Au Isotopes Research Articles

COMPLIS experiments: COllaboration for spectroscopy Measurements using a Pulsed Laser Ion Source

Laser spectroscopy measurements have been carried out on very neutron-deficient isotopes of Au, Pt and Ir, produced as daughter elements from a Hg ISOLDE beam. For these transitional region nuclides, the hyperfine structure (HFS) and isotope shift (IS) were measured by Resonance Ionization Spectroscopy (RIS). Magnetic moments μ, spectroscopic quadrupole moments Qs and changes of the nuclear mean square charge radius δ〈rc 2〉along isotopic series have been extracted. For some results, a detailed comparison with theoretical predictions is presented.

High-spin structure in181,183Au

High-spin states were studied in ${}^{181,183}\mathrm{Au}$ and resulted in the identification of several new prolate rotational bands based on $\ensuremath{\pi}{i}_{13/2},$ $\ensuremath{\pi}{h}_{9/2},$ $\ensuremath{\pi}{f}_{7/2},$ and $\ensuremath{\pi}{h}_{11/2}$ configurations. The alignment and moment of inertia features of the intruder bands are compared with ground-state bands in Pt nuclei. From these features, it can be concluded that a strongly interacting $(\ensuremath{\pi}{h}_{9/2}{)}^{2}$ alignment is occurring in the $\ensuremath{\pi}{i}_{13/2}$ bands in Au and the ground-state bands in Pt. In addition, bandhead energies and deformation parameters are calculated for deformed configurations in the framework of a microscopic-macroscopic shell-correction model. These calculations are compared with experimental values in Re and Ir, as well as, Au isotopes. Interaction properties between known $\ensuremath{\pi}{h}_{9/2}$ and $\ensuremath{\pi}{f}_{7/2}$ rotational bands are also discussed and compared with results from a cranked-shell model. Experimental $B(M1)/B(E2)$ ratios between these bands are compared with results from a particle-rotor calculation.

Levels of187Au: A detailed study of shape coexistence in an odd-mass nucleus

The decays of ${}^{187}$Hg (2.2 min; ${J}^{\ensuremath{\pi}}$=13/2${}^{+})$ and ${}^{187}$Hg (2.4 min; ${J}^{\ensuremath{\pi}}$=3/2${}^{\ensuremath{-}})$ have been studied with mass-separated sources at the UNISOR facility. Multiscaled spectra of $\ensuremath{\gamma}$ rays, x rays, and conversion electrons, as well as $\ensuremath{\gamma}\ensuremath{\gamma}t$, $\ensuremath{\gamma}\mathrm{xt}$, $e\ensuremath{\gamma}t$, and $\mathrm{ext}$ coincidences were obtained. Decay schemes have been constructed incorporating $>$99$%$ of the decay intensities assigned to the high-spin and low-spin decays. The $\ensuremath{\gamma}$-ray gated conversion-electron spectra permitted determination of 367 conversion coefficients. A variety of coexisting band structures are established in ${}^{187}$Au. Some of these have near-identical analogs in the heavier odd-mass Au isotopes. The remaining bands reveal new degrees of freedom at low excitation energy in ${}^{187}$Au. Nine electric monopole $(E$0) transitions are observed to deexcite members of these new bands. The work represents an undertaking to achieve a benchmark in complete spectroscopy following radioactive decay. The most notable band structure in ${}^{187}$Au has two bands with identical spins, nearly identical relative energies, and electric monopole transitions connecting the favored members. These bands can be understood as $\ensuremath{\pi}{h}_{9/2}$ and $\ensuremath{\pi}{f}_{7/2}$ intruder configurations coupled to coexisting prolate or near-prolate $(\ensuremath{\gamma}$ $<~$ 20$\ifmmode^\circ\else\textdegree\fi{})$ cores having diabatic configurations that differ only in the number of protons occupying the $N$=5 intruder configurations.

Excitation function measurement and reaction mechanism analysis for alpha-induced reactions on

Excitation functions have been measured for and produced by -particle-induced reactions on in the incident energy range 34-50 MeV. The excitation functions of these nuclei and those of , reported earlier, are analysed in terms of direct, pre-equilibrium and evaporation emissions. The two most commonly used models of pre-equilibrium reactions, the exciton and the hybrid models, have both been used and compared. The choice of the initial exciton number, the role of the pre-equilibrium cluster and multiple nucleon emissions have been investigated. The direct emission of clusters are found to significantly affect the excitation functions of and Au isotopes.

