Polonium-210, Part I.

It's bigger news in the UK than elsewhere but it's still big news. Apparently Russian dissident and former KGB agent Alexander Litvinenko was fatally poisoned with Polonium 210. Time for some science.

Polonium 210 is a radioisotope, meaning it is an isotope of the element Polonium that is radioactive. Three things here: element, isotope and radioactive.

Things in our world are made of chemicals and the chemicals are made of elementary building blocks, called, naturally enough, elements. Last time I checked there were 117 different flavors, ninety four of which occur naturally and the rest can be produced artificially. The physical embodiment of an element is the atom, which means something that can't be subdivided further, i.e., a basic building block. Of course we know now that there are sub-atomic particles that make up the atom, but the type of element still identifies how the atom behaves chemically, so this remains a useful category. An element is an elementary chemical form whose combinations make up other chemicals ("chemical compounds"). You probably knew all this, but I want to make sure we are on the same page before going on.

If we look "inside" an atom we see the oldest recognized subatomic particles. For the quantum mechanics out there, gird yourself. This is going to be painful. Shut your eyes. The easiest way to imagine the atom is the old solar system model of Rutherford. There is a sun that has two kinds of subatomic particles in it, called neutrons and protons (yes, I know Hydrogen only has a proton; so sue me). Whirling around the nucleus are a third particle, the electron. There are exactly the same number of electrons as protons in an intact atom. The number of neutrons varies, although it is roughly the same as the number of protons. Neutrons have no electric charge (they are neutral, get it?) while protons have a positive charge and electrons a negative one. Protons are a few thousand times more massive than electrons. You can think of a neutron as made up of a proton and an electron whose charges cancel each other out (disregard the screams of pain from the physicists reading this).

Protons and neutrons are so much heavier than electrons that almost all the weight of the atom is in the nucleus. The total number of protons and neutrons, therefore, is called the Atomic Weight. On the other hand, the chemical behavior of the atom rests with the orbiting electrons. Since there are the same number of electrons as protons, the number of protons also signals the chemical behavior of the atom and is called the Atomic Number. The elements have different chemical behaviors, true, but they also have certain broad similarities and can be grouped into clusters. We can make a big table of the groups called the Periodic Table of the Elements, where chemically similar elements are grouped together in a systematic way. Since an atom can have different numbers of neutrons for the same number of protons. Carbon, for example, has 6 protons and therefore 6 electrons, but can have 6, 7 or 8 neutrons. It has Atomic Number 6 but exists with three different Atomic Weights (6 + 6 = 12, 6 + 7 = 13 and 6 + 8 = 14. We designate these isotopes as carbon-12, carbon-13 and carbon-14.). Since it's the electrons (and therefore protons) that determine the chemistry, all three of these atoms are found in the "same place" in the Periodic Table. Greek for "same place" is isotope (iso is Greek for "the same" and topos, Greek for "place," as in topography). These atoms may reside in the same place of the Table and behave similarly chemically, but they can also be very different in another respect. Some atoms, it turns out, are stable and others are unstable. Sometimes one isotope of an element is stable and another isotope of the same element unstable. We call the unstable ones "radioactive."

What does "unstable" mean in this context? The instability resides in the nucleus and can have several sources. For example, atomic nuclei like to have a balance of neutrons and protons. Carbon-14 has 6 protons and 8 neutrons. If one of the neutrons decides to decompose into its constituent proton and electron combo and then spit out the electron, we'll have 7 protons and 7 neutrons. Of course 7 protons is no longer carbon, it's nitrogen. So carbon-14 has "decayed" into nitrogen 14 by spitting out an electron from its nucleus. We don't think of electrons as being in the nucleus, of course. In this case they were hidden in combination with a proton in a neutron (to the physicists: this is the last time I'm going to tell you, stop screaming!).

So here's the picture. Carbon-14 wanted to get more comfortable ("balanced") and transformed itself into the more stable nitrogen-14 by barfing up an electron. Just to make things more complicated, we'll change the name of the barfed up electron and call it a beta particle. An electron by any other name, etc., etc. (apologies to Shakespeare).

There are other ways that unstable atoms more toward more stability than barfing up beta particles (aka, electrons of nuclear origin). One of them is by releasing some internal energy in the form of electromagnetic radiation (EM). Someday we'll write more about EM, here, but not now. Just know that there are different forms of EM, like light, radiowaves, x-rays and something called gamma rays. They are all the same thing physically, but of different frequencies, like two radiostations transmit at different frequencies or light is of different frequencies ("colors"). Polonium-210 (the isotope of Polonium with Atomic Weight of 210; since the Atomic Number of Polonium is 84, meaning it has 84 protons and 84 electrons orbiting around its nucleus, we know that it must have 210 - 84 = 126 neutrons) is unstable and emits very weak gamma rays. We're not that worried about them, however. It's the other particle that Po-210 (the chemical symbol for Polonium) emits that is lethal. A very energetic alpha particle.

