I
X-R
F
X-R
R
M
R
H
M
’
D
S
1

2
1
2
There are scarce data on the content of rare heavy metals in soils, which is explained by the difficulties in their identification.
Using several methodological approaches to Xray fluorescence analysis we have established the contents rare heavy metals (Zr, Nb, Hf,
Ta, Th, U) in soils. The problem of the true intensities of Th- and UL -lines is solved in despite of “interfering" lines Pb L  and Rb K  , and Hf- and ThL -lines in despite of
"interfering" lines Ni K  , Cu K  , Ni K  . The equations of the relationship between the intensities of the spectral lines and the concentrations of the studied elements were found.
This allowed to determine the content of Hf, Ta, Th, U in soils with their higher content.
The improvement of X-ray radiometric analysis permitted us to analyze a significant group of lanthanides in soils, i.e. La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, and Dy. Methods of diagnostics are developed for different groups of lanthanides. The new procedure permitted achieving high accuracy in the measurement; the limit of the lanthanide identification in soils is equal to 2–5 mg/kg. The new procedure allows revealing the particularities of heavy lanthanides' distribution depending on the lithogenic and anthropogenic factors.
The procedures are applicable for revealing rare heavy metals and determining their content in soils within positive anomalies and background soils.
Keywords : rare heavy metals, X-ray fluorescence analysis, X-ray radiometric analysis, soils

E-mail: yu.vodyan@mail.ru.

2 Yu. N. Vodyanitskii and A. T. Savichev
Heavy metals are considered to be from vanadium (V) to uranium (U). They are divided into main metals - from vanadium (V, Z=23) to strontium (Sr, Z=38), according to Peroidic
Table - and rare metals (the rest). Rare metals are divided into d-elements - from zirconium
(Zr) to mercury (Hg), according to the groups in Periodic Table; p-elements - from gallium
(Ga) to bismuth (Bi); and f-elements (lanthanides and actinides) (Savichev, Vodyanitskii,
2011).
Lanthanides (Ln) include 14 elements from lanthanum La (Z=57) to lutetium Lu (Z=71), which are classified as a special group in the periodic system. Yttrium Y (Z=39) is also related to this group. Lanthanides are subdivided into two groups: (1) the cerium group includes lighter elements, i.e., lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium
(Nd), samarium (Sm), and europium (Eu), whereas (2) the yttrium group comprises heavier elements, i.e., gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), and yttrium (Y).
They include to actinides elements from thorium (Th) to lawrencium (Lr), although there are only two actinides in quantities of practical interest: thorium (Th) and uranium (U).
For a long time, the lanthanides were considered to be biologically inert elements, although their high reactive capacity was well known (Greenwood and Earnshow, 1997). It was found out that lanthanides interact intensely with proteins binding calcium (Furie et al.,
1973). Lanthanides intensify the biological cycle of nitrogen with the redox conditions of the medium being of decisive importance for this process: nitrification is intensified under oxidative conditions, while ammonification is intensified under reductive conditions (Zhu et al., 2002).
Some microorganisms (iron-reducing chemolithotrophic bacteria, in particular) favor the accumulation and biogenic fractionation of lanthanides (Tsuruta, 2005). The Gallionella ferruginea bacterium is wide spread among them; it is capable of accumulating lanthanides in amounts thousands of times exceeding their content in rocks and millions of times their concentrations in the soil–ground water (Anderson and Pederson, 2003). Iron-oxidizing chemolithotrophic bacteria induce the accumulation of a high amount of lanthanides in Fe-Mn concretions.
Recently, lanthanides were found to impact plants intensely. Agrochemists revealed the positive effect of a low dosage of lanthanides on the development of a number of plants
(Rogan et al., 2006; Tyler, 2004; Tyler and Olsson, 2001; Wu and Guo, 1995). At the same time, this effect was not universal, which was explained by the insufficient knowledge of soils. Identifying territories with negative anomalies of lanthanides, where the application of
Ln-fertilizers must be the most efficient, appears to be the most important task. Without knowledge of the lanthanides content in natural soils, the extension of Ln-fertilizers applicability beyond China’s boundaries (where they are widely applied) will be difficult.
There are absolutely insufficient data on the content of lanthanides in Russian soils, which is explained by their identification difficulty.
Physical methods appear to be the most reliable for the identification of lanthanides, because they permit analyzing solid samples and do not require the preliminary decomposition of soils. Spectrometric methods such as atomic absorption (AAS) and mass spectrometry with inductively coupled plasma (ICP–MS) need sample preparation

Improvement of X-Ray Fluorescence and X-Ray Radiometric Methods … 3
(conversion of a powder sample to a true solution). The routine procedures of soil decomposition for determining the total content of lanthanides either do not provide for the high productivity of the analytic work with acceptable labor expenditures or lead to significant analytic errors caused by the loss of elements during the sample preparation for the analysis (Karandashev et al., 2007). Neutron activation analysis (NAA), γ-spectrometry (γ-S), and X-ray fluorescence are the most efficient physical methods for analyzing the total content of lanthanides in soils.
The aims of the present study are as follows: (1) to improve the technique of X-ray determination of Hf, Ta, Th, U in soils; (2) to improve the X-ray radiometric method of lanthanide diagnostics in soils; (3) to use all kinds of X-ray fluorescence method (including
X-ray radiometric method) for the study of rare heavy d-metals (Zr, Nb, Hf, Ta), lanthanides
(Y, La, Ce , Pr, Nd, Sm, Eu, Gd, Tb, Dy) and actinides (Th, U) in soil of geochemical anomalies of Khibiny-Lovozero province, Kola Peninsula (Russia).
X-ray fluorescence analysis (RFA) appears to be the simplest and the cheapest method of analyzing heavy metals in soils (Savichev and Sorokin, 2000). However, not all rare metals can be studied by this method. It is used only for detecting the content of zirconium and niobium and yttrium among lanthanides.
Naturally, the classic RFA is not applicable for the study of the lanthanide content. On excitation of the X-ray fluorescent spectrum of soil samples using an X-ray tube with an Mo,
Rh, or Ag anode (voltage of 30–35 kV), only L -lines of lanthanides (much less bright than K lines) will be excited; these weak L -lines will be superimposed on bright K -lines of macroelements, the content of which is several orders higher than the content of lanthanides.
For exciting K -lines of lanthanides, it appears convenient to use the RFA variety, i.e., the Xray radiometric (RRA) method; it implies excitation of the analyzed sample with the isotope source radiation. We used the 241 Am isotope source with the emission line energy of 59.48 keV and radiation intensity of 3.7 × 10 10 sec -1 . Note that the K -lines of the lanthanides are not superposed by any lines of microelements.
When using X-ray fluorescence method a number of rare metals, e.g., d-metals (Hf, Ta) and actinides (Th, U) can not be identified due to low Clarke, but in soils of geochemical anomalies where the content of these metals is increased, it is possible to identify them. Ways to overcome the technical difficulties at the same time will be presented in this paper.
X-ray fluorescence determination of d-metals (Hf, Ta) and actinides (Th, U).
Diagnostics of Hf, Ta, Th, U using K-lines, unfortunately, is impossible by traditional X-ray fluorescence approach, nor by X-ray radiometric approach. The characteristic K -lines of elements occur at the transition of electrons from the excited state to the K -shell, which is closest to the atomic nucleus. For excitation of the K -line of any element there is a rule: the energy of the exciting radiation must exceed the energy of the K-edge absorption band of this line (i.e. the energy required to remove an electron from the K -shell of the atom). For most low-energy element of this group – hafnium (Hf) K -edge absorption band lies on energy 65.31 Kev. It is clear that even when X-ray radiometric approach when the sample is excited by radiation from