Multiple neutron capture by U, Am, Tm, and Au isotopes in a flux of thermalized neutrons from a nuclear explosion in the "Zond" experiment

Multiple neutron capture by U, Am, Tm, and Au isotopes in a flux of thermalized neutrons from a nuclear explosion in the "Zond" experiment

Yield of near-target product interaction of 47 MeV/A12C ions with bismuth targets

Formation cross sections of near-target products from the reaction of 47MeV/A12C with209Bi targets have been measured. Their independent yields were obtained from their cumulative and partially cumulative yields according to the experimental data measured in this work and correction for mother-daughter decay. From the yield distribution curves of Pt, Au and Hg isotopes constructed it was found that for their peak positions at mass numbers A=188.1, 190.9 and 195.8, the widths of charge distributions are σ = 3.08, 2.80 and 3.74, respectively. The formation cross sections for some near-target neutron-rich new isotopes were extrapolated from the isotopic yield distribution curves.

Decay of mass-separated 189mHg (8.7 min) and 189gHg (7.7 min) to 189Au

Abstract The decays of 189Hg (8.7 min; J π = 13 2 + ) and 189Hg (7.7 min; J π = 3 2 − ) have been studied with mass-separated sources from the UNISOR facility. Multiscaled spectra of γ-rays, X-rays, and conversion electrons, as well as γγt, γXt, eγt, and eXt coincidences were obtained. Decay schemes have been constructed incorporating > 95% of the decay intensities assigned to the high-spin and low-spin decays. The γ-ray gated conversion-electron spectra permitted the determination of 119 conversion-electron subshell ratios. Portions of the level scheme bear a remarkable resemblance to the heavier and lighter odd-mass Au isotopes. An extensive band of states is observed built upon the h 9 2 intruder state at 325 keV. This band is markedly different from the corresponding bands in 187Au and 185Au, indicating a major change in the cores, i.e. between 188Pt and 186,184Pt. Evidence for oblate-hole-prolate-particle symmetry in 189Au is discussed. Completeness of complex decay schemes far from stability is addressed.

Measurements of spectroscopic quadrupole moments of neutron-deficient Au isotopes with quadrupole-interaction-resolved NMR-ON

We report on measurements of quadrupole-interaction-resolved nuclear magnetic resonance on oriented nuclei ( QI-NMR-ON) of 3 2 + 193 Au (T 1 2 = 17.5 h)and 3 2 + 195 Au(T 1 2 =183 d) hcp-Co. The results for the magnetic and electric hyperfine splittings are: 193Au: ν M = 67.72(2) MHz; ν Q = − 15.69(4) MHz; 195Au; ν M = 71.65(1) MHz; ν Q = − 14.34(2) MHz. Taking into account hyperfine anomalies, the magnetic moments are deduced to be: μ( 193 Au) = 0.1396(6) μ N ; μ( 195 Au) = 0.1487(6) μ N . With the known quadrupole moment of 193Au, Q = + 0.664(20), b, the electric field gradient of Au in hcp-Co is deduced to be eq = − 0.977(29) × 10 17 V/ cm 2, with which Q( 195 Au) = + 0.607(18) b is obtained for the spectroscopic quadrupole moment of 195Au. In addition, the experimentally known quadrupole splitting frequencies of 186Au, 198Au and 199Au in hcp-Co can be reinterpreted, giving the results: Q( 186 Au) = + 3.14(16) b ; Q( 198 Au) = + 0.640(19) b ; Q( 199 Au) = + 0.510(16) b .

Electromagnetic properties and shapes of ground states in Pt−Au−Hg region

We present a comprehensive calculation of odd-A isotopes of Pt, Au and Hg in the mass region 177≤A≤195. Two nuclear models have been used. The particle-triaxial rotor model with modified oscillator s.p. potential (PTR-MO) yielded deformation parameters e2 and γ as a result of fitting to a wide range of experimental data. Also, mean field calculations based on the Woods-Saxon potential with Strutinsky shell corrections were performed to predict deformation parameters β2, β4 and γ form Total Routhian Surfaces (TRS). Subsequent PTR calculation using these deformation parameters and Woods-Saxon s.p. potential (PTR-WS) yielded ground state properties of all nuclei in question in very good agreement with experiment. The deformation parameters e2 and β2 showed the same general trend as a function of neutron number. The fitted parameter γ from (PTR-MO) calculation indicated a smooth change from prolate (N≈100) to oblate shape (N≈115) via triaxial in Pt, Au and Hg. The value of γ extracted from TRS calculations predicts a smooth change in Pt isotopes but much sharper change in Au and Hg nuclei.

