Coupling of one and two quasiparticles to a Bohr-Mottelson core in195,196,197,198Hg

A new model for coupling the motion of particles to that of a quadrupole collective core with rotations andβ andγ vibrations is proposed. The Hamiltonian describing the core is obtained by quantising the classical Hamiltonian associated with the quadrupole degrees of freedom. The inertial parameters and the deformation energy surface are determined microscopically. The spherical shell model particles interacting among themselves by pairing are coupled to the core by aλ ²-pole (λ=0, 2, 4) potential. The theory is applied to^195–198Hg. The predicted results agree very well the experimental data. A comparison of the present model to the other formalism is also given.     

Shape evolution in <Superscript>76,78</Superscript>Kr nuclei at high spins in tilted axis cranking Hartree-Fock-Bogoliubov approach

A two-dimensional tilted axis cranking Hartree-Fock-Bogoliubov (CHFB) calculation is performed for ⁷⁶Kr and ⁷⁸Kr nuclei up to high spins J = 30 employing a pairing-plus-quadrupole (PPQ) model interaction Hamiltonian. Intricate details of the evolution of single particle structures and shapes as a function of spin have been investigated. The results show the existence of energy levels with high K quantum numbers lying close to the yrast line in both the nuclei. Such high K states should exhibit isomeric characteristics due to the K-selection rules for the γ-decays. Moreover, in ⁷⁸Kr a new band with J = 20–30 lying below the observed ground band is predicted.      

The yrast bands in 77Kr and 76Kr

High-spin states of both parities in ⁷⁷Kr have been studied in the reaction ⁶³Cu(¹⁶O, pn). On the basis of γγ- and nγ-coincidence experiments, we extended the yrast bands up to spin $\text{I}{}^{\mathrm{\pi }}\text{=}\text{25}\text{2}{}^{\mathrm{+}}$ and $\text{21}\text{2}$^t-. Doppler-shift attenuation and recoil-distance measurements have been performed for some fifteen states. In addition, lifetimes of some yrast states in ⁷⁶Kr have been determined in the reaction ⁶³Cu(¹⁶O, p2n). Transition energies and E2 strengths in ⁷⁶Kr have been interpreted with the IBA-2 and different collective and microscopic triaxial rotor models, those in ⁷⁷Kr with the triaxial rotor plus quasiparticle model.     

Microscopic study of yrast bands and backbending anomaly in 78-82Kr isotopes

The yrast spectra of ^78-82Kr are studied by using the projected shell model (PSM) approach. The energy states are obtained by taking oblate as well as prolate quadrupole deformations for ^78-82Kr. The structure of yrast states and backbending phenomena are investigated. The theoretical results predict low-lying states in ^{78, 82}Kr to be oblate and coexistence of oblate-prolate shapes for ⁸⁰Kr. The B(E2) transition probabilities and g-factors are obtained and compared with the available experimental data.     

Study of a fast collective mode in deep inelastic reactions: Quantal fluctuations

We have measured for the 430 MeV⁸⁶Kr+^92.98Mo systems the triple differential cross sectiond ³ σ/dEdAdZ (E=kinetic energy,A=mass andZ=atomic number) of the reaction products in the angular range (θ=25, 45°). We focussed attention on a fast collective mode in deep inelastic reactions: the neutron excess or charge equilibration. This mode is shown to relax very quickly to equilibrium within a time scale of the order of 10^?22s. It is shown that this collective degree of freedom exhibit a quantal behavior which can be seen in the observation of quantal fluctuations. The experimental results are discussed in terms of a simple equilibrium model. The giant dipole resonance of the composite system could be closely connected to this neutron excess mode.     

Properties of indium phosphite and selected compounds under irradiation with swift heavy ions

Surface and bulk properties of indium phosphate single crystals with initial and previously irradiated by 25 MeV electrons structures were irradiated with ⁸⁶Kr (253 MeV) and ¹⁹⁷Au (200 MeV) up to various fluences. The modern methods of condensed matter studies were used for research of InP property changes before and after irradiation as scanning (SEM) and high resolution transmission electronic microscopy (HTEM), Rutherford backscattering spectroscopy (RBS/C) and atomic force microscopy (AFM). The comparison of obtained results with the results of other authors is carried out. The surface structure change of InP single crystal irradiated by high-energy 86Kr ions and electrons is studied. It is shown the changes of the InP surface have complicated character and caused by inelastic sputtering processes. It is observed the twice irradiated layer swells with the cracks creation on the surface. The swelling with cracks and strong sputtering of twice irradiated by electrons and ions with high energy layers of the InP and GaAs surfaces are explained using the model based on the influence of ionizing energy loss of swift ⁸⁶Kr ions. The small crystalline objects are detected on the InP surface irradiated with ⁸⁶Kr ions which may be nano- and micro-crystals of InP. All obtained effects are discussed in frame of models based on ionizing energy loss of swift heavy ions.     

