Total Routhian Surface Research Articles

Excited states and terminating bands in123,124I

High spin states in123,124I were populated via the116Cd(11B,xn) reaction at 38 MeV bombarding energy and via the110Pd(18O,pxn) reaction at 75 MeV energy. γ-ray energies, intensities, γγ coincidences and DCO ratios were measured with the GASP spectrometer. The level schemes were extended considerably. Band terminations were observed in both nuclei. In123I the rotational band, which is built on the πh 11/2 single-particle state was extended to spinI π=(35/2)−; at higher spin the level spacings and the feeding pattern were found to become irregular, indicating a structure change. The (39/2)− state and the higher-lying (43/2)− level were interpreted as aligned oblate states. In124I a decoupled band was found to terminate in the same spin region. Total Routhian surface calculations were performed which support the occurrence of a band termination.

In-beam γ-ray spectroscopy of 103Cd

Excited states of 103Cd were studied in the reaction 58Ni( 50Cr,4pn) 103Cd. The NORDBALL array with neutron and charged particle detectors was employed for the detection of γ rays and light evaporated particles. The level scheme of 103Cd was significantly extended. A strong cascade of E2 transitions connecting negative parity states was found. Shell model calculations were performed and positive parity excited states were interpreted in terms of neutron-particle and proton-hole excitations with respect to the doubly magic N = Z = 50 core. The negative parity band was well reproduced by the total routhian surface calculations.

Band termination in123I

High-spin states in the nucleus ${}^{123}$I were populated by the ${}^{110}$Pd${(}^{16}$O,$p4n)$ reaction at 75 MeV. $\ensuremath{\gamma}$-ray energies, intensities, $\ensuremath{\gamma}$-$\ensuremath{\gamma}$ coincidences, and directional correlation ratios were measured. The rotational band built on the $\ensuremath{\pi}{h}_{11/2}$ single-particle state was extended to spin ${I=35/2}^{\ensuremath{-}}$; at higher spin the level spacings and the feeding pattern were found to become irregular, indicating a sudden change of structure. The 39/2${}^{\ensuremath{-}}$ state and a higher-lying ${43/2}^{\ensuremath{-}}$ level were interpreted as aligned oblate states, in line with the systematics of the lighter odd-$A$ iodine isotopes. Total Routhian surface calculations were performed and were found to support the occurrence of a band termination. Higher-lying levels that feed the ${h}_{11/2}$ band were identified, reaching spin $Ig~47/2$ and an excitation energy of about 9 MeV.

Systematics of even-even Tz= 1 nuclei in the A= 80 region: High-spin rotational bands in 74Kr, 78Sr, and 82Zr

High-spin states of T-z = 1 nuclei were studied with the reactions Ni-58(Si-28,3 alpha)Kr-74,Ni-58(Si-28,2 alpha)Sr-78, and Ni-58(Si-28,2p2n)Zr-82 at 130 MeV beam energy. The Gammasphere array in conjunction with the 4 pi charged-particle detector array Microball was used to detect gamma rays in coincidence with evaporated light charged particles. The known pi = +, alpha = 0 yrast bands were extended to I = 28 (h) over bar at 20 MeV excitation energy. For all three nuclei, a number of positive- and negative-parity sidebands were established; altogether 15 new rotational bands were found. The data are discussed using the pairing-and-deformation self-consistent total Routhian surface (TRS) model: High-spin structures of Kr-74 and Sr-78 are governed by the shell gaps at large prolate deformation while Zr-82 seems to exhibit shape coexistence. Nearly identical bands were established which may be explained as arising from the fp orbits acting as spectators at very elongated shapes. The experimental data in these T-z = 1 nuclei are in good agreement with predictions of the TRS model using conventional T = 1 like-nucleon pairing correlations. (Less)

Rotational bands and shape changes in105Rh

The ${}^{105}$Rh nucleus has been studied by in-beam $\ensuremath{\gamma}$ spectroscopy with the heavy-ion fusion-evaporation reaction ${}^{100}$Mo${(}^{11}$B, $\ensuremath{\alpha}$2$n\ensuremath{\gamma})$ at 39 MeV. Gamma-gamma-$t$ coincidences and directional correlation ratios were measured. Four rotational bands have been identified with similar characteristics to those in other $A$\ensuremath{\approx}100 odd-proton nuclei. The positive-parity yrast band based on the $\ensuremath{\pi}{g}_{9/2}$ configuration and the negative-parity $\ensuremath{\pi}{p}_{1/2}$ band, showing large signature splittings, exhibit band crossings at the frequencies of 0.38 MeV and 0.48 MeV, respectively. Experimental Routhians and alignments as well as $B(M1)/B(E2)$ ratios were extracted. The structure of the bands was interpreted within the framework of the cranked shell model and total Routhian surface calculations.

