Spectroscopy of195Hg and196Hg

High-spin states in the oblate-deformed nuclei¹⁹⁵Hg and¹⁹⁶Hg were populated in the¹⁹⁸Pt(α, xn) reaction and investigated by in-beamγ-ray spectroscopy using six Compton-suppressed Ge detectors. The level schemes of both nuclei are extended considerably. The level structure is interpreted within the framework of the cranked shell model. Good agreement is obtained between model predictions and experimental results.     

Multiple Coulomb excitation of198Hg and200Hg

Multiple Coulomb excitation measurements on^{198, 200}Hg have been performed with 5MeV/amu²⁰⁸Pb projectiles andB(E2)-values are determined for transitions between states up to spin 8⁺. In¹⁹⁸Hg a reduction of theB(E2)-value for the yrast transition 8⁺→6⁺ by a factor of 3 as compared to the rigid rotor prediction is observed, which supports the earlier proposed idea that the ground state band is crossed between the 6⁺ and 8⁺ state by a weakly interactingvi ₁₃ ^2/2 rotation aligned band. In each of the two nuclei,¹⁹⁸Hg and²⁰⁰Hg, a state with a possibleI ^π=8⁺ assignment is observed, which is tentatively interpreted as the 8⁺ member of the ground state band.     

Multiple coulomb excitation of202Hg and204Hg

Multiple Coulomb excitation measurements on^{202, 204}Hg have been performed with 5 MeV/u²⁰⁸Pb projectiles. The ground bands are excited up to the newly discovered 6⁺ states and B(E2) values are derived for the 4⁺→2⁺ and 6⁺→4⁺ transitions. Whereas the 2⁺ and 4⁺ levels in the Hg isotopes with 196≦A≦204 have an almost constant energy, the 6⁺ levels increase in²⁰²Hg and²⁰⁴Hg, compared to the lighter isotopes, by approximately 100 and 300 keV, respectively. The relative B(E2) values in both nuclei show that the collectivity in the neutron rich Hg nuclei is of more complex origin than expected from the few proton and neutron holes with respect to the 82 and 126 major shells.     

Superdeformed bands in193Hg and194Hg

By analyzing the thick target yield curve of resonant (p,γ) reactions on²³Na and²⁶Mg for various target temperatures within a Monte Carlo approach, we are able to define the Debye and Einstein temperature of the target material in the surface region. The obtained surface temperatures are noticeably higher than the respective calorimetric values.     

Identification of Hg and shape coexistence in odd-A Hg isotopes

In-beam γ-ray transitions in ¹⁸¹Hg, the lightest odd-A Hg isotope known thus far, have been identified from fragment mass-γ and γ-γ coincidence measurements. Five prolate deformed rotational bands were placed in the level scheme. A decoupled band built on the strongly prolate deformed 1/2⁻[521] ground state was observed up to 29/2⁻. A 5/2⁻[512] configuration is suggested for a pair of strongly coupled bands displaying no signature splitting. The other two bands are also signature partner bands. They are populated with the largest intensity and exhibit splitting. They have been associated with the mixed neutron i_13/2 orbitals and are proposed to decay to an i_13/2 isomeric state associated with an oblate state.     

Levels of195Au from the decays of195g Hg and195m Hg

The levels of¹⁹⁵Au were analyzed by observingγ-singles andγγ-coincidences following the¹⁹⁵Hg decay. Nine new lines are found which require two new levels at 778 and 946 keV. An interpretation of the level scheme is given on the basis of the de Shalit core-excitation model. A qualitative understanding of all levels up to 1 MeV excitation energy is obtained.     

Photochemical production of the 204Hg isotope

Technologies for photochemical separation of highly enriched mercury isotopes are being developed and an appropriate experimental setup has been designed at the National Research Centre ??Kurchatov Institute.?? The process is based on the reaction of oxidation of selectively excited mercury atoms in the presence of 1.3-butadiene. Along with the ¹⁹⁶Hg, ¹⁹⁸Hg, ¹⁹⁹Hg, ²⁰⁰Hg, and ²⁰²Hg isotopes with concentrations from 90 to 99%, the ²⁰⁴Hg isotope with a concentration of 98% has been separated for the first time.     

Photodisintegration of Hg isotopes

Yields of photonuclear reactions of several Hg isotopes are measured on a bremsstrahlung photon beam with a maximal energy of 19.5 MeV using a gamma-activation analysis. Cross sections of photonuclear reactions on stable Hg isotopes are calculated within bonds of the collective model taking isospin splitting of giant dipole resonance into account. The experimental results are compared with the results of theoretical calculations and earlier experimental studies.     

Quenching of 6s6d and 6s7d Hg atoms by Hg*-Hg,Hg*-Ar and Hg*-N2 collisions

The radiative decays and collisional quenching of Hg 6¹D₂, 6³D₂, 7¹D₂ and 7³D₂ atoms were investigated by time-resolved methods. Hg vapour, pure or mixed with a buffer gas in a fluorescence cell, was irradiated with u.v. light pulses from a frequency-doubled N₂ laser-pumped dye laser, populating selectively each state in turn by 2-photon absorption from the 6¹S₀ ground state. Fluorescent components arising from the decays to the 6¹P₁ or 6³S₀ state were resolved with a spectrometer and their time evolutions recorded with a transient digitizer or time-to-amplitude converter and pulse-height analyzer, yielding the respective decay rates. The quenching cross sections were obtained from variations of measured decay rates with Hg or buffer-gas density.     

