76. Osmium alloys are really hard and don’t bend easily, so they contribute to the production of electrical contacts, which are the points in a circuit that allow a current to pass from one conductor to another. Every electronic device uses electrical contacts—that’s how electrical currents flow.
78. Platinum: Apart from being crafted into fine jewelry, platinum is used in vehicle-emissions control systems, specifically in catalytic converters. Platinum is often the catalyst that converts the toxic by-products of combustion in the exhaust to a less toxic substance.
80. Mercury: Owing to its acoustic properties, mercury acted as the propagation medium in delay-line memory devices used in early digital computers of the mid-20th century.
81. Thallium is used in photo-resistors, which appear in everything from streetlights to alarm clocks. Most things that react to light, especially in a basic sense, use photo-resistors.
84. Polonium: Polonium serves as an atomic heat source, because it spontaneously heats up to about 932 degrees Fahrenheit. In the 1970s, scientists working for the Soviet Union's Lunokhod used polonium to keep the internal components of moon rovers, specifically the Lunokhod 2 Moon Rover, warm during lunar nights.
85. Astatine is highly radioactive and is available only in tiny quantities, typically because it has a short half-life. It was named the rarest element on earth by the Guinness Book of World Records.
86. Radon is extremely radioactive and is considered a highly dangerous material, so it isn't found or used in the production of common consumer items. However, it is sometimes employed to treat cancer, in the form of radiotherapy-implantable seeds.
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The rest of the elements aren't typically used for commercial product development, because they are too rare, too new, too expensive to produce, too dangerous, or all of the above. They're mostly just the subjects of research for now, but some have potential applications in fuel, power, light, medical treatment, and more.
87. Francium is rare and considered unpredictable, so it hasn’t been used commercially yet. So far, it has been used only in research.
88. Radium is extremely radioactive and produces serious medical side effects if humans have prolonged contact with it. Although it used to be a component of glow-in-the-dark paint, it is now considered too dangerous. However, equipment makers can use it in devices such as calibrators and lightning rods.
89. Actinium is rare, expensive to produce, and highly radioactive, so it doesn’t have much commercial application. It’s mainly used for neutron production.
90. Thorium can act as a nuclear fuel source, and research and investment in thorium fuel began in 1996. On a commercial level, a thorium compound—thorium dioxide—is used in magnetron tubes, which are installed in microwave ovens.
91. Protactinium is highly radioactive, rare, and very toxic, so it currently has no uses outside of research.
92. Uranium is mostly used for nuclear power. Because it is highly radioactive, it isn't widely employed in commercial products anymore—but it was used to color Fiestaware, a type of glass dinnerware, from 1936 to 1944.
93. Neptunium: There are no major commercial applications of neptunium, as it’s mostly used for research. It’s radioactive and harmful, but it is present in neutron detective equipment.
94. Plutonium is highly radioactive and is commonly employed in nuclear weapons—the atomic bombing of Japan during World War II used nuclear bombs with a plutonium core. This element emits a lot of thermal energy, which makes it well suited for electrical power generation for devices that must function without direct maintenance for prolonged periods. As a result, plutonium has been used in radioisotope heater units in the Cassini, Voyager, and New Horizons space probes.
95. Americium is a synthetic element commonly present in household smoke detectors. The americium compound passes through the smoke detector's ionization chamber, which is an air-filled space between two electrodes, and permits a small, constant current between those electrodes. Any smoke that enters the chamber absorbs the alpha particles, which reduces the ionization and affects this current, which then triggers the alarm.
96. Curium: One of the most practical uses of curium isn’t in a commercial product, but in space exploration. Curium is employed in alpha particle X-ray spectrometers (APXS); these instruments were built on the Sojourner, Mars, Mars 96, Spirit, Athena, and Opportunity rovers, and were used to analyze surface rocks on Mars. The Curiosity rover currently on Mars also features an APXS with curium at the helm.
97. Berkelium has no practical application outside of scientific research.
98. Californium is the heaviest element to occur naturally on earth. It mainly serves as a neutron startup source for nuclear reactors, but it is also used in radiation therapy for cervical and brain cancers.
99. Einsteinium was discovered as a component of the debris of the first hydrogen bomb explosion in 1952. It has no uses outside of scientific research.
100. Fermium is a synthetic and highly toxic element. Owing to the small amounts of produced fermium and its short half-life, it currently has no uses outside of basic scientific research.