Rotational structures in107Ag

The ${}^{107}$Ag nucleus has been investigated with the ${}^{100}$Mo${(}^{11}$B,$4n\ensuremath{\gamma})$ reaction at 39 MeV beam energy. Gamma-gamma coincidences and angular correlations were measured. The ground state band has been extended to higher spins and a three-quasiparticle rotational band has been established. The results were interpreted within the cranked shell model and total Routhian surface predictions.

Rotational and vibrational states in 115Te

High-spin states of the 115Te were studied by in-beam spectroscopy with the 89Y (29Si, p2n) fusion-evaporation reaction at a beam energy of 108 MeV. γ−γ coincidence and γ−γ angular correlation analyses were employed for determining the level scheme of 115Te. We have identified two vibrational-like bands built on the νh11/2 and νg7/2 quasiparticle states and the noncollective oblate states from the full alignment of quasiparticle configurations. In addition, a regular ΔI = 2 sequence with positive-parity was found for the first time in odd-A Te nuclei. This sequence is interpreted as a deformed structure resulting from three-quasiparticle alignment having the [π(g7/2, h11/2) ⊗ ν(h11/2)] configuration. Calculations of total Routhian surfaces and cranked shell model were performed and were used for assigning quasiparticle configurations to the states in 115Te.

M1bands and intruder bands in113In

High spin states in ${}^{113}$In have been established up to 6.2 MeV in excitation energy and to a tentative spin of (43/2${}^{\ensuremath{-}})$ through the reaction ${}^{110}$Pd${(}^{7}$Li, ${4n)}^{113}$In at a beam energy of 40 MeV. In-beam measurements involved $\ensuremath{\gamma}$-$\ensuremath{\gamma}$ coincidences, angular distribution of emitted gamma rays, and directional correlation of oriented states. $M$1 bands consisting of $\ensuremath{\Delta}I=1$ dipole transitions have been observed. Possible quasiparticle configurations suggest that these bands are similar to the shears bands observed in Pb nuclei. Two intruder bands based on the $\ensuremath{\pi}{h}_{11/2}$ orbital and $\ensuremath{\pi}{g}_{7/2}$ orbital have been observed. Results of the total Routhian surface and cranked shell model calculations are compared with the experimental data. Alignment features of the intruder bands in the $N=62$ and 64 isotones are discussed.

Fragmentation of the yrast band in186Os atI π =18+ and disappearance of the collective minimum

High-spin states in186Os have been populated by the186W(4He,4n)-reaction at 55MeV. The emittedγ-radiation was detected with the OSIRIS spectrometer. The yrast band, for which the nucleus has a prolate shape, was found to terminate atIπ=18+. Theγ-ray intensity is then distributed between several irregular sequences. Different to other cases of band termination, the minimum in the total routhian surface corresponding to a collective shape is calculated to disappear in this spin region, although the available spin of the valence nucleons is far from being exhausted. A different structure, which is dominated by non-collective states becomes yrast.

High spin states in121Te

High spin states of121Te, populated in the114Cd(11B,p3n) reaction, have been studied throughγ-ray spectroscopy. The level scheme has been established up toJπ=51/2−. Three-quasiparticle states, based on the πg7/22⊗νh11/2 andπg7/2d5/2⊗νh11/2 configurations, have been identified. A favoured 39/2− state is suggested to be the fully aligned [πg7/22]6+⊗[νh11/2327/2− yrast non-collective oblate configuration. This assignment is supported by Total Routhian Surface (TRS) calculations which also suggest a similar oblate assignment to the states atJπ=21/2− and 23/2−. A higher 47/2− state is also found and is suggested to be the fully aligned [πg7/22]6+⊗[νh11/25]35/2− configuration.

Superdeformed structures in 197,198Pb.

Two new superdeformed bands, which possess almost constant dynamic moments of inertia as a function of rotational frequency, have been observed in $^{197}\mathrm{Pb}$. They are thought to be based upon the favored and unfavored signature components of an N=7 neutron intruder orbital. Previous work tentatively assigned a superdeformed band to $^{198}\mathrm{Pb}$. The present work has confirmed this assignment. The properties of all the bands are discussed in terms of extended total Routhian surface calculations. \textcopyright{} 1996 The American Physical Society.

