Measurement of the 36Ar(n, p) 36Cl cross section at thermal energies using the AMS technique

Abstract

The 36Cl production mechanism in the atmosphere is of interest in understanding the formation of this cosmogenic radioisotope and its applications in geological studies. The 36Ar(n, p) 36Cl reaction has been suggested by Onufriev as a source of 36Cl in the atmosphere. Onufriev derived this estmation by assuming the 36Ar(n, p) 36Cl reaction to be caused by slow neutrons with a cross section of the same order of magnitude as that of the 14N(n, p) 14C reaction [1]. However, no data existed for the slow neutron cross section of 36Ar(n, p) 36Cl. We irradiated enriched 36Ar gas in a reactor and used the AMS technique to detect 36Cl. We obtained an upper limit for the thermal neutron cross section of 1.5 mb. This value is three orders of magnitude lower than the value assumed by Onufriev.