Beta decay of the bindings of the atom. How does the mass number change during the disintegration of atomic nuclei?
1. PHYSICS OF THE ATOMIC NUCLEUS 1.4. β-decay
1.4. Beta decay.
See the power of beta decay. Elements of the theory of beta decay. Radioactive families
Beta decay nuclei is the process of transient transformation of an unstable nucleus into an isobar nucleus as a result of the dissolution of an electron (positron) or the entrapment of an electron. There are approximately 900 beta radioactive nuclei. About 20 of them are natural, the back is trimmed with a piece of fabric.
See the power of beta decay
There are three types β -dissolution: electronic β - Decay, positronic β + - Rozpad and electronic burying ( e- buried). The main type is the first one.
At electronic β – - disintegration One of the neutrons of the nucleus transforms into a proton with the vibration of an electron and an electron antineutrino.
Apply: disintegration of a free neutron
, T 1/2 = 11.7 xv;
tritium decay
, T 1/2 = 12 rocks.
At positronic β + - disintegration one of the protons of the nucleus transforms into a neutron with the vibration of a positively charged electron (positron) and an electron neutrino
. (1.41b)
butt
·
From the equal periods of the ancestral families' decline with the geological time of the Earth's life (4.5 billion years), it is clear that near the Earth's river, thorium-232 has been preserved, perhaps all of it, uranium-238 having decayed by about half, uranium-235 - great, neptunium-237 is practically all .
Beta decay - disintegration, radioactive disintegration of an atomic nucleus, which is coupled with the nucleus of an electron or a positron. This process involves the fleeting transformation of one of the nucleons of the nucleus into a nucleon of a different kind, and itself: the transformation of either a neutron (n) into a proton (p), or a proton into a neutron. At the first junction, an electron (e-) leaves the nucleus - this is called β-decay. In the other type, a positron (e+) comes from the nucleus – β+ decay occurs. They are violating for B.-r. electronics and positrons are called beta-frequencies. The mutual transformation of nucleons is accompanied by the appearance of one more particle - a neutrino ( ν
) in case of β+ decay or antineutrino A, equal to the initial number of nucleons in the nucleus, does not change, and the nuclear product is the isobar of the output nucleus, which stands as a new right-hander in the periodic table of elements. However, with β + -decay, the number of protons changes by one, and the number of neutrons increases by one, and an isobar is created that is equal to the content of the exit nucleus. Symbolically offended by the process of B.-r. sign up in the upcoming view: de -Z neutrons. The simplest example (β - - decay is the transformation of a free neutron into a proton with the transformation of an electron and an antineutrino (the period of neutron decay is ≈ 13) xv): Larger collapsible stock (β - decay - decay of the important isotope water - tritium, which consists of two neutrons (n) and one proton (p): Obviously, this process is reduced to the β-decay associated with the (nuclear) neutron. In this case, the β-radioactive tritium nucleus is transformed into the nucleus of the leading element in the periodic table - the nucleus of the light isotope helium 3 2 He. With the butt of β + -decay, the decomposition of the carbon isotope 11 can occur using the offensive scheme: The transformation of a proton into a neutron in the middle of the nucleus can occur as a result of the proton burying one of the electrons from the electron shell of the atom. The most common occurrence is electron burying B.-r. Be careful with both naturally radioactive and artificially radioactive isotopes. In order for the core to be unstable in relation to one of the types of β-resolution (so that B.-r. could be tested), the sum of the mass of particles in the left part of the reaction is responsible for being greater than the sum of the mass of the transformation products. Tom for B.-r. Visible energy appears. Energy B.-r. Eβ can be calculated as a result of the difference in mass, based on the relationship E = mc2, de h - The fluidity of light in a vacuum. When β-decay occurs de M - masses of neutral atoms During β+ decay, a neutral atom loses one of the electrons from its shell, the energy of the B.-r. more expensive: de me - electron mass. Energy B.-r. is divided between three particles: electron (or positron), antineutrino (or neutrino) and nucleus; The skin from light particles can take almost any energy from 0 to E β, so that their energy spectra are consistent. In the case of K-buried neutrinos, they again take away that same energy. Also, during β-decay, the mass of the exit atom exceeds the mass of the terminal atom, and during β+-decay, the excess becomes no less than two electron masses. Dosledzhennia B.-r. Nuclei have repeatedly presented them with unimaginable mysteries. After the discovery of radioactivity in the B.-r. For a long time it was seen as an argument on the truth of the presence of electrons in atomic nuclei; This assumption was revealed in a clear contradiction with quantum mechanics (marvelous atomic nucleus). Then, the abundance of energy of electrons that fly for the B.-R., has given rise in some physicists to the law of conservation of energy, because It was clear that from whose transformation they took the part of the core, which from the entire singing energy. The maximum energy of electrons that fly from the nuclei is the current difference in the energies of the cob and end nuclei. But in such a situation, it was unclear where the energy goes, since the electrons that float carry less energy. The idea of the German scientist W. Pauli about the creation of a new particle - the neutrino - was described as the law of conservation of energy, and another important law of physics - the law of conservation of momentum. The fragments of the spin (then the power moments) of the neutron and proton are equal to 1/2, then to save the spin in the right part of the level of B.-r. You can have less than the same number of particles with a spin of 1/2. However, during the β-decay of a neutron, n → p + e - + ν, only the appearance of an antineutrino turns on the violation of the law of conservation of the moment of speed. B.