Alpha Particles consists of two protons and two neutrons bonded together into a particle identical to the helium-4 nucleus. They are generally produced in alpha decay processes, but can also be produced in other ways. Alpha particles are named after the first letter in the Greek alphabet,. The symbol for the alpha particle? or? 2 . Since they are identical to helium nuclei, they are sometimes also written as 2
or 4
2 He 2 show helium ion with charge 2 (missing two electrons). If ions get electrons from their environment, alpha particles become normal helium atoms (electrically neutral) 4 2 He .
Alpha particles, such as helium nuclei, have a zero net rotation. Due to their production mechanism in standard alpha radioactive decay, alpha particles generally have a kinetic energy of about 5 MeV, and a speed at about 5% the speed of light. (See the discussion below for the limits of these numbers in alpha decay.) They are a form of highly ionized particle radiation, and (when generated from radioactive alpha decay) have a low penetration depth. They can be stopped by a few centimeters of air, or by the skin.
However, the so-called long-alpha particles of ternary fission are three times more energetic, and penetrate three times farther. As noted, the helium nuclei that make up 10-12% of the cosmic rays also typically have much higher energy than those produced by nuclear decay processes, and thus capable of deeply penetrating and capable of traversing the human body as well as many solid solid shielding meters, on their energy. At a lower level, this also applies to very high-energy helium nuclei produced by particle accelerators.
When alpha particles emit digested isotopes, they are much more dangerous than the half-rate or decay they would suggest, because the relatively high biological effectiveness of alpha radiation causes biological damage. Alpha radiation is on average about 20 times more dangerous, and in experiments with alpha emitters being inhaled up to 1000 times more dangerous, than equivalent activity by emitting beta or radioisotope gamma emission.
Video Alpha particle
Name
Some science writers use a double ionized helium core ( He 2 ) and alpha particles as interchangeable terms. The nomenclature is not well defined, and thus not all high velocity helium nuclei are considered by all authors to be alpha particles. Like beta and gamma rays/particles, the name used for particles brings some mild connotations about its production and energy processes, but this is not strictly applied. Thus, alpha particles can be loosely used as a term when referring to the star's helium core reaction (eg the alpha process), and even when they appear as components of cosmic rays. A higher energy version of Alpha than produced in alpha decay is a common product of unusual nuclear fission called fission termari. However, the helium nuclei produced by particle accelerators (cyclotrons, synchrotrons, and the like) are less likely to be called "alpha particles".
Maps Alpha particle
Sources of alpha particles
Alpha Decay
The most famous source of alpha particles is the heavier alpha decay of atoms (& gt; 106 u atomic weight). When an atom emits alpha particles in alpha decay, the number of atomic masses decreases by four because of the loss of four nucleons in the alpha particle. The atomic number of atoms decreases twice as a result of the loss of two protons - atoms into new elements. An example of such nuclear transmutation is when uranium becomes thorium, or radium into a radon gas, due to alpha decay.
Alpha particles are generally emitted by all larger radioactive nuclei such as uranium, thorium, aktinium, and radium, as well as transuranic elements. Unlike other types of decay, alpha decay as a process must have a minimum size atomic nucleus that can support it. The smallest core to date has been found to produce alpha emission is the lightest nuclide of tellurium (element 52), with a mass amount between 106 and 110 (with the exception of beryllium-8). The alpha decay process sometimes leaves the nucleus in an excited state, where gamma ray emission then eliminates excess energy.
Production mechanism in alfa decay
Unlike the beta decay, the fundamental interaction responsible for alpha decay is the balance between the electromagnetic force and the nuclear force. The alpha decay results from Coulomb repulsions between alpha particles and the rest of the nucleus, both of which have a positive electrical charge, but which are constantly checked by nuclear forces. In classical physics, the alpha particle does not have enough energy to escape from the strong potential of power within the nucleus (it also involves the release of strong forces to rise to one side of the well, followed by an electromagnetic force causing push-off rejection on the other ).
However, the effects of quantum tunnels allow Alpha to escape even though they do not have enough energy to overcome the nuclear force. This is made possible by the nature of the material waves, allowing alpha particles to spend part of their time in an area so far away from the nucleus that the potential of disgusting electromagnetic forces has completely offset the appeal of the nuclear force. From this point on, alpha particles can escape, and in quantum mechanics, after a certain time, they do so.
