Beta decay on the associated state of the atom. Types of nuclear transformations, alpha and beta decay break Mass number of nuclear
In accordance with the types of radioactive emissions, there are several types of radioactive decay (types of radioactive transformations). The radioactive transformations are subject to elements, in the kernels of which too many protons or neutrons. Consider the types of radioactive decay.
1. Alpha decay It is characteristic of natural radioactive elements with a large sequence number (i.e., with small binding energies). About 160 alpha active species of nuclei are known, mainly the sequence number of them more than 82 (z\u003e 82). The alpha decay is accompanied by emission from the nucleus of an unstable element of the alpha particle, which is the kernel of the helium atom no (in its composition 2 proton and 2 neutron). The kernel charge decreases by 2, a mass number - by 4.
ZAK → Z-2 A-4 y + 2 4Ne; 92 238U → 24 not + 90 234th;
88 226RA → 2 4HE + 86 222RA + γ.
Alpha - more than 10% of radioactive isotopes are decomposed.
2. beta decay. A number of natural and artificial radioactive isotopes undergo a decay with emitting electrons or positrons:
a) Electronic beta decay. It is characteristic both for natural and for artificial radionuclides, which have overpriced neutrons (i.e., mainly for heavy radioactive isotopes). About 46% of all radioactive isotopes are subjected to electronic beta-decay. In this case, one of the neutrons turns into, and the kernel eats and antineutrino. The charge of the nucleus and, accordingly, the atomic number of the element increases by one, and the mass number remains unchanged.
Az x → az + 1 y + e- + v-; 24194PU → 24195am + E- + V-; 6429CU → 6430ZN + E- + V-; 4019K → 4020CA + E- + V-.
When the β-particles of the nucleus of atoms can be in an excited state, when an excess of energy is found in the subsidiary, which is not captured by the corpuscular particles. This excess energy is highlighted in the form of gamma quanta.
13785cs → 13756 V + E - + V- + γ γ;
b) positron beta decay. Some artificial radioactive isotopes are observed, which in the kernel there are surplus protons. It is characteristic of 11% of radioactive isotopes located in the first half of the Table D.I. Mendeleev (Z<45). При позитронном бета-распаде один из протонов превращается в , заряд ядра и соответственно атомный номер уменьшается на единицу, а массовое число остается без изменений. Ядро испускает позитрон и нейтрино.
AZX → AZ-1U + E + + V +; 3015p → 3014SI + E + + V +; 6428ni + E + + V +.
The positron, flying out of the nucleus, breaks with an "extra" atom or interact with a free electron, forming a pair of "positron-electron", which instantly turns into two gamma quantum with an equivalent mass of particles (E and E). The process of turning the "positron-electron" pair of two gamma quantum was called annihilation (destruction), and the emerging electromagnetic radiation - annihilation. In this case, the transformation of one form of matter (particles of the substance) to another - gamma photons;
c) electronic capture. This is a type of radioactive transformation when the atom core captures an electron from the energy to-level nearest to the core (electronic to-capture) or less than 100 times - from L level. As a result, one of the kernel protons is neutralized by an electron, turning into. The sequence number of the new kernel becomes smaller, and the mass number does not change. The kernel emits antineutrino. The released place, which occupied in to or L-level captured, is filled with an electron of more remote from the core of energy levels. Excess energy released at this transition is emitted by an atom in the form of a characteristic X-ray radiation.
AZH + E- → AZ-1 y + V- + X-ray radiation;
4019К + E- → AR + V- + X-ray radiation;
6429СU + E- → 6428 Ni + V- + X-ray radiation.
Electronic K-capture is characteristic of 25% of all radioactive nuclei, but mainly for artificial radioactive isotopes located in the other half of the Table D.I. Mendeleev and having surplus protons (z \u003d 45 - 105). Only three natural elements undergo K-capture: Potassium-40, Lantan-139, Lutherations-176 (4019K, 15957LA, 17671LU).
Some nuclei can disintegrate in two or three ways: by alpha and beta decay and to-capture.
Potassium-40 is subjected to as already noted, electronic decay - 88%, and to-capture - 12%. Copper-64 (6428cu) turns into nickel (positron decay - 19%, K-capture - 42%; (electronic decay - 39%).
