In atomic nucleus the attraction forces act between its nucleons, so to segregate nucleus into constituent elements it needs to perform a work against this forces and to expend some energy. Marginally necessary energy for concrete nucleus is called the nucleus binding energy. The binding energy is equal to difference between total energy of free protons and neutrons and total energy of nucleus. The ratio of nucleus binding energy to total number nucleons in it (A) is called a specific binding energy. Two graphics are presented in that simulation: graphic Z(N), illustrating correlation between number of protons Z and number of neutrons N in stable nucleus, and graphic E (A), illustrating as specific binding energy E depends on atomic mass A. This simulation allows create the arbitrary nucleus. To do that, set with help of floating band controls number of protons and number of neutrons in nucleus. To test its stability you must start the simulation. If you made stable nucleus the red points occur on graphics Z(N) and E(A). Against, if nucleus is unstable, in left below window you can see its decay.