Nuclear Physics A最新文献

We discuss the sensitivity of tunneling processes to the initial preparation of the quantum state. We compare the case of Gaussian wave packets of different positional variances using a generalized Woods-Saxon potential for which analytical expressions of the tunneling coefficients are available. Using realistic parameters for barrier potentials we find that the usual plane wave approximation underestimates fusion reactivities by an order of magnitude in a range of temperatures of practical relevance for controlled energy production.

A naive Bayesian model averaging (NBMA) method is developed to predict nuclear masses. In the NBMA method, the weights of different models may be different for each nucleus, which are sensitive to the model accuracies to describe the nuclear masses of the isotopes and isotones with the same proton and neutron numbers of that nucleus. Therefore, there are remarkable local structures for the weights of different models on the nuclear chart, which well eliminates the local deviations between the model predictions and the experimental masses and thus achieves better accuracy of mass predictions than the traditional arithmetic mean method (AMM) and weighted average method (WAM). Based on the latest atomic mass evaluation of AME2020, the root-mean-square (rms) mass deviation of the NBMA method is 0.293 MeV, while the rms deviations of AMM and WAM are 0.634 and 0.361 MeV, respectively. This accuracy of the NBMA method is even 28% better than the best accuracy of the mass models used in the NBMA method. The extrapolation ability of the NBMA method is also verified with the experimental nuclear masses which are not used in the training of the NBMA method.

We present an extended application of the analytic quadrupole octupole axially symmetric model, originally employed to study the octupole deformation and vibrations in light actinides using an infinite well potential (IW). In this work, we extend the model's applicability to a broader range of nuclei exhibiting octupole deformation by incorporating a sextic potential instead of the Davidson potential. Similarly to conventional models, such as AQOA-IW (for infinite square potential) and AQOA-D (for the Davidson potential), our proposed model is referred to as AQOA-S. By employing the sextic potential, phenomenologically represented as $v\left(\tilde{\beta }\right)=a_1{\tilde{\beta }}^2+a_2{\tilde{\beta }}^4+a_3{\tilde{\beta }}^6$, we can derive analytical expressions for the energy spectra and transition rates (B(E1), B(E2), B(E3)). The energy spectra of the model are essentially governed by two critical parameters: ${\varphi }_0$, indicating the balance between octupole and quadrupole strain, and α, a key factor in adjusting the shape and behavior of the spectra through the sextic potential. In terms of applications, the study encompasses five isotopes, namely ^222−226Ra and ^224,226Th. Significantly, our model demonstrates remarkable agreement with the corresponding experimental data, particularly for the recently determined B(EL) transition rates of ²²⁴Ra, surpassing the performance of the model that employs the Davidson potential. The stability of the octupole deformation in ²²⁴Ra adds particular significance to these findings.

The paper presents a first time attempt on a combined fit of the $K^{-}p$ low-energy data and the πΣ photoproduction mass spectra, performed without fixing the meson-baryon rescattering amplitudes to a specific $\pi \Sigma -\overline{K}N$ coupled channels model obtained from fitting exclusively the $K^{-}p$ data. The formalism adopted to describe the photoproduction process is based on chiral perturbation theory and employs a limited number of free parameters. The achieved description of the photoproduction mass distributions is not quite satisfactory, leaving a room for improving the photo-kernel construction. Although the presented models tend to constrain the positions of the $\Lambda \left(1405\right)$ poles it is difficult to draw any conclusions before accomplishing better data reproduction.

Fusion reactions ⁴⁰Ar + ¹¹⁶Sn, ⁴⁰Ar + ¹²²Sn and ⁴⁰Ca + ¹²⁴Sn have been examined by employing coupled channel (CC) approach using code-CCFULL. Here we aim to investigate the influence of multi-neutron transfer channels in addition to coupling of collective excitations on sub-barrier fusion enhancement. Incorporation of inelastic excitations alone reproduced the experimental results for ⁴⁰Ar + ¹¹⁶Sn system while for ⁴⁰Ar + ¹²²Sn contribution of 2n transfer channel is required to explain the experimental data. However, CC calculations with 2n transfer could not explain the enhancement at sub-barrier energies for ⁴⁰Ca + ¹²⁴Sn system. Therefore, the empirical coupled channel (ECC) calculations have been carried out to include the effect of multi-neutron transfer channels and it is found that the incorporation of sequential 4n transfer channel reproduced the experimental results in entire energy region. Nevertheless, it is observed that multi-neutron transfer coupling significantly contributed in raising the sub-barrier fusion cross sections particularly for the reactions where colliding partners are spherical. Importantly, it is also found that transfer of even number of neutrons play dominating role in sub-barrier fusion enhancement.

The quantum shape phase transition between the spherical and deformed γ-unstable ($U\left(5\right)-O\left(6\right)$) even-even nuclei within the frameworks of Interacting Boson Model-1 and 2 (IBM-1,2) for low-lying states, using the “entanglement entropy” (S) has been studied. In both frameworks, the theoretical results showed that there exist minimum and maximum entanglement values between s bosons in the U(5) and O(6) limits, respectively. In order to confirmation of the theoretical results, we have calculated and analyzed the entanglement entropy of $s-d$ bosons and proton (π) - neutron (ν) bosons in Cerium (${}_{58}{}^{122-136}Ce$) isotopes. The results indicate that the entanglement entropy correctly describes the transition from U(5) to O(6), for ground state ($0_1^{+}$), but it cannot accurately determine the transitional nucleus.

In this paper, we tried to describe both normal and intruder levels of the ground and first excited beta and gamma rotational bands of ^162,164,166Dy deformed nuclei in the framework of the interacting boson model. A normal Hamiltonian of SU(3) dynamical symmetry limit is extended by adding a 2p-2 h excitation term. Also, the results are compared with the predictions of the partial dynamical symmetry for these levels of considered nuclei. The results show that, this extension removes the degeneracy suggested by the pure SU(3) symmetry and makes satisfactory agreement with the experimental counterparts for the energy levels, too. Also, a comparison between the results of this extended formalism and partial dynamical symmetry shows the advantages of the first one in the description of intruder levels, whereas the latter, makes exact results for the normal energy levels of beta and gamma energy bands. The predictions of pure SU(3), partial dynamical symmetry SU(3) and mixed formalism for different quadrupole transition rates between normal and intruder levels of this nucleus are compared with the predictions of pseudo-SU(3) model and the advantages of each model have explained in detail.