3. The emission of γ-radiation is not a type of radioactive decay (it does not transform the elements), and is a flow of electromagnetic waves arising from the alpha and beta-decay of atomic nuclei (both natural and artificial radioactive isotopes) when The subsidiary is an excess of energy, not captured by the corpuscular radiation (alpha and beta particle). This excess is instantly highlighted in the form of gamma quanta.
13153i → 13154xe + e- + v- + 2γ quanta; 226888 → 42He + 22286RN + γ Kvant.
4. - emitting proton from the kernel is basically condition. This process may be observed in artificially obtained nuclei with a large neutron deficit:
lutes - 151 (15171LU) - in it 24 neutron is less than in a stable isotope 17671lu.
Alpha decay(A-decay) - type of radioactive decay of atomic nuclei, when an alpha particle is emitted, the nucleus charge decreases by 2 units, a mass number - by 4. Alpha decay is characteristic of radioactive elements with large atomic number Z.
Fig. one. Schematic image of a-decay.
Alpha decay is called spontaneous transformation of the atomic nucleus with the number of protons Z. and neutrons N. To another (subsidiary) core containing the number of protons Z.-2 and neutrons N-2. In this case, the A-particle is emitted - the kernel of the helium atom 4 // ^ +.
When a-decay of the original core, the atomic number of the formed nucleus decreases by two units, and the mass number decreases by 4 units, according to the scheme:
Examples of A-decay can be the disintegration of uranium-238 isotope:
(At the same time, the decay of the core of the thorium and the car diffuses with kinetic energies of 0.07 MeV and 4.18 MeV) and radium-226:
Here, a shift rule, formulated by Fayans and Soddy, is manifested: an element formed from another element when emitting a-ray occupies a place in the periodic system to two groups of the left of the source element.
The degree of nestability of the nuclei is characterized by the value of the half-life - the period of time during which half of the cores of this radioactive isotope disintegrates. Most radioactive isotopes have complex decay schemes. In such cases, the diagrams indicate the percentage of this type of radiation relative to the total number of transitions (Fig. 1 and 2).
Fig. 2. Demolition scheme 230 TH.
Complete energy of A-decay:
where E A. - Energy A-particles, E TL - The energy of the atom of return and I "SB is the energy of the excitation of a subsidiary core.
For more easy-to-wear nuclides (l
Kinetic energy of A-particles with alpha decay (E and) Determined by the masses of the source and final nucleus and A-particle. This energy can be somewhat decreased if the final core is formed in an excited state and, on the contrary, it was slightly increased if the kernel emitting a particle was excited (such a-particles with increased energy are called long-end). However, in all cases, the decay energy is always associated with the difference in masses and the levels of excitation of the initial and final nuclei, and therefore the spectrum of emitted A-particles is always not solid, but a lineal.
Energy released at the decay
where Ma. and M A -4 - the masses of the maternal and subsidiary, M a - Mass of a-particle. Energy E. It is divided between a-particle and a subsidiary is inversely proportional to their masses, from where the energy of A-particles:
Distant energy:
The return energy of the subsidiary nucleus is usually in the area of \u200b\u200bO, 1 MeV, which corresponds to the length of the run in the air equal to several millimeters.
On earthly conditions there are about 40 A-radioactive isotopes. They are combined into three radioactive rows, which begin with 2 3 6 U ( BUT \u003d 477), 2 3 8 u (BUT \u003d 477 + 2), 2 35U ( BUT \u003d 477 + 3). These can be conditionally (because the isotopes of this series managed to disperse during the existence of the Earth), attribute the fourth row, which begins with 2 3? NP (L \u003d 477 + 1). After a series of consecutive decays, stable kernels are formed with close or equal magic numbers by the number of protons and neutrons (z \u003d 82, n \u003d 126), respectively, 2O8 PB, 2O6 PB, 2 ° 7 Р, 2 ° 9B. The times of life "-Asive cores lie within yu 17.years (2 ° 48) to 3rd * 7c (212 RO). Long-lived are nuclides and 2 sections, * 44ne, 17 4hf, whose half-life are
(2 + 5) 10 * 5 years.
Fig. 3. Flat bundles of a ray from the source of small size: A - source 210 RO, one group of a ray; b - source 227 th, two groups with close-length runs; B - source 2U Bi + 2n Po, two A-particles are visible 211p0; G is a source of ~ 8 Th with products of its decay ^ Ra, 2 3-Th, 21b ro, 212 Bi + 212 PO 6 groups.
