Background measurement

The characteristic peaks must be separated from the background. In EDS this is usually accomplished by mathematical filtering of the spectrum or by background modeling. In WDS, the peak is sufficiently sharp to permit background measurement by detuning the spectrometer. 

In this paper, we discuss studies based on comparison with background measurements that may have a skew distribution. We discuss below the design of such a study. The design is intended to insure that the model for the comparison is valid and that the amount of skewness is minimized. Subsequently, we present a statistical method for the comparison of the background measurements with the largest of the measurements from the suspected region. This method, which is based on the use of power transformations to achieve normality, is original in that it takes into account estimation of the transformation from the data. 

To provide a framework for the design of the study, let us specify the model for the measurements in statistical terms. The background measurements, which we denote by xgi, i l,...,ng, are a random sample from some population. The measurements from the suspected region, denoted by xgi, i l,...,n , are, in the case of no excess contamination, a second, independent random sample from this same population. 

Although we usually do not know the values of X and t that transform the background measurements to normality, let us consider the case in which we do. Using Equation 1, we transform the measurements X3i and xgi to yg and ysi> respectively. To compare the maximum... 

Since we do not know the proper values for X and t, we need a way of Judging plausible values of X and t from the data. We do this by testing the transformed background measurements for normality. Our choice of a test for normality is the probability plot correlation coefficient r (12). The coefficient r is the correlation between the ordered measurements and predicted values for an ordered set of normal random observations. We denote the ordered background measure-ments by yB(l). where yB(l) < yB(2) < yBCnn) denote the... 

The previous section presents a test that is based on the assumption that for some (X,t) Equation 1 transforms the background measurements to nomality but is otherwise conservative. The test contains no explicit restriction on ng or ng except ng > 2. However, the test cannot be expected to be satisfactory for all values of ng and ng. First, the test is based on extrapolation of the distribution of the background measurements to higher values than are represented in the data. If extrapolation is carried too far, the results will not be satisfactory. Second, the test is conservative and may be too conservative for some values of ng and ng. In this section, we present an example based on analogous data that shows values of ng and ng for which the test is useful. 

Background measurements, soil samples, 119-20 Blood-lead levels In preschool... 

For solution nebulization MC-ICPMS and MC-TIMS, typical runs consist of up to 100 ratios collected over 30 minutes to 1 hour. This includes time for background measurement (typically monitored at half mass on either side of the peak) and peak centering, but excludes filament warm-up time for TIMS and nebulizer cleaning for MC-ICPMS. Sample sizes of-1000-10 ng of total U for TIMS and MC-ICPMS are required to attain 2a measurement uncertainties of a permil or better on (e.g., Stirling et... 

The property needs to be of a nature that control or background measurements also can be made so that the effects of the pollutant can be precisely determined (4) The property needs to be sensitive enough to indicate pollution but also sufficiently robust not to give false alarms (5) The property needs general scientific validity based upon reliable and... 

The refrigerator itself is shielded with a 20 cm thick low activity lead and a 10 cm thick borated PET. Nitrogen is fluxed between the external lead shield and the cryostat to avoid any Rn contribution to the detector background. Measurements of residual radioactivity have been carried out on several Pb samples [103], For the roman lead, a contamination lower than 4 mBq/Kg (in 210Pb) is to be compared with 250 mBq/Kg of a modem lead (Johnson Mattey). 

Brunke EG, Allen RJ. 1988. Tropospheric background measurements of CFC 3, CFFCCP, and CCk at Cape Point, South Africa, and their long-term trends. South African J Sci 84 266- 270. 

Noth To date, none of the above groups has reported a calculation of steady-state spurious HO production relative to ambient HO production with a simple transport-free model, and none has implemented both real-time reference background measurement and real-time reference HO measurement. The averaging times listed alxjve are those displayed for ambient HO in recent publications. All of these methods are undergoing continuous improvement. 

In addition, the background subtraction is a source of systematic error. A background measurement is performed immediately before or after each SN observation. The systematic errors in the process of background subtraction was estimated to be about 1 % and is incorporated in the error estimation of the SN flux. 

Hyvarinen A-P, Kolmonen P, Kerminen V-M, Virkkula A, Leskinen A, Komppula M, Hatakka J, Burkhart J, Stohl A, Aalto P, Kulmala M, Lehtinen KEJ, Viisanen Y, Lihavainen H (2011) Aerosol black carbon at five background measurement sites over Finland, a gateway to the Arctic. Atmos Environ 45 4042-4050... 

The application of inductively coupled plasma atomic emission spectrometry and graphite furnace atomic absorption spectrometry to the determination of cadmium (and molybdenum) in soils has been discussed by Baucells et al. [53]. Baucells et al. chose the 228.802 nm cadmium line because it is well resolved from the 228.763 nm iron line with the spectrometer used in this work. Background measurements could only be carried out at +0.05 nm. These workers obtained good agreement between cadmium values obtained by direct graphite furnace atomic absorption spectrometry and inductively coupled plasma atomic emission spectrometry. Chelation extraction procedures that require extensive sample handling are avoided. 

From Table 3 data it follows that in the course of the first 10 days after the submarine sinking radionuclide composition of bottom sediments was determined (99%) by " k -natural-origin radionuclide the remaining 1% was due to man-caused Cs which concentrations (3-5 Bq/kg) were attributed to global fallouts. That conclusion was confirmed by the results of radiation background measurements and independents surveys (see Reference [8]). 

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