Ternary fission
Energetic alpha particles primarily derived from nuclear processes are produced in a relatively rare nuclear fission nuclear process (one in several hundred). In this process, three charged particles are generated from events, not two normal, with the smallest possible particles being charged (90% probability) into alpha particles. These alpha particles are called "long-range alphas" because in their typical energy of 16 MeV, they are at a much higher energy than those produced by alpha decay. Binary fission occurs in both neutron-induced fission (nuclear reactions occurring in a nuclear reactor), and also when the fission and fissile actinide nuclides (ie, fissionally weighty atoms) undergo spontaneous fission as a form of radioactive decay. In both induced and spontaneous fission, the higher energy available in the heavy nucleus produces a higher energy alpha higher than that derived from alpha decay.
Accelerator
The energetic helium nuclei can be produced by cyclotrons, synchrotrons, and other particle accelerators, but they are not usually referred to as "alpha particles."
Sun core reaction
As noted, helium nuclei can participate in nuclear reactions in stars, and sometimes and historically these have been referred to as alpha reactions (see eg alpha three processes).
Cosmic rays
In addition, the very high energy helium nuclei sometimes referred to as alpha particles form about 10 to 12% of cosmic rays. The cosmic ray production mechanism continues to be debated.
Energy and absorbency
The energy of the alpha emitted in the alpha decay is slightly dependent on the half-life for the emission process, with many large-order differences in the half-life associated with less than 50% energy change (see alpha decay).
The emitted energy of emitted alpha particles varies, with higher alpha particle energy emitted from larger nuclei, but most alpha particles have energy between 3 and 7 MeV (mega-electron-volt), corresponding to very long half-lives and very short of alpha-emitting nuclides, respectively.
This energy is a large amount of energy for one particle, but its high mass means that the alpha particle has a lower velocity (with a typical 5 MeV kinetic energy, its speed is 15,000 km/s, which is 5% of the speed). light) of other common types of radiation (particlesparticles, neutrons, etc.) Due to the massive charge and mass, the alpha particles are easily absorbed by the material, and they can travel only a few centimeters in the air. They can be absorbed by tissue paper or the outer layer of human skin (about 40 micrometers, equivalent to some deep cells).
Biological effects
Because of the short range of absorption and inability to penetrate the outer layer of the skin, alpha particles are not, in general, harmful to life unless the source is digested or inhaled. Because of this high mass and strong absorption, if alpha-emitting radionuclides do enter the body (after being inhaled, swallowed, or injected, as with the use of Thorotrast for high-quality X-ray images before the 1950s), alpha radiation is a form of ionizing radiation the most damaging. It is the most powerful ionizer, and in large doses can cause any or all of the symptoms of radiation poisoning. It is estimated that the chromosomal damage of alpha particles is between 10 and 1000 times greater than that caused by equivalent amounts of gamma or beta radiation, with an average set at 20 times. A study of European nuclear workers exposed internally to alpha radiation from plutonium and uranium found that when relative biological effectiveness is considered 20, the carcinogenic potential (in lung cancer) alpha radiation appears to be consistent with those reported for external gamma radiation dose ie dose alpha-particles inhaled provide the same risk with gamma radiation doses 20 times higher. Strong Alpha emitter polonium-210 (milligram 210 Po emits 2 alpha particles per second as 4,215 grams 226 Ra) allegedly plays a role in the lungs. cancer and bladder cancer associated with smoking tobacco. 210 Po was used to kill Russian dissidents and former FSB official Alexander V. Litvinenko in 2006.
History of discovery and usage
In 1899 and 1900, physicist Ernest Rutherford (working at McGill University in Montreal, Canada) and Paul Villard (working in Paris) separated radiation into three types: ultimately named alpha, beta, and gamma by Rutherford, based on object penetration and deflection by magnetic field. The alpha rays are defined by Rutherford as those that have the lowest penetration of ordinary objects.
Rutherford's work also includes measuring the ratio of the mass of alpha particles to their charge, leading to the hypothesis that alpha particles are given a double charge of helium ions (later shown as bare helium nuclei). In 1907, Ernest Rutherford and Thomas Royds eventually proved that alpha particles are indeed helium ions. To do this they allow the alpha particle to penetrate the very thin glass wall of the evacuated tube, thus capturing the large amount of helium ions hypothesized inside the tube. They then cause electrical sparks inside the tube, which provide the rain of electrons picked up by the ions to form neutral atoms from the gas. Subsequent studies of the resulting gas spectrum show that it is helium and that the alpha particle is indeed a hypothesized helium ion.
