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Monday, October 24, 2011

Alpha, Beta, and Gamma Rays

Hey Everyone,

 know me posting up this type of materiel is crazy I know if you are a victim of electromagnet impulse you may have already readied this . But Alpha, Beta, and Gamma Rays is what I wanted to put up today. I hope you like it and find something inserting...

Thank You.....

In the years 1899 and 1900, physicists Ernest Rutherfordand Paul Villard separated radiation into three types: alpha, beta, and gamma, based on penetration of objects and ability to cause ionization.[7] Alpha rays were defined by Rutherford as those having the lowest penetration of ordinary objects.
Rutherford's work also included measurements of the ratio of an alpha particle's mass to its charge, which led him to the hypothesis that alpha particles were doubly charged helium ions (later shown to be bare helium nuclei).[8] In 1907, Ernest Rutherford and Thomas Royds finally proved that alpha particles were indeed helium ions.[9] To do this they allowed alpha particles to penetrate a very thin glass wall of an evacuated tube, thus capturing a large number of the hypothesized helium ions inside the tube. They then caused an electric spark inside the tube, which provided a shower of electrons that were taken up by the ions to form neutral atoms of a gas. Subsequent study of the spectra of the resulting gas showed that it was helium and that the alpha particles were indeed the hypothesized helium ions.

It was found that some of the alpha particles were deflected at much larger angles than expected (at a suggestion by Rutherford to check it) and some even bounced almost directly back. Although most of the alpha particles went straight through as expected, Rutherford commented that the few particles that were deflected was akin to shooting a fifteen-inch shell at tissue paper only to have it bounce off, again assuming the "plum pudding" theory was correct. It was determined that the atom's positive charge was concentrated in a small area in its center, making the positive charge dense enough to deflect any positively charged alpha particles that came close to what was later termed the nucleus.
Because alpha particles occur naturally, but can have energy high enough to participate in a nuclear reaction, study of them led to much early knowledge of nuclear physics. Rutherford used alpha particles emitted by radium bromide to infer that J. J. Thomson's Plum pudding model of the atom was fundamentally flawed. In Rutherford's gold foil experiment conducted by his students Hans Geiger and Ernest Marsden, a narrow beam of alpha particles was established, passing through very thin (a few hundred atoms thick) gold foil. The alpha particles were detected by a zinc sulfide screen, which emits a flash of light upon an alpha particle collision. Rutherford hypothesized that, assuming the "plum pudding" model of the atom was correct, the positively charged alpha particles would be only slightly deflected, if at all, by the dispersed positive charge predicted.

Rutherford went on to use alpha particles to accidentally produce what he later understood as a directed nuclear transmutation of one element to another, in 1917. Transmutation of elements from one to another had been understood since 1901 as a result of natural radioactive decay, but when Rutherford projected alpha particles from alpha decay into air, he discovered this produced a new type of radiation which proved to be hydrogen nuclei (Rutherford named these protons). Further experimentation showed the protons to be coming from the nitrogen component of air, and the reaction was deduced to be a transmutation of nitrogen into oxygen in the reaction
Note: Prior to this discovery, it was not known that alpha particles are themselves atomic nuclei, nor was the existence of protons or neutrons known. After this discovery J.J. Thomson's "plum pudding" model was abandoned, and Rutherford's experiment led to the Bohr model (named for Niels Bohr) and later the modern wave-mechanical model of the atom.

14N + α → 17O + proton 
This was the first-discovered nuclear reaction.

Alpha radiation consists of helium-4nucleus and is readily stopped by a sheet of paper. Beta radiation, consisting of electrons, is halted by an aluminium plate. Gamma radiation is eventually absorbed as it penetrates a dense material. Lead is good at absorbing gamma radiation, due to its density  

Alpha particles (named after and denoted by the first letter in the Greek alphabetα) consist of two protons and twoneutrons bound together into a particle identical to a heliumnucleus, which is classically produced in the process of alpha decay, but may be produced also in other ways and given the same name. The alpha particle can be written as He2+4
or 4
 (as it is possible that the ion gains electrons from the environment; also, electrons are not important in nuclear chemistry).
The nomenclature is not well defined, and thus not all high-velocity helium nuclei are considered by all authors as alpha particles. As with beta and gamma rays/particles, the name used for the particle carries some mild connotations about its production process and energy, but these are not rigorously applied.[3] Some science authors may use doubly ionized helium nuclei (He2+) and alpha particles as interchangeable terms. Thus, alpha particles may be loosely used as a term when referring to stellar helium nuclei reactions (for example the alpha processes), and even when they occur as components of cosmic rays. A higher energy version of alphas than produced in alpha decay is a common product of an uncommon nuclear fission result called ternary fission. However, helium nuclei produced by particle accelerators (cyclotronssynchrotrons, and the like) are less likely to be referred to as "alpha particles."
Alpha particles, like helium nuclei, have a net spin of zero and (due to the classical mechanism of their production in nuclear decay), have a classical total energy of about 5 MeV. They are a highly ionizing form of particle radiation, and (when resulting from radioactive alpha decay) have low penetration depth. They are able to be stopped by a few centimeters of air, or by the skin. Long range alpha particles from ternary fission penetrate three times as far. As noted, the helium nuclei that form 10-12% of cosmic rays are usually of much higher energy than those produced by all such nuclear processes, and are thus capable of being highly penetrating and able to traverse the human body and also many meters of dense solid shielding, depending on their energy. To a lesser extent, this is also true of high-energy helium nuclei produced by particle accelerators.
When alpha particle emitting isotopes are ingested, they are far more dangerous than their half-life or decay rate would suggest, due to the high relative biological effectiveness of alpha radiation to cause biological damage, after alpha-emitting radioisotopes enter living cells. Ingested alpha emitter radioisotopes (such as transuranics or actinides) are an average of about 20 times more dangerous, and in some experiments up to 1000 times more dangerous, than an equivalent activity of beta emitting or gamma emitting radioisotopes.

