Radiocarbon Production Rate near Sea Level

The natural production of radiocarbon by cosmic-ray neutrons has been observed experimentally. Proportional counters, filled with 2 atm of nitrogen, have been employed to detect the exoergic ${\mathrm{N}}^{14}\mathrm{}(n,p)\mathrm{}{\mathrm{C}}^{14}$ reaction. Electronic pulse-shape discrimination is utilized to discriminate against meson- and photon-induced events. A ${\mathrm{C}}^{14}$ production rate of $(1.89\mathrm{}\ne 0.08)\times {10}^{-7\mathrm{}}$/sec/${\mathrm{cm}}^3$ has been obtained for the air-land interface at the Argonne National Laboratory site. This result represents the average value for a time duration of one month, November-December, 1966. Fluctuations as large as 25% from this average value were observed. The density of slow neutrons can also be determined from this experimental result. An average value of (1.19±0.06)×${10}^{-8\mathrm{}}$ neutrons/${\mathrm{cm}}^3$ was found for the air-land interface at the Argonne National Laboratory site (53° N geomagnetic latitude).