Alpha emission is a third way nuclei have of relieving internal stress. One is ejecting a beta particle. Another is emitting some internal energy via EM radiation (gamma emission). A third, like beta emission, actually ejects nuclear contents, a combination of two neutrons and two protons, the alpha particle. Since a proton is 1850 times as heavy as an electron, an alpha particle is 7400 times as heavy as a beta particle. It is a cannonball versus a bee-bee.

Po-210 is an alpha-emitter as well as a weak gamma emitter. This will turn out to have great biological significance, which we will turn to in tomorrow's post.

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I'm sorry, but I just can't help myself. I am a deeply troubled amateur physicist who was away from the world for the weekend. I was unaware that Litvinenko had died. Until I read your article he was in a superposition of quantum states, alive and dead, until some person unwittingly made the observation that he was dead. Then he wasn't really dead, for me at least until someone reported his death to the press, and you picked up the news and wrote this article, which I read. This of course makes him very dead for me, now.

But, it really wasn't the plutonium-210 that killed him, or the possible decay into a alpha particle. It was that someone made the observation that he was dead and collapsed his wave function. But, from another point of view, for those who haven't read of his death, he is equally alive and dead. And even now, he may still be alive in another, parallel universe.

Actually, you might help save him yet. You could change the title of this article to 'Help save a life - Don't read this article'.

Just kiddin' whicha! Have a great holiday season.


By Snicklefritz (not verified) on 27 Nov 2006 #permalink

Snick: I didn't see his wave function collapse, but i'm not that observant. I was just repeating the interpretation from reporters in Copenhagen. But there might be a hidden variable, right? Sorry. I know, it's Bohring. Maybe I'll do an agnostic piece for Sunday Sermonette.

I hope you add a bit about alpha radiation, skin barriers, and Coleman lantern mantles, and keeping precious bits of expensive fluff from flying off micro weighing scales. A mentor at UC-LANL (Los Alamos National Lab) always explained plutonium couldn't penetrate a cigarette pack cellophane (or skin) but it is what happens inside the skin barrier and amount that counts.

[13C/12C stable carbon isotopes do not date but nevertheless lead full lives. mpb]

mpb: Tomorrow I will handle some of that but not Coleman laterns, just Polonium since that's the news hook. You can put radium or polonium in your pocket perfectly safely.

mpb: Really? I thought they had trace amojnts of thorium.

Hmmm .. what about the purely chemical aspects of toxicity? Revere, or somebody, please correct me if my information is off. But as I understand it, radioactivity is only one component of the toxicity of Plutonium 239. It is also supposed to be an extremely potent chemical toxin in its own right, so much so that it could very easily be lethal even without the emission of ionizing radiation.

If the same is true of Polonium, then its use as a weapon of assassination could be a case of "multiple strings for the bow". Or "multiple mechanisms of toxicity, however you want to put it.

By Charles Roten (not verified) on 27 Nov 2006 #permalink

Charles: I think it's toxicity is from radiation poisoning. It is lethal in microgram amounts, too little for chemical toxicity (chemically it is like bismuth).

"Bohring" - omg, painful - good one though =)

My understanding is that it is found near/beside/inside (???) Uranium and rare. So, I'm guessing is monitored by someone somewhere. Is there any indication about the origin?

Since Radon and Polonium are 1st degree relatives, are you up for an EH post about Radon in the home / What happened to Litvenko could be happening to you / EPA levels / etc..?

Darin: Probably won't do radon, although I published a paper about it once upon a time. Another alpha emitter, though (at least the daughters).

I read in another blog (lost the ref, sorry) that the amount of Pollonium required for the fatal dose was worth about $250K. If this is correct, or even somewhat so, why use such an expensive, and possibly traceable, poison, when there are other much cheaper and undetectable methods?

By david1947 (not verified) on 27 Nov 2006 #permalink

Oak Ridge sells Polonium for 32,000 per microcurie. This was a wicked way to die. Basically he was cooked from the inside out. Add a dash of beryllium and you have a neutron weapon; if you can get enough of it. What I really want to know is how did they get it to do the job?. Its murder plain and simple but it was a message killing too. You dissent and you are dead. They could have done a drive by, cut his throat, smashed his head in with a board. Typical murders in a metropolitan area, but Polonium. Did they think that they wouldnt notice?