-r. It has a place in the elements of all parts of the periodic table. The tendency to β-transformation stems from the fact that a number of isotopes have an excess of neutrons or protons at the same level, which indicates maximum stability. Thus, the tendency to β+-decay or K-accumulation is characteristic of neutron-deficient isotopes, and the tendency to β-decay is characteristic of neutron-deficient isotopes. There are approximately 1500 β-radioactive isotopes of all elements of the periodic table, including the most important ones (Z ≥ 102). Energy B.-r. none of the known isotopes lie between periods of continuous laying at wide intervals of 1.3 10 -2 s_k(12 N) to Beta decay 21013 rocks (natural radioactive isotope 180 W). Nadali Vivchennya B.-r. has repeatedly led physicists to the collapse of old phenomena. It was installed that B.-r. to create forces of a completely new nature. Regardless of the troubling period that has passed since the hour of B.-R.’s discovery, the nature of the interaction that B.-R. understands has not been fully understood. Qiu mutualism was called “weak”, because. It is 10 12 times weaker than nuclear and 10 9 times weaker than electromagnetic (it overrides gravitational interactions; div. Weak interactions). Weak interactions have power over all elementary particles (except photons). Just after the century passed, first physicists discovered that B.-R. The symmetry between “right” and “left” may be destroyed. This neglect of space parity was attributed to the authorities of weak relationships. Vivchennya B.-r. little more respectful side. The hour of life of the core of the B.-r. And the shape of the spectrum of β-particles lies in those positions in which the output nucleon and the product nucleon are located in the middle of the nucleus. Therefore, the influence of B.-R., in addition to information about the nature and power of weak interactions, has significantly increased the number of discoveries about the structure of atomic nuclei. Imovirnist B.-r. It really lies down to how close the nucleons are in the cob and end nuclei. If the position of the nucleon does not change (the nucleon of the sky is lost at some point), then the reliability is maximum and the consistent transition of the cob to the end is called permissible. Such transitions are attached to the B.-R. light nuclei. Light nuclei contain at least as many neutrons and protons. More important nuclei have more neutrons than protons. Become nucleons of different coils and are completely consistent with each other. This complicates B.-r.; appear to be moving, among some B.-r. It is expected with little confidence. The transition is also made more difficult by the need to change the spin of the nucleus. Such transitions are called fenced in. The nature of the transition is indicated by the shape of the energy spectrum of β-particles. Experimental investigation of the energetic distribution of electrons released by β-radioactive nuclei (beta spectrum) is carried out with the help of Beta spectrometers. The application of β-spectra is aimed at Small 1
і Small 2
. Lit.: Alpha, beta and gamma spectroscopy, ed. K. Zigbana, prov. from English, art. 4, M., 1969, goal. 22-24; Experimental nuclear physics, ed. e. Segre, prov. z eng., T. 3, M., 1961. E. M. Leikin. Beta spectrum of a neutron. The abscis axis shows kinetic. energy of electrons E in kev, on the ordinate axis - the number of electrons N (E) in the leading units (vertical risks marking the boundaries between the values of electrons with the same energy value). Great Radyanska Encyclopedia. - M: Radyansk Encyclopedia.
1969-1978
.
Wonder what “Beta decay” is in other dictionaries:
Beta decay, the radioactive transformation of atomic nuclei, in the process up to 60 nuclei releases electrons and antineutrinos (beta decay) and positrons and neutrinos (beta + decay). Flying at Bi. electronics and positrons are called zagalne. beta particles. At… … Great Encyclopedic Polytechnic Dictionary
Suchasna encyclopedia
Beta decay- (b decay), a type of radioactivity in which a nucleus that decays releases electrons or positrons. During the electron decay of beta (b), a neutron (internal or external) transforms into a proton with the transformation of an electron and an antineutrino (marvel... ...). Illustrated encyclopedic dictionary
Beta decay- (β decay) radioactive transformation of atomic nuclei, in which nuclei release electrons and antineutrinos (β decay) and positrons and neutrinos (β+ decay). Flying at Bi. electrons and positrons are called beta particles (β particles). Russian Encyclopedia of Protection
- (b disintegration). instantaneous (spontaneous) transformation of a neutron n into a proton p and a proton into a neutron in the middle of the at. nuclei (as well as the transformation into a proton of a strong neutron), which is accompanied by vibrations on e or positron e+ and electron antineutrinos... Physical encyclopedia
The rapid transformation of a neutron into a proton and a proton into a neutron in the middle of the atomic nucleus, as well as the transformation of a free neutron into a proton, which is accompanied by the transformation of an electron or a positron and a neutrino or an antineutrino. Sub-phase beta decay. Nuclear energy terms
- (Div. beta) radioactive transformation of the atomic nucleus, in which an electron and an antineutrino or a positron and a neutrino are produced; During beta decay, the electrical charge of the atomic nucleus changes to one, but the mass number does not change. New dictionary. Dictionary of foreign words of Russian language
beta decay- beta promeni, beta disintegration, beta particles. The first part is visible [beta] ... Dictionary of difficult words and words in the current Russian language
Noun, number of synonyms: 1 division (28) Glossary of synonyms ASIS. V.M. Trishin. 2013… Glossary of synonyms
Beta breakup, beta breakup. Spelling dictionary
Beta decay- (ß decay) radioactive transformation of the atomic nucleus (weak interaction), in which an electron and an antineutrino or a positron and a neutrino are exchanged; at Bi. The electric charge of the atomic nucleus changes to one, but the mass does not change. Great Polytechnic Encyclopedia
Books
- About the problems of propaganda and speech in physics. Critical analysis of fundamental theories: the metaphysical nature of quantum mechanics and the illusory nature of quantum field theory. An alternative is the model of fusible particles, Petrov Yu.I. , The book is dedicated to the analysis of problems of unity and continuity to understand the “shape” and “part”. In the search for the most current problems, the mathematical foundations of the fundamental...
