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 (T_1/2=53 s) and¹⁸³Au (T_1/2=42 s) in the 6s²S_1/2 → 6p²P_1/2 (λ=267 nm) transition. The Au isotopes were obtained as daughters in the decay of^184,183Hg produced and mass separated at the new ISOLDE-3 facility at CERN. It was found that the strong deformationβ ₂}-0.25 setting in at¹⁸⁶Au persists down to¹⁸³Au.     

Disparity in transient field characteristics for Au ions traversing Fe and Gd hosts through measurements ofg-factors in197Au

Transient field precessions were measured for levels in the nuclides of^182,184,186W and¹⁹⁷Au as their ions simultaneously traversed polarized Fe and Gd hosts. Consistent sets of gyromagnetic ratios were inferred for the lowest 5/2⁺ and 7/2⁺ states in¹⁹⁷Au using these two ferromagnetic host media, provided that (i) the transient field for Au ions in Gd is calibrated using the W in Gd precessions (simultaneously measured) and, (ii) the transient field for Au in Fe is calibrated using the field strength and velocity dependence for Pt in Fe (previously measured). The presentg-factor results are: g(5/2 ₁ ⁺ ;¹⁹⁷Au)=0.296±0.023, g(7/2 ₁ ⁺ ;¹⁹⁷Au)=0.241±0.021, and g(5/2 ₁ ⁺ ;¹⁹⁷Au)=1.2±0.2.     

Quasielastic transfer reactions in 238U + 197Au and 197Au + 197Au collisions near the Coulomb barrier

Differential cross sections as a function of cm angle were measured for 1n- and 2n-transfer reactions in ²³⁸U + ¹⁹⁷ Au and¹⁹⁷ Au + ¹⁹⁷ Au collisions in the energy range from 0.881 V_c to 1.093 V_c and 0.825 V_c to 0.964 V_c, respectively. For ¹⁹⁸Au and ¹⁹⁹Au from the ²³⁸U + ¹⁹⁷Au collisions, for reduced distances of closest approach d _o 1.55 fm, the angular distributions at all bombarding energies are well described by the semiclassical theory. Equivalently, the transfer probabilities show the expected exponential decrease with increasing d _o over many orders of magnitude. For all other transfer products from ²³⁸U + ¹⁹⁷Au collisions, and for all transfer products from ¹⁹⁷Au + ¹⁹⁷Au collisions, markedly reduced cross sections relative to the semiclassical theory are observed for central collisions at all bombarding energies, even for values of d _o that are well outside the region where absorption is known to set in. Only for the more peripheral collisions, one observes agreement of the angular distributions (transfer probabilities) with the semiclassical expectations. The deviations for central collisions are absent for reactions with positive Q _gg values and scale roughly with increasingly negative values of Q _gg, i.e. with increasing Q-value mismatch. Channel coupling is proposed as the relevant mechanism.     

Isotope shifts of neutron-deficient gold isotopes with 193≧A≧190

The isotope shift between¹⁹⁷Au (stable) and the radioactive Au isotopes¹⁹⁰Au,¹⁹¹Au,¹⁹²Au and¹⁹³Au were determined by resonance fluorescence spectroscopy in the 6s ² S _1/2–6p ² P _1/2.λ=267.6nm line. The unstable Au isotopes were produced at the ISOLDE mass separator at CERN. The nuclei were investigated semi on-line in a resonance vessel, heated to 1,400°C. The results areδν ^190,197=?11.12(39) GHz,δν ^191,197=?9.67(12) GHz,δν ^192,197=?8.32(15) GHz,δν ^193,197=?6.29(11) GHz, corresponding to a change of the mean-square charge radius byδ〈r ²〉^190,197 =0.261(12) fm²,δ〈r ²〉^191,197=0.227(5) fm²,δ〈r ²〉^192,197=0.195(5) fm²,δ〈r ²〉^193,197 =0.148(4) fm².     

