2 The Methodology of the Study
15
The neutron flux density characteristics in the channel equipped with a pneumatic
system are given by Frontasyeva and Pavvlov (2000). NAA is a sensitive analytical
technique that is useful for performing both qualitative and quantitative multi-element
analysis of major, minor, and trace elements in samples of scientific or technical
interests (Biziuk et al. 2010). INAA is characterized as an analytical method relatively
free from matrix effects and interferences, its high accuracy and very low or zero
contributions from the blank (Filby 1995). Beside it, the INAA is a nondestructive
method that provides precise and accurate results of high sensitivity and selectivity for
a large number of elements in the periodic table, by making this technique attractive
to multi-element analysis (Frontasyeva and Steinnes 1997).
The elements Co, Cr, Fe, Ti, Se, Br, Sb, Zr, Hf, Ta, Mo, W, Sc, La, Ce, Nd, Sm,
Eu, Gd, Tb, Tm, Yb, Th, U, Rb, and Cs were determined by epithermal neutron activation Analysis (ENAA) at the IBR-2 pulsed fast reactor FLNP JINR Dubna, Russia
(Frontasyeva 2011). Moss samples were pelletized by using a simple press form
and heat sealed in polyethylene foil for the analysis of the elements associated with
short-lived radionuclides, while the samples analyzed for the elements of long-lived
radionuclides were packed in aluminium cups. To determine elements associated
with long-lived radionuclides the samples were irradiated for 100 h in the cadmium
screened channel Ch1 with neutron flux density ϕ epi = 3.31 * 10
12 n/(cm
2
× s).
The containers with samples were cooled for 4 days and then were repacked and
measured twice, using high purity germanium detectors; the first time measurements
were done directly after the repacking process and the second time measurements
were done after 20 days of the end of the irradiation. The measurement time was
0.5 and 1.5 h respectively. To determine short-lived radio-nuclides (only Ti in the
current work) the samples were irradiated for 3 min in the second channel (Ch2)
of the reactor. After irradiation, gamma-ray spectra were recorded twice for each
irradiation using a high-purity Ge detector (Frontasyeva and Pavvlov 2000). The
processing of the spectral data was performed using the software developed at FLNP
JINR (Ostrovnaya et al. 1993; Ostrovnaya 2000) and the content of each element in
moss samples was calculated. The quantification limits of the elements calculated
from the GEINE 2000 software for the concentrations range of each element in the
current moss samples are shown in Table 2.1.
2.3 Quality Control
M2 and M3 international moss reference materials (Steinnes et al. 1997) were used
to perform the quality control of the ICP-AES and ETAAS Analysis (Stafilov et al.
2018). Moss reference materials were analyzed together with moss samples at each
10 samples interval. The determined ICP-AES reference values reported by Stafilov
et al. (2018) and Balabanova et al. (2010) were in good agreements with the recommended values. In addition, blank samples were measured in parallel to the analysis
of the moss samples. International plant reference material IAEA-140/TM (Fucus
homogenate) was used for checking the quality control of the CVAAS analysis (Lazo
15
The neutron flux density characteristics in the channel equipped with a pneumatic
system are given by Frontasyeva and Pavvlov (2000). NAA is a sensitive analytical
technique that is useful for performing both qualitative and quantitative multi-element
analysis of major, minor, and trace elements in samples of scientific or technical
interests (Biziuk et al. 2010). INAA is characterized as an analytical method relatively
free from matrix effects and interferences, its high accuracy and very low or zero
contributions from the blank (Filby 1995). Beside it, the INAA is a nondestructive
method that provides precise and accurate results of high sensitivity and selectivity for
a large number of elements in the periodic table, by making this technique attractive
to multi-element analysis (Frontasyeva and Steinnes 1997).
The elements Co, Cr, Fe, Ti, Se, Br, Sb, Zr, Hf, Ta, Mo, W, Sc, La, Ce, Nd, Sm,
Eu, Gd, Tb, Tm, Yb, Th, U, Rb, and Cs were determined by epithermal neutron activation Analysis (ENAA) at the IBR-2 pulsed fast reactor FLNP JINR Dubna, Russia
(Frontasyeva 2011). Moss samples were pelletized by using a simple press form
and heat sealed in polyethylene foil for the analysis of the elements associated with
short-lived radionuclides, while the samples analyzed for the elements of long-lived
radionuclides were packed in aluminium cups. To determine elements associated
with long-lived radionuclides the samples were irradiated for 100 h in the cadmium
screened channel Ch1 with neutron flux density ϕ epi = 3.31 * 10
12 n/(cm
2
× s).
The containers with samples were cooled for 4 days and then were repacked and
measured twice, using high purity germanium detectors; the first time measurements
were done directly after the repacking process and the second time measurements
were done after 20 days of the end of the irradiation. The measurement time was
0.5 and 1.5 h respectively. To determine short-lived radio-nuclides (only Ti in the
current work) the samples were irradiated for 3 min in the second channel (Ch2)
of the reactor. After irradiation, gamma-ray spectra were recorded twice for each
irradiation using a high-purity Ge detector (Frontasyeva and Pavvlov 2000). The
processing of the spectral data was performed using the software developed at FLNP
JINR (Ostrovnaya et al. 1993; Ostrovnaya 2000) and the content of each element in
moss samples was calculated. The quantification limits of the elements calculated
from the GEINE 2000 software for the concentrations range of each element in the
current moss samples are shown in Table 2.1.
2.3 Quality Control
M2 and M3 international moss reference materials (Steinnes et al. 1997) were used
to perform the quality control of the ICP-AES and ETAAS Analysis (Stafilov et al.
2018). Moss reference materials were analyzed together with moss samples at each
10 samples interval. The determined ICP-AES reference values reported by Stafilov
et al. (2018) and Balabanova et al. (2010) were in good agreements with the recommended values. In addition, blank samples were measured in parallel to the analysis
of the moss samples. International plant reference material IAEA-140/TM (Fucus
homogenate) was used for checking the quality control of the CVAAS analysis (Lazo