4 Yu. N. Vodyanitskii and A. T. Savichev radioisotope 241 Am source with the energy line at 59.48 Kev, the excitation of K -lines of these elements is impossible.
L -lines are formed by the transition of electrons from the excited state to the L -shell (the second from the nucleus) of these elements can be excited in the traditional X-ray fluorescence approach. L -absorption edge for the most high-energy element U is at 21.75 keV energy; therefore X-ray tube with Ag-anode (energy of Ag K  -line is 22.16 keV) is suitable for the optimal excitation. The X-ray fluorescence energy-dispersive analyzer “ReSPEKT”
(Tolokonnikov, 2003) corresponds to this requirement.
X-ray fluorescence spectrometry, as well as any other one, solves the two main problems: the correct measurement of the intensities of the spectral lines of elements diagnosed, and the search for the connection between the measured intensities and concentrations of analyzed elements.
Difficulties in solving the first problem are related to the following factors: the intensities of L -lines are significantly lower than intensities of K -lines; L -lines of diagnosed elements are superimposed on the bright K -line of other elements. Because of the low intensity of the L line diagnostics of these elements are not possible at Clarke level. However, this possibility appears to soil samples of geochemical or technogenic anomalies.
Figure 1 shows a part of the spectrum containing the L -lines of Th and U for a sample of podzolic soil (profile 9, horizon BT) from Khibiny-Lovozero geochemical anomaly, Kola
Peninsula, Russia.
Figure 1. T he spectrum part of the sample from KhibinyLovozero geochemical anomaly with visible lines of elements: Th and U. Location of spectral lines: 1 – Pb L
β
, 2 – Th L
α
, 3 – Rb K
α
, 4 – U L
α
, 5 – Sr
K
α
; 6 - distribution, given by the multichannel analyzer (reference spectrum, solid curve) , 7 - approximation of the background radiation. The dashed line shows the true contours of spectral lines after the deconvolution procedure of the spectrum.

Improvement of X-Ray Fluorescence and X-Ray Radiometric Methods … 5
It is noticeable that lines Pb L  and Rb K

are interfering for L  -lines of Th and U. To find the true intensities of the lines Pb L  , Th L  , Rb K  , Sr K  (shown in Figure 1, dashed) we used the spectral deconvolution (Malenkina and Savichev, 1994). The key point in this scheme is the choice of the shape of the spectral line, which is slightly different from the standard form corresponding to a Gaussian distribution. The best approximation was
Gaussian, whose dispersion varies linearly along the line contour.
Figure 2 shows a portion of the spectrum containing the L -lines of Hf and Ta for a sample, taken from the peat-podzolic soil (profile 5, horizon C) of Khibiny-Lovozero geochemical anomaly. A similar scheme were for the true intensity of Hf L  - and Ta L  lines, which interfere with Ni K  , Cu K  , Ni K  -lines. The second problem is the finding the equations of the relationship between the intensities of the spectral lines and the concentrations of the investigated elements.
It has been solved by the method of standard-background, in which there was select the intensity of the spectral line, normalized to the intensity of incoherent scattering exciting radiation as an analytical parameter, i.e. relationship was found in a linear fashion with a small degree of nonlinearity:
C i
=
 i
( I i
/ I in sc
)
 i , (3)
Figure 2. T he spectrum part of the sample from KhibinyLovozero geochemical anomaly with visible lines of elements: Hf and Ta. Location of spectral lines: 1 – Ni K
α
, 2 – Hf L
α
, 3 – Cu K
α
, 4 – Ta L
α
, 5 –
Ni K
β
; 6 - distribution, given by the multichannel analyzer (reference spectrum, solid curve) , 7 - approximation of the background radiation. The dashed line shows the true contours of spectral lines after the deconvolution procedure of the spectrum.

6 Yu. N. Vodyanitskii and A. T. Savichev where C i
is the concentration of the i -th element, I i
is the intensity of the spectral lines of the i -th element, I in sc
- incoherently scattered intensity of the exciting radiation, coupling coefficient,

