0000000001188801
AUTHOR
S. Frauendorf
Self-Consistent Tilted-Axis-Cranking Study of Triaxial Strongly Deformed Bands inEr158at Ultrahigh Spin
Stimulated by recent experimental discoveries, triaxial strongly deformed (TSD) states in $^{158}\mathrm{Er}$ at ultrahigh spins have been studied by means of the Skyrme-Hartree-Fock model and the tilted-axis-cranking method. Restricting the rotational axis to one of the principal axes---as done in previous cranking calculations---two well-defined TSD minima in the total Routhian surface are found for a given configuration: one with positive and another with negative triaxial deformation $\ensuremath{\gamma}$. By allowing the rotational axis to change direction, the higher-energy minimum is shown to be a saddle point. This resolves the long-standing question of the physical interpretation o…
High-spin spectroscopy of 140Nd
The population of the high-spin states in 140Nd was investigated using the reaction 96Zr(48Ca,4n). The results from two experiments, one with the EUROBALL array and one with the JUROGAM II + RITU + GREAT setup employing the recoil decay tagging technique, have been combined to develop a very detailed level scheme for 140Nd. Twelve bands of quadrupole transitions and eleven bands of dipole transitions were identified and their connections to low-lying states were established. Calculations using the cranked Nilsson-Strutinsky and the tilted axis cranking models were used to interpret the observed structures. The overall good agreement between the experimental results and the calculations assu…
Evidence for isovector neutron-proton pairing from high-spin states inN=Z74Rb
High-spin states in the odd-odd N=Z nucleus Rb-74(37)37 were studied using the Ca-40(Ca-40,alphanp) reaction. A previously observed odd-spin T=0 band has been extended to I-pi=(31(+)) and an even-spin T=0 band has been observed for the first time to I-pi=(22(+)); both have a pi(g(9/2))circle timesnu(g(9/2)) structure. A strongly coupled low-spin T=0,K=3 band has been interpreted as being based upon a pi[312]3/2 circle timesnu[312]3/2 configuration. Cranked relativistic Hartree-Bogoliubov calculations, which are corrected for the t=1 np-pair field by restoring isospin symmetry, reproduce the observed spectrum. These new results provide evidence for the existence of an isovector pair field th…
Central depression in nuclear density and its consequences for the shell structure of superheavy nuclei
The influence of the central depression in the density distribution of spherical superheavy nuclei on the shell structure is studied within the relativistic mean field theory. Large depression leads to the shell gaps at the proton Z=120 and neutron N=172 numbers, while flatter density distribution favors N=184 for neutrons and leads to the appearance of a Z=126 shell gap and to the decrease of the size of the Z=120 shell gap. The correlations between the magic shell gaps and the magnitude of central depression are discussed for relativistic and non-relativistic mean field theories.
Description of rotating N=Z nuclei in terms of isovector pairing
A systematic investigation of the rotating $N=Z$ even-even nuclei in the mass $A=58-80$ region has been performed within the frameworks of the Cranked Relativistic Mean field, Cranked Relativistic Hartree Bogoliubov theories and cranked Nilsson-Strutinsky approach. Most of the experimental data is well accounted for in the calculations. The present study suggests that there is strong isovector $np$-pair field at low spin, the strength of which is defined by the isospin symmetry. At high spin, the isovector pair field is destroyed and the data are well described by the calculations assuming zero pairing. No clear evidence for the existence of the isoscalar $t=0$ $np$-pairing has been obtaine…
Evidence for Magnetic Rotation in the Light Tin Region
Lifetimes have been measured for three M1 bands in light Sn/Cd nuclei using the DSAM technique. B(M1) values deduced from these measurements show a rapid decrease with increasing spin for a given configuration. The results have been compared with both Tilted axis cranking and semi-empirical model calculations. These suggest that the shears mechanism is present in this mass region, and that the band in 106Sn appears to be the first example of almost pure magnetic rotation.
