neutron-activation tests. These involve the irradiation 

 of coins to be analyzed in a neutron pile. The gamma- 

 radiation resulting from the neutron bombardment 

 is characteristic in wavelength and half-life according 

 to the content of the specimen. The radiation must be 

 sorted out and measured carefully in order to ascertain 

 the composition of the object. 



Experiments were conducted in February 1960 

 concerning the application of the principle of X-ray 

 diffraction as a nondestructive means for determining 

 techniques used in the manufacture of coins and 



Fig. 54. — ItN-DuLiAR CJoLD Piece issued about 

 1849 by J. S. Orsmby & Co. in Sacramento, 

 California. 



medals. Deceptive centrifugal casts may be readily 

 ascertained and eliminated tiirough this method. 

 This was demonstrated in tests conducted in coopera- 

 tion with the United States Secret Service and the 

 Bureau of Standards. X-ray-back-reflection patterns 

 of two United States 1 -dollar gold pieces showed 

 definite differences as can be seen from the juxtaposed 

 photographs (fig. 140). The rings on the right are 

 much narrower and less spotty than those on the left. 

 They correspond to a struck, genuine piece on the 

 right and a cast, counterfeit one on the left."* These 

 experiments are based on the fact that the structure 

 in this type cast metal is crystalline with extremely 

 small crystallites due to the rapid cooling, while the 

 processes in the manufacture of a struck piece induce 

 distortions in the crystalline lattice. These differences 

 of the structure of the metal result in diff"erent X-ra\- 

 back-reflection patterns. 



In 1964 tests were conducted by the Division of 

 Numismatics in cooperation with the Bureau of 

 Standards to determine metallurgical details in con- 

 nection with a platinum 50-ccnt piece dated 1814, 

 a Russian 3-ruble piece, and two 5-dollar gold pieces 

 issued in 1849 by the Massachusetts and California 

 Gold Compan>-. X-ray radiographic and diffraction 

 techniques were used, and the experiments were 



USA'.y/ Report, I960, p. 49. 



Fig. 55. — Five- and 10-Dollar Gold Pieces 

 issued in 1849 by the Pacific Co. in San 



Francisco. 



continued in the spectrochemical analysis section of 

 the Bureau of Standards."" 



Through the cooperation of the Naval Research 

 Laboratory, it was possible to conduct comparative 

 analyses of an ancient silver quarter shekel, struck 

 during the first year (A.D. 66 67) of the Jewish 

 war against the Romans, and of a silver shekel struck 

 during the third year of the same war. The compo- 

 sition of the quarter shekel was found to be silver, with 

 2 to 3 percent copper and approximately 1 percent 

 arsenic, according to X-ray fluorescence analysis. 



Fig. 56. — Ten-Dollar Gold Piece issued in 1861 

 by J. J. Conway and Co., Colorado. 



The shekel was made instead of practically pure silver, 

 Willi only 1 percent copper and no other elements 

 were present. The interpretation of the X-ray diffrac- 

 tion patterns allows some conclusions concerning the 

 manufacture of the pieces, the quarter shekel was 

 apparently worked cold, while the shekel planchet 

 was subject to a long annealing process with very 

 little, if any, cold work. '" Such analyses are iin- 



'" US.\.\1 Report, 1964, p. 66. 

 '" Ibid., pp. 66-67. 



32 



BULLETIN 229: CONTRIBUTIONS FROM TIIK MUSEUM OF HISTORY .\ND TECHNOLOGY 



