Induced radioactivity
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2008-03-16T23:45:42Z
Velela
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sp as per [[WP:SULF]]
'''Induced radioactivity''' is when a previously stable material has been made [[radioactive]] by exposure to specific [[radiation]]. Most radioactivity does not induce other material to become radioactive.
[[Neutron activation]] is the main form of induced radioactivity, which happens when free [[neutron]]s are captured by nuclei. This new heavier isotope can be stable or unstable (radioactive) depending on the [[chemical element|element]] involved.
Due to the fact that free neutrons disintegrate within minutes outside of an atomic [[Atomic nucleus|nucleus]], [[neutron radiation]] can be obtained only from [[nuclear disintegration]]s, [[nuclear reaction]]s, and high-energy reactions (such as in [[cosmic radiation]] showers or accelerator collisions). Neutrons that have been slowed down through a [[neutron moderator]] ([[thermal neutron]]s) are more likely to be captured by nuclei than fast neutrons.
A less common form involves removing a neutron with the [[photoneutron effect]]. This is where a high energy photon ([[gamma ray]]) strikes a nucleus with an energy greater than the [[binding energy]] of the [[atom]], releasing a neutron. This starts at energies at 2 [[Electronvolt|MeV]] (for [[hydrogen]]) and most radionuclides do not produce gamma rays that powerful.
The [[isotope]]s used in [[food irradiation]] ([[Cobalt]]-60, [[Caesium]]-137) both have peaks below this. Caesium-137 at 662 keV and Cobalt-60's two peaks are 1.2 and 1.3 MeV.
Some induced radioactivity is produced by [[background radiation]], which is mostly natural. However, since natural radiation is not very intense in most places on [[Earth]], the amount of induced radioactivity in a single location is usually very small.
The conditions inside certain types of [[nuclear reactor]]s with high neutron flux can cause induced radioactivity. The components in those reactors may become highly radioactive from the radiation they are exposed to. Induced radioactivity increases the amount of [[nuclear waste]] that must eventually be disposed, but it is not referred to as [[radioactive contamination]] unless it is uncontrolled.
== See also ==
* [[Neutron activation]]
* [[Radioactive decay]]
* [[Radioactivity]]
* [[Slow neutron]]
== External links ==
* [http://www.physlink.com/Education/AskExperts/ae636.cfm PhysLink.com - Ask the Experts "Gamma ray food irradiation"]
[[Category:Radioactive waste]]
[[Category:Radioactivity]]
[[Category:Radiation effects]]