Gold Isotopes Research Articles

New developments of the in-source spectroscopy method at RILIS/ISOLDE

At the CERN ISOLDE facility, long isotope chains of many elements are produced by proton-induced reactions in target materials such as uranium carbide. The Resonance Ionization Laser Ion Source (RILIS) is an efficient and selective means of ionizing the reaction products to produce an ion beam of a chosen isotope. Coupling the RILIS with modern ion detection techniques enables highly sensitive studies of nuclear properties (spins, electromagnetic moments and charge radii) along an isotope chain, provided that the isotope shifts and hyperfine structure splitting of the atomic transitions can be resolved. At ISOLDE the campaign to measure the systematics of isotopes in the lead region (Pb, Bi, Tl and Po) has been extended to include the gold and astatine isotope chains. Several developments were specifically required for the feasibility of the most recent measurements: new ionization schemes (Po, At); a remote controlled narrow line-width mode of operation for the RILIS Ti:sapphire laser (At, Au, Po); isobar free ionization using the Laser Ion Source Trap, LIST (Po); isobar selective particle identification using the multi-reflection time-of-flight mass separator (MR-ToF MS) of ISOLTRAP (Au, At). These are summarized as part of an overview of the current status of the in-source resonance ionization spectroscopy setup at ISOLDE.

Study of fusion and nucleon transfer channels in the 197Au + 6He reaction in an energy range of 6He to 20 Mev/A

New data on the cross sections of reactions occurring during the interaction of 6He nuclei with 197Au at energies of 6He from 40 to 120 MeV are presented. The experiments were performed in the ACCULINNA secondary beam separator of the Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research. To identify the reaction products, the activation method for measuring the gamma activity of the target assembly of thin foils was used. The excitation functions for fusion reactions involving the evaporation of up to ten neutrons from the compound nucleus as well as reactions with the emission of charged particles and nucleon transfer in the investigated energy region are obtained. Data analysis was carried out using two codes: ALICE-MP and NRV. The cross sections for the (6He, xn) reactions occurring through the compound nucleus are mostly in agreement with the results of model calculations based on the statistical approach. It is shown that, up to the energies of 114 MeV, the cross-section drop in the complete fusion reactions is negligible. The experimental excitation functions of reactions leading to the formation of isotopes of mercury and gold (transfer reaction) indicate that the main contribution to their formation is made by direct processes and that evaporation reactions (6He, pxn) and (6He, αxn) play a minor role, as is evidenced by a comparison of the measured cross sections with the calculation results.

Investigating the nuclear fusion and nucleon transfer channels in the 197Au + 6He reaction at 6He energies up to 20 MeV/A

New data on the cross sections of reactions that proceed during the interaction of 6He and 197Au nuclei in the 6He energy range of 40 to 120 MeV are reported. The experiments were performed using the secondary beam of the ACCULINNA separator at the Flerov Laboratory of Nuclear Reactions (FLNR), JINR. Reaction products are identified by means of activation method to measure the gamma activity of a thin-foil target assembly. Excitation functions for 6He fusion reactions with subsequent emission of up to 10 neutrons from the compound nucleus are measured. Cross sections for reactions with emission of charged particles and nucleon transfer were also measured. The experimental cross sections for the (6He, xn) reactions that proceed via the formation of a compound nucleus agree in general with calculations using models that involve the statistical approach. It is shown that the complete fusion reaction cross section drops slightly up to an energy of 114 MeV. The experimental excitation functions for the reactions resulting in the formation of mercury and gold isotopes indicate that the main contribution to their formation comes from direct processes, while the evaporation reactions (6He, pxn) and (6He, αxn) are of minor importance.

Shape coexistence in odd-mass Au isotopes: Determination of the excitation energy of the lowest intruder state in 179Au

Phenomenon of the shape coexistence has been investigated in 17979Au100. This very neutron-deficient isotope, 18 neutrons away from the stable gold isotope 19779Au118, was studied by a combination of α-decay and isomer-decay spectroscopy employing the ritu gas-filled separator and the great focal-plane spectrometer at the University of Jyväskylä. A new isomer with t1/2=328(2) ns was observed and states associated with πd3/2−1, πs1/2−1, πf7/2+1 and πh9/2+1 structures were revealed. The implications of these results on the systematics of πh9/2+1 and πf7/2+1 intruder structures in the odd-mass gold isotopes are discussed. The minimum of the parabolic trend is at N=104, i.e. exactly at the mid-shell point and the πf7/2+1 structure is dropping in energy relative to the πh9/2+1 with decreasing mass number.

