Spallation cross sections for the reaction Ar-40(p, 2p3n)Cl-36 are mea
sured in the energy range 47-1000 MeV. The results are used to calcula
te the production of cosmogenic Cl-36 on atmospheric argon by solar pr
otons and by galactic cosmic rays. The dependence of the fall-out rate
of atmospheric cosmogenic Cl-36 on geomagnetic latitude and solar act
ivity is calculated.