delayed-fission probability are presented for some isotopes of elements whose charge number Z ranges from 103 to 107.     

Investigation of the reaction mechanism for the four-particle photodisintegration of a carbon nucleus

The four-particle photodisintegration of a carbon nucleus in the reactions ¹²C(γ, p)³H2α and ¹²C(γ, n)³H2α is investigated by a method that employs a diffusion chamber in a magnetic field. It is shown that these reactions proceed according a sequential-type scheme: excited states of ¹¹B and ¹¹C nuclei decay to weakly excited states of ⁸Be, ⁷Li, and ⁷Be nuclei. It is concluded that nucleons are knocked out from the s shell. In the excitation curve for the 2α system in the reaction ¹²C(γ, p)³H2α, a resonance is found between the maxima corresponding to the ground and the first excited state of the ⁸Be nucleus, and this resonance is identified as a ghost anomaly. The branching fractions of the decay modes are determined. The angular distributions of nucleons in the reaction c.m. frame are measured. The energy dependence of the asymmetry coefficient for the angular distributions is obtained. A fast increase in this coefficient is observed in the energy range 38–40 MeV. It is concluded that the asymmetry coefficient depends on the excitation energy of the final nucleus in the region of intermediate photon energies.     

Experimental indication of the onset of nuclear deformation in neutron-rich Sr isotopes at mass 98

A partial decay scheme for 0.1 sec ⁹⁸Rb has been deduced from γ-singles, γ-multispectra ana γγ coincidence measurements taken at the OSTIS mass-separator system at the Institut Laue-Langevin. The low-lying levels of ⁹⁸Sr follow the energy level systematics of the even-AN = 60 isotones. The onset of nuclear deformation in even-A neutron-rich Sr isotopes appears to occur at mass 98, as the first 2⁺ level energy drops from the nearly constant value of about 800 keV for masses 90–96 to 144 keV at mass 98. Energy level systematics indicate that a transition in the nuclear structures of the more neutron-rich nuclei near mass 100 occurs rather sharply at neutron number N = 60.     

Elastic and inelastic scattering of polarized protons from even n=82 nuclei near isobaric analog resonances

Excitation curves for the elastic and the inelastic scattering of polarized protons on the target nuclei ¹³⁸Ba, ¹⁴⁰Ce, ¹⁴²Nd and ¹⁴⁴Sm have been measured in the energy region of prominent isobaric analog resonances. A detailed analysis of the data is presented. Definite J^π assignments are given for a number of parent analog states. Spectroscopic factors and amplitudes for configurations with the core in the ground state or in the 2₁⁺ excited state are derived from the elastic and inelastic proton decay amplitudes. They show consistency with sum rules including orthogonality conditions. Different methods for the-calculation of single particle decay widths have been applied. The qualitative agreement with present unified model calculations is remarkable; an overestimattion of the weak coupling structure, however, becomes apparent.     

Measurement of the ββ-decay rate of 100Mo to the first excited 0+ state in 100Ru

A new and independent confirmation of ββ(2ν) decay of ¹⁰⁰Mo to the first 0⁺ excited state in ¹⁰⁰Ru has been made. This was accomplished using a two-photon coincidence counting technique in which two HPGe detectors were used to observe the two emitted γrays (E _γ1 = 590.8 keV and E _γ2 = 539.6 keV) from the daughter nucleus as it deexcites to the ground state (0⁺ → 2⁺ → 0⁺). The half-life of this decay has been estimated as ～(5–8)×10²⁰ yr.     

Decay of high-spin isomers in Os nuclei by barrier penetration

A decay scheme for the 130±20 ns high-spin isomer in ¹⁸²Os has been established. The excitation energy of the isomer is 7049±1 keV and it has I^π = 25⁽⁺⁾. A 2.4% decay directly to the yrast 24⁺ level at 5988 keV is observed. In ¹⁸⁴Os a 20±5 ns isomer is observed at 2366±1 keV excitation energy with I^π = 10⁺. Again, direct transitions into the yrast 8⁺ and 10⁺ levels are observed. Contrary to previous speculations, there is no compelling evidence for stable triaxial shapes in the structure of the levels through which the isomers decay. The abnormally short half-lives observed, as well as the unusual decay patterns, are best understood in terms of a γ-soft nuclear potential. Motion in the γ-direction allows the isomer to decay via barrier penetration from an axially symmetric prolate shape with the angular momentum along the nuclear symmetry axis (deformation aligned state) via oblate shapes to another prolate shape with the angular momentum perpendicular to the nuclear symmetry axis (rotation-aligned state).     

