` :::1. Your source is a book written by a dance teacher and a microbiologist; my source is an article written by a nuclear safety expert. With all respect to the book's authors, it is not a reliable source in nuclear issues. :::2. Buying hundreds of Po-containing devices cannot be a big problem for a potential nuclear terrorist in any case. In other article by Acton, Rogers, and Zimmerman, they write: ``A Briton, Dhiren Barot, was sentenced to life imprisonment in 2006 for planning to build a dirty bomb out of some 10,000 smoke detectors, each of which contains a small radioactive source, for use in London.`` 10,000 is two orders of magnitude more then hundreds.  :::3. Actually, no need to buy small devices. Zimmerman says about 16 Ci of Po-210 (that's 200 times more than 3 GBq) one may get without a strict state control. There are air ionizers with sources of as much as 7.4 GBq on the market (2.5 times the dose Litvinenko was killed by). They can be bought by anybody under ``modest restraints`` (see http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1717/nureg-1717.pdf , page 4-5; there are estimations on the page 4-7 that ~10000 of 7.4GBq air ionizers are produced and distributed annually in the US market).  :::4. The quoted articles by Zimmerman et al. clearly say about danger of illicit use of Po-containing devices by a group of nuclear terrorists. Just due to this Zimmerman propose to restrict the availability of such devices.  :::5.Other theories suggest that the polonium that killed Litvinenko might have been obtained from an officially tracked commercial supply after it reached its final customer. Polonium is commonly used in static eliminators in printing plants, photography labs and textile mills. In these applications, it is bound in extremely small quantities with other metals. Extracting the substance from the molds in which these mixtures are made would be difficult because ``polonium science is quite complicated,`` Priest said. But with qualified scientists and the right lab conditions, it is possible. ``I can see how they could be used to brew up a dose to kill one person,`` said Peter D. Zimmerman, a nuclear physicist and professor of science and security at King's College London. ``It would require very delicate lab work.``()  :::6. So, I provided you the recent secondary sources by experts which claim that the amount of polonium Litvinenko was poisoned by could be received from non-state-controlled supply. These opinions should be reflected in the article.   `