Letters to the editors 253
The activity of this sample was measured also by an ionization method. The radiation was filtered through 5 mm of lead and comparative measurements were made against a radium standard using an electrometer, Type SG-1M. The sample activity was found to be equal to 47.1 mg-equiv of radium. In order to estimate the absolute activity of the equilibrium 140Ba + laXa sample, the specific gram-equivalent of radium, after filtering through 5 mm of lead, was calculated. It was found to be 1.3. The gamma-ray outputs of lroBa and laoLa were derived from the data of &KHAN-GEL'SKI~~) and DZHELEPCIV and PEKER .cB) Good agreement was obtained between the activity of the laoLa sample found by the ionization method and that determined using the 4~ beta-counter.
The absolute intensity of the 2.5 MeV laoLa gamma-ray was found to be: 6.6 x 10' quanta/set 35 x 3.7 x lo* decayisec = 0.05 quanta/decay
The mean square error of the determination is estimated at 15 per cent.
In beryllium, we observed only a very small photo-effect from the l*OLa gamma-radiation, other than that caused by the 2.5 MeV radiation. This shows that most of the gamma-radiation from lroLa has, in fact, an energy which is below the photo-nuclear threshold in beryllium. According to the published data, the energy of the principal laoLa gamma-ray is 1.597 MeV.@' V. A. ARKIPOV * Translated by D. L. ALLAN from Atomnaya Energiya 3, 10 (1957) [Reprint No. AE 176.1