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.