Alpha Deceiver or ? - decay is a type of radioactive decay in which the atomic nucleus emits alpha particles (helium nuclei) and thereby converts or 'decomposes' to an atom with a reduced mass of four and a reduced atomic number of two. Alpha particles are identical to the helium-4 atomic nucleus, which consists of two protons and two neutrons. It has a charge of 2Ã, e and mass 4Ã, u . For example, uranium-238 decays to form thorium-234. Alpha particles have a charge of 2 e , but as nuclear equations describe nuclear reactions without considering electrons that do not imply that nuclei always occur in atomic neutrons - its charge is not usually shown.
Alfa decay usually occurs in the heaviest nuclides. Theoretically, this can happen only to heavier nuclei than nickel (element 28), where the overall binding energy per nucleon is no longer a minimum and the nuclide is unstable against spontaneous fission type processes. In practice, this mode of decay is only observed in nuclides much heavier than nickel, with the lightest alpha emitter known as the lightest isotope (mass number 106-110) of tellurium (element 52). However, remarkably, beryllium-8 decays into two alpha particles.
Alpha decay is by far the most common form of decay of the group, in which the parent atoms removes a predetermined set of daughter nucleons, leaving behind the other product specified behind. This is the most common form due to the combination of very high bonding energies and the relatively small mass of alpha particles. Like the decay of other clusters, alpha decay is essentially a process of quantum firing. Unlike beta decay, it is governed by the interaction between the nuclear force and the electromagnetic force.
Alpha particles have a typical 5 MeV kinetic energy (or 0.13% of their total energy, 110 TJ/kg) and have a speed of about 15,000,000 m/s, or 5% of the speed of light. There is a very small variation around this energy, due to the heavy dependence of the part-time process on the energy produced (see equations in Geiger-Nuttall law). Because of their relatively large mass, electric charge 2Ã, e and relatively low speed, alpha particles are highly likely to interact with other atoms and lose their energy, and forwards their motion can be stopped by several centimeters of air. About 99% of the helium produced on Earth is the result of alpha decay from underground deposits of minerals containing uranium or thorium. Helium is brought to the surface as a by-product of natural gas production.
Video Alpha decay
History
The alpha particle was first described in a radioactivity probe by Ernest Rutherford in 1899, and in 1907 they were identified as Dia 2 ion.
In 1928, George Gamow had solved the alpha decay theory through tunneling. Alpha particles are trapped in a potential well by the nucleus. Classically, it is forbidden to escape, but according to (then) the principles of newly discovered quantum mechanics, it has a small probability (but not zero) "tunneling" through the barrier and appears on the other side to escape from the nucleus.. Gamow solves a potential model for the nucleus and is derived, from the first principles, the relationship between half the life of decay, and emission energy, which had previously been discovered empirically, and is known as Geiger-Nuttall law.
Maps Alpha decay
Mechanism
The nuclear force holds the nuclei of atoms together very strongly, generally more powerful than the disgusting electromagnetic force between protons. However, the nuclear force is also a short distance, falling rapidly in forces beyond about 1 femtometre, while the electromagnetic force has unlimited range. The pulling force of the nuclear force keeps the nucleus together proportionately to the number of nucleons, but the annoying electromagnetic force that tries to break apart nuclei is roughly proportional to the square of its atomic number. A nucleus with 210 or more nucleons is so large that a strong nuclear force holding them together can hardly compensate for the electromagnetic repulsion between the protons it contains. Alpha decay occurs in such nuclei as a means of increasing stability by reducing size.
One curiosity is why alpha particles, helium nuclei, should be emitted in a special way compared to other particles such as single protons or neutrons or other nuclei. Part of the answer comes from the conservation of symmetry of the wave function, which prevents particles from spontaneously changing from showing off Bose-Einstein statistics (if they have the same number of nucleons) with Fermi-Dirac statistics (if having an odd number of nucleons) or vice versa. A single proton emission, or emission of any particles with an odd number of nucleons would violate this conservation law. The rest of the answer comes from a very high alpha particle bonding energy. Calculates the total disintegration energy given by the equation:
Di mana adalah massa awal nukleus, adalah massa inti setelah emisi partikel, dan adalah massa partikel yang dipancarkan, menunjukkan bahwa emisi partikel alfa biasanya akan mungkin hanya dengan energi dari nukleus itu sendiri, sementara mode peluruhan lainnya akan membutuhkan energi tambahan. Sebagai contoh, melakukan perhitungan untuk uranium-232 menunjukkan bahwa emisi partikel alfa hanya akan membutuhkan 5,4 M MeV, sementara emisi proton tunggal akan membutuhkan 6,1 M MeV. Sebagian besar energi disintegrasi ini menjadi energi kinetik dari partikel alfa itu sendiri, meskipun untuk melestarikan pelestarian momentum bagian dari energi ini menjadi pengusiran inti itu sendiri. Namun, karena jumlah massa dari radioisotop yang memancarkan alfa paling banyak melebihi 210, jauh lebih besar daripada jumlah massa partikel alfa (4) bagian dari energi yang menuju ke penarikan inti pada umumnya cukup kecil.
