Properties of the 13/2+ isomeric decay in201Hg

The isomeric decay of theT _1/2=94 us isomeric state in²⁰¹Hg was studied in beam via the reaction¹⁹⁸Pt(α, n). Gamma-ray and conversion-electron spectra were recorded. From the conversion coefficients, the multipolarities of the two depopulating transitions were determined to beM 2 + 10%E 3 andE 2, respectively. These assignments give the depopulating transitions to be 13/2⁺ → 9/2^? and 9/2^? → 5/2^?, and these thus substantiate the previous suggestion that the isomeric state hasJ ^π=13/2⁺. For the 13/2⁺ → 9/2^? M 2 transition a detailed study ofE 3 andM 4 admixed amplitudes was done. The microscopic properties of the 13/2⁺ and 9/2^? states are discussed, and a comparison to the corresponding ones in^199,203,205Hg is made.     

g-factors of the lowest 2+ and 4+ states in198, 200, 202Hg

Theg-factors of the 2 ₁ ⁺ and 4 ₁ ⁺ states in^198,200,202Hg were simultaneously measured by means of the transient-field perturbed angular correlation method in Coulomb excitation using multi-isotopic targets and thin polarized Gd foils as ferromagnetic host. Theg(2 ₁ ⁺ ) andg(4 ₁ ⁺ ) were found identical within errors in^{198, 200}Hg, while in²⁰⁰Hg lowerg-factor values have been determined. The experimentalg-factors were compared with the predictions of the pairing-plus-quadrupole, dynamical deformation and interacting boson models.     

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.     

g-factor measurements in stable Hg isotopes

The g-factor of the first 2⁺ state in¹⁹⁸Hg,²⁰⁰Hg and²⁰²Hg has been measured using the thin foil Transient Field technique. The values were calibrated to the known g-factor of the first 5/2⁻ state in¹⁹⁹Hg. The levels were Coulomb excited by 217 MeV nickel ions with gadolinium acting as ferromagnetic medium. The obtained values are rather constant and contradict a previously observed dip at²⁰⁰Hg. Two other g-factors have been remeasured in¹⁹⁹Hg.     

Vergleich der Davydov-Theorie mit dem Modell des achsialsymmetrischen Kreisels mit Rotation-Vibrations-Wechselwirkung für deformiertegg-Kerne

For deformed even-mass nuclei the model of the axial-symmetric vibrating top with rotation-vibration-interaction is compared to the Davydov-model without and with aβ-band. TheE2-transition-probabilities are calculated. The coefficientsB _ze andC fromE=A I(I+1) ?B _ze I ²(I+1)²+C I ³(I+1)³ are obtained. For the transition-probabilities from the states of the γ-band to the states of the ground state band as well as forB andC the Davydov-model yields values only about half of those obtained from the RV-theory. A comparision to the present availuable experimental data is made. In the RV-model the agreement is better than in the Davydov-theory.     

Magnetic hyperfine interaction in muonic indium,osmium and mercury

The magnetic hyperfine interaction in several muonic atoms has been measured. The magnetic splittings of the 1s _1/2, 2s _1/2 and 2p _1/2 muon states in the 9/2⁺ ground state of¹¹⁵In, determined by measuring muonic X rays areΔE _mag(1s _1/2,¹¹⁵In 9/2⁺)=3580±70 eVΔE _mag(2s _1/2,¹¹⁵In 9/2⁺)=525±120 eVΔE _mag(2p _1/2,¹¹⁵In 9/2⁺)=850±180 eV. The magnetic splitting of nuclearγ rays in the presence of a muon in the 1s _1/2 state yields for the 1/2^? ground state in¹⁹⁹HgΔE _mag(1s _1/2,¹⁹⁹Hg 1/2^?)=468±115 eV and the following values for the first excited 2⁺ states in the nuclei^190,192Os and²⁰⁰Hg:ΔE _mag(1s _1/2,¹⁹⁰Os 2⁺)=665± ₄₀ ⁸⁰ eVΔE _mag(1s _1/2,¹⁹²Os 2⁺)=800±80 eVΔE _mag(1s _1/2,²⁰⁰Hg 2⁺)=655± ₇₅ ¹⁰⁵ eV. These data are compared with calculations using different nuclear models.     