Since alpha particles occur naturally, but can have high enough energy to participate in nuclear reactions, the study of them led to a great deal of early knowledge about nuclear physics. Rutherford uses an alpha particle emitted by radium bromide to conclude that Plum J. J. Thomson's pumding model on atoms is essentially defective. In Rutherford's gold foil experiments performed by his students Hans Geiger and Ernest Marsden, a narrow alpha particle beam is formed, passing very thin (several hundred atoms thick) of gold foil. Alpha particles are detected by a zinc sulphide screen, which emits flashes of light on an alpha particle collision. Rutherford hypothesizes that, assuming the "plum pudding" model of the atom is true, the positively charged alpha particle will only be slightly deflected, if at all, by a predictable positive charge dispersed.
It was found that some alpha particles were deflected at a much larger angle than expected (at a suggestion by Rutherford to examine it) and some even bounced almost directly back. Although most alpha particles go straight as expected, Rutherford comments that some of the deflected particles are similar to firing a fifteen-inch shell on tissue paper just to reflect it, again assuming the "pudding plum" theory is correct. It was determined that the positive charge of the atom is concentrated in a small area at its center, making the positive charge dense enough to bend the positively charged alpha particle closer to what is then called the nucleus.
Prior to this invention, it is unknown that the alpha particle itself is an atomic nucleus, nor is there any known proton or neutron. After this discovery, J.J. Thomson's "plum pudding" model was abandoned, and Rutherford's experiments led to the Bohr model (named after Niels Bohr) and then the modern atom-mechanical wave model.
Rutherford went on to use alpha particles inadvertently generating what was then understood as nuclear transmutation directed from one element to another, in 1917. Transmutation of elements from one to another has been understood since 1901 as a result of natural radioactive decay, but when Rutherford projected alpha particles from alpha decay into the air, he found this produced a new type of radiation that proved to be a hydrogen nucleus (Rutherford named this proton). Further experiments show that the proton is derived from the air nitrogen component, and the reaction is summed up to nitrogen transmutation into oxygen in the reaction.
- 14 N? -> 17 O p,
This is the first nuclear reaction to be found.
For nearby images: According to Bragg's energy-loss curve it can be recognized that alpha particles are losing more energy at the end of the trail.
Anti-alpha particles
In 2011, members of the international STAR collaboration using the Relativistic Heavy Ion Collider at the National Laboratory of Brookhaven National Energy detected antimatter partners of the helium nucleus, also known as anti-alpha. The experiment uses gold ions that move at nearly the speed of light and crash head to produce antiparticles.
Apps
- Some smoke detectors contain a small amount of the americium-241 alpha emitter. The alpha particle ionizes the air in a small gap. Small currents passed through the ionised air. The smoke particles from the fire entering the air gap reduce the current flow, sound an alarm. Isotopes are very dangerous if inhaled or swallowed, but the danger is minimal if the source remains sealed. Many municipalities have established programs to collect and dispose of old smoke detectors, to keep them away from the general waste stream.
- Alpha decomposition can provide a safe resource for radioisotope thermoelectric generators used for spacecraft and artificial pacemakers. Alpha decay is more easily protected than other forms of radioactive decay. Plutonium-238, the source of alpha particles, requires only 2.5 mm of lead protectors to protect against unwanted radiation.
- Static removers usually use polonium-210, alpha transmitters, to ionize the air, allowing "static cling" to disappear faster.
- Researchers are now trying to use the damaging properties of radionuclides that emit alpha in the body by directing a small amount toward the tumor. Alpha damages the tumor and stops its growth, while their small penetration depth prevents radiation damage to surrounding healthy tissue. This type of cancer therapy is called an unsealed source radiotherapy.
Alpha radiation and DRAM error
In computer technology, dynamic random access memory (DRAM) "soft error" is associated with alpha particles in 1978 in Intel DRAM chips. This discovery led to strict control of radioactive elements in the packing of semiconductor materials, and this problem was largely considered to be solved.
See also
- Beta particles
- Cosmic rays
- Helion, helium-3 nucleus rather than helium-4
- List of alpha emitters
- Rutherford scattered
- Nuclear physics
- Particle physics
- Radioactive isotope
- Rays:
- ? (beta) rays
- ? Gamma rays
- ? Sinar Delta
- ? Epsilon Radiation
References
Further reading
-
Tipler, Paul; Llewellyn, Ralph (2002). Modern Physics (4th ed.). W. H. Freeman. ISBN 0-7167-4345-0.
External links
Source of the article : Wikipedia
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