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Compositional study of Parthian silver coins using PIXE technique
Nuclear Instruments and Methods in Physics Research B 289 (2012) 56–58
Contents lists available at SciVerse ScienceDirect
Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb
Compositional study of Parthian silver coins using PIXE technique M. Hajivaliei a,⇑, F. Khademi Nadooshan b a b
Department of Physics, Bu-Ali Sina University, Hamedan, Islamic Republic of Iran Department of Archaeology, Tarbiat Modares University, Tehran, Islamic Republic of Iran
a r t i c l e
i n f o
Article history: Received 29 February 2012 Received in revised form 31 July 2012 Available online 10 August 2012 Keywords: Parthian Coins Silver PIXE X-ray
a b s t r a c t The study of the elemental composition of silver coins minted in the Ecbatana mint houses during the Parthian period can help to elucidate key questions such as provenance of the silver metal and the socio-economic situation of that period. Commercial activity and population growth increased the demand for silver, forcing the Parthian to look for new sources of this metal. The aim of this work is to study the chemical composition of some Parthian coins to find any relation between the mines used for extraction of silver and the actual silver coins minted at that time. Using PIXE technique, the metallic elements Ti, Fe, Cu, Zn, Ag, Au, and Pb were observed. The results show that Parthian’s kings used almost two types of mines for their coins. Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction Study of ancient coins may indicate the economic and political circumstances in the time of their issue. In relation to the iconography, the archaeological issue concerns dating, provenance, technology and authenticity. Since coins play an important role in the Iranian cultural heritage, coins which belong to Orodes II and Phraates IV were studied. From the historical point of view, it is valuable to mention that one of the commanders of Orodes II (57-38 B.C.) named Surena, defeated Crassus in the battle of Carrhe in 53 B.C. After Orodes II, Phraates IV (38-2 B.C.) one of Orodes II sons came to power, killing his father and many of his family members. He fought in northwestern Iran with the powerful Roman general, Mark Antony (Marcus Antonius), and pushed him back to Rome. Phraates IV, to show his success, carved his name on coins left by Roman troops. Finally, in 20 B.C. he released all war prisoners and returned their flags taken as booty during the battle between Orodes II and Crassus. Ultimately peace agreement was achieved when the first Roman emperor, Augustus, gave as a gift, a beautiful slave, Musa to Phraates IV [1]. Using proton induced X-ray emission (PIXE) technique to study ancient coins is one of the prevailing methods for finding the chemical composition of ancient metals [2]. Such a technique highlighted several aspects of the study period. This information can be used as a means to deduce information on economic conditions and possible sources of metals. Among various spectroscopic ⇑ Corresponding author. Tel.: +98 811 8381470; fax: +98 811 8381172. E-mail address: [email protected] (M. Hajivaliei). 0168-583X/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.nimb.2012.07.039
techniques, PIXE is both a useful and non-destructive one providing archaeologists highly useful information [3–5]. PIXE has also been applied non-destructively in order to detect trace elements [6]. PIXE offers the maximum sensitivity for elements ranging approximately from Ar to Zr. The variation of the proton beam energy enables the characterisation of layered structures at the surface [7]. Using PIXE as an analytical technique, we have focused on metals once used in the Parthian period in Iran.
