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What is Radioactivity?


Radioactivity is the spontaneous and continual decay or disintegration of certain atoms, with the release of radiation and enormous amount of energy. The cause of this phenomenon is that the size of the nuclei of these atoms are very large, hence, they are highly unstable. They therefore seek stability by breaking up into smaller masses.

In 1896 Henri Becquerel, a French physicist, made the chance observation that potassium uranyl tetraoxosulphate(VI), K2SO4.UO2SO4.2H2O, emits penetrating radiation spontaneously and continuously. Becquerel found that the radiation: affect photographic plates even when they were wrapped in light proof black paper in much the same way as light; is similar to X rays in penetrating materials that are opaque to ordinary light; and in ionizing the molecules of air in the immediate vicinity, as demonstrated by the discharge of an electroscope. Another physicist Mme. Marie Sklodowska Curie called this remarkable property radioactivity.

Examples of radioactive substances

thorium, 23490Th; uranium, 23892U; and palladium 23491Pa.

In 1898, Mme. Curie began a series of experiments with the aim to quantify and to compare the radioactivities of several radioactive materials. She discovered that the radioactivities of all compounds of uranium are proportional to the quantities of uranium they contain and that all compounds of thorium are radioactive.

She also observed that a certain element found in two uranium minerals, pitchblende and carnotite are more radioactive than uranium itself. Mme. Curie was joined by her husband, Pierre Curie, and together the Curies were able to isolate this element, which is 400 times as radioactive as uranium and called it polonium in honor of Mme. Curie’s native Poland. Continuing their work they isolated, in December 1898, another substance 900 times as radioactive as uranium and called it radium in recognition of the high intensity of its radiation.

The Curies and Becquerel were together honored in 1903 with a Nobel prize in physics for the discovery and early investigation of radioactivity. Mme Curie again received the 1911 Nobel prize in chemistry for her singular efforts at determining the atomic weight of radium from 0.1 g of radium chloride, RaCl2, which she had isolated.

Note: radioactivity is different from ordinary chemical reactions in the following ways:

(1). It occurs in the nucleus, involving the protons and neutrons.

(2). It leads to the destruction of substances to form new ones.

(3). Its rate is independent of changes that would affect ordinary experimental conditions, such as temperature, chemical change, pressure, gravitational, electric and magnetic field.

(4). Its rate is independent of the oxidation state in which an element occurs.

(5). It produces usually greater amount of energy than ordinary reactions.


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