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.     

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.     

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     

Lifetimes of excited levels of Kr I and Kr II

The lifetimes of eight levels belonging to the 6p configuration of KrI and thirteen levels belonging to different configurations of KrII have been measured. The levels were excited by short electron pulses of appropriate energy and the lifetimes determined by a delayed coincidence method using single photon counting techniques. All measurements were carried out at different gas pressures. The measured lifetimes of the KrII levels are compared with other experimental results obtained by a different method (beam-foil spectroscopy) and with calculations made in the intermediate coupling scheme.     

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     

Third virial coefficients of Ar+Kr and Kr+Xe mixtures

Third virial coefficients, calculated from the potentials of Lee, Henderson and Barker are given for Ar+Kr and Kr+Xe mixtures. The contributions of the three-body triple-dipole, dipole-dipole-quadrupole, and fourth-order triple-dipole interactions are included.     

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.     

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.     

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.     

Photo-stimulated luminescence of solid Kr

The emission spectra of solid Kr films at 10 K are investigated by irradiation with ultraviolet light in vacuum. Two emissions appear at 5.5 and 8.0 eV. Through the measurements of the excitation spectra, it is found that the high-energy band is emitted by excitation into the intrinsic exciton bands and can be regarded as an intrinsic emission, while the low-energy emission is associated with an impurity.     

The decay of75Kr

The decay of the isotope⁷⁵Kr (T_1/2=4.5 ±0.3 m) has been studied using mass separated sources produced at the ISOLDE facility at CERN. A decay scheme is proposed based on gamma, positon, and conversion electron singles and coincidence measurements. The total decay energy was measured to be Q_EC=4.4 ± 0.2 MeV. The resulting spin-parity assignments and the absence of a 9/2⁺ isomeric state in⁷⁵Br are discussed.     

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.     

The decay of76Kr

The decay properties of⁷⁶Kr have been investigated using mass separated samples produced by the ISOLDE facility. New information on energies, spins, parities and transition probabilities concerning levels in⁷⁶Br is presented. No direct β-feeding of the⁷⁶Br ground state was found resulting in a spin-parity assignment of 1^? to this state.     

Rotational bands in79Kr

The level scheme of⁷⁹Kr has been studied through the⁷⁹Br(p,n)⁷⁹Kr reaction at proton energies from 1·7 to 5·0 MeV.γ-ray and internal conversion electron measurements were made using Ge(Li) detectors and a six gap “Orange” electron spectrometer. The level scheme was established by determining the thresholds of variousγ-rays and byγ-γ and n-γ coincidence measurements. New levels at 402, 450, 660, 676, 695, 720, 810, 836, 907 and 1038 keV not observed in earlier radioactivity studies have been established. DefiniteJ ^π assignments have been made to most of the levels below 800 keV. Many of the low-lying levels are identified as rotational levels based on the (301 ↓) 1/2^?, (301 ↑) 3/2^? and (431 ↓) 1/2⁺ Nilsson states.     

Rotational bands in77Kr

Collective bands in⁷⁷Kr have been studied with the help ofγ singles spectra,γγ coincidences,γ ray angular distributions and recoil-distance life time experiments measured during the irradiation of⁶³Cu and⁶⁴Ni targets with¹⁶O ions. Positive and negative parity bands with the following level energies, spins, and parities have been found: g.s. 5/2⁺; 150.1 keV 7/2⁺; 279.1 9/2⁺; 784.8 11/2⁺; 1003.7 13/2⁺; 1660.5 15/2⁺; 1919.1 (17/2⁺); 66.5 keV (3/2)^?; 245.3 (5/2)^?; 499.6 (7/2)^?; 799.5 (9/2)^?; 1177.3 (11/2)^?; 1569.9 (13/2)^?; 2063.2 (15/2)^?. A mean life time of 170±17 nsec for the 66.5 keV state was measured withγγt coincidences and a mean life time of 48±13 psec for the 245.3 keV state was obtained with a recoildistance Doppler shift measurement.     

Thomson-scattering diagnostics of Kr/Ne and Kr/He plasmas using a picosecond laser

Thomson scattering from plasmas in high-pressure discharges for rare-gas-halide excimer-laser pumping was observed using a frequency-doubled 300 ps Nd: YAG laser. A temporal resolution of 1 ns was realized for the Thomson-scattering measurement, and detailed temporal changes of the electron density and temperature were measured in Kr/Ne and Kr/He plasmas. Calculations using a computer simulation showed good agreement with the experimental results, implying that the plasma dynamics is properly treated in the simulation.