2. Background of research It seems Caley’s work [8] on the chemical compositions of Parthian coins as one of the excellent works, which has been done on Parthian numismatic. However he has not referred to anything about silver mines, which had been explored by Parthians for issuing silver coins of Orodes II. Other scholars, carrying spectroscopic studies on silver coins, have proposed suggestions for possible sources of this metal, which may show the politico-economic condition of the era under study. One of the authors of present work [9] is a pioneer for the study of ancient Iranian silver coins by PIXE technique. Among the foreign scholars Hughes [10], not only has worked on the Sasanian silver metals but has compared them with the Roman ones. One of the products of cupellation applied for the exploration of Galena (PbS) by oxidation of Pb and Zn, is silver. Since they were not able to separate Au from the produced metals, its amount remained the same as in the coins. This phenomenon has been reported by both Meyers [11] and Gordus [12]. Hence, gold has been used as an indication of mineral source. Gordus has also used Pt group. However, there is a problem when the Ag is reeled by Ag from different sources. In another research study,
57
M. Hajivaliei, F. Khademi Nadooshan / Nuclear Instruments and Methods in Physics Research B 289 (2012) 56–58
Kallithrakas-Kontos et al. [13] who have worked on the Alexander silver coins, showed Bi possibly might be used as an indication of mines. The same method has been applied by Guerra [3,14–16] for Au mines and coins. Throughout this study we try to find the relation between silver metals, which have been used for issuing the coins and the source of metal being used for mint house of Ecbatana. 3. Selection of samples The selected Parthian silver coins had been found in the archaeological excavations. After choosing, they were classified. Their weights show that all of them were Drachmas. The Parthian coins belong to Orodes II and Phraates IV, the two powerful kings. All coins were minted in Ecbatana mint house which was the capital of Medes satraps. Nearly all the coins were cleaned after registration in museum cabinet. The method of cleaning of coins are as follows; they were kept in 3–5% formic acid solution for few min, scrubbed with tooth brush, and finally cleaned with alcohol soaked cotton. 4. Experimental setup Fig. 1. Percentage of Au/Ag vs. Cu in the silver coins by PIXE.
A 2 MeV proton beam with a current of 2–3 nA from Atomic Energy Organization of Iran (AEOI), Van de Graff accelerator was used to bombard the coins. They were kept in a multipurpose scattering chamber under high vacuum (10 5 Torr). The emitted characteristic X-rays from samples were detected by an ORTEC Si(Li) detector (FWHM 170 eV at 5.9 keV). The GUPIX software was employed to analyse the obtained spectra. The results are shown in Table 1. Major elements are those contributing 10% to overall composition, minor elements 0.1–10% and trace elements less than 0.1%, down to detection limits. Overall uncertainty for the PIXE method was 5% for major elements, 5–10% for minor elements and 15% for trace elements. The uncertainties are not only statistical, but they also originate from the roughness of coin surface and from the chemical corrosion and/or wearing of the objects, altering the accuracy of the results. 5. Results and discussion The metallic elements Ti, Fe, Cu, Zn, Ag, Au, and Pb were observed in studied coins. The ratio of Ag to Au shows that two sources of Ag have been used for exploration and issuing the coins by the Satraps of Medes. Considering the errors, we may say that both Orodes II and Phraates IV used their own mines. The change of Cu percentage, used for coin hardening, in the Ag coins of Phraates IV shows that his reign has faced eco-political problems. However, with Orodes II coins no such changes from one coin to
Fig. 2. A typical PIXE spectrum of analysed silver coins.
the other is observed, indicating a more stable and powerful government. Possibly, today about half of the silver metals are
Table 1 The percentage of chemical elements present in the Parthian coins by PIXE.
a
Coin No.
