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.     

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.     

Coulomb excitation of 182, 184, 186W and 166Er with 4He and 16O ions

The Coulomb excitation reaction induced by ⁴He ions selectively excites 2⁺ and 3^? states by direct E2 and E3 Coulomb excitation. In this paper, we present new results from γ-ray spectroscopy with 15 MeV ⁴He ions on a natural abundance target of W. In particular, a 3^? state in each isotope, ^{182, 184, 196}W, was observed by direct E3 excitation. In addition to obtaining B(Eλ, 0 → J = λ) for excitation of each state, information on the reduced transition probabilities for the different decay modes of these states is given. The Coulomb excitation probabilities of the 2'⁺ states at 786 keV in ¹⁶⁶Er and at 737 keV in ¹⁸⁶W were measured with ¹⁶O and ⁴He ions by the backscattered particle-gamma coincidence method in order to determine the static electric quadrupole moment Q_2'. We obtain for ¹⁶⁶Er Q_2' = 2.11 ± 0.37 e· b which is in agreement with (Q_2')_rot and for ¹⁸⁶W Q_2' = 1.17 ± 0.30 e · b which is in agreement with Kumar-Baranger model calculations and is significantly smaller than (Q_2')_rot. This deviation of the measured Q_2' from (Q_2'rot implies in the framework of the Kumar-Baranger calculations a strong coupling between β- and γ-vibrational bands. On the other hand, our observed upper limit for B(E2,2″ → 2′) does not confirm this implication.     

Reorientation effect measurements in 124Te, 126Te and 128Te

Coulomb excitation probabilities of the first 2⁺ states of ¹²⁴Te, ¹²⁶Te and ¹²⁸Te have been determined. The measurement was performed by resolving the inelastically and elastically backward scattered ⁴He and ¹⁶O projectiles using an annular surface barrier detector. Quadrupole moments (Q₂₊) as well as the B(E2, 0⁺ → 2⁺) values were extracted by analyzing the excitation probabilities with the Winther-de Boer multiple Coulomb excitation program. The Q₂ deduced for the positive sign of the 2⁺ interference term are ?0.41 ± 0.08 e · b, ?0.144 ± 0.11 e · b and ?0.12 ± 0.09 e · b for ¹²⁴Te, ¹²⁶Te and ¹²⁸Te, respectively.     

Determination of the static quadrupole moment of the first 2+ states of 122Te, 124Te,and 130Te by heavy-ion coulomb excitation

A Coulomb excitation experiment has been performed on the first 2⁺ states of ¹²²Te, ¹²⁴Te and ¹³⁰Te. The relative excitation probabilities of the first 2⁺ states were measured at backward and forward projectile scattering angles. Particle-γ coincidences were used to identify the inelastic events. The data were analyzed with the aid of the Winther-deBoer multiple Coulomb excitation program. Separate γ-ray angular distribution measurements were made as a function of target recoil velocity to determine the influence of the deorientation effect. The projectile and bombarding energy were chosen to minimize the effect on the experiment of higher state interference due to Coulomb excitation of the first 2⁺ state via the second 2⁺ state. For positive higher state interference the extracted quadrupole moments of the first 2⁺ states are Q₂₊ = ?0.43 ± 0.08 b, ?0.49 ± 0.08 b and ?0.08 ± 0.08 b for ¹²²Te, ¹²⁴Te and ¹³⁰Te respectively. These results and other measurements of Q_2⁺ for the doubly even Te isotopes are used to discuss the model dependent calculations of Q_2⁺.     

Electric quadrupole and magnetic dipole moments of the first excited 2+ states of186Os and188Os

The spectroscopic quadrupole moments and the magnetic dipole moments of the lowest 2⁺ states in¹⁸⁶Os (137 keV) and¹⁸⁸Os (155 keV) have been determined by Mößbauer transmission experiments. The electric quadrupole momentsQ ₂₊(Os 186)=? (1.80±0.22) b andQ ₂₊(Os 188)=?(1.81±0.24) b as well as their ratioQ ₂₊(Os 188)/Q ₂₊(Os 186)=1.00±0.07 within the limits of error agree withB(E2) data, if a comparison on the basis of the rotational model is made. For the g-factors and their ratio g₂₊(Os 186)=0.281±0.008, g₂₊(Os 188)=0.305±0.015 andg ₂₊(Os 188)/g ₂₊(Os 186)=1.08±0.05 was obtained. All results are compared with recent model calculations.     

