Radioactivity, plasma, decay

Fig. 1. Plasma radioactivity decay curves of apolipoproteins C-I, C-II, and C-in (compared with apo A-I) as a function of time...

In animals, diisopropyl methylphosphonate absorbed from the gastrointestinal tract is rapidly distributed to the tissues as indicated by the decay in peak plasma levels after absorption (Hart 1976 Ivie 1980). In mice, plasma radioactivity declined slowly from 15 minutes to 1 hour after exposure and then dropped rapidly during the next 2 hours. At the end of 24 hours, the label in the blood was 0.63 g/mL or 0.3% of the 173- g/mL peak concentration (Hart 1976). The radiolabel in the plasma of rats after 24 hours was nearly identical to that in mice (0.61 g/L) and was 0.4% of the peak concentration. Clearance of label was slower in dogs with 1.3% of the 276- g/L peak concentration present after 24 hours. 

Atmospheric pressure plasmas, just like most other plasmas, are generated by a high electric field in a gas volume. The few free electrons which are always present in the gas, due to, for example, cosmic radiation or radioactive decay of certain isotopes, will, after a critical electric field strength has been exceeded, develop an avalanche with ionization and excitation of species. Energy gained by the hot electrons is efficiently transferred and used in the excitation and dissociation of gas molecules. In a nonequilibrium atmospheric pressure plasma, collisions and radiative processes are dominated by energy transfer by stepwise processes and three-body collisions. The dominance of these processes has allowed many... 

The decay pattern of plasma radioactivity (Figure 1) indicated that a three-compartment model could be chosen for calculation of the kinetic data. The chosen model consists of a central compartment (Figure 2) into which dietary ascorbate is absorbed and from which it is eliminated unchanged. Two other compartments are equilibrated with the central compartment. In compartment 2 the metabolism is assumed to take place and from this compartment metabolites are eliminated. Compartment 3 is a deep pool that acts as a storage compartment. 

Early in the history of mass spectrometry (MS), large biomolecules were not analyzed because efficient methods to transport these molecules into the gas phase were unknown. Degradation typically occurred during vaporization of these nonvolatile molecules so that electron ionization of the intact molecular ion was not possible. Ionization by fast atom bombardment (FAB), field desorption (FD), secondary ionization mass spectrometry (SIMS), and plasma desorption (PD)" from the radioactive decay of Cf finally made the ionization and analysis of peptides possible. These latter techniques, although still used today, are not as popular as electrospray... 

Studies that have included measurement of urinary and fecal excretion of radioactivity have helped to confirm these studies of total volumes of distribution of the thyroid hormones. When excreted radioactivity is subtracted from injected radioactivity and the result divided by plasma radioactivity (all in the same units and corrected for radioactive decay), the quotient is taken as the volume of distribution. The problem with this approach is that it is difficult to ensure complete collection of excreta. 

Not to blow the new creation out of existence it is necessary to assume that after this brief period, activity of inflation energy had to be arrested, so as not to interfere with the subsequent evolution of the universe. Quantum mechanics is invoked to explain the conversion of inflationary energy into radiation, by a chance process, likened to radioactive decay, and which creates exactly the required random fluctuations to seed the growth of stars and galaxies within the dark-matter plasma. ... 

Archaeologists use inductively coupled plasma-mass spectrometry to help find the origin of artifacts containing lead. Different locations where lead is mined have different ratios of lead isotopes. Variation occurs because different isotopes of lead are produced by radioactive decay of and Th, whose occurrence varies... 

A gamma-ray line at 0.511 MeV results from the mutual annihilation of an electron and a positron, a particle-antiparticle pair. A number of radioactive decay chains (see Table I) result in the emission of a positron as a decay product, which will annihilate upon first encounter with an electron. Also of astrophysical importance is the production of electrons and positrons via the photon-photon pair-creation process. Such pair plasmas are found in the vicinity of compact objects, such as neutron stars and black holes, that are associated with heated accretion disks and relativistic flows and jets, within which particle acceleration is known to occur. Thus, relatively narrow lines of 0.511-MeV annihilation radiation are expected to arise in the interstellar medium through the decay of dispersed, nucleosynthetic radionuclides, while broadened, Doppler-shifted, and possibly time-variable lines may occur in the high-energy and dense environments associated with compact objects. 

Figure 1. Radioactivity in plasma (6), Details of the absorption phase are shown under the diagonal line and the rapid decay during the washout phase is to the right of the vertical line. (Reproduced, with permission, from Ref. 6. Copyright 1979, American Journal of Clinical Nutrition.)...

As the plasma moves through the centre of maximum curvature it is forced through the vacumn interface into a space-time domain of inverted chirahty and decreasing pressme. New matter (antimatter) emerges beyond the interface as an equilibrimn mixture of cosmic rays, in a soup of a-particles, as it is squirted out from the black hole into free space. Some of the newly formed nuchdes decay radioactively on moving into regions of lower curvatme and a set of nuclides, characteristic of local cmvatme, smvives. In the solar system the set consists of the 264 stable isotopes of 81 elements described before. The closed periodic sytem of nuclides and anti-nuclides, related by inversion, is consistent with the proposed mode of cosmic circulation of mass. 

The plasma decay curves of Apo C-I, C-II, and C-III shown on Fig. 1 seem comparable in normal subjects. The decay of the three Apo Cs is faster than that of Apo A-I, but even between the Cs, C-III decrease is quicker than Apo C-I and Apo C-II decrease. Radioactivity was determined directly in total plasma and in the VLDL, IDL+LDL, HDL and d 1.25 infranate without further processing of the... 

The curie (Ci) is a commonly used unit for measuring nuclear radioactivity 1 curie of radiation is equal to 3.7 X 10 decay events per second (the number of decay events from 1 g radium in 1 s). A 1.7-mL sample of water containing tritium was injected into a 150-lb person. The total activity of radiation injected was 86.5 mCi. After some time to allow the tritium activity to equally distribute throughout the body, a sample of blood plasma containing 2.0 mL water at an activity of 3.6 juCi was removed. From these data, calculate the mass percent of water in this 150-lb person. 

If an essential amino acid such as leucine is used to study protein turnover, the only sources are from dietary intake (I) or protein breakdown (B). Amino adds like leudne can be removed from the plasma, either for protein synthesis (S), oxidation (O), or incorporation into other metaboUc pathways after transamination/deamina-tion. In the case of leucine, this amino acid can also be completely oxidized in the human body to COj, allowing for the measurement of O as well. A simple model in the measurement of protein tumover/flux therefore takes into consideration the above factors so that flux (Q) is equal to I + B, which is in turn equal to S + O (i.e., Q = I + B = S-i- O). Isotope studies are used to derive these variables of protein turnover, since amino acid tracers can be used to measure Q and O, and if intake equals zero, then Q = B, and by subtraction, S = Q - Isotopes are molecules that share the same atomic number (protons), yet have different numbers of neutrons (atomic mass). Stable isotopes occur naturally and do not emit ionizing radiation, whereas radioactive isotopes undergo spontaneous decay. For these reasons, stable isotopes have become very popular in exercise research.Although useful, this model is very simplistic in that there are multiple amino acid pools mining over at very different rates. 

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