Radioactive Decay

Marie Curie named the process of radioactivity while studying rays being emitted by the element uranium. Elements are radioactive when their nuclei spontaneously emit energy without absorbing any energy. The disintegration of radioactive atoms is called radioactive decay. The rate of decay is measured as the number of atoms that disintegrate per second, day or year. A commonly used measurement is the half-life of a radioactive substance. This is the time required for one-half of the radioactive substance to decay. Radiation is often put to beneficial use. For example, gamma rays are used for protection against food spoilage retarding the growth of organisms such as bacteria, molds and yeasts. Another example is the use of radioactive isotopes as radioactive tracers in chemical reactions and biological processes. This allows scientists to monitor a reaction or process from start to finish. Lastly, but no less important, radioactive isotopes are used in nuclear medicine in diagnosis and therapy. Imaging, a technique in which the radioisotope accumulates at the site of an internal disorder, is used to provide information about the location and size of medical disorders, such as tumors.

This program simulates radioactive decay of four radio-isotopes: uranium-238, radon-222, hydrogen-3, and carbon-14. The amount of decaying material (in pounds) is plotted as a function of time.

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INSTRUCTIONS

1. Select a radioactive element by clicking on one of the radio-isotope option buttons.
2. To begin the decay process, click on the clock. Clicking on the right mouse button will increase the time in small increments whereas clicking on the left button will increase the time by larger increments.

Radioactive decay is represented graphically, pictorially, and numerically. The amount of the isotope at the beginning of the experiment is 20 pounds, and the number of pounds remaining is displayed as the simulation progresses, which is indicated by the size of the picture of the radioactive substance as well. The initial time is zero and as the experiment progresses, the time elapsed is displayed underneath the clock. The rate of decay, or amount disintegrated per unit time, is best observed by analyzing the graph.