Spontaneous division

Nuclear processes
	Radioactive decay Alpha decay; Beta decay; Cluster decay; Double beta decay; Electronic capture; Dual electronic capture; Gamma radiation; Internal conversion; Isomeric transition; Neutron decay; Positron Decay; Proton decay; Spontaneous division; Nucleosynthesis Thermonuclear reaction Proton-proton cycle; CNO cycle; Triple helium reaction; Helium flash; Nuclear carbon burning; Carbon detonation; Nuclear Burning Neon; Nuclear combustion of silicon; ; Neutron capture r process; s process; ; Proton Capture: p-process; rp process; ; Neutronization; Cleavage reactions;

Spontaneous fission is a type of radioactive decay of heavy atomic nuclei . Spontaneous fission is a fission of the nucleus that occurs without external excitation (forced fission), and gives the same products as forced fission: fragments (nuclei of lighter elements) and several neutrons . According to modern concepts, the tunnel effect is the cause of spontaneous fission.

The probability of spontaneous fission increases with an increase in the number of protons in the nucleus. This probability depends on the parameter. $Z^{2}/A,$ ${\ displaystyle Z ^ {2} / A,}$ ${\ displaystyle Z ^ {2} / A,}$ where Z is the number of protons and A is the total number of nucleons . When this parameter approaches 45, the probability of spontaneous fission tends to unity, which imposes restrictions on the possibility of the existence of superheavy nuclei .

For nuclei of elements such as uranium and thorium , spontaneous fission is a very rare process; their nuclei decay much more often through other decay channels (the value of the parameter Z ² / A for uranium and thorium nuclei is of the order of 35). With an increase in Z ² / A, the probability of spontaneous fission of nuclei increases rapidly.

The phenomenon of spontaneous fission is used in the method of radioisotope dating of the age of fossil remains, meteorites, etc.

Content

Spontaneous Division Speed

Fission rates and their probabilities, as well as the number of neutrons produced per 1 fission for some nuclei are given in the table ^[1] :

Core	Half-life, years	Spontaneous division probability	Neutron yield per 1 fission	Neutron flux, g ⁻¹ · s ⁻¹
²³⁵ U	7.0410 ⁸	2.010 ⁻⁹	1.86	3.0 × 10 ⁻⁴
²³⁸ U	4.47 · 10 ⁹	5.410 ⁻⁷	2.07	0.0136
²³⁹ Pu	2.41 · 10 ⁴	4.410 ⁻¹²	2.16	2.210 ⁻²
²⁴⁰ Pu	6569	5.0 × 10 ⁻⁸	2.21	920
²⁵⁰ Cm	8300	0.80	3.3	2.110 ¹⁰
²⁵² cf	2,638	3.0910 ⁻²	3.73	2.310 ¹²

History

The first open nuclear fission process was the forced fission of the uranium-235 isotope by neutrons.

Spontaneous fission was discovered in 1940 by Soviet physicists G. N. Flerov and K. A. Petrzhak as a result of observations of the decay of uranium ^[2] . Since cosmic rays create a measurable neutron flux in the cosmic rays generated by them, it is experimentally difficult to separate the events of spontaneous fission from stimulated fission during experiments on the surface of the earth. To reduce the background from cosmic rays interfering with the study of the phenomenon, a multimeter layer of soil or water can serve as a screen. Therefore, the experiments were carried out in the Moscow metro (at the Dynamo station ) at a depth of 60 meters ^[3] ^[4] .

Notes

↑ Shultis, J. Kenneth; Richard E. Faw. p. 141, tab. 6.2 // Fundamentals of Nuclear Science and Engineering. - CRC Press, 2008. - ISBN 1-4200-5135-0 .
↑ Discoveries of Soviet Scientists, 1979 , p. 220.
↑ K. A. Petrzhak, G. N. Flerov: Report at the Conference on the Atomic Nucleus in Moscow in 1940
↑ K. Petrzhak: How spontaneous division was discovered

Literature

Konyushaya Yu. P. Discovery of Soviet scientists. - M .: Moscow Worker, 1979.- 688 p. - 50,000 copies.

[1] Shultis, J. Kenneth; Richard E. Faw. p. 141, tab. 6.2 // Fundamentals of Nuclear Science and Engineering. - CRC Press, 2008. - ISBN 1-4200-5135-0 .

[_7d4d176b53853257-2] Discoveries of Soviet Scientists, 1979 , p. 220.

[3] K. A. Petrzhak, G. N. Flerov: Report at the Conference on the Atomic Nucleus in Moscow in 1940

[4] K. Petrzhak: How spontaneous division was discovered