By M. Randolph Kruger (not verified) on 28 Nov 2006 #permalink

I suspect that Litvinenko wasnt poisoned directly with Polonium-210. Po-210 is difficult to transport undetected. It emits relatively energetic gamma rays (803 keV) that can be picked up easily by airport security radiation detectors. To prevent detection, a sample would have to be transported in a lead cylinder about 10 cm in diameter. Besides weighing several kilos, the whole set up is awfully hard to get past x-ray machines.

My guess: Lead-210. Lead-210 is a naturally occurring (Uranium Series) weak B- emitter with low energy gamma radiation (47 keV) that does not require thick lead shielding. I don't know much about polonium compounds but Po-210 is only soluble in acid. Lead compounds such as lead nitrate and the pleasantly sweet-tasting lead acetate are both quite soluble in water making it easy to slip into food or drink. In order to get enough activity to kill a person, lets say around 0.3 Ci, you would need about 13 mg of Lead-210, which would cause mild lead poisoning symptoms (lowest recorded dose of acute lead poisoning: 1.47mg/kg).

Pb-210 has t1/2 = 22.3 years. As it decays to Bi-210 (t1/2 = 5 days) and then Po-210 it would take about 10 days for any appreciable alpha radiation to show up and about 60 days to reach an activity of 0.3 Ci making Pb-210 an excellent poison because after two months whos going to be able to trace you? Was Litvinenko ever tested for lead poisoning? Also, Pb-210 is expensive but only about $1000/uCi.

What do you think?

esl: Interestingly, accounts often describe Po-210 as a pure alpha emitter or at best a weak gamma emitter. I looked at the gamma spectrum yesterday and indeed the gammas seem relatively energetic, although I wasn't aware it needed a lot of shielding, which you suggest. This clearly has a bearing on detectability. Do you have some internet cites/links as to radiation protection and measurement protocols for Po-210?

FYI, lantern mantles used to contain thorium, which is predominantly a beta emitter. They no longer contain thorium or other radioisotopes. This I know from having written a paper in the early 1980s on the potential for high-tech terrorism, that included a detailed section on "radiological dispersal weapons" (presently known as "dirty bombs").

As a genreralization, the presence of radioisotopes in commonly-available materials has been cleaned up significantly over the past 30 years. This may have been due to general public health concerns, but has also had the effect of removing from circulatiaon a number of things that might otherwise have made radiological terrorism painfully easy to accomplish.

g2: Thanks. Then there is the famous orange Fiesta plates (no longer available, alas, for those of us who want a keepsake) that could keep your food hot without having to put it in the oven. There are still alpha emitters around in abundance, though. Americium-241 is an example, in ionization smoke detectors.

Sorry, I dont know of any transportation and detection protocols on the net. Im just speculating on the basis of my nuclide chart which includes the gamma emission lines.

CRC says: A milligram [of 210Po] emits as many alpha particles as 5 g of radium. The energy released by its decay is so large (140 W/g) that a capsule containing about half a gram reaches a temperature above 500 deg C. The capsule also presents a contact gamma-ray dose rate of 0.012 Gy/h.

Shielding would be necessary to prevent detection. A 0.3Ci sample of Po-210 would emit 3.64 uCi of gamma radiation (Igamma = 0.00121%), which is within detection limits. It just seems that transporting and administering Po-210 would be difficult. 0.3 Ci is about 66.8 ug, such a tiny amount to keep track of. Pb-210 is much easier to deal with, both quantity-wise, and chemically. Working with Pb-210 is a pain if only because when you think you have worked extremely carefully and found your lab to be radiation free about a month later everything is hot due to Po-210 contamination. Sort of like the way Po-210 contamination is turning up all over now in London. Its just so much more radioactive than Pb-210.

esl: Nick Priest, a UK expert working on the case, said that Po-210 kept sealed in a glass vial would be hard to detect. This assumes, of course, that there is some heat dissipation mechanism since it doesn't take much to generate a lot of heat from the alpha emissions.

The traces of radiation found in various locales that are being talked about are not being identified. I am assuming it is a result of excretion by Litvinenko but I don't know. The airplane reports are a puzzle. What are they detecting, exactly? Anyone know?

Much the highest concentrations were apparently in the toilets of the hotel where L. met the suspects. Would it be possible to add the poison to a dose of cocaine?

smekhovo: No. He was excreting it. I'll have a post up later today.