Interaction strength and shape difference for the h9/2 and h11/2 configurations in163Tm
The strongly shape driving πh9/2[541]l/2− configuration with α=+1/2 exhibits some anomalous, and so far unexplained, features concerning the crossing frequency, ħωc, the aligned angular momentum, ix, and interaction strength, at the alignment of the first pair of i13/2 quasineutrons in several odd-Z rare earth-nuclei. The h9/2[541]1/2− and h11/2[523]7/2− bands have been studied in the stably deformed rare-earth nucleus163Tm to investigate these features. A difference in band crossing frequency of ∼ 80 keV between the two bands is found. Rotational bands built on these two configurations have been found to cross in the spin range I=25/2–29/2 ħ. Theγ-decay pattern between the two bands is est…
Evidence for Shears Bands in108Cd
High-spin states were populated in ${}^{108}\mathrm{Cd}$ using the ${}^{96}\mathrm{Zr}{(}^{16}\mathrm{O},4n)$ reaction at a beam energy of 72 MeV. Two magnetic dipole bands have been observed, both of which contain weak $E2$ crossover transitions. Lifetimes for the stronger of the two bands were measured via the Doppler shift attenuation method. The configuration assignment for this band has been determined from comparison with tilted axis cranking model calculations to be $\ensuremath{\pi}[{g}_{9/2}^{\ensuremath{-}3}{g}_{7/2}]\ensuremath{\bigotimes}\ensuremath{\nu}[{h}_{11/2}{(g}_{7/2}{d}_{5/2}{)}^{1}]$ and $\ensuremath{\pi}[{g}_{9/2}^{\ensuremath{-}3}{g}_{7/2}]\ensuremath{\bigotimes}\ensu…
Probing the gateway to superheavy nuclei in cranked relativistic Hartree-Bogoliubov theory
The cranked relativistic Hartree+Bogoliubov theory has been applied for a systematic study of the nuclei around 254No, the heaviest nuclei for which detailed spectroscopic data are available. The deformation, rotational response, pairing correlations, quasi-particle and other properties of these nuclei have been studied with different relativistic mean field (RMF) parametrizations. For the first time, the quasi-particle spectra of odd deformed nuclei have been calculated in a fully self-consistent way within the framework of the RMF theory. The energies of the spherical subshells, from which active deformed states of these nuclei emerge, are described with an accuracy better than 0.5 MeV fo…
High-spin states in205Rn:A new shears band structure?
The high-spin structure of {sup 205}Rn has been investigated for the first time following the {sup 170}Er({sup 40}Ar,5n) and {sup 197}Au({sup 14}N,6n) reactions at beam energies of 183 MeV and 90{endash}110 MeV, respectively, using the Jurosphere and YRAST Ball arrays. Two new cascades have been identified which dominate the high-spin decay. One of these, consisting of ten stretched M1 transitions with unobserved E2 crossover transitions, is interpreted as a shears structure based on the {nu}i{sub 13/2}{sup {minus}1}{circle_times}{pi}i{sub 13/2}{sup 2} (or {nu}i{sub 13/2}{sup {minus}1}{circle_times}{pi}h{sub 9/2}i{sub 13/2}) configuration. {copyright} {ital 1999} {ital The American Physical…
Shears Mechanism in theA∼110Region
Lifetimes of states in a rotational-like $M1$ band in ${}^{110}\mathrm{Cd}$ have been determined through a Doppler-shift attenuation method measurement performed with the Gammasphere array. The deduced $B(M1)$ values, which agree well with the predictions of the tilted axis cranking model, clearly confirm that it has the character of a shears band. Using a semiclassical scheme of the coupling of two long $j$ vectors we deduce information on the strength and form of the effective interaction between the constituent nucleons. These results are the first definitive evidence of the shears mechanism and ``magnetic rotation'' in this mass region.
Neutron-proton pairing in rotating N ∼ Z nuclei: dominance of the isovector component
Theoretical calculations of rotating N ≈ Z nuclei with A = 58 − 80 within the cranked Nilsson+Strutinsky approach, cranked relativistic mean field and cranked relativistic Hartree+Bogoliubov theories show good agreement with experiment. They point on the presence of the isovector t = 1 np -pairing, but do not show any indications of the isoscalar t = 0 np -pairing.