g factor measurements of high spin isomeric states in 187,189,191 Au

The g factors of three high spin isomers in ^187,189,191Au have been measured, using the time differential perturbed angular distributions. The reactions used and the results obtained for the g factors and the lifetimes are: ¹⁷²Yb(¹⁹F, 4nγ) ¹⁸⁷Au, g (31/2- or 35/2-) = 0.25 (3), T_1/2 = 102 (5) ns; ¹⁸¹Ta ( ¹²C, 4nγ) ¹⁸⁹Au, g (31/2+) = 0.42 (2), T_1/2 = 242 (10) ns; and ¹⁷⁶Yb(¹⁹F, 4nγ) ¹⁹¹Au, g (31/2+) = 0.42 (3) T^1/2 = 402 (20) ns. These results show that the structure of these isomers is consistent with a 1 proton, 2 neutrons structure. The experimental set-up was cheked by measuring the g factor of the Coulomb excited 197 keV, T_1/2 = 89.3 ns level of the ¹⁹F beam stopped in the lead backing.     

Die Hyperfeinstrukturaufspaltung des Grundzustandes2 S 1/2 und das magnetische Kerndipolmoment von Au197

The hyperfine structure of the groundstate 6s ² S _1/2 and the nuclear magnetic dipole moment of gold 197 have been studied by the atomic beam magnetic resonance technique. A special high frequency arrangement is described. The hyperfine structure separationΔ v was determined fromΔF=1 transitions. The magnetic dipole momentμ _I was measured by a direct method. The experiments yield the following results:Δv (²S_1/2)=(6099,309±0,010) Mc/secμ _I (Au¹⁹⁷)=+(0,1445±0,0014)μ _K.     

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 (T_1/2=53 s) and¹⁸³Au (T_1/2=42 s) as well as for 15 isotopes of platinum in the range between¹⁹⁸Pt (stable) and¹⁸³Pt (T_1/2=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)μ _N .     

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.     

Magnetic dipole moments of the 11/2− isomers of193, 195, 197Au

Nuclear orientation techniques have been used to derive the magnetic dipole moments of the three 11/2^? isomers of^{193, 195, 197}Au. The derived q-factors are: 1.121(17) for^193mAu, 1.122(17) for^195mAu, and 1.17(7) for^197mAu. For the first two isotopes, the NMR-ON method could be used. In the latter case, the temperature dependence of nuclear orientation has been used.     

Solid-state synthesis and atomic ordering in thin Cu/Au films (atomic ratio, Cu : Au = 3 : 1)

In situ transmission electron microscopy investigations of the processes of solid-state synthesis and atomic ordering in bilayer Cu/Au nanofilms (atomic ratio, Cu: Au = 3: 1) are conducted. It is found that solid-state synthesis starts at 170°C. A Cu₃Au atomic-disordered structure (Fm3m space group; lattice constant, a = 3.76 ± 0.01 Å) forms at 280°C. Annealing the film for 1 hour at 380°C produced a Cu₃AuI (L1₂ type) atomic-ordered superstructure, a Pm-3m space group, and lattice constant, a = 3.76 ± 0.01 Å in the bulk of the film.     

Measurement of Neutral pions in √NN=200 GeV and 62.4 GeV Au+Au collisions at RHIC-PHENIX

Neutral pions (π⁰) in √_NN=200 GeV and 62.4 GeV Au+Au collisions were measured at RHIC-PHENIX Year-4 Run. In √_NN=200 GeV, π⁰ spectra are measured up to p _T=20 GeV/c. A strong suppression by a factor of ～5 is observed and stays almost constant up to 20 GeV/c.     