The accumulation of important ions reveals new capabilities in the implanted berries of exotic nuclei. However, the smell is allowed to accumulate and over the course of three hours vikorize the surface of the ionized atoms - the “naked” nuclei. As a result, it becomes possible to trace the power of atomic nuclei, which lack electron depletion and in which the daily Coulomb infusion of the outer electron shell with the atomic nucleus.
Small 3.2 Scheme of e-burial in isotopes (left-handed) and surface ionized atoms (right-handed)
The breakdown of the connection between the atom and the beginning of the phenomena in 1992. Prevent β-decay of the surface of the ionized atom in a bonded atomic station. The 163 Dy nucleus is shown in black on the N-Z diagram of atomic nuclei. This means that it has a stable core. Indeed, entering the warehouse of a neutral atom, the 163 Dy nucleus is more stable. Yogo main camp (5/2+) can be populated as a result of e-burying from the main camp (7/2+) core 163 Ho. The 163 Ho nucleus, sharpened by an electron shell, is radioactive and during this period it gradually becomes ~10 4 rocks. However, this is true if you can see the core in the sharpened electron shell. For publicly ionized atoms the picture is completely different. Now the main stage of the 163 Dy core appears behind the energy above the main stage of the 163 Ho core and the potential for the disintegration of 163 Dy appears (Fig. 3.2)
| → + e - + e. | (3.8) |
The electron that is created as a result of decay may end up in the vacant K or L shell of the ion. As a result, expansion (3.8) looks like
→ + e - + e (in connection with the situation).
The energies of β-decays in the K and L-shells of the region are (50.3±1) keV and (1.7±1) keV. To prevent disintegration at the junction of the K- and L-shells, 108 surface-ionized nuclei were accumulated in the ESR storage ring in GSI. Over the course of an hour of accumulation, the nuclei were dissolved as a result of β+ decay (Fig. 3.3).
Small 3.3. Dynamics of ion accumulation: a - stream accumulated at the ESR storage ring of Dy 66+ ions during various stages of the experiment;
Since the Ho 66+ ions are practically the same M/q as the ions of the primary Dy 66+ beam, they accumulate in the same orbit. The accumulation hour became ~ 30 minutes. In order to suppress the period of decay of the Dy 66+ nucleus and accumulations in orbit, the beam had to be cleaned from the home of Ho 66+ ions. To clean the ion beam, an argon gas stream with a density of 6·10 12 atoms/cm 2 and a diameter of 3 mm was injected into the chamber, which moved the accumulated ion beam in a vertical direction. Due to the fact that the Ho66+ ions were choking up electrons, the stinks were emitted from an equally important orbit. The beam was purified for approximately 500 s. After which the gas stream was interrupted and the Dy 66+ ions continued to circulate in the rings and re-established (after the gas stream became wet) as a result of the disintegration of the Ho 66+ ions. The severity of this stage varied from 10 to 85 minutes. Detection and identification of Ho 66+ were based on the fact that Ho 66+ can be ionized even more strongly. For this purpose, at the last stage, the gas jet was again injected into the accumulator ring. The remaining electron from the 163 Ho 66+ ion was stripped, resulting in the 163 Ho 67+ ion. Using a gas jet, a position-sensitive detector was deployed, which registered the ions that vibrated from the 163 Ho 67+ beam. In Fig. Figure 3.4 shows the accumulation of numbers that are established as a result of the β-decay of 163 nuclei at the time of accumulation. The inset shows the spacious separate building of the position-sensitive detector.
Thus, the accumulation of 163 Ho nuclei in the 163 Dy beam became proof of the possibility of decay.
→ + e - + e (in connection with the situation).
Small 3.4. The progression of daughter ions 163 Ho 66+ to the primary ions 163 Dy 66+ depends on the time of accumulation. At the time of peak 163 Ho 67+ registrations by internal detector
By varying the hour interval between cleaning the beam from the Ho 66+ house and the hour of registering the house of Ho 66+ ions that are re-entered into the beam, you can observe the period of rapid decline in the surface of the ionized ion. zotope Dy 66+. It turned out to be equal to ~0.1 fate.
There is a similar dispersion of occurrences for 187 Re 75+. This result is very important for astrophysics. On the right is that the neutral atoms of 187 Re have a period of 4·10 10 years and are victorious like a radioactive year. The period of rapid decline 187 Re 75+ becomes less than 33±2 rocks. Therefore, in astrophysical conditions it is necessary to make various corrections, because in the eyes of 187 Re is most often found in the ionized state.
The study of the powers of the surface ionized atoms opens up a new direction for the investigation of the exotic powers of nuclei, reducing the Coulombian influx of the external electron shell.
The periods of decay of the emitted α-radioactive nuclei vary at intervals. Thus, the tungsten isotope 182 W has a reverse period T 1/2 > 8.3 10 18 s, and the tungsten isotope 219 Pa has T 1/2 = 5.3 10 -8 s.