 i
- the desired i
- exponent unsignificantly different from 1. For the construction of calibration curves for Th and U we used reference samples of granites SG-1A, SG-2, SG-3, and a reference sample of syenite SNS-2, in which these elements are acceptable for our problem in the range of concentrations (Arnautov, 1987).
There was more complicated situation with the construction of calibration curves for Hf and Ta. Hf and Ta contents are at Clarke level in reference samples and Hf- and Ta-lines in this method of analysis can not be seen. Way out has been found by using the energy closeness of Hf L  -, Ta L  - and Cu K
α
-lines. There was found, that the ratio of coupling coefficients between the intensities of K and L -lines, which are in energy closeness, and the concentrations of the respective elements is constant in a wide range of lines from 4 to 15 keV (Tolokonnikov et al, 2009). Representative examples of these K-L -pairs are Ba L  (4.47 keV) - Ti K  (4.51 keV) and Pb L  (10.55 keV) - As K  (10.54 keV); in this case: Hf L  (7.90 keV) - Ta L  (8.14 keV) - Cu K  (8.05 keV). Thus, knowing the coupling coefficient between the analytical line parameter Cu K  and copper concentration we can calculate the similar coefficients for Hf and Ta. Taking into account the low intensity of L -lines, the determination of Hf and Ta is possible only under a low-copper content in the soil (no more than 40-50 mg/kg). Soils of Khibiny-Lovozero geochemical anomaly with a high content of heavy rare metals are depleted in copper, that allowed to determine the content of Hf and Ta.
Impact of Pb L  - and Rb K  -lines on Th L  -line is small and diagnostics of Th is limited only by its low content. Impact of Rb K  -line on U L  -line is sufficiently large and accurate diagnostics of U is possible with contents of Rb no more than 350-400 mg/kg. Due to the low intensity of L -lines, in order to achieve detection limits of these elements - 10 mg/kg, we set time range of spectrum accumulation up to 1200 sec. For elements diagnosable by K -lines the time is 200-300 seconds.
Groups of lanthanides and their X-ray radiometric analysis . Formally, the 241 Am isotope source is classified as a γ-source, because its emission line is generated upon nuclear transitions. However, soil samples emit X-ray lines upon excitement by this source due to the electron transition from the upper to lower shells. The electron transitions to the closest to the nucleus K -shell appear to be the most interesting as it is these transitions that produce the characteristic K -lines of elements (Savichev and Vodyanitskii, 2011).
Although Ba is not related to the group of lanthanides, it is appropriate to consider its identification simultaneously with lanthanides, since it is an interfering element upon measuring the intensities of their lines. Earlier, we proved the applicability of the RRA method for the identification of the Ba, La, and Ce content in soils –first group of elements
(barium and light lanthanides) (Savichev and Vodyanitskii, 2009). The further improvement of the RRA approach permitted the identification of Pr, Nd, and Sm - the second group of elements (middle lanthanides) (Savichev and Vodyanitskii, 2011). These two groups of elements differ both in the energy interval of the analytic lines (31–35 and 35–41 keV, for the light and middle lanthanides respectively) and the laboriousness of the analysis.
The first group of elements (Ba, La, and Ce) posed practically no difficulties in the measurement of the true intensities of the analytical lines with a sufficient number of standard soil and rock samples being available for building the calibration plots. These elements may be distinguished at their Clarke content and lower.
For the second group (Pr, Nd, and Sm), the measurement of the true intensities of the spectral lines is complicated by the fact that their analytical α-lines are superposed by βcomponents of lines produced by the first group elements. Therefore, to analyze the secondgroup elements, we have to subtract the interfering β-components of the lines produced by the first group elements. The insufficient number of the standard soil and rock samples certified

Improvement of X-Ray Fluorescence and X-Ray Radiometric Methods … 7 for these elements poses another difficulty for the diagnostics of the second-group elements.
This problem was solved by building a generalized calibration curve, which assumed a constant ratio between the spectral line intensity and the content of the analyzed elements from La to Sm. The forwarded hypothesis is proved by a few standard samples. The identification of elements of the second group is possible at the Clarke level and higher.
In this paper, by the RRA method’s improvement we mean its extension for the identification of a group of still heavier lanthanides, i.e., Eu, Gd, Tb, and Dy (the third group of elements, heavy lanthanides).
Equipment.
The analytical measurement of all the groups of elements was performed using the X-ray fluorescent energy dispersion analyzer “ReSPEKT” (Tolokonnikov, 2003).
The RRA method implies the sample excitement by the irradiation from a radioisotope source rather than by the emission from an X-ray tube. The choice of the isotope source proceeded from the following condition: the energy of the exciting radiation line should exceed the energy of the K -edge of the adsorption band of the heaviest analyzed element. In our case, the energy of the K -edge of the adsorption band constitutes 53.79 keV for Dy. The isotope source has the following advantages over an X-ray tube for the analysis of elements with high energy of the characteristic K -lines: the high energy of the emission line (which is hardly available for tubes); high stability (its half-life time is about 465 years); high monochromatism, i.e. a high ratio between the radiation line’s intensity and the continuum’s intensity; and a small geometric size.
The sample preparation is very simple for RRA. The powder ground to 70–150 μm
(without any special requirements concerning the grinding process due to the high energy of the analyzed line quanta) was poured into a polyethylene dish 32 mm in diameter with a 5-μm thick polystyrene bottom. The mass of the analyzed powder was about 8 g (there are no strict requirements concerning the specimen weight). The sample was not used up upon the analysis. To achieve the required detection threshold (about 2 mg/kg), the exposition period was equal to 1.5–2.5 hours.
Preparation of standard samples.
For the studied elements of the third group (Eu, Gd, Tb, and Dy), there are no certified standard samples of soils and rocks in the range of concentrations above 6 mg/kg. For constructing the calibration curves, we made up artificial standard samples for the analyzed elements. The standard sample MU-2 (dunite) was selected from the set of standard samples of magmatic rocks collected in the IGEM RAS as a basis
(matrix) of the standard samples (or a reference sample) (Khitrov, 1984). The minimal content of Pr, Nd, Sm, Eu, Gd, Tb, and Dy (less than 2 mg/kg) was the reason for selecting this sample as a matrix. The compounds of five elements (Nd, Sm, Eu, Gd, and Dy) were added to this matrix. A similar method was used to produce a set of standard soil samples contaminated with heavy metals, i.e., a soddy-podzolic sandy–loamy soil, a red soil, a calcareous grey soil, and a typical chernozem (Arnautov, 1987).
The following compounds were used for manufacturing the artificial standard samples: neodymium oxide, samarium carbonate, gadolinium sulfate, and dysprosium sulfate. The double dilution method was applied for error mitigation upon the samples' preparation. At the first stage, five preliminary standard samples (one for each element) were prepared; 60 mg of each of the enumerated standard elements were mixed into 10 g of the powdered matrix to achieve a concentration equal to 6000 mg/kg of each element in the preliminary standard samples. At the second stage, the final polyelement standard samples were produced from the preliminary standard samples in a similar way; the element concentrations ranged from 5 to
150 mg/kg by varying the dilution coefficient for each element.
Measurement of the true intensities of the spectral lines. Figure 3a shows the spectrum of an artificial standard sample with the content of Gd and Dy equal to 25 and 66 mg/kg, respectively. Similar to the other spectra, the background radiation in this spectrum was

