Table of contents

It has become increasingly evident of recent years that a detailed study of the processes occurring in gas discharges often requires a means of analysing and studying separately the various ionic species. This is true even in the case of the inert gases.

This paper describes the development, and analyses the action, of a versatile probe which can readily be moved radially into and out of a discharge tube and which is able to distinguish between ions (positive or negative) of various masses. With this instrument it is therefore now possible to make probe studies on a particular species of ion in the presence of others.

Basically the instrument is a very small 12-stage linear accelerator which discriminates in favour of ions of a particular mass-charge ratio passing through its sampling orifice. It is of high sampling efficiency and this together with its mobility and the absence of a magnetic field gives it certain pronounced advantages over the magnetic method of analysis.

The relative wall-currents of molecular and atomic ions have been measured in hot-cathode d.c. discharges in several of the inert gases. The radio-frequency mass spectrometer probe was used for this investigation and results were taken over a range of pressures up to 1 mm Hg and tube currents from 50 to 500 mA. From a study of the results the probable formation process for the molecular ions is found to be that involving collisions between normal atoms and atoms in highly excited states.

Methods of utilizing the recoil motion of excited nuclei produced in disintegrations, to obtain estimates of the half-lives of excited states, are described. They involve measurement either of the distance moved by the recoiling nucleus before radiation occurs, or of the small Doppler shift in frequency produced by the recoil motion. Details are given of the application of some of the methods to the measurement of the half-lives of the levels of ¹⁶O at 6.13 MeV (E3 transition), 6.9 MeV (E2) and 7.1 MeV (E1), with the following results: 6.13 MeV, 5 × 10^-12 less, similar τ less, similar 10^-11 sec; 6.9 MeV, τ less, similar 1.2 × 10^-14 sec; 7.1 MeV, τ less, similar 8 × 10^-15 second.

The magnetic susceptibility of potassium manganicyanide has been measured at temperatures from 4.2°K to 300°K. The susceptibility, which at room temperature approximately follows Curie's law, approaches a temperature-independent value at very low temperatures. This behaviour is compared with the theoretical prediction of Kotani.

The angular correlation between all γ-rays leading to ThC' ground state and the ThC'D α-rays has been measured and found isotropic, in agreement with theory. The angular correlation between the 6.04 MeV α-ray and the 40 keV γ-ray in ThCC'' has been measured and found anisotropic, the best fitting curve being W(Θ) = 1 - (0.22 ± 0.05) cos² Θ. Spin assignments of 1 or 2, 4 and 5 are deduced for the levels ThC (ground), ThC'' (40 keV) and ThC'' (ground) respectively. The total internal conversion coefficient of the 40 keV ThCC'' γ-ray has been measured and a value for the L shell conversion coefficient of α_L = 15.7 ± 1.6 is deduced. This is in much better agreement with theoretical prediction than previous measurements.