Observation of the weakly deformedvi 13 2/2 band in188Hg

High-Spin states in¹⁸⁸Hg have been investigated using the¹⁶⁸Er(²⁴Mg,4n) reaction. The rotation aligned vi ₁₃ ^2/2 band, which intersects the weakly oblate ground state band atI≈10, is observed up toI ^π =20⁺ with an isomeric 12⁺ level with T_1/2=134(15)ns. The coexisting strongly deformed band, built on the 825 keV 0⁺ level, is observed up to the 14⁺ state. The systematics of the vi ₁₃ ^2/2 rotation aligned bands is discussed.     

Nuclear deformations in 186Hg from lifetime measurements

Using the recoil-distance Doppler-shift method, we have measured the half-lives of the 2⁺, 4⁺, 6⁺ and 8⁺ states in ¹⁸⁶Hg following the reaction ¹⁷⁰Yb(²⁰Ne, 4n) ¹⁸⁶Hg. We find a strong enhancement of the 6⁺→4⁺ transition probability, B(E2, 6⁺→4⁺)=1.9±0.8 e²b², over the 2⁺→0⁺ value, B(E2, 2⁺→0⁺)=0.28±0.05 e²b². These results indicate that ¹⁸⁶Hg makes an angular-momentum-induced transition from nearly spherical to strongly deformed shapes.     

Deformed states of high spin in42Ca

The⁴²Ca levels at 4,715 and 6,633 keV excitation energy have been investigated using the³⁹ K(α,pγ reaction atE _α=14 and 15 MeV. From particle-γ-ray angular correlations the spin assignmentsJ(4,715)=6, 4 andJ(6,633)=8, 6, 4 have been obtained. Lifetime measurements using the Doppler-shift attenuation method yieldedτ (4,715)=120±46 fs andτ(6,633)=52±21 fs. Both levels have positive parity and decay by enhancedE2 transitions. They are interpreted as theJ ^π=6⁺ and 8⁺ members, respectively, of theK ^π=0⁺ rotational band which has theE _x =1,837, 2,423 and 3,250 keV states as further members. The enhancement of inbandE2 transitions is 50 _?16 ⁺³⁵ W.u. (6→4) and 63 W.u. (8→6) respectively. The intrinsic quadrupole moments which have been derived on the basis of the coexistence model, areQ ₀=1.13?0.16/+0.37b(8→6) andQ ₀=1.36±0.25b(6→4), respectively. TheJ ^π=10⁺ member of the rotational band has possibly been observed as a level at 8,856±5 keV excitation energy.     

High-spin states in189Hg

High-spin levels in¹⁸⁹Hg have been populated via the¹⁷⁵Lu(¹⁹F, 5n) reaction. A rotation-aligned band built on a 13/2⁺ state originating from theνi _13/2 subshell is identified which is interpreted within the framework of “quasiparticle+rotor” models. A negative parity band built on a 21/2^? state which can be accounted for by a three quasi-particle state is also observed.     

Oblate shapes of200, 202, 204Hg

Measurements of the reorientation effect for the first excited 2⁺ states in^{200, 202, 204}Hg were performed by exploiting the dependence of theγ-ray yield on Q₂+ for different projectiles. For²⁰⁰Hg, a positive quadrupole moment of Q₂=0.96±0.11 eb (for negative interference) or Q₂=1.11±0.11 eb (for positive interference) was determined indicating an oblate shape. Small positive Q₂ values were also found for²⁰²Hg and²⁰⁴Hg. Nine B(E2) values for excitation of the 2⁺, 2⁺′ and 4⁺ states in^196–204Hg measured.     

The electric quadrupole moment of the first excited state of 204Hg

The static electric quadrupole moment Q₂₊ and the B(E2; 0⁺ → 2⁺) value of the 2⁺ first excited state of ²⁰⁴Hg have been determined using the reorientation effect in Coulomb excitation. An annular Si surface-barrier detector was used to detect back-scattered ⁴He, ¹²C and ¹⁶O projectiles. In a subsidiary experiment, spectra were obtained from ²⁰⁴Hg(p, p')²⁰⁴Hg using Si surface-barrier detectors, and the results were used in conjunction with previously existing data to provide information on higher states of ²⁰⁴Hg which might participate in the Coulomb excitation of the 2⁺ state. From a 3-level analysis, we find Q₂₊ = +0.40 ± 0.20 e · b and B(E2; 0⁺ → 2⁺) = 0.423 ± 0.005 e² · b². These results are in good agreement with the predictions of particle-vibrational coupling calculations. The value obtained for $\text{Q}{}_{\mathrm{2+}}\text{(}{}^{204}\text{Hg)}$ is substantially smaller in magnitude than values of Q₂₊ previously determined for ^{198, 200, 202}Hg.     

