Here is one of the best midterm 1 essays on radioactivity, chosen by James. Congratulations Jocelyn Blore!

Question: How dangerous is radioactivity? Discuss the real and imagined dangers. Give examples, along with numbers. Which risks are known from direct observation, and which are known only from calculations? What assumptions are made in calculating risk?

Answer: In general, there are a lot of public misconceptions about the presence and deanger of radioactivity. Let me begin by saying that if you were NOT radioactive, you're dead and have been dead for a long time. Radioactive elements such as potassium-40 and carbon-14, isotopes of the more familiar forms, exist naturally in our bodies. We are exposed to radioactivity every day and most of the time we remain perfectly healthy.

The risks and potential biological damage to cells can be measured in "rems," an acrynym standing for Roentgen Equivalent in Man. A whole body dose of 1 rem means that there are approximately a billion gamma rays penetrating every square centimeter of your body. Sounds like a lot, doesn't it? Let me put it into perspective: it takes approximately 100 to 200 rems to experience bad radiation sickness characterized by nausea, fatigue and hair loss. This is a lot of radioactivity. In the 1986 Chernobyl nuclear reactor incident, the median dose for people exposed as 45 rem. [This is in the city of Chernobyl.] I'll return to the risks associated with this exposure later. At 300 rem, or the LD50 dose, there's a 50% chance of dying. Increasing amounts of rem exposure after 300 leads to increasing chances of incapacitation and death.

The most common risk associated with radioactivity, however, is cancer. Let me introduce what scientists call the "linear hypothesis," a risk only presupposed through calculations. This theory holds that for every 2500 rem released, there will be one cancer death. How can that be when 50% of people left untreated dies at 300 rem and chances of fatality increase from there? Well, suppose we spread this 2500 rem doxe over a group of 2500 people, each with exposure to 1 rem. This probabilitic hypothesis holds that one of those 2500 people will die of cancer. We also must keep in mind that scientists believe cancer to stem from a series of cell mutations, maybe 3 or 4, of which radioactivity affects the last.

Here are a couple more notes on radioactivity. Many people fear that radioactive elements used in nuclear bombs and reactors, such as plutonium-239, can contaminate water supplies or air; however, the fatal dose of ingesting plutonium is 500 milligrams, much more than the lethal dose of the poison cyanide. Damage done by inhaling plutonium takes a much lesser dose than 500 milligrams, but it is different to get into the critical part of one's lungs because it must travel in bits of microscope dust. Lastly, remember that we are more likely to die of our own radioactivity (six chances in a million) than we are to win the lottery. The risks of radioactivity have been overstated because 20% of people die of cancer anyway. Chances of developing cancer from exposure to radiation pale in comparison to getting cancer from other things.