Production of Kr2+ in collisions of rare gas ions with Kr

Total and differential cross sections for the production of fast Kr²⁺ ions in collisions of He⁺, Ne⁺ and Ar⁺ with Kr were measured at primary energies below 500 eV. In the system Ar⁺+Kr most of these reactions occur in close collisions and are accompanied by a large momentum transfer. For Ne⁺+ Kr collisions the angular distribution in the centre of mass system is approximately isotropic over a wide angular range. The cross section values for the Kr²⁺ production amount to 1% of the total charge transfer cross section in the investigated energy range.     

Fragment distribution in ~(78,86)Kr+~(181)Ta reactions

Within the framework of the isospin-dependent quantum molecular dynamics model, along with the GEMINI model, the ~(86)Kr+~(181)Ta reaction at 80, 120 and 160 MeV/nucleon and the ~(78)Kr+~(181)Ta reaction at 160 MeV/nucleon are studied, and the production cross sections of the generated fragments are calculated. More intermediate and large mass fragments can be produced in the reactions with a large range of impact parameter. The production cross sections of nuclei such as the isotopes of Si and P generally decrease with increasing incident energy.Isotopes near the neutron drip line are produced more in the neutron-rich system ~(86)Kr+~(181)Ta.     

Sampling measurement of soft-x-ray-pulse shapes by femtosecond sequential ionization of Kr+ in an intense laser field

We propose a sampling technique for measuring the shape of ultrashort soft-x-ray pulses. The technique uses the transient state of Kr+ ions that is produced by the femtosecond sequential evolution of Kr ions during optical-field-induced ionization as an ultrafast x-ray-absorption sampling gate. We demonstrate the technique by measuring the pulse shape of the 51st harmonic (15.6 nm) generated by a 100-fs titanium:sapphire laser pulse. The measured pulse duration is 220 fs. Our experimental result confirms that the sequential evolution of Kr+ ions from neutral Kr to Kr2+ is the dominant contribution to the ionization process from the aspect of time-domain measurement.     

Electron spin resonance in X-irradiated sodium sulphate

Reliable results are reported for the various triple-dipole dispersion energy coefficients needed to evaluate the (exact) triple-dipole dispersion energy for all three-body interactions involving He, Ne, Ar, Kr, Xe, H₂, N₂, CO, O₂ and NO, and at least one molecule. A total of 645 unique coefficients, corresponding to 185 unique interactions, are considered.     

Complete fusion and quasi-fission reactions induced by Kr ions on heavy targets

Cross sections for fission (complete fusion) and quasi-fission are measured at a given angle for the systems Kr + Ho, Kr + W, Kr + Bi, Kr + U in the energy range 450–525 MeV. The cross sections for complete fusion are unexpectedly low and the cross sections for quasi-fission are high. The cross section for close collisions (sum of the complete fusion and quasi-fission cross sections) is compared to the value calculated with the critical distance concept. The possibility that complete fusion does not occur for the lowest impact parameters is discussed.     

Differential cross sections for charge transfer in collisions of He+, Ne+ and Ar+ with Kr

Differential charge transfer cross sections for collisions of He⁺, Ne⁺ and Ar⁺ with Kr were measured at collision energies below 500 eV. A remarkable fraction of these collisions (2–30 %) occurs with large momentum transfer and small impact parameters. These close collisions lead to an excitation of the product particles, the measured reaction channels are strongly endothermic. In the system Ar⁺+Kr one reaction channel may be described in terms of a curve crossing.     

