Zur Folge nach der Entstehung des 2,3 Tage-Isotops des Elements 93 aus Uran G-151 (27 February 1942) by Otto Hahn and Fritz Straßmann was published in Kernphysikalische Forschungsberichte (Research Reports in Nuclear Physics), an internal publication of the German Uranverein. Reports in this publication were classified as "Top Secret". The reports therefore had very limited distribution, and the authors were not allowed to keep copies. The reports were confiscated under the Allied Operation Alsos and sent to the United States Atomic Energy Commission for evaluation. In 1971, the reports were declassified and returned to Germany. The reports are available at the Karlsruhe Nuclear Research Center and the American Institute of Physics.