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Register a new userSuperdeformed band in the $N = Z+4$ nucleus $^{40}$Ar: A projected shell model analysis
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It has been debated whether the experimentally-identified superdeformed rotational band in $^{40}$Ar [E. Ideguchi, et al., Phys. Lett. B 686 (2010) 18] has an axially or triaxially deformed shape. Projected shell model calculations with angular-momentum-projection using an axially-deformed basis are performed up to high spins. Our calculated energy levels indicate a perfect collective-rotor behavior for the superdeformed yrast band. However, detailed analysis of the wave functions reveals that the high-spin structure is dominated by mixed 0-, 2-, and 4-quasiparticle configurations. The calculated electric quadrupole transition probabilities reproduce well the known experimental data and suggest a reduced, but still significant, collectivity in the high spin region. The deduced triaxial deformation parameters are small throughout the entire band, suggesting that triaxiality is not very important for this superdeformed band.
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The superdeformed band, recently discovered in Ca-40 is analysed in an spherical shell model context. Two major oscillator shells, sd and pf are necessary to describe it. The yrast band of the fixed 8p-8h configuration fits extremely well with the experimental energies and transition rates of the superdeformed band. The 4p-4h configuration generates a normally deformed band plus a gamma-band pattern, both are also present in the experimental data.
Experimentally observed superdeformed (SD) rotational bands in $^{36}$Ar and $^{40}$Ar are studied by the cranked shell model (CSM) with the paring correlations treated by a particle-number-conserving (PNC) method. This is the first time the PNC-CSM calculations are performed on the light nuclear mass region around $A=40$. The experimental kinematic moments of inertia $J^{(1)}$ versus rotational frequency are reproduced well. The backbending of the SD band at frequency around $hbaromega=1.5$ MeV in $^{36}$Ar is attributed to the sharp rise of the simultaneous alignments of the neutron and proton $1d_{5/2}[202]5/2$ pairs and $1f_{7/2}[321]3/2$ pairs, which is the consequence of the band crossing between the $1d_{5/2}[202]5/2$ and $1f_{7/2}[321]3/2$ configuration states. The gentle upbending at the low frequency of the SD band in $^{40}$Ar is mainly effected by the alignments of the neutron $1f_{7/2}[321]3/2$ pairs and proton $1d_{5/2}[202]5/2$ pairs. The PNC-CSM calculations show that besides the diagonal parts, the off-diagonal parts of the alignments play an important role in the rotational behavior of the SD bands.
Recent experimental observation of the direct links between superdeformed and normal-deformed structures in the A~190 mass region offers a unique information on the absolute nuclear binding energy in the 2:1 minima, and hence on the magnitude of shell effects in the superdeformed well. In the present paper, the self-consistent mean-field theory with density-dependent pairing interaction is used to explain at the same time the two-particle separation energies in the first and second wells, and the excitation energies of superdeformed states in the A~190 and A~240 mass regions.
The yrast band in the heavy $N = Z$ nucleus $^{88}$Ru is studied in the framework of the $alpha$-cluster model in combination with double-folding potentials. It is found that the excitation energies of the yrast band in $^{88}$Ru can be nicely described within the $alpha$-cluster approach using a smooth and mildly $L$-dependent adjustment of the potential strength. This result is similar to well-established $alpha$-cluster states in nuclei with a (magic core $otimes$ $alpha$) structure. Contrary, the yrast bands in neighboring $N e Z$ nuclei deviate from such a typical $alpha$-cluster behavior. Finally, the $alpha$-cluster model predicts reduced transition strengths of about 10 Weisskopf units for intraband transitions between low-lying states in the yrast band of $^{88}$Ru.
High intensity monoenergetic muon neutrinos of energy 236 MeV from kaon decay at rest (KDAR) at the medium energy proton accelerator facilities like J-PARC and Fermilab are proposed to be used for making precision measurements of neutrino-nucleus cross sections in $^{12}C$ and $^{40}Ar$ and perform neutrino oscillation experiments in $ u_mu to u_mu$ and $ u_mu to u_e$ modes. In view of these developments, we study the theoretical uncertainties arising due to the nuclear medium effects in the neutrino-nucleus cross sections as well as in the angular and energy distributions of the charged leptons produced in the charged current (CC) induced reactions by $ u_mu$ and $ u_e$ in $^{12}C$ and $^{40}Ar$ in the energy region of $E_{ u_e( u_mu)}<$ 300 MeV. The calculations have been done in a microscopic model using the local density approximation which takes into account the nuclear effects due to the Fermi motion, binding energy and long range correlations. The results are compared with the other calculations available in the literature.
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