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Over the next three to four years , milligram quantities of americium and microgram amounts of curium were accumulated that allowed production of isotopes of berkelium ( Thomson , 1949 ) and californium ( Thomson , 1950 ) .
 Thomson, Thomson
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Thomson, Thomson