Investigation of high spin states in23Na and23Mg and the12C+12C resonance atE c.m.=19.3 MeV

The resonance in the¹²C+¹²C system atE _c.m.=19.3 MeV has been studied in the neutron and proton decay channels. From(p, γ), (n, p) and (n, γ) coincidence measurements high spin states could be localized inA=23 nuclei, in²³Mg up to possibly 21/2⁺. These states were resonantly populated. The present data favorJ ^π=17/2⁺ for the 9.61 MeV state in²³Mg and therefore also for the probable parent state at 9.81 MeV in²³Na. AJ ^π=12⁺ assignment to the resonance is supported and evidence was found that the resonant excitation of the lowest 15/2⁺ and 17/2⁺ states in mass 23 nuclei is caused by a change of the intrinsic structure of the Yrast levels aroundJ ^π=15/2⁺ towards larger deformation.     

Testing the single-state dominance in two-neutrino double-beta decay

The single-state-dominance hypothesis (SSDH) states that the decay rates of the two-neutrino double beta decay are governed by a virtual two-step transition connecting the initial and final ground states through the first 1⁺ state, 1 ₁ ⁺ , of the intermediate odd-odd nucleus, for those odd-odd nuclei where the 1 ₁ ⁺ state is the ground state. To investigate the validity the SSDH we have performed a systematical theoretical analysis of all known double-beta-decay transitions where the SSDH conditions are fulfilled. The analysis shows that the SSDH is realized either through a true dominance of the first intermediate 1⁺ state or by cancellations among the contributions of higher lying 1⁺ states of the intermediate nucleus.     

Structure of excited states in100Mo and102Mo from spectroscopy using18O induced reactions

The lifetimes have been determined for the 2⁺, 0^+～ and 4⁺ states in¹⁰⁰Mo and¹⁰²Mo using the recoil-distance Doppler-shift method. The states have been excited in¹⁰⁰Mo by Coulomb excitation and in¹⁰²Mo by the two-neutron transfer reaction induced by¹⁸O ions on a¹⁰⁰Mo target. The study of the excitation function for the elastic and inelastic scattering on the ground and first excited 2⁺ state in¹⁰⁰Mo at beam energies between 20 and 61 MeV shows that 40 MeV is the highest incident energy for pure Coulomb excitation. Above this energy nuclear absorption sets in and nuclear scattering contributes to the excitation of the 2⁺ state of¹⁰⁰Mo. From the lifetimes of the 2⁺ and 4⁺ states deformation parameters of ¦β¦= 0.21 and ¦β¦=0.31 for¹⁰⁰Mo and¹⁰²Mo respectively were deduced. The 0^+′ levels are not shape isomeric states, as suggested earlier, but they decay by enhancedE2 transitions to the first 2⁺ states. From a comparison with similar states in other transitional nuclei it is suggested that they are band heads forβ vibrational bands.     

Tensor features and dynamical deformation of the 24Mg(2+) nucleus in the reaction 24Mg(d,dγ)24Mg at E d = 15.3 MeV

The results obtained by reconstructing of the experimental angular dependences of polarization tensors, the tensors of orientation of multipole moments, and the dynamical deformation of ²⁴Mg nuclei produced in the 2⁺ state at 1.369 MeV in inelastic deuteron scattering on ²⁴Mg nuclei at E _d = 15.3 MeV for deuteron scattering angles between 25° and 165° in the laboratory frame are presented. The experimental results are compared with the results of calculations based on various versions of the coupled-channel method. The role of spin-orbit and tensor d ²⁴Mg interactions is discussed along with the influence of the reorientation effect. The correlation features of the 2⁺ state of the ²⁴Mg nucleus at 1.369 MeV that were determined in inelastic deuteron and alpha-particle scattering on ²⁴Mg are compared.     

