Xe Nuclei Research Articles

Triaxial rotor plus particle description of negative-parity states in proton-odd Cs nuclides

Excitation energies and branching ratios in 125,127,129Cs from recent Stony Brook experiments are reproduced by triaxial-rotor-plus-particle calculations. In particular the signature splitting between favored and unfavored yrast states can be reproduced, allowing the γ deformation to be determined. A systematics of deformation parameters (ϵ, γ) is given and compared with values for the neighboring even-even and neutron-odd Xe and Ba nuclei. Core wave functions are discussed, and differences with respect to the neutron-odd Xe, Ba nuclei are examined.

Octupole excitations in light xenon and barium nuclei.

The properties of light even and odd Xe and Ba nuclei (N and Z close to 56) with respect to octupole deformation have been studied by the Hartree-Fock+BCS and the generator coordinate methods. None of the considered nuclei possess a stable static octupole deformation. However, we find that octupole collectivity is enhanced by dynamical correlations. Cranked shell model calculations indicate that octupole effects should persist at least up to spins around 10\ensuremath{\Elzxh}.

Theoretical description of octupole correlations in the 138-148Xe nuclei.

The Gogny force is used to study, in the framework of the mean field theory and the collective Hamiltonian method, the octupole correlations present in the [sup 138--148]Xe nuclei. The energy splittings between the ground state and the lowest-lying negative parity state are computed as well as the [ital B]([ital E]1) and [ital B]([ital E]3) transition probabilities. A peculiar behavior of the [ital B]([ital E]1)'s as a function of neutron number is predicted.

Systematics of triaxial deformation in Xe, Ba, and Ce nuclei.

The ([beta],[gamma]) deformation parameters of even-even Xe, Ba, and Ce nuclei have been calculated by using the triaxial rotor model. Deformation parameters calculated, on one hand, from decay properties and, on the other hand, from energies are in good agreement. The smooth dependence of the deformation parameters on [ital Z] and [ital N] is discussed. The results are compared with those extracted from properties of odd-[ital A] nuclei.

Observation of subthreshold double strangeness production in [formula omitted] annihilations on Xe nuclei; search for stable H dibaryon

The double strangeness production has been observed in two final states of annihilation of antiprotons at momentum less than 0.9 GeV/ c on Xe nuclei: K + K + X (8 events) and K + K 0 ΛX (6 events). The probabilities of the reaction pXe → K +K +X vary from 2 · 10 −5 (at rest) up to 7 · 10 −5 (in flight). The reaction pXe → K +K 0ΛX is observed only in flight with probability 3 · 10 −4. The properties of the observed reactions are similar to those resulting from the cascade process with production of Ξ hyperon: pN → K ∗−K ∗, K ∗ → Kπ, −K ∗N → ΞK, ΞN → ΛΛ . The new upper limit on the production probability of the stable H( S = −2) dibaryon in the reaction Xe → K +K +H(H → Σ − p)X was obtained to be < 2 · 10 − (90% C. L.).

Octupole shapes and shape changes at high spins in the Z

The shapes of rotating Xe, Ba, Ce, Nd, and Sm nuclei (84\ensuremath{\le}N\ensuremath{\le}94) are calculated using the cranking model with the Woods-Saxon average potential and pairing. The lightest isotopes of Xe and Ba have nearly spherical ground states, but develop octupole and quadrupole deformations under rotation which remain up to very high spins. The ground states of the heavier isotopes have octupole and quadrupole deformations which persist up to medium spins (I\ensuremath{\approxeq}12\ensuremath{\Elzxh}). At higher spins, a shape transition is predicted to reflection-symmetric aligned many-quasiparticle configurations.

Orbital rotational vibrations in the A=130 mass region.

The rotational vibrations (${\mathit{K}}^{\mathrm{\ensuremath{\pi}}}$=${1}^{+}$ states) in 16 even-even Xe, Ba, and Ce nuclei are studied in the quasiparticle random-phase approximation with a mean field given by a deformed Woods-Saxon potential and residual forces: a self-consistent quadrupole-quadrupole interaction, a spin-spin interaction, and a force that restores the rotational invariance of the Hamiltonian. A shell effect is found which is typical for this mass region: a strong orbital character of almost all low-energy (2.5--5 MeV) excitations, while the higher-energy ones are predominantly spin flip. The comparison of random-phase approximation M1 transition densities and (e,e') form factors with the microscopic realization of the two-rotor model ${1}^{+}$ state allow us to conclude that the strongly orbital low-energy random-phase approximation states perform the scissor-type motion described by the two-rotor model, but only few particles are involved in this motion.