Level structure of 76Br from the 75As(α,3nγ) reaction

Hitherto unknown states of ⁷⁶Br were excited through the (α, 3nγ) reaction on ⁷⁵As at E_α = 30 to 55 MeV. Excitation functions, γ-ray angular distributions, γ-γ coincidences and the γ-ray emission time with respect to the beam bursts were determined. Levels above the 1^? ground state at energies (in keV) with the following spin-parity assignments are proposed: 141.8, 2; 253.7, 3^?; 491.8, 4; 584.9, 5^?; 1016.3, 6. These levels exhibit the energy spacings of a Coriolis-perturbed rotational band and the branching ratios show collective behavior. The comparison of these levels with those of the $\text{5}\text{2}$⁺ ground-state band recently reported in ⁷⁷Kr show that (a) the Coriolis effects are quite similar and (b) the first two excited levels lie very close in energy in both cases. The possibility that these two facts indicate the validity of the rotation aligned coupling scheme in a doubly odd system is discussed.     

Infrared spectra of the Kr—CO and Xe—CO van der Waals complexes

The infrared spectra of the weakly bound complexes Kr—CO and Xe—CO have been studied in the region of the CO stretching vibration (4.7 μm) using a high-resolution tuneable diode laser probe. The complexes were observed in a long path (200 m) low temperature (76 K) gas cell (Kr—CO) and in a pulsed supersonic jet expansion (Kr—CO and Xe—CO). Previous long path cell measurements on these complexes at lower resolution analysed only the K = 0 and 1 stacks of rotational levels in the ground intermolecular vibrational state. The new data extend up to K = 3 (Xe—CO) or 4 (Kr—CO), and also include K = 0 and 1 stacks in the excited bending state, ν₂ = 1. The bending frequencies for Kr—CO and Xe—CO (in the ν_co = 1 upper state) were determined to be 13.156cm_?1 and 13.794cm^?1, respectively. Detailed molecular parameters were determined to describe the rotational energy levels of each complex using a simple empirical Hamiltonian. These results enable parameters to be compared for the entire series of rare gas—carbon monoxide complexes, from He—CO to Xe—CO. Also they will guide the future development and evaluation of accurate intermolecular potential energy surfaces for Kr—CO and Xe—CO.     

Fissionlike exit channel in the 5.8 MeV/u84Kr on24Mg reaction

Fissionlike (FL) phenomena for systems around mass 100 have been shown previously interpretable in terms of dynamical fission. This appears to be dependent on the entrance channel mass asymmetry. We have studied the fissionlike exit channel in the⁸⁴Kr+²⁴Mg reaction atE(Kr)=5.8 MeV/u. This energy is just above the threshold of fission, so that a clear separation between the Deep Inelastic Component (DIG) and the FL one can be achieved. The bombarding energy corresponds to the same excitation energy in the composite system¹⁰⁸Cd (E ^*=101 MeV) as in the³²S (158 MeV) on⁷⁶Ge reaction we studied earlier and for which fusion-evaporation along with fission-like contributions were measured. The width of the FL distribution confirms the previously observed dependence with the mass asymmetry in the entrance channel which is consistent with the extra push model.     

Irreducible U(3) tensor interactions in the symplectic collective model

The potential V(β, γ) of the Bohr-Mottelson and symplectic collective models is expressed as a linear combination of U(3) irreducible tensor operators in the symplectic enveloping algebra. This many-body collective potential is then projected onto the symplectic two-body tensor operators. The projected two-body potential is shown to give results similar to the many-body potential in ²⁰Ne. Hence, in the symplectic shell model, one has obtained a collective model with two-body forces.     