Shape change along the highly-deformed band in 137Nd

Lifetimes of states of the highly-deformed (HD) band in 137Nd have been measured using the Doppler shift attenuation method. A line-shape analysis has been carried out for individual states, resulting in transition quadrupole moments which decrease with increasing spin. This represents the first confirmation of previous total routhian surface (TRS) calculations that predicted a drift towards positive γ values of the HD minimum (at essentially constant β deformation). The lifetime data show a rather modest deformation of the HD band structure, indicating a softening of the nuclear potential at HD shape.

High-spin states in 107Pd, 108Pd, and 109Ag.

High-spin states in 107,108Pd and 109Ag have been studied by charged-particle-γ, γ-γ, and charged-particle-γ-γ coincidence measurements of heavy-ion fusion-evaporation reactions. The high-spin level schemes of these nuclides have been significantly extended and new deformed rotational bands have been found in each nuclide. These bands exhibit the general property of back bends corresponding to the rotational alignment of a pair of h11/2 quasineutrons. Band properties are compared with predictions of the cranked shell model and total Routhian surface calculations. The properties of the yrast and near-yrast bands of all three nuclides are generally consistent with predictions of moderate (β2 = 0.2) prolate deformation.

Effects of intruder states inIr179

High-spin states of the odd-A $^{179}\mathrm{Ir}$ have been studied via heavy-ion fusion reaction. Bands built on five different Nilsson states (\ensuremath{\pi}${\mathit{h}}_{9/2}$, \ensuremath{\pi}${\mathit{i}}_{13/2}$, \ensuremath{\pi}${\mathit{d}}_{5/2}$, \ensuremath{\pi}${\mathit{h}}_{11/2}$, and \ensuremath{\pi}${\mathit{f}}_{7/2}$) have been established, among which the \ensuremath{\pi}${\mathit{f}}_{7/2}$ (1/${2}^{\mathrm{\ensuremath{-}}}$[530]) band is identified for the first time in Ir isotopes. Experimental aligned angular momenta, band-crossing frequencies, and relative transition rates are analyzed and compared with the cranked shell model and the particle-rotor model calculations. Effects of intruder states, particularly \ensuremath{\pi}${\mathit{h}}_{9/2}$ and \ensuremath{\pi}${\mathit{i}}_{13/2}$, have been discussed on three aspects: deformation driving, shape evolution, and quasiparticle alignment. It is found that the \ensuremath{\pi}${\mathit{i}}_{13/2}$ orbital has a strong, positive-${\mathrm{\ensuremath{\beta}}}_{2}$ driving effect on the shape of Ir nuclei, while the driving force of the \ensuremath{\pi}${\mathit{h}}_{9/2}$ orbital is minimized when the Fermi level reaches the shell. The total Routhian surface calculations suggest that the \ensuremath{\pi}${\mathit{h}}_{11/2}$ and \ensuremath{\pi}${\mathit{d}}_{5/2}$ configurations in $^{179}\mathrm{Ir}$ possess relatively large ${\mathrm{\ensuremath{\beta}}}_{2}$ deformation (\ensuremath{\sim}0.26), which is consistent with the particle-rotor calculations. The possible contribution of the \ensuremath{\pi}${\mathit{h}}_{9/2}$ crossing to the gradual alignment gains observed in the \ensuremath{\pi}${\mathit{h}}_{11/2}$ and \ensuremath{\pi}${\mathit{d}}_{5/2}$ bands is discussed from the influence of deformation and interaction strength. \textcopyright{} 1996 The American Physical Society.

Competing mechanism for generating high spin excitations in γ-soft nuclei: the 136Nd case

High-spin structures in 136Nd have been investigated via the 110Pd( 30Si,4n) reaction at 125 MeV using the GASP array. Several bands consisting of stretched quadrupole transitions were identified. Two of them reach spins comparable to those of the highly-deformed (HD) band in 136Nd, which is based on a neutron i 13 2 - h 9 2 f 7 2 configuration. Total routhian surface (TRS) calculations indicate that regular high-spin excitations in this γ-soft nucleus, can be also generated through successive pairs of h 11 2 protons and neutrons coupled to a stable small-deformation triaxial core. The previously reported γ-ray transitions of an excited HD band, identical to the yrast HD band, are not confirmed by our data.