Triaxiality in the proton-neutron interacting boson model: Perturbed O(6) symmetry with application to the mass A

In the present article, we discuss the Xe and Ba nuclei in the A\ensuremath{\simeq}130 mass region. This mass region has been shown to constitute a new region of O(6)-like nuclei. A number of deviations, however, from a pure O(6) dynamical symmetry are experimentally observed, in particular the energy staggering in the gamma band. Here, we study the influence of triaxial perturbations, i.e., introducing terms in the Hamiltonian that are of ${\mathrm{SU}}^{\mathrm{*}}$(3) type, on the energy spectra of the $^{124\mathrm{\ensuremath{-}}130}\mathrm{Xe}$ and of the $^{128\mathrm{\ensuremath{-}}134}\mathrm{Ba}$ nuclei. We also address the problem of B(E2) transitions, connecting the ${2}_{\ensuremath{\gamma}}^{+}$, ${3}_{\ensuremath{\gamma}}^{+}$, ${4}_{\ensuremath{\gamma}}^{+}$, ${5}_{\ensuremath{\gamma}}^{+}$, and ${0}_{3}^{+}$ levels to the ground state and the gamma band.

Decay study of the117Cs and117Xe nuclei

Gamma rays and conversion electrons emitted in the 117Cs and 117Xe decays have been studied from on-line mass-separated 117Cs sources at the ISOLDE facility. A new 117Xe decay scheme has been constructed and a level scheme has been established for the 117Cs decay. The results are discussed in the framework of the recent understanding of the odd-mass neutron-deficient I and Xe systematics.

Breakdown of the Z = 64 shell gap below N = 82

The systematic behavior of 2 1 + and 4 1 + state energies in GdXe nuclei, below the neutron N = 82 shell gap, are examined in terms of the product of numbers of valence proton and neutron particles, N p N n. To produce a smooth dependence of these spectroscopic quantities as functions of N p N n, requires that the Z = 64 shell gap disappears for neutron numbers less than, or approximately equal to, N = 78.

Effect of the Pauli principle on collective states in transitional Xe, Ba and Ce nuclei

It is shown how the modified harmonic method can be used to correct the quadrupole operator of the interacting boson model for the effect of the Pauli principle on states with several d-bosons. This gives a possible explanation for the observed strange reduction of ground-state band B(E2) values in the xenon-barium region.

On the difference of the dynamic moment of inertia [formula omitted]band(2) for Xe and Ba nuclei

The γ-rays following the 112, 117, 122Sn + 12C and 123Sb + 12C reactions have been investigated using six NaI(Tl) detectors in a two-dimensional arrangement. The γ-ray multiplicities have been measured and the dynamic moments of inertia I band (2) of 118, 122Xe and 128, 130Ba extracted from the energy-correlation spectra. The behaviour of these nuclei and the observed difference of I band (2) in Xe and Ba nuclei are interpreted in terms of high-spin collective properties.

High-spin states in even-mass Xe nuclei and backbending phenomena

High-spin states in 122, 124, 126, 128, 130Xe have been studied by in-beam γ-ray spectroscopy. The 10 + and 12 + levels were observed in every isotope of 122–130Xe. In 126Xe, the second 10 + level was assigned near the first 10 + level, and the 14 + level was also identified. Backbending phenomena in the yrast bands were observed systematically in 122–130Xe. These phenomena are explained by the mechanism of the quasi-ground band crossing another quasi-band with a v( h 11 2 ) 2 configuration. The reduction of B(E2; 10 + → 8 +) in 130Xe confirms this interpretation.

Cosmic-ray abundances of Sn, Te, Xe, and BA nuclei measured on HEAO 3

Elements with even atomic number ( Z) in the interval 50 ~ Z ~ 56 have been resolved in the cosmic radiation using the Heavy Nuclei Experiment on the HEAO 3 satellite. The observation that 50Sn and 56Ba are more abundant than 52Te Elements with even atomic number ( Z) in the interval 50 ~ Z ~ 56 have been resolved in the cosmic radiation using the Heavy Nuclei Experiment on the HEAO 3 satellite. The observation that 50Sn and 56Ba are more abundant than 52Te and 54Xe is inconsistent with a purer-process cosmic-ray source. Adjustment of source abundances for an enhancement of those elements with a low first ionization potential does not change this conclusion and 54Xe is inconsistent with a purer-process cosmic-ray source. Adjustment of source abundances for an enhancement of those elements with a low first ionization potential does not change this conclusion.

