Patent ID: 7828939

Claim:
A method for concentrating a heavy nitrogen isotope 15 N in which 14 N 15 N and/or 15 N 2 , which are molecules containing a heavy nitrogen isotope of 15 N, are concentrated, wherein the method comprises: distilling successively raw material nitrogen N 2 using plural distillation columns each of which comprises a condenser and a reboiler and is arranged in series, and a part of nitrogen in the distillation is drawn out to be subjected to isotope scrambling, and nitrogen after the isotope scrambling is returned to the distillation to produce nitrogen N 2 with a 15 N concentration of 50 atom % or more, wherein supplying N 2 from a certain distillation column other than a final distillation column to another distillation column which is the next stage is performed using a pressure difference between the two distillation columns as driving force, and N 2 is present from a distillation column other than a first column to another distillation column of a former stage using a liquid head pressure of nitrogen as a driving force, and wherein a cooling fluid used in the condenser is nitrogen N 2 which is other than nitrogen N 2 to be distilled in the distillation step to control the pressure at the top of the distillation column provided with the condenser, and a pressure difference which is a driving force to supply N 2 to the distillation column is obtained.