Very high rotational frequencies and band termination in73Br
Rotational bands in ${}^{73}\mathrm{Br}$ have been investigated up to spins of $I=65/2$ using the EUROBALL III spectrometer. One of the negative-parity bands displays the highest rotational frequency $\ensuremath{\Elzxh}\ensuremath{\omega}=1.85\mathrm{MeV}$ reported to date in nuclei with $Ag~25.$ At high frequencies, the experimental ${\mathcal{J}}^{(2)}$ dynamic moment of inertia for all bands decreases to very low values, ${\mathcal{J}}^{(2)}l~10{\ensuremath{\Elzxh}}^{2}{\mathrm{MeV}}^{\ensuremath{-}1}.$ The bands are described in the configuration-dependent cranked Nilsson--Strutinsky model. The calculations indicate that one of the negative-parity bands is observed up to its terminatin…
Collective rotation of an oblate nucleus at very high spin
International audience; A sequence of nine almost equidistant quadrupole transitions is observed in Nd137. The sequence represents an extremely regular rotational band that extends to a spin of about 75/2 and an excitation energy of ≈4.5MeV above yrast. Cranked mean-field calculations of the Nilsson-Strutinsky type suggest an oblate shape for the band. They reproduce the observed I(I+1) dependence of the rotational energy whereas predicting a pronounced decrease in the deformation, which is the hallmark of antimagnetic rotation.
Cranked Relativistic Hartree-Bogoliubov Theory: probing the gateway to superheavy nuclei
The cranked relativistic Hartree+Bogoliubov theory has been applied for a systematic study of the nuclei around 254No, the heaviest elements for which detailed spectroscopic data are available. The deformation, rotational response, pairing correlations, quasi-particle and other properties of these nuclei have been studied with different parametrizations for the effective mean-field Lagrangian. Pairing correlations are taken into account by a finite range two-body force of Gogny type. While the deformation properties are well reproduced, the calculations reveal some deficiencies of the effective forces both in the particle-hole and particle-particle channels. For the first time, the quasi-pa…
Very high rotational frequencies and band termination in 73Br
Rotational bands in 73Br have been investigated up to spins of 65/2 using the EUROBALL III spectrometer. One of the negative-parity bands displays the highest rotational frequency 1.85 MeV reported to date in nuclei with mass number greater than 25. At high frequencies, the experimental dynamic moment of inertia for all bands decrease to very low values, indicating a loss of collectivity. The bands are described in the configuration-dependent cranked Nilsson-Strutinsky model. The calculations indicate that one of the negative-parity bands is observed up to its terminating single-particle state at spin 63/2. This result establishes the first band termination case in the A = 70 mass region.
Experimental evidence for chirality in the odd-A 105Rh
Abstract High-spin states in 105 Rh were populated by the 96 Zr( 13 C, p3n) reaction at beam energies of 51 and 58 MeV, and studied using the EUROBALL IV γ -ray spectrometer and the DIAMANT charged particle array. A pair of nearly degenerate Δ I = 1 three-quasiparticle bands with the same spins and parity have been observed. Comparison of the experimental results with tilted axis cranking calculations confirms the chiral character of the two bands, while arguments based on the excitation of particles within the π g 9 / 2 ν ( h 11 / 2 ) 2 configuration of the yrast band and comparison with the previously observed γ band exclude the other possible interpretations. This is the first experiment…
Shears mechanism in109Cd
Lifetimes of high-spin states in two $\ensuremath{\Delta}I=1$ bands and one $\ensuremath{\Delta}I=2$ band in ${}^{109}\mathrm{Cd}$ have been measured using the Doppler shift attenuation method in an experiment performed using the ${}^{96}\mathrm{Zr}{(}^{18}\mathrm{O},5n)$ reaction with the GAMMASPHERE array. Experimental total angular momenta and reduced transition strengths for both $\ensuremath{\Delta}I=1$ bands were compared with tilted axis cranking (shears mechanism) predictions and the $\ensuremath{\Delta}I=2$ band with principal axis cranking predictions, based on configurations involving two proton ${g}_{9/2}$ holes and one or three valence quasineutrons from the ${h}_{11/2}$ and mi…
Very high rotational frequencies and band termination in 73Br
Rotational bands in 73Br have been investigated up to spins of 65/2 using the EUROBALL III spectrometer. One of the negative-parity bands displays the highest rotational frequency 1.85 MeV reported to date in nuclei with mass number greater than 25. At high frequencies, the experimental dynamic moment of inertia for all bands decrease to very low values, indicating a loss of collectivity. The bands are described in the configuration-dependent cranked Nilsson-Strutinsky model. The calculations indicate that one of the negative-parity bands is observed up to its terminating single-particle state at spin 63/2. This result establishes the first band termination case in the A = 70 mass region.