This substance was used in a tracer in a 1950 paper whose authors included 
This substance was used in a tracer in a 1950 paper whose authors included JA Bassham and his graduate advisor. One source of it is the Clinton pile where ammonium nitrate is irradiated and the product is shipped through barium carbonate. The existence of this substance was demonstrated by Ruben and Kamen, while Libby helped develop a notable application. It is produced in the atmosphere when cosmic ray neutrons collide with nitrogen. The resulting heavy product is then incorporated into organic compounds thanks to photosynthesis.  It has a half-life of 5,730.  For 10 points, name this isotope of carbon used in radiometric dating that has two more neutron than carbon-12.
This substance was used in a tracer in a 1950 paper whose authors included JA Bassham and his graduate advisor.
Carbon 14 [or C14]