The alpha decay is possible if the binding energy of the A-particle relative to the maternal nucleus is negative. In order for the core to be a radioactive, the condition is a consequence of the law of energy conservation
M (ah?) \u003e M (L-4 ^ -2) + M A, (9)
where M (A, Z) and M (a-4, Z-2) - Mass of rest of the initial and final nuclei, respectively, M A. - Mass a-particles. In this case, as a result of the decay, the final core and a-particle acquire the total kinetic energy. E.
The kinetic energies of A-particles vary from 1.83 MeV (* 44ND) to 11.65 MeV (Izomer 212Sh RO). The energy of the A-particles emitted by heavy ras from the main states is 4 + 9 MeV, and the emitted by the rare-earth elements 2 + 4.5 MeV. Mileage a-particle with typical energy E. A \u003d 6 MeV is -5 cm in air under normal conditions and ~ o, 05 mm in A1.
Fig. four. Experimental A- spectrum of plutonium isotopes.
The spectrum of the particles arising from the decay of the maternal nucleus often consists of several mono-energy lines corresponding to quantum transitions to various energy levels of the subsidiary core.
Since the a-particle has no back, the rules for the selection at the time of movement I-L. And the readiness that arise from the relevant conservation laws are simple. Angular moment L. OR particles can take values \u200b\u200bin the interval:
where /, and If.- The angular moments of the initial and final state of the nuclei (maternal and subsidiary). At the same time, only the values \u200b\u200bof L are allowed, if the readiness of both states coincide, and odd, if parity does not coincide.
Fig. 5. Dependence of LG. T. from E A "1/2 For ballot isotopes, Polonia, Radon and Radia.
The property of a-decay is the presence of a certain and more successful dependence between the energy of the "-caditz emitted and the half-life of the" -radoactive nuclei of the half-life. With a small change in the energy of the A-particles, the periods of the half-life (T) are changing for many orders. So in 2 s 2 t to? "\u003d 4.08 MeV, 7 \u003d 1.41 10 yu l, and 2l8 th E A \u003d.9.85 MeV, T. \u003d Yu MKS. The change in energy is twice the change in the half-life of 24 orders.
For one-way isotopes of one element, the dependence of the half-life of the energy of A-decay is well described by the ratio (Geiger-Nettolla law):
where Ci and C 2 are constants, weakly dependent on Z.
For a constant decay, the law of Geiger-Nesol has the form:
where binb 2 - Constants, and b 2 - General, A. B - individual for each natural row, R - Male Length A-particle in the air, E A - Energy A-particles.
The dependence of this kind was empirically established in 1912 G.Gejer and J. Nyollom and theoretically substantiated in 1928. G. Gamov as a result of a quantum-mechanical consideration of the process of A-decay, which occurs through the tunnel transition. The theory describes the transitions between the main states of the ballroom nuclei. For odd, ball, non-vertical and odd nuclei, the overall trend is preserved, but their half-life of 2-1000 times more than for a well-known nuclei with Z and E a.
The prevalence of A-radioactivity is largely determined precisely the strong dependence of the lifetime of such nuclei on the energy of their collapse. This energy is positive if the half-life is within a kg 12 sect \u003d Yu 1B years of activity 1 g of isotope with BUT\u003d 200 is only 1.810 m2 ki).
For isotopes of elements with Z.
More than 200 A-active kernels are known, located mainly at the end of the periodic system, behind lead (Z\u003e 82), which completes the filling of the proton nuclear shell with Z \u003d 82. Alpha decay is associated with
coulomb repulsion, which increases as nuclei size increases faster (as Z 2) than nuclear forces of attraction that increase linearly with increasing mass number A.
Fig. 6. The dependence of the energy of the a-decay of isotopes of elements starting from polonium (Z \u003d 84) to the Fermia (Z \u003d IOO) from the number of neutrons in the nuclei.
There are also about 20 A-radioactive isotopes of rare earth elements (A \u003d I40-RI6O). Here a-disintegration is most characteristic of the cores with N \u003d 84, which, when emitting A-particles, turn into a kernel with a neutron shell filled (N \u003d 82). There is also a small group of emitters in the interval between rare earth and heavy nuclei and there are several emitting neutron-deficient nuclei with a ~ software.
