Natural Tritium Production

Cosmic ray neutrons interact in the upper atmosphere with nitrogen, producing 15N, which is radioactive and disintegrates into common carbon (12C) and tritium  

The tritium atoms are oxidized to water and become mixed with precipitation and so enter the groundwater. The natural production of tritium introduces about 5 TU to precipitation and surface water. 

In the saturated zone, water is isolated from the atmosphere and the tritium concentration drops due to radioactive decay the original tritium concentration of 5TU drops to 2.5 TU after 12.3 years, only 1.2TU are left after another 12.3 years, and so on. 

Provided the natural production of 5TU is the only source of tritium in the groundwater, we would have at hand a water dating tool. For example, water pumped from a well with 3TU has preserved 3 x 100/5 = 60% of its natural tritium content, equivalent to an age of 9 years (readable from Fig. 10.1). However, a hydrologist s life is not that simple. Most aquifers have a capacity equal to several annual recharges, or, in other words, water accumulates in the aquifer for many years and the age we have just calculated from the tritium concentration is not a real age, but rather an 

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The manmade tritium, which reached several thousand TU in precipitation during 1963, completely masked the natural tritium production discussed in the previous section. The awareness of the potential importance of tritium to hydrology arose only after the nuclear tests began. By that time the natural tritium content in precipitation could no longer be measured, but a unique solution was found—measurements in stored and dated wine bottles,... 

He is present in natural gases with a concentration of MO-7 of that of 4He and 1(T6 of the helium in the atmosphere. The separation is very expensive. Hence 3He is instead obtained as by-product of tritium production in nuclear reactors. Tritium in fact produces, by beta decay (the half life is 12.26 years), 3He the separation of 3He is obtained through a diffusion process. 

The average global production of tritium is —2,500 atom m s (Solomon and Cook, 2000). The deposition rate of the tritium varies with latitude, but it is also mixed with the bulk of precipitation originating from the ocean (which has a very low tritium content), and thus the average tritium content of precipitation tends to vary inversely with annual precipitation. Natural tritium in precipitation varies from —1 TU in oceanic high-precipitation regions to as high as 10 TU in arid inland areas. 

It is feasible to breed more tritium in a lithium cooled reactor than is used in the reaction. The excess tritium can be used to start other reactors or in a reactor using some coolant other than lithium that prevents it from breeding its own tritium. Nature has been kind with the properties of lithium. It is an excellent choice for transferring heat from the reactor and it is the raw material needed for the continual production of more fuel. Both these functions can be provided by the use of liquid lithium as the blanket material. The isotopic composition of the lithium may be adjusted to provide the proper balance of lithium 6 and lithium 7 to optimum heat transfer and production of tritium. The lithium can also be diluted with metallic sodium or potassium to aid in adjusting the tritium production rate. 

Natural tritium concentrations in ocean surface waters and in young groundwater are of the order of 1 tritium atom per 10 hydrogen atoms. This is the reason that tritium concentrations are reported as TU (Tritium Units). One TU stands for a tritium to hydrogen ratio [ H]/[H] of 10. The activity of a water sample with a tritium concentration of 1 TU is equivalent to 3.2 pCi or 0.12 Bq per liter of H2O. The production rate of natural tritium is about 0.5 0.3 atoms cm s (Craig and Lai 1961) leading to natural tritium values in ocean surface waters of about 0.2 TU (Dreisigacker and Roether 1978). 

Clarke WB, Jenkins WJ, Top Z (1976) Determination of tritium by mass spectrometric measurement of He. Inti J Appl Rad Isotopes 27 515-522 Craig H, Lai D (1961) The production rate of natural tritium. Tellus 13 85-105... 

Tritium collection. Tritium in air is usually in the form of water vapor and less commonly in the elemental or organic-bound forms. It is generated in nature by cosmic-ray interactions, and at nuclear reactors and tritium-production facilities by ternary fission and neutron activation. Tritium as HT tends to oxidize to water vapor in air. Conversion to and from organic-bound tritium occurs in biota (NCRP 1979). 