10.1007/s11450-008-3001-8

An experiment in which the gold isotope 197Au was irradiated with a beam of bremsstrahlung photons having an endpoint energy of E = 67.7 MeV and originating from the RTM-70 racetrack microtron of the Institute of Nuclear Physics at Moscow State University was performed. The gammaray spectra of the residual beta activity of an irradiated sample were measured. Multinucleon photonuclear reactions on 197Au nuclei were observed in the experiment. Photonuclear reactions on a 197Au nucleus that involve the emission of up to seven neutrons were recorded for the first time. The experimental results in question suggest the important role of the quasideuteron photodisintegration mechanism in the energy region behind the giant dipole resonance.

Discovery of the gold isotopes

Thirty-six gold isotopes have been observed so far and the discovery of these isotopes is discussed here. For each isotope a brief summary of the first refereed publication, including the production and identification method, is presented.

Multineutron photodisintegration of the 197Au nucleus behind the giant dipole resonance

An experiment in which the gold isotope 197Au was irradiated with a beam of bremsstrahlung photons having an endpoint energy of E γ m = 67.7 MeV and originating from the RTM-70 racetrack microtron of the Institute of Nuclear Physics at Moscow State University was performed. The gammaray spectra of the residual beta activity of an irradiated sample were measured. Multinucleon photonuclear reactions on 197Au nuclei were observed in the experiment. Photonuclear reactions on a 197Au nucleus that involve the emission of up to seven neutrons were recorded for the first time. The experimental results in question suggest the important role of the quasideuteron photodisintegration mechanism in the energy region behind the giant dipole resonance.

Experimental constraints on strangelets and other exotic nuclear matter

A reanalysis of data from a recent search for ultraheavy isotopes of gold and iron leads to new constraints on several classes of exotic objects. These include strangelets, MEMOs (metastable exotic multihypernuclear objects), and CHAMPs (charged massive particles) which may have been present in the data, but which could have nonetheless gone undetected due to the design of the original experiment. As a result of the new analysis we are able to greatly enlarge the exclusion regions for exotic particles of mass M and charge Z, and provide limits as low as ${10}^{\ensuremath{-}11}$ for small $M/Z,$ and ${10}^{\ensuremath{-}7}$ for $M/Z$ up to 120.

Learning from Others

I once believed that there are several naturally occurring isotopes of gold. When asked, “Are there several naturally occurring isotopes of gold?” either I would simply say, “Yes,” or, if I was in the mood to be more explicit, I would say, “There are several naturally occurring isotopes of gold.” But four years ago, while browsing through the Encyclopedia Britannica article titled “Gold”, I read the sentence “The element’s only naturally occurring isotope is gold-197.” I took the author’s words at face value—I took him to have asserted that the element’s only naturally occurring isotope is gold-197—and I accepted that the element’s only naturally occurring isotope is gold-197 solely because I trusted him. I thereby took myself to have learned from him that the element’s only naturally occurring isotope is gold-197. It ordinarily goes without saying that we can learn from others in this way—by taking their words at face value and accepting what they write or say solely because we trust them. C. A. J. Coady has recently argued that we can justify our trust in what others write or say by appealing to Donald Davidson’s principle of charity, which exhorts us to interpret another speaker’s words in such a way that under the assigned interpretation, what the speaker asserts is true by our own lights. Against this, I will argue that if Davidson’s principle of charity is a constraint on correctly interpreting what others write or say, then our ordinary impression that we can learn from others by taking their words at face value and accepting what they write or say is an illusion created by habitual but unjustified misinterpretations of their utterances. The reason is that in a large number of cases in which we take ourselves to be learning from others by accepting what they write or say, what we take them to write or say, given ~what Davidson sees as! our tacit interpretations of what we read or hear, is not true by NOUS 36:4 ~2002! 525–549

Nuclear conversion of 195AuFe into 195PtFe centers in silicon: observations by magnetic resonance

For the purposes of the reported experiments iron-doped silicon samples were implanted with nuclei 195Hg, which due to nuclear instability transmute via radioactive gold into stable platinum. Electron paramagnetic resonance was applied to monitor the conversion of 195AuFe centers into 195PtFe centers. On the basis of the hyperfine interactions both centers were unambiguously ascribed to gold and platinum impurities with mass 195, having their origin in the implantation. From the observation of centers with an equal geometrical structure, it is concluded that no atomic displacements due to recoil occur. Intensities of 195AuFe decrease with time and are accompanied by a simultaneous increase of 195PtFe signals, revealing the nuclear process. Deviation of the time dependence from the 183 days half-life of the 195Au isotope is ascribed to iron diffusion and to shift of the Fermi level in the samples during the center transformation. Accurately measured hyperfine interactions with the gold isotopes indicate a hyperfine structure anomaly of 195Au with respect to 197Au less than 1%.