The times of the A-active nuclei fluctuates widely: from 3-10- "sec (for 2.2 RO) to (2-5) -10 * 5 l (natural isotopes' 4 2 CE, * 44ND, WH. Energy A-decay lies within 44-9 MeV (with the exception of the case of long-term A-particles) for all heavy nuclei and 24-4.5 MeV for rare earth elements. Summary of data on the energies of A-decay of A-radioactive isotopes of elements with z \u003d 84 -100 is presented in Fig. 6
In the theory of A-decay, it is assumed that the maternal core is for a - particles of a potential pit, which is limited by a potential barrier. The energy of A-particles in the kernel is insufficient to overcome this barrier. The departure of A-particles from the kernel is possible only due to a quantum-mechanical phenomenon, which is called the tunnel effect. According to quantum mechanics, there are different from zero the likelihood of particle pass through the potential barrier. The phenomenon of tunneling is probabilistic.
Tunnel effect(tunneling) - overcoming the microparticle of a potential barrier in the case when its total energy (remaining in tunneling is unchanged) less than the height of the barrier. Tunnel effect - the phenomenon of quantum nature, impossible in classical mechanics; An analogue of the tunnel effect in the wave optics can be the penetration of the light wave inside the reflective medium under conditions when, from the point of view of geometric optics, there is a complete internal reflection. The phenomenon of the tunnel effect underlies many important processes in atomic and molecular physics, in physics of the atomic nucleus, solid body, etc. Ultimately, tunneling is explained by the ratio of uncertainty.
Fig. 7.
The main factor determining the likelihood of A-decay and its dependence on the energy of A-particle and the charge of the kernel is the Coulomb barrier. The simplest a-decay theory is reduced to the description of the movement of the A-particle in a potential pit with a barrier (Fig. 7). Since the energy of A-particles is 5th MeV, and the height of the Coulomb barrier at the heavy nuclei of 254-30 MeV, the departure of the A-particles from the nucleus can occur only due to the tunnel effect, the probability of which is determined by the barrier permeability. The probability of a-decay exponentially depends on the energy of a-particle.
In fig. 7 shows the dependence of the potential energy of the interaction of a-particle with a residual core, depending on the distance between their centers. Coulomb potential is cut at a distance R, which is approximately equal to the radius of the residual kernel. The height of the Coulomb barrier is directly proportional to the charge of the nucleus, charge A-particles and inversely proportional R \u003d R (A 1 / s, G 0 - the radius of the kernel. It is quite significant, for example, for 2 s ** and the Coulomb barrier has a height of 30 MeV, therefore, according to classical ideas, a particle with an energy of 4.5 MeV cannot overcome such a barrier. However, due to their wave properties, a particle such a barrier still overcomes.
In the energy diagram of the kernel, three areas can be distinguished:
i "- a spherical potential pomestic pit V. In classical mechanics A-particle with kinetic energy E A + V 0 can move in this area, but it is not capable of off. In this area, there is a strong interaction between the A-particle and the residual core.
R area of \u200b\u200ba potential barrier in which the potential energy is greater than the energy of a-particle, i.e. This is an area forbidden for a classic particle.
7 *\u003e Mr - area outside the potential barrier. In quantum mechanics, there is a passage of a-particle through the barrier (tunneling), but the probability of this is quite small.
The theory of tunneling Gamova explained the strong dependence of the period of the half-life of A-emitting nuclides from the energy of A-particles. However, the values \u200b\u200bof the half-life for many nuclei were predicted with great errors. Therefore, Gamova's theory was repeatedly improved. It was taken into account as the possibility of decaying the nuclei with a nonzero orbital momentum and the strong deformation of the nuclei (A-particles are more accurately flying along the large axis of the ellipsoid, and the average probability of departure is different from that for the spherical kernel), etc. In the theory of Gamov, the structure of the states of the initial and final nuclei and the problem of the formation of a-particle in the core, the likelihood of which was relying equal to 1. For balloons, this approximation is quite well described by experiment. However, if the restructuring of the structure of the original nuclei to the final is noticeably difficult, then the calculated values \u200b\u200bof the half-life can change by two orders of magnitude.
Alpha particle does not exist in the A-disintegrating nucleus all the time, and with some finite probability it occurs on its surface before departure. In the surface layer of heavy nuclei there are A-partial groups of nucleons consisting of two protons and two neutrons (A-clusters). It is known that a - decay goes on 2- ^ 4 of the order faster when a-particle is formed from neutron and proton pairs, compared with the decay, when the A-particle is formed from unpaired nucleons. In the first case, A-decay is called favorable, and all A-transitions are provided between the main states of the ballroom nuclei. In the second case, the decay is called unfavorable.
