Large quantities of mail were quarantined as soon as the anthrax attack was identified in September 2001.
This mail was sanitized with ionizing energy in the form of accelerated electron beams or X-rays. All mailings addressed to government offices in Washington, D.C. were sanitized with this method as a precautionary measure. This process is still ongoing.
Other methods of sanitizing the mail were considered and rejected by the USPS.
Sanitizing the Mail |
Ionization, the removal of atomic electrons from molecules, can be lethal to all forms of life when sufficient dose is absorbed. So the lethal effects are mainly due to ionization, not temperature rise.
The mail processed is ionized either by E-beam or by X-rays.
The thickness of material that can be treated from opposite sides with 10 MeV electrons, is equivalent to a bundle of about 90 envelopes, each one containing three sheets of paper folded into nine layers, or about 1,200 sheets of typical copy paper. Bundles of flat mail, such as magazines, brochures and reports, can be sanitized with energetic electron beams.
X-rays are emitted when energetic electrons strike any material – a water-cooled tantalum target in this case – and can therefore be produced by the same electron accelerator.
This second ionization method provides a more uniform dose throughout packages containing a variety of materials with different densities. Greater penetration is a major advantage of X-rays vs. electrons for treating mail
If all of the mail in the USA were to be processed in this way, similar facilities would be needed at about 350 collection and distribution centers.
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The Rhodotron® is a recirculating accelerator where electrons gain energy by crossing a coaxial-shaped accelerating cavity several times.
