Conclusion
Radionuclide X-ray fluorescence (RXRF) analysis takes up an important place among
other nuclear analytical methods. This nondestructive method enables to identify a great
number of elements of the periodic table on the basis of their characteristic X rays excited by
radionuclide sources. It predestinates this method for its usage for the check-up of
composition and purity of materials and recently also for the monitoring of pollutants in
various parts of environment.
At the Department of Nuclear Physics of FMFI, CU, which is a prominent workplace
in the sphere of monitoring of radioactivity in the environment and which trains specialists in
this field, X-ray fluorescence method has not been worked out and widely used so far. Hence,
the aim of my work was to participate in building experimental set-up for RXRF method,
optimise its parameters and show the possibilities of its application for the analysis of
environmental samples as well as metal materials.
Within the framework of optimisation of experimental parameters chiefly the
influence of voltage applied across the Si(Li) detector and of shaping time constant of the
linear amplifier on energy resolution of our spectrometer was studied. We determined 300 V as
optimum voltage of operation of the Si(Li) spectrometer and 12 s as convenient shaping time
constant of the linear amplifier. Moreover, in this section of work we presented that relative
energy resolution worsens rapidly for energies of X rays below 15 keV and improves only
slowly for energies above 15 keV. In addition, we compared Si(Li) and HPGe detectors
belonging to the Department of Nuclear Physics, FMFI, CU in terms of their detection
efficiency and energy resolution for 23,174 keV of characteristic X rays of Cd. Relative
energy resolution of the Si(Li) detector is about 1,8 % while for the HPGe detector it
increases up to 5 % . On the contrary, the HPGe detector reaches approximately 64 times
higher detection efficiency than the Si(Li) detector. As a result of these tests, it is more
convenient to use the Si(Li) detector for measurements, for which a high energy resolution is
a need. Conversely, if energy resolution is not a decisive factor, but rather a good detection
efficiency is required, it is more advantageous to use the HPGe detector.
In the part devoted to metal analysis about 60 different pure metals and metal objects
were tested. The capabilities of identification of particular metals and determination of
composition of various metal objects were studied using our spectrometer. It turned out that
rather light pure metals of Z  22 – 50 we can identify according to Ki-lines using gamma
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radiation source 241Am of 59,5 keV energy within 200 s of measurement. Heavier pure metals
of Z > 70 are possible to be identified according to Li-lines within time of 1000 – 5000 s.
Possibilities of the usage of RXRF method and our spectrometer for polycomponent
express qualitative analysis of metal materials were studied mainly on the set of coins and
several “gold” objects. It was found out that measured element composition of Slovak coins
dating from 1993 – 1996 was in agreement with the composition of these alloys declared by
National Bank of Slovakia. Furthermore also tests of golden objects were successful. The
presence of gold was detected even in objects, where gold was not revealed by the standard
jewellery method. Likewise the differences in composition of gold objects were found out by
means of RXRF analysis as demonstrated by our results. This method was found very
convenient for express analysis of purity of gold objects. The ratio of L / L lines was
constant for most of the gold objects.
In the part devoted to RXRF usage for the determination of water composition we
analysed 2 types of waters: mineral waters (5 samples) and drinking-waters (9 samples). In
mineral waters all elements of Z  20, declared by producers at labels of bottles, were
identified by our spectrometer. In addition also the presence of strontium was observed. Using
55
Fe source for excitation of Ca (K) X rays the efficiency of Ca identification in mineral
waters was approximately 2,5 times higher, when compared to
hand the advantage of the usage of
241
241
Am source. On the other
Am source for Ca detection is that the dependence of
counts under Ca (K) peak on the ratio of mCa/ mt is linear in the whole range of mCa/ mt (mCa
is mass of Ca in the analysed sample, mt is the total mass of the sample). For analyses carried
out with 55Fe source this dependence is linear only for mCa/ mt >0,3 using saturated samples.
Further also the dependence of counts rate on mass and areal mass of samples was
investigated for K X rays of iodine in potassium iodide (KI) using
241
Am source. The main
result of this part of work is the discovery, that the total detection efficiency of the detector
can be evaluated out of the measured dependence for the actuated K X rays. This is the
factor, which is experimentally difficult to determine with X-ray fluorescence analysis.
Outcomes of the analysis of drinking-waters confirmed that the applied experimental
set-up used for RXRF analysis is sensitive enough also for the identification of metals in these
waters. In general, using samples prepared only from the volume of 1 ℓ the time of one
measurement did not exceed 24 hour span.
In the last part of this thesis we dealt with the usage of RXRF analysis for the
identification of metals in solid substances taken up on filters after their exposure to several
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thousands m3 of filtered atmospheric air. Altogether there were analysed 20 sets of filters
from different periods of the year 2001. After 1-3 day measurement of a sample, elements like
Fe, Cu, Zn, Pb and Cd could be identified on filters. A high correlation was found out
between count rates under Cu (K); Cd (K) peaks and masses of solid matters caught on
filters.
We suppose that results of this thesis could be used also in pedagogical process by the
training of specialists in nuclear and environmental physics within the framework of
laboratory lessons. It could illustrate processes taking place in atomic shells and their usage
for analytical purposes. This work can also stimulate interest in the study of interaction
processes of different types of radiation with atoms as well as encourage further development
of applications of radionuclide X-ray fluorescence analysis.
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