Name king
Mint house
Unit weight
Weight (g)
Ti (%)
Fe (%)
Cu (%)
Zn (%)
Ag (%)
Au (%)
Pb (%)
Au/Ag
1 2 4 5 6 7 8 9 10 11 12 13 14 15
Orodes II Orodes II Orodes II Orodes II Orodes II Orodes II Orodes II Orodes II Orodes II Phraates IV Phraates IV Phraates IV Phraates IV Phraaates IV
Ecbatana Ecbatana Ecbatana Ecbatana Ecbatana Ecbatana Ecbatana Ecbatana Ecbatana Ecbatana Ecbatana Ecbatana Ecbatana Ecbatana
Drachma Drachma Drachma Drachma Drachma Drachma Drachma Drachma Drachma Drachma Drachma Drachma Drachma Drachma
4.01 3.35 3.93 3.99 4.09 4.00 3.91 4.03 4.50 3.61 3.92 3.94 3.62 3.69
0.19 ± 0a 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.12 ± 0a 0.07 ± 0a 0.0 0.0 0.0
1.4 ± 0.1 0.1 ± 0a 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.9 ± 0.1 0.6 ± 0.1 0.1 ± 0a 0.4 ± 0a 0.1 ± 0a
25.3 ± 1.3 5.0 ± 0.5 10.1 ± 0.5 9.9 ± 1.0 8.2 ± 0.8 6.8 ± 0.7 16.5 ± 0.8 9.1 ± 0.9 9.6 ± 1.0 19.9 ± 0.9 23.7 ± 1.2 9.6 ± 0.9 6.1 ± 0.6 12.6 ± 0.6
3.1 ± 0.3 0.1 ± 0a 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1 ± 0a 0.0 0.0 0.0 0.0
65.2 ± 3.3 92.1 ± 4.6 86.7 ± 4.3 88.1 ± 4.4 90.2 ± 4.5 90.8 ± 4.5 81.2 ± 4.0 89.5 ± 4.5 87.7 ± 4.4 77.8 ± 3.9 74.2 ± 3.6 88.9 ± 4.4 92.1 ± 4.6 86.1 ± 4.3
2.2 ± 0.2 2.0±.0.2 1.2 ± 0.1 1.0±.0.1 0.8 ± 0.1 1.0 ± 0.1 1.1 ± 0.1 0.7 ± 0.1 1.1 ± 0.1 0.6 ± 0.1 0.5 ± 0.1 0.5 ± 0.1 0.7 ± 0.1 0.5 ± 0.1
2.6 ± 0.3 0.1 ± 0a 1.1 ± 0.1 1.1 ± 0.1 0.8 ± 0.1 1.4 ± 0.1 1.2 ± 0.1 0.7 ± 0.1 1.6 ± 0.2 0.5 ± 0.1 0.9 ± 0.1 0.8 ± 0.1 0.4 ± 0a 0.7 ± 0.1
0.034 0.022 0.014 0.011 0.009 0.011 0.014 0.008 0.012 0.008 0.007 0.006 0.008 0.006
Out of accuracy limit.
58
M. Hajivaliei, F. Khademi Nadooshan / Nuclear Instruments and Methods in Physics Research B 289 (2012) 56–58
Fig. 3. Obverse and reverse of Parthian coins (a) Orodes II and (b) Phraates IV.
produced from Lead ores and in the antiquity, it was more [10]. Table 1 shows that only cerussite (PbCO3) mines have been explored for extraction of silver in the Satrapy of Medes. It means that all the Parthian silver coins, which were minted in Ecbatana mint house, have been extracted from cerussite mines. According to Meyers [11], if the silver were produced from cerussite, then the gold content would vary approximately from 0.2% to 1.5%, which is true for our case. Furthermore, it may be said that the concentrations of trace element of Au in the silver coins are the same as in the mines from which this element was extracted. In the spectra obtained by PIXE technique (Fig. 2), the Au is a trace element. The comparison of Au/Ag ratio with Cu content of coins shows (Fig. 1) that two mines of cerussite type have been explored for issuing coins: one mine for Phraates IV coins, whose Au/Ag ratio ranges from 0.005 to 0.01, and another one for Orodes II coins with Au/Ag ratios from 0.01 to 0.015. Coins No. 1 and 2, are different from the other ones. In the case of coin number 1 with more Zn, it seems that either the cupellation process was not used or this coin might be a forged one. Of course, Cu is not dissolved in cupellation process and remains as base metal in silver [10]. However, amounts above 1% are used for hardness and are ensured standard in silver metals. The coin number 2 with less Cu, is indicative of good eco-political condition in Orodes II period. The presence of Ca in the Ag coins (not given in Table 1) is due to the fact that its removal was impossible at that time during the metallurgical process. Furthermore, the presence of Fe and Br may be attributed to the surface contaminations. The study of Orodes II silver coins shows a strong negative correlation between Ag and Cu, the more the Ag content, the less will be that of Cu. Moreover, negative correlation between Ag and Pb are also seen. Similar trends are also observed for Phraates IV silver coins. In addition, negative correlation between Au and Pb is also observed for these coins. The obverse and reverse of Parthian coins are given in Fig. 3. 6. Conclusion According to above mentioned results and historical evidence, we may conclude that only the cerussite mines were used by Parthian kings; however, these mines were different regarding their gold content. According to the used metals, these mines can be classified in Parthian period i.e. the two kings used different alloys for their coins.