8 Yu. N. Vodyanitskii and A. T. Savichev approximated according to the “background template” correction (Savichev and Vodyanitskii,
2009) with the MU-2 dunite matrix spectrum having been taken as a “template”. This spectrum shows the true ratio between the intensities of the K
α1
- and K
α2
-lines of the Gd and
Dy elements, which is close to 3 : 2. However, this is an ideal case with no superimposed lines of other elements.
The further approximation to the actual spectrum is necessary for revealing the effect of the superimposed lines of other elements. For this purpose, we analyzed the spectrum of the artificial standard sample with the following content of elements (mg/kg): Nd - 60; Sm - 145;
Eu - 6; Gd - 25; and Dy - 66 (Figure 3b). The proportion between the lines in this spectrum differs from the actual one for Gd and Dy because of the superposition of the β-components of the Nd and Sm elements. However, the K
α1
-components of the Gd and Dy lines remain almost undistorted by the superposition.
Figure 4a manifests the spectrum of an actual soil sample from the mineral horizon sampled in the place of a strong geochemical anomaly of the Khibiny-Lovozero province.
The Kα- and Kβ-lines of all the elements in the energy range of 36–48 keV (Pr, Nd, Sm, Eu,
Gd, Tb, and Dy) are marked in this spectrum. The pattern of the lines' superposition is rather complicated. As is seen from this spectrum, the β-components of the second group elements
(Pr, Nd, and Sm) are superimposed on the K
α2
-lines of Eu, Gd, and Dy; at the same time, the
Kα1-lines are subject to very weak superposition, which may be overcome by a routine procedure of the spectrum deconvolution.
The spectrum deconvolution is the procedure of finding the true intensities of the spectral lines under the conditions of their mutual superposition; it is common for the X-ray fluorescenсe analysis of macro- and microelements in soils (Savichev and Stepanov, 2007).
Deconvolution refers to inverse tasks. However, all the approaches to solving this inverse task assume a fixed ratio between the intensities of the spectral line components, e.g., the α- and βcomponents. As was noted earlier (Savichev and Vodyanitskii, 2011), these ratios are actually subject to a matrix effect; i.e., they depend on the sample composition.
It is this circumstance that prevented us from using deconvolution for finding the true line intensities for the second group of elements (middle lanthanides - Pr, Nd, and Sm) and forced us to match the ratio coefficient individually for each sample. If we take the intensity of the
K
α1
- components as a measure of the spectral line intensity for the third group of elements
(Eu, Gd, Tb, and Dy), the deconvolution procedure may produce satisfactory results and permit avoiding the superposition effect.
Figure 4b shows in detail the spectrum of the same sample in the area of the identified elements from Eu to Dy with deconvolution of the spectral lines, i.e. with the displayed true intensities of the spectral lines. The true line intensities are represented in the spectral areas with the significantly superposed lines. The K α1 -components of the identified element lines are vividly shown to be virtually unaffected by the superimposed β-components of the second group elements (these K
α1
-components are numbered 5, 7, 9, and 11 in the figures) unlike the
К
α2
-components (numbers 6, 8, 10, and 12). Both analytical lines of terbium are free from superposition due to the absence of promethium in the soils (all the isotopes of which are radioactive and short-living). As the β-components of the lines influence weakly the K
α1
-lines of Eu, Gd, Tb, and Dy lanthanides, the intensities of their K
α1
-lines may be taken as a measure of the true intensities of their spectral lines.
Building calibration plots.
The calibration plots were compiled for Eu, Gd, and Dy. Ten artificial standard samples were prepared with varying contents of Eu, Gd, and Dy from 5 to
100 mg/kg.
We changed the content of Gd and Dy in inverse proportion, we randomly varied the content of Nd and Sm, and we took deliberately too high concentrations as compared to the true soil samples.

Improvement of X-Ray Fluorescence and X-Ray Radiometric Methods …
A
9
B
Figure 3. X-ray radiometric spectra of the artificial standard samples with the background irradiation approximation. Content of elements, mg/kg: (A) Gd, 25; and Dy, 66; (B) Nd, 60; Sm, 145;
Eu, 6; Gd, 25; and Dy, 66. Here and in Fig. 4, the position of the spectral lines is as follows. The αcomponents used for the identification of the elements are as follows: ( 1 ) Nd Kα1 ; ( 2 ) Nd Kα2 ; ( 3 ) Sm
Kα1 ; ( 4 ) Sm Kα2 ; ( 5 ) Eu Kα1 ; ( 6 ) Eu Kα2 ; ( 7 ) Gd Kα1 ; ( 8 ) Gd Kα2 ; ( 9 ) Tb Kα1 ; ( 10 ) Tb Kα2 ; ( 11 ) Dy
Kα1 ; ( 12 ) Dy Kα2 . The β-components interfering with the actual intensities of the lines are as follows:
( 13 ) Ba Kβ1 ; (14) Ba Kβ2 ; ( 15 ) La Kβ1 ; ( 16 ) La Kβ2 ; ( 17 ) Ce Kβ1 ; ( 18 ) Ce Kβ2 ; ( 19 ) Pr Kβ1 ;
( 20 ) Pr Kβ2 ; ( 21 ) Nd Kβ1 ; ( 22 ) Nd Kβ2 ; ( 23 ) Sm Kβ1 ; ( 24 ) Sm Kβ2 .

10 Yu. N. Vodyanitskii and A. T. Savichev
A
B
Figure 4. X-ray radiometric spectrum of the natural soil sample from the mineral horizon of the strong geochemical anomaly in the Khibiny-Lovozero province: (A) a general outline of the spectrum in the interval of the analytic lines from Nd to Dy with the background irradiation approximation;
(B) a detailed view of the spectrum in the interval of the analytic lines from Eu to Dy with the background irradiation approximation and the deconvolution of the lines (the deconvolution is shown in those spectral areas where the effect caused by the superposition of the lines is substantial).