However, this disintegration energy is much smaller than the potential barrier provided by the nuclear force, which prevents alpha particles from escaping. The required energy is generally in the range of about 25 MeV, the amount of work to be done on electromagnetic repulsion to bring alpha particles from infinity to a point near the nucleus beyond the reach of nuclear force influence. The alpha particle can be considered as inside a potential barrier with a wall of 25 MeV. However, the decay of alpha particles has only 4 MeV kinetic energy up to about 9 MeV, far less than the energy required to escape.
Quantum mechanics, however, provides a ready explanation, through a quantum tunneling mechanism. The alpha quantum alter tunneling theory, independently developed by George Gamow and Ronald Wilfred Gurney and Edward Condon in 1928, is hailed as a very surprising confirmation of quantum theory. Basically, the alpha particle passes from the nucleus by its quantum tunneling pathway. Gurney and Condon make the following observations in their paper about it:
To date it is necessary to postulate some of the 'instability' of the special nucleus of the nucleus; but in the following note shows that disintegration is a natural consequence of the laws of quantum mechanics without specific hypotheses... Much has been written about the explosive violence by which particles are thrown from its place in the nucleus.. But from the process described above, people would rather say that the "particle" is barely noticed.
The theory presupposes that alpha particles can be regarded as independent particles in a constantly moving nucleus, but are within the nucleus by nuclear power. At each collision with a potential barrier of nuclear force, there is a small non-zero probability that will find its way out. An alpha particle with a speed of 1.5o, 10 7 m/s in a nuclear diameter of about 10 -14 m will collide with a barrier of more than 10 21 times per second. However, if the probability of escape in any collision is very small, the radioisotope half-life will be very long, since this is the time required for the total runaway probability to reach 50%. As an extreme example, the half-life of the bismuth-209 isotope is 1.9 x 10 19 years.
Working on theoretical details leads to equations related to the life-span of radioisotopes to the alpha particle's decay energy, the theoretical derivation of the empirical Geiger-Nuttall law.
Usage
Americium-241, an alpha transmitter, is used in smoke detectors. The alpha particles ionize the air in the open ion space and the small current flows through the ionized air. The smoke particles from the fire coming into space reduce the current, triggering smoke detector alarms.
Alpha decomposition can provide a safe resource for radioisotope thermoelectric generators used for spacecraft and used for artificial pacemakers. Alpha decay is more easily protected than other forms of radioactive decay.
Static removers typically use polonium-210, alpha transmitters, to ionize the air, allowing 'static cling' to disappear faster.
Toxicity
Very heavy and heavy, alpha particles lose some MeV of their energy in small volumes of material, as long as the free path means very short. This increases the chance of double-strand breaks into DNA in cases of internal contamination, when ingested, inhaled, injected or introduced through the skin. Otherwise, touching alpha sources is usually harmless, since alpha particles are effectively protected by several centimeters of air, a sheet of paper, or a thin layer of dead skin cells that make up the epidermis; However, many alpha sources are also accompanied by daughter radios that emit beta, and both are often accompanied by gamma photon emissions.
RBE relative biological effectiveness quantifies the ability of radiation to cause certain biological effects, particularly cancer or cell death, for equivalent radiation exposure. Alpha radiation has a high linear energy transfer coefficient (LET), which is about one ionisation of a molecule/atom for each travel angstrom by alpha particles. RBE has been set at a value of 20 for alpha radiation under various government regulations. RBE is set at 10 for neutron irradiation, and at 1 for beta radiation and ionizing photons.
However, recalling the parent nucleus (alpha recoil) provides a large amount of energy, which also causes ionization damage (see ionizing radiation). This energy is about the weight of alpha (4 u) divided by the parent weight (usually about 200 times) times the total energy of the alpha. By some estimates, this may account for most of the damage to internal radiation, since the recoil nucleus is part of a much larger atom than an alpha particle, and causes a very dense ionisation trace; Atoms are usually heavy metals, which preferentially collect on chromosomes. In some studies, this results in an RBE approaching 1,000 rather than the value used in government regulations.
The biggest natural contributor to the dose of public radiation is radon, a natural radioactive gas found in soil and rock. If gas is inhaled, some radon particles can stick to the inner lining of the lungs. These particles continue to decay, emitting alpha particles, which can damage cells in the lung tissue. Marie Curie's death at the age of 66 due to aplastic anemia may be due to prolonged exposure to high-dose ionizing radiation, but it is unclear whether this is due to alpha or X-ray radiation. Curies work extensively with radium, which decomposes into radon, along with other radioactive materials that emit beta and gamma rays. However, Curie also worked with X-ray tubes not exposed during World War I, and the analysis of the skeleton during repetition showed relatively low levels of radioisotopes.
The Russian assassination, Alexander Litvinenko, 2006, the murder of radiation poisoning allegedly carried out with polonium-210, the alpha transmitter.
References
- Alpha emitter with increased energy (Appendix 1)
Note
External links
- LIVEChart of Nuclides - IAEA with filters in alpha decay
- Alpha decay with 3 animated instances that show girls' retreat
Source of the article : Wikipedia
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