Radioactive counting

The next thing, of course, is to see whether things work out as they should. Do radioactive counts in fact distribute themselves according to the unique Gaussian defined by N and < = VN As Figure 10-3 shows, Rutherford and Geiger6 proved in 1910 that they do. 

C. By harvesting cells and using radioactive counting to determine which molecules gained enhanced... 

The discovery that mass spectrometry would soon usurp many of the tasks performed by radioactive counting was in itself serendipitous. It came about because a fundamental issue in cosmochemistry was at stake. Although variation in had... 

Soon after this discovery the harnessing of the technique to the measurement of all the U isotopes and all the Th isotopes with great precision immediately opened up the entire field of uranium and thorium decay chain studies. This area of study was formerly the poaching ground for radioactive measurements alone but now became part of the wonderful world of mass spectrometric measurements. (The same transformation took place for radiocarbon from the various radioactive counting schemes to accelerator mass spectrometry.)... 

The internal standard and analyte should be resolved chromatograph-ically to baseline (except for isotoplcally labelled samples when mass discrimination or radioactive counting are used for detection), elute close together, respond to the detection system in a similar way, and be present in nearly equal concentrations. 

For example, a) in (radioactivity) counting experiments a non-Poisson random error component, equal in magnitude (variance) to the Poisson component, will not be detected until there are 46 degrees of freedom ( ), and b) it was necessary for a minor component in a mixed Y-ray spectrum to exceed its detection limit by -50 , before its absence was detected by lack-of-fit (x, model error) (7). 

The range of applicability of equation 11.122 depends on the limits of detection of in the sample. The current maximum age attained by direct radioactivity counting is about 4 X 10" a. To measure residual radioactivity, the total carbon in the sample is usually converted to CO2 and counted in the gas phase, either as purified CO2 or after further conversion to C2H2 or CH4. To enhance the amount of counted carbon, with the same detection limit (about 0.1 dpm/g), counters attain volumes of several liters and operate at several bars. More recent methods of direct detection (selective laser excitation Van de Graaif or cyclotron acceleration) has practically doubled the range of determinable ages (Muller, 1979). 

Quantitative measurement of diffusional uptake and carrier-mediated transport of nutrients and drugs in experimental animals was greatly facilitated with the introduction of Olden dorfs brain uptake index (BUI) [42].Test and reference tracers are injected as an intraarterial bolus into the carotid artery of the anaesthetized animal. After 5 s the animal is killed and the brain is removed for radioactivity counting. This method measures the ratio of the unidirectional brain extraction, E, of the test substance and of the reference ([ H]-water, [ " C]-butanol), which are labelled with different isotopes, during a single passage through the brain capillary bed ... 

Dahlquist et al. also provided a useful appendix for converting radioactivity counting data into observed isotope effects. 

Fig. 6. Elution profiles of three alkyl 2-acetamido-2-deoxy- -D-glucopyranosides 4a (a. n=8 b. n=ll c. n=14) in gel filtration chromatography on sepharose 4B (exclusion 2.10 Da, exclusion volume 10 mL) monitored by and radioactivity countings (normed to 1.0 for reason of convenience). ( ) H countings of H-labelled phosphatidyl choline (x) C...

A gamma spectrometer system is used for radioactivity counting. 

Explain why it is easier to measure traces of radioactive, a-emitting isotopes of long half-life by ICP/MS rather than by radioactivity counting. 

B) ATP-14C adsorption to brain lipid. (%), 10 5M ATP-14C + 10 5M CaCl2 (O), same except EDTA-treated lipid . . . ., same—no lipid ordinate, radioactive counts/min. abscissa, time in hours... 

Fixed volumes of original solution and of collapsed foams were taken with a micro (overflow type) pipet and transferred to respective sample plates which were coated partly with silicone oil to prevent wetting. The solution was dried gradually with infrared ray lamp and then radioactive counts were determined. On the other hand, the concentration of the solution of collapsed bubbles was determined by weighing. The accuracy of this method was confirmed by drying the solution of known concentration at respective experiments. The loss of acetic acid... 

Signal to noise in absorbance, circular dichroism, fluorescence, and radioactive counting... 

An error in an experimental measurement is defined as a deviation of an observed value from the true value. There are two types of errors, determinate and indeterminate. Determinate errors are those that can be controlled by the experimenter and are associated with malfunctioning equipment, improperly designed experiments, and variations in experimental conditions. These are sometimes called human errors because they can be corrected or at least partially alleviated by careful design and performance of the experiment. Indeterminate errors are those that are random and cannot be controlled by the experimenter. Specific examples of indeterminate errors are variations in radioactive counting and small differences in the successive measurements of glucose in a serum sample. 

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