1. Physics of the atomic core 1.4. β-decay
1.4. Beta decay.
Types and properties of beta decomposition. Elements of beta-decay theory. Radioactive families
Beta decay The nuclei is called the process of spontaneous conversion of the unstable nucleus in the core-isobar as a result of the emission of an electron (positron) or an electron capture. About 900 beta radioactive cores are known. Of these, only 20 are natural, the rest are obtained by artificially.
Types and properties of beta decay
There are three types β -Rest: electronic β - -spad, positron β + -Spad and electronic grip ( e.- Capture). The main view is the first.
For electronically β – -Adead One of the neutrons of the nucleus turns into a proton with the emission of an electron and an electron antineutrino.
Examples: free neutron decay
, T. 1/2 \u003d 11.7 min;
disintegration of tritium
, T. 1/2 \u003d 12 years.
For positron β + -Adead One of the kernel protons turns into a neutron with the emission of a positively charged electron (positron) and electronic neutrino
. (1.41b)
Example
·
From the comparison of the periods of the half-life of the generic teams of families with the geological time of the life of the Earth (4.5 billion years), it is clear that in the substance of the land of Torium-232 almost all, uranium-238 broke up approximately half, uranium-235 - mostly, neptune-237 almost All.
Alpha and beta radiation are generally called radioactive decays. This is a process that is emissions from the kernel originating at a huge speed. As a result, the atom or its isotope can turn from one chemical element to another. Alpha and beta decays nuclei are characteristic of unstable elements. These include all atoms with a charge number greater than 83 and a massive number exceeding 209.
Conditions of reaction
Disintegration, like other radioactive transformations, is natural and artificial. The latter occurs due to any foreign particle in the core. How much alpha and beta decay can undergo atom - it depends only on how the stable state is reached soon.
With natural circumstances, Alpha and Beta-minus decays are found.
With artificial conditions, there is neutron, positron, proton and other, more rare varieties of decays and transfers of the nuclei.
These names gave the study of radioactive radiation.
The difference between the stable and unstable core
The ability to decay directly depends on the state of the atom. The so-called "stable" or non-reactive core is characterized by unprecedented atoms. In theory, observation of such elements can be carried out to infinity to finally be convinced of their stability. It takes this in order to separate such nuclei from unstable, which have the extremely long half-life.
By mistake, such a "slow" atom can be adopted for stable. However, a bright example can be Tellur, and more specifically, its isotope with a number 128, having 2.2 · 10 24 years old. This case is not partial. Lanthan-138 is subjected to a half-life, which is 10 11 years. This period is thirty times more than the age of the existing universe.
The essence of radioactive decay
This process is randomly. Each disintegrating radionuclide acquires the rate that is a constant for each case. The decay rate cannot change under the influence of external factors. It does not matter, the reaction will occur under the influence of a huge gravitational force, with absolute zero, in an electric and magnetic field, during any chemical reaction and so on. It is possible to influence the process only by direct influence on the inside of the atomic nucleus, which is almost impossible. The spontaneous reaction and depends only on the atom in which its internal state occurs.
At the mention of radioactive decontaminations, the term "radionuclide" is often found. Those who are not familiar with it should be aware that this word denotes a group of atoms that have radioactive properties, their own mass number, atomic number and energy status.
Various radionuclides are used in technical, scientific and other spheres of human life. For example, in medicine, these elements are used in diagnosing diseases, drug processing, tools and other items. There is even a number of therapeutic and prognostic radio products.
Equally important is the definition of isotope. This word is called a special type of atoms. They have the same atomic number, like a conventional element, however, a great mass. This difference is caused by the amount of neutrons that do not affect the charge, as protons and electrons, but change the mass. For example, in simple hydrogen there are integers 3. This is the only element, the names of which were assigned the names: deuterium, tritium (the only radioactive) and duty. In other cases, names are given in accordance with atomic masses and the main element.
Alpha decay
This is a type of radioactive reaction. It is characteristic of natural elements from the sixth and seventh period of the table of chemical elements of Mendeleev. In particular, for artificial or transuranone elements.
Elements subject to alpha decay
Metals for which this decay is characterized by thorium, uranium and other elements of the sixth and seventh period from the periodic table of chemical elements, counting from bismuth. The process is also exposed to isotopes from the number of heavy elements.
What happens during the reaction?
With alpha decay, emissions begins from the kernel of particles consisting of 2 protons and neutron pairs. The particle selected itself is the kernel of the helium atom, with a mass of 4 units and charge +2.