Small 2.1. The duration of the period of decay of a radioactive element in the form of kinetic energy is parts of a naturally radioactive element. Dashed line - Geiger-Nettall law.
For paired-paired isotopes, the occurrence of the period of reverse decay in α-decay energy Q α described empirically Geiger-Nettall law
where Z is the charge of the terminal nucleus, the period of decay is T 1/2 in seconds, and the energy of the α-particle E α is in MeV. In Fig. 2.1 shows the experimental values of the decay periods for α-radioactive pair-pair isotopes (Z changes from 74 to 106) and their description for additional relationship (2.3).
For unpaired-unpaired, paired-unpaired and unpaired-unpaired nuclei there is a latent tendency
lg T 1/2 in Q α is saved, but during periods of reverse decay 2–100 times greater, lower for paired nuclei with the same Z and Q α.
In order for α-decay to occur, it is necessary that the mass of the exit nucleus M(A,Z) be greater than the sum of the masses of the terminal nucleus M(A-4, Z-2) and the α-particle M α:
de Q α = c 2 – energy of α-decay.
Fragments M α<< M(A-4, Z-2),
the main part of the energy of α-decay is carried away by α ‑
often and more than ≈ 2% - terminal core (A-4, Z-2).
The energy spectra of α-frequencies of rich radioactive elements consist of many lines (fine structure of α-spectra). The reason for the appearance of a fine structure-spectrum is the disintegration of the cob kernel (A, Z) into the awakening kernel (A-4, Z-2). Vibrating spectra of α-frequencies can be used to obtain information about the nature of awakening states
cores (A-4, Z-2).
For the designated region of the value of A and Z nuclei, for which energetically possible α-decay, there are experimental data on the energy of binding nuclei. The energy content of α-decay Q in terms of mass number A is shown in Fig. 2.2.
3 fig. 2.2 it is clear that α-decay is energetically possible, starting from A ≈ 140. In the regions A = 140–150 and A ≈ 210, the value of Q α shows clear maxima, as a result of the shell structure of the nucleus. The maximum at A = 140-150 bonds from the filling of the neutron shell with the magic number N = A – Z = 82, and the maximum at A ≈ 210 bonds from the filling of the proton shell at Z
= 82. Due to the very shell structure of the atomic nucleus of the first (rare earth) atomic nucleus, the region of α-active nuclei begins with N = 82, and important α-radioactive nuclei become especially numerous, starting with Z = 82.
Small 2.2. Deposit of energy - decay in mass number A.
The wide range of periods of decay, as well as the great significance of these periods for rich α-radioactive nuclei, is explained by the fact that the α-particle cannot be removed from the nucleus, regardless of those that are energetically significant. In order to deplete the nucleus, the α-particle must build up the potential barrier - the area between the nuclei, which is created by the potential energy of the electrostatic interaction of the α-particle and the terminal nucleus and the gravitational forces between the nucleons. According to the classical physics of the α-part, we cannot overcome the potential barrier, since the kinetic energy is not necessary for this. However, quantum mechanics allows for such a possibility - α ‑
Often the song has the ability to pass through the potential barrier and lose the core. This quantum mechanical phenomenon is called the tunnel effect or tunnel effect. The greater the height and width of the bar'er, the less consistent the tunneling, and the period of decay is significantly longer. Wide range of periods up and down
α-viprominuvachiv is explained by various connections of kinetic energies of α-frequencies and the height of potential barriers. If the barrier did not exist, then the α-part would deprive the nucleus for its characteristic nuclear
hour ≈ 10 -21 - 10 -23 s.
The simplest model of α-decay was proposed in 1928 by G. Gamov and, independently of G. Gernit, by E. Condon. This model showed that the α-part is permanently located at the nucleus. While the α-particle is in the nucleus, there are nuclear gravitational forces on it. The radius of their action can be equalized with the radius of the nucleus R. The depth of the nuclear potential is V 0 . Beyond the nuclear surface at r > R the potential is the Coulomb potential
V(r) = 2Ze 2 /r.
Small 2.3. The energy of the α-frequency E α depends on the number of neutrons N
at the exit nucleus. Lines connect isotopes of the same chemical element.
A simplified diagram of the overall effect of the nuclear gravity potential and the Coulomb potential is shown in Figure 2.4. In order to go beyond the nuclei of the α-part with energy E α, you must go through a potential barrier located in the area from R to R c. The affinity of α-decay is mainly determined by the affinity of D for the passage of the α-particle through the potential barrier
Within the framework of this model, it was possible to explain the strong depository nature of α ‑ disintegration of the energy of the α-part.
Small 2.4. Potential energy of α-particle. Potential bar'er.
In order to develop the constant decay of λ, it is necessary to multiply the coefficient of passage of the α-particle through the potential barrier, first, by the consistency w α of the fact that the α-particle has settled in the nucleus, and, in another way, by the consistency of the fact that will appear at the boundaries of the core. If the α-particle in the core of radius R has a velocity v, then it approaches the cordon in the middle ≈ v/2R times per second. As a result, for a gradual breakup, a relationship emerges
 |
(2.6) |
The fluidity of the α-particle in the nucleus can be estimated from its kinetic energy E α + V 0 in the middle of the nuclear potential, which gives v? (0.1-0.2)s. It is clear from this that due to the presence of α-particles in the nucleus, they have the ability to pass through the barrier D<10 -14 (для самых короткоживущих
относительно α‑распада тяжелых ядер).
The roughness of the estimate of the overexponential multiplier is not very accurate, because the constant decay lies below the exponential indicator.
