Nuclear physics fundamentals

An important property of physical structures, from particles to molecules, is the identity of all the systems of a given type. All the atoms of oxygen, for instance, are absolutely identical, and for that reason their binding energies have the same constant value. In the experiments the authors use particle beams to bombard the atomic systems. A group of such particles can excite almost simultaneously many systems. An important characteristic of atomic structures is that a large number of systems excited at the same time do not get deexcited simultaneously. The deexcitation is a statistical process. All the identical systems, brought to the identical excited state, have the same probability of deexcitation in a given time interval. It means that in a unit time, such as a second, only a part of the total number of excited systems shall make a transition to the stable state. In the next second again a part shall decay, but now their number will be smaller, because after the first second there are less excited systems left. In the following time intervals smaller and small numbers shall be decaying. When the authors plot the number of decays per unit time, and exponential curve is obtained. It is a natural curve representing many processes in nature and society