Gyromagnetic ratios of the 4+ and 6+ rotational states of184W

The nuclear Larmor precession has been observed for the 2⁺, 4⁺ and 6⁺ rotational states of¹⁸⁴W in the hyperfine field of WFe by application of the TDPAC and the IPAC techniques. A carrier free radioactive source of^184m Re alloyed with high purity iron was used for all three measurements. From the Larmor precession observed in the 2⁺ state by TDPACω _L = 944(15) MHz and the knowng-factor the hyperfine fieldB _{300 K} ^hf (WFe)=?69.6(27)T was derived. The deviation from the result of a spin echo experiment with¹⁸³WFe extrapolated to room temperature may be caused by the Bohr-Weisskopf effect (hyperfine anomaly). IPAC measurements with the same sample polarized in an external magnetic field of 1.6T gave for the 4⁺ and 6⁺ rotational states: ω _L τ(4⁺)=0.0609(22) andω _L τ(6⁺)=0.00735(102). By use of experimentalB(E2)-values theg _R -factors were derived asg _R (4⁺)=+0.276(26) andg _R (6⁺)=+0.281(45). The directional correlation of the 537?384 keVγ-γ cascade has been analysed in terms of anE1/M2/E3 mixture for theK-forbidden 537keV transition. We obtained the mixing ratiosδ(M2/E1)=±0.086(16),δ(E3/E1)=?0.028(5) with the sign convention of Krane and Steffen.     

EquilibriumK-shell excitation of highly ionized neon

Reorientation effect and multiple Coulomb excitation measurements have been performed for^{198, 200, 202, 1204}Hg. By measuring particle spectra after Coulomb excitation of an enriched¹⁹⁸Hg target with⁴He and¹⁶O beams, a positive quadrupole moment of Q₂ = 0.66±0.18 eb (for negative interference) or Q₂=0.80±0.18 eb (for positive interference) andB(E2,0→2)=0.991±0.006 e²b² were obtained. All otherB(E2) values and quadrupole moments were determined relative to these numbers from preciseγ-ray yields obtained from Coulomb excitation of a frozen^natHg target with⁴He and¹⁶O projectiles. Oblate shapes of all Hg isotopes were found. The data have been interpreted in terms of triaxial rotation and anharmonic vibrations.     

Directional correlations in the decay of 1200y 166Ho

γγ-directional correlations have been measured between the ground state band transitions 6→4, 4→2 and 2→0 and the γ-rays depopulating the levels of the gamma vibrational band and the negative parity states of¹⁶⁶Er. Thereby angular momenta could be assigned to the latter states andM2/E1 multipole mixtures determined for the depopulating γ-transitions. TheE2/M1 mixing ratios were obtained for a series ofI _γ→I _g transitions up toI _γ=8⁺. These are used to investigate the angular momentum dependence of theE2/M1 admixtures.     

Static quadrupole moments of the first excited states of 200Hg and 202Hg

The static quadrupole moments Q_2⁺ and B(E2; 0⁺ → 2⁺) values of the 2⁺ first excited states of ²⁰⁰Hg and ²⁰²Hg have been determined using the reorientation effect in Coulomb excitation. An annular silicon surface-barrier detector was used to detect backscattered ⁴He, ¹²C and ¹⁶O projectiles. It is found that for ²⁰⁰Hg, Q_2⁺ = +1.07 ± 0.19 e · b(+0.98 ± 0.19 e · b) for destructive (constructive) interference from the 2^+′ state, and B(E2; 0⁺ → 2⁺) = 0.853 ± 0.007 e² · b². For ²⁰²Hg, we find Q_2⁺ = +1.01 ± 0.13 e · b (+0.87 ± 0.13 e · b) and B(E2; 0⁺ → 2⁺) = 0.605 ± 0.005 e² · b². The Q_2⁺ value obtained for ²⁰⁰Hg is in agreement with previous work, but that for ²⁰²Hg is not. The results obtained are compared with the predictions of various nuclear models, and the mass dependence of Q_2⁺ in the region 182 ≦ A ≦ 206 is examined.     

