Radioactive Argon

When bombarded with high speed deuterons, argon gas is found to yield a radioactive product which emits negative electrons, and decays with a period of 110±1 minutes. Chemical tests show that the activity is due to an isotope of argon, and the reaction involved is doubtless ${\mathrm{A}}^{40}$+${\mathrm{H}}^2$=${\mathrm{A}}^{41}$+${\mathrm{H}}^1$. Absorption measurements of the $\beta$-particles indicate that their maximum energy is about 1.1 MV. This is in satisfactory agreement with the results of a cloud chamber study of their distribution curve made by Kurie, Richardson and Paxton, which shows a strong group with an upper limit at 1.5 MV, and apparently also a weak group with an upper limit at about 5 MV. The radioactivity is accompanied by the emission of a $\gamma$-ray, the energy of which is 1.39 MV, as measured by the energies of its Compton recoils in a cloud chamber. The excitation function of the radioactivity favors the Oppenheimer-Phillips theory for this type of reaction, rather than the Gamow theory for the penetration of the potential barrier by a charged particle. The same radioactive substance has been made by subjecting argon to an intense bombardment with neutrons.