This page is still under construction, using sources and lecture material developed in these slides: RadiationMadness.pdf


Let's play from free word association. I will say a word, and you say the first word that comes into your mind. Let's give it a try: No doubt, when you got to that last one, a negative word came out of your mouth. Perhaps something like "danger," or "bad," or "cancer." In popular culture, "radiation" is associated only with negative outcomes. Yet, few people understand radiation. Fewer still understand that there are different kinds - some can cause damage, others cannot. In this page, we'll explore the definition of radiation, different kinds of radiation, and finally explore some current topics connected to the pseudoscientific application of popular knowledge about radiation.

What is "radiation"

Very simply, radiation is the "transport of energy from one point to another without the need for physical contact between the points." Radiation is everywhere, and not just in the form you probably think of when someone says "radiation." Here are different kinds of radiation: Radiation can be classified in two groups:

Different Examples of Potentially Dangerous Radiation

Ionizing radiation comes in two different forms: Let's discuss these different kinds of ionizing radiation. We demonstrate all of the above in class.

How much is too much?

Ionizing radiation doses are measured in "Sieverts," denoted "Sv." A typical US citizen is exposed to about 6.2 milli-Sieverts each year - half from natural sources, and half from human sources (e.g. medical diagnostics, like x-rays). In order to die from exposure to ionizing radiation, a person must receive 1 Sv ALL AT ONCE - that is almost 200 times more than a person receives normally in one year.

The following chart is used by the US Nuclear Regulatory Commission (NRC) in their web page illustrating the typical ionizing radiation dose in the US, per person, per year. The chart uses units of exposure called "rems" - 100 milli-rem is equivalent to 1 milli-Sv, so 620 milli-rem is 6.2 milli-Sv.

SOURCE: "Fact sheet on Biological Effects of Radiation" ( http://www.nrc.gov/reading-rm/doc-collections/fact-sheets/bio-effects-radiation.html) and NCRP Report 160 (2009).

We see that radiation is all around us, and as such our bodies are use to handling some typical amounts of ionizing radiation, even though ionizing radiation can in principle be hazardous. This is because biological systems on Earth evolved under conditions of constant exposure to such radation - in fact, a biological consequence of ionizing radiation, called "mutation," is a necessary component in order to explain the diversity of life on Earth. So ionizing radiation is, in part, responsible for the vast diversity of life on Earth.

A Demonstration of Ionizing and Non-ionizing Radiation

Atoms are "quantum systems" - that means that you can't just send in any old electromagnetic wave of any energy and expect to remove an electron (that is, "ionize" an atom). Atoms must receive a minimum amount of energy before they will give up their electrons, even the ones bound furthest from the nucleus. In biological systems, you have to put in at least as much energy as the weakest chemical bonds (Hydrogen bonds) in order to disrupt the chemical basis of the system.

We demonstrate the quantum nature of atoms in class. Please see this video below for the demonstration.


We learn some very valuable things from this:

  1. Mobile phone radiation is INCAPABLE of ionizing.
  2. Green or red laser light are INCAPABLE of ionizing.
  3. In fact, all the visible light and heat from a set of bright incandescent bulbs (each about 60 Watts!) is INCAPABLE of ionizing.
  4. But, the UV-C light from the sanitizing wand, with a wavelength of about 253 billionths of a meter (nanometers) and a bulb wattage of just 6 Watts, is easily capable of removing the charge from the aluminum can (ionization!).

The Physics of EM Waves - Energy, Wavelength, and Frequency

Quantum physics, which has withstood repeated testing for about 100 years, tells us how to relate energy and the properties of EM waves, such as wavelength and frequency. These properties are illustrated below:

The wavelength and frequency of EM waves are related to the speed of light, denoted c = 2.998 x 108 m/s:

c = λ * f

where λ is the wavelength (the distance between like parts of neighboring waves) and f is the frequency of the wave (the number of times per second that the same part of neighboring waves passes a common point in space). Wavelength is measured in meters (m) and frequency in a unit called the "Hertz" (Hz) which is just given by "per second" or 1/s.

Quantum physics also relates the ENERGY carried by the wave to its frequency:

E = h * f

where h is Planck's Constant, h = 4.136 x 10-15 eV*s. An "eV" is an "electron-Volt," a convenient measure of energy on the scale of an atom. 1 eV is the energy gained by a single electron when it is accelerated between the two terminals of a 1 Volt battery (for example).

Here is a table illustrating the energy carried by EM waves of different wavelengths and frequencies:

Let's see if we can get Cas Milner's notes Let's play word association: I say RADIATION, you say ... Different kinds alpha - Apollo mission Pu for thermal generator (movie?) beta neutron gamma, X-ray (chiropractors, mammograms, CT scans) lethal overdose in the news etc. Ionizing versus non-ionizing Demonstration with Geiger-Mueller counter absorption in materials 1/r^2 law half-life (dice) cell phones *YOU* radiate in the IR Naturally occurring radiation cosmic rays - demonstration, has anybody ever flown in a plane? evolution granite bananas - B.E.D. salt substitute KCl brazil nuts How to dispose of the waste Yucca Mountain - 1 million years? C'mon! NIMBY