Alpha decay



Nuclear physics
Nuclear fusion
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  Alpha decay is a type of atomic number 2 less. For example:

{}^2{}^{38}_{92}\hbox{U}\;\to\;{}^2{}^{34}_{90}\hbox{Th}\;+\;{}^4_2\hbox{He}^{2+},[1]

although this is typically written as:

{}^{238}\hbox{U}\;\to\;^{234}\hbox{Th}\;+\;\alpha.

(The second form is preferred because the first form appears electrically unbalanced. Fundamentally, the recoiling nucleus is very quickly stripped of two electrons to neutralize the ionized helium cation.)

An helium-4 nucleus, and both mass number and atomic number are the same. Alpha decay is a form of beta decay, alpha decay is governed by the strong nuclear force.

Alpha particles have a typical kinetic energy of 5 MeV (that is ≈0.13% of their total energy, i.e. 110 TJ/kg) and a speed of 15,000 km/s. This corresponds to a speed of around 0.05c. Because of their relatively large mass, +2 charge and relatively low velocity, they are very likely to interact with other atoms and lose their energy, so they are effectively absorbed within a few centimeters of air.  

Most of the helium is brought to the surface as a by-product of natural gas production.

History

By 1928, George Gamow had solved the theory of the alpha decay via tunneling. The alpha particle is trapped in a potential well by the nucleus. Classically, it is forbidden to escape, but according to the then newly discovered principles of Quantum mechanics, it has a tiny (but non-zero) probability of "tunneling" through the barrier and appearing on the other side to escape the nucleus.

Uses

ionize air between a small gap, leading to a small current that can be easily interrupted by smoke particles.

Alpha decay can provide a safe power source for radioisotope thermoelectric generators used for space probes and lead shielding to protect against unwanted radiation.

Toxicity

Being relatively heavy and positively charged, alpha particles tend to have a very short dose.

The largest natural contributor to public radiation dose is gamma rays.

The 2006 assassination of Russian dissident Alexander Litvinenko is thought to have been caused by poisoning with Polonium-210, an alpha emitter.

References

  1. ^ Suchocki, John. Conceptual Chemistry, 2007. Page 119.
  2. ^ http://www.ans.org/pi/resources/dosechart/
  3. ^ EPA Radiation Information: Radon. October 6 2006, [1], Accessed Dec. 6 2006
  4. ^ Health Physics Society, "Did Marie Curie die of a radiation overexposure?" [2]
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This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Alpha_decay". A list of authors is available in Wikipedia.