Acknowledgments We are thankful to the Prof. Guerra who is the head of laboratory of Louvre museum of Paris, Mr. Saffari responsible for XRF and XRD laboratory of Tarbiat Modares University, Prof. LamehiRachti and Mrs. Oliaiy the in-charge of Van de Graff Laboratory and Miss Baseri in-charge of cabinet of coins in the national museum of Iran. References [1] A.D.H. Bivar, The Cambridge History of Iran, vol. 3–1, Cambridge University Press, London, 1983, pp. 21–99. [2] Z. Smit, Recent development of material analysis with PIXE, Nucl. Instr. and Meth. B 240 (2005) 258–264. [3] M.F. Guerra, Elemental analysis of coins and Glasses, Appl. Radiat. Isot. 46 (1995) 583–588. [4] M. Torkiha, M. Lamehi-Rachti, O.R. Kakuee, V. Fathollahi, An external submilliprobe optimized for PIXE analysis of archaeological sample, Nucl. Instr. and Meth. B 268 (2010) 1517–1522. [5] M. Roumie, B. Nsouli, G. Chalhoub, M. Hamdan, Quality control of coins mint using PIXE and RBS analysis, Nucl. Instr. and Meth. B 268 (2010) 1916–1919. [6] B. Constantinescu, V. John Kennedy, G. Demortier, On relevent PIXE information for determining the compositional analysis of ancient silver and bronze coins, Int. J. PIXE 9 (1999) 487–493. [7] R. Linke, M. Schreiner, G. Demortier, The application of photon, electron and proton induced X-ray analysis for the identification and characterisation of medieval silver coins, Nucl. Instr. and Meth. B 226 (2004) 172–178. [8] E. Caley, Chemical Composition of Parthian Coins, American Numismatic Society, New York, 1955. [9] M. Hajivaliei, Y. Mohammadifar, K. Ghiyasi, B. Jaleh, M. Lamehi-Rachti, P. Oliaiy, Application of PIXE to study ancient Iranian silver coins, Nucl. Instr. and Meth. B B266 (2008) 1578–1582. [10] M.J. Hughes, J.A. Hall, X-ray fluorescence analysis of late Roman and Sasanian silver plate, J. Arch. Sci. 6 (1979) 321–344. [11] P. Meyers, Production of silver in Antiquity: ore Type identified based upon elemental compositions of ancient silver artifacts, Patterns and Process: A Festschrift in Honor of Dr. Edward V. Sayre, 2003, pp. 271–288. [12] A.A. Gordus, Quantitative non-destructive neutron activation analysis of silver in coins, Archaeometry 10 (1967) 78. [13] N. Kallithrakas-Kontos, A.A. Katsanos, J. Touratsoglou, Trace element analysis of Alexander the Greats silver tetradrachms mint in Macedonia, Nucl. Instr. and Meth. B 171 (2000) 342. [14] M.F. Guerra, Analysis of Archaeological Metals. The Place of XRF and PIXE in the Determination of Technology and Provenance, X-Ray Spectrom. 27 (1998) 73. [15] M.F. Guerra, Fingerprinting ancient gold with proton beams of different energies, Nucl. Instr. and Meth. B 226 (2004) 185. [16] M.F. Guerra, M. Radtke, I. Reiche, H. Riesemeier, E. Strub, Analysis of trace elements in gold alloys by SR-XRF at high energy at the BAMline, Nucl. Instr. and Meth. B 266 (2008) 2334.