Improvement of X-Ray Fluorescence and X-Ray Radiometric Methods … 11
A wide range of Nd and Sm variation was taken for revealing the efficiency of the deconvolution procedure, which should overcome the interfering influence of their βcomponents on the useful analytic lines of Gd and Dy.
The ratio between the true intensity of the spectral line and the intensity of the incoherent scattered exciting radiation I i
/ I in sc was selected as an analytic parameter of the i -th element; i.e., the standard background method was applied, which took into consideration the sample composition’s influence on the analytic parameter value (Savichev and Vodyanitskii, 2009).
The K-factor, i.e., the ratio between the absolute error in the concentration measurement and the square root of the measured concentration K = ΔC / C 0.5
, was taken as an error measure.
The independence of this value from the concentration (unlike the absolute ΔC or relative
ΔС/С deviation) appears to be the main advantage of this error measure, which was comprehensively scrutinized by us earlier (Savichev and Vodyanitskii, 2009). The value of the К factor of about a unit (upon concentrations of the analyzed elements of about 10 mg/kg) corresponds to the third accuracy category as agreed by the Scientific Council on Analytic
Methods (Berenshtein et al., 1979).
Metrological data.
The following values of the К-factors were obtained from the dependences between the analytic parameter and the concentrations of the analyzed elements:
1.16 for Eu, 1.12 for Gd, and 1.17 for Dy. The К-factor was equal to about 2 for the elements of the second group. As is seen, the error was less for Eu, Gd, and Dy, because, having chosen the K
α1
-lines as an intensity measure, we avoided the subtraction of the interfering βcomponents increasing the error.
The К-factor value shows that the calibration accuracy must be controlled by the sample weight precision upon the preparation of artificial standard samples. The relationship coefficients p i between the concentration and the analytic parameter ( I i
/ I in sc
= p i
C i
) for Eu,
Gd, and Dy differs by more than 3% (relative). This fact proves the generalized calibration curve for Eu, Gd, and Dy to be quite reliable. The same relationship coefficients may be also used for Tb.
The analytical threshold for Eu, Gd, Tb, and Dy constitutes about 5 mg/kg for the exposition time of 2 hours; therefore, their identification is possible only in soils of positive geochemical anomalies. The lower analytic threshold for the third-group elements is explained by the K
α1
-line taken as the intensity measure, because, by increasing the accuracy of the measurement of the true line intensities (and thus decreasing the K-factor), we lose the absolute intensity of the line and thus make the determination threshold worse.
Correction of the metrological data.
Table 1 lists in detail the metrological data. Upon building the calibration curves for the second group elements, we applied the approach based on the generalized calibration curve implying the permanent relationship coefficient pi between the analytic parameter I i
/ I in sc and the concentration C i
of the analyzed elements
(sensitivity). The application of artificial standard samples permits us to check this hypothesis. The artificial standard samples containing La, Ce, Pr, Nd, and Sm were prepared by the above described method. The samples of ultrabasic rocks MU-1, MU-2, and MU-4 selected from the set of standard samples of magmatic rocks collected in the IGEM RAS were used as a matrix for their preparation.
Table 1 lists the relative sensitivity of the elements p i rel
= p i
/ p
Ba
both for the natural and artificial standard samples. First, it shows that the relationship coefficients between the analytic parameter and the concentration (sensitivity) coincide very well for La and Ce both in the natural and artificial standard samples. Second, the hypothesis of the generalized calibration curve using the artificial standard samples is confirmed for the elements of the second group (middle lanthanides).

12 Yu. N. Vodyanitskii and A. T. Savichev
Table 1. Metrological data on the X-ray radiometric determination of barium and lanthanides in soils
Group of elements
Element Natural standard samples
Relative sensitivity
К-factor
Artificial standard samples
Relative sensitivity
К-factor
Analytic lines; method of measuring actual intensities
Detection limit, mg/kg
1 -
-barium and light lanthanides
2-
-middle lanthanides
3-
-heavy lanthanides
Ba
La
Ce
Pr
Nd
Pm*
Sm
Eu
Gd
Tb
Dy
1
0.997
0.995
Not det.
»
»
1.28
1.02
1.07
Not det.
0.998
0.993
0.991
0.988
0.980
Not det.
1.04
1.08
1.96
1.85
1.91
K 
1,2
; direct
»
»
K 
1,2
; subtraction of interfering βcomponents
»
»
2
2
2
2
2
2
»
»
»
»
0.975
0.967
0.955
1.16
1.12
1.17
K 
1
; deconvolution
»
»
5
5
5
* All the isotopes of Pm are radioactive and short-living.
This hypothesis is also virtually true for the third group of elements (heavy lanthanides) with a constancy of no less than 5% (relative). The given facts (the equal sensitivity of the natural and artificial standard samples and the wide range of the generalized calibration curve) support the validity of the developed procedure. The relative decrease in the sensitivity with the growing atomic number is explained by the decreasing efficiency of the X-ray detector efficiency with the growing quantum energy. This effect is related to the small spatial size of the crystal detecting the X-ray radiation in the “ReSPEKT” analyzer.
We studied soils both enriched and background contents in rare heavy metals.
Soils of Khibiny–Lovozero province (Kola Peninsula, Russia)) were studied at three different sites. The peat–podzolic soils (profiles 10 and 11) were analyzed in the background territory on the shore of Umbozero Lake. The region of the geochemical anomaly produced by the nearby rare-metal deposit of loparite ores is subdivided into two parts. The anomaly is weak on Lovozero Lake shore in the deposit’s periphery, where the influence on the chemical composition of the soils is insignificant. A cambisols (profile 2) and peat soils (profile 1) are

