It is thrown out and a nucleus has more stability complex of nucleons. Positron β-disintegration is described by the equation:

The charge of a nucleus and accordingly atomic number of an element decreases for unit, and the mass number remains without change.

Beta - radiation of the same elements contains particles with various energy within the limits of from the smallest up to some maximal size. Therefore a spectrum β- radiations continuous. The scientist Pauli to explain difference in energy β-particles at disintegration of nucleus of the same elements. Century in 1931 Pauli has assumed, that neutral particles way out from a nucleus together with β- particles at β-disintegration. This particles have very small mass and energy, which have some significant. The sum of this energy with energy of β-particles is constant significant ε_o. In the further these particles have been found out experimentally. The particle is radiated together with a positron, has been named neutrino ν. The equations of mutual transformation of nucleons look like:

Transformation of a proton into a neutron can happen as by capture by a nucleus of one of electron from the K atomic level

This phenomenon is named to as electronic capture or К-capture, for example, transformation of an isotope Be in Li (lithium):

Spontaneous disintegration of nucleuses of heavy elements is radioactive disintegration also, for example, isotopes of uranium disintegrate on two splinters, relatives among themselves under atomic number and mass number.

The some elements have chain of such consecutive disintegrations, last disintegration create stability element. Set of the elements, forming a similar chain, is named radioactive family, or radioactive line.

The basic law of radioactive disintegration in the differential form. A constant of disintegration.

Radioactive disintegration of nucleuses of the same elements happens gradually and has various speed at various elements. Radioactive disintegration - the statistical process, submitting to laws of probability theory. The moment of disintegration of each nucleus cannot be specified in advance, but this theory allows to determine probability of disintegration of one nucleus for the time unit. This probability is characterized by coefficient λ, which is named a constant of disintegration and depends upon nature of element.

The basic law of radioactive disintegration install: The same quantity of nucleuses of the given element breaks up for equal time intervals. The constant of disintegration λ to determine this quantity.

The quantity dN of nucleuses, which are breaking up for a time interval dt, is proportional to quantity of the nucleuses, which have not broken yet to the beginning of the given time interval, and a time interval dt from the law:

(The sign a minus shows decrease of number N during the time).

The basic law of radioactive disintegration in the differential form.

The decision of the equation is exponential function

Where N₀ - initial (during the moment t = 0) quantity of nucleuses. Thus, the number N – quantity of nucleus, which did not disintegrate (i.e. active) decreases during the time. We can calculate this quantity in any moment of time by formula

or with help graph. The number ΔN of the broken nucleuses changes in during the time on dependence