Beta-delayed proton emission from heavy nuclei: (I). The observation of coincidences between protons and γ-rays

Coincidences have been detected between γ-rays and β-delayed protons emitted after the decay of very neutron-deficient nuclei. In the three cases studied the decay proceeds to the ground state with branches to the first excited (2⁺) state of the even daughter nucleus of (58±7) % (¹¹⁵Xe to 709 keV in ¹¹⁴Te), (14±3) % (¹¹⁷Xe to 679 keV in ¹¹⁶Te), and (50±10) % (¹⁸¹Hg to 158 keV in ¹⁸⁰Pt). Upper limits of 2 and 6 % can be placed on the branches to the 4⁺ states of ¹¹⁴Te and ¹⁸⁰Pt. For the cases of ^115,117Xe, coincidences with annihilation radiation were also observed; the measured positon/proton ratio determines the difference Q—B_p, between the energy available for electron capture and the proton separation energy for the daughter. For ¹¹⁵Xe the result is 6.20±0.13 MeV, for ¹¹⁷Xe 4.10±0.20 MeV.     

Nuclear Structure of 12,14Be Within Deformed Quasi-Particle Random Phase Approximation (DQRPA)

We developed a deformed quasi-particle random phase approximation (DQRPA) to describe the Gamow–Teller (GT) transitions on even–even neutron-rich nuclei. To describe deformed nuclei, we exploited the deformed axially symmetric Woods–Saxon potential, the deformed BCS, and the deformed QRPA with realistic two-body interaction calculated by Brueckner G-matrix based on Bonn CD potential. The deformed single particle states are expanded in terms of the spherical harmonic oscillator basis in order to take the realistic G-matrix stored in the spherical basis. We calculated GT strength distributions, B(GT), of two nuclei ^12,14Be for many different deformation parameter β ₂ values as a function of the excitation energy E _ex w.r.t. the ground state of a parent nucleus. Our results for ¹²Be predict to prefer a prolate shape and B(GT) results of ¹⁴Be turn out to be independent of the β ₂ values.     

Systematic study of the single-state dominance in 2νββ decay transitions

The single-state-dominance hypothesis (SSDH) states that the decay rates of the two-neutrino double-beta decay are governed by a virtual two-step transition connecting the initial and final ground states through the first 1⁺ state, 1_l⁺, of the intermediate odd-odd nucleus, for those odd-odd nuclei where the 1_l⁺ state is the ground state. To investigate the validity of the SSDH we have performed a systematical theoretical analysis of all known double-beta-decay transitions where the SSDH conditions are fulfilled. the calculations are based on the quasiparticle random-phase approximation (QRPA) and the results have been obtained by using realistic single-particle bases and realistic interactions. We have studied the double β⁻ decays of ¹⁰⁰Mo, ¹¹⁰Pd, ¹¹⁴Cd, ¹¹⁶Cd and ¹²⁸Te and the double electron-capture transitions in ¹⁰⁶Cd and ¹³⁶Ce. The analysis shows that the SSDH is realized either through a true dominance of the first intermediate 1⁺ state or by cancellations among the contributions of higher lying 1⁺ states of the intermediate nucleus.     

α decay properties of ~(297)Og within the two-potential approach

The α decay half-life of the unknown nucleus ~(297)Og is predicted within the two-potential approach, andα preformation probabilities of 64 odd-A nuclei in the region of proton numbers 82 Z 126 and neutron numbers 152 N 184, from ~(251)Cf to ~(295)Og, are extracted. In addition, based on the latest experimental data, a new set of parameters for α preformation probabilities considering the shell effect and proton-neutron interaction are obtained.The predicted α decay half-life of ~(297)Og is 0.16 ms within a factor of 4.97. The predicted spin and parity of the ground states for ~(269)Sg,~(285)Fl and ~(293)Lv are 3/2~+, 3/2~+ and 5/2~+, respectively.