This work is an introduction to neutrino oscillation model for physics students. We present the neutrino mixing model based on the concept of state superposition. In particular, we consider the case were neutrinos propagate in the vacuum. The flavor mixing hypothesis leads to the so-called flavor oscillations induced by mass diference, or simply flavor oscilations. In this process the neutrino is converted between the three possible flavors during its way from source to detection. One intent that this phenomenon might be able to solve the apparent solar neutrinos disappearance, known as the solar neutrino problem. For didactic reasons, we consider only the case of two flavor mixing (one of them is a mixing of the other two) and so derive the probability of an eletron-neutrino to 'survive' in its way to Earth. One simple verification reveals us that this model can not explain the Super-Kamiokande experimental data (one of the most important related to solar neutrinos) while the same model, by the other way, is able to explain the disappearance of reactors neutrinos located in Japan and observed by the KamLAND experiment. Since the difference between these two cases is the existence of the dense solar matter, in the first case, it follows that a satisfactory model must take the neutrino interactions with matter in account in order to provide a complete solution to the solar neutrino problem.
neutrino; flavor mixing; vacuum oscillations