Experimental limits on the existence of strongly interacting massive particles bound to gold nuclei

We report the results from an experimental search for strongly interacting massive particles bound to gold nuclei. A scan for heavy gold isotopes with masses ranging from 186.3 to $325.9 \mathrm{GeV}{/c}^{2}$ was performed on laboratory gold and gold from western Australia using PRIME Lab, the Purdue Accelerator Mass Spectrometer facility. The results provide significant new constraints on current models which predict the existence of such particles with abundance ratios in the range ${10}^{\ensuremath{-}11}\char21{}{10}^{\ensuremath{-}10}.$

Half-lives of Au, Hg, and Pb isotopes from photoactivation

The ground state half-lives of the gold isotope ${}^{196}\mathrm{Au},$ the mercury isotopes ${}^{195,197,203}\mathrm{Hg},$ the lead isotope ${}^{203}\mathrm{Pb},$ and the half-lives of two isomers in ${}^{199}\mathrm{Hg}$ and ${}^{204}\mathrm{Pb}$ have been measured with high precision using the photoactivation technique. The $\ensuremath{\gamma}$-ray activity was counted over several half-lives with high-purity germanium detectors. The measured half-lives are: ${T}_{1/2}{(}^{196}\mathrm{Au})=6.1669\ifmmode\pm\else\textpm\fi{}0.0006$ d; ${T}_{1/2}{(}^{195}\mathrm{Hg})=10.53\ifmmode\pm\else\textpm\fi{}0.03$ h; ${T}_{1/2}{(}^{197}\mathrm{Hg})=64.94\ifmmode\pm\else\textpm\fi{}0.07$ h; ${T}_{1/2}{(}^{203}\mathrm{Hg})=46.6\ifmmode\pm\else\textpm\fi{}0.1$ d; ${T}_{1/2}{(}^{204}\mathrm{Pb})=51.95\ifmmode\pm\else\textpm\fi{}0.01$ h; ${T}_{1/2}{(}^{199m}\mathrm{Hg})=42.67\ifmmode\pm\else\textpm\fi{}0.09$ min; ${T}_{1/2}{(}^{204m}\mathrm{Pb})=1.14\ifmmode\pm\else\textpm\fi{}0.04$ h.

The COMPLIS experiment on neutron deficient Au, Pt and Ir isotopes

The COMPLIS (COllaboration for spectroscopic Measurements using a Pulsed Laser Ion Source) experiment is carried out at the ISOLDE Booster facility at CERN. The aim is to measure the hyperfine structure and the isotope shift of a series of radioactive laser desorbed atoms by multiple step laser ionization. This technique is especially suitable for refractory elements not directly available as beams from the isotope separator. By collecting a primary radioactive beam, it is possible to delay the laser desorption as long as necessary to obtain the particular daughter of interest. Laser spectroscopy measurements have been carried out on very neutron deficient gold, platinum and iridium isotopes. Magnetic moments μI, spectroscopic quadrupole moments \(\user1{Q}_{\text{s}} \) and changes of the nuclear mean square charge radius \(\delta \left\langle {\user1{r}_{\text{c}}^{\text{2}} } \right\rangle \) along each isotopes series have been extracted. From some results, a detailed comparison with the predictions of the models is presented.

Silver and Gold NMR

Silver and gold, together with copper, form the transition metal group IB elements in the periodic table and possess very different nuclear magnetic resonance (NMR) spectroscopic properties. While there is only one gold isotope (197Au), which has a spin of 3/2 and therefore a quadrupole moment, silver occurs in two isotopic forms (109Ag and 109Au), both of which have a spin 1/2 and similar NMR spectroscopic properties. The unfavorable properties of gold have prevented its NMR spectroscopic investigation thus far. On the other hand, there are several reports of silver NMR. However, the low sensitivity of silver, combined with its long relaxation times have rendered the direct detection of silver possible only with concentrations greater than a few tenth molar. Reviewed here are the general limitations of silver NMR and some techniques to partially overcome these limitations, as well as a summary of currently available chemical shift and scalar coupling data on 109Ag.

