 What do popcorn and uranium have in common? Both popcorn and uranium can change forms spontaneously and can't ever change back. In uranium we call it radioactive decay, but with popcorn we call it snack time. Elements like potassium, thorium and uranium can undergo this spontaneous radioactive decay, just like the popcorn kernels in our experiment. Today Jeremy will show us just how common radiation can be. There's radiation in the rocks below us, the sky above, from the cosmos. We ourselves are radioactive. The Geiger counter is a device for measuring radiation. It's simply a power source, a big battery, and a meter on the top which measures, shows you the radiation level, and the detector itself. Table salt is sodium chloride, this is potassium chloride. There's about 150 grams of potassium in this, which is about the same amount of potassium that's in the human body. Less than one percent of that potassium is naturally radioactive. Each beep you hear is a unit of radiation being detected. Other naturally radioactive foods include bananas, potatoes, lima beans, Brazil nuts, and even carrots. Have you ever had a dental x-ray? An x-ray is radiation that passes right through the skin, but gets stopped by teeth and bone, giving us an image of the inside of your mouth. Have you ever used a bandage like this one? The contents of this package have gone through the process of irradiation, where gamma rays were used to kill off any bacteria and sterilize the product. In the same way, some foods, cosmetics, and other products have been irradiated to ensure that they're clean and free of harmful bacteria. Directing and pinpointing this radiation also allows doctors to irradiate and kill cancer cells. Behind me is an example of one of the early cobalt cancer therapy machines that was created in Canada for the first time in 1951. Nuclear reactors are capable of making large quantities of the radioactive element cobalt-60, which were used in this machine. You would have a patient lie on this bed, and in this bulbous head above them would be a lump of cobalt-60, which is radioactive, shielded from the patient initially by a lead shutter. You would move this so that the source was directly pointed at the cancer itself, and then open the shutter and let a beam of radiation go insert itself into the cancer and kill the cancer cells. Radiation therapy like this is widely used today to treat cancer, with many different techniques to target various cancer cells. Most of the radiation that humans receive doesn't come from dental x-rays, cancer therapy, or even from the sun. 70% of it comes from the Earth. Radioactive elements in the Earth's core are constantly keeping the interior molten hot, and keeping you and I alive.