Spectrum Shape ofK-Orbital Shakeoff Electrons and Accompanying Nuclear Beta Particles in the Decay ofPr143

The composite ($K$-orbital shakeoff plus nuclear) electron spectrum shape in coincidence with $K$ x rays in the pure $\beta$ emitter ${\mathrm{Pr}}^{143}$ ($E_0=930\mathrm{}$ keV) was measured with the Argonne magnetic-lens spectrometer and a NaI scintillation x-ray spectrometer. It yields an ordinary Kurie plot nearly linear from $E_{max}=888\mathrm{}\pm 5$ keV [930 keV — ($K$ binding energy)] to ∼160 keV, below which the contribution from the $K$ shakeoff spectrum appears as a sharply rising component down to $\frac{W}{p}$. Significant differences of both component shapes with this modified theory remain. Comparison of the measured shape to that calculated from the formulation of Feinberg for direct collision indicates that this process contributes negligibly to the decay. The ratio of the higher-energy Kurie component (mainly the nuclear $\beta$ component) of the composite spectrum to the singles intensity gives a total $K$-ionization probability $P_K=(2.95\mathrm{}\pm 0.3)\times {10}^{-4\mathrm{}}$; relativistic self-consistent-field wave-function overlap integrals give 3.0×${10}^{-4\mathrm{}}$.