The phenomenon of radioactivity was opened in 1896 by A. Bekkerel. It consists in spontaneous emission of radioactive radiation some chemical elements. This radiation consists of alpha particles, beta particles and gamma quanta.
Experiments with radioactive elements
The complex structure of radioactive radiation was found by means of a simple experiment. The sample of uranium was placed in a lead box with a small opening. Opposite to an opening put a magnet. It was recorded that radiation "was divided" into 2 parts. One of them deviated towards the North Pole, and another - towards southern. The first was called alpha radiation, and the second - beta radiation. At that time did not know that there is also the third type, gamma quanta. They do not react to magnetic field.
Alpha decay
Alpha decay is an emission by a kernel of a certain chemical element of a positively charged kernel of helium. At the same time the law of shift works, and it turns into other element with other charging and mass number. The charging number decreases by 2, and mass - on 4. The helium kernels which took off from a kernel in the course of disintegration are called alpha particles. For the first time they were found by Ernest Rutherford in the experiments. He opened a possibility of transformations of some elements in others. This opening became a turning point in all nuclear physics.
Alpha decay is characteristic of chemical elements which have not less than 60 protons. In this case radioactive transformations of a kernel will be energetically favorable. The average energy which is released at alpha decay lies in the range from 2 up to 9 MeV. Nearly 98% of this energy are carried away with itself by a helium kernel, other is the share of return of a maternal kernel at disintegration. The half-life period of alpha emitters accepts various values: of 0.00000005 sec. up to 8000000000 years. Such wide spacing is explained by the potential barrier existing in a kernel. It does not allow a particle to take off from it even if it will be energetically favorable. According to representations of classical physics, the alpha particle cannot break at all a potential barrier as its kinetic energy is very small. The quantum mechanics entered the amendments into the theory of alpha decay. With some share of probability the particle after all can get through a barrier, despite the shortage of energy. Such effect is called tunnel. The transparency coefficient determining the probability of passing of a particle through a barrier was entered. The wide spacing of half-life periods of the alpha radiating kernels is explained by the different height of a potential barrier (i.e. energy for its overcoming). The barrier is higher, the half-life period is more.