Orientation of199mHg by optical pumping detected by γ-radiation anisotropy

^199mHg was produced and mass separated at the ISOLDE facility (CERN). Nuclear orientation achieved by optical pumping via the resonance line 6s ^{2 1} S ₀→6s6p ³ P ₁,λ=2537Å was monitored by means of the anisotropy of theγ-radiation emitted in the cascade^199mHg(I=13/2⁺) $${}^{199m}Hg(I = 13/2^ + )\xrightarrow[{M4}]{}{}^{199*}Hg(I = 5/2^ - )\xrightarrow[{E2}]{}{}^{199}Hg(I = 1/2^ - ).$$ ^199*Hg(I=5/2^?)¹⁹⁹Hg(I=1/2^?). Maximum anisotropies of 35% (2,8%) were found in the M4 (E2) transition. A Zeeman scanning of the³ P ₁ state yielded the positions ofF=13/2 and theF=15/2 hfs components relative to the reference isotope²⁰⁴Hg at 15.13 (15) GHz and ?2.86 (15) GHz respectively. Isotopic shift and the quadrupole interaction constant were deduced from these values using the knownA factor.δv ^199m/2O4=v ^2O4?v ^199m=12.20 (16) GHzB=?0.86 (25) GHz. From theB factor the spectroscopic quadrupolment was calculated asQ _s =1.54 (44) barn.     

Magnetic hyperfine field of Hg in nickel and the sign of magnetic moment of 197mAu by NMR-ON

Nuclear magnetic resonance on oriented nuclei (NMR-ON) measurements were performed on the successive decay of ^197mHg–^197mAu in Ni. The NMR-ON resonance spectra of ^197mHgNi were obtained by detecting the 134 keV γ-ray from the decay of ^197mHg and the 279 keV γ-ray from the decay of ^197mAu. The magnetic hyperfine splitting frequency of ^197mHgNi in an external magnetic field of 0.2 T has been determined as 16.55(6) MHz. With the known g-factor of ^197mHg the hyperfine field of B₈₂(^197mHgNi)= -13.53(6) T was deduced. The anisotropy of the 279 keV γ-ray (^197mAu to ¹⁹⁷Au) increased at the resonance. This phenomenon was explained using the spin inversion process including the lifetime of the isomer and the spin–lattice relaxation time. The sign of the g-factor of ^197mAu was determined to be positive. This revised version was published online in August 2006 with corrections to the Cover Date.     

Investigation of new neutron-rich gold isotopes203Au and205Au

Using a²⁰⁸Pb beam of the UNILAC accelerator at GSI we produced the new isotopes²⁰³Au and²⁰⁵Au and identified them by measuring their-decay properties. Their half-lives were found to be 60(6)s and 31(2)s, respectively, and theQ-value of²⁰³Au was determined to beQ =2040(60)keV. Nuclear structure information of^203,205Hg was derived from this measurement. Furthermore, production cross-sections of^203,205Au are given and compared to those obtained in other experiments.This work has been supported by the Federal Ministry for Research and Technology (BMFT) under contract number 06 Gö 451-1/2     

Mössbauer determination of the E2/M1 mixing ratio of the 77 keV transition in197Au and of the sign of the electric field gradient in KAu(CN)2

A Mössbauer measurement of the E2/M1 mixing ratio of the 77 KeV transition in¹⁹⁷Au yielded δ=?0.352±0.005. With this result, Mössbauer absorption spectra of KAu(CN)₂ single crystals show that the electric field gradient at¹⁹⁷Au in this compound is negative. This implies that the field gradient is mainly produced by 6p_z electrons. The data also indicate a large vibrational anisotropy of Au in KAu(CN)₂.     

Inclusive fragment production in84Kr +197Au atE/A=35 MeV

Inclusive cross sections of intermediate mass fragments from the reaction⁸⁴Kr+¹⁹⁷Au atE/A=35 MeV were measured over the range 8°≦Θ _lab≦70° with a low detection threshold. A moving-source parameterization was used to fit the double-differential cross sections. The integrated cross section for fragment production exceeds the total reaction cross section thus indicating a large probability for multi-fragment processes. The deduced large temperature parameters can be explained by assuming emission from a rotating source. From the comparison to reactions with¹²C and⁴⁰Ar projectiles at E/A=30 MeV a systematics of inclusive fragment production as a function of the projectile mass is obtained.     

