Counting gamma-ray

Figure 2B.1 Typical curve of gamma-ray counting efficiency vs. energy for Ge detector...

Carefully swirl to mix. Be certain to cover the bottom evenly, but do not swirl the solution up onto the container walls. The total initial volume is 5.0 mL. Screw the lid on the container and carefully place in position in the germanium gamma-ray detector counting chamber it should be centered and level. Count twice for a sufficient time period to accumulate 2000 counts (typically 100 s). Check to confirm that at least 2,000 counts have been accumulated at each of the peaks used for calibration. Collect the gross gamma-ray count rates for the full-energy peaks in Data Table 2B.1. 

Data Table 2B.2 Calculated Gamma-Ray Counting Efficiencies... 

Problem A purified radium sample is counted for gamma rays, 5.2 days after the chemical separation of barium sulfate from a water sample. (5.2 days is the interval from the separation time to the mid-time of the counting period). What fraction of the activity of 226Ra is observed in the gamma ray count ... 

Sample volume (V) Chemical Yield Fraction (Y) Ingrowth factor (D) Net gamma ray count rate (R) Branching ratio (Fj) 0.358 0.448... 

Transfer an aliquot of the sample into a container for which the detector has been calibrated in terms of gamma-ray counting efficiency (count per gamma-ray emission), as in Experiment 2B. After transferring the solution... 

A sample from an unknown origin comes into the laboratory. At the first gamma-ray count you observe a large amount of 239Np. What qualitative conclusion could you make ... 

Cohen, B.L. Liquid scintillation versus gamma ray counting in radon measurement with charcoal. Am. J. Publ. Health, 81(12) (1991)... 

Powdered samples of the materials to be analyzed and standards, all of similar weight, are pressed into pills of constant dimension. For gamma-ray counting they are guided to a reproducible position above the detector. This ensures that the solid angle of each sample in relation to the detector is controlled. The maintenance of constant pill size is also involved in the following item. 

Figure 32-5 is a schematic of a well-type scintillation counter that is used for gamma-ray counting. I fere, the sample is contained in a small vial and placed in a cylindrical hole, or well, in the. scintillating crystal of the counter. 

A special benefit of counting radiations in coincidence is that the process permits the absolute measurement of the activity of the radionuclide. For the beta-particle counting efficiency sp and the gamma-ray counting efficiency y (in count/disintegration), the activity A is related to the three count rates. The count rate Rp of beta particles in the beta-particle counter, the count rate Ry of gamma rays in the gamma-ray counter, and the coincidence count rate Rpy (in count/s) yield A (in Bq) by ... 

Uncertainty evaluation for gamma-ray spectral analysis is more complicated than for most other radiation measurements. First, gamma-ray counts for one... 

Fig. 14. Curves for detector gamma ray counting rate vs. neutron time of flight for 35-22 meters for a l/ = 103.3 barns/ atom thickness sample of normal Ag at the detector position (D only) and for foils having l/ = 103.3 bams/atom thickness at both detector and transmission positions. The measurements were made using the Columbia Nevis velocity spectre-meter system with 0,25 xsec detection interval gates for / O.Ol (isec/m resolution.

The counting rates of the Beacon rocks appear to depend on the concentration of organic matter they contain. For example, the average gamma-ray counting rate of Devonian rocks of the Beacon... 

Table 11.5 Average gamma-ray counting rates relative to ice based on airborne measurements in the Transantarctic Mountains...

Fig. 11.18 The gamma-ray counting rate of snow and firn in a pit close to South Pole Station decreases with depth but rises at 1.4, 3.1, and 4.4 m. These peaks represent fallout from the testing of nuclear weapons between 1970/71 at Mururoa Island (1.4 m), thermonuclear detonations in September of 1961 (3.1 m), and tests that ended in 1958 (4.4 m) (Picciotto and Wilgain 1963). The background activity decreased with increasing depth because the detector was increasingly shielded from cosmic rays. The year of deposition of the snow was determined by counting layers in the walls of the pit (Adapted from Dreschhoff and Zeller 1978)...

Colorimetric determinations have been used occasionally In the past by radlochemlsts (Cf. ref. M6, H16). It Is expected that as the techniques requiring the use of very small amoxuits of carrier material, such as four pi beta particle, or gamma ray counting, become more widely used, the high sensitivity and precision of colorimetric methods will become more attractive to radlochemlsts. The normal, limits of sensitivity for colorimetric... 

Fig. 1.20. Gamma-ray counting (a) single-channel (b) coincidence system.

FIGURE 5.3 Frequency distribution of the gamma-ray counting rate of drill cores for the depth interval of 0-3900 m n, number of samples 1, metabasites 2, gneisses. A/ter a figure from Bucker et al. (1989). 

The measurement scale of the gammalog is the American Petroleum Institute (API) unit. This reference standard allows consistent comparisons between different gamma-ray counting devices. The API standard is a calibration test pit at the University of Houston. The American Petroleum (API) facility is constructed of concrete with an admixture of radium to provide uranium decay series, monazite ore as a source of thorium and mica as a source of potassium. The facility has 4.07% K, 24.2 ppm Th and 13.1 ppm U (Ellis, 1987). The API standard gives 200 API, equal to twice the mean of an average shale. Table 5.8 gives mean API values for some rock-forming minerals. 

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