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<br />Water Resources <br /> <br />THE YEAR'S WORK. . . tritium as a ground-water tracer-waler balance <br />dala-tecbnology in uJoter dCl/r/opment-flood plain occupance-a com- <br />pariso'" of water !-'allles ill New MexicD---'wafer resource administration in <br />Florida-the "comprehensive plan"-economic efficiency in multiple purpose <br />rll1fT development-the Columbia RiveT Basin. <br /> <br />Requirements and Supplies <br /> <br />- Physical scientists now recognize that atoms of a given element may <br />have slight differences in their atomic weights. There are three well- <br />known varieties of atoms of hydrogen having atomic weights of 1, 2, and <br />3, respectively. These varieties, known as Uisotopes" of hydrogen, are <br />named protium, deuterium, and tritium. Tritium, which as its name sug- <br />gests has an atomic weight of 3, turns out to be radioactive with a half-life <br />period of 12.5 years. Tritium is continually disappearing from the earth <br />due to radioactive changes, but it is also being replenished. It is formed <br />by high-energy cosmic ray bombardment on nitrogen atoms in the outer <br />atmosphere. It then combines with the oxygen of the atmosphere to form <br />a kind of water which also is radioactive. The rate of formation is ap- <br />parently quite constant. The amount of such water in rain water is <br />exceedingly small but, using Geiger counter methods, it can be measured <br />with a high degree of accuracy. Where comparatively simple aquifer Aow <br />conditions are involved, measurement of tritium shows promise in dis- <br />tinguishing between "recent" and "old" water, i.e., water from rains of the <br />preceding few months or years versus many years or centuries. This <br />information is important because, when viewed in relation to other known <br />facts about the aquifer, tritium analysis can give us a better answer to the <br />llwater-mining" question than was previously possible. Determinatio~ <br />as to age is only valid, however, if the only route of tritium disappearance <br />is through natural radioactive decay. If the tritium should be adsorbed <br />on clay, or sand, or rocks in general, in greater proportion than is founrl <br />in the original rain water, the age arrived at would obviously be in error. <br />To find out whether such an error might occur in tritium determina- <br />tions of underground water, Resources for the Future entered into a <br />research agreement with the Nuclear Science and Engineering Corporation. <br /> <br />I <br />I <br />, <br />, <br /> <br />12 <br />