Constraints on the universe as a numerical simulation

The level scheme above the proton threshold in ²⁶Si is crucial for evaluating the ²⁵Al(p, γ)²⁶Si stellar reaction, which is important for understanding the astrophysical origin of the long-lived cosmic radioactivity ²⁶Al(T _1/2 = 7.17 × 10⁵ y) in the Galaxy. The excited states in ²⁶Si have been studied using an in-beam γ-ray spectroscopy technique with the ²⁴Mg(³He, nγ)²⁶Si reaction. γ-rays with energies up to 4.6 MeV emitted from excited states in ²⁶Si have been measured using large volume HPGe detectors. The spin-parity of one of the most important states reported recently at 5890.0keV has been assigned as 0⁺ by γ-γ angular correlation measurements in this work.     

Gamma deexcitation of the 180m Ta isomer

Vibrational states built on the K ^π = 9^? isomer and on the ground state (K ^π = 1⁺) in ¹⁸⁰Ta are calculated within the quasiparticle-phonon nuclear model using the ¹⁷⁸Hf nucleus as a core. A procedure for calculating the rates of K-allowed γ-ray transitions from vibrational states built on the isomer to those built on the ground state is presented. The probabilities of two-step processes consisting of a dipole excitation of the isomer and successive E1 and E2 transitions from them to vibrational states built on the ground state of the ¹⁸⁰Ta nucleus are calculated. Two-step transitions from the isomer to vibrational states below 2.7 MeV and to the vibrational states built on the ground state appear to be very weak. There are many E1 transitions from the vibrational states built on the isomer to the vibrational states built on the ground state. They are weak and cannot be responsible for the strong deexcitation of ^180m Ta in the relevant (γ, γ′) reaction. A decisive role is played by collective E2 transitions from dipole excitations in several excitation energy intervals ranging between 2.7 and 4.0 MeV. These highly intense K-allowed two-step γ-ray transitions can be responsible for the strong deexcitation of the ^180m Ta state in the (γ, γ′) reactions.     

Spectroscopy of highly excited states in29Si

Particleγ-ray coincidences have been measured in the²⁸Si (d,pγ) reaction at 6.5 and 7 MeV bombarding energy, in the²⁶Mg (α,nγ) reaction at 12, 14 and 15 MeV, and in the²⁷A1 (τ,pγ) reaction at 9 MeV. Theγ-decay has been observed for all bound states of²⁹Si and for 56 unbound states up to 12,960 KeV excitation energy. Particleγ-ray angular correlations were measured in the²⁸Si (d,pγ) reaction at 6.5 MeV and in the²⁶Mg (α,nγ) reaction at 12 MeV. Spin (-parity) assignments or restrictions were obtained for nearly all bound states and some high-spin states above the binding energy. The assignment of mirror levels in²⁹Si and²⁹P has been extended to 8.2 MeV excitation energy. The excitation energies of 41 positive-parity states are reproduced by shell model calculations. The possible existence of aK ^π=5/2⁺ band with prolate deformation is discussed.     

Ab initio calculation of the spin-rotation constant for 2Π diatomics: Test of the Van Vleck approximation

Ab initio calculations are carried out to determine γ^Π (true), the first-order contribution to the spin-rotation constant, γ^Π, for the X²Π ground states of OH, HF⁺, and HCl⁺ and their deuterated analogs. These calculations demonstrate that the contribution of this term to the experimentally determined value of γ^Π is small, as has been previously conjectured. Furthermore, it is found in the cases under study that the Van Vleck approximation to γ^Π (true) significantly overestimates its importance, and a more realistic approximation is presented.     

Gamma decay of the giant dipole resonance and feeding of superdeformed states in 143Eu

The γ decay of the giant dipole resonance (GDR) built on excited nuclear states has been measured in coincidence with the low-energy γ discrete transitions for the nucleus ¹⁴³Eu. The reaction used was ¹¹⁰Pd(³⁷Cl, 4n)¹⁴³Eu at a beam energy of 165 MeV. The EUROBALL spectrometer (for the measurement of discrete γ transitions) coupled with the HECTOR array (for high-energy γ-ray detection) has been used. The high-energy γ-ray spectrum in coincidence with superdeformed (SD) discrete transitions of ¹⁴³Eu shows an “excess” between 9–12 MeV if compared with the one associated to cascades which do not pass through the SD configurations. Such an “excess” is in the energy region where one expects the low-energy component of the GDR strength function built on a SD state. The measured intensity can be reproduced by the statistical model assuming that the superdeformation survives only few MeV above the yrast line. A similar and consistent scenario has also been obtained by comparing the high-energy γ-ray spectra of ¹⁴³Eu in coincidence with its spherical (which is fed by the SD configuration) and its triaxial configuration (which is bypassed by the decay of the SD states).     

