Yrast Superdeformed Research Articles

Description of the yrast superdeformed bands in even-even nuclei in A $\sim$ 190 region using the nuclear softness model

A two-parameter nuclear softness (NS2) model for the transition energies is proposed by treating the variation of the moment of inertia with spin. The model has been applied to the yrast superdeformed (SD) bands in even-even nuclei in the mass region A � 190. The model parameters have been determined from thetting procedure in order to minimize the relative root mean square deviation between the experimental E2 transition -ray energies and the calculated ones. The basic experimental data on SD bands are given in the form of a series of -ray transitional energies and the spins were determined in our previous works. The excellent agreement between the theory and the experiment give good support to the model. The presence of identical bands between the two isotopes 192 Hg and 194 Pb is investigated because their differences in -ray energies are small and constant up to rotational frequency ℏ! � 0.25 MeV. Our analysis also leads to the appearance of ∆ I = 2 staggering effect in 194 Hg (SD1). A comment on equilibrium

Discrete decay of the yrast superdeformed band in theTb151nucleus

The Euroball array has been used to search for linking transitions between the superdeformed (SD) and the normal deformed (ND) wells in Tb-151. Many. rays in the energy range 2-4 MeV have been observed in coincidence with the yrast SD band. It is proposed that the highest energy transition of 3748 keV and the strongest line (2818 keV) of the previously observed transitions both decay from the same SD level as their links with the ND states have been identified. The current spectra have insufficient statistics to completely identify the decay point in the SD band. Theoretical calculations covering SD bands in the A approximate to 150 region enable the two possible spin assignments to be compared with experimental data on proposed links in Gd-149 and Dy-152. It is concluded that the energy of the lowest SD band member in Tb-151 has an excitation energy of 12861 keV and a spin of 65/2(+).

Decay-out properties of a linked superdeformed band inZr84

Three discrete transitions were observed between the yrast superdeformed (SD) band and states of normal deformation (ND) in the nucleus {sup 84}Zr. This is the first observation of such linking transitions in the mass-80 SD region. The properties of the decay out of the SD well in {sup 84}Zr are compared with those in other SD mass regions. Calculations suggest that there is extensive mixing of configurations in the SD and ND potential minima, leading to an abrupt and highly fragmented decay-out process. A study of least-action tunneling paths indicates that the potential barrier separating the SD and ND wells is very small.

Projected shell model description of N = 114 superdeformed isotone nuclei

A systematic description of the yrast superdeformed (SD) bands in N = 114, Z = 80–84 isotone nuclei using the projected shell model is presented. The calculated γ-ray energies, moment of inertia and M1 transitions are compared with the data for which spin is assigned. Excellent agreement with the available data for all isotones is obtained. The calculated electromagnetic properties provide a microscopic understanding of those measured nuclei. Some predictions in superdeformed nuclei are also discussed.

Microscopic Mechanism of the ω Variation in Moments of Inertia for the Yrast Superdeformed Bands 194Tl(1a,1b)**The project supported by National Natural Science Foundation of China under Grant Nos 1047205, 19835010, and 10047001, the Major State Basic Research Development Program under Grant No. G2000-0774-07 and the Knowledge Innovation Project of the Chinese Academy of Sciences under Grant No.KJCX2-SW-NO2

The variation in moments of inertia (J(1) and J(2)) with rotational frequency for the superdeformed bands in odd-odd nuclei, 194Tl(1a,1b), is investigated by using the particle-number conserving method for treating the pairing interaction (monopole and quadrupole). The observed variations of J(1) and J(2) with ω are reproduced quite well in the calculation and the contributions from each major shell are clearly displayed.

Linear polarization measurement of interband transitions in superdeformed 190hg: model-independent evidence for octupole vibrational structures.

