Radioactive zones detection

Thus, for the investigation of buried polymer interfaces, several techniques with molecular resolution are also available. Recently NMR spin diffusion experiments [92] have also been applied to the analysis of a transition zone in polymer blends or crystals and even the diffusion and mobility of chains within this layer may be analyzed. There are still several other techniques used, such as radioactive tracer detection, forced Rayleigh scattering or fluorescence quenching, which also yield valuable information on specific aspects of buried interfaces. They all depend very critically on sample preparation and quality, and we will discuss this important aspect in the next section. 

In Chapter 7, approaches for visualization of zones in chromatograms are discussed, including use of nondestructive and destructive dyeing reagents, fluorescence quenching on layers with a fluorescent indicator, and densitometry. In Chapter 8, additional detection methods, such as those used for biologically active and radioactive zones, as well as the recovery of separated, detected zones by scraping and elution techniques are covered. 

A phosphor screen can be used like an autoradiography film to detect radioactive zones on PLC plates. The available screens are sensitive to x-rays and beta and gamma emissions from isotopes such as H, bij 32p 33p -pjjg screen captures... 

There are two ways to operate the stop-flow mode. The by-level mode, which is based upon the defined count zone(s), operates by signaling the instalment to continue running until a radioactive peak above a designated level is detected. The instrument will then stop and count the predefined fraction (in seconds), which is defined in the count zone. A second way to operate the stop-flow mode is the by-fraction mode. The instalment will stop and count every fraction (in seconds) within the predefined count zone, regardless of whether any radioactivity is detected or not. The fraction size in the stop-flow mode and the volume of liquid scintillant used for counting can be automatically calculated by the instalment or the parameters can be defined by the user. 

Besides increasing the sensitivity of detection methods, labeled molecules may be used to establish the identity of an unknown spot. If, after addition of a known, labeled substance to an unknown mixture of unlabeled substances, chromatography results in a spot in which the radioactive zone coincides in every detail with an unknown spot, also... 

By contrast, when Kr-85 was injected into the oil feedstock no radioactivity was detected in the combustion chamber to within one inch of the oil stream (injector) (Fig. 11). This pattern is also illustrated by the data in the restriction ring however, now the oil-black has expanded to where it occupies about half of this cylindrical volume. At the exit of the restriction violent turbulence causes an almost explosive expansion of the oil-black across the diameter of the tunnel. The gradient of the radioactivity from the wall to the center of the reactor smooths out beyond the reaction zone indicating homogeneous distribution of all constituents. 

After a pulse-label of one hour with [ C] glucose, and a further hour of chasing in the absence of label, a single radioactive zone was detected on the... 

Radioactive zones can be detected on thin layers by film autoradiography, digital autoradiography with a multiwire proportional chamber, use of charged-coupled devices, or bioimaging/phosphor imaging techniques. These methods differ in terms of factors such as simplicity, speed, sensitivity, resolution, linear range, and accuracy and precision of quantification, and the method of choice depends on the available instrumentation, the type of experiment, and the information needed. 

TLRC can be used for animal, human, and plant metabolism analysis radiochemical purity and stability assessment toxicology and biochemical studies and separation, detection, and quantification of separated radioactive zones of all compound classes. Traditional film autoradiography and LSC continue to be widely used, but phosphor imaging and layer scanners are being increasingly applied. The instruments for these methods are highly automated and... 

Cl-Araoh idon io acid (AA) conversion by rabbit vasculature (see text for methods), The radioactive zones were detected by auto radiogra phy Hatched bars indicate the location of standard compounds and the Rf values are in parenthesis ... 

Notes 2- In order to Insure ready Identification of the components (except Po) whose concentrations are very low (or carrier-free) a simultaneous calibration run with an Inactive mixture of the same components may be made on an unused portion of the same paper. An alternative method Is to spot each component separately using KI as a strealc reagent. In the calibration run, concentrations are high enough to permit detection with streak reagents. The radioactive zones will be In the same relative positions as the Inert zones. 

Radiocarbon and tritium can be used to determine the approximate age of water masses. Three age—depth zones were deduced from the distribution of tritium and C in the groundwater. As shown in Fig. 19 B, there is an upper zone containing tritium that extends from the water table down to a depth of 6—21 m. The levels of tritium indicate that the source is probably fallout from atmospheric nuclear-fission bomb tests. Inasmuch as the testing of fission devices began in 1954, the age of water in this depth zone is probably less than 25 yr. An intermediate zone in which tritium is absent but radiocarbon is detected extends to a depth of 75m below the upper zone. If the possibility of loss of by mechanisms other than radioactive decay is neglected, a residence time of 10 —10 yr. is indicated. The deepest zone contains no detectable radiocarbon. It is in this zone that the regional groundwater flows system moves to the northeast, as previously indicated on section A—A. ... 

Fast moving neutrons emitted from a radioactive source (usually Radium-Berrylium or Americium-Beryllium) upon collision with a particle having mass nearly equal to its own, like hydrogen atom in the soil, release their energy and gets thermalized or slowed down. The thermalized neutrons are detected by a detector and recorded on a scalar. Usually BFg gas is used as detector of slowed down neutrons. Increased thermalization indicates higher water content of the soil. The zone of influence is normally about 15-20 cm arormd the detector. 

Detection of separated zones by radioactivity measurement gained considerable... 

Other detection methods include radioactivity for labeled compounds (a non-destructive physical method) and biological methods (e.g., immunochemical or enzymatic reactions). Coupled detection methods such as TLC/ infrared spectrometry (TLC/IR) or TLC/mass spectrometry (TLC/MS) can be used for confirmation of zone identity as well as quantification in some cases. 

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