A recent review of neutron activation analysis (NAA) applications in forensic science by Guinn has again focused attention on the utility of barium and antimony determinations on residues removed from the hands as indication of recent gun firing by the individual. This method has been well established and is in routine use by state, local, and federal law enforcement groups in the United States and by governmental agencies in other countries. Increasing use of this technique has made reduction in sample analysis time imperative.
Accurate determination of the calibration constant is essential for the reliable determination of indoor radon air concentrations using alpha-track detectors. One possible source of error in the application of this method of radon assay is an effect of air density on the calibration factor. Such an effect, if present, could contribute to systematic errors in radon measurements where the calibration facility and the location measured were at different altitudes above sea level. To investigate this question, cellulose nitrate alpha-track detectors were exposed to known air concentrations of 222Rn over a range of air pressure in a systematic study of the effect of simulated altitude on the calibration constant (track density)/(integrated radon exposure). The values obtained for the calibration constant at known air-pressure values were used to establish correction factors as a function of equivalent altitude for this alpha-track method of radon assay. This correction may then be applied to compensate for the effect of altitude on radon-in-air determinations by this method. Altitude effects were evaluated for two detector configurations (the closed-can geometry and the open, or bare-detector geometry). The calibration constants (tracks cm-2) (kBq h m-3)-1 obtained exhibit an inverse relationship with air pressure (i.e., vary directly with altitude). The results indicate (as an example) that for an increase in altitude of approximately 1,000 m above sea level, the calibration constant for Kodak LR 115 II detectors increases by 28% for the closed-can geometry. For an altitude of 1,500 m above sea level, the calibration constant increases by 41% for closed detectors and by 63% for the open (bare) detectors.
SummaryThe diffusivities of Agllom and Snlls in bulk Ag,Sn were measured using the method of Gruzin. The volume diffusion coefficients were determined over the temperature range 200 to 4OO0C, with temperature dependence given by Dv**E 7 1.03 x exp (-22,80O/RT) cm2/sec. The fact that silver is the faster moving species in bulk Ag,Sn is important to the amalgamation process. On the other hand, it was found that along grain boundaries, tin tracer atoms diffused faster than did silver atoms. Faster grain boundary diffusion of tin, however, may not be a decisive factor in the actual amalgamation process, since mercury penetration exceeds the migration of tin atoms along grain boundaries.
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