Thursday, September 26, 2013

Background radiation, muons and us!

A cell's DNA takes a direct muon hit!
Radiation coming from both the sky and the earth, in all its forms, is a fact of life here on earth. Most of it is very beneficial; we wouldn't be here were it not for the light and heat coming from the sun. some of it, however, can be harmful. Ever since humans (and all life forms for that matter) first evolved, we've been bombarded by radiation, of one type or another, both from outer space and from radioactive materials in the Earth itself. We've all seen this solar electromagnetic spectrum chart (see below), that depicts the wide range of energy that can affect us daily. Most of the energy, including the visible spectrum and everything to the left are innocuous at normal levels.

This is not the case for energy of higher frequencies found on the left side of the visible spectrum. Because they vibrate so much faster, they can ionize any organic matter that they strike. Most people know that too much exposure to UV-B waves can cause sunburns that, over a long period of time, can result in some for of cancer for an unlucky few. We are even more susceptible to X-Rays and Gamma rays, but thankfully, our thick atmosphere filters most of these out before they can reach the surface!

Were all that not enough, there are also the very harmful Cosmic particles that come to our planet either from deep space or, more infrequently, from mass corneal ejections of the sun. The majority (80%) of these particles are single protons which are simply hydrogen atoms that have been stripped of their electrons (although heavier nuclei like iron can come blasting in). They are created when a star somewhere in this or another galaxy goes nova and so ejects material at great velocities. And, since these particles have mass and are traveling at close to the speed of light, they can really pack a wallop if they hit a living cell! (Thankfully, the magnetic field around the earth helps to shield us from much of this nastiness). Of the cosmic rays that do hit the atmosphere, most smash into air molecules (most often nitrogen) and cause a billiard ball effect or 'air showers' of secondary particles (see below).

The little blue spheres are the muons!

Once again and thanks to the thickness of our atmosphere (35 miles), most of the cosmic rays never make it to the ground as their energies are absorbed by the constant collisions with other air molecules. How many do make it? On a surface of about the size of a hand, approximately one secondary particle hits every second. And of these, most are little nasties called muons which I like to think of as fat electrons. While extremely light (just 200 x's more heavy than an electron), muons can do a real number on a humans DNA over time and constitute about a third of the ionizing radiation our bodies have to deal with. [Note: The closer you live to sea level, the better. People living in mountainous areas like Denver Colorado receive over 300% more of these bad guys that those of us living lower down, like say Chicago...Sure hope the view there is worth it]!

The good news, in all this, is that we've been living with radiation ever since life evolved and have long ago developed repair mechanisms that mediate most all of the damage. Radiation dosages are often measured in Sieverts with a dose of one Sievert per year responsible for about a 5.5% increase in the rate of cancer. Here, where I live in Forsyth Missouri, the background levels of radiation are actually quite low – about .11 uSv/h (micro Sieverts per hour). That's a tenth of a thousandths of a Sievert per hour, or put another way it would take a level of 114.1 ╬╝Sv/h every day for a whole year to equal a dose of just 1 Sievert! Now that's a background level of radiation I can live with!

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