K-Electron Capture in Radioactive ArgonA37

A radioactive gas possessing a half-life of 34.1±0.3 days has been produced by bombarding solid samples containing potassium, chlorine, calcium, or sulfur. The observed data require that this activity be assigned to ${\mathrm{A}}^{37}$ in accord with the following reactions: $\{{\mathrm{K}}^{39}+{\mathrm{H}}^2,\to {\mathrm{A}}^{37}+{\mathrm{He}}^4\}\{{\mathrm{Cl}}^{37}+{\mathrm{H}}^2,\to {\mathrm{A}}^{37}+2n\}\{{\mathrm{Cl}}^{37}+{\mathrm{H}}^1,\to {\mathrm{A}}^{37}+n\}\{{\mathrm{S}}^{34}+{\mathrm{He}}^4,\to {\mathrm{A}}^{37}+n\}\{{\mathrm{Ca}}^{40}+n,\to {\mathrm{A}}^{37}+{\mathrm{He}}^4.\}$ Alpha-bombardment of chlorine has failed to produce a measurable quantity of this activity by an ($\alpha ,d$) reaction. The detection of 4.72A Cl $K\alpha$ x-rays by means of critical absorption measurements in gaseous compounds of chlorine and sulfur reveals that ${\mathrm{A}}^{37}$ decays by $K$-electron capture. Cloud-chamber observations and aluminum absorption measurements indicate that $K$-electron capture accounts for more than 99.9 percent of the total number of disintegrations. The probability of the x-ray quantum being internally converted has been calculated to be 0.96±0.03. No gamma-rays were observed.