This simulation shows the vibrating liquid drop model of the nuclear  giant resonances, with special emphasis on their categorization according to the multipolarity and isospin.

In order to visualize the vibrations, the nucleus is modeled as two "merged-together" liquid drops - the proton-drop, and the neutron-drop. The program shows the shape and the density of the proton-drop with red color, and those of the neutron-drop wtih blue color. The upper part of the right-hand side picture shows the changes of the shape in fucntion of the time. The shapes have cylindrical symmetry around the z-axis. The lower part of the picture shows the density distribution of the two components along the z-axis. 

The shape of the nucleus at any time can be expanded according to the spherical harmonics. The time development of the shape is described by the time-dependent expansion coefficients. The different terms in the expansion are called multipoles, and are referred to as monopole (L = 0), dipole (L = 1), quadrupole (L = 2) etc. In principle the expansion contains infinite number of terms, but this simulation program shows only the first three terms ( L = 0, 1, 2). According to the isospin the vibrations can be either isoscalar - when protons and neutrons vibrate in-phase -, or isovector, when they vibrate in opposite phase. 

The program shows altogether 6 types of vibrations, according to the two parameters mentioned above. The higher multipolarity (L > 2) isoscalar and isovector vibrations - although they exist in Nature - are not shown here.

The incompressibility of the nuclear matter

For most types of vibrations the nuclear matter can be considered as an incompressible liquid. However, there are two types of vibrations where the compressibility of the nuclear matter should be taken into account. These are the L = 0 (monopole) vibrations and the isoscalar dipole (L = 1) vibration. Therefore from the experimental studies of these particular vibrational modes the compressibility of the nuclear matter can be deduced. This parameter is important also for certain astrophysical models; for example for the description of neutron stars.