Improvement of X-Ray Fluorescence and X-Ray Radiometric Methods … 13 exposed on the western bank of Lake Lovozero. A strong anomaly is registered in the centre of the ore field at the northern shore of Seidozero Lake, where it controls the soil enrichment with lanthanides. A cambosol (Profile 5) is studied there. Three profiles are also cut at the bank of the Elmorayok River. These are the following: an illuvial– humus soil (profile 7), a fluvisol (profile 8), and a podzol (profile 9). All the soils are acidic with the water extract pH varying from 3.6 to 5.6; these are light-texture soils (ranging from sand to sandy loam) according to the particle-size distribution (Vodyanitskii et al., 2010).
Clarkes.
Clarkes of studied rare metals in the Earth's crust are (mg/kg): Zr = 162; Nb =
20; Hf = 2.8; Ta = 1.7; Y = 31; La = 35, Ce = 66, Pr = 9.1; Nd = 40, Sm = 7; Eu = 2.1; Gd =
6.1; Tb = 1.2; Dy = 4.5; Th = 8.1; U = 2.3 (Greenwood and Ernshow, 1997).
Raimann and de Caritat (1998) give similar values, but crust Clarkes for Nd, Sm, Eu, Gd,
Tb, Dy in these sources are differ. According to Raimann and de Caritat (1998) Clarke values are lower (mg/kg): Nd = 28, Sm = 4.7; Eu = 1.2; Gd = 2.2; Tb = 0.6; Dy = 3. These data seem to us more plausible and we use them in our studies.
The most reliable data on the Clarkes values of rare heavy metals in soil are Soil
Wordwide data after Kabata-Pendias and Pendias (Kabata-Pendias, 2011). There is doubt as to the meaning of Y Clarke (12 mg/kg); we believe a more realistic value of Y Clarke is 23 mg/kg.
In soils Clarkes of the same rare metals are higher than in the Earth's crust (mg/kg) for Zr
= 300; Hf = 3; Ta = 1.1; Th = 8.2: U = 3.7 and lower for Nb = 12; Y = 23; La = 26; Ce = 49;
Nd = 19; Pr = 7.6; Sm = 3.1; Gd = 2.2; Tb = 0.4; Dy = 0.7 (Kabata-Pendias, 2011).
Consequently, during their formation the soils are enriched with Zr, Hf, Th, U and depleted with Nb, Y, La, Ce, Nd, Pr, Sm, Gd, Tb, Dy. Soil enrichment by stable zirconium is used as the label in the study soil formation.
The properties of heavy rare metals are very different. On the one hand, d-elements (Zr,
Nb, Hf, Ta), which are included in the stable minerals, are accumulated in the soil compared to the crust. This is expressed in ratio between soil Clarke of this element in the Earth’s crust
Clarke (K (s / c)), exceeding 1 for two of them: Zr (K (s / c) = 1.85), Hf (K (s / c) = 1.07). For
Nb and Ta, this rule is not observed (Nb (K (s/ c) = 0.60 ), Ta (K(s/c) = 0.68) which is probably due to the underestimated soil Clarke of these elements.
On the other hand, the lanthanides (Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy) form strong complexes with organic ligands, which contributes to their leaching from soil. Therefore, for all of them K (s / c) <1. Indeed, for Y K(s / c) = 0.74, for La K (s / c) = 0.74, for Ce K (s / c) =
0.74, for Pr K (s / c) = 0.83, for Nd K (s / c) = 0.68, for Sm K (s / c) = 0.66.
There are also differences in the properties of lanthanides. In the studied series (La-Sm) two extreme metal differ maximally in atomic weight: from 138.9 (La) to 150.3 (Sm). In geochemical sense the ratio Nd : La is most significant, it reflects different biophylity of rare earth elements and their different mobility.
Situation with actinides (Th, U) is more complicated. They are actively leached by soil formation process, but their soil Clarkes are close to their Clarkes in the crust, which is most

14 Yu. N. Vodyanitskii and A. T. Savichev likely due to the low reliability of soil Clarkes actinides. It is believed, that Th is more accumulated in the humus horizon, and U is more washed out (Vodyanitskii, 2012).
The content of the rare heavy metals.
It is known, that Lovozero mine contains significant reserves of loparites (Savichev, Vodyanitskii, 2011). Amount of rare earth metals is large in loparites: in terms of oxides from 24% to 35%. Here are the average chemical composition of the conditional formula of loparite: NaCeTi2O6; based on the oxides it contains: rare earth metals (30%), Ti (40%), Nb (12%), Na (8%), Sr (3%), Ca (5%), Ta (0.8%) (Savichev,
Vodyanitskii, 2011). There is very high content of zirconium, niobium, hafnium, tantalum, thorium and uranium.
Cerium (49.6%), lanthanum (28.45%), praseodymium (3.4%), neodymium (15.5%), samarium (2.4%) predominate among the rare earth metals; the content of each of the other
(heavy) lanthanide is less than 0.5%. Thus, source rocks, containing loparites, are enriched in light lanthanides significantly, especially niobium, which will affect the composition of soils formed on them.
The content of heavy lanthanides is below the detection limit in the reference soils of the province (profiles 10 and 11). However, within the geochemical anomaly, their content is enough to be revealed by X-ray radiometry. As is seen from Table 2, the content of gadolinium constitutes 10 – 16 mg/kg and that of dysprosium, 9 – 15 mg/kg in the area of the weak anomaly. The europium and terbium content is below the detection limit.
Table 2. Content of lanthanides in the soils of the Khibiny–Lovozero province, mg/kg
Horizon Depth, cm
Y La Ce Pr Nd Sm Eu Gd Tb Dy
Background
Profile 10. Umbozero lake bank. Peat-podzolic soil
T*
E
ВT
С
0-12 19 34 55
12-18 8 16 24
18-28 10 17 27
7
4
2
16
8
7
5
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Т
E
ВT
С
28-47 15 30 46 4 15 - -
Profile 11. Umbozero lake bank. Peat-podzolic soil
-
0-8
8-10
23 57 97
8 20 30
10-29 12 21 33
29-49 12 25 44
13 30
3
3
3
7
6
11
8
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Т1*
Т2
BHF
0-6
6-18
16
Profile 12. Umbozero lake bank. Cambisols
41 55
16 26 38
18-25 13 25 38
11
5
5
17
12
10
7
5
3
-
-
-
Weak geochemical anomaly
-
-
-
-
-
-
-
-
-
Т1*
Т2
9-32
Profile 1. Lovozero lake bank. Peat soil
53 291 553 44 141 16 -
32-40 107 171 307 22 87 19 -
14
17
-
-
11
14