Electric moments of the first excited state of 18O

The static quadrupole moment Q_2⁺ and the B(E2; 0⁺ → 2⁺) value of the first excited state of ¹⁸O at e_x = 1.982 MeV have been determined using the reorientation effect in Coulomb excitation. Surface-barrier detectors at laboratory angles of 90° and 174° were used to detect ¹⁸O ions elastically and inelastically scattered from ²⁰⁸Pb. At both angles, we determined experimentally the maximum bombarding energies at which nuclear interference effects were negligible. It is found that Q_⁺ = ?0.023 ± 0.021 e · b (?0.052 ± 0.021 e · b) for destructive (constructive) interference from higher states. This result is in good agreement with theoretical expectation. For the transition moment we find B(E2; 0⁺ → 2⁺) = 0.00390 ± 0.00018 e² · b² (0.00371 ± 0.00018 e² · b²) for destructive (constructive) interference.     

The quadrupole moment of 26Mg as a test of shell-model interactions

The static quadrupole moment Q_21⁺, and the B(E2; 0₁⁺ → 2⁺₁) value of the first excited state of²⁶Mg have been measured using the reorientation effect in Coulomb excitation of ²⁶Mg projectiles. It is found that Q_21⁺ = ?13.6±3.0 (?9.5±3.0) e ·fm² and B(E2; 0⁺₁ → 2⁺₁) = 322±16 (328±16) e² ·fm⁴ for constructive (destructive) interference from higher states. The result for Q₂ clearly differentiates among several alternative effective interactions which have been used in shell-model calculations.     

Reorientation effect measurements of 122Te and 130Te

Coulomb excitation probabilities of the first 2 ⁺ states of ¹²²Te and ¹³⁰Te have been determined. The measurement was performed by resolving the inelastically and elastically scattered ⁴He and ¹⁶O projectiles using eight surface barrier detectors between 44° and 173°. Quadrupole moments Q₂⁺ as well as B(E2, 0⁺ → 2⁺) values were deduced. The Q₂⁺ found for the positive sign of the 2₂⁺ interference term are ?0.46±0.05 e · b and ?0.15±0.10 e · b for ¹²²Te and ¹³⁰Te respectively.     

Coulomb excitation of the Kπ=16+ rotational band in 178Hf

A heavy-ion multiple Coulomb excitation experiment on a very exotic target containing microweight quantities of ¹⁷⁸Hf in the K^πn = 16⁺ isomeric state has been performed at 4.77 MeV/u ²⁰⁸Pb beam energy. The first excited I^π = 17⁺ state has been observed at an excitation energy of 357.4 ± 0.3 keV with respect to the isomeric state. The intrinsic electric quadrupole moment of Q ₀ = 8.2 ± 1.1 b has been derived from the experimental data within the rigid rotor model.     

Coulomb excitation of the Kπ=16+ rotational band in178Hf

A heavy-ion multiple Coulomb excitation experiment on a very exotic target containing microweight quantities of¹⁷⁸Hf in the K^π = 16⁺ isomeric state has been performed at 4.77 MeV/u²⁰⁸Pb beam energy. The first excited I^π = 17⁺ state has been observed at an excitation energy of 357.4±0.3 keV with respect to the isomeric state. The intrinsic electric quadrupole moment ofQ ₀=8.2±1.1 b has been derived from the experimental data within the rigid rotor model.     

Electric quadrupole moments of the first excited states of 194Pt, 196Pt and 198Pt

Coulomb excitation of ^{194, 196, 198}Pt by ⁴He, ¹²C and ¹⁶O projectiles has been used to determine the static electric quadrupole moments Q(2₁⁺) of the first excited states of ^194,196,198Pt, together with values of B(E2; 0₁⁺ → 2₁⁺). It is clearly established that Q(2₁⁺) is positive for each nucleus, having values of 0.48 (14)e · b and 0.66 (12)e · b for ¹⁹⁴Pt and ¹⁹⁶Pt, respectively, and 0.42 (12)e · b or 0.54 (12)e · b for ¹⁹⁸Pt, depending on whether the interference term P₄(2₂⁺) is positive or negative. Results obtained for B(E2; 0₁⁺ → 2₁⁺) are 1.661 (11)e² · b², 1.382 (6)e² · b² and 1.090 (7)e² · b² for ^{194, 196, 198}Pt respectively. The results are compared with the predictions of various nuclear models.     

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.     

