5. Comparison between small and large samples' elemental concentration results

KayWin software calculated the efficiencies of the large sample accordingly, and the calculated Fc,Au–factors for the large sample obtained for Al-0.1% Au monitors were described by a linear equation. Then, it was decided to verify the experimental mass fractions for the small (Vial 3) and the large sample (Vial 1). The samples were measured at 2, 5, 10 and 20 cm at detector D4 (50% relative efficiency), and the elemental concentrations were calculated for each distance and for several distances, called RP, a routine procedure of analysis for customers, i.e., suitable distance sample-detector depending on the activity/dead-time. The experimental results and recommended values for reference material IAEA-SOIL-7 calculated by KayWin are shown in Menezes and Jaćimović [16].

Table 2 shows the normalised values of small and large samples to IAEA-SOIL-7 recommended data. It is possible to observe that majority of results are within 95% of confidence interval for assigned values. For the small sample, 88% of the results presented deviations from the recommended values lower than 10%, while for cylindrical samples, the deviations were 74%. For both samples measured at 10 cm, they presented 12% of deviations, and it was the best


takes into account the expanded uncertainty of both values with a coverage factor k = 2 (95% confidence interval). At CDTN, the uncertainty of the k0-NAA established is considered

> En <sup>¼</sup> Xlab � Xref ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi U2 lab <sup>þ</sup> <sup>U</sup><sup>2</sup>

where Xlab and Xref are laboratory and reference (assigned value) values, respectively; Ulab and Uref are expanded uncertainties with a coverage factor k = 2 of laboratory and reference values, respectively. The criterion |En| ≤ 1 was applied to compare the results of the two geometries with reference data, meaning that the evaluation of the performance of the method was satisfactory, producing values with a level of confidence of about 95% and if |En| > 1, the

) Experimental values

(mg kg�<sup>1</sup>

As 13.4 � 0.85 14.2 � 0.5 0.59 14.2 � 0.5 0.56 Ce 61 � 6.5 60.8 � 2.1 0.03 59.9 � 2.1 0.13 Co 8.9 � 0.85 9.33 � 0.33 0.40 9.17 � 0.32 0.25 Cr 60 � 12.5 68.9 � 4.0 0.60 63.6 � 2.6 0.27 Cs 5.4 � 0.75 5.69 � 0.20 0.35 5.83 � 0.21 0.50 Eu 1.0 � 0.2 0.95 � 0.03 0.24 1.12 � 0.16 0.33 Hf 5.1 � 0.35 5.33 � 0.20 0.43 5.34 � 0.19 0.46 La 28 � 1 29 � 1 0.44 29 � 1 0.42 Nd 30 � 6 26.3 � 1.2 0.57 27.9 � 1.3 0.32 Rb 51 � 4.5 53.0 � 2.4 0.31 51.8 � 2.5 0.12 Sb 1.7 � 0.2 1.83 � 0.07 0.54 1.73 � 0.06 0.14 Sc 8.3 � 1.05 9.29 � 0.33 0.80 9.09 � 0.32 0.65 Sm 5.1 � 0.35 4.87 � 0.19 0.44 5.22 � 0.18 0.24 Ta 0.8 � 0.2 0.73 � 0.03 0.33 0.78 � 0.03 0.11 Tb 0.6 � 0.2 0.66 � 0.02 0.30 0.69 � 0.02 0.45 Th 8.2 � 1.1 8.35 � 0.29 0.12 8.61 � 0.30 0.32 U 2.6 � 0.55 2.21 � 0.13 0.64 2.55 � 0.10 0.09 Yb 2.4 � 0.35 2.39 � 0.09 0.03 2.37 � 0.09 0.08

Uncertainties of recommended values are given at a confidence interval of 95% (k = 2), while experimental values are

Table 3. Experimental results and recommended values for IAEA-SOIL-7 analysed as small (Vial 3) and large samples

ref <sup>q</sup> (4)

http://dx.doi.org/10.5772/intechopen.83812

101

An Overview of the Establishment of Methodology to Analyse up to 5g-Sample…

Small sample Large sample

) |En| (mg kg�<sup>1</sup>

) |En|

as 3.5% with a coverage factor k = 1. En-score is calculated as follows:

performance was unsatisfactory. Table 3 displays the results for this test.

Element Recommended values (mg kg�<sup>1</sup>

given as combined standard uncertainty.

(Vial 1) [37].

El., element; RP, calculations carried out according to the usual procedure to the customers.

Table 2. Normalised values of small (Vial 3) and large samples (Vial 1) obtained at specific distance to IAEA-SOIL-7 on recommended data [16].

performance. Kennedy and St-Pierre [49] in their work observed a similar conclusion, where 10 cm distance sample-detector shows the best performance. The authors used an HPGe detector with 29% relative efficiency. Same conclusion can be explained due to the same method used for the absolute calibration procedure of an HPGe detector. Nevertheless, results presented in Table 2 for IAEA-SOIL-7 show relatively small differences between measurement distance sample-detector. So, it is possible to conclude that the impact from different measurement positions (or ratio between measurement and reference position) contributed relatively small systematic error to the final result.