From formula (2.6) it follows that the period is in flux under the radius of the nucleus R, so the radius R is included not only in the overexponential multiplier, but also in the exponential indicator, as between integration. Therefore, α-decay can be determined by the radii of atomic nuclei. The radii obtained in this way are found to be 20–30% higher than those found in studies of electron dissipation. This difference is due to the fact that in the traces of liquid electrons the radius of the distribution of the electric charge in the nucleus varies, and in the α-decay the distance between the nucleus and the α-particle changes, on which they cease to There are nuclear forces.
The presence of a stationary Planck in the exponential display (2.6) explains the strong occurrence of the period of energy decay. A small change in energy can lead to a significant change in the exponent and thus a very sharp change in the period of decline. Therefore, the energies of the α-frequencies that float are strongly limited. For important nuclei, α-particles with energies above 9 MeV are practically mitten, and with energies below 4 MeV they live in the nucleus for so long that α-decay cannot be registered. For rare earth α-radioactive nuclei, the offending energy decreases according to the change in the radius of the nucleus and the height of the potential barrier.
In Fig. Figure 2.5 shows the energy content of α-decay of Hf isotopes (Z = 72) as mass number A in the sphere of mass numbers A = 156–185. Table 2.1 shows the energy of α-decay, the period of reverse decay and the main channels of decay of isotopes 156–185 Hf. It can be seen that as the mass number A increases, the energy of α-decay changes, which leads to a change in the intensity of α-decay and an increase in the intensity of β-decay (Table 2.1). The isotope 174 Hf, being a stable isotope (the natural content of isotopes has a value of 0.16%), proteus decays with a decay period T 1/2 = 2·10 15 due to the proliferation of the α-part.
Small 2.5. Energy content of α-decay of Q α isotopes Hf (Z = 72)
type of mass number A.
Table 2.1
The energy content of α-decay Q α, the period of reverse decay T 1/2,
different modes of decay of isotopes H f (Z = 72) depending on the mass number A
| Z | N | A | Q α | T 1/2 | Modi split (%) |
|---|---|---|---|---|---|
| 72 | 84 | 156 | 6.0350 | 23 ms | α(100) |
| 72 | 85 | 157 | 5.8850 | 110 ms | α (86), e (14) |
| 72 | 86 | 158 | 5.4050 | 2.85 z | α (44.3), e (55.7) |
| 72 | 87 | 159 | 5.2250 | 5.6 z | α (35), e (65) |
| 72 | 88 | 160 | 4.9020 | 13.6 z | α (0.7), e (99.3) |
| 72 | 89 | 161 | 4.6980 | 18.2 z | α (<0.13), е (>99.87) |
| 72 | 90 | 162 | 4.4160 | 39.4 z | α (<8·10 -3), е (99.99) |
| 72 | 91 | 163 | 4.1280 | 40.0 s | α (<1·10 -4), е (100) |
| 72 | 92 | 164 | 3.9240 | 111 s | e (100) |
| 72 | 93 | 165 | 3.7790 | 76 s | e (100) |
| 72 | 94 | 166 | 3.5460 | 6.77 hv | e (100) |
| 72 | 95 | 167 | 3.4090 | 2.05 xv | e (100) |
| 72 | 96 | 168 | 3.2380 | 25.95 hv | e (100) |
| 72 | 97 | 169 | 3.1450 | 3.24 hv | e (100) |
| 72 | 98 | 170 | 2.9130 | 16.01 year | e (100) |
| 72 | 99 | 171 | 2.7390 | 12.1 years | e (100) |
| 72 | 100 | 172 | 2.7470 | 1.87 year | e (100) |
| 72 | 101 | 173 | 2.5350 | 23.4 year | e (100) |
| 72 | 102 | 174 | 2.4960 | 2 10 15 l | e (100) |
| 72 | 103 | 175 | 2.4041 | 70 days | e (100) |
| 72 | 104 | 176 | 2.2580 | stab. | |
| 72 | 105 | 177 | 2.2423 | stab. | |
| 72 | 106 | 178 | 2.0797 | stab. | |
| 72 | 107 | 179 | 1.8040 | stab. | |
| 72 | 108 | 180 | 1.2806 | stab. | |
| 72 | 109 | 181 | 1.1530 | 42.39 days | β - (100) |
| 72 | 110 | 182 | 1.2140 | 8.9 10 6 l | β - (100) |
| 72 | 111 | 183 | 0.6850 | 1.07 year | β - (100) |
| 72 | 112 | 184 | 0.4750 | 4.12 year | β - (100) |
| 72 | 113 | 185 | 0.0150 | 3.5 hv | β - (100) |
Hf isotopes with A = 176-180 are stable isotopes. These isotopes also contain positive energy for α-decay. However, the energy of α-decay ~1.3–2.2 MeV is too low and α-decay of these isotopes has not been detected, regardless of the zero reactivity of α-decay. With a further increase in the mass number A > 180, β-decay becomes the dominant decay channel.
During radioactive decays, the terminal nucleus may appear not only in the main, but also in one of the awakening states. However, the intensity of α-decay in the energy of α-particles is strong, leading to the fact that decays on the awakening of the terminal nucleus are forced to proceed at a very low intensity, so that when the terminal nucleus is awakened, α-particle energy. Therefore, it is experimentally possible to prevent disintegration on the external levels, which have a relatively low awakening energy. Disintegrations on the awakening level of the terminal nucleus lead to the breakdown of the fine structure of the energetic spectrum of particles that flutter.