Contents lists available at SciVerse ScienceDirect
Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb
Compositional study of Parthian silver coins using PIXE technique M. Hajivaliei a,⇑, F. Khademi Nadooshan b a b
Department of Physics, Bu-Ali Sina University, Hamedan, Islamic Republic of Iran Department of Archaeology, Tarbiat Modares University, Tehran, Islamic Republic of Iran
a r t i c l e
i n f o
Article history: Received 29 February 2012 Received in revised form 31 July 2012 Available online 10 August 2012 Keywords: Parthian Coins Silver PIXE X-ray
a b s t r a c t The study of the elemental composition of silver coins minted in the Ecbatana mint houses during the Parthian period can help to elucidate key questions such as provenance of the silver metal and the socio-economic situation of that period. Commercial activity and population growth increased the demand for silver, forcing the Parthian to look for new sources of this metal. The aim of this work is to study the chemical composition of some Parthian coins to find any relation between the mines used for extraction of silver and the actual silver coins minted at that time. Using PIXE technique, the metallic elements Ti, Fe, Cu, Zn, Ag, Au, and Pb were observed. The results show that Parthian’s kings used almost two types of mines for their coins. Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction Study of ancient coins may indicate the economic and political circumstances in the time of their issue. In relation to the iconography, the archaeological issue concerns dating, provenance, technology and authenticity. Since coins play an important role in the Iranian cultural heritage, coins which belong to Orodes II and Phraates IV were studied. From the historical point of view, it is valuable to mention that one of the commanders of Orodes II (57-38 B.C.) named Surena, defeated Crassus in the battle of Carrhe in 53 B.C. After Orodes II, Phraates IV (38-2 B.C.) one of Orodes II sons came to power, killing his father and many of his family members. He fought in northwestern Iran with the powerful Roman general, Mark Antony (Marcus Antonius), and pushed him back to Rome. Phraates IV, to show his success, carved his name on coins left by Roman troops. Finally, in 20 B.C. he released all war prisoners and returned their flags taken as booty during the battle between Orodes II and Crassus. Ultimately peace agreement was achieved when the first Roman emperor, Augustus, gave as a gift, a beautiful slave, Musa to Phraates IV [1]. Using proton induced X-ray emission (PIXE) technique to study ancient coins is one of the prevailing methods for finding the chemical composition of ancient metals [2]. Such a technique highlighted several aspects of the study period. This information can be used as a means to deduce information on economic conditions and possible sources of metals. Among various spectroscopic ⇑ Corresponding author. Tel.: +98 811 8381470; fax: +98 811 8381172. E-mail address: [email protected] (M. Hajivaliei). 0168-583X/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.nimb.2012.07.039
techniques, PIXE is both a useful and non-destructive one providing archaeologists highly useful information [3–5]. PIXE has also been applied non-destructively in order to detect trace elements [6]. PIXE offers the maximum sensitivity for elements ranging approximately from Ar to Zr. The variation of the proton beam energy enables the characterisation of layered structures at the surface [7]. Using PIXE as an analytical technique, we have focused on metals once used in the Parthian period in Iran.
2. Background of research It seems Caley’s work [8] on the chemical compositions of Parthian coins as one of the excellent works, which has been done on Parthian numismatic. However he has not referred to anything about silver mines, which had been explored by Parthians for issuing silver coins of Orodes II. Other scholars, carrying spectroscopic studies on silver coins, have proposed suggestions for possible sources of this metal, which may show the politico-economic condition of the era under study. One of the authors of present work [9] is a pioneer for the study of ancient Iranian silver coins by PIXE technique. Among the foreign scholars Hughes [10], not only has worked on the Sasanian silver metals but has compared them with the Roman ones. One of the products of cupellation applied for the exploration of Galena (PbS) by oxidation of Pb and Zn, is silver. Since they were not able to separate Au from the produced metals, its amount remained the same as in the coins. This phenomenon has been reported by both Meyers [11] and Gordus [12]. Hence, gold has been used as an indication of mineral source. Gordus has also used Pt group. However, there is a problem when the Ag is reeled by Ag from different sources. In another research study,
57
M. Hajivaliei, F. Khademi Nadooshan / Nuclear Instruments and Methods in Physics Research B 289 (2012) 56–58
Kallithrakas-Kontos et al. [13] who have worked on the Alexander silver coins, showed Bi possibly might be used as an indication of mines. The same method has been applied by Guerra [3,14–16] for Au mines and coins. Throughout this study we try to find the relation between silver metals, which have been used for issuing the coins and the source of metal being used for mint house of Ecbatana. 3. Selection of samples The selected Parthian silver coins had been found in the archaeological excavations. After choosing, they were classified. Their weights show that all of them were Drachmas. The Parthian coins belong to Orodes II and Phraates IV, the two powerful kings. All coins were minted in Ecbatana mint house which was the capital of Medes satraps. Nearly all the coins were cleaned after registration in museum cabinet. The method of cleaning of coins are as follows; they were kept in 3–5% formic acid solution for few min, scrubbed with tooth brush, and finally cleaned with alcohol soaked cotton. 4. Experimental setup Fig. 1. Percentage of Au/Ag vs. Cu in the silver coins by PIXE.