The analytical performance of the experiments and the agreement of element contents with recommended values, the assigned values for IAEA-SOIL-7, i.e., the data given in the Certificate of analysis in 2000 [47] were evaluated by the statistical test called En-score [50]. This score takes into account the expanded uncertainty of both values with a coverage factor k = 2 (95% confidence interval). At CDTN, the uncertainty of the k0-NAA established is considered as 3.5% with a coverage factor k = 1. En-score is calculated as follows:

$$E\_n = \frac{\mathbf{X}\_{lab} - \mathbf{X}\_{ref}}{\sqrt{\mathbf{U}\_{lab}^2 + \mathbf{U}\_{ref}^2}}\tag{4}$$

where Xlab and Xref are laboratory and reference (assigned value) values, respectively; Ulab and Uref are expanded uncertainties with a coverage factor k = 2 of laboratory and reference values, respectively. The criterion |En| ≤ 1 was applied to compare the results of the two geometries with reference data, meaning that the evaluation of the performance of the method was satisfactory, producing values with a level of confidence of about 95% and if |En| > 1, the performance was unsatisfactory. Table 3 displays the results for this test.


performance. Kennedy and St-Pierre [49] in their work observed a similar conclusion, where 10 cm distance sample-detector shows the best performance. The authors used an HPGe detector with 29% relative efficiency. Same conclusion can be explained due to the same method used for the absolute calibration procedure of an HPGe detector. Nevertheless, results presented in Table 2 for IAEA-SOIL-7 show relatively small differences between measurement distance sample-detector. So, it is possible to conclude that the impact from different measurement positions (or ratio between measurement and reference position) contributed relatively small

Table 2. Normalised values of small (Vial 3) and large samples (Vial 1) obtained at specific distance to IAEA-SOIL-7 on

El., element; RP, calculations carried out according to the usual procedure to the customers.

Normalised values on IAEA-SOIL-7 recommended data (date of issue: 2000)

2 5 10 20 RP 2 5 10 20 RP

Ratio result obtained at specific distance (cm)/recommended value Small sample (200 mg) Large sample (5 g)

As 13.4 0.85 1.11 1.05 1.07 1.04 1.09 1.17 1.15 1.15 1.12 1.15 Ce 61 6.50 1.00 0.97 0.95 0.95 1.00 1.04 0.99 0.98 0.97 1.01 Co 8.9 0.85 1.05 1.03 1.02 1.07 1.05 1.06 1.04 1.04 1.02 1.06 Cr 60 12.5 1.22 1.18 1.16 1.15 1.15 1.30 1.25 1.26 1.22 1.30 Cs 5.4 0.75 1.05 1.05 1.05 1.05 1.05 1.11 1.09 1.09 1.08 1.10 Eu 1.0 0.2 1.02 1.07 1.10 0.85 0.95 1.12 1.17 1.08 1.10 1.12 Hf 5.1 0.35 1.04 1.02 1.01 1.01 1.04 1.05 1.04 1.04 1.01 1.03 La 28 1 1.06 1.01 1.02 1.01 1.04 1.07 1.05 1.04 1.03 1.04 Nd 30 6 0.87 0.94 0.92 0.95 0.88 0.98 1.10 1.02 1.09 1.08 Rb 51 4.5 1.04 0.99 0.97 0.97 1.04 1.09 1.03 1.03 1.04 1.04 Sb 1.7 0.2 1.08 1.06 1.08 1.07 1.08 1.07 1.03 1.02 1.03 1.03 Sc 8.3 1.05 1.12 1.10 1.08 1.08 1.12 1.13 1.11 1.10 1.09 1.11 Sm 5.1 0.35 0.96 0.98 0.93 0.92 0.96 1.03 1.01 0.98 0.96 1.01 Ta 0.8 0.2 0.91 0.94 0.93 0.93 0.91 0.95 0.98 0.98 0.97 0.95 Tb 0.6 0.2 1.10 1.13 1.10 1.10 1.10 1.22 1.19 1.14 1.15 1.21 Th 8.2 1.1 1.02 1.01 0.98 0.97 1.02 1.08 1.06 1.05 1.03 1.08 U 2.6 0.55 0.90 0.85 0.87 0.85 0.85 0.99 0.90 0.91 0.89 0.90 Yb 2.4 0.35 1.00 0.98 0.95 0.94 1.00 1.06 0.99 0.99 0.98 0.99 Zr 185 10.5 1.12 1.11 1.13 1.12 1.13 1.29 1.14 0.94 1.06 1.30

The analytical performance of the experiments and the agreement of element contents with recommended values, the assigned values for IAEA-SOIL-7, i.e., the data given in the Certificate of analysis in 2000 [47] were evaluated by the statistical test called En-score [50]. This score

systematic error to the final result.

recommended data [16].

El. Recommended values (mg kg<sup>1</sup>

)

100 Advanced Technologies and Applications of Neutron Activation Analysis

Uncertainties of recommended values are given at a confidence interval of 95% (k = 2), while experimental values are given as combined standard uncertainty.

Table 3. Experimental results and recommended values for IAEA-SOIL-7 analysed as small (Vial 3) and large samples (Vial 1) [37].
