Impact of magnetic field on the giant dipole resonance of ${}^{40}\mathrm{Ca}$ using an extended quantum molecular dynamics model

By taking into account the magnetic field in the extended quantum molecular dynamics model, we analyzed its effects on giant dipole resonance (GDR) by studying the responses and strengths of the dipole moments. The selected system is the ${}^{40}\mathrm{Ca}$ nucleus which is excited through the Coulomb interaction by ${}^{16}\mathrm{O}$. The particle acceleration term in the Liénard-Wiechert potential is discussed which, however, has small impact on the magnetic field. The peak energy, strength, and width of GDR, temperature, and angular momentum of ${}^{40}\mathrm{Ca}$ as a function of beam energy are investigated. It is found that the magnetic field enhances the peak energy, strength, and width of GDR which is not only due to the temperature effects, but also due to the enhancement of the angular momentum of nucleus. At beam energy $E >$ 200 MeV/nucleon, the magnetic field maintains a constant value for the strength of GDR. The paper sheds light on examining important roles of the magnetic field on the nuclear structure in low-intermediate energy heavy-ion collisions.

Figure 1

(a) Time evolution of the magnetic field at the central point (0,0,0) of ${}^{16}\mathrm{O}+{}^{40}\mathrm{Ca}$ at the beam energy of 100 MeV/nucleon and impact parameter of 7.13 fm. (b) The dependence between magnetic-field integral over time and beam energy for ${}^{16}\mathrm{O}+{}^{40}\mathrm{Ca}$ at 7.13 fm.

Figure 2

(a) Time evolution of the dipole moments and (b) $\gamma$-emission probability for ${}^{40}\mathrm{Ca}$ excited by ${}^{16}\mathrm{O}$ at incident energy $100\mathrm{MeV}$/nucleon.

Figure 3

(a) The dependence of peak energy, (b) strength, and (c) width of the GDR spectrum on incident energy for ${}^{40}\mathrm{Ca}$ excited by ${}^{16}\mathrm{O}$ in the cases whether or not to consider acceleration. The symbol denoted by “a” represents the results with particle acceleration effect, whereas “neglect a” represents the ones without. The lines are fits to the dots. The hatched area represents the experimental result.

Figure 4

(a) The dependence of peak energy, (b) strength, and (c) width of the GDR spectrum on incident energy for ${}^{40}\mathrm{Ca}$ excited by ${}^{16}\mathrm{O}$ in the cases without or with the magnetic field.

Figure 5

(a) Temperature and (b) the $y$ component of angular momentum as a function of incident energy for ${}^{40}\mathrm{Ca}$ excited by ${}^{16}\mathrm{O}$ in the cases of without and with magnetic fields.

Figure 6

(a) The dependences of peak energy, (b) strength, and (c) width of GDR spectrum on temperature for ${}^{40}\mathrm{Ca}$ in the cases without or with magnetic fields.