Nuclides origin

Although the results on counterion distributions in nucleic acid systems from X-ray crystallography are fragmentary, there exist several NMR studies about metals in DNA systems. - The data from NMR experiments proved to be difficult to interpret. The quadrupolar relaxation mechanism of this nuclide, originating from the electric field gradients, obfuscates the results, but in general the data are consistent with the counterion condensation theory. 

Successful age determinations are possible providing (1) the rock or mineral has remained closed and changes in the numbers of parent and daughter atoms are due to nuclear decay only (2) the decay constant is known accurately (3) the number of daughter nuclides originally present (at time t = 0) is known and (4) the numbers of daughter and parent atoms can be measured accurately. 

Nuclear-physical methods ai e the basic ones in controlling environmental pollution which results from nucleai -power complexes and power plants work. Oil and gas production leads to the extraction of radio nuclides of natural origin in considerable amounts, which later spread from oil-slimes and water wastes in the neighborhoods of oil and gas producing entei prises. Similaidy, toxic and radioactive elements can pollute environment in case of mineral deposits extraction. 

Decay of the nuclide itself. The conceptually simplest approach is to take a known quantity of the nuclide of interest, P, and repeatedly measure it over a sufficiently long period. The observed decrease in activity with time provides the half-life to an acceptable precision and it was this technique that was originally used to establish the concept of half-lives (Rutherford 1900). Most early attempts to assess half lives, such as that for " Th depicted on the front cover of this volume, followed this method (Rutherford and Soddy 1903). This approach may use measurement of either the activity of P, or the number of atoms of P, although the former is more commonly used. Care must be taken that the nuclide is sufficiently pure so that, for instance, no parent of P is admixed allowing continued production of P during the experiment. The technique is obviously limited to those nuclides with sufficiently short half-lives that decay can readily be measured in a realistic timeframe. In practice, the longest-lived isotopes which can be assessed in this way have half-lives of a few decades (e.g., °Pb Merritt et al. 1957). 

Polyak VJ, McIntosh WC, Provencio P, Giiven N (1998) Age and Origin of Carlsbad Caverns and related caves from " °Ar/ Ar of alunite. Science 279 1919-1922 Porcelli D, Swanzenski PW (2003)The behavior of U- and Th- series nuclides in groundwater. Rev Mineral Geochem 52 317-361... 

The origin of chemical elements has been explained by various nuclear synthesis routes, such as hydrogen or helium burning, and a-, e-, s-, r-, p- and x-processes. "Tc is believed to be synthesized by the s (slow)-process in stars. This process involves successive neutron capture and / decay at relatively low neutron densities neutron capture rates in this process are slow as compared to /1-decay rates. The nuclides near the -stability line are formed from the iron group to bismuth. 

Radiocerium can also gain entry into food crops through irrigation or flooding of fields with waters containing these nuclides. However, only small amounts of radiocerium enter food crops by this route compared to the more soluble radioelements that have been studied. Cerium-144 originating from both the Hanford reactors and worldwide... 

Three primary problem areas exist in dating groundwater. These are (1) Formulation of realistic geochemical-hydrodynamic models needed to interpret data which are generated by field and laboratory measurements, (2) development of sensitive and accurate analytical methods needed to measure trace amounts of various stable and unstable nuclides, and (3) theoretical and field oriented studies to determine with greater accuracy the extent and distribution of the subsurface production of radionuclides which are commonly assumed to originate only in the atmosphere. 

The vacancy left in the low-energy K-shell will be filled by an electron from a higher level with the resultant emission of radiations of extra nuclear origin, X-rays, which are distinguished from the accompanying nuclear y radiation. It should be noted that the n p criterion is the same for both positron and electron capture processes and it is not unusual to find both occurring with different atoms of the same nuclide. 

Russell WA, Papanastassiou DA, Tombrello TA (1978) Ca isotope fractionation on the earth and other solar system materials. Geochim Cosmochim Acta 42 1075-1090 Sahijpal S, Goswami JN, Davis AM, Grossman L, Lewis RS (1998) A stellar origin for the short-lived nuclides in the early Solar System. Nature 391 559-561... 

The exposure to ionizing radiation from natural sources is continuous and unavoidable. For most individuals, this exposure exceeds that from all human-made sources combined (UNSCEAR 2000a). The two main contributors to natural radiation exposures are high-energy cosmic ray particles incident on the earth s atmosphere and radioactive nuclides that originate in the earth s crust and are present everywhere in the environment, including the human body itself. 

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