Radioactivity The spontaneous disintegration

If you look at the periodic table, you will notice that all elements after bismuth, atomic number 83, have their atomic weight denoted by an integer within parentheses. Such large nuclei are unstable and undergo radioactivity, the spontaneous disintegration by the emission of particles. The atomic weight shown on the periodic table is the mass number of the most common isotope of each radioactive element. 

RADIOACTIVITY. The spontaneous disintegration of the nucleus of an atom with the emission of radiation. This phenomenon was discovered by Becquerel in 1896 by the exposure-producing effect on a photographic plate by pitchblende (uranium-containing mineral) while wrapped m black paper in the dark, Soon after this, it was found that uranium minerals and uranium chemicals showed more radioactivity than could be accounted for by the uranium content. About the same dmc. radioactivity of thorium minerals and thorium chemicals was also discovered. 

Natural radioactivity The spontaneous disintegration of the nuclei of certain naturally occurring elements like uranium, thorium, polonium, radium, etc. is known as natural radioactivity. 

Roentgen s discovery of x-rays stimulated great interest in this new form of radiation worldwide. Antoine Henri Becquerel (1852-1908) accidentally discovered the process of radioactivity while he was studying x-rays. Radioactivity involves the spontaneous disintegration of unstable atomic nuclei. Becquerel had stored uranium salts on top of photographic plates in a dark drawer. When Becquerel retrieved the plates, he noticed the plates contained images made by the uranium salts. Bec-querel s initial discovery in 1896 was further developed by Marie Curie (1867-1934) and Pierre Curie (1859-1906). Marie Curie coined the word radioactive to describe the emission from uranium. 

The spontaneous disintegration of a nucleus is a first-order kinetic process. That is, the rate of radioactive decay of TV atoms (—dN/dt, the change of TV with time, t) is proportional to the number of radioactive atoms present (Equation 6.4). 

In spite of all the new approaches which illuminated the outer regions of the atom, the center or nucleus of the atom continued to remain a bundle of uncertainties. Something of the composition of the nuclei of a few elements was already known. This information came from a study of the spontaneous disintegration of radium and other radioactive elements, such as thorium, polonium, uranium, and radon. These elements break down of their own accord into simpler elements. Soon after the Curies discovery of radium, Rutherford and Frederick Soddy, his student and collaborator, had found that the spontaneous breaking down of radium resulted in the emission of three types of rays and particles. Radium ejected alpha particles (ionized helium atoms), beta particles (electrons), and gamma rays (similar to X-rays). In radioactive elements, at least, it was believed that the nucleus contained electrons, protons, and electrified helium particles. 

Radioactivity The spontaneous breakdown of the nucleus of an atom through the emission of particles (alpha and beta particles) and gamma radiation. Although all atomic nuclei can theoretically disintegrate, under normal conditions only a few of the naturally occurring elements such as uranium and radium undergo any significant rate of decay. 

Radioactivity is the spontaneous disintegration of the nucleus of an atom with the emission of radiation, accompanied by the emission of... 

A stable nucleus remains intact indefinitely, but the great majority of nuclei are unstable. An unstable nucleus exhibits radioactivity it spontaneously disintegrates, or decays, by emitting radiation. In the next section, you ll see that each type of unstable nucleus has its own characteristic rate of radioactive decay, which can range from a fraction of a second to billions of years. This section introduces important terms and notation for nuclei, describes the common types of radioactive emissions and decay, and discusses how to predict whether and how a given nucleus will decay. 

The properties described earlier in this book are, in principle, a function of the outer electron configuration of each individual atom, and the nucleus of each atom can be regarded as simply providing mass. However, some of the heaviest atomic nuclei have been found to be unstable. The elements that show this phenomenon are said to be radioactive. It is now known that radioactivity is an external manifestation of the spontaneous disintegration of a nucleus. 

Natui radioactivity is the result of the spontaneous disintegration of naturally occurring radioisotopes. Many radioisotopes can be arranged in three radioactive series. The rate of disintegration is uninfluenced by chemical changes or any normal changes in... 

Radioactivity— The spontaneous decay or disintegration of an unstable atomic nucleus, usually... 

In this chapter we consider some of the experiments that led to the conclusion that the atom is electrical in nature. Dalton s concept of a structureless atom provided no mechanism to explain these observa tions. These experiments, started over 150 years ago, also culminated in the discovery of X rays and radioactivity (Section 25.1). The spontaneous disintegration of naturally radioactive atoms into smaller particles contradicts the Daltonian hypothesis that atoms are unalterable. In turn, these discoveries inaugurated a more complete theory of the structure of atoms—the nuclear theory of the atom—and reaffirmed the atom as the unit of chemical changes. 

Radioactivity the spontaneous decay or disintegration of an unstable atomic nucleus, usually accompanied by the anission of ionizing radiation Radiography medical use of radiant energy (such as x-rays and gamma rays) to image body systans Radioisotope isotopes of an elanent that have an unstable nucleus, commonly used in science, industry, and medicine... 

Atoms with the same number of protons but a different number of neutrons are called isotopes. To identify an isotope we use the symbol E, where E is the element s atomic symbol, Z is the element s atomic number (which is the number of protons), and A is the element s atomic mass number (which is the sum of the number of protons and neutrons). Although isotopes of a given element have the same chemical properties, their nuclear properties are different. The most important difference between isotopes is their stability. The nuclear configuration of a stable isotope remains constant with time. Unstable isotopes, however, spontaneously disintegrate, emitting radioactive particles as they transform into a more stable form. 

Radioactive materials Elements that have unstable nuclei that spontaneously disintegrate, releasing radiation in the form of subatomic particles and energy. 

Radioactivity The property of spontaneous disintegration possessed by certain unstable nucelides. 

Radioactivity The process of spontaneous disintegration by a parent radionuclide, which releases one or more radiations and forms a daughter nuclide. When half the radioactivity remains, that time interval is designated the half-life (Tb 1/2). The Tb 1/2 value gives some insight into the behavior of a radionuclide and into its potential hazards. 

Radioactivity Property or characteristic of radioactive material to spontaneously disintegrate with the emission of energy in the form of radiation measured in curies or becquerel. 

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