The main factor that determines the power of α-decay is the passage of α-frequency through the potential barrier. Other factors are revealed weakly, but in some cases they make it possible to obtain additional information about the structure of the nucleus and the mechanism of α-decay of the nucleus. One of these factors is the appearance of a quantum mechanical subcenter barrier. As the α-part emerges from the nuclei (A,Z), which causes spin J i , and at which the terminal nucleus is created
(A-4, Z-2) at the station with spin J f , then the α-part is responsible for taking the new moment J, which is indicated by the relationship
Since the α-part has a zero spin, its final moment J is avoided by the orbital momentum of the hand l
As a result, a quantum mechanical subcenter barrier appears.
Changing the form of the potential barrier for the rate of subcenter energy is slightly higher through the fact that the subcenter energy falls from the rise significantly more than a coulomb (as 1/r 2, and not as 1/r). However, the remainder of this change is divided by the constant Planck and is consumed in the exponent, then with large l it will lead to a change in the life time of the kernel.
In Table 2.2, the penetration of the sub-center bar'er B l for α-frequencies that float with orbital momentum is determined to be the same as the penetration of the sub-center bar'er B 0 for α-frequencies that float with orbital momentum l = 0 for a nucleus with Z = 90 , energy α- α = 4.5 MeV. It can be seen that with an increase in the orbital momentum l carried by the α-particle, the penetration of the quantum mechanical subcenter barrier drops sharply.
Table 2.2
Excellent penetration of the central barrier forα -Parts,
what floats with orbital momentum l
(Z = 90, E α = 4.5 MeV)
A significant factor causing a sharp overdistribution of the affinity of different molecules to α-decay may be the need for a significant reorganization of the internal structure of the nucleus when the α-particle is promoted. Since the cob kernel is more spherical, and the main body of the end kernel is strongly deformed, then in order to evolve into the main body of the end kernel, the outer kernel in the process of vibration of the α-part may re-awaken, greatly changing its shape. Such a change in the shape of the nucleus involves a large number of nucleons and a system with few nucleons, such as α ‑
a part that has lost its core may not appear in the mind of its protection. This means that the possibility of the formation of the terminal nucleus in the main stage will be insignificant. If, in the middle of the awakening stages of the terminal kernel, a state close to spherical appears, then the cob kernel can move to the next one without any disturbance as a result of α ‑
disintegration, the diversity of the population of such a region may appear great, which significantly outweighs the diversity of the population of the lower camps, including mainly.
From the diagrams of α-decay of isotopes 253 Es, 225 Ac, 225 Th, 226 Ra, one can see the strong intensity of α-decay upon the awakening of the energy of the α-particle and the orbital momentum l carried by the α-particle.
α-decay can also occur from the awakening of atomic nuclei. As an example, Tables 2.3 and 2.4 indicate the decay of the main and isomer states of isotopes 151 Ho and 149 Tb.
Table 2.3
α-decay of the main and isomer 151 Ho
Table 2.4
α-decay of the main and isomer 149 Tb
In Fig. 2.6 is induced by energy diagrams of the decay of the main and isomeric states of isotopes 149 Tb and 151 Ho.
Small 2.6 Energy diagrams of the decay of the main and isomer states of isotopes 149 Tb and 151 Ho.
α-decay from the isomer to the isotope 151 Ho (J P = (1/2) + , E isomer = 40 keV) is larger (80%), lower accumulation on this isomer. At that very hour, the main stun of 151 Ale falls apart most importantly in the result of e-capture (78%).
In the 149 Tb isotope, the decay of the isomer (J P = (11/2) - , E isomer = 35.8 keV) occurs most importantly as a result of e-accumulation. The particularities of the decay of the main and isomer stages, which must be avoided, are explained by the magnitude of the energy of the α-decay and e-burst and the orbital moments carried by the α-particle or neutrino.
Alpha Decay(A-decay) - a type of radioactive decay of atomic nuclei, when the alpha part is lost, the charge of the nucleus changes by 2 units, the mass number - by 4. Alpha decay is characteristic of radioactive elements with a great atomic number Z.
Small 1. Schematic representation of the breakdown.
Alpha decay is called the rapid transformation of an atomic nucleus with a number of protons Z and neutrons N into another (daughter) nucleus to accommodate a large number of protons Z-2 ta neutrons N- 2. In this case, the a-part is released - the nucleus of the helium atom 4//^+.
During the a-decay of the output nucleus, the atomic number of the nucleus that has been dissolved changes by two units, and the mass number changes by 4 units, similar to the diagram:
Butts of a-decay can but decompose the isotope uranium-238:
(during this decay, the thorium nucleus and a-particle scatter with kinetic energies of 0.07 MeV and 4.18 MeV) and radius-226:
Here the rule of conjugation, formulated by Faience and Soddi, is manifested: an element that is created from another element during the alternation of a-changes takes a place in the periodic system two groups to the left of the output element.
The stage of instability of nuclei is characterized by the magnitude of the decay period - the period of an hour during which half of the nuclei of a radioactive isotope decay. Most radioactive isotopes exhibit complex decay patterns. In such transitions, the diagrams indicate hundreds of this type of progression in relation to the total number of transitions (Fig. 1 and 2).
Small 2. Scheme of disintegration of 230 Th.
Full energy of decay:
de E a- energy of a-parts, E tl- the energy of the atom is released and I'm - the energy of the awakening of the daughter nucleus.