Alpha-decay study of188Pb and180,182Hg

Theα decay of mass-separated¹⁸⁸Pb and^180,182Hg has been studied at the GSI on-line mass separator. Alpha singles spectra as well asα-X-t andα-e-t coincidence events were collected. Fine structure in theα decay of¹⁸⁸Pb was measured for the first time, feeding the 2₁ ⁺ and 0₂ ⁺ states in¹⁸⁴Hg. Theα decay of^180,182Hg feeds low-lying states in^176?178Pt. One of these states could be identified as a 0⁺ state. The deexcitation pattern could be established. As a by-product an alpha-decay scheme of¹⁸⁰Au towards levels in¹⁷⁶Ir is given.     

Investigation of level energies and B(E2) values for rotation-aligned bands in Hg isotopes

High spin states in ^{191, 192, 193, 195, 197, 199}Hg were investigated by observing γ-rays and conversion electrons in the compound reactions ${}^{\mathrm{192,\; 194,\; 198}}\text{Pt(α, x}\text{n}\text{)}\text{and}{}^{192}\text{Pt}\text{(}{}^3\text{He}\text{, 4}\text{n}\text{)}$. In ¹⁹⁷Hg the decoupled band built on the $\text{13}\text{2}{}^{\mathrm{+}}$ state and the semi-decoupled negative-parity band are observed up to $\text{I}{}^{\mathrm{\pi }}\text{=}\text{41}\text{2}{}^{\mathrm{+}}\text{and}\text{33}\text{2}{}^{\mathrm{?}}$, respectively. A careful investigation of ¹⁹⁹Hg revealed no new high spin states above the previously known levels with $\text{I}{}^{\mathrm{\pi }}\text{=}\text{25}\text{2}{}^{\mathrm{+}}\text{and}\text{31}\text{2}$^?. Half-lives were determined for the 10⁺, 7^?, 8^? and 16^? states in ¹⁹²Hg, the if$\text{33}\text{2}{}^{\mathrm{+}}$$\text{states in}{}^{\mathrm{191,193}}\text{Hg and the}$ (frc states in ^{191, 193, 195, 197}Hg. The systematics of the level energies and B(E2) values for the positive-parity ground and $\text{13}\text{2}{}^{\mathrm{+}}$ bands and the negative-parity semi-decoupled bands in ^190–200Hg is discussed.     

High-spin states in26Mg

Theγ-decays of levels in²⁶Mg have been investigated up to 12.5 MeV excitation energy by proton-γ-ray coincidence measurements in the²³Na(α, pγ) reaction at 14.2 and 16 MeV bombarding energy. Lifetime-measurements, made with the Doppler-shift attenuation method, and proton-γ-ray angular-correlation measurements were performed at E_α=14.2 MeV. Many high-spin states were observed, among them levels at 6,978 (5⁺), 7,283(4^?), 7,395(5⁺), 7,953(5^?), 8,202(6⁺), 8,472(6⁺), 9,065(5), 9,112(6⁺), 9,169(6^?), 9,383 (6⁺), 9,542(5), 9,829(7⁺), 9,989(6⁺) and 12,479(8⁺, 7^?) keV excitation energy. The spectrum of positive-parity states and their electromagnetic properties are reproduced with good accuracy by shell-model calculations which employ a unifieds-d shell Hamiltonian and the unrestricted configuration space of the 0d _5/2 1s _1/2 0d _3/2 shell. Members of five inferred rotational bands, withK ^π=0⁺, 2⁺, 3⁺, 0⁺ and 3^? have been observed up to at leastI=6. TheK ^π=2⁺ band shows strong anomalies of excitation energies andE2 transition rates near theI=6 state. The static intrinsic quadrupole moments calculated from the shell model wave functions indicate transitions from prolate to oblate deformation within theK ^π=2⁺ band and also the ground state band. The lowest lyingI ^π=4⁺ state appears to be “spherical” and cannot be associated with a rotational band.     

Reorientation effect measurements and multiple coulomb excitation in102Ru

The quadrupole moment of the first 2⁺ state in¹⁰²Ru and fourB(E2) values have been measured by means of Coulomb excitation. The results are:Q ₂₊=?0.68(8)eb;B(E2, 01/+→21/+)=0.617(5)e ² b ²;B(E2, 01+→22/+)=0.013 (2)e ² b ²;B(E2, 21/+→22/+)= 0.07(1)e ² b ²;B(E2, 2 ₁ ⁺ →4 ₁ ⁺ )=0.30(6)e ² b ². The results are discussed within the frame of the Interacting Boson Approximation.