Time resolved on-line nuclear orientation (TR-OLNO)

Conventional on-line nuclear orientation (OLNO) involves continuous implantation of unpolarised nuclei which are cooled to milli-Kelvin temperatures by nuclear spin lattice relaxation. Anisotropy of radiation from the cold, polarised nuclei is analysed to yield nuclear moments and decay properties. Incomplete relaxation prior to decay complicates analysis and, as half-lives shorten on moving further from stability, places an ultimate limit on the range of nuclei which can be studied by OLNO. This paper introduces a new method, time resolved on-line nuclear orientation (TR-OLNO) in which the implanted beam is pulsed and study is made of the nuclear relaxation itself to yield nuclear g-factors. Decay scheme parameters can also be extracted when the relaxation is observed. This method has its optimum application as half-life and relaxation time become comparable, thus extending the range of the OLNO technique. The basic principles of the new method are introduced and its application to the study of decay chains of implanted even- and odd- A nuclei is discussed. The ability to deal with “inherited” orientation in a decay sequence is emphasised. Examples are given of existing TR-OLNO studies of light Au isotopes by the NICOLE Collaboration.

Identification of band gap states by deep level transient spectroscopy on radioactive probes

The deep level transient spectroscopy technique has been applied to silicon doped with radioactive isotopes of the elements Au, Pt, Ir, and Os. The disappearance or appearance of features in the spectra as the incorporated radioactive atoms transmute unambiguously identifies an impurity involved in the centers observed.

Mixtures of molten metals and graphite as targets for on-line mass separators

Targets consisting of fine-grained powders of graphite and metals which do not form thermostable carbides have been investigated. The targets were heated to temperatures well above the melting point of the respective metals. A target of Pt powder mixed with graphite powder is found to be suitable for production of neutron deficient Au isotopes, when irradiated with 910 MeV 3He projectiles. The yields of neutron deficient Cd isotopes from a target of Sn powder mixed with graphite powder are also reported.

Charge radii and shape transitions in short-lived Hg, Au and Pt isotopes

The hyperfine structure and the isotope shift of very neutron-deficient Au and Pt isotopes have been determined at the on-line isotope separator ISOLDE/CERN by resonance ionization mass spectroscopy combined with pulsed-laser induced desorption of the implanted radioactive sample. The changes of the mean-square charge radii were determined for the isotopes184Au (T1/2=53 s) and183Au (T1/2=42 s) as well as for 15 isotopes of platinum in the range between198Pt (stable) and183Pt (T1/2=6.5 min). The strong deformation of185Au (|β2|≃0.25) persits down to183Au. In183Pt nearly the same value of |β2| is reached but the deformation is build up rather smoothly in contrast to the neighbouring isotopes of gold and mercury. The magnetic moment of183Pt was found to be μ1=+0.51(3)μN.

Equilibrium deformations and excitation energies of single-quasiproton band heads of rare-earth nuclei

Noncollective single-proton states in odd-Z (Eu, Tb, Ho, Tm, Lu, Ta, Ir and Au) rare-earth nuclei have been calculated using the shell correction method with an average Woods-Saxon potential and a monopole pairing residual interaction. Calculated equilibrium deformations of the lowest single-proton states are presented, and calculated band head excitation energies are compared with experimental proton band heads for odd-Z rare-earth nuclei. Good agreement is found between the experimental and calculated band heads. We find that strong polarisation effects due to the odd proton explain many of the systematic trends of known band heads. Different deformation driving forces of the odd-proton orbitals can also partly explain deviations seen in high-spin data. Shape co-existence effects in Ir and Au isotopes are discussed. In addition, equilibrium deformations of even-even rare-earth nuclei are computed and compared with experimental values.

