01/17/2007
Newsworthy Isotopes
Two isotopes have been in the news recently, in totally different contexts. For those who are not comfortable with isotopes, here’s a quick review, taking hydrogen as the simplest example. Ordinary hydrogen consists of a nucleus of one positively charged proton and one electron orbiting around the nucleus. We can call this H-1. Another form of hydrogen, deuterium, has a proton plus a neutron (uncharged) in its nucleus. We can call this H-2 (totaling the number of protons and neutrons). Tritium is a third isotope of hydrogen with 2 neutrons and one proton in its nucleus. We can call this H-3. There’s another term, the “atomic number”, which is the number of protons in the nucleus (which equals the number of electrons in orbit – have to balance the charges). The atomic number of hydrogen is 1.
When I was in school, there were 92 elements in the periodic table and our solar system had nine planets. Now there are at least 117 elements and only 8 planets – go figure. Surely you’ve heard the big news about hassium-270, with an atomic number of 108? No? Well, I’m ashamed to admit that I haven’t kept up with my elements and hadn’t heard of hassium until I saw mention of it in an article by Mitch Jacoby in the December 21 Chemical and Engineering News (C&EN). Hassium, named after the Latin word for the German state of Hessen, has only been around since 1984, when a team in Germany slammed iron ions into a lead target in an accelerator and made hassium-265. Don’t go looking for any hassium-265; it doesn’t hang around very long with a half-life of only a couple thousandths of a second!
Theoreticians had predicted that hassium-270 would have what they call a “doubly magic” number of neutrons and protons and should last a lot longer. I won’t try to explain “doubly magic”; I’m not even comfortable with just plain “magic” numbers! Well, Jan Dvorak and 23 coworkers in Germany announced in the December 15 issue of Physical Review Letters that they had succeeded in making all of four atoms of hassium-270. Would you believe that after, these researchers went to all the trouble of making these four atoms, two of them were probably gone in about 22 seconds, the half-life of the unstable hassium-270. Of the 2 atoms that were left, one of those should have decayed after another 22 seconds – that’s what the half-life means. I admit that with only four atoms, statistics don’t mean much. However, I guess the theoreticians were happy – hassium-270 does last about 10 thousand times longer than hassium-265.
OK, I imagine that you probably couldn’t care less about hassium and, frankly, I don’t either. However, I do think it’s amazing that these nuclear guys and gals can make these exotic elements and, with only a handful of atoms or less, separate them chemically from the other debris of the nuclear reactions, measure a half-life and sometimes do a bit of chemistry on them before the atoms decay into some other element or elements.
The other isotope in the news is one I’m virtually certain you’ve heard about unless you’ve been on a desert island the past month or so. Polonium-210 is the poison used to kill former Soviet spy Alexander Litvinenko and now is being found in the bodies of others who came in contact with Litvinenko as well as on various items and in various venues and aircraft associated with those individuals. Unlike hassium, polonium is not a newcomer to the periodic table of elements. Polonium dates back to 1898, when Marie Curie and her husband Pierre were working with pitchblende, a uranium ore. Marie found that something other than uranium was radioactive in the ore. The new element was polonium, which was named after Poland, Marie’s beloved native country. She was Marya Sklodowska before becoming Marie Curie.
Polonium-210 has a half-life of 138 days and is a product of the decay of radium, later discovered by the Curies in pitchblende. With a half-life of 1620 years, radium became the focus of their work and they never isolated pure polonium. It’s probably fortunate that the Curies found the radium and didn’t concentrate on polonium or they might have died even sooner than they did. A half-century or so after its discovery, polonium-210 was used as a trigger in early atomic bombs.
Today, aside from its use to poison ex-spies, it’s used as a heat source in spacecraft and, surprising to me, in antistatic applications and film cleaners. I went online and found I could buy an antistatic brush containing polonium-210! Russia is the prime supplier of polonium-210 and sells over 3 ounces a year to the U.S., according to an article by William Broad in the December 3 New York Times. Broad points out that six of these brushes contain enough polonium-210 for a lethal dose – if you have the chemical experience to know how to retrieve the element from the brush. And the six brushes would only cost around $200.
In an article in the December 15 C&EN, Ivan Amato discusses why polonium-210 is such a deadly poison; it only took 22 days to kill Litvinenko after his exposure. One conjecture is that it could have been slipped into his tea. Polonium dissolves readily in acids and in solution in a sealed vial or container it can be transported safely. It wouldn’t be hard to surreptitiously slip some polonium salt solution into a cup or pot of tea. However, it’s clear from the findings of polonium-210 all over the place after Litvinenko’s poisoning that it’s not easy to contain the isotope once the polonium has been turned loose, so to speak.
Why is it safe to transport this highly toxic radioactive element in a vial or other closed container? Polonium-210 decays by emitting high-energy alpha particles (an alpha particles is the nucleus of a helium atom with 2 protons and 2 neutrons). A sheet of paper can stop these alpha particles. One might think that if a sheet of paper can stop the alpha particles they shouldn’t be particularly worrisome. However, put polonium-210 in your body and those alpha particles are deadly. The polonium atoms hook up with proteins and spread to every corner of your body. Even a mere millionth of a gram of polonium contains 3 quadrillion (3 followed by 15 zeroes) atoms. Each alpha particle can travel through several cells and as it does it splits chemical bonds, ionizes atoms, destroys proteins and tears apart DNA. In the bone marrow, the alpha particles kill stem cells needed for the replacement of red blood cells and important immune cells, a worst-case scenario that may have caused Litvinenko’s rapid demise.
As a graduate student at the University of Pittsburgh in the late 1940s, I worked with an isotope of sulfur that emitted radiation that could be stopped by a sheet of paper. In retrospect, I should have been much more careful in my handling of the material. However, those were the days when the dangers of radiation were not fully appreciated. I’ve mentioned before that a fellow who was then connected with the cyclotron at Pitt would put coins in the machine, take them out in his hands and show visitors how they would “light up” a Geiger counter! I understand he died early of cancer. Fortunately, in my case, the radioactive sulfur emitted low-energy electrons, not high-energy alpha particles. And I’ve just passed my 79th birthday.
Allen F. Bortrum
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