Spectrum shape ofK-orbital shakeoff electrons and accompanying nuclear beta particles. II. Decay ofPm147

The composite $K$-orbital-shakeoff plus nuclear-electron spectrum was measured in coincidence with $K$ x rays in the $\beta$ emitter ${}_{}{}^{147}{}_{}{}^{}\mathrm{Pm}$ ($E_0=227\mathrm{}$ keV) using the Argonne double-lens magnetic spectrometer and a Ge(Li) photon spectrometer. A bare NaI(Tl) scintillation electron detector allowed coincidence data to be recorded reliablydown to an electron energy of ∼5 keV. The measured spectrum showed prominently the expected intensity of Sm $L$-Auger lines at 5-6 keV following $K$ x rays, and also the $K$ internal conversion line of the 121.2 keV transition in Sm populated by the weak (5.7 ± 0.7 × ${10}^{-5\mathrm{}}$; $logft=10.5\mathrm{}$) inner $\beta$ group of ${}_{}{}^{147}{}_{}{}^{}\mathrm{Pm}$. Neither of these features was seen in earlier measurements. Corrections for the small contribution of the inner $\beta$ group with its measured spectrum shape and intensity, and for the $L$-Auger peak were made. The resulting spectrum shape and the total $K$-ionization probability, $P_K=8.7\mathrm{}\pm 0.7\times {10}^{-5\mathrm{}}$, are both in good agreement with the $K$ shakeoff theory of Law and Campbell, including a 9% contribution to the spectrum from $K$ shakeup excitation. The spectrum shape agreement rejects a contribution to $K$ ejection by the direct collision mechanism exceeding 60% of that due to shakeoff, compared with Feinberg's theoretical estimate of 21% and to earlier experimental indications. This latter evidence firmly rejects a recent proposal by Isozumi et al. which suggests a direct collision contribution equal to shakeoff to make up for their twofold lower shakeoff prediction.