FCs-EK: a new sampling of the Fish Canyon Tuff ⁴⁰Ar/³⁹Ar neutron flux monitor

Sanidine from the Fish Canyon Tuff is regularly used as a neutron flux monitor by ⁴⁰Ar/³⁹Ar geochronologists. A new sampling of the Fish Canyon Tuff (denoted FCs-EK) has yielded sanidine that relative to FC-2 is confirmed here to have an <em>R</em> value of 0.9997±0.0100, which is indistinguishable from 1. The new sample will allow for continuity as many ⁴⁰Ar/³⁹Ar laboratories have exhausted their supplies of FC-2. FCs-EK is now available in significant quantities from the Scottish Universities Environmental Research Centre.