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تسجيل مستخدم جديدSuperdeformation: Perspectives and prospects
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تأليف
J. Dobaczewski
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We present a review of the mean-field approaches describing superdeformed states, which are currently used and/or being developed. As an example, we discuss in more details the properties of superdeformed A~60 nuclei, and present results of calculations for the rotational band in the doubly magic superdeformed nucleus 32S.
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Superdeformed (SD) states in $^{40}$Ar have been studied using the deformed-basis antisymmetrized molecular dynamics. Low energy states were calculated by the parity and angular momentum projection (AMP) and the generator coordinate method (GCM). Bas
is wave functions were obtained by the energy variation with a constraint on the quadrupole deformation parameter $beta$, while other quantities such as triaxiality $gamma$ were optimized by the energy variation. By the GCM calculation, an SD band was obtained just above the ground state (GS) band. The SD band involves a $K^pi = 2^+$ side band due to the triaxiality. The calculated electric quadrupole transition strengths of the SD band reproduce the experimental values appropriately. Triaxiality is significant for understanding low-lying states.
The superdeformation and hyperdeformation in $^{108}$Cd have been studied for the first time within the framework of the fully self-consistent cranked mean field theory, namely, cranked relativistic mean field theory. The structure of observed superd
eformed bands 1 and 2 have been analyzed in detail. The bumps seen in their dynamic moments of inertia are explained as arising from unpaired band crossings. This is contrary to an explanation given earlier within the framework of projected shell model. It was also concluded that this nucleus is not doubly magic SD nucleus.
The $^{174}$Yb($^{29}$Si,5n) reaction at 148 MeV with thin targets was used to populate high-angular momentum states in $^{198}$Po. Resulting $gamma$ rays were observed with Gammasphere. A weakly-populated superdeformed band of 10 $gamma$-ray transit
ions was found and has been assigned to $^{198}$Po. This is the first observation of a SD band in the $A approx 190$ region in a nucleus with $Z > 83$. The ${cal J}^{(2)}$ of the new band is very similar to those of the yrast SD bands in $^{194}$Hg and $^{196}$Pb. The intensity profile suggests that this band is populated through states close to where the SD band crosses the yrast line and the angular momentum at which the fission process dominates.
A superdeformed (SD) band has been identified in a non - alpha - conjugate nucleus 35Cl. It crosses the negative parity ground band above 11/2- and becomes the yrast at 15/2-. Lifetimes of all relevant states have been measured to follow the evolutio
n of collectivity. Enhanced B(E2), B(E1) values as well as energetics provide evidences for superdeformation and existence of parity doublet cluster structure in an odd-A nucleus for the first time in A = 40 region. Large scale shell model calculations assign (sd)16(pf)3 as the origin of these states. Calculated spectroscopic factors correlate the SD states in 35Cl to those in 36Ar.
Background: The observation of the superdeformed (SD) bands in $^{60,62}$Zn indicates a strong SD-shell effect at the particle numbers 30 and 32, where two and four neutron single-particles are considered to be promoted to the intruder $1g_{9/2}$ she
ll. However, the SD-yrast band in $^{62}$Zn is assigned negative parity. Purpose: I investigate various SD configurations in the rapidly rotating $^{60,62}$Zn isotopes, and attempt elucidating the different roles of the SD magic numbers 30 and 32. Method: I employ a nuclear energy-density functional (EDF) method: the configuration-constrained cranked Skyrme-Kohn-Sham approach is used to describe the rotational bands near the yrast line. Results: I find that the neutron number 32 favors stronger deformation than 30; a competing shell effect of protons and neutrons makes the SD-yrast structures of $^{62}$Zn unique. Due to the coherent shell effect, the positive-parity band emerges in $^{64}$Ge as an SD-yrast band with greater deformation than that in $^{60,62}$Zn. Furthermore, the present calculation predicts the occurrence of the hyperdeformed (HD) magic numbers 30 and 32 at a high rotational frequency $sim 2.0$ MeV$/hbar$. Conclusions: The negative-parity SD bands appear higher in energy than the positive-parity SD-yrast band in $^{60}$Zn and $^{64}$Ge, indicating that both the particle numbers 30 and 32 are SD magic numbers. The positive-parity HD states appear as the yrast band at $I sim 50hbar$ in $^{60}$Zn and $^{64}$Ge. The particle numbers 30 and 32 are magic numbers of SD and HD.
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