High spin states in 121Te

High spin states of 121Te, populated in the 114Cd (11B, p3n) reaction, have been studied through γ-ray spectroscopy. The level scheme has been established up to Jπ= 51/2−. Three-quasiparticle states, based on the πg 7/22 ⊗ vh11/2 and πg 7/2d5/2⊗ vh11/2 configurations, have been identified. A favoured 39/2− state is suggested to be the fully aligned [πg7/22]6 + ⊗ [vh11/23]27/2− yrast non-collective oblate configuration. This assignment is supported by Total Routhian Surface (TRS) calculations which also suggest a similar oblate assignment to the states at Jπ= 21/2− and 23/2−. A higher 47/2− state is also found and is suggested to be the fully aligned [πg7/22]6+ ⊗ [vh11/25]35/2− configuration.

Rotational bands in the doubly odd nucleus 134Pr

Abstract The band structures of the doubly odd 134 Pr nucleus has been investigated via the 119 Sn( 19 F,4n) 134 Pr and 110 Pd( 28 Si,p3n) 134 Pr reactions at beam energies of 87 and 130 MeV, respectively. The three previously known rotational bands based on the π[541] 3 2 − (α=± 1 2 )⊗ν[514] 9 2 − and π[423] 5 2 + ⊗ν[514] 9 2 − configurations have been extended to higher spins. The difference of ≈2ħ in the experimental alignment of the bands based on the signature partners of the [541] 3 2 − h 11 2 proton orbital is discussed in terms of shape coexistence and coupling with the γ-phonon but no consistent interpretation can be found. A new band consisting of quadrupole transitions has also been identified and linked unambiguously to the low-lying levels of the yrast band. Total routhian surface and cranked shell model calculations suggest a (π h 11 2 ) 3 ⊗ν[530] 1 2 − configuration for this band. The experimental ratios of reduced transition probabilities B( M 1) B( E 2) of the various rotational structures are compared to the theoretical values obtained from a semiclassical model and from the two-particle plus triaxial-rotor model.

Favored noncollective oblate states in light tellurium isotopes.

We have used cranking calculations, based on the total Routhian surface formalism, to investigate the medium spin structure ({ital I}{lt}25{h_bar}) of light tellurium isotopes with {ital A}{le}122. Several energetically favored noncollective oblate ({gamma}=+60{degree}) states, based on the aligned {pi}[({ital g}{sub 7/2}){sup 2}]{sub 6{sup +}}{direct_product}{nu}[({ital d}{sub 5/2}){sup {ital x}}({ital h}{sub 11/2}){sup {ital y}}] configuration ({ital x}=0,1, {ital y}=1{minus}4), are found to coexist with weakly deformed collective structures. Particularly favored 16{sup +} states are predicted for the even Te isotopes, while 39/2{sup {minus}} states are predicted for the odd Te isotopes. The theoretical results are compared to available experimental data.

Lifetime measurements within the superdeformed minimum of 133Ce and 132Ce.

The average transitional quadrupole moment of two superdeformed bands in $^{133}\mathrm{Ce}$ and the yrast superdeformed band in $^{132}\mathrm{Ce}$ have been measured as ${\mathit{Q}}_{\mathit{t}}$=7.5\ifmmode\pm\else\textpm\fi{}0.8 e b using the Doppler shift attenuation method and exploiting target-thickness induced Doppler broadening. These results are consistent with total Routhian surface calculations and indicate that the occupation of the \ensuremath{\nu}[530]1/2 orbital has little polarizing effect upon the shape of the superdeformed core.

In-beam γ-ray spectroscopy with GASP

The performance of the multi-detector array GASP is described in detail with emphasis on the improvement due to utilization of ancillary detectors. GASP has been running for three years producing interesting new data on different nuclear structure topics. The study of the decay-out of superdeformed bands in the A=130 mass region is presented. The sudden disappearance of the superdeformed bands in the odd133, 135, 137Nd isotopes is explained by the Total Routhian Surface calculations through a change of the nuclear shape which is microscopically related to the transfer of the valence neutron from a N=6 to a N=4 Nilsson orbital. A transient fieldg-factor measurement in the superdeformed band of133Nd will also be presented. A meang-factor of\(\bar g = 0.31(8)\) has been determined at the I*=41/2+ superdeformed state. The experimental value is compared with theoretical predictions and supports the assignment of the superdeformed band to thev[660]1/2+ Nilsson intruder orbital.