The density of states of b.c.c. Nb3Au: A comparison with A-15 Nb3Au

When Nb₃Au is converted from the A-15 structure to the b.c.c. allotrope, a sharp decrease in the superconducting transition temperature, T_c, occurs (11.1 to 1.5 K). To study possible causes for this sharp decrease, specific heat measurements have been made on the b.c.c. form of Nb₃Au yielding values of γ=19.2 mJ/mole-K², β=0.274 mJ/mole-K⁴ and θ_D=305 K. These parameters compared with published values for the A-15 Nb₃Au indicate that a sharp drop in the density of states at the Fermi level, N(0), occurs when the A-15 structure is converted to the b.c.c. form.     

Structure and magnetotransport properties of the new quasi-two-dimensional molecular metal β″-(BEDT-TTF)4H3O[Fe(C2O4)3] · C6H4Cl2

The β″-(BEDT-TTF)₄A^I[M^III(C₂O₄)₃] · G(A^I=NH ₄ ⁺ , H₃O⁺, K⁺, Rb⁺; M^III=Fe, Cr; G = “guest” solvent molecule) family of layered molecular conductors with magnetic metal oxalate anions exhibits a pronounced dependence of the conducting properties on the type of neutral solvent molecules introduced into the complex anion layer. A new organic dichlorobenzene (C₆H₄Cl₂)-containing conductor of this family, namely, β″-(BEDT-TTF)₄H₃O[Fe(C₂O₄)₃] · C₆H₄Cl₂, is synthesized. The structure of the synthesized single crystals studied by X-ray diffraction is characterized by the following parameters: a = 10.421(1) Å, b= 19.991(2) Å, c= 35.441(3) Å, β = 92.87(1)°, V= 7374(1) ų, space groupC2/c, and Z = 4. In the temperature range 0.5&;2-300 K, the conductivity of the crystals is metallic without changing into a superconducting state. The magnetotransport properties of the crystals are examined in magnetic fields up to 17 T at T = 0.5 K. In fields higher than 10 T, Shubnikov-de Haas oscillations are detected, and the Fourier spectrum of these oscillations contains two frequencies with maximum amplitudes of about 80 and 375 T. The experimental results are compared with the related data obtained for other phases of this family. The possible structural mechanisms of the effect of a guest solvent molecule on the transport properties of the β″-(BEDT-TTF)₄A^I[M^III(C₂O₄)₃] · G crystals are analyzed.     

Some peculiarities in the interaction of 6He with 197Au and 206Pb

Excitation functions were measured for fusion followed by the evaporation of neutrons in the reactions ²⁰⁶Pb(⁶He, 2 _n )²¹⁰Po and ¹⁹⁷Au(⁶He, xn)^203−xn T1, where x = 2−7, as well as for the transfer reactions on a ¹⁹⁷Au target with the formation of the ¹⁹⁶Au, ¹⁹⁸Au, and ¹⁹⁹Au isotopes. The experiment was carried out at the Dubna Radioactive Ion Beams (DRIBs) complex of FLNR, JINR. The ⁶He beam intensity was about 5 × 10⁶ pps, the maximum energy being (60.3 ± 0.4) MeV. A significant increase in the cross section was observed below the Coulomb barrier for the fusion reaction with the evaporation of two neutrons compared to statistical model calculations. Unusual behavior for the production of ¹⁹⁸Au is observed, whereas the cross section for the formation of ¹⁹⁹Au is very low. The analysis of the data in the framework of the statistical model for the decay of excited nuclei, which took into account the sequential fusion of ⁶He, has shown good agreement between the experimental and calculated values of the cross sections for the case of sub-Coulomb-barrier fusion in the ²⁰⁶Pb + ⁶He reaction. The text was submitted by the authors in English.