Improvement of X-Ray Fluorescence and X-Ray Radiometric Methods … 15
Ат
Е
ВТ
С
Horizon Depth, cm
Aт*
А1
ВHF
ВС
0-5
5-12
31
Profile 2. Lovozero lake bank. Peat-podzolic soil
104 203 19 58
35 61 120 14 44
12-40 61 108 198 13 57
16
11
10
-
-
-
40-50
Y
43
La
97
Ce
185
Pr
12
Nd
59
Sm
10
Eu
-
Strong geochemical anomaly
Profile 5. Seidozero lake bank. Cambisols
0-13
13-24
24-40
40-62
130
144
186
227
190
145
201
259
390
277
390
498
35
21
30
46
144
104
142
198
29
18
23
35
-
-
-
6
Profile 7. Elmorayok river bank. Illuvial-humus soil
АТ
В
ВС
0-15
15-23
23-40
320
281
269
434
439
423
830
836
747
71
75
58
269
250
255
37
46
40
7
7
7
Profile 8. Elmorayok river bank. Fluvisols
Gd
16
11
10
11
27
17
21
32
36
39
36
Т
ВНF
0-15
15-47
346
231
292
255
655
500
47
41
201
158
32
25
6
-
32
23
Aт*
E
ВT
С
0-5
5-15
163
Profile 9. Elmorayok river bank. Podzol
170 327 22 98 20 -
199 147 294 22 106 16 -
15-30 246 218 460 36 156 26 -
30-52 281 349 785 55 224 32 -
19
17
25
31
Tb Dy
6
6
6
-
-
-
-
-
-
-
-
6
-
25
14
17
25
15
9
9
10
29
30
29
26
18
-
-
-
-
16
14
20
24 crust
Clarke soil
31
23
35 66
26 49
9 28
7.6 19
4.7 1.2
3.1 1.2
5.4
2.2
0.6 3
0.4 0.7
* Low-ash peat horizons.
Note. Here and after : a dash designates no data.
The content of heavy lanthanides grows in the territory of the strong anomaly. The gadolinium content reaches 17–39 mg/kg, and that of dysprosium, 14–30 mg/kg. Europium and terbium are found not in every sample. The illuvial–humus soil on the bank of the
El’morayok River turned out to be the richest one, as it contained Eu - 7mg/kg and Tb - 6 mg/kg, which is 3–5 times higher than the Clarke values.
The contents of the rare heavy metals, determined by X-ray fluorescence method, are shown in Table 3. It is obvious heterogeneity of geochemical anomaly in space. The difference in the content of rare metals can be related to the heterogeneity of enrichment by lanthanides of source rocks, and to differences in soil texture. According to Samonova (1992), soils in Volga region (Russia) of the heavy particle size composition are more enriched by lanthanides than the light ones. Consequently, in these soils we can expect significant positive association between clay particles and lanthanides, which is not confirmed statistically. In soils from background area there is no communication of any content of rare earth metals

16 Yu. N. Vodyanitskii and A. T. Savichev with aluminum content or the content of the clay fractions. In the territory of a strong geochemical anomaly there is also no connection between the content of heavy metals and silt. Consequently, in soils of light particle size composition on the territory of the Khibiny-
Lovozero province lanthanides concentration depends only on the proximity of the ore body.
Table 3. Rare heavy metals content (mg/kg) in mineral horizons and in the ash of organogenic horizons in the soils of Khibiny-Lovozero province
Horizon Depth, cm Zr Nb Hf Ta Th U
Т*
Е
ВТ
С
Background area
0–12
Profile 10. Umbozero lake bank. Peat-podzolic soil
245 28
– –
12–18 144 26
– –
18–28
28–47
117
200
15
31
–
–
–
–
–
–
–
–
–
–
–
–
Т*
Е
ВТ
С
0–8
Profile 11. Umbozero lake bank. Peat-podzolic soil
252 49
– –
8–10
10–29
155
192
20
25
–
–
–
–
29–49 232 33 – –
Weak geochemical anomaly
–
–
–
–
–
–
–
–
Ат*
А1
ВНF
ВС
0–5
5–12
12–40
40–50
Profile 2. Lovozero lake bank. Cambisols
755 92
– –
774
1373
1140
81
134
145
–
–
–
–
–
–
Strong geochemical anomaly
15
19
16
14
–
–
–
Ат*
E
ВТ
С
0–13
13–24
24–40
40–60
Profile 5. Seidozero lake bank. Cambisols
3087 475 61 37
3434
3668
359
345
90
85
22
53
4211 466 80 52
Profile 8. Elmorayok river bank. Fluvisols
Т*
ВНF
Ат*
Е
ВТ
С
Clarke (crust)
Clarke (soil)
0–15
15–47
0–5
5–15
15–30
30–52
7410
4296
670
526
118
59
Profile 9. Elmorayok river bank. Podzol
3838 465 - -
43
49
5164
6571
770
578
88
103
56
57
5757
162
300
531
20
12
92
2.8
3
* – the metal content in the ash; questionable Clarkes are underlined.
32
1.7
1.1
63
61
77
78
53
81
20
30
124
83
8.1
8.2
–
–
34
19
2.3
3.7
15
13
18
19
13
19

