noun Physics, Chemistry.
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Words nearby radioactivity
Example sentences from the Web for radioactivity
Speculation: The scorch might have been made by radioactivity attendant upon the resurrection.
But the dial indicated an increase in radioactivity as newly created neutrons spread their poison like a cancer.Voyage To Eternity|Milton Lesser
It will have passed the peak of its radioactivity by tomorrow and you can start back for The Pass.The Wealth of Echindul|Noel Miller Loomis
Back on the asteroid, a pit that glowed with radioactivity marked the site of the first blast.Rip Foster in Ride the Gray Planet|Harold Leland Goodwin
Actinium, an element or elementary substance obtained in minute quantities in connection with the study of radioactivity.
Remove them and measure the radioactivity produced from the sample.The Atomic Fingerprint|Bernard Keisch
British Dictionary definitions for radioactivity
Medical definitions for radioactivity
Scientific definitions for radioactivity
A Closer Look
In the nuclei of stable atoms, such as those of lead, the force binding the protons and neutrons to each other individually is great enough to hold together each nucleus as a whole. In other atoms, especially heavy ones such as those of uranium, this energy is insufficient, and the nuclei are unstable. An unstable nucleus spontaneously emits particles and energy in a process known as radioactive decay. The term radioactivity refers to the particles emitted. When enough particles and energy have been emitted to create a new, stable nucleus (often the nucleus of an entirely different element), radioactivity ceases. Uranium 238, a very unstable element, goes through 18 stages of decay before becoming a stable isotope of lead, lead 206. Some of the intermediate stages include the heavier elements thorium, radium, radon, and polonium. All known elements with atomic numbers greater than 83 (bismuth) are radioactive, and many isotopes of elements with lower atomic numbers are also radioactive. When the nuclei of isotopes that are not naturally radioactive are bombarded with high-energy particles, the result is artificial radioisotopes that decay in the same manner as natural isotopes. Each element remains radioactive for a characteristic length of time, ranging from mere microseconds to billions of years. An element's rate of decay is called its half-life. This refers to the average length of time it takes for half of its nuclei to decay.
Cultural definitions for radioactivity
The emission of elementary particles by some atoms when their unstable nuclei disintegrate (see half-life). Materials composed of such atoms are radioactive. (See alpha radiation, beta radiation, and gamma radiation.)