Amateur Radiation Detection
and Experimentation Page

Purpose:

Types of Radiation:

• Alpha Particles: Helium nuclei, generally emitted from heavy elements such as uranium and thorium. Alpha particles only travel a few inches in the air, and can be stopped by a piece of paper. Special geiger tubes with a mica window are necessary to detect them, as other windows will stop alpha particles.
  
  
• Beta Rays: Electrons moving at extremely high (often relativistic) speeds. They are more penatrating than alpha particles. They can pass through light elements, such as paper and aluminum (but only small thicknesses).
  
  
• Gamma Rays: Electromagnetic waves, similar to light, but at a much higher energy. Much more penetrating than alpha or beta radiations. High energy gamma rays can pass through several inches of metal. Note that X-Rays and Gamma Rays are really the same thing, the term X-Ray is used when the radiation is produced by electrons striking a material, such as in an X-Ray tube.

Available Now!
The low cost GM-10 Radiation Detector.

Typical Geiger Counter Circuit:

                                            GM Tube
                       10 M                --------------
          ------------/\/\/\/-----*--------O            |-----
          |                       |        --------------    |
      +   |                       |                          |
        -----                     |                        -----
 500V    ---                      |                         ---
          |                       |                          _
          |                       |--------) (----- Output
        -----                             100 pF
         ---
          -

Typically, the counts are summed over a one minute period, and therefore the common unit is Counts Per Minute (CPM). The number of CPM depends on the size and efficiency of the GM Tube. A larger tube naturally will detect more particles.

I've built a circuit which powers the GM tube strictly from the serial port handshake lines - no other power supply is necessary. The circuit then conditions the detected pulse and sends it back to the computer, where software can tally the number of pulses detected over a time period, typically CPM - Counts Per Minute.

This detector is now available as the GM-10, check out the details!

Sources of Radiation:

The US Geological Survey has a Radon WWW Page. It contains a great deal of useful information, maps of radon levels in the US, and links to other sites.

Note that even though most of the heavy elements are alpha emitters, they can still be dangerous, if they get inside your body. Your skin stops alpha particles if the source is outside your body, but your internal organs and tissues have no such protection. Radioactive dust can be hazardous. Radioactive dust? Read on...

High Altitude Radiation from Airplane Flights

Recently I took a transcontinental flight, and of course a GM-10 Radiation Detector came along for the ride!

The graph below shows the background radiation levels on the ground, as well as when we were at our crusing altitude (around 35,000 feet). Note the huge difference in radiation levels! The CPM (Counts Per Minute) went from about 12 on the ground to 360 in flight, or 30 times the level!

Radioactive Dust

As an experiment, I wiped some dust from the TV screen onto a tissue, and placed it in front of the radiation detector. The reading went from a background reading around 10 CPM to around 1300 CPM, or 130 times the reading!

This graph shows the radiation (in Counts Per Minute, CPM) over time, as the daughter products decay. In addition to plotting the raw data, I've also estimated the initial amounts of Radium B (Pb₂₁₄), Radium C (Bi₂₁₄) and Pb₂₁₂:

Radium B and Radium C are decay products of Radon. The Radon is produced by Uranium that naturally occurs in the soil, after a rather long decay process. Radon has a half life of just under 4 days. In addition to being produced by local sources, Radon (and it's daughter products) can be blown in by the winds from distant locations. So just because you don't have a radon problem in your basement doesn't mean that you won't find radioactive dust in your house!

The Radon decays into Polonium, which them decays into Radium B, an isotope of Lead. This decays with a half life of about 27 minutes in Radium C, an isotope Bismuth. This decays with a half life of about 20 minutes into another Polonium isotope, which quickly (164 microseconds) decays into an isotope of Lead. The Lead decays with a very long half life of 22 years, so we don't get much radiation from it, or any further products.