A 2 MeV proton beam with a current of 2–3 nA from Atomic Energy Organization of Iran (AEOI), Van de Graff accelerator was used to bombard the coins. They were kept in a multipurpose scattering chamber under high vacuum (10 5 Torr). The emitted characteristic X-rays from samples were detected by an ORTEC Si(Li) detector (FWHM 170 eV at 5.9 keV). The GUPIX software was employed to analyse the obtained spectra. The results are shown in Table 1. Major elements are those contributing 10% to overall composition, minor elements 0.1–10% and trace elements less than 0.1%, down to detection limits. Overall uncertainty for the PIXE method was 5% for major elements, 5–10% for minor elements and 15% for trace elements. The uncertainties are not only statistical, but they also originate from the roughness of coin surface and from the chemical corrosion and/or wearing of the objects, altering the accuracy of the results. 5. Results and discussion The metallic elements Ti, Fe, Cu, Zn, Ag, Au, and Pb were observed in studied coins. The ratio of Ag to Au shows that two sources of Ag have been used for exploration and issuing the coins by the Satraps of Medes. Considering the errors, we may say that both Orodes II and Phraates IV used their own mines. The change of Cu percentage, used for coin hardening, in the Ag coins of Phraates IV shows that his reign has faced eco-political problems. However, with Orodes II coins no such changes from one coin to
Fig. 2. A typical PIXE spectrum of analysed silver coins.
the other is observed, indicating a more stable and powerful government. Possibly, today about half of the silver metals are
Table 1 The percentage of chemical elements present in the Parthian coins by PIXE.
a
Coin No.
Name king
Mint house
Unit weight
Weight (g)
Ti (%)
Fe (%)
Cu (%)
Zn (%)
Ag (%)
Au (%)
Pb (%)
Au/Ag
1 2 4 5 6 7 8 9 10 11 12 13 14 15
Orodes II Orodes II Orodes II Orodes II Orodes II Orodes II Orodes II Orodes II Orodes II Phraates IV Phraates IV Phraates IV Phraates IV Phraaates IV
Ecbatana Ecbatana Ecbatana Ecbatana Ecbatana Ecbatana Ecbatana Ecbatana Ecbatana Ecbatana Ecbatana Ecbatana Ecbatana Ecbatana
Drachma Drachma Drachma Drachma Drachma Drachma Drachma Drachma Drachma Drachma Drachma Drachma Drachma Drachma
4.01 3.35 3.93 3.99 4.09 4.00 3.91 4.03 4.50 3.61 3.92 3.94 3.62 3.69
0.19 ± 0a 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.12 ± 0a 0.07 ± 0a 0.0 0.0 0.0
1.4 ± 0.1 0.1 ± 0a 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.9 ± 0.1 0.6 ± 0.1 0.1 ± 0a 0.4 ± 0a 0.1 ± 0a
25.3 ± 1.3 5.0 ± 0.5 10.1 ± 0.5 9.9 ± 1.0 8.2 ± 0.8 6.8 ± 0.7 16.5 ± 0.8 9.1 ± 0.9 9.6 ± 1.0 19.9 ± 0.9 23.7 ± 1.2 9.6 ± 0.9 6.1 ± 0.6 12.6 ± 0.6
3.1 ± 0.3 0.1 ± 0a 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1 ± 0a 0.0 0.0 0.0 0.0
65.2 ± 3.3 92.1 ± 4.6 86.7 ± 4.3 88.1 ± 4.4 90.2 ± 4.5 90.8 ± 4.5 81.2 ± 4.0 89.5 ± 4.5 87.7 ± 4.4 77.8 ± 3.9 74.2 ± 3.6 88.9 ± 4.4 92.1 ± 4.6 86.1 ± 4.3
2.2 ± 0.2 2.0±.0.2 1.2 ± 0.1 1.0±.0.1 0.8 ± 0.1 1.0 ± 0.1 1.1 ± 0.1 0.7 ± 0.1 1.1 ± 0.1 0.6 ± 0.1 0.5 ± 0.1 0.5 ± 0.1 0.7 ± 0.1 0.5 ± 0.1