Improvement of X-Ray Fluorescence and X-Ray Radiometric Methods … 17
1) The diagnostics of d-metals (Hf, Ta) and actinides (Th, U) at X-ray fluorescence approach has not been previously developed. Their diagnostics based on the strongest K -lines is impossible, but using L -lines, with the traditional X-ray fluorescence approach, diagnostics is complicated, because the L-lines of diagnosed elements are overlapped by bright K -lines of other elements. Because of the low intensity of the L -lines diagnostics of these elements, therefore, are impossible at their low levels, however, for samples from geochemical anomalies or technogenic anomalies with a high concentration of rare heavy metals such determination is possible. The problem of the true intensities of Th- and U -L -lines is solved in despite of “interfering" lines Pb L  and Rb K  , and Hf- and ThL -lines in despite of
"interfering" lines Ni K  , Cu K  , Ni K  . The equations of the relationship between the intensities of the spectral lines and the concentrations of the studied elements were found.
This allowed to determine the content of Hf, Ta, Th, U in soils with their higher content.
(2)The improved method of X-ray radiometric analysis permitted the determination of a significant group of lanthanides in the soils: La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, and Dy.
Identification procedures have been developed differing for various groups of lanthanides.
Calibration plots are suggested. The new method permitted us to achieve high accuracy of the measurements; the detection limit for lanthanides in soils constitutes 2–5 mg/kg.
(3)The new procedures allow revealing the particularities of the rare heavy metals distribution depending on the lithogenic and anthropogenic factors. The procedures are applicable for revealing the technogenic anomalies of heavy lanthanides and for the determination of their content in the soils of positive anomalies and in the background soils.
The authors are grateful to Kosareva N. V., who provided samples for the analysis.
Anderson C. R. and Pederson K. (2003). In Situ Growth of Gallionella Biofilms and
Partitioning of Lanthanides and Actinides between Biological Material and Ferric
Oxyhydroxides. Geobiology, V. 1.
169–178.
Arnautov N. B. (1987). Standard Samples of chemical composition of natural minerals.
Guidelines.
N
. 204p. (in Russian).
Berenshtein L. E., Masolovich N. S., Sochevanov V. G., and Ostroumov G. V. (1 9 79 ).
Metrological Basics of Quality Control in Analytical Works. Methodological Basics of
Studying the Chemical Composition of Rocks, Ores, and Minerals.
(Nedra, Moscow).
23–118. (in Russian).
Furie B., Eastlake F., Schechter A. N. and Anfinsen C. B. (1973). The Interaction of the
Lanthanide Ions with Staphylococcal Nuclease . J. Biol. Chem., V . 248. 5821–
5825.

18 Yu. N. Vodyanitskii and A. T. Savichev
Greenwood N. N. and A. Earnshow A. (1997). Chemistry of the Elements, 2nd edition,
Butterworth-Heinemann, Oxford, UK.
Kabata-Pendias A. (2011). Trace Elements in Soils and Plants. CRC Press. 585p.
Karandashev V. K., Turanov A. N., Orlova T. A., Lezhnev A. E., Nosenko S. V., Zolotareva
N. I., and Moskvina I. R. (2007). The Use of Inductively-Coupled Plasma with Mass
Spectrometry for the Element Analysis of Environmental Objects. Factory Laboratory ,
V.73(1). 12-22.
Khitrov V. G. (1984). Results of Evaluation of a System of Standards of the Chemical
Composition of Magmatic Rocks. USSR Akad. Sci. Reports. Ser. Geol., № 11.
37–52.
Malenkina S. Yu. and Savichev A. T. (1994). Uranium Geochemistry of Mesozoic
Phosphorites in Central Part of East-European Platform. High School Reports. Geology
Exploration, № 4. 54-58. (in Russian).
Reimann C. and de Caritat P. (1998). Chemical Elements in the Environment. Springer-
Verlag. Berlin.
Rogan N., Serafimovski T., Dolenec M, Tasev G. and Dolenec T. (2006). The Distribution of Rare Earth elements (REEs) in Paddy Soil and Rice Seeds from Kocani Field
(Eastern Macedonia). RMZ-Materials and Geoenvironment, 433–444.
Savichev A. T. and Sorokin S. E. (2000).
X-ray Fluorescence Analysis of Micronutries and
Heavy Metals in Soils. Eur. Soil Sci., V.
33 .
Supplement 2. S.161-S.164.
Savichev A. T. and Stepanov S. S. (2007). Assessment of Signal Overlapping and
Approximation of Background Radiation in the X-Ray Fluorescence and Microprobe
Energy-Dispersive Analysis. Surface: Rentg. Sinkhrotr. Neutron. Studies, No. 2.
85–89.
Savichev A. T. and Vodyanitskii Yu. N. (2009). Determination of Barium, Lanthanum and Cerium Contents in Soils by the X-Ray Radiometric Method. Eur. Soil Sci., V.
42 (13). 1461–1469.
Savichev A. T. and Vodyanitskii Yu. N. (2011). X-Ray Radiometric Determination of
Lanthanides (Praseodymium, Neodymium, and Samarium) in Soils. Eur. Soil Sci.,
V .
44 (4), 386–393.
Samonova O. A. (1992). Rare Earth Elements: Lanthanum, Cerium, Samarium, Europium in
Steppe Soils of Volga Upland . Eur. Soil Sci., V.
25(6). 45-50.
Tolokonnikov I. A. (2003). Energy-Dispersive X-ray Fluorescence Analyzer of Substance
Composition. Atomic Energy , V. 95(1). 69-70.
Tolokonnikov I. A., Savichev A. T. and Moskalets A. S. (2009). New Possibilities of Energy-
Dispersive X-Ray Fluorescence Technique in the Analysis of Potable Water. J. Anal.
Chem., V.64(9). 921-925.
Tsuruta T. (2003). Separation of Rare Elements by Microorganisms. J. Nucl. Radiochem.,
V .
6 .
81-84.
Tyler G. (2004).
Rare earth elements in soil and plant systems – A review. Plant Soil, V .
267 .
191-206.
Tyler G., Olsson T. (2001). Plant Uptake of Major and Minor Elements as Influenced by Soil
Acidity and Liming. Plant Soil, V .
230 .
307-321.
Vodyanitskii Yu. N., Kosareva N. V. and Savichev A. T. (2010). The Contents of
Lanthanides (Y, La, Ce, Pr, Nd, Sm) and Actinides (Th, U) in Soils of the Khibiny-
Lovozero Province. Dokuchaev Soil Science Institute Bulletin, V .
65 .
75–86.

Improvement of X-Ray Fluorescence and X-Ray Radiometric Methods … 19
Vodyanitskii Yu. N. (2012).
Geochemical fractionation of lanthanides diagnostics in soils and rocks: A review of publications. Eurasian Soil Science, V.45. 56-67.
Wu Z. M. and Guo B. S. (1995). Application of Rare Earth Elements in Agriculture and
Medicines. Bioinorganic Chemistry of Rare Earth Elements. Ed. by J. Z. Ni, (Science
Press, Beijing). 13–55.
Zhu J. G., Chu H. Y., Xie Z. B. and Yagi K. (2002). Effects of Lanthanum on Nitrification and Ammonification in Three Chinese Soils. Nutr. Cycl. Agroecosyst., V. 63.
309-
314.