The two Radium isotopes both undergo beta decay, and it is their radiation we detect in this experiment. Notice that we initially start with much more Radium B than Radium C. The Radium B decays, producing more Radium C, initially at a rate faster than the Radium C is decaying. So The amount of Radium C starts to increase. Eventually, there is not enough Radium B decaying into Radium C, and the amount of Radium C starts to drop.

Here's the process:

• Radon (Rn₂₂₂) does an alpha decay into Polonium (Po₂₁₈) with a half life of 3.824 days.
• Polonium (Po₂₁₈) does an alpha decay into Lead (Pb₂₁₄) with a half life of 3.05 minutes.
• Lead (Pb₂₁₄) does a beta decay into Bismuth (Bi₂₁₄) with a half life of 26.8 minutes.
• Bismuth (Bi₂₁₄) does a beta decay into Polonium (Po₂₁₄) with a half life of 19.8 minutes
• Polonium (Po₂₁₄) does an alpha decay into Lead (Pb₂₁₀) with a half life of 164 microseconds.
• Lead (Pb₂₁₀) does a beta decay into Bismuth (Bi₂₁₀) with a half life of 22.3 years.
• Bismuth (Bi₂₁₀) does a beta decay into Polonium (Po₂₁₀) with a half life of 5.01 days.
• Polonium (Po₂₁₀) does an alpha decay into Lead (Pb₂₀₆) with a half life of 138.38 days.
• Lead (Pb₂₀₆) is stable.

The black line at the bottom of the graph shows the amount of Lead-212 present. This is a daughter product of Thoron, an isotope of Radon which is produced by Thorium, rather than Uranium. Thoron has a very short half life, about 1 minute. Lead-212 has a much longer half life, almost 11 hours.

I was doing laundry one day, and decided to check out the lint that collects in the lint filter in the clothes dryer. It produced counts around 240 CPM, again much higher than the background readings. This is probably due to the numerous uranium/thorium atoms and daughter products that are floating in the air, which get stuck to your clothes, and are sucked into the dryer.

Many parts of the US, including Maryland, where I live, have relatively high amounts of radon gas. This was never a problem in the past, but many modern homes are very air-tight, to reduce energy costs. This means that the radon gas is more likely to be trapped in the house, where it can decay into the much more dangerous daughter products.

Radon is much more of a problem for smokers. The radiation dust attaches itself to the smoke particles, and they get trapped to the sticky goo that gets stuck inside your lungs, bombarding your tissue with alpha radiation. (As if smoking was bad enough for you)

Radon Test Kits:

A curie is a measure of the activity of radiation. It is equal to 37 billion decays per second. The metric equivilent is the becquerel, which is one decay per second. So a picocurie is 37 decays per second. Currently the EPA considers 4 picocuries to be the safe limit. This would be 148 radon decays per second. Radon has a half life of about 3.83 days, this equates to around 100 million radon atoms per liter of air. Again, radon itself is not dangerous, the risk comes from the radioactive daughter products (dust) that can get inside your body.

Be sure to take a look at our new Radioactive Products and Other Sources Of Radiation page!

Other sources of information:

• Sources of Natural Radiaion
  
  
• The Atomic Mac - A Periodic Table of the Elements for the Macintosh, also contains detailed nuclear information, half lives, decay modes, etc.
  
  
• Atomic Rocks - a great site for information on radioactive minerals.
  
  
• WHO WILL SPEAK FOR TRUTH? The Case of Nuclear Radiation
  
  
• LND, Inc. 3230 Lawson Boulevard, Oceanside, NY 11572 , (516) 678-6141, (516) 678-6704 - FAX. Mfg of Geiger tubes, Proportional Counters, Ionization Chambers, etc.
  
  
• Radioactivity in Nature - great info on naturally occuring radiation
  
  
• Terrestrial Gamma Radioactivity Map of the US showing levels of radiation due to Potassium, Thorium, and Uranium
  
  
• Uranium Minerals A great site showing where you can find your own radioactive minerals
  
  
• Natural Nuclear Reactor at Oklo, Gabon, West Africa
  
  
• Carbon 14 Dating