Final answer:
X-ray generators are used by USPS to irradiate suspicious mail, including periodicals, as a security measure against bioterrorism, which may leave markings or alter the mail's physical properties.
Step-by-step explanation:
The United States Postal Service (USPS) and the Federal Bureau of Investigation (FBI) implemented security measures to combat bioterrorism threats sent via the postal system. Sophisticated equipment, such as x-ray generators, are used to irradiate suspicious mail, which includes periodicals.
This process is designed to neutralize harmful biological agents like bacteria and some viruses.
Although irradiation can alter the physical properties of mail, such as color, texture, and smell, by changing the chemical composition of the paper, it does not make the mail radioactive. But it can result in markings or changes that indicate it has been processed for safety.
In response to changes in consumer preferences, the USPS has also seen a change in demand for traditional mail services, as more people shift towards digital communication methods. This shift impacts the supply and demand balance in the postal ecosystem.