On the influence of the atomic electrons on theγ-decay of U-235m

Theγ-decay probability is represented by a perturbation expansion, the higher-order correction terms implying manifold multiple-interactions between nucleus and electromagnetic field, but also between field and atomic electrons (virtual intermediate processes). The energy conservation applies only to the initial and final states of the system nucleus/field/electrons, thus the virtual processes may be resonant and nonresonant. As regards the virtual intermediate processes for theγ-decay, the present paper includes generalized virtual internal conversion (IC) processes together with theγ-quantum emission by virtual electron transitions. The intermediate electron states belong to the continuous as well as to the discrete spectrum. By reason of the extraordinarily favoured real IC of U-235m (73 eV; E3) the corrections mentioned yield contributions to theγ-decay constant to such a degree (factor 1.5×10⁵) that theγ-decay takes place essentially owing to the mere presence of the atomic electrons. Therefore the IC coefficient amounts to 3.2×10¹⁵ instead of 4.8×10²⁰ in usual approximation.     

Main channels of the decay of the giant dipole resonance in the 20,22Ne nuclei and isospin splitting of the giant dipole resonance in the 22Ne nucleus

Data published in the literature on various photonuclear reactions for the ^20,22Ne isotopes and for their natural mixture are analyzed with the aim of exploring special features of the decay of giant-dipole-resonance states in these two isotopes. With the aid of data on the abundances of the isotopes and on the energy reaction thresholds, the cross sections for the reactions ^20,22Ne[(γ, n)+(γ, np)] and ^20,22Ne[(γ, p)+(γ, np)] are broken down into the contributions from the one-nucleon reactions (γ, n) and (γ, p) and the contributions from the reactions (γ, np). The cross sections for the reactions ^20,22Ne(γ, n)^19,21Ne and ^20,22Ne(γ, p)^19,21F in the energy range E _γ=16.0–28.0 MeV and the cross sections for the reactions ^20,22Ne(γ, np)^18,20F in the energy range E _γ=23.3–28.0 MeV are estimated. The behavior of the cross-section ratio r=σ(γ, p)/σ(γ, n) for the ²²Ne nucleus as a function of energy is analyzed, and the isospin components of the giant dipole resonance in the ²²Ne nucleus are identified. The contributions of the isospin components of the giant dipole resonance in the ²²Ne nucleus to the cross sections for various photonuclear reactions are determined on the basis of an analysis of the diagram of the excitation and decay of pure isospin states in the ²²Ne nucleus and in nuclei neighboring it, which are members of the corresponding isospin multiplets. The isospin splitting of the giant dipole resonance and the ratio of the intensities of the isospin components are determined to be ΔE=4.57±0.69 MeV and R=0.24±0.04, respectively.     

Gammadecay of quasimolecular resonances in the12C+12C system

We have studied the heavy-ion radiative capture reaction¹²C(¹²C,γ)²⁴Mg forE _cm =4.7–6.0 MeV. Transitions to the ground-, first and unresolved second and third excited states in the final nucleus²⁴Mg have been observed with cross sections as low as 1 nb/sr. Forγ ₁ two strong resonance-like structures at 4.9 and 5.0 MeV were found correlated in energy with established 2⁺ resonances. Statistical model calculations cannot account for the observed yield. The branching ratioΓ _γ /Γ associated with theγ ₁ decay channel of the 5 MeV resonance was estimated to be 1.1·10^?5 yielding aγ-ray strength of 0.8 eV. The experimental result is in agreement with calculations based on the generator coordinate method where broad barrier resonances are viewed as short lived states of quasimolecular nature.     

High-spin levels in137,139Ce and139,141Nd evidence for hole-core coupling

Excited states of the¹³⁷Ce,¹³⁹Ce,¹³⁹Nd and¹⁴¹Nd nuclei have been studied using the¹³⁸Ba(α, 5nγ)¹³⁷Ce,¹³⁸Ba(³He, 4nγ)¹³⁷Ce,¹³⁸Ba(α, 3nγ)¹³⁹Ce,¹⁴⁰Ce(α, 5nγ)¹³⁹Nd,¹⁴⁰Ce(³He,4nγ)¹³⁹Nd,¹⁴⁰Ce(α, 3nγ)¹⁴¹Nd and¹⁴²Ce(α, 5nγ)¹⁴¹Nd reactions. Singlesγ-ray spectra,γ —γ coincidence spectra, angular distributions and time distributions ofγ-rays with respect to beam pulses have been measured. Gamma transitions between excited states with spin values up to 21/2, 23/2 or 25/2 have been observed. Isomeric states with T_1/2=70 ns have been observed in¹³⁹Ce at 2631.5 keV (19/2) and in¹⁴¹Nd probably at 2952.0 keV (19/2). The level structure observed in the nuclei studied can be explained if the neutron-holes are coupled to the doubly even core excitations. The coupling of theh _11/2 neutron-hole with the 2⁺, 4⁺ and 3^? collective excitations are calculated in terms of the weak and intermediate coupling models. The intermediate coupling results seem to be in better agreement with the experimental data. The energies of theree-particle states, being the result of the coupling of theh _11/2 neutron-hole with the two-proton excitations in the core, are well reproduced in the calculations when empirical values of the two-body interaction matrix elements were used.     