Conductivity of irradiated Kapton in relation to energy loss of ions and electrons

Abstract

We have studied the effects of 2.5 MeV electron irradiation and ion (C, N, F, Si and Kr) bombardment on the electrical conductivity of a polyimide (Kapton-H) with ion energies ranging between 320 keV (N) and 1.25 GeV (Kr). In this wide range of situations we have tried to sort out the respective effects of nuclear and electronic excitation energy losses.

For all ion irradiation the conductivity is found to scale with the electronic excitation absorbed dose: i.e. a power law of conductivity versus absorbed dose with an exponent around 9 is observed. At a given absorbed dose (in Gray units) the efficiency of each ion to enhance conductivity is found to be proportional to the electronic energy loss; electrons are much less efficient than ions and thus collective excitations are required to achieve this process.

The nuclear energy loss can perhaps play some role at conductivities higher than 100 Ω^?1 m^?1, but its effects are negligible in the range explored here.     

Microscopic study of low-lying collective bands in77Kr

The structure of the collective bands in⁷⁷Kr is investigated within our deformed shell model (DSM) based on Hartree-Fock states. The different levels are classified into collective bands on the basis of their B(E2) values. The calculatedK = 5/2⁺ ground band agrees reasonably well with the experiment. An attempt has been made to study the structure of the 3-quasiparticle band based on large J state in this nucleus. The calculated collective bands, the B(E2), and B(M1) values are compared with available experimental data. The nature of alignments in the low-lying bands is also analyzed.     

Anomalous behaviour of transition probabilities in75Kr

Two collective bands of⁷⁵Kr have been extended up to spin 21/2 using the compound reactions⁶⁴Zn(¹⁴N,p2n)⁷⁵Kr and⁵⁰Cr(²⁸Si, 2pn)⁷⁵Kr. Spins and parities were assigned from neutron-gatedγ-ray angular distributions and excitation functions using the OSIRIS anti-Compton spectrometer. The bands are interpreted to be built on the well-deformed Nilsson states: [442] 5/2 and [301] 3/2. Energies for both bands and the order of magnitude of the mixing ratios in thef _5/2 band can be reproduced within the single-particle-plus-rotor model, while the experimentalQ(I→I?1)/Q(I→I?2) ratios, deduced from mixing ratios and branching ratios, exhibit large deviations by a factor 4 to 6 from theoretical values (which are around one). An explanation of this effect may be found by treating the two rotational bands each as a result of mixing between rotational bands of oblate and prolate states; thus explaining the large difference between B(E2,I→I?1) andB(E2, I →I?2) in the bands of⁷⁵Kr.     

Electron stimulated desorption of Xe,Kr, and Ar

Electron stimulated desorption cross sections have been measured for Xe, Kr, and Ar overlayers on the Ag(111) surface. The Xe cross section is less than 10^?4 Ų; the Kr cross section is strongly temperature dependent, rising from 0.1 Ų at 10 K to 0.18 Ų at 50 K; the Ar cross section is 4 Ų and temperature independent. These results are rationalized using a model of the stimulated desorption similar to that proposed by Antoniewicz [Phys. Rev. B21 (1980) 3811], in which an atom is ionized by the incident beam, accelerates towards its image and is neutralized, desorbing only if the kinetic energy gained is greater than the neutral atom binding energy at the neutralization position. Fitting these data requires an exceedingly rapid dependence of the neutralization on distance for these slow ions. Rather than the effect of the mass on the ion velocity, the most important effect in determining the diverse behavior of the different gases is that the equilibrium position for the heavier gases is farther up the overlap repulsive potential and so in a region of more rapid neutralization. The model identifies several contributions to the isotope effect, predicting it to be temperature dependent. The results are extremely sensitive to the anharmonicity of the holding potential.     

Der Zerfall des77Kr

⁷⁷Kr (T _1/2=1.2 h) was produced by bombarding⁷⁶Se with 48 MeV-α-particles. After irradiation the radioactive⁷⁷Kr gas was collected in glass ampoules filled with charcoal and cooled by liquid air. The decay of⁷⁷Kr has been investigated using Ge(Li)-counters and a Ge(Li)-Ge(Li)-coincidence circuit. 27 γ-transitions, 13 of them unknown up to the present, have been found and their relative intensities have been determined. A level scheme for⁷⁷Kr→⁷⁷Br having 14 levels is proposed. This accounts for all the observed γ-transitions.