2.6 ± 0.3 0.1 ± 0a 1.1 ± 0.1 1.1 ± 0.1 0.8 ± 0.1 1.4 ± 0.1 1.2 ± 0.1 0.7 ± 0.1 1.6 ± 0.2 0.5 ± 0.1 0.9 ± 0.1 0.8 ± 0.1 0.4 ± 0a 0.7 ± 0.1
0.034 0.022 0.014 0.011 0.009 0.011 0.014 0.008 0.012 0.008 0.007 0.006 0.008 0.006
Out of accuracy limit.
58
M. Hajivaliei, F. Khademi Nadooshan / Nuclear Instruments and Methods in Physics Research B 289 (2012) 56–58
Fig. 3. Obverse and reverse of Parthian coins (a) Orodes II and (b) Phraates IV.
produced from Lead ores and in the antiquity, it was more [10]. Table 1 shows that only cerussite (PbCO3) mines have been explored for extraction of silver in the Satrapy of Medes. It means that all the Parthian silver coins, which were minted in Ecbatana mint house, have been extracted from cerussite mines. According to Meyers [11], if the silver were produced from cerussite, then the gold content would vary approximately from 0.2% to 1.5%, which is true for our case. Furthermore, it may be said that the concentrations of trace element of Au in the silver coins are the same as in the mines from which this element was extracted. In the spectra obtained by PIXE technique (Fig. 2), the Au is a trace element. The comparison of Au/Ag ratio with Cu content of coins shows (Fig. 1) that two mines of cerussite type have been explored for issuing coins: one mine for Phraates IV coins, whose Au/Ag ratio ranges from 0.005 to 0.01, and another one for Orodes II coins with Au/Ag ratios from 0.01 to 0.015. Coins No. 1 and 2, are different from the other ones. In the case of coin number 1 with more Zn, it seems that either the cupellation process was not used or this coin might be a forged one. Of course, Cu is not dissolved in cupellation process and remains as base metal in silver [10]. However, amounts above 1% are used for hardness and are ensured standard in silver metals. The coin number 2 with less Cu, is indicative of good eco-political condition in Orodes II period. The presence of Ca in the Ag coins (not given in Table 1) is due to the fact that its removal was impossible at that time during the metallurgical process. Furthermore, the presence of Fe and Br may be attributed to the surface contaminations. The study of Orodes II silver coins shows a strong negative correlation between Ag and Cu, the more the Ag content, the less will be that of Cu. Moreover, negative correlation between Ag and Pb are also seen. Similar trends are also observed for Phraates IV silver coins. In addition, negative correlation between Au and Pb is also observed for these coins. The obverse and reverse of Parthian coins are given in Fig. 3. 6. Conclusion According to above mentioned results and historical evidence, we may conclude that only the cerussite mines were used by Parthian kings; however, these mines were different regarding their gold content. According to the used metals, these mines can be classified in Parthian period i.e. the two kings used different alloys for their coins.
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