Low-spin states of153Gd observed in the decay of153Tb

Level structure of the 89-neutron nucleus¹⁵³Gd has been investigated by studying theEC-decay of isotope-separated¹⁵³Tb sources with several semiconductor detectors. In addition to singles gamma and electron spectra,γ-γ ande ^?-γ coincidences were investigated by using Ge(Li) and Si(Li) spectrometers and a high-capacity two-parameter recording system. In all, 191γ-rays are assigned to the decay of the 2.4d¹⁵³Tb. The proposed level scheme of¹⁵³Gd containing most of the observed transitions shows a very high density of low-spin states (45 states below 1.5MeV). Spin and/or parity assignments based mainly on coincidence data and measured transition multipolarities are proposed for a majority of these states. Nilsson model classifications of some levels are discussed. On the basis of logf t values the spin and parity of the ground state of¹⁵³Tb are suggested to be 3/2⁺ or 5/2⁺.     

Fragmentation of the yrast band in186Os atI π =18+ and disappearance of the collective minimum

High-spin states in¹⁸⁶Os have been populated by the¹⁸⁶W(⁴He,4n)-reaction at 55MeV. The emittedγ-radiation was detected with the OSIRIS spectrometer. The yrast band, for which the nucleus has a prolate shape, was found to terminate atI ^π =18⁺. Theγ-ray intensity is then distributed between several irregular sequences. Different to other cases of band termination, the minimum in the total routhian surface corresponding to a collective shape is calculated to disappear in this spin region, although the available spin of the valence nucleons is far from being exhausted. A different structure, which is dominated by non-collective states becomes yrast.     

Structure of the doubly odd nucleus 180Ta: Description of 23 bands

The structure of the doubly-odd nucleus ¹⁸⁰Ta has been studied by γ–γ coincidence measurements with a DC beam at 52 and 57 MeV and time-correlated γ–γ coincidence measurements with a pulsed beam at 55 MeV via the ¹⁷⁶Yb(¹¹B, α3n)¹⁸⁰Ta reaction. In all measurements, γ-rays were detected in coincidence with charged particles. In the time-correlated γ–γ coincidence measurements with a pulsed ¹¹B beam, three rotational bands and one octupole vibrational band have been identified above the I^π=15⁻ T_1/2=30 μs isomer. The configuration of three bands built on 8⁺ states has been discussed by means of three-band mixing calculations. BCS calculations with blocking have been used in support of configuration assignment of four- and six-quasiparticle structures. Totally, 19 rotational bands, one β-, one γ- and two octupole-vibrational bands, plus one intrinsic state have been identified with two-, four- and six-quasiparticle configurations. The K values of these bands range from 0 to 19. The K-forbidden transition rates are discussed on the basis of mixing between states with widely different K-values. The BBCS calculations predict a K^π=22⁻ isomer not identified experimentally in this nor in previous works.A search for specific intermediate states which could explain the transformation from K^π=9⁻ to 1⁺ during the astrophysical s- and r- processes was negative.     

Low-lying excited states of106Ag studied with the103Rh (α,nγ)106Ag and104Pd (α,pnγ)106Ag Reactions

The level scheme of¹⁰⁶Ag has been studied using the¹⁰³Rh(α,nγ)¹⁰⁶Ag and¹⁰⁴Pd(α,pnγ)¹⁰⁶Ag Reactions. The experimental information is taken fromγ-ray coincidence data using Ge(Li)-Ge(Li) and HPGe-planar Ge(Li) configurations andγ-ray angular distributions. With these measurements 126 γ rays have been assigned to¹⁰⁶Ag with 116 deexciting 78 states below 2.26 MeV in excitation. The location of the 8.4-day 6⁺ isomer is established at 89.63±0.09 keV. Many of the low-lying states are interpreted in terms of a slightly deformed rotor model.     

