فهرست مطالب مسعود آقا حسینی

The accuracy of isotopic compositions measurement is affected by all the ICP-MS instruments because of the phenomenon known as mass bias, where it is defined as difference between the measured and true values in an isotopic analysis. This research has introduced mass bias and also evaluated the effective parameters including concentration of uranium, electrical field behind the second or skimmer cone, detector voltage, plasma power and nebulizer flow. The least mass bias with a relative error -0.3% for the isotopic analysis of uranium results in aqueous media without interference of the matrix with 1.2% RSD of 0.3 mg/L concentration, while the voltages of ion lens 1 and 2 in the ICP-TOF-MS were -700V and -550V, respectively. The instrument was set in the plasma power of 1000 watts, nebulizer flow of 0.78 ml/min, and the detector voltage of -2450V.

Replacement of four individual, time-consuming and expensive ASTM standard methods for determination of Mo, As, Th and K in samples having uranium matrix with one new proficient method is considered. The main advantages of this method are overcoming the mentioned shortages and preserving the precision and accuracy of the analysis results for the desired technical specification of materials and nuclear industries. In the new method, the interfering uranium matrix was removed by extraction with a mixture of tri (2- ethylhexyl) phosphate (TEHP): n-Heptane. The elements were determined by inductively coupled plasma-optical emission spectrometry (ICP-OES) simultaneously. The effective parameters on the extraction including: pH, the remained uranium and temperature were studied. The dynamic range of calibration curve related to the element type was linear (R2>0.999) at 10-500 μg/g U. The method detection limits (MDL) of 0.51, 0.66, 1.1 and 0.55 μg/g U were obtained for Mo, As, Th and K, respectively. The obtained quantity of En for all elements was less than 0.26. The analytical precision and bias of current method at two different concentration levels were determined and compared with the available standard methods denoting an evidence of the method verification. The decreased analysis of time duration from ~24 hr to <2 hr and the remarkably reduced instrumental and material charges are some of the joined industrial and applied properties of the present method.