Radioactive flux

Several methods are available today to test candidate ion channel active drugs (ICADs) electrophysiology (patch clamp), binding assays, radioactive flux assays, membrane potential-sensitive fluorescent dyes, ion-sensitive dyes, and voltage sensing based on fluorescence resonant energy transfer (FRET). 

If an intensifier, such as the 85 mm presented here, is now replacing the screen, a relative gain of the order of x50 is obtained which results in a conversion factor of 1 to 7.5 (1 incident X photon --> 7.5 electrons). This conversion efficiency not only resolves the quantum sink problem but also increases the light level significantly to compensate for the low gamma fluxes obtained from radioactive sources. 

The analysis of steady-state and transient reactor behavior requires the calculation of reaction rates of neutrons with various materials. If the number density of neutrons at a point is n and their characteristic speed is v, a flux effective area of a nucleus as a cross section O, and a target atom number density N, a macroscopic cross section E = Na can be defined, and the reaction rate per unit volume is R = 0S. This relation may be appHed to the processes of neutron scattering, absorption, and fission in balance equations lea ding to predictions of or to the determination of flux distribution. The consumption of nuclear fuels is governed by time-dependent differential equations analogous to those of Bateman for radioactive decay chains. The rate of change in number of atoms N owing to absorption is as follows ... 

All NAA experiments are conducted in two steps irradiation and counting as indicated in Figure 1. Samples are made radioactive by placing them in a neutron field. Typically a research nuclear reactor provides the necessary neutron flux. Elements present in the sample capture neutrons, and often become radioactive isotopes. This part of the experiment is known as irradiation. A typical irradiation in a reac-... 

A scram causes the control rods to drop into the core, absorb neutrons and stop the chain reaction. Some rods perform both controlling and scram functions. The control rods are raised to increase the neutron flux (and power) or lowered to reduce it by magnetic jacks (W and CE) or a magnetic "clamshell" screw (B W). The chemical volume and control system (CVCS - not siiown) controls the water quality, removes radioactivity, and varies the reactivity by controUing the amount of a boron compound that is dissolved in the water - called a "poison." Thus, a PWR coiiirols reactivity two ways by the amount of poison in the water and by moving the control rods. 

Since the amount of fissile material in the fuel assemblies is only about 3 percent of the uranium present, it is obvious that there cannot be a large amount of radioactive material in the SNF after fission. The neutron flux produces some newly radioactive material in the form of uranium and plutonium isotopes. The amount of this other newly radioactive material is small compared to the volume of the fuel assembly. These facts prompt some to argue that SNF should be chemically processed and the various components separated into nonradioac-tive material, material that will be radioactive for a long time, and material that could be refabricated into new reactor fuel. Reprocessing the fuel to isolate the plutonium is seen as a reason not to proceed with this technology in the United States. 

When a nucleus is placed in a flux of neutrons, it may capture another neutron. It thus is often unstable toward further decay by j3 -emission. The induced radioactivity is critical to the study of chemical consequences of neutron capture, since so few of these new nuclei are produced that generally they cannot be observed by any other means. This radioactivity is not, however, a part of the phenomenon which we wish to observe and, moreover, is occasionally a distraction. 

The total radioactivity, Ag, of a specified nuclide in a target containing N atoms of the appropriate isotope, irradiated in a flux, /, of neutrons for t seconds and allowed to decay for T seconds after the end of the irradiation, is given by... 

Of these radioactive atoms, a fraction Fj are produced in a specified form the value of Fj may depend on the irradiation temperature, T, the y-flux, and consequently on the irradiation time, t. This fraction may be altered by subsequent thermal treatment and by a variety of spurious reactions, to an extent expressible as T, y. ..). Thus, the activity of a given species, i, can be expressed as... 

Figure 16. Schematic representation of a degassing magma reservoir in a physical steady-state (mass M of magma constant). ( ) and [Ik] denote fluxes and radionuclide Ik concentrations, respectively. Indices 0, L, G, E, I, R, refer to deep undegassed magma (in radioactive equilibrium), degassed lava, gas phase, and erupted, intended, or recycled degassed magma, respectively (after Gauthier and Condomines 1999).

Steady state vs. non-steady state profiles. Determination of " Th deficits is relatively simple. Production is balanced against decay and export, with the expectation that in the absence of the latter, " Th should be in radioactive equilibrium with and the flux is given by the integral term in Equation (9) ... 

As discussed elsewhere in this volume, another field where the use of U-series disequilibria has proven to be very useful is the study of chemical transport in waters, either marine (see Cochran and Masque 2003 Henderson and Anderson 2003), estuarine (Swarzenski et al. 2003) or continental waters. In the continental domain, in addition to characterization of transfer processes related to groundwater flows (Porcelli and Swarzenski 2003), radioactive disequilibria have also helped in constraining chemical exchanges between particulate, dissolved and colloidal loads of waters, as well as the origin of chemical fluxes carried by waters. 

The refrigerator itself is shielded with a 20 cm thick low activity lead and a 10 cm thick borated PET. Nitrogen is fluxed between the external lead shield and the cryostat to avoid any Rn contribution to the detector background. Measurements of residual radioactivity have been carried out on several Pb samples [103], For the roman lead, a contamination lower than 4 mBq/Kg (in 210Pb) is to be compared with 250 mBq/Kg of a modem lead (Johnson Mattey). 

Capsules were equilibrated with a tracer solution overnight. A capsule pellet (0.2-0.5 ml) was then placed in 5 ml test buffer (PBS or RPMI-1640 medium, Gib-co/BRL, New York, NY) on a shaker and a 0.2-ml aliquot was immediately sampled by a screen-protected pipette with further samples being taken over the next 700 s. The tracer quantity was assayed using the methods described below. A final sample was taken after the capsules has been in contact with the buffer for several hours (equilibrated tracer quantity) and the increment to the tracer concentration at each time was calculated. From the progress of tracer to equilibrium on a semilog plot a slope denoted as the zero -order rate flux constant was obtained and has been used as a measure of capsule permeability. [3H] -Glucose (580 daltons),insulin (6.2 kDa), and ovalbumin (45 kDa) have been used as tracers. Radioactivity was measured by means of a Packard 2000CA Liquid Scintillation Counter (Packard Instruments,... 

From the earliest measurements of tissue calcium, it was clear that total calcium is largely a measure of stored calcium. Through the years, scientists have used a variety of indirect measures of [Ca2+]j. These include shortening of or tension in muscles secretion from secretory cells the activity of Ca2+-dependent enzymes, most notably glycogen phosphorylase and flux of K+, or K+ currents, as a reflection of Ca2+-activated K+ channels. In addition, investigators often use the radioactive calcium ion [45Ca2+] as an indirect indicator of Ca2+ concentrations and Ca2+ movements. 

Nuclear bombardment reactions in which the product is radioactive constitute the basis of radioactivation analysis (p. 456). Although in principle any bombardment-decay sequence may be used the analyst is largely concerned with thermal neutron activation. Equation (10.13) relates the induced activity to the amount of the parent nucleide (analyte). However, practical difficulties arise because of flux inhomogeneities. It is common therefore to irradiate a standard with very similar characteristics alongside the sample, e.g. for a silicate rock sample a standard solution would be evaporated on to a similar amount of pure silica. On the assumption that identical specific activities for the analyte are then induced in the sample and standard, the amount w2 of analyte is readily calculated from... 

A sample was irradiated in a neutron flux and the induced radioactivity monitored after it was removed from the flux. The fully corrected results are presented below. 

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