![]() ![]() All other man-made elements heavier than uranium are radioactive as well.Īmericium-241, a radioactive element best known for its use in smoke detectors, is a good example of an element that undergoes alpha decay. There are eight other naturally radioactive elements: polonium, astatine, radon, francium, radium, actinium, thorium and protactinium. Uranium is the best example of such an element and is the heaviest naturally occurring radioactive element. The process by which it turns into helium is called radioactive decay.Ĭertain elements are naturally radioactive in all of their isotopes. That is, if you have a container full of tritium and come back in a million years, it will have turned into helium-3 (two protons, one neutron), which is stable. ![]() The deuterium isotope of hydrogen is stable.Ī third isotope, hydrogen-3 (also known as tritium), has one proton and two neutrons. While it acts like hydrogen-1 (for example, you can make water out of it), it can be toxic in high concentrations. Deuterium is very rare in nature, making up about 0.015 percent of all hydrogen. (Because there is only one proton in the nucleus, there is no need for the binding effects of neutrons.)Īnother isotope, hydrogen-2 (also known as deuterium), has one proton and one neutron. Normal hydrogen, or hydrogen-1, has one proton and no neutrons. Hydrogen is a good example of an element with multiple isotopes, one of which is radioactive. In some elements, all of the isotopes are radioactive. The part that scientists didn't understand until about 100 years ago is that certain elements have isotopes that are radioactive. Both isotopes act and look the same, and both are stable. Atoms of both isotopes of copper have 29 protons, but a copper-63 atom has 34 neutrons while a copper-65 atom has 36 neutrons. Up to about 100 years ago, scientists thought that all atoms were stable like this, but many atoms come in different forms.įor example, copper has two stable forms: copper-63 (making up about 70 percent of all natural copper) and copper-65 (making up about 30 percent). Aluminum-27 is therefore called a stable atom. If you take an atom of aluminum and put it in a bottle and come back in several million years, it will still be an atom of aluminum. The "27" is the atomic mass number, or the sum of the number of neutrons and protons in the nucleus. If you group millions of aluminum atoms together you get a substance that is aluminum - you can form aluminum cans, aluminum foil and aluminum siding out of it.Īll aluminum that you find in nature is called aluminum-27. For example, if you combine 13 protons with 14 neutrons to create a nucleus and then spin 13 electrons around that nucleus, what you have is an aluminum atom. The number of protons in the nucleus determines the behavior of an atom. Because the protons all have the same charge and would naturally repel one another, the neutrons act as "glue" to hold the protons tightly together in the nucleus. Their purpose in the nucleus is to bind protons together. In most cases, the number of electrons and protons are the same for an atom (making the atom neutral in charge). Protons and electrons have opposite charges and therefore attract one another (electrons are negative and protons are positive, and opposite charges attract). Protons and neutrons bind together to form the nucleus of the atom, while the electrons surround and orbit the nucleus. Material that can sustain a nuclear fission chain reaction is said to be fissile or fissionable.Inside every atom are three subatomic particles: protons, neutrons and electrons. If this process continues, a nuclear chain reaction occurs. \): The fission of a large nucleus, such as U-235, produces two or three neutrons, each of which is capable of causing fission of another nucleus by the reactions shown.
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