Heavy-ion in-beam studies of the nucleus87Nb

High spin states in the transitional nucleus⁸⁷Nb up to 14 MeV excitation have been established for the first time via the reactions⁴⁰Ca(⁵⁰Cr, 3p)⁸⁷Nb and⁵⁸Ni (³²S, 3p)⁸⁷Nb. The⁸⁷Nbγ-radiations have been identified throughγ-ray spectra taken in coincidence with the evaporation residues detected in the Daresbury recoil separator or with multiple proton emission. Gamma-gamma coincidences, DCO ratios,γ-ray angular distributions and lifetimes have been measured. A total of some 100 transitions have been placed into a level scheme comprising of sixty states. The one-quasiparticle (1qp) bands of either parity and several other band-like structures have been identified, some containing alignedg _9/2 nucleons. Moderately enhancedE2 in-band transitions of 13–48 W.u. as well as several weakE2 yrast transitions connecting bands with different quasiparticle numbers have been found. Similarities with respect to theN=46 isotones⁸³Rb,⁸⁴Sr,⁸⁵Y,⁸⁶Zr and⁸⁸Mo are discussed.     

In-beam study of 102Sn

Excited states in ¹⁰²Sn have been identified for the first time, in an in-beam γ-ray spectroscopic experiment. Two γ-ray transitions with energies 1472 and 497 keV following the decay of the seniority 6⁺ isomer with t_1/2 = 1.0(5) μs were unambiguously assigned to ¹⁰²Sn. Due to the very low cross section of about 2 μb for producing ¹⁰²Sn in the reaction ⁵⁰Cr(⁵⁸Ni,1α2n), a highly selective detector setup utilizing NORDBALL ancillary detectors and a recoil catcher device was used. High γ-ray detection efficiency was achieved with two EUROBALL Ge cluster detectors.     

A comparative study of the electric giant dipole resonance of 24−26Mg

The electric giant dipole resonance of ^24?26Mg has been explored up to 30 MeV excitation energy with bremsstrahlung. ΔE, E spectra of charged photo-particles and spectra of prompt deexcitation γ-rays from excited residual nuclear states were obtained at various bremsstrahlung endpoint energies. The ²⁵Mg(γ, p₀), (γ, d), ^24,25Mg(γ, α) differential cross sections as well as ^24?26Mg(γ, xγ′) integrated cross sections are presented. The results are discussed in terms of one-particle, one-hole excitations and isospin composition of giant resonance states. A comparison with calculations for ²⁴Mg gives poor agreement. Excitations from deeper shells were found in the giant dipole resonance of ²⁴Mg, but do not seem to be concentrated at higher energies. In ²⁵Mg, only weak excitations of this kind were found, and they are completely absent in ²⁶Mg.     

High-spin states in the single-closed-shell nucleus 142Nd

The excited states of ¹⁴²₆₀Nd₈₂ have been studied using the ¹⁴⁰Ce(α, 2nγ)¹⁴²Nd and ¹⁴²Ce(α, 4γ)¹⁴²Nd reactions. Singles γ-ray, γ-γ coincidence spectra and angular distributions of γ-rays with respect to the beam direction have been measured. Excited states up to 6.7 MeV with spin values up to 14 are populated. The energy spacings between the lower excited states with spin values up to 8 are similar to those found in the lighter N = 82, even-Z isotones. The majority of the observed states with spin values up to 10 can be explained as two-quasiparticle states. Several of the highest-spin states can be explained qualitatively as fourquasiparticle states. Strong population of the highest excited states (at about 5.7 MeV) is noted, like in other N = 82 isotones. The observed levels in ¹⁴²Nd are compared with the shell model predictions using a simple δ-force interaction between two nucleons.     

Isospin mixing in the electric-dipole He(γ, n) and He(γ, p) reactions

Possible isospin mixing of the J^π = 1⁻ excited states of ⁴He leading to sizable differences in the ⁴He(γ, n)³He and⁴He(γ, p)³H cross sections in the giant-resonance region is examined in a bound-state approximation. Results indicate that the general features of certain experimental data can be accounted for by the presence of Coulomb mixing of the (S = 1, T = 0) and (S = 1, T = 1) states in addition to the usual spin-orbit mixing of the (S = 0, T = 1) and (S = 1, T = 1) states.     

In-beamγ-ray spectroscopy of102In

Neutron deficient nuclei close to ¹⁰⁰Snhave been investigated in-beam by γ-ray spectroscopic methods using the NORDBALL detector array. A beam of 270 MeV ⁵⁸Niwas used to bombard a target of ⁵⁴Fe.Reaction channel separation was achieved with a 4π charged particle multidetector setup together with a 1π neutron detector wall placed in the forward direction. Excited states of ¹⁰²Inwere identified for the first time. The level scheme constructed from γ-γ-particle-coincidence and γ-γ-angular correlation analysis is presented. The structure of ¹⁰² In is discussed and compared to neighboring nuclei in the framework of the nuclear shell-model.