Structure of high spin states of76Kr and78Kr nuclei

Following a fully self-consistent cranked Hartree-Fock-Bogoliubov (CHFB) approach with a pairing+quadrupole+hexadecapole model interaction Hamiltonian the structure of the yrast states of^76,78Kr nuclei is studied up to angular momentumJ = 24. Evolution of the shape with spin, and rotation alignment of proton as well as neutron 0g_9/2 orbitals is investigated along with the inter and intra-nucleus variations of theg factors as a function ofJ. We find that the shape of⁷⁸Kr remains prolate all through up toJ = 24, whereas⁷⁶Kr becomes triaxial beyondJ = 12     

Nuclear reactions in the 86Kr + 139La system at 710 MeV

Two distinct groups of reaction products are observed in the ⁸⁶Kr + ¹³⁹La system at 710 MeV. Partially damped events show an angular distribution peaked near the grazing angle while fully damped products exhibit a strongly forward-peaked angular distribution suggestive of nuclear orbiting.     

Vacuum ultraviolet absorption in Xe+CF4 and Kr+CF4 mixtures

The absorption spectra of Xe + CF₄ and Kr + CF₄ mixtures in the vacuum ultraviolet region are presented. A considerable broadening of the short-wavelength wings of the atomic absorption lines is explained by a repulsive character of the Rg*-CF₄ interaction potential. This repulsive character is also considered to be the most probable reason for the anomalously small cross sections of the quenching of electronically excited atoms of rare gases by CF₄ molecules. The influence of CF₄ on the emission rate of the trapped resonance radiation of Xe from the cell is discussed.     

Transition probabilities in Kr II and Kr III spectra

On the basis of the relative line intensity ratio (RLIR) method, transition probability values of the spontaneous emission (Einsteins A values) of 14 transitions in the singly (Kr II) and 7 transitions in doubly (Kr III) ionized krypton spectra have been obtained relatively to the reference A values related to the 435.548 nm Kr II and 324.569 nm Kr III, the most intensive transitions in the Kr II and Kr III spectra. Our Kr III transition probability values are the first data obtained experimentally using the RLIR method. A linear, low-pressure, pulsed arc operated in krypton discharge was used as an optically thin plasma source at a 17 000 K electron temperature and 1.65 x 10²³ m^-3 electron density. Our experimental relative A values are compared with previous experimental and theoretical data.Received: 16 June 2003, Published online: 16 September 2003PACS: 52.70.Kz Optical (ultraviolet, visible, infrared) measurements - 32.70.Cs Oscillator strengths, lifetimes, transition moments - 32.70.Fw Absolute and relative intensities     

The excitation of the 1sσ and 2pσ quasimolecular radiation in Nb+Kr collisions

The absolute yields of quasimolecular (MO) radiation lying above the characteristic KX-rays emitted in the asymmetric Nb+Kr (43 MeV) and Kr+Nb (47 MeV) collisions have been determined. The comparison of the MO yields obtained in the gas and solid target experiments shows that the 2pσ MO radiation (C1) is emitted predominantly in primary collisions, whereas the 1sσ MO radiation (C2) is produced in secondary collisions.     

Diffusion model predictions for heavier systems: The reaction 197Au + 620 MeV 86Kr

The cross sections and angular distributions for fragments emitted in the reaction 620 MeV ⁸⁶Kr + ¹⁹⁷Au have been calculated using the Diffusion Model to describe the approach to equilibrium of the reaction system along the mass-asymmetry coordinate. The calculated quantities are compared with experimental results, and extensions of the theory are discussed.     

New isomers in83Br,85Rb,85Kr and86Kr

Using methods of in-beam spectroscopy in connection with 35 MeV⁷Li bombardment of⁸²Se targets four new isomers have been identified. They are observed in⁸³Br at 3070 keV (T_1/2=0.6±0.2 μs), in⁸⁵Rb at 2826 keV (T_1/2=12.5±0.6 ns), in⁸⁵Kr at 1991 keV (T_1/2=1.2+ _0.4 ^1.0 μs) and in⁸⁶Kr at 2250 keV (T_1/2=3.1±0.6 ns). Spin and parity 19/2^? have been assigned to the new isomer in⁸⁵Rb that is interpreted as the coupling of a p_3/2 proton to the g ₉ ^2/?2 two-neutron excitation of the N=48 neutron system. Using the TDPAD method an upper limit for the g-factor of ¦g¦≦0.17 has been estimated for this isomer. The same two-neutron excitation is also believed to be responsible for the new isomer in⁸³Br. The new isomers in⁸⁵Kr and⁸⁶Kr are interpreted as configurations containing the two-proton excitation (f ₅ ^2/?1 , p ₃ ^2/?1 ) where in the isomeric 17/2⁺ level of⁸⁵Kr an additional g_9/2 neutron hole is involved.     

