Spontaneous disintegration

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. 

Decay The spontaneous disintegration of an unstable atomic nucleus to form another more stable element or isotope of a lower atomic mass. 

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. 

Spontaneous nuclear fission takes place when the natural oscillations of a heavy nucleus cause it to break into two nuclei of similar mass (Fig. 17.21). We can think of the nucleus as distorting into a dumbbell shape and then breaking into two smaller nuclei. An example is the spontaneous disintegration of americium-244 into iodine and molybdenum ... 

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. 

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. 

Thorium is a relatively reactive, metallic radioactive element. Because thorium is a radioactive element, evaluation of adverse health effects due to exposure to thorium requires a slightly different approach than with chemicals. Radiation is a health risk because radioactive elements can emit energetic particles or electromagnetic radiation that can damage cells. Radioactive elements are those that undergo spontaneous disintegration (decay) in which energy is released (emitted) either in... 

Like all radioactive elements, it undergoes continuous, spontaneous disintegration into elements of lower atomic weight. M. and Mme. Curie had noticed that when air comes into contact with radium compounds it, too, becomes radioactive. The correct explanation was first given in... 

Thorium A quickly decays into thorium B, another rather short-lived product, which spontaneously disintegrates, as shown by Rutherford, into thorium C (53). By heating a lead-encased platinum wire charged with the mixture to 700°, Miss J. M. W. Slater, Bathurst student at Newnham College, Cambridge, succeeded in volatizing the thorium B° from the platinum and condensing it on the cold lead cylinder. At 1000° almost pure thorium C remained on the wire (32). 

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. 

If a product of one of these man-made reactions is unstable and spontaneously disintegrates further, it is said to be "artificially radioactive." In the preceding equation, for example, jjfCo is artificially radioactive, disintegrating as... 

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). 

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. 

The spontaneous emission of radioactive rays by an unstable atomic nucleus is called radioactivity. Spontaneously disintegrating atoms are called radioactive atoms and the nuclei of these atoms are unstable. 

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

For a spontaneous disintegration, the mass of the parent nucleus must exceed the sum of the masses of the products. Most tables, however, record atomic masses rather than nuclear masses. Neglecting the mass of the neutrino, show that for jd" decay,... 

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. 

Subsequent experiments, notably those of /./. Thomson (discoverer of the electron), E. Rutherford (who established that the atom was made of a dense, central core called a nucleus, positively charged by protons, and separated from moving electrons by empty space), and others such as A. Becquerel and Marie Curie (on the spontaneous disintegration of some nucleus with the emission of particles and radiation), were necessary, however, to complete the understanding of atoms. 

We have no control over spontaneous disintegration of naturaiiy occurring radioactive isotopes. 

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