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K -Electron Capture and Internal Conversion in Cr 51

1940; American Institute of Physics; Volume: 57; Issue: 3 Linguagem: Inglês

10.1103/physrev.57.171

1536-6065

H. J. WALKE, F. Christian Thompson, J.R. Holt,

Electron and X-Ray Spectroscopy Techniques

${\mathrm{Cr}}^{51}$ has been chemically isolated from titanium which has been bombarded with high speed alpha-particles and chromium which has been activated with deuterons. Its half-life is 26.5\ifmmode\pm\else\textpm\fi{}1.0 days and its identification depends on its formation in the reactions ${\mathrm{Ti}}^{48}+{\mathrm{He}}^{4}\ensuremath{\rightarrow}{\mathrm{Cr}}^{51}+{n}^{1}; {\mathrm{Cr}}^{50}+{\mathrm{H}}^{2}\ensuremath{\rightarrow}{\mathrm{Cr}}^{51}+{\mathrm{H}}^{1}; {\mathrm{Cr}}^{50}+{n}^{1}\ensuremath{\rightarrow}{\mathrm{Cr}}^{51}+\ensuremath{\gamma}.$ ${\mathrm{Cr}}^{51}$ decays mainly by $K$-electron capture but is probably unstable against positron emission as it emits strong $\ensuremath{\gamma}$-radiation of energy 0.5 Mev and 1.0 Mev. No positrons of energy > 100,000 ev have been detected, the lower limit of the ratio $K$ capture to emission of positrons of energy > 100,000 ev being 10,000.The $\ensuremath{\gamma}$-ray of energy 1.0 Mev is due to a nuclear transition in ${\mathrm{V}}^{51}$. It is internally converted to an extent of 0.1 percent, the conversion electrons having been found by absorption measurements. Electrons of energy 0.35\ifmmode\pm\else\textpm\fi{}0.05 Mev are also emitted by a strong source of ${\mathrm{Cr}}^{51}$. It is probable that these are recoil electrons due to the 0.5-Mev $\ensuremath{\gamma}$-rays.