As a result, a new element appears, which is located on two cells to the left of the original in the periodic table. Such a location is determined by the fact that the initial atom lost 2 proton and at the same time the initial charge. As a result, the mass of an isotope arose for 4 mass units decreases compared with the initial state.
Examples
During such a collapse of uranium, thorium is formed. Radium appears from Thoria, from it - Radon, who eventually gives polonium, and at the end - lead. At the same time, the isotopes of these elements arise in the process, and not they themselves. So, it turns out uranium-238, thorium-234, radium-230, radon-236 and further, right up to the occurrence of a stable element. The formula of such a reaction is as follows:
TH-234 -\u003e RA-230 -\u003e RN-226 -\u003e PO-222 -\u003e PB-218
The speed of the isolated alpha particle at the time of emission ranges from 12 to 20 thousand km / s. Being in a vacuum, such a particle would have begged the globe for 2 seconds, moving along the equator.
Beta decay
The difference between this particle from the electron - at the place of appearance. The disintegration of beta occurs in the nucleus of the atom, and not an electronic shell surrounding it. Most often occurs from all existing radioactive transformations. It can be observed by almost all currently existing chemical elements. It follows from this that each element has at least one exposured isotope. In most cases, the beta-decomposition of beta-minus decomposition.
Being reaction
With this process, discharge from the electron core, which arose due to spontaneous transformation of the neutron into electron and proton. At the same time, the protons due to the larger mass remain in the nucleus, and the electron, called beta-minus particle, leaves the atom. And since the protons became more per unit, the kernel of the element itself changes in a large side and is located to the right of the original in the periodic table.
Examples
The breakdown of beta with potassium-40 turns it into the calcium isotope, which is located on the right. Radioactive calcium-47 becomes scandium-47, which can turn into a stable titanium-47. What does such a beta decay look like? Formula:
CA-47 -\u003e SC-47 -\u003e TI-47
The rate of departure of the beta particle is 0.9 from the speed of light, equal to 270 thousand km / s.
In nature, beta active nuclides are not too much. Of these are quite small. An example may be potassium-40, which in the natural mixture contains only 119/10000. Also natural beta-minus active radionuclides from among the most significant products are the products of the alpha and beta decay of uranium and thorium.
The breakdown of beta has a typical example: thorium-234, which, with alpha decay, turns into protactinium-234, and then in the same way becomes uranium, but its other isotope at number 234. This uranium-234 is again due to alpha decay becomes a thorium , but already another variety. Then this thorium-230 becomes radiat-226, which turns into radon. And in the same sequence, right up to thallium, only with various beta transitions back. This radioactive beta decreases the occurrence of stable lead-206. This transformation has the following formula:
Th-234 -\u003e PA-234 -\u003e U-234 -\u003e TH-230 -\u003e RA-226 -\u003e RN-222 -\u003e AT-218 -\u003e PO-214 -\u003e BI-210 -\u003e PB-206
Natural and significant beta-active radionuclides are K-40 and elements from thallium to uranium.
Distribution beta plus
There is also a beta plus transformation. It is also called positron beta decay. It occurs in the particle kernel under the name of the positron. The result becomes the transformation of the source element in the standing left, which has a smaller number.
Example
When the electronic beta decay occurs, Magnesium-23 becomes a stable sodium isotope. Radioactive Europe-150 becomes samarium-150.
The resulting reaction of beta decay can create beta + and beta emission. Particle departure rate in both cases is 0.9 from the speed of light.
Other radioactive decays
Apart from such reactions as the alpha decay and beta decay, the formula of which is widely known, there are other, more rare and characteristic of artificial radionuclides processes.
Neutron decay. There is an emission of a neutral particle of 1 massion units. During it, one isotope turns into another with a smaller mass. An example is to be the conversion of lithium-9 in lithium-8, helium-5 in Helium-4.
When irradiated with gamma-quanta, iodine-127 stable isotope, it becomes an isotope with a number 126 and acquires radioactivity.
Proton decay. It is extremely rare. During it there is an emission of a proton having a charge of +1 and 1 unit of mass. Atomic weight becomes less per value.
Any radioactive transformation, in particular, radioactive decays are accompanied by the release of energy in the form of gamma radiation. It is called gamma quanta. In some cases, X-ray radiation is observed, having less energy.
