Tritium abundance

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 ... 

Properties of T2O. Some important physical properties of T2O are Hsted in Table 2. Tritium oxide [14940-65-9] can be prepared by catalytic oxidation of T2 or by reduction of copper oxide using tritium gas. T2O, even of low (2—19% T) isotopic abundance, undergoes radiation decomposition to form HT and O2. Decomposition continues, even at 77 K, when the water is fro2en. Pure tritiated water irradiates itself at the rate of 10 MGy/d (10 rad/d). A stationary concentration of tritium peroxide, T2O2, is always present (9). AH of these factors must be taken into account in evaluating the physical constants of a particular sample of T2O. 

When specifically labelled compounds are required, direct chemical synthesis may be necessary. The standard techniques of preparative chemistry are used, suitably modified for small-scale work with radioactive materials. The starting material is tritium gas which can be obtained at greater than 98% isotopic abundance. Tritiated water can be made either by catalytic oxidation over palladium or by reduction of a metal oxide ... 

The overall reaction releases 3 X 108 kj for each gram of deuterium consumed. That energy corresponds to the energy generated when the Hoover Dam operates at full capacity for about an hour. Additional tritium is supplied to facilitate the process. Because tritium has a very low natural abundance and is radioactive, it is generated by bombarding lithium-6 with neutrons in the immediate surroundings of the reaction zone ... 

The intracellular distribution of steroid hormone receptors has long been the object of controversy. The first theoretical formulation on the intracellular location of the ERs was elaborated by Jensen in 1968 and is known as the two-step theory. Its execution was based entirely on biochemical observations obtained by means of tritium-marked estradiol. The ERs, in cells not exposed to hormones, are found abundantly in the soluble cell fraction, or cytosol (Fig. 1.1). Treatment with hormones confines the receptors to the particulated or nuclear fraction and causes their disappearance from the cytosol. The two-step theory established that the receptor is found in the cytoplasm naturally and upon the arrival of a hormone it is transformed into a complex hormone-receptor (first step) capable of translocating itself to the nucleus and of modifying gene expression (second step). 

Water is a mixture of varying isotopic composition (Franks, 2000). In addition to the two most common isotopes, 160 and there are two stable oxygen isotopes (170, lsO), one stable hydrogen isotope (2H, deuterium), and one radioactive hydrogen isotope (3H, tritium, half-life = 12.6 years). Water also contains low concentrations of hydronium (H30+) and hydroxide ions (OH-) and their isotopic variants. In total, water consists of more than 33 chemical variants of HOH however, these variants occur in relatively minor amounts (Fennema, 1996). Table II gives the natural abundance isotopic composition of the four major water species. 

The comprehensive dedicated research ultimately made it possible to decode the patterns of labelling in almost any type of tritium labelled compound at low isotopic abundance (e.g., 3 x 10 4 to 3 x 10 2 per cent. 3H per site) with the aid of 3H-NMR directly, rapidly, reliably and non-destructive analytical means. Since, 1971, the 3H-NMR spectroscopy, utilizing only millicurie (mCi) quantities of radioactivity, emerged as a most useful analytical tool for the study of tritium labelled compounds. 

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. 

Examples of isotopes are abundant. The major form of hydrogen is represented as H (or H-1), with one proton H, known as the isotope deuterium or heavy hydrogen, consists of one proton and one neutron (thus an amu of 2) and is the isotope of hydrogen called tritium with an amu of 3. Carbon-12 ( C or C-12) is the most abundant form of carbon, though carbon has several isotopes. One is the C isotope, a radioactive isotope of carbon that is used as a tracer and to determine dates of organic artifacts. Uranium-238 is the radioactive isotope (Note The atomic number is placed as a subscript prefix to the element s symbol—for example, —and the atomic mass number can be written either as a dash and number fol-... 

Until 1931 it was assumed that hydrogen consisted of only one isotope. Urey et al. (1932) detected the presence of a second stable isotope, which was called deuterium. (In addition to these two stable isotopes there is a third naturally oc-curing but radioactive isotope, H, tritium, with a half-life of approximately 12.5 years). Rosman and Taylor (1998) gave the following average abundances of the stable hydrogen isotopes ... 

Deuterium is abundant, naturally occurring and in wide use now as D20 in heavy-water-mo derated reactors. Tritium is a radioactive isotope with a 12.3-year half-life and does not occur in natnre. Tritium emits an electron and decays to stable helium-3. 

In other words, 1 MBq of tritium contains about 3 ng of tritium. Thus, an important feature of radionuclides becomes apparent—we routinely work with extremely small quantities of material. Pure samples of radioisotopes are called carrier free. Unless a radionuclide is in a carrier-free state, it is mixed homogeneously with the stable nuclides of the same element. It is, therefore, desirable to have a simple expression to show the relative abundances of the radioisotope and the stable isotopes. This specification is readily accomplished by using the concept of specific activity, which refers to the amount of radioactivity per given mass or other similar units of the total sample. The SI unit of specific activity is Bq/kg. Specific activity can also be expressed in terms of the disintegration rate (Bq or dpm), or... 

Tritium (tm = 12.3 y) is used to date relatively recent samples in a technique similar to carbon-14 dating. For example, tritium is used to determine the age of groundwater. The ratio of and 3H abundances in rain and snow is stable over time. However, once the water seeps into the ground, it cannot mix with the water in the atmosphere, and the tritium nuclei that decay are not replaced. To determine the age of groundwater, we can measure the concentrations of both tritium and its daughter nuclide, helium-3. The age of the groundwater can help determine properties such as the depth of its source. 

As mentioned in Section 2.5, there are three isotopes of hydrogen protium, or ordinary hydrogen (]H) deuterium, or heavy hydrogen ( H or D) and tritium (3H or T). Nearly all (99.985%) the atoms in naturally occurring hydrogen are protium. The terrestrial abundance of deuterium is only 0.015 atom %, and tritium is present only in trace amounts (—10—16 atom %). 

To build heavier elements than He4, collisions of rare deuterium, tritium, He3 with He4 are required. But, most of deuterium, tritium and He3 are burned to He4. In fact, very little synthesis of heavier elements will be done. More precisely, we will see that the calculated abundances of He3 and deuterium are of the order of 10-4 to 10—5, while those of Li7 are of the order of 10-9 to... 

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