Hg 199(n,ce) Hg200 studies

The conversion-electron spectrum from slow neutron capture in Hg 199 has been measured with the beta spectrometer at the reactor FRM. Approximately 100 conversion-electron lines with energies between 200 and 2300 keV were observed. The multipolarities and mixing ratios of about 50 transitions were determined. Branching and mixing ratios are compared with theoretical predictions.     

Spin Determination of Superdeformed Bands in 189Hg and 190Hg1

The superdeformed bands in ¹⁸⁹Hg and ¹⁹⁰Hg are investigated. The spin value of the lowest levels observed in ¹⁸⁹Hg (fed by 366.0 keV) is assigned to be 31/2 and that of ¹⁹⁰Hg (fed by 360.0 keV) is 15, rather than the previously proposed value 14.     

Radiative lifetimes of some excited states of Hg+ and Hg2+

A delayed-coincidence method with pulsed electron excitation was used to measure the radiative lifetimes of some 5d⁹6snl states of Hg⁺. Radiative lifetimes of five long lived 5d⁸6s² states of Hg²⁺ and some Hg²⁺ spectral line transition probabilities are also reported. The data are obtained for the first time.     

The magnetic moments and halflives of the 5/2− states in199Hg and197Hg and the discrepancies in the experimental hyperfine fields at Hg in Fe

The Larmor-precession frequencies for¹⁹⁷Hg in Fe have been determined to beω _L = 1291 ±25 MHz at 293 K andω _L = 1334±25 MHz at 105 K. For¹⁹⁹Hg in Feω _L =1372±50 MHz has been measured at 293 K. The half-lives of the 5/2^? states in¹⁹⁷Hg and¹⁹⁹Hg have been remeasured asT _1/2(¹⁹⁷Hg)=8.1±0.16 nsec andT _1/2(¹⁹⁹Hg)=2.45±0.05 ns, respectively. The magnetic moment of the 5/2^? 158keV state in¹⁹⁹Hg was redetermined by the integral perturbed angular correlation method in an external magnetic field of 47kG asμ(5/2 ^? ) = 0.905±0.091 nm. With this new value consistency for the magnetic hyperfine fields at Hg in Fe measured with the TDPAC-method and with the NMR/ON-method is obtained. This fact is used to determine theg-factors of the 5/2^? states in¹⁹⁷Hg and¹⁹⁹Hg more precisely fromω _L -values given above:g(¹⁹⁷Hg)=0.342(6);g(¹⁹⁹Hg)=0.352(13). The magnetic moments of the first excited 2⁺ states in^198–204Hg isotopes which rely on calibrations with the¹⁹⁹Hg-g-factor, are revised.     

Alpha decay of the new isotope 174Hg

Neutron deficient mercury isotopes were produced in the reaction ³⁶Ar + ¹⁴⁴Sm using bombarding energies of 180–230 MeV. Fusion products were separated in-flight from the primary beam using a gas-filled recoil separator. An alpha line with the alpha particle energy and half-life of (7069±11) keV and (2.1 _?0.7 ^+1.8 ) ms, respectively, was assigned to the new mercury isotope ¹⁷⁴Hg.     

Characterization of the superdeformed band in189Hg

New measurements of the pionic double charge exchange on⁵⁶Fe exhibit a pronounced energy dependence of this reaction at low energies in accordance with similar observations on other nuclei. We show that this peculiar energy dependence finds its natural explanation by a resonance in theNN subsystem withJ ^p =0^–,T=0 and a mass of 2.065 GeV.This work has been funded by the German Federal Minister for Research and Technology (BMFT) under the contract numbers 06 TÜ 656 and 06 KA 266 and by the DFG (Mu 704/3, Graduiertenkolleg)     

Semi-decoupled bands in the even Hg isotopes

The odd-parity yrast states of the isotopes ^190–200Hg are studied in a model of two quasiparticles coupled to an oblate rotor and interacting by a surface delta interaction. The experimental energy spectra and the enhancement of E2 transition probabilities are well explained by the model. The pure Coriolis coupling problem (i.e., the problem obtained when the residual interaction is suppressed) is investigated in detail. It is shown that the main effect of the Coriolis force is to decouple the high-spin quasiparticle originating in the neutron $\text{1}\text{i}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}$ subshell from the system of the rotor and the low-spin quasiparticle. We study the coupling of a particle to an axially symmetric rotor, which has an intrinsic spin along its symmetry axis, and derive a good approximate solution to the problem.     

After-effects in the decay of As and Hg

After-effects following internal conversion processes in the decay of ⁷⁵Se and ^197mHg are investigated. Time differential electron-γ and time integral electron-γ, γ-electron and γ-γ directional correlation measurements are performed, and a magnetic decoupling technique is used. For certain insulating source backing materials after-effects are found. Relaxation time constants for the time-dependent perturbation and recombination time constants for the ionized atoms, as well as the strength of the time-dependent internal magnetic fields are deduced.