Over the years, a variety of fuel types were employed. Originally, natural uranium slugs canned in aluminum were the source of plutonium, while lithium—aluminum alloy target rods provided control and a source of tritium. Later, to permit increased production of tritium, reactivity was recovered by the use of enriched uranium fuel, ranging from 5—93%. 

Deuterium is abundant in and easily separated from water. There is enough deuterium on earth to provide power for geological time scales. In contrast, tritium is not available in nature, but can be produced from n+ lithium reactions (see Lithium and lithium compounds). Natural Hthium is exhaustible, but sufficient tritium can be provided from it until fusion energy production is efficient enough to involve only D-D reactions ... 

Production in Fission of Heavy Elements. Tritium is produced as a minor product of nuclear fission (47). The yield of tritium is one to two atoms in 10,000 fissions of natural uranium, enriched uranium, or a mixture of transuranium nucHdes (see Actinides and transactinides Uranium). 

Tritium, 5 456-480 23 759 analytical methods, 5 477-478 chemical properties, 5 472-474 health and safety factors, 5 478-479 natural production and occurrence, 5 474-475... 

Separation of 6Li from natural abundance (7.4%) feed to synthesize 6LiD (an important component of the fuel used in hydrogen fusion weapons (hydrogen bombs)). This, because the (n,T) cross section for 6Li is much larger than that of 7Li, so production of tritium is much enhanced in the triggering explosion. 

Starting with the atmospheric thermonuclear tests, tritium concentration in the Northern Hemisphere has increased considerably above the natural background of approximately 10 pCi/liter of water (5). Since the cessation of these tests, environmental tritium concentrations have decreased gradually. Tritium is, however, produced in every nuclear reactor to some extent as a product of fission (1) or the activation of deuterium. In particular, reactors with heavy water as the moderator or cooling agent produce a large amount of tritium. Inasmuch as no... 

Helium-3 is a decay product of radioactive tritium (3H, half-life = 12.44 years) that has been produced by nuclear bombs as well as naturally by cosmic rays in the upper atmosphere. Because virtually all 3He atoms escape from the surface ocean to the atmosphere, the 3He/tritium ratio in subsurface seawater samples indicates the time since the water s last exposure to the atmosphere. Both 3He and tritium are measured by gas mass spectrometry. Alternatively, tritium may be measured by gas counting with a detection limit of 0.05 to 0.08 tritium unit, where 1 tritium unit represents a 3H/H ratio of lxl0 18. A degassed water sample is sealed and stored for several months to allow the decay product 3He to accumulate in the container. The amount of 3He is then measured by mass spectrometry, yielding a detection limit of 0.001 to 0.003 tritium unit when 400-gram water samples are used. With this technique, the time since a water mass left the surface can be determined within a range from several months to 30 years. 

In many situations, the experimenter will prefer to buy labeled compounds from commercial suppliers rather than attempt to synthesize them. The radiochemical purity of such purchased compounds cannot be assumed. Radiation-induced selfdecomposition (radiolysis) can result in the formation of a variety of labeled degradation products, which must be removed before experimental use of the compounds. The extent of radiolysis depends on the nature of the labeled compound, how long it has been stored, and the manner of storage. Radiolysis is most significant with low-energy (3 emitters (especially tritium) since the decay energy is dissipated almost entirely with the compound itself. Furthermore, impurities involving other radionuclides may be present. 

Tritium is present naturally in the atmosphere, but the amounts were increased greatly in the late 1950s and 1960s by production and testing of thermonuclear weapons. Tritium is also a fission product and activation product produced in power reactors. Releases occur from reactors and reprocessing plants. Its use will increase greatly if fusion power is developed. 

Plutonium-239 and tritium for use as military explosives are the two major transmutation products. The nuclear process for Pu-239 production is the same as for energy generation, but there are some differences (a) metallic natural uranium clad with aluminum facilitates later dissolution for plutonium recovery, and the reactor operates at a relatively low temperature because of the aluminum clad and better heat transfer (due to the metallic natural uranium) (b) the irradiation cycle is limited to a few months to minimize the Pu-239 conversion to Pu-240 and Pu-241 and (c) a carbon or a heavy water moderator is used to increase the neutron efficiency. 

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