It is a stream of gamma quanta. It is electromagnetic radiation, more rigid than X-ray, which is used in medicine. As a result, gamma quanta appear, or energy flows from the atomic nucleus. X-ray radiation is also electromagnetic, but arises from the electronic shells of an atom.
Mileage of alpha particles
Alpha particles with a mass of 4 atomic units and charge +2 move straightly. Because of this, we can talk about the mileage of alpha particles.
The value of the run depends on the initial energy and ranges from 3 to 7 (sometimes 13) cm in the air. In a dense medium, there is a hundredth of millimeter. Such radiation can not break the sheet of paper and human skin.
Because of the own mass and the charge number of the alpha particle, has the greatest ionizing ability and destroys everything on the way. In this regard, Alpha Radionuclides are most dangerous for people and animals when exposed to the body.
Penetrating capacity of beta particles
Due to a small mass number, which is 1836 times less than proton, negative charge and size, beta radiation has a weak effect on a substance through which flies, but more than a flight longer. Also, the path of the particle is not straightforward. In this regard, they speak about the penetrating ability, which depends on the energy obtained.
Penetrating abilities in beta particles arising during radioactive decay, in the air reaches 2.3 m, in liquids, the calculation is carried out in centimeters, and in solids - in fractions from centimeter. Human body fabrics are 1.2 cm deep into depth. To protect against beta-radiation, a simple layer of water can be served to 10 cm. The flow of particles with a sufficiently large decay energy of 10 MeV is almost all absorbed by such layers: air - 4 m; aluminum - 2.2 cm; iron - 7.55 mm; Lead - 5.2 mm.
Considering the small dimensions, the beta-radiation particles have a small ionizing ability to compare with alpha particles. However, when they get inside, they are much more dangerous than during external irradiation.
The greatest penetrating indicators among all types of radiation currently has neutron and gamma. The mileage of these radiation in the air sometimes reaches tens and hundreds of meters, but with smaller ionizing indicators.
Most of the isotopes of gamma quanta in energy do not exceed the indicators of 1.3 MeV. The occasion is the values \u200b\u200bof 6.7 MeV. In this regard, layers of steel, concrete and lead are used to protect against such radiation for extinction of attenuation.
For example, to ten times to weaken the cobalt gamma radiation, lead protection is needed by a thickness of about 5 cm, for a 100-fold weakening, it will take 9.5 cm. Concrete defense will be 33 and 55 cm, and aqueous - 70 and 115 cm.
Ionizing neutrons depend on their energy indicators.
With any situation, the best protective method from radiation will be the maximum distance from the source and as few pastime in the high radiation zone.
Division of nuclei atoms
Under atoms is meant spontaneous, or under the influence of neutrons, into two parts, approximately equal in size.
These two parts become radioactive isotopes of elements from the main part of the chemical element table. Start from copper to lanthanides.
During the isolation, a pair of extra neutrons is broken and an excess of energy in the form of gamma quanta, which is much larger than when radioactive decay occurs. So, with one act of radioactive decay, one gamma-quantum arises, and 8.10 gamma quanta appears during the act of division. Also scattered fragments have greater kinetic energy, moving into thermal indicators.
The released neutrons can provoke the separation of a pair of similar cores if they are located near and neutrons got into them.
In this regard, the likelihood of the branching, accelerating chain reaction of the separation of atomic nuclei and creating a large amount of energy.
When such a chain reaction is controlled, it can be used at certain purposes. For example, for heating or electricity. Such processes are carried out on nuclear power plants and reactors.
If you lose control of the reaction, the atomic explosion happens. This is used in nuclear weapons.
In vivo there is only one element - uranium, having only one dividing isotope with number 235. It is weapon.
In the ordinary uranium atomic reactor from uranium-238 under the influence of neutrons, a new isotope is formed under the number 239, and from it - plutonium, which is artificial and does not occur in natural conditions. At the same time, the emerging plutonium-239 is used in weapons purposes. This process of dividing atomic nuclei is the essence of all atomic weapons and energy.
Such phenomena like alpha decay and beta decay, the formula of which is studied at school, is widespread in our time. Thanks to these reactions, there are nuclear power plants and many other productions based on nuclear physics. However, do not forget about the radioactivity of many such elements. When working with them requires special protection and compliance with all precautions. Otherwise, this can lead to an irreparable catastrophe.