For more light guy nuclides (L
Kinetic energy of a-frequency during alpha decay (E ta) is indicated by the masses of the output and terminal cores and a-parts. This energy can change slightly as the terminal nucleus settles into an awakened state and, however, further increases as the nucleus is awakened and releases an a-particle (such as a-parts with increased energy). energy are called long-running). However, in all phases, the energy of a-decay is always associated with the difference in mass and the levels of excitation of the exit and terminal nuclei, and therefore the spectrum of a-frequencies that are released is always not continuous, but linear.
Energy seen during a-decay
de Ma i M A -4 - the masses of the mother and daughter nuclei, Ma - Masa a-chastki. Energy E The division between the a-particle and the daughter nucleus is proportional to their masses, indicating the energy of the a-frequency:
Energy output:
The output energy of the daughter nucleus is expected to be in the region of about 1 MeV, which indicates a long distance in the world that is equal to several millimeters.
Earthly minds have approximately 40 a-radioactive isotopes. The smells are organized into three radioactive series, starting with 2 3 6 U ( A = 477), 2 3 8 U (A = 477 +2), 2 35U ( A = 477 +3). Before them, you can intellectually (since the isotopic series began to disintegrate during the hour of the Earth’s drying), add a fourth row, which begins with 23? Np (L = 477 +1). After low successive decays, stable nuclei are created with close and equal magic numbers of protons and neutrons (Z=82, N=126) like 2o8 Pb, 2o6 Pb, 2 ° 7 Pb, 2 ° 9 Bi. Pori life of active nuclei lie at the boundaries of Yu 17 rokiv (2 °4Рь) to 3rd* 7 z (212 Rho). Long-lived nuclides include 2 Ce, *44Ne, 17 4Hf, which gradually become
(2+5) 10*5 rocks.
Small 3. Flat bundles of a-promens from a dzherel of small sizes: a - dzherel 210 Po, one group of a-promens; b - dzherelo 227 Th two groups with close distances; c - dzherelo 2u Bi + 2n Po, two a-particles 211P0 are visible; g - dzherelo ~ 8 Th with products of the decomposition of Ra, 2 3-Th, 21b Po, 212 Bi + 212 Po 6 group.
Alpha decay is possible, since the energy of the connection between the a-particles and the maternal nucleus is negative. In order for the nucleus to be a-radioactive, it is necessary to change the mind, which follows the law of conservation of energy.
M(Huh?) >M(L-4^-2) + Ma, (9)
de M(A,Z)і M(A- 4,Z-2) - the mass of the calmness of the output and terminal nuclei is evident, Ma- Masa a-chastki. When, as a result of disintegration, the terminal nucleus and a-part increase in total kinetic energy e.
The kinetic energies of a-particles change from 1.83 MeV (*44Nd) to 11.65 MeV (isomer 212n Po). The energy of a-particles that are released from the main frames is 4+9 MeV, and the energy of rare earth elements that are released is 2+4.5 MeV. Travel of a-parts with typical energy E a = 6 MeV becomes -5 cm near the surface for normal people i ~o, 05 mm in A1.
Small 4. Experimental a-spectrum of plutonium isotopes.
The spectrum of particles that emerge during the disintegration of the mother nucleus often consists of several mono-energetic lines, which indicate quantum transitions at different energy levels of the daughter nucleus.
Since a part does not have a back, the rules for selection are based on the moment of strength of the hand I-L Those contradictions that arise from the basic laws of saving appear to be simple. Kutovy moment L or-parts can take values in the intervals:
where i If- the critical moments of the cob and end stages of the nuclei (mother and daughter). In which case the paired values of L are allowed, when the pairings of both sides are avoided, and the unpaired ones, when the pairings are not avoided.
Small 5. Deposit lg T view E a "1/2 for paired isotopes polonium, radon and radium.
Due to the power of a-decay, there is a clear and extremely strong continuity between the energy of the particles that are released and the period of rapid decay of radioactive nuclei. With a small change in the energy of a-particles, the periods of decay (T) change by many orders of magnitude. So 2 з 2 ТЪ?„=4.08 MeV, 7=1.41 10 yu l, and 2l8 Th E a = 9.85 MeV, T=yu μs. The change in energy shows a change in the period of 24 orders of magnitude.
For paired-paired isotopes of one element, the occurrence of the period of decay in the energy of a-decay is best described by the relationship (Geiger-Nettall law):
de Ci і з 2 - constants that weakly lie in Z.
For gradual decay, the Geiger-Netall law looks like this:
de binb 2 - constant, and b 2 - zagalna, and b- individual for the skin’s natural needs, R- dovzhina mileage and parts in the world, E a - energy of a-parts.
Deposit of this kind was empirically established in 1912. G. Geiger and J. Netall and theoretically lined in 1928. G. Gamov, as a result of a quantum mechanical analysis of the process of a-decay, which appears to be the path of the tunnel transition. The theory describes well the transitions between the main stages of paired nuclei. For unpaired-paired, paired-paired and unpaired-paired nuclei, the underlying tendency is preserved, but their periods are 2-1000 times greater than for paired-paired nuclei with Z and data E a.
The expansion of a-radioactivity is largely determined by the duration of the life of such nuclei in relation to the energy of their decay. This energy is positive, since the period of rapid decline is between kg 12 sec = 1 in rocks activity 1 g isotope A=200 becomes less than 1.810 m2 Ki).
