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Radioactivity - Decay and Instability of Atoms
Nuclear Energy .. Physics

Radioactivity - Decay and Instability of Atoms

The stability of the nucleus depends on the value of the binding energy in it, and it reaches its maximum in light atoms where the number of protons is equal to the number of neutrons, as happens in helium, for example (which has two protons and two neutrons). It is known that the repulsive forces between protons increase as the mass of the atom increases, and that the most stable atoms are the heavy atoms in which the number of neutrons exceeds the number of protons.

There is another type of isotopes known as radioactive isotopes, which are characterized by their instability, and that they spontaneously emit their rays in three types. The first type consists of beta particles, which have a great ability to penetrate objects (penetrating rays), while the second type is easily absorbed by matter and is called alpha particles.

The third and last type is gamma rays, known for their high energy. This type usually accompanies one of the other two types. It is known that the beta particle is an energetic electron emitted from the nucleus and launched at a tremendous speed, resulting in an increase in its charge, which increases the atomic number, while the atomic mass remains the same as before. An example of this is phosphorus, which transforms as follows: 23/15 Fu - 32/15 Kp + beta. Since the nucleus of the atom is free of electrons, the beta particle is produced as a result of the transformation of the neutron into a proton, electron, and neutrino. It must be noted that the kinetic energy of beta particles remains constant if they are emitted alone from the nucleus, and that it is equal to the difference between the mass of the nucleus of the parent isotope and the masses of the materials resulting from its decay. However, due to the diversity of the amounts of this energy, it has been proven that the neutrino accompanies the electron during its launch and that the sum of their energies remains constant despite the change in the energy of each of them separately. It must be noted that the process of emitting an electron-neutrino pair from the nucleus is similar to the process of emitting a photon from an excited atom. Therefore, we can consider the neutron as a nucleus at a very high energy level and the proton as a nucleus at a low energy level.

(The series consisting of the decay of 238 U)
(The decay curve of a radioactive isotope)

As for alpha particles, they are the nuclei of helium atoms carrying positive charges. It is known that the atom, after emitting alpha rays from it, turns into a different atom characterized by losing two of its charges and a specific number of its nuclei. An example of this is radium 226/88R -- 222/88D + alpha.
The decay rate of the radioactive isotope is determined by the number of its atoms, not by its physical and chemical state. The number of decays in it decreases as the number of atoms that have not yet reached the expected decay state decreases. The half-life of the radioactive isotope is defined as the time it takes for half of its atoms to decay. After two half-lives, only half of what remains after the first half-life has passed, i.e. a quarter of the original amount, remains.
The half-lives of isotopes range from microseconds to 100 billion years.

The atomic numbers of naturally occurring radioactive isotopes range practically between 81 and 92, and can be limited to three sequences: the uranium sequence, the radium sequence, and the actinium sequence. Each element in the sequence is the result of the decay of the element immediately preceding it as a result of alpha or beta emission. The last element in the sequence is characterized by being a non-radioactive element.