The Radiations from Hafnium

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---₇₂Hf¹⁷⁵; 19-second---₇₂Hf179*; 5.5-hour---₇₂Hf180*; 45-day---₇₂Hf¹⁸¹.70-day period.---The photographic spectrograms of the internal conversion electrons associated with the 70-day period in ₇₂Hf¹⁷⁵ 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 ₇₂Hf¹⁷⁵ leading to an excited state of ₇₁Lu¹⁷⁵.45-day period.---An investigation of the internal conversion electron spectrum in the Argonne 180^∘{} beta-ray spectrometer indicated the presence of one beta-ray of 0.42±{}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 ₇₃Ta¹⁸¹. 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 ₇₂Hf¹⁸⁰.19-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 ₇₂Hf¹⁷⁹.