What are alpha rays? How are they produced?

Beta particle

Beta particles are high-energy, high-speed electrons orpositrons emitted by certain types of radioactive nuclei such as potassium-40. The beta particles emitted are a form ofionizing radiation also known as beta rays. The production of beta particles is termed beta decay. They are designated by the Greek letter beta (β). There are two forms of beta decay, β and β+, which respectively give rise to the electron and the positron.


Henri Becquerel, while experimenting with fluorescence, accidentally found out that uranium exposed a photographicplate, wrapped with black paper, with some unknown radiation that could not be turned off like X-raysErnest Rutherfordcontinued these experiments and discovered two different kinds of radiation:
  • alpha particles that did not show up on the Becquerel plates because they were easily absorbed by the black wrapping paper
  • beta particles which are 100 times more penetrating than alpha particles.
He published his results in 1899.[1]

Gamma ray

This article is about the term's use in physics. For other uses, see Gamma ray (disambiguation).

Gamma radiation, also known as gamma rays or hyphenated as gamma-rays (especially in astronomy, by analogy with X-rays) and denoted as γ, iselectromagnetic radiation of high frequency (very short wavelength). Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei (gamma decay). Important natural sources are also high-energy sub-atomic particle interactions resulting from cosmic rays. Such high-energy reactions are also the common artificial source of gamma rays. Other man-made mechanisms include electron-positron annihilationneutral pion decayfusion, and induced fission. Some rare natural sources are lightning strike and terrestrial gamma-ray flashes, which produce high energy particles from natural high-energy voltages. Gamma rays are also produced by astronomical processes in which very high-energy electrons are produced. Such electrons produce secondary gamma rays by the mechanisms ofbremsstrahlung, inverse Compton scattering and synchrotron radiation. Gamma rays are ionizing radiation and are thus biologically hazardous.

A classical gamma ray source, and the first to be discovered historically, is a type of radioactive decay called gamma decay. In this type of decay, an excited nucleus emits a gamma ray almost immediately on formation, although isomeric transition can produce inhibited gamma decay with a measurable and much longer half-life. Paul Villard, a French chemist and physicist, discovered gamma radiation in 1900, while studying radiation emitted from radium.[1][2] Villard's radiation was named "gamma rays" by Ernest Rutherford in 1903.[3]
Gamma rays typically have frequencies above 10 exahertz (or >1019 Hz), and therefore have energies above 100 keVand wavelength less than 10 picometers, less than the diameter of an atom. However, this is not a hard and fast definition but rather only a rule-of-thumb description for natural processes. Gamma rays from radioactive decaycommonly have energies of a few hundred keV, and almost always less than 10 MeV. On the other side of the decay energy range, there is effectively no lower limit to gamma energy derived from radioactive decay. By contrast, energies from astronomical sources can be much higher, ranging over 10 TeV (this is far too large to result from radioactive decay).[4]
The distinction between X-rays and gamma rays has changed in recent decades. Originally, the electromagnetic radiation emitted by X-ray tubes almost invariably had a longer wavelength than the radiation emitted by radioactive nuclei (gamma rays).[5] Older literature distinguished between X- and gamma radiation on the basis of wavelength, with radiation shorter than some arbitrary wavelength, such as 10−11 m, defined as gamma rays.[6] However, with artificial sources now able to duplicate any electromagnetic radiation that originates in the nucleus, as well as far higher energies, the wavelengths characteristic of radioactive gamma ray sources vs. other types, now completely overlaps. Thus, gamma rays are now usually distinguished by their origin: X-rays are emitted by definition by electrons outside the nucleus, while gamma rays are emitted by the nucleus.[5][7][8][9] Exceptions to this convention occur in astronomy, where high energy processes known to involve other than radioactive decay are still named as sources of gamma radiation. A notable example is extremely powerful bursts of high-energy radiation normally referred to as long duration gamma-ray bursts, which produce gamma rays by a mechanism not compatible with radioactive decay. These bursts of gamma rays, thought to be due to collapse of stars called hypernovas, are the most powerful single events so far discovered in the cosmos.

See also

1 comment:

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