Instrumental neutron activation analysis (INAA) is a powerful technique for trace element determination in rocks. Nine alabaster samples were collected from Wadi El-Nakhil located at the intersection of lat. 26°10′50′′N and long. 34°03′40′′E, central Eastern Desert, Egypt, for investigation by INAA and Energy Depressive X-Ray Fluorescence (EDXRF). The samples were irradiated by thermal neutrons at the TRIGA Mainz research reactor at a neutron flux of 7 × 1011 n/cm2·s. Twenty-two elements were determined, namely, As, Ba, Ca, Co, Cr, Sc, Fe, Hf, K, Mg, Mn, Na, Rb, U, Zn, Zr, Lu, Ce, Sm, La, Yb, and Eu. The chemical analysis of alabaster indicated having high contents of CaO and MgO and LOI and low contents of SiO2, Al2O3, Na2O, K2O, MnO, and Fe2O3.
Neutron activation analysis (NAA) is based on the irradiation of a sample with neutrons from a neutron source like a nuclear reactor and the subsequent measurement of the induced radioactivity. The NAA has become a very capable multielement analysis technique with improved sensitivity. In many cases, more than 30 elements can be determined from a single experiment [
The Egyptian alabaster is one of the ornamental stones used by ancient Egyptian for art and decorative purposes. The term Egyptian alabaster is applied to a beautifully banded rock composed of crystalline calcium carbonate. It occurs in several locations in the Eastern Desert near the Nile Valley, at Wadi El Assuity, at Wadi Sannur, opposite Beni Suef and Sohag area and near El-Minya El-Gedida, and East Wadi El Shurafa [
Wadi El-Nakhil alabaster is located at the intersection of lat. 26°10′50′′N and long. 34°03′40′′E, central Eastern Desert, Egypt. The studied alabaster deposits at Wadi El-Nakhil occur in the form of veins of lensoidal shaped bodies along fault plane trending N59W enclosed in the Eocene limestones. The contacts between alabaster and the enclosing limestones are sharp. The extension of the vein reaches up to 100 m and its thickness ranges from 30 cm to 1 m. The alabaster usually displays some xenoliths of limestones up to 30 cm in diameter. El-Nakhil alabaster is hard, compact body with banded textures and is characterized by attractive colors and beautiful shapes. The banding is the result of the change in the physicochemical environment of mineralization with time [
Location map of the occurrence of alabaster in the Eastern Desert, Egypt. The full points in the map indicate the sampling sites.
Nine alabaster rock samples were collected from Wadi El-Nakhil located at the intersection of lat. 26°10′50′′N and long. 34°03′40′′E, central Eastern Desert, Egypt, for investigation by instrumental neutron activation analysis. The samples, each about 1 kg in weight, were dried in an oven at about 105°C to ensure that moisture is completely removed. The powdered samples were sieved using a standard set of sieves to a diameter range of less than 125
Irradiation conditions of elements determined [
Irradiation time | Decay time | Counting time | Elements determined |
---|---|---|---|
1 min | 5 min | 4 min | Mg |
5 min | 1 h | 15 min | K, Mn, Na |
6 h | 2 d | 1 h | U, Sm, La, As |
6 h | 14 d | 8 h | Ba, Ce, Co, Cr, Sc, Eu, Fe, Hf, Lu, Rb, Yb, Zn, Zr |
The measuring of activity concentration for radionuclide in studied samples was defined using gamma-ray spectrometer system by HPGe detector with its electronic circuit. The HPGe detector was equipped with specifications as follows: energy resolution (FWHM) is 1.70 keV at 1.33 MeV Co-60, peak-to-Compton ratio Co-60 is 65.2, and relative efficiency is 29.2 at 1.33 MeV Co-60. The measurements were analyzed and performed by using the Inter-Gamma Software. In all measurements, the electronic dead time is less than 10% and the Inter-Gamma Software performed the correction automatically [
The chemical analyses of major oxide contents in this study were conducted on a Thermo Scientific QUANT’X EDXRF spectrometer, located in the department of physics; all powder samples were dried at a temperature of 105°C and stored in desiccators, until they were analyzed. Fill up 3/4 parts of the cup with the sample analyzed. Then, cover the cup with the film. Fix the slim ring by sliding it down and fix the thick ring at the top of the cup. When the cups are prepared, place them on the sample stage inside the spectrometer chamber, with the side to be analyzed facing down toward the X-ray tube (QUANT’X Technical Manual, Thermo Fisher Scientific, 2008).
Table
The nuclear data and the average concentrations of elements determined in alabaster.