Level structure in 123Xe

The level structure of 123Xe has been studied with the 122Te( 3He, 2n) and 123Te( 3He, 3n) reactions using in-beam γ-ray spectroscopic methods. Band-like level structures based on the unique-parity h 11 2 neutron state and different low- j states are observed. The isomeric state proposed earlier is established at 185.4 keV with a half-life of 5.6 ± 0.3 μs, and a new spin assignment of 7 2 − is proposed for this level. A triaxial-rotor-model calculation has been performed to interprete the negative-parity level system. Because of the 7 2 − state, we do not obtain a consistent description of the negative-parity states with the triaxial rotor model, unlike the heavier odd- A Xe nuclei. On the other hand, the positive-parity level structures are interpreted in terms of the core-quasiparticle model supposing a vibrational core. This indicates different core shapes for the positive- and negative-parity level systems.

In-beam study of 127, 129Xe and collective description of the level structures in odd- A Xe nuclei

The levels in 127Xe have been studied with the 126Te( 3He, 2n) and 128Te( 3He, 4n) reactions and in 129Xe with the 130Te( 3He, 4n) and 126Te(α, n) reactions using enriched Te targets and inbeam γ-ray and conversion-electron spectroscopic methods. In addition to the h 11 2 level structures, positive-parity bands based on different low- j; states were observed in both nuclei. The observed g 7 2 band head at 342.2 keV in 127Xe is an isomeric state with a half-life of 37 ± 3 ns. Both triaxial-rotor and core-plus-quasiparticle model calculations have been carried out to explain the observed band structures in 123–129Xe. The calculations indicate different shapes for the positive- and negative-parity level systems.

Band structure in neutron-deficientXe117,119,121nuclei

Collective features of odd-N /sup 117,119,121/Xe have been investigated via /sup 106,110/Cd(/sup 14/N,p2n)/sup 117,121/Xe and /sup 106/Cd(/sup 16/O,2pn)/sup 119/Xe reactions. In-beam ..gamma..-ray excitation, ..gamma..-..gamma.. coincidence, and ..gamma..-W(theta) measurements were performed to establish decay schemes, ..gamma..-ray multipolarities, and J/sup ..pi../ assignments. Strong ..delta..J=2 band structures, associated with the 1h/sub 11/2/ quasi-neutron band, were observed on 11/2/sup -/ states in the /sup 117,119,121/Xe nuclei. The unfavored ..delta..J=2 sidebands, which crossover in energy at the N=64 subshell (/sup 119/Xe core), were weakly observed down to the 9/2/sup -/ member in all three nuclei. Systematics of these 1h/sub 11/2/ band structures in odd-Xe nuclei are presented and discussed in terms of the current theoretical models. A second collective feature, a ..delta..J=1 band structure built on 1g/sub 7/2/ quasi-neutron-hole states, was observed in the /sup 119,121/Xe nuclei.

The decay of127Cs

The gamma rays emitted in the decay of 6.2 h 127Cs to levels in 127Xe have been studied in singles and coincidence with Ge(Li) detectors. A decay scheme for 127Cs has been constructed on the basis of the results of these measurements. The resulting level scheme for 127Xe is discussed in the light of present knowledge of the level schemes of the other odd-mass Xe nuclei and the results of nuclear model calculations.

Quasi-gamma bands in even-mass Xe AND Ba nuclei

Abstract Low-lying excited states of 124,126 Xe and 132 Ba have been studied by means of in-beam γ-ray spectroscopy in (p, x n y ) reactions. Excitation functions, angular distributions and γ-γ coincidence spectra were obtained. The 2 2 + , 3 + , 4 2 + and 5 + levels were observed at the following excitation energies in keV: 846.4(2 2 + ), 1247.5(3 + ), 1437.3 (4 2 + ), 1836.6(5 + ) in 124 Xe, 879.7(2 2 + ), 1317.3(3 + ), 1488.2(4 2 + ), 1903.1(5 + ) in 126 Xe and 1032.1(2 2 + ), 1511.3(3 + ), 1729.9(4 2 + ) in 132 Ba. The 2214.3 and 2561.7 keV levels in 126 Xe were tentatively assigned as the 6 2 + and 7 + levels, respectively. These 2 2 + , 3 + , 4 2 + , 5 + , 6 2 + and 7 + levels are interpreted as members of a quasi-γ band. The E2/M1 mixing ratios of the 2 2 + → 2 1 + transitions in 124,126 Xe and 132 Ba were obtained as + 6.3 +5.3 −2.0 + 10.8 7.8 −3.2 and + 8.3 +4.9 −2.2 , respectively.

High-spin states in odd Xe nuclei

Levels of odd Xe isotopes ( A = 125–129) have been studied in Te (α, 3n) reactions. Measurements of γ-ray intensities, angular distributions and excitation functions have been made. The level structure of high-spin states in Xe isotopes is discussed.