The Radiations from Hafnium

Abstract

The 70-day, 45-day, 5.5-hour, and 19-second activities of Hf have been investigated by spectrometric, spectrographic, absorption, and coincidence methods. From activation experiments on the separated Hf isotopes, the following assignments have been made: 70-day---$_{72}\mathrm{Hf}^{175}$; 19-second---$_{72}\mathrm{Hf}^{179*}$; 5.5-hour---$_{72}\mathrm{Hf}^{180*}$; 45-day---$_{72}\mathrm{Hf}^{181}$.70-day period.---The photographic spectrograms of the internal conversion electrons associated with the 70-day period in $_{72}\mathrm{Hf}^{175}$ indicated the presence of four gamma-rays. The association of Lu work functions with the various lines confirmed the hypothesis of K electron capture in $_{72}\mathrm{Hf}^{175}$ leading to an excited state of $_{71}\mathrm{Lu}^{175}$.45-day period.---An investigation of the internal conversion electron spectrum in the Argonne 180\ifmmode^\circ\else\textdegree\fi{} beta-ray spectrometer indicated the presence of one beta-ray of 0.42\ifmmode\pm\else\textpm\fi{}0.01 Mev and five gamma-rays. An upper limit of 1 percent may be placed on any more energetic beta-ray. Single and coincidence absorptions in lead and aluminum showed the three strongest gamma-rays and the single beta-ray. Delayed coincidence absorption indicated that the 0.42-Mev beta-ray leads directly to the 22-microsecond metastable state of $_{73}\mathrm{Ta}^{181}$. No delayed gamma-coincidences were found. Thus, all gamma-rays appear to follow the 22-microsecond state. Additional coincidence measurements showed internal conversion electron groups corresponding to three of the gamma-rays. The decay scheme proposed by Chu and Wiedenbeck, as modified by Cork et al. was confirmed.5.5-hour period.---Activation of extremely pure Hf samples showed an activity of 5.5 hours in addition to the 45-day period. The assignment of this activity to Hf was confirmed by chemical methods. No delayed coincidences were observed. Internal conversion electron groups corresponding to five gamma-rays were resolved; absorption in lead indicated three of the photon components. Aluminum absorptions indicated coincidences between internal conversion electron groups from at least two of the gamma-rays. Activation of separated isotopes shows that this activity is one of an isomeric state of $_{72}\mathrm{Hf}^{180}$.19-second period.---A photographic spectrogram of the internal conversion electrons showed the presence of a single gamma-ray; the association of Hf work functions with the four lines observed verified the hypothesis of an isomeric state in $_{72}\mathrm{Hf}^{179}$.