The linear polarization of gamma rays between excited and yrast superdeformed (SD) states in 190Hg was measured using the four-element CLOVER detectors of the EUROBALL IV gamma-ray spectrometer. This measurement shows in a model-independent way that the interband transitions which compete with the highly collective in-band quadrupole transitions are largely enhanced electric dipoles. Not only do these results represent the first measurement of the multipolarity of transitions between different SD states, but they also provide strong evidence for the interpretation of the structures in the SD minimum of the A approximately 190 region in terms of octupole excitations.

Accurate Lifetime Measurements of Superdeformed Bands inA∼80Nuclei

Comparative measurements of the lifetimes of yrast superdeformed (SD) states in ${}^{80--83}\mathrm{Sr}$, ${}^{83}\mathrm{Y}$, and ${}^{84}\mathrm{Zr}$ have been performed using the Doppler-shift attenuation method. Thus, the transition quadrupole moments ( ${Q}_{t}$) of these structures have been determined accurately. The yrast SD bands in ${}^{80--83}\mathrm{Sr}$ possess ${Q}_{t}\ensuremath{\sim}3.5e\mathrm{b}$, while the ${}^{83}\mathrm{Y}$ and ${}^{84}\mathrm{Zr}$ cases display ${Q}_{t}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}4.4e\mathrm{b}$ and $5.6e\mathrm{b}$, respectively. Intruder orbital assignments based on these results demonstrate a previously unnoticed transition in the structure of the SD bands when the proton number changes from $Z\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}38$ to $Z\ensuremath{\ge}39$.

Decay-out of the yrast superdeformed band in136Nd: Towards an experimental extraction of the neutron pairing gap at large deformation

A study of the 136Nd nucleus has been performed with the EUROBALL III multidetector to establish the decay-out of the yrast superdeformed (SD) band. Three discrete linking transitions (754, 1456, and 1493 keV) have been discovered, establishing the position of the SD band at 7.03 MeV excitation energy with proposed spin and parity 17(−) for the lowest observed SD state. Neutron pairing gap parameters for SD shapes have been extracted in Nd isotopes, using the strong-coupling model and odd-even mass difference formulas. The major conclusion of our phenomenological analysis is that the pairing correlations do subsist in the SD configurations of nuclei in the A=130 mass region.Received 15 October 1998DOI:https://doi.org/10.1103/PhysRevC.60.064313©1999 American Physical Society

First evidence for linking transitions between the superdeformed yrast band and the normal deformed states in 149Gd

Double step resolved γ-ray transitions linking the yrast superdeformed (SD) band of 149Gd to the normal deformed (ND) level scheme have been observed using the EUROGAM phase II spectrometer. The excitation energy of the 47/2 − SD state above the 7/2 − ground state has thus been determined to be 10.625 MeV. The most likely multipolarity of the linking transitions is deduced, which permits the assignment of the most probable spins for this SD band. This measurement represents the first observation of discrete γ-ray transitions linking SD and ND states in the A∼150 mass region of the nuclear chart.

Decay and properties of the yrast superdeformed band in192Pb

The {sup 173}Yb({sup 24}Mg,5n) reaction at E({sup 24}Mg) = 134.5 MeV with a gold-backed target was used to populate high-angular momentum states in {sup 192}Pb. Resulting {gamma} rays were detected with Gammasphere located at the 88-Inch Cyclotron. A discrete transition of energy E{sub {gamma}} = 2057.7(6) keV has been identified in the depopulation the yrast superdeformed (SD) band in {sup 192}Pb. This transition has been tentatively placed in the level scheme based on coincidence relationships. Thus, the excitation energy of the SD level populated by the 262-keV in-band transition is tentatively assigned E{sub x} = 4.572(1) MeV. Confidence limits are discussed. Other transitions in coincidence with the SD band and general features of the band and its decay are also presented. In particular, we confirm that the J{sup (2)} of the SD band decreases by {approx}13{percent} at the lowest frequency. Also, by comparing the masses of the SD ground states in {sup 192,194}Pb to liquid drop model expectations and to each other we have been able to confirm enhanced stability for N=112 at superdeformation. {copyright} {ital 1997} {ital The American Physical Society}