Element | Activation |
Energy |
|
Concentrations |
---|---|---|---|---|
Na% | 24Na | 1369 | 15 h | 0.20 |
Mg% | 27Mg | 1014 | 9.5 min | 5.47 |
Ca% | 49Ca | 3984 | 8.7 min | 45.3 |
Mn% | 56Mn | 846 | 2.6 h | 0.13 |
Fe% | 59Fe | 1099 | 44.5 d | 0.93 |
K% | 42K | 1524.7 | 12.4 h | 0.86 |
Sc ppm | 46Sc | 1120 | 38.8 d | 0.54 |
Cr ppm | 51Cr | 320 | 27.7 d | 7.04 |
Co ppm | 60Co | 1332 | 5.3 y | 0.27 |
Zn ppm | 65Zn | 1115.5 | 244 d | 7.62 |
As ppm | 76As | 559 | 26.3 h | 29.05 |
Rb ppm | 86Rb | 1076 | 18.6 d | 0.20 |
Zr ppm | 95Zr | 756.7 | 64 d | 28 |
Ba ppm | 131Ba | 496 | 11.8 d | 5.08 |
La ppm | 140La | 1596 | 40.3 h | 50.37 |
Ce ppm | 141Ce | 145 | 32.5 d | 0.43 |
Eu ppm | 152Eu | 1408 | 13.3 y | 0.04 |
Sm ppm | 153Sm | 103 | 46.3 h | 4.17 |
Yb ppm | 169Yb | 198 | 32 d | 0.15 |
Lu ppm | 177Lu | 208.4 | 161 d | 0.17 |
Hf ppm | 181Hf | 428 | 42.4 d | 0.37 |
U ppm | 239Np | 106 | 2.4 d | 2.3 |
The statistical counting errors were
2–5% for Eu, La, Cr, Fe, Ce, Yb, and Lu, 5–10% for Zn, As, K, Mg, and Ca, 10–15% for Rb, Ba, and U.
Quantitative analysis was carried out for each isotope by comparing the activities from the most favorable peaks in the gamma spectra of samples with those of the standard reference material. In this analysis the highest-energy peaks were usually used, as in the case of
The rare earth elements determined are La, Ce, Sm, Eu, Yb, and Lu. The selection of photopeaks for the analysis is briefly discussed below for each element. For lanthanum, the high abundance photopeak of
The concentration of uranium via
The isotopes 140La, 141Ce, and 147Nd commonly used in the activation analysis of the corresponding elements are also produced by fission of 235U. There is a possibility of interference of the 320 keV
Interferences due to energy and reactions.
Radionuclide |
|
Reaction interferences | |
---|---|---|---|
Interfering reaction | Interfering contribution |
||
140La | 1596.2 | U |
0.032 |
141Ce | 145.5 | U |
0.201 |
147Nd | 91.1 | U |
0.187 |
The results of chemical analysis of alabaster samples are given in Table
Chemical analysis of major oxide contents (wt%) of Wadi El-Nakhil alabaster.
Oxides | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | Average |
---|---|---|---|---|---|---|---|---|---|---|
CaO | 62.2 | 50.45 | 66.32 | 64.36 | 69.68 | 69.6 | 70.75 | 64.4 | 66.3 | 64.9 |
MgO | 12.22 | 21.56 | 7.23 | 8.9 | 3.23 | 1.21 | 4.03 | 8.8 | 7.3 | 8.28 |
SiO2 | 1.2 | 0.06 | 0.05 | 0.04 | 0.04 | 1.61 | 0.95 | 1.42 | 1.8 | 0.79 |
Fe2O3 | 1.08 | 1.35 | 1.08 | 1.08 | 1.24 | 1.58 | 1.10 | 1.07 | 1.08 | 1.18 |
Na2O | 0.18 | 0.27 | 0.22 | 0.54 | 0.21 | 0.18 | 0.19 | 0.53 | 0.23 | 0.28 |
K2O | 1.03 | 1.09 | 1.04 | 1.02 | 1.03 | 1.03 | 1.02 | 1.02 | 1.03 | 1.03 |
P2O5 | 0.01 | 0.1 | 0.01 | 0.04 | 0.01 | 0.07 | 0.01 | 0.04 | 0.01 | 0.03 |
LOI | 24.9 | 24.6 | 25.6 | 25.1 | 25.8 | 25.15 | 24.8 | 25.2 | 25.5 | 25.2 |
Twenty-one elements were determined including major and trace elements in addition to some rare earth elements. The chemical analyses of alabaster reveal the enrichment of CaO and MgO and LOI and the depletion of SiO2, Al2O3, Na2O, K2O, MnO, and Fe2O3. The source of calcium is dissolution of Eocene limestone due to the action of meteoric water.
The authors declare that they have no competing interests.
This work was funded by the Deanship of Scientific Research (DSR), King Abdulaziz University, Jeddah, under Grant no. 363-651-D1435. The authors, therefore, acknowledge with thanks DSR technical and financial support.