Application of deuteron–deuteron (D–D) fusion neutrons to 40Ar/39Ar geochronology

Neutron irradiation of samples for 40Ar/39Ar dating in a 235U fission reactor requires error-producing corrections for the argon isotopes created from Ca, K, and, to a lesser extent, Cl. The fission spectrum includes neutrons with energies above 2–3 MeV, which are not optimal for the 39K(n,p)39Ar reaction. These higher-energy neutrons are responsible for the largest recoil displacements, which may introduce age artifacts in the case of fine-grained samples. Both interference corrections and recoil displacements would be significantly reduced by irradiation with 2.45 MeV neutrons, which are produced by the deuteron–deuteron (D–D) fusion reaction 2H(d,n)3He. A new generation of D–D reactors should yield sufficiently high neutron fluxes (>1012 n cm−2 s−1) to be useful for 40Ar/39Ar dating. Modeling indicates that irradiation with D–D neutrons would result in scientific benefits of improved accuracy and broader applicability to fine-grained materials. In addition, radiological safety would be improved, while both maintenance and operational costs would be reduced. Thus, development of high-flux D–D fusion reactors is a worthy goal for 40Ar/39Ar geochronology.