Decay out of the superdeformed band in194Pb: Electromagnetic properties

Lifetimes of the 14${}^{+}$, 12${}^{+}$, 10${}^{+}$ states and, for the first time, the 8${}^{+}$ state in the yrast superdeformed (SD) band of ${}^{194}$Pb were measured at Gammasphere with the recoil-distance Doppler-shift method. Constant transition quadrupole moments with an average of 18.8 (11) $e$b were found at the bottom of the SD band. The decay out of the SD band can be viewed as governed by a small admixture of normal deformed (ND) states to the SD wave function which is assessed for the 8${}^{+}$ and 10${}^{+}$ SD states based on a simple mixing model. The electromagnetic properties of the ND states involved in the decay out are extracted for the first time by investigating the decay strength of the discrete linking transitions. Despite the large intensity of observed linking transitions, the new data show that the decay out of the SD band is statistical in nature.

Systematic Description of Yrast Superdeformed Bands in Even-Even Nuclei of the Mass-190 Region

Yrast superdeformed bands for even-even nuclei of the mass-190 region are described by the projected shell model. Excellent agreement with available data for all isotopes is obtained. Our calculation of electromagnetic properties and pairing correlations provides a microscopic understanding of the observed gradual increase of dynamical moments of inertia with angular momentum in this mass region and suggests that for superdeformation it is not very meaningful to distinguish between Coriolis antipairing and gradual high-j orbital alignment. {copyright} {ital 1997} {ital The American Physical Society}

Observation of the single step links of the yrast superdeformed band in 194Pb

The EUROGAMarray has been used to investigate the decay out of the yrast superdeformed (SD) band in 194Pb. Eigth single step decays from the lowest observed SD states to low-lying states at normal deformation (ND) have been identified. From this observation, the excitation energy (4877 ± 1.5 keV) and the spin (6+) of the lowest observed SD state in 194Pb are established.

Single step links of the superdeformed band in 194Pb: a measure of the absolute excitation energy, spin and parity of the superdeformed states

The EUROGAM array has been used to investigate the decay out of the yrast superdeformed (SD) band in 194Pb. Six single step decays from the lowest observed SD states to low-lying states at normal deformation (ND) have been identified. From this observation, the excitation energy of the SD band in 194Pb is established at 4877 ± 1.5 keV for the 6 + SD state. The most probable spins and parities of all members of the SD band are also deduced assuming that the SD states have even spin and positive parity.

The yrast superdeformed band in 194Pb. Differences with 192Hg

The yrast superdeformed (SD) structure of 194Pb has been studied using the EUROGAM γ-ray spectrometer. New results have been obtained at low as well as at high spin values. At low frequency, the SD band has been extended to the lowest-spin SD state ever observed in the A ∼ 190 region. The energies of 194Pb and 192Hg SD bands are identical for ω < 0.25 MeV. However, they diverge for higher frequency, which rules out the idea that these two SD bands are identical. Moreover, the SD band of 194Pb is populated at lower spin values than that of 192Hg and de-excites towards normally-deformed (ND) states at a spin value lower than that of 192Hg. This suggests that the barrier separating the SD and ND minima in the potential energy surface is higher in 194Pb than in 192Hg.

First observation of a superdeformed nucleus produced in an α xn reaction channel

Recent data from the EUROGAM array have revealed the population of the yrast superdeformed (SD) band of192Hg in the α4n exit channel of the16O+184W reaction at 113 MeV beam energy. The nucleus assignment was made on the basis of the SD band transition energies, and the observation of characteristic X-rays and lowlying yrast γ-transition of192Hg in coincidence with the SD band γ-rays. Both the feeding and decay-out patterns of the observed SD band have been found similar to the ones previously measured in the (36S,4n) reaction.