Measurement of the mean lifetimes of low spin states in the superdeformed band in133Nd

The mean lifetimes of the lower spin states of the superdeformed band in¹³³Nd have been measured with the coincidence recoil distance method. The reaction used to populate the band was¹⁰⁵Pd (³²S, 2p2n)¹³³Nd at a beam energy of 152 MeV, and the gamma-rays were detected with the POLYTESSA array. The differential decay curve method was used to analyse the data and transition quadrupole moments,Q ₀, were extracted from the measured lifetimes. The results obtained from the three lowest transitions in the superdeformed band are:Q ₀=6.3±0.9 eb (21+/2→17+/2),Q ₀=6.7±1.1 eb (25+/2→21+/2) andQ ₀>5.0 eb (29+/2→25+/2). These results are consistent with previous results for the high spin members of the band, and are compared to theoretical calculations of total routhian surfaces. The calculation of reduced transition probabilities for the transitions that feed out of the band, allows the effect of hindrance due to K-forbiddenness to be investigated.     

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.     

The quadrupole momentQ 2+ of32S

The static quadrupole moment of the first excited 2⁺ state in³²S was determined by comparing, in coincidence with³²S ions backscattered from⁶⁰Ni, the gamma-ray yields of the 2 ₁ ⁺ →0 ₁ ⁺ transitions in both nuclei for bombarding energies around 70MeV. Depending on the sign of the interference term for transitions via the second excited 2⁺ state in³²S, the following two values were determined:Q ₂ ⁺ =(?18±4)e·fm² andQ ₂₊=(?15±4)e·fm².     

A study of deuteron quadrupole moment effects in sub-coulomb scattering of tensor polarized deuterons

Measurements of the tensor analyzing power T₂₀ are presented for deuteron elastic scattering from ²⁰⁸Pb at energies below the Coulomb barrier. It is found that, for energies below about 7 MeV, T₂₀ arises primarily from the interaction of the deuteron quadrupole moment with the nuclear electric field gradient. Contributions to T₂₀ from nuclear interactions with the target are shown to be very small for E_d ? 5 MeV. Measurements of T₂₀ at E_d = 4 MeV, accurate to ± 8 × 10^?5, are presented. After correcting for deuteron stretching and a number of additional small effects, the data are used to make a new determination of the quadrupole moment. The result, Q = 0.282 ± 0.019 fm², is in good agreement with the conventional value deduced from molecular hyperfine structure data.     

Mössbauer studies and nuclear quadrupole moments of186, 188, 189, 190 Os

Mössbauer transmission experiments with the 137, 155, 69 and 187 keV gamma rays of^{186, 188, 189, 190}Os, respectively, yielded the electric quadrupole splitting of these gamma resonance lines in OsO₂ and OsP₂. From the results the following ratios of quadrupole moments were derived:Q ₂ ⁺(¹⁸⁶Os, 137 keV):Q ₂ ⁺(¹⁸⁸Os, 155keV):Q ₂ ⁺(¹⁹⁰Os, 187 keV):Q _3/2 ^?(¹⁸⁹Os, g.s.)=(+1.100±0.020): 1.0:(+0.863±0.051): (?0.586±0.011) andQ _5/2 ^?(¹⁸⁹Os, 69 keV)/Q _3/2 ^?(¹⁸⁹Os, g.s.)=?0.735 ±0.012. The ratios for^{180, 188, 190}Os are, within their limits of error, in agreement with the expectation of the rotational model, indicating that the pairing-plusquadrupole model calculations of Kumar and Baranger predict too rapid a transition form rotational to vibrational nuclei. Applying this argument to¹⁸⁶Os in particular and using the measured ratios, one obtains a set of values for the quadrupole moments themselves, namelyQ ₂ ⁺ (¹⁸⁶Os)=?(1.50 ± 0.10)b,Q ₂ ⁺(¹⁸⁸Os)=?(1.36± 0.09) b,Q ₂ ⁺ (¹⁹⁰Os)=?(1.18 ± 0.08) b,Q _3/2 ^?(¹⁸⁹Os)=+ (0.80 ± 0.06) b, andQ _5/2 ^? (¹⁸⁹Os)=? (0.59 ± 0.05) b. For the electric field gradient at Os nuclei in Re metal a value ofV _zz=?(3.3 ± 0.6) · 10¹⁷ V/cm² was found. A measurement with a magnetically split source yielded δ=+ 0.685 ± 0.025 for theE2/M1 mixing parameter of the 69 keV transition of¹⁸⁹Os,g _5/2 ^?/g _3/2 ^?=0.895 ± 0.006 for the ratio of theg-factors of the 69 keV state and the groundstate, andH _i=?(1135 ± 20) kOe for the hyperfine field at Os nuclei in an iron matrix.