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The drift velocities of electrons, the saturation characteristics of ionization and the W -values for internal conversion electrons emitted from 207 Bi in liquid argon, liquid argon-gas (xenon, nitrogen, methane and ethylene) mixtures and liquid xenon have been measured by using gridded ionization chambers. The drift velocity of electrons in xenon or nitrogen-dopes liquid argon shows little increase compared with that in liquid argon, while that in liquid argon-methane or -ethylene mixtures shows a remarkable increase. From each saturation curve, the so-called “recombination coefficient” k is obtained, assuming that the electric field ( E ) dependence of the collected charge ( Q ) is represented by Q∝( 1+ k E ) −1 , and the values for liquid rare gases as shown above are tabulated. The W -values in liquid argon-xenon mixture and liquid xenon have been determined by comparing with that in liquid argon. It is shown that admixing liquid argon with a small amount of xenon results in the reduction of the W -value and that the W -value in liquid xenon is much smaller than that in the gas phase. On the basis of these experimental results, the applicability of the liquid rare gases to detector medium is discussed.

The alpha particle energy and the half-life of Gd150 have been measured with a double-grid ionization chamber. Backgrounds are minimized by the grid-collector coincidence technique. The alpha particle energy is determined as 2.715±0.018 MeV by referring to that of Sm147 (Eα = 2.23±0.02 MeV) reported by Macfarlane. The half-life is estimated to be (1.4±0.4)×106 y from the observed counting rate and the total number of Gd150 nuclei contained in the specimen. The number is estimated from the observed beta-decay rate of the parent nuclei Eu150, which are produced by a photonuclear reaction Eu151(γ, n)Eu150. The experimental half-life thus obtained agrees within a factor of 4.4 with the theoretical half-life calculated from the observed alpha-particle energy on the basis of a conventional barrier-penetration theory. The results show that Gd150 behaves quite normally in the systematics of rare-earth alpha-decay.

An improved method of measuring the alpha-gamma angular correlation is proposed. The apparatus consists of a gridded ionization chamber and a NaI scintillation counter. In a gridded chamber, generally, the cathode pulse yields information on the emission angle of an alpha-particle, while the collector pulse gives information on its energy. Accordingly, the alpha-gamma angular correlation of mixed alpha-sources, in which some isotopes emitting alpha-particles of different energies and subsequent gamma-rays of almost the same energy are included, can be easily measured from the pulse height distribution of the cathode pulses coincident with the scintillation pulses and the collector pulses in the desired energy intervals, respectively. As examples, the angular correlation for two decay series in the daughter products of ThB, which are 1. ThC′ ∗ (γ)ThC′(α)ThD and 2. ThC(α)ThC″ ∗ (4+)(γ) ThC″(5+), were measured. The results are in good agreement with theoretical prediction and those obtained by other workers.