Today I want to introduce you to the wonderfully unstable element of 37 protons: Rubidium. This element is extremely rare to find in the universe and in our planet. Its creation is prohibitevly difficult. They can only be forged in the fires of huge explosions. And I mean huge as a Supernova explosion or even the Big Bang explosion kind of huge.
First of all, what do physicists mean by unstable? Imagine the situation of a different kind of equilibrium. Imagine a coin on a table, just chilling flat. You know that, if undisturbed, the coin will remain in this position forever. This is what real stability means. If you pull up the coin a little bit from one side, you would be creating unstability, for you are positive that the coin will eventually fall again to its stable position if you let it go.
The Rubidium we find in our planet may be unstable, but it is so close to stability that it would just take one step to transform it into a much more stable element: Strontium. The only thing it needs to do is to change one proton by one neutron, and all that it takes to do that is to shoot away a positron. One shot and the atom will gain eternal stability.
That shot will eventually happen. In the same way the coin would eventually fall flat on the table. The only question is when. The shooting of a positron is a random process. We are positive that it will eventually happen, but we can not conclude how much time it will take. The average time that has been computed for a Rubidium to decay into Strontium is around 70 billion years. You may not realize that at first, but this is really a lot of time. 70 billion years is much more than the age of the universe. That means that if you were looking at a Rubidium atom from its creation in the Big Bang until know, you wouldn’t expect it to pop out a positron yet. In reality, though we see this process occurring in some rocks of our planet, and we even use it to measure the age of some ancient minerals.
At this point you might wonder How is that such an improbable event can be spotted rutinely? Because within this rocks I am talking about, you can find up to septillions of Rubidium atoms. And even though the desintegration of one of them is almost impossible, you should know that improbable things happen a lot, if you have enough observations.
Rubidium does not enjoy the kind of mass media attention other elements do. Partly because we don’t make such a great use out of it. And that is not because of a lack of interesting properties, but because some other more common and cheaper elements share the same electronical configuration, such as Potassium. The chemical behaviour of the Rubidium and Potassium is so similar that your body sometimes missplaces Rubidium atoms as if they were Potassium, if you eat some of them accidentally. In fact, you already have plenty of Rubidium flowing through your veins, travelling from one cell to another, interacting with organelles and - of course - firing positrons around like a wild rich texan. All of that being mistaken by Potassium. You have been doing all that your entire life and you didn’t even notice. And thank God you do.
The human body is an extremely complex machine that is able to repair itself in a great variety of situations outstandingly well. Despite that, sometimes it engages in weird patterns. One specially rare behaviour is when some cells start an abnormal growth at breakneck speed. They stop doing their usual job and just spend all their time replicating themselves into more cells that will commit the same reckless behaviour. This is what we casually name cancer.
Among other particularities, one curious characteristic of cancer cells is that they tend to absorb a lot of potassium, in order to fuel their jumbo growth. And as we have seen, wherever Potassium goes, some Rubidium is going too. Hence, cancer cells happen to be filled with Rubidium atoms that are crazy-shooting positrons in all directions. In hospitals, there are machines that perform what is called a Positron Emission Tomography. The purpose of this machine is to detect positrons and trace back their direction and origin; thus drawing an accurate map of the location and size of tumors and other cancer cells.
Picture this in your head for a moment: There is an atom of Rubidium that was created billions of years ago in an unstable form, in the core of a Supernova, that has travelled undescribable distances to land in our planet Earth, to get accidentally within your body and being misplaced by Potassium and smuggled inside some random cancer cell just to pop a positron for its first time ever, ceasing to be a Rubidium but becoming Strontium, just in time you are getting a Tomography and thus ratting out and locating your cancell cells.
Isn’t that wonderful?
Written on 19 Apr 2018 by Alejandro Jiménez Rico