With the death of Yazdgerd III (632-652 AD), an independent dynasty called the Dabuyi Gobaregan was formed in Tabaristan, and Farkhan (712-731 AD), son of Dabuyi, minted coins that were not different from the coins of the Sassanid era but in size and weight. With the death of Khurshid (748-761 AD), the last king of this dynasty, after enduring the Umayyad and Abbasid invasions for about a century and a half, Tabaristan was finally opened during the reign of Mansur Abbasid (137-158 AH) and Abbasid governors took over the administration of affairs. With the only notable difference being the rendering of the emir's name in Kufic script, the coinage continued in the same style.
       In this research, eighteen coins from the Mostazafan Foundation Museums Cultural Institution and four coins from the collection of Mr. Mojtaba Zadeh Khorasani, owned by Abbasid governors, were tested in the Vandograf section of the Atomic Energy Organization using the Pixie method.
       A research based on historical texts, numismatic sources, and laboratory results of elemental analysis of coins, attempts to provide a relative understanding of the economic and political situation and the authenticity of the coins in question. The results of the analysis show the fineness of coins is inextricably linked to the political and economic conditions prevailing in society, and a high amount of silver, a small percentage of gold and bismuth, and a small amount of copper can indicate the authenticity of the coin.
Introduction
Archaeometry is a modern branch of archaeological studies with laboratory methods that assist archaeologists in authenticity, dating, manufacturing technology, and material analysis. Elemental analysis of coins provides the ability to identify mints, mines, and economic conditions and metal extraction technology, and is important for quantitative and qualitative measurement of coins and accurate dating.
The data of this article includes 22 half-dirham silver coins from the Abbasid period of Tabaristan, 18 of which belong to the Foundation museums and 4 to the Mojtaba Zadeh Khorasani collection. The two main questions of this research are as follows:
       What is the economic situation and monetary policies of Tabaristan during this period, based on laboratory results? What analysis of the elemental composition of the coins does the elemental analysis of the Abbasid governors of Tabaristan provide? For more information and a better analysis of the economic and political conditions, selected coins were tested in the Vandograph laboratory of the Atomic Energy Organization using the pixie method

based on that, the method of extracting metals from ore, re-melting, the type of mine, the constituent elements, and the fineness of the coins can be determined.

Theoretical Basics
With the death of Yazdgerd III (20 Yazdgerd-31 AH-652 AD) and the fall of the Sassanid, an independent dynasty called the Dabuyi Espahbadans was formed in Tabaristan and minted coins whose type of calligraphy, motifs, and symbolic signs are a complete imitation of the coins of the late Sassanid kings.

       On one side of the coin, the king's profile and name, religious words and symbolic symbols are engraved, and on the other side, the hearth, the guardians, and the date and place of minting are engraved in the Sassanid Pahlavi script. The date of origin of the coins is June 11, 652 AD, corresponding to 31 AH, and the day of the death of Yazd Gerd III. The coins are mainly made of silver, with a few bronze coins in existence. A dynasty that lasted until 142 or 143 AH and finally collapsed during the caliphate of Mansur Abbasid (136-158 AH) and the administration of affairs was entrusted to governors elected by the Abbasid caliphs.
       The Abbasid caliphs attempted to achieve cultural dominance through political supremacy, but they were unsuccessful and the coins of this period continued in the same style as before. The coins are written in both Pahlavi and Kufic scripts. Historical sources and numismatic evidence have identified 43 Arab or Iranian governors appointed by the Abbasid caliphs.
       Out of these numbers, 23 are mentioned in written sources, 15 in numismatic and historical sources, and 5 have entered the field of history only through numismatic sources. From the time Abu al-Khasib (141-142 AH) was commissioned to conquer Tabaristan to Muthanna ibn al-Hajjaj (179-180 AH), the last Arab ruler in Tabaristan ruled this region continuously from 107 or 108 AH (141 or 142 AH) to 143 AH (178 or 179 AH), for a total of 36 or 37 years. Of course, with an interval of 18 years, Fadl ibn Sahl minted a coin in the previous style in 161 AH (197 AH).


Discussion and Analysis
Of the ten analyzed coins named after Khalid ibn Barmak, Omar ibn al-Ala, Saeed ibn Daalaj, Hani ibn Hani, Sulayman, Muqatil, and Abdullah ibn Qahtaba from the Abbasid period, three coins from the years 124 Umar, 138 Hani, and 139 Muqatil have more than 90 percent silver, and among them, the Muqatil coin has the best quality with 95.96 percent silver.
       The average silver content of Abbasid coins is 90.49% and copper is 7.08%, indicating a relative change in the monetary system and economic situation. The changes and devaluation of the currency do not seem to be very severe, but this small amount indicates the occasional instability of the political and economic situation in Tabaristan at this historical point.
       During the years 129 to 143 AD, nameless coins with the word Afzot were minted in Tabaristan, and 12 of these coins were dated 129, 130, 131, 132, 135 (two coins), 136 (two coins), 137, 141 (two coins), and 143 AD.
       Among them, three coins dated 131, 136 and 1/141 lack bismuth and gold elements, and low silver and high copper strengthen the possibility of counterfeiting. The remaining coins dated 129, 130, 132, 135 (two), 136, 137, 141/2, 143 with an average silver content of 85.05% show a decrease of more than 5% compared to the coins of the Abbasid Emirs. The decrease in silver with an average increase in copper of 10.13% leaves no doubt that these shifts were driven by economic necessity. The amount of gold (0.09) and bismuth (0.17) on the coins further supports the notion that the copper content was deliberately manipulated.
 
Conclusion
 Elemental analysis shows the type and amount of metals in the coins and their dominant compositions. Since the only name on the coins as a mint is the generic term Tapuristan, referring to the entire province, it is not possible to locate the mines and minerals used unless historical silver ore mines are examined, and the compositions present in them are analyzed, and by comparing them, the origin of the mineral used is identified. The most important achievement of the elemental analysis of coins is the representation and reflection of the political, economic and monetary conditions of Tabaristan during this period. The coins of the Abbasid provinces are of lower quality and purity than those of the Dabu'i Espahbadan, and this situation may have arisen due to the rapid change and relocation of Emirs, the interference and simultaneous rule of governors, and the resulting instability. The lowest grade obtained from the elemental analysis belongs to the nameless coins with the word "Afzot", a ratio that could indicate the fact that the coins were minted by subordinates and associates of the Abbasid governorate in a part of the province of Tabaristan and therefore suffered from deficiencies and imperfection.
       In elemental analysis of this collection, sometimes contradictory data from the same date were obtained, and this complexity makes it challenge to provide an accurate report. For example, two anonymous coins from the date 141 has given different results.
       Accordingly, one coin contained 85.67 percent silver and the other 76.52 percent silver, and 11.42 and 19.37 percent copper, disparate amounts that further complicate the issue. The first coin lacks bismuth and gold, while the second coin, with less silver, contains the element bismuth.