Dynamics of superheavy system in 86Kr + 208Pb reaction

The dynamics of the excited superheavy system with Z = 118 in the reaction ⁸⁶Kr + Pb at E _Kr = 600 MeV has been investigated. The mass and kinetic energy of binary fragments were measured by the time-of-flight method. Double differential distributions of neutrons and α particles were measured in coincidence with fragments. Neutron and α-particle probes were used for determination of the fragmentation time scale. Evidence of the neck fragmentation was obtained from analysis of double differential α spectra. Properties of the α-particle neck fragmentation component are close to those known from the ternary fission of actinide nuclei, but the multiplicity is much larger. The total kinetic energy distribution of fragments tagged by neutrons or α particles shifts towards lower energies. Fragment yields in the symmetric region increase substantially when fragments are tagged by α particles.     

The β+-electron capture decay of 73Kr

The β⁺– electron capture decay of ⁷³Kr, produced at the ISOLDE CERN facility, has been studied by β-delayed proton and gamma emission. The established decay scheme involves 15 up to now unreported gamma emitting levels in ⁷³Br. The total proton branching ratio has been measured to be 0.0025 ± 0.0003. From this work, a spin and parity 3/2⁻ is assigned to the ⁷³Kr ground state, on the basis of the allowed β branch to the ⁷³Br J^π= 1/2⁻ ground state and the feeding of the 5/2⁺ level located at 286 keV in ⁷³Br. Received: 17 September 1998 / Revised version: 25 January 1999     

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.     

Lifetime measurement in 74Kr and 76Kr

Lifetimes of excited states in the ground-state bands of ⁷⁴Kr and ⁷⁶Kr were measured using the recoil-distance Doppler-shift and the differential decay curve methods. The states were populated in the ⁴⁰Ca(⁴⁰Ca, α2p) and ⁴⁰Ca(⁴⁰Ca, 4p) reactions. Gamma rays were detected with the GASP array which was coupled to the Cologne Plunger device. The results resolve discrepancies between earlier lifetime measurements and a recent Coulomb excitation experiment. Experimental transition rates are compared to theoretical calculations. The results support a strong mixing between prolate and oblate configurations for the low-spin states, and represent an important basis for the interpretation and understanding of the shape coexistence phenomenon in this mass region.     

Evidence for non-axial shapes in81, 82, 83Kr

Excitations up to I=12 have been found in⁸²Kr during an (α, 2n) in-beam experiment. Several levels are interpreted as due to (g9/2)² neutron excitations. A comparison with g9/2 neutron bands in^{81, 83}Kr and with cranked shell model calculations indicates non-axial deformation in connection with a rotation-aligned band starting with an 8⁺ level. Non-collective excitations, 8⁺ (and 6⁺), have been interpreted as deformation-aligned two-neutron states.     

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.     

Spins and parities of low-lying states in 79Kr from the 78Kr(d,p)79Kr reaction

The structure of Kr has been investigated via the ⁷⁸Kr($\text{d}$, p)⁷⁹ Kr reaction using an isotopically enriched gas target and an 11.0 MeV vector-polarized deuteron beam. Differential cross sections, σ, and vector analyzing powers, A_y, have been measured from 25° to 95° for 10 proton groups below 2.5 MeV excitation energy. Comparisons of these distributions to DWBA calculations and empirical shapes were made to extract spectroscopic factors and values of spin and parity for these states.