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07 January 2009

Answer to Question #1927 Submitted to "Ask the Experts"

Category: Industrial Radiation — Industrial Exposures

The following question was answered by an expert in the appropriate field:

Do the structural materials of which a cyclotron are constructed retain any form of long-term (greater than 20 years) radiation after the cyclotron is dismantled? In particular, I am asking about the copper coils and other initially nonradioactive metals.

In general, most of the activity in accelerator components and surrounding material, such as shielding, is short lived. To predict specific amounts of particular nuclides one needs to know the exact material composition (including impurities), the energy of the primary beam, and the geometry of the beamline components and surrounding environment. Activation is generated by the primary beam and secondary neutrons. There will be a greater variety of activated species at higher energies where spallation is likely to occur. Among the many activation products encountered at accelerators, the following have half-lives longer than one year:

Isotope	T[a]	Where
²²Na	2.6	Al
²⁶Al	740,000	A1
⁵⁵Fe	2.6	Fe
⁶⁰Co	5.26	Ni, Cu, concrete
⁶³Ni	92	Cu
¹⁵²Eu	13.5	concrete
¹⁵⁴Eu	8.59	concrete
¹³⁴Cs	2.07	concrete

The second column indicates the half-life in years and the third in what material this nuclide is generated. If you would like to make estimates of produced activity for your particular facility, I would suggest several references: Barbier M. Induced radioactivity. New York: John Wiley & Sons; 1969. Silberberg R, Tsao CH. Astro. Phys. J. Suppl. 25: 315-333; 335-368; 1973. - two papers Accelerator Radiation Protection. Special issue of Radiation Protection Dosimetry, 96 (4) 2001 - several papers in this issue talk about and provide further references on activation (for example, papers by Moritz, Stevenson, Silari . . .).

Vashek Vylet, PhD
Duke University

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