For isotopes of elements with Z
There are more than 200 a-active nuclei, distributed mainly at the end of the periodic system, behind lead (Z>82), which completes the filling of the proton nuclear shell Z=82. Alpha disintegration of knittings
Coulomb compounds, as the size of nuclear nuclei increases worldwide (such as Z 2), lower nuclear gravity forces, which increase linearly with increases in the mass number A.
Small 6. The energy content of a-decay of isotopes of elements, ranging from polonium (Z=84) to fermium (Z=ioo) depending on the number of neutrons in nuclei.
There are also about 20 a-radioactive isotopes of rare earth elements (A=i40-ri6o). Here a-decay is most characteristic of nuclei N= 84, which, when a-frequency is vibrated, transforms into nuclei with a filled neutron shell (N= 82). Apparently there is also a small group of viprominent nuclei between rare earth and important nuclei and a handful of a-viprominent neutron-deficient nuclei with A~po.
The life hours of a-active nuclei vary between: from 3-10-"sec (for 2.2 Po) to (2-5)-10*5 l (natural isotopes '4 2 Ce, *44Nd, WHO. Energy a -decay lies in the range of 44-9 MeV (behind the fall of long-running a-frequencies) for all important nuclei and 24-4.5 MeV for rare earth elements -100 is shown in Fig. 6.
Theoretically, a-decay is transferred to the mother nucleus for a-particles by a potential well, which is surrounded by a potential barrier. The energy of the a-parts in the core is insufficient to support the barrier. The occurrence of fragments from the nucleus appears to be due to a quantum mechanical phenomenon called the tunnel effect. Based on quantum mechanics, it is clear that the passage of a portion through a potential barrier is zero-neutral. The phenomenon of tunneling is of an incredible nature.
Tunnel effect(tunnel) - edged with a microparticle of the potential barrier whenever its total energy (which is lost during tunneling unchanged) is less than the height of the barrier. Tunnel effect - a phenomenon of quantum nature, impossible for classical mechanics; An analogue of the tunnel effect in cowtail optics may be the penetration of light cornea into the middle, knocking the middle out of the minds, if, from the perspective of geometric optics, there is an external internal bias. The phenomenon of the tunnel effect underlies many important processes in atomic and molecular physics. V physics of the atomic nucleus, solid state, etc. By the way, tunneling is explained by the relationship of insignificances.
Small 7.
The main factor that determines the reliability of a-decay is the concentration of the energy of the a-particle and the charge of the nucleus, the Coulomb barrier. The simplest theory of a-decay is reduced to a description of the collapse of the a-part in a potential well with a barrier (Fig. 7). The energy of fragments of a-particles becomes 5-gu MeV, and the height of the Coulomb barrier at important nuclei is 254-30 MeV, the flight of a-particles from the nuclei can be caused by the tunnel effect, the reactivity of which is determined by penetration Stu Bar'er. The intensity of a-decay is exponentially dependent on the energy of the a-part.
In Fig. Figure 7 shows the deposit of potential energy between the a-particle and the excess core, which lies between their centers. The Coulomb potential is cut off at the substation R, which is approximately equal to the radius of the excess core. The height of the Coulomb bar is directly proportional to the charge of the nucleus, the charge of the a-part, and in turn proportional to R=r(A 1/s, r 0 – core radius. The value is significant, for example, for 2 s** and the Coulomb bar'er has a height of 30 MeV, therefore, due to classical phenomena, and partly with an energy of 4.5 MeV, such a bar'er cannot be raised. However, in spite of their weak authorities, sometimes such a barrier still fails.
On the energy diagram of the nucleus, three areas can be seen:
i" - spherical potential pit with clay V. The classical mechanism has a part with kinetic energy E a +V 0 You can collapse at this place, or leave it. This galus has a strong interaction between the a-particle and the excess nucleus.
R area of the potential barrier, which potential energy is greater than the energy of the a-part, then. This area is fenced off with classical parts.
7*>g e - area posture with a potential bar'er. Quantum mechanics allows particles to pass through a barrier (tunneling), the resistance of which is very low.
Gamow's theory of tunneling explained the strong depository period of the decay of a-viprominent nuclides from the energy of a-particles. However, the magnitude of the periods of decline for many nuclei was subject to great losses. That’s why Gamow’s theory has been thoroughly refined more than once. It was considered that there is a possibility of decay of nuclei with a non-zero orbital momentum, and strong deformation of nuclei (a-particles tend to float along the great axis of the ellipsoid, and the average velocity varies according to this for a spherical nucleus) then. Theoretically, Gamow did not take into account the structure of the cob and terminal nuclei and the problem of illumination of a-particles in the nucleus, the consistency of which was equal to 1. For paired nuclei in close proximity, the experiment describes well. However, since the transition of the structure of the output nuclei in the terminal is significantly complicated, the dynamic values of the periods can suddenly change by two orders of magnitude.
The alpha part does not stay in the core, which is disintegrating, for the entire hour, but with some terminal equanimity it appears on its surface in front of the villot. At the surface of important nuclei there are a-partial groupings of nucleons, which consist of two protons and two neutrons (a-clusters). It appears that the a-decay is 2-4 orders of magnitude faster when the a-particle is created from neutron and proton pairs, and equal to the decay when the a-particle is created from unpaired nucleons. In the first phase, the a-disintegration is called accommodating, and all a-transitions between the main stages of paired nuclei are revealed as such. In other types, a-decay is called unfriendly.