Quadrupole moments and nuclear shapes of neutron-deficient gold isotopes

The hyperfine structure splitting and the isotope shift of the neutron-deficient gold isotopes 194−191Au in the optical transition 5 d 9 6 s 2 2 D 3 2 → 5 d 10 6 p 2 P 1 2 (627.8 nm) have been determined by collinear laser spectroscopy at the on-line isotope separator ISOLDE. The nuclear magnetic moments, spectroscopic quadrupole moments and changes in the mean square charge radii are deduced. Experimental electromagnetic moments and deformation parameters are compared with results of a particle-triaxial-rotor model calculation for both odd- A and odd-odd gold nuclei. Very good overall agreement between calculation and experimental data has been achieved. We find, for the first time, consistent evidence for a relatively large contribution from hexadecapole deformation ( ϵ 4 = 0.06, β 4 = −0.05) to odd- A gold isotopes ground states in the region of 183 ≤ A ≤ 197. Calculated values of quadrupole deformation are consistent with the prolate-to-oblate shape change between ground states of 186Au and 187Au. In addition, our results suggest another shape change between 190Au (oblate) and 191Au (triaxial). The former change is accompanied by a considerable change in quadrupole deformation, the latter occurs at almost constant deformation.

PILIS: Post-ISOCELE Laser Isobar Separation — a high efficiency apparatus for laser spectroscopy

A new experimental setup PILIS II has been installed on line with the ISOCELE isotope separator (IPN, Orsay). The mass-separated ions are slowed from 30 kV to 500 V and implanted on a graphite collecting disk. The atoms are then thermally desorbed at the implantation region by Nd-YAG laser pulses and selectively ionised by three laser beams. The ions created are mass identified by a time-of-flight (TOF) system. Two versions of the TOP system with accelerating voltage of 1.5 and 30 kV were used to carry out hyperfine structure measurements. With the 30 kV system we obtained an overall detection efficiency of 8.4 × 10 −5. First measurements were performed on very light gold isotopes. It has been shown that PILIS II is well adapted to study very short half-life isotopes ( T 1 2 ∼ 1 s ).

PILIS: post-ISOCELE laser isobar separation; a high efficiency apparatus for laser spectroscopy

A new experimental setup PILIS II has been installed on-line with the ISOCELE isotope separator (IPN, Orsay). The mass-separated ions are slowed from 30 kV to 500 V and implanted on a graphite collecting disk. The atoms are then thermally desorbed at the implantation region by Nd: YAG laser pulses and selectively ionized by three laser beams. The ions created are mass identified by a time-of-flight (TOF) system. Two versions of the TOF system with accelerating voltages of 1.5 and 30 kV were used to carry out hyperfine structure measurements. With the 30 kV system we obtained an overall detection efficiency of 1.4 × 10 −5. First measurements were performed on very light gold and platinum isotopes. It has been shown that PILIS II is well adapted to study very short half-life isotopes ( T 1 2 ∼ 1 s ).

On-line laser spectroscopy by resonance ionization of laser-desorbed, refractory elements

Resonance ionization mass spectroscopy was applied at the on-line isotope separator ISOLDE-3/CERN, Geneva to the refractory elements Au and Pt. The hyperfine structures and isotope shifts of gold and platinum isotopes were studied in long isotopic chains in the range from the stable isotopes down to the neutron-deficient ones with A = 183. Spins, magnetic moments, quadrupole moments and the differences in mean-square nuclear charge radii were determined. A mass-selected Hg ion beam was implanted into a graphite target. After the decay to Au or Pt, a pulsed atomic beam was formed by pulsed laser desorption. The atoms were ionized by three-colour, three-step resonant excitation. The photoions were detected mass-selectively by a time-of-flight mass spectrometer. An overall efficiency of ϵ ⋍ 10 −5 was achieved defined as the number of atoms detected in the optical resonance to the number of Hg atoms implanted into the target. The background was as low as 1 event per 1000 laser shots. The publication gives a detailed description of the applied method, the experimental setup and its performance.

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.

Laser spectroscopy of laser-desorbed gold isotopes

Changes in mean-square charge radius δ〈r2〉, and magnetic dipole moments μ1 have been measured for a series of neutron-deficient gold isotopes between A = 186 and 196, and for neutronrich 198,199Au, using the PILIS system on-line with the ISOCELE mass separator. These measurements confirm the existence of the shape transition between A = 186 and 187. The measured μ1 values have been compared with calculations using Nilsson, and symmetric-rotor-plus-quasiparticle models. The results are consistent with the interpretation that 186Au is prolate, and that the heavier isotopes have oblate, or possibly triaxial deformation.