Heavy ion drives open fundamentally new opportunities in the study of the properties of exotic nuclei. In particular, they allow accumulating and for a long time to use completely ionized atoms - "naked" nuclei. As a result, it becomes possible to investigate the properties of atomic nuclei, which have no electronic environment and in which there is no Coulomb impact of the outer electronic shell at the atomic core.
Fig. 3.2 E-capture scheme in isotope (left) and completely ionized atoms and (right)
The decay on the bound state of the atom was first discovered in 1992, the β - -enspad was observed completely ionized atom into associated atomic states. The kernel of 163 DY on the N-z diagram of atomic nuclei is marked with black. This means that it is a stable core. Indeed, entering the neutral atom, the kernel 163 dy is stable. Its main state (5/2 +) can be settled as a result of E-capture from the main state (7/2 +) kernel 163 Ho. The kernel 163 HO, surrounded by electronic shell, β - -radioactively and its half-life is ~ 10 4 years. However, this is true only if we consider the kernel surrounded by an electronic shell. For completely ionized atoms, the picture is fundamentally different. Now the main state of the nucleus 163 DY is due to the energy above the main state of the kernel 163 Ho and the possibility of decay 163 dy (Fig. 3.2)
| → + E - + E. | (3.8) |
The electron-mounted electron can be captured on a vacant or L-shell ion. As a result, the decay (3.8) has the form
→ + E - + E (in the associated state).
The energy of β-decays on K and L-shell is equal to (50.3 ± 1) keV and (1.7 ± 1) CEV. To observe the decay on the associated states of the K and L-shell in the ESR cumulative ring in GSI, 10 8 completely ionized cores were accumulated. During the accumulation time, the kernels were formed as a result of β +-wait (Fig. 3.3).
Fig. 3.3. The dynamics of the accumulation of ions: A - Current accumulated in the ESR ion-accumulated ring during different stages of the experiment, the β-intensity of DY 66+ and HO 67+ ions, measured by external and internal positional and sensitive detectors, respectively
Since HO 66+ ions have almost the same M / Q ratio as the DY 66+ primary beam ions, they accumulate on the same orbit. The accumulation time was ~ 30 minutes. In order to measure the half-life of the DY 66+ kernel, the beam accumulated on the orbit was necessary to clean from the impurity ions HO 66+. For cleaning the beam from ions to the chamber, an argon gas jet was injected with a density of 6 · 10 12 atom / cm 2, with a diameter of 3 mm, which crossed the accumulated beam of ions in the vertical direction. Due to the fact that ionsHO 66+ captured electrons, they dropped out with an equilibrium orbit. The beam cleaning took place for approximately 500 s. After that, the gas jet overlapped and in the ring continued to circulate DY 66+ ions and the newly formed (after turning off the gas jet) as a result of the decay of HO 66+ ions. The duration of this stage varied from 10 to 85 minutes. The detection and identification of HO 66+ were based on the fact that HO 66+ can be ionized even more. To do this, at the last stage, a gas jet was again injected into the cumulative ring. There was a robbing of the last electron from ion 163 HO 66+ and the result was ion 163 HO 67+. A positional-sensitive detector was located near the gas jet, which were recorded from the bunch of ions 163 HO 67+. In fig. 3.4 shows the dependence of the number of generated as a result of the β-decay of the nuclei 163 Ho on the accumulation time. The inset shows the spatial resolution of the positional and sensitive detector.
Thus, the accumulation in the beam 163 DY nuclei 163 Ho was proof of the possibility of decay
→ + E - + E (in the associated state).
Fig. 3.4. The ratio of subsidiaries 163 HO 66+ to the primary 163 DY 66+, depending on the accumulation time. On the insertion of peak 163 HO 67+, registered internal detector
Variating the time interval between the purification of the beam from the impurity HO 66+ and the reception time of the HO 66+ ions of the ions of the HO 66+, one can measure the half-life of the ionized DY 66+ ionized isotope. It turned out to be equal to ~ 0.1 years.
A similar decay was detected for 187 Re 75+. The result obtained is extremely important for astrophysics. The fact is that neutral 187 re atoms have a half-life of 4 · 10 10 years and are used as a radioactive clock. The half-life of 187 RE 75+ is only 33 ± 2 years. Therefore, in astrophysical measurements, it is necessary to make appropriate amendments, because In the stars, 187 re is most often in an ionized state.
The study of the properties of fully ionized atoms opens up a new direction of studies of the exotic properties of nuclei, deprived of the Coulomb effects of the outer electronic shell.
