Gold-195, radioactive decay

The experiment conducted by Rutherford and his co-workers involved bombarding gold foil with alpha particles, which are doubly charged helium atoms. The apparatus used in their experiment is shown in Figure 14-9. The alpha particles are produced by the radioactive decay of radium, and a narrow beam of these particles emerges from a deep hole in a block of lead. The beam of particles is directed at a thin metal foil, approximately 10,000 atoms thick. The alpha particles are delected by the light they produce when they collide with scintilltaion screens, which are zinc sulfide-covered plates much like the front of the picture tube in a television set. The screen... 

Write the balanced nuclear equation for each of the following radioactive decays (a) p + decay of boron-8 (b) p decay of nickel-63 (c) a decay of gold-185 (d) electron capture by beryllium-7. 

For very many years, the alchemist s dream of changing base metals into gold was ridiculed even by the most reputable of scientists. Although it was known that the nuclei of certain atoms undergo alteration in the course of natural radioactive decay, researchers inability to exercise any control over the nature or rate of these spontaneous decompositions probably did much to foster the belief that the nucleus of the atom was inviolate. However, in the year 1919 the English physicist Ernest Rutherford accomplished the first transmutation of an element, and this notable discovery was quickly followed by other equally significant developments. 

In most cases nuclear reactions result in a nuclear transmutation from one element to another. Transmutation was originally connected to the mythical "philosopher s stone" of alchemy that could turn cheaper elements into gold. When Frederick Soddy and Ernest Rutherford first recognized that radioactive decay was changing one element into another, Soddy remembered saying, "Rutherford, this is transmutation " Rutherford replied, "Soddy, don t call it transmutation. They ll have our heads off as alchemists."... 

This reaction would have been of great interest to the alchemists, but unfortunately it does not occur at a rate that would make it a practical means for changing mercury to gold. The various types of radioactive decay are summarized in Table 21.2. 

In general, the number of nuclei produced in a nuclear reactor can have several sources and several routes that reduce the number. Direct formation by nuclear reaction and decay of a parent nuclide formed in the bombardment increase the desired product and radioactive decay of the product decreases it. Also, neutron absorption by the radioactive product, transforming it into another species may be significant. An important example of this situation occurs in the production of the medically useful gold isotopes Au and Au (Hainfeld et al. 1990). The cross section for thermal neutron capture in Au is a respectable 98.7 b, but the neutron capture cross section of Au going to Au is a huge 25,000 b. 

The Voyager space vehicle launched in 1977 contained a gold-plated copper disk electroplated with a patch of pure uranium-238 isotope. If this disk were recovered by some advanced alien civilization, the disk s age could be determined from the radioactive decay rate of the isotope. 

In natural radioactive decay we find an example of the alchemist s get-rich-quick dream of converting one element to another. But the natural process for uranium does not yield the gold coveted hy the alchemist rather, it produces the element lead, with which the dreamer wanted to begin his transmutation. The question remained after radioactivity was discovered Can we initiate the transmutation of one ordinarily stable element into another ... 

The simplest substances are the elements. They cannot be broken down into simpler constituents by chemical reactions. Ninety-two elements exist in nature although some additional ones can be created experimentally by the techniques of nuclear physics, they exist only for very short periods of time before decaying radioactively. The elements can be arranged in basic groupings based on their properties a fundamental division is into metals (e.g. iron, copper, gold, sodium) and nonmetals (e.g. carbon, oxygen, hydrogen, sulfur). 

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