Equilibrium deformations and excitation energies of single-quasiproton band heads of rare-earth nuclei

Noncollective single-proton states in odd- Z (Eu, Tb, Ho, Tm, Lu, Ta, Ir and Au) rare-earth nuclei have been calculated using the shell correction method with an average Woods-Saxon potential and a monopole pairing residual interaction. Calculated equilibrium deformations of the lowest single-proton states are presented, and calculated band head excitation energies are compared with experimental proton band heads for odd- Z rare-earth nuclei. Good agreement is found between the experimental and calculated band heads. We find that strong polarisation effects due to the odd proton explain many of the systematic trends of known band heads. Different deformation driving forces of the odd-proton orbitals can also partly explain deviations seen in high-spin data. Shape co-existence effects in Ir and Au isotopes are discussed. In addition, equilibrium deformations of even-even rare-earth nuclei are computed and compared with experimental values.

An investigation of laser desorption of Au by PIXE and RBS techniques using a He beam

Abstract Laser desorption has become an important tool for the production of atomic beams of refractory metals and has already been used successfully in laser-spectroscopic studies of Au and Pt isotopes. In the present experiment we have desorbed Au atoms implanted at 1 and 30 keV, to determine the optimum conditions for desorption and to follow the migration of the implanted atoms at selected laser fluences and in various substrates. The implanted Au surface densities ranged from 10 13 to 10 16 atoms/cm 2 . A Nd-YAG laser operated with a frequency-doubled output at 532 nm and a pulse duration of 10 ns was used for the desorption. This laser beam was focussed to a 5 mm 2 spot, superimposed on the 2 mm 2 beam spot of 3 MeV alpha particles used for simultaneous PIXE-RBS analysis. The YAG fluence was varied step by step up to about 900 mJ/cm 2 and after each step the PIXE and RBS spectra were recorded. The quantity of material desorbed was found to be large for graphite, boron nitride and Macor, and much less for the other materials.

Nuclear data sheets for A = 185

Evaluated spectroscopic data for all nuclei with mass number A=185, and corresponding level schemes from radioactive decay and reaction studies, are presented. New experimental evidence indicates a possible coexistence of prolate and oblate nuclear shapes in the Au and Hg isotopes. This evaluation for A=185 supersedes the earlier one by Y. A. Ellis-Akovali (81E111). published in Nuclear Data Sheets 33, 557 (1981).

The charge radii of198Pt-183Pt

The changes of the mean-square charge radii have been measured for198Pt-183Pt by means of resonance ionization mass spectroscopy (RIMS) at the new on-line isotope separator ISOLDE-3/CERN. As in the case of the neighbouring isotopes of Au and Hg, a strong nuclear deformation of ¦β2¦ −-0.24 is reached at the neutron mid-shell nucleus183Pt, but no indication for a sharp shape transition is observed from the study of the isotope shifts.

Nucleon transfer in highly mass-asymmetric reaction systems between197Au and relatively light projectiles in the energy region below 10 MeV/u

Mechanisms of heavy-ion induced nuclear reactions in mass-asymmetric systems were studied by focusing on the nucleon transfer reaction. Excitation functions and projected mean recoil ranges for the target-like products in37-,16O-,14N-, and12C-induced reactions on197Au were measured by means ofγ-ray spectrometry. The energy range studied was near the Coulomb barrier of the systems with incident energies below 10 MeV/u. Nucleon transfer reactions were discussed by distinguishing the products from quasi-elastic transfer (QET) and those from deep inelastic transfer (DIT). The tendency towards equilibration of theN/Z value and the energy damping, which are the characteristic features of DIT, were found in the production of Au isotopes. Observations are consistent with the generally accepted concept that QET takes place along a trajectory near the Coulomb trajectory. QET was made to be connected with the interaction radius and most of the cross section ratios were reproduced well by an extended tunneling model.

Observation of strongly deformed ground-state configurations in184Au and183Au by laser spectroscopy

Resonance ionization mass spectroscopy (RIMS) and pulsed-laser induced desorption (PLID) have been combined in order to study the isotope shift (IS) and hyperfine structure (HFS) of184Au (T1/2=53 s) and183Au (T1/2=42 s) in the 6s2S1/2 → 6p2P1/2 (λ=267 nm) transition. The Au isotopes were obtained as daughters in the decay of184,183Hg produced and mass separated at the new ISOLDE-3 facility at CERN. It was found that the strong deformationβ2}-0.25 setting in at186Au persists down to183Au.