Making radioactive isotopes

Many artificial (likely radioactive) isotopes can be created through nuclear reactions. Radioactive isotopes of iodine are used in medicine, while isotopes of plutonium are used in making atomic bombs. In many analytical applications, the ratio of occurrence of the isotopes is important. For example, it may be important to know the exact ratio of the abundances (relative amounts) of the isotopes 1, 2, and 3 in hydrogen. Such knowledge can be obtained through a mass spectrometric measurement of the isotope abundance ratio. 

Because exposure to radiation is a health risk, the administration of radioactive isotopes must be monitored and controlled carefully. Isotopes that emit alpha or beta particles are not used for Imaging, because these radiations cause substantial tissue damage. Specificity for a target organ is essential so that the amount of radioactive material can be kept as low as possible. In addition, an Isotope for medical Imaging must have a decay rate that is slow enough to allow time to make and administer the tracer compound, yet fast enough rid the body of radioactivity in as short a time as possible. 

Although there are three Rji isotopes in the U- and Th-decay series, only is sufficiently long lived tm= 3.8 days) to be a useful estuarine tracer. Radioactive decay of Ra continuously produces Rn, which because of its short half-life is generally in secular equilibrium in seawater. Being chemically non-reactive except for very weak Van der Waals bonding makes this isotope a unique marine tracer in that it is not directly involved in biogeochemical cycles. 

Another isotopic anomaly, discovered in Allende inclusions, concerns magnesium, for which an intrinsically low abundance in these samples makes its isotope ratios sensitive to small effects. Certain of the inclusions show a correlation between 26Mg and 27 Al, indicating an origin of excess 26Mg from radioactive decay of 26 A1 (mean life 1 Myr), the existence of which had previously been postulated as a heat source for meteorite parent bodies (Fig. 3.32). Other short-lived activites that seem to have been alive in the early Solar System are 10Be (mean life 2.2 Myr) from a correlation of 10B with 9Be, and 41Ca (mean life 0.15 Myr) from a correlation of... 

ISOTOPES Cs-133 is the only stable isotope of cesium, and it makes up all of the naturally occurring cesium found in the Earth s crust. In addition to Cs-133 there are about 36 radioactive isotopes of Cs, most of which are artificially formed in nuclear reactors. All are produced in small numbers of atoms with relatively short half-lives. The range of Cs isotopes is from Cs-113 (amu = 112.94451) to Cs-148 (amu = 147.94900). Most of these radioisotopes produce beta radiation as they rapidly decay, with the exception of Cs-135, which has a half-life of 3x10 yr, which makes it a useful research tool. Cs-137, with a half-life of 33 years, produces both beta and gamma radiation. 

ISOTOPES There are 27 isotopes of vanadium. Only vanadium-51 is stable and makes up 99.75% of the total vanadium on Earth. The other 0.25% of the vanadium found on Earth is from the radioisotope vanadium-50, which has such a long half-life of 1.4x10+ years that it is considered stable. The other radioactive isotopes have half-lives ranging from 150 nanoseconds to one year. 

ISOTOPES There are 30 isotopes of manganese, ranging from Mn-44 to Mn-69, with only one being stable Mn-55 makes up 100% of the element in the Earth s crust. All the other isotopes are artificially radioactive with half-lives ranging from 70 nanoseconds to 3.7x10 years. Artificial radioisotopes are produced in nuclear reactors, and because most radioactive isotopes are not natural, they do not contribute to the elemenfs natural existence on Earth. 

ISOTOPES There are 38 isotopes of zinc, ranging in atomic weights from Zn-54 to Zn-83. Just four of these are stable, and those four, plus one naturally radioactive isotope (Zn-70) that has a very long half-life (5x10+ years), make up the element s existence on Earth. Their proportional contributions to the natural existence of zinc on Earth are as such Zn-64 = 48.63%, Zn-66 = 27.90%, Zn-67 = 4.10%, Zn- 68 = 18.75%, and Zn-70 = 0.62%. All the other isotopes are radioactive and artificially produced. 

ISOTOPES There are a total of 59 radioactive isotopes for bismuth, ranging in half-lives from a few milliseconds to thousands of years. At one time it was thought that there was just one stable isotope (Bi-209), but it was later found that Bi-209 is radioactive with a half-life of 19,000,000,000,000,000,000 years. Such a long half-life means that BI-209 has not completely disintegrated and Is still found In nature, and Is thus considered stable. In this case, BI-209 makes up 100% of Bismuth s natural abundance. 

Nuclear incineration of the gluttonous white dwarf thus synthesises a considerable amount of nickel-56 (0.5-0.6 Mq) and radioactivity left over after its departure makes it shine with dazzling brilliance, like some lavish stellar requiem. This radioactive isotope is the source of the exceptional luminosity of type la supernovas, both in the optical region, as has already been observed, and in gamma rays, as yet only a prediction. 

Inductively coupled-plasma mass spectrometers (ICPMS) are relatively new to cosmochemistry, although they have been widely used in other fields. The plasma source makes most of the periodic table accessible to measurement, so several radioactive isotope systems that used to be impractical to use for chronology are now routinely used (see Chapters 8 and 9). 

Recovery of technetium, present as pertechnetate in aqueous acidic solution, is of utmost importance because of its long half-life of 2.13 x 105 years and its relative mobility in the environment. The close relation between TCO4 and the isoelectronic perrhenate Re04 makes the latter a widely used model for artificially produced technetium, which only possesses radioactive isotopes. 

An isotope of carbon called carbon-14 offers a glimpse of how humans may have lived thousands of years ago. The radioactive isotope decays steadily to become nitrogen-14 in a way that is similar to the decay of potassium into argon, making it useful for dating plants, bones, and other organic materials that once contained... 

Compounds such as 40 are valuable as scintillators that convert the radiation emitted by radioactive isotopes into visible light, which can easily be measured [155], Substances such as 24 are preferentially absorbed by fungi, making them easily detectable in the skin or other types of cells allowing accurate clinical diagnosis and control [156],... 

Chlorine-36 is an isotope that can be measured by specialized laboratories and its sample collection in the field is simple. It is a radioactive isotope with a half-life of 3 x 105 years, making it useful for groundwater age determinations in the range of 105-106 years. 

Powerful methods for the determination of diffusion coefficients relate to the use of tracers, typically radioactive isotopes. A diffusion profile and/or time dependence of the isotope concentration near a gas/solid, liq-uid/solid, or solid/solid interface, can be analyzed using an appropriate solution of - Fick s laws for given boundary conditions [i-iii]. These methods require, however, complex analytic equipment. Also, the calculation of self-diffusion coefficients from the tracer diffusion coefficients makes it necessary to postulate the so-called correlation factors, accounting for nonrandom migration of isotope particles. The correlation factors are known for a limited number of lattices, whilst their calculation requires exact knowledge on the microscopic diffusion mechanisms. 

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