Production of Very Soft Rontgen Radiation by the Impact of Positive and Slow Cathode Rays

Sir James Dewar was kind enough to supply me with large quantities of the residues obtained from the evaporation of many thousand tons of liquid air. These residues had been absorbed by charcoal which had been kept in a sealed vessel. I have analysed these residues by the Positive Ray Method. The general arrangements were the same as those described in my book on Positive Rays. Some alterations, however, were necessary, as I used for these investigations a much more powerful induction coil than the one I had hitherto employed. With this coil so much heat was developed in the part of the tube near the cathode that any wax joints in that neighbourhood, even though they were cooled by a water jacket, gave off enough gas to spoil the vacuum for positive ray purposes. To avoid this difficulty I substituted for the wax joint, which formed the connection between the glass bulb in which the discharge takes place and the brass vessel which contains the camera, a joint made by a method used by Mr. Roebuck, and described by him in the ‘Physical Review.' vol. 28, p. 264 (1909). The method consists in first making on the outside of the glass tube a deposit of platinum by one or other of the devices used for platinising glass, and then depositing slowly by electrolysis a layer of copper on the platinum. With care this layer can be made thick and firm enough to enable a brass tube connected with the camera vessel to be soldered on to it, and an air-tight joint obtained which does not give off gas when heated by the discharge. The method adopted to analyse the gas was to put some of the charcoal containing the gaseous residues into a small vessel A, which was fused on to the discharge tube B; there was a tap between A and B, and this was turned until B had been exhausted to a very low pressure; there was also a very fine capillary tube in the circuit between A and B, and when the pump used for exhausting the discharge tube was kept in action a continuous stream of gas from A could be kept flowing through the discharge tube without making the pressure too high to obtain good photographs. Just before the tap between A and B was opened a photograph was taken with ordinary air going through the discharge tube, and the lines in this were compared with those on the photograph obtained when the gas from A was flowing through the tube.

When Goldstein's report on the "positive light" (or what is known as "Kanalstrahlen", canal rays) in gas discharge tubes first appeared in 1886, Willy Wien had just finished his thesis at the Helmholtz Institute in Berlin. Eleven years later he performed his first experiments on canal rays and found that they consisted of inert, charged and neutral particles. The charged component in canal rays could be de ected using electric and magnetic fields, enabling Wien to roughly determine their mass-to-charge ratio. Improving vacuum conditions and detection efficiency, Thomson finally resolved the lightest constituents of canal rays: the hydrogen ions H+ and H2+. This marked the beginning of mass spectrometry. The first mass spectrographs were parabola-image instruments being used by Thomson to discover isotopes. Until about 1923, canal rays became the most common ion source. Also Aston used canal rays as an ion source for the first double focussing mass spectrometer. - Wien continued his work on canal rays up to the end of his life (he died in 1928). He investigated their interaction with matter, i.e. the mean free path of canal rays in gases with respect to charge exchange and atomic excitation. His particular interest was addressed to the physics of light emission by canal rays, such as the line spectrum and the splitting of these lines in magnetic and electric fields, the Doppler effect and lifetimes.

In 1886, Goldstein observed that when the cathode in a vacuum tube was pierced with holes, the electrical discharge did not stop at the cathode; behind the cathode, beams of light could be seen streaming through the holes in the way represented in Figure 1. He ascribed these pencils of light to rays passing through the holes into the gas behind the cathode; and from their association with the channels through the cathode he called these rays Kanalstrahlen. The colour of the light behind the cathode depends on the gas in the tube: with air the light is yellowish, with hydrogen rose colour, with neon the gorgeous neon red, the effects with this gas being exceedingly striking. The rays produce phosphorescence when they strike against the walls of the tube; they also affect a photographic plate. Goldstein could not detect any deflection when a permanent magnet was held near the rays. In 1898, however, W. Wein, by the use of very powerful magnetic fields, deflected these rays and showed that some of them were positively charged; by measuring the electric and magnetic deflections he proved that the masses of the particles in these rays were comparable with the masses of atoms of hydrogen, and thus were more than a thousand times the mass of a particle in the cathode ray. The composition of these positive rays is much more complex than that of the cathode rays, for whereas the particles in the cathode rays are all of the same kind, there are in the positive rays many different kinds of particles. We can, however, by the following method sort these particles out, determine what kind of particles are present, and the velocities with which they are moving. Suppose that a pencil of these rays is moving parallel to the axis of x, striking a plane a right angles to their path at the point O; if before they reach the plane they are acted on by an electric force parallel to the axis of y, the spot where a particle strikes the plane will be deflected parallel to y through a distance y given by the equation

THE first part of the paper contains a discussion of the evidence afforded by the positive rays as to the nature of the ionisation of the gases in a discharge tube and the properties of atoms. The positive rays consist of:—

This investigation was undertaken in order to discover whether the socalled canal rays (Canalstrahlen) discovered by Goldstein, which, at suitable pressures, visibly stream through the apertures in a perforated cathode, backward away from the anode, share with cathode rays the property discovered, as regards the latter, by Sir William Crookes many years ago, of producing a sufficient mechanical pressure to cause small and light mica mill-wheels to rotate. Several tubes were constructed and experimented with, and all showed that canal rays do cause mica mill-wheels to rotate quite rapidly. Fig. 1 is the form of tube with which this was most conclusively demonstrated. A 1 is the anode, the lower end of which is tipped with a glass plate, so as to preclude the transmission of cathode rays vertically downwards in the event of this electrode acquiring at any moment a negative charge due to oscillations in the electric discharge.

Hydrogen canal rays accelerated in fields up to 40 kv were allowed to impinge on a metal target and the beam of particles and radiation emitted from the target were investigated. Pinhole images of the focal spot were obtained on Schumann plates and plates coated with molybdenum trioxide. The presence of atomic hydrogen was shown by a characteristic light blue color produced on molybdenum trioxide plates. By means of a deflecting magnetic field it was found that the beam from the target consisted mainly of neutral particles (or of radiation) but contained a smaller number of protons whose velocity was practically equal to that of the protons incident on the target. The neutral particles by virtue of their ability to affect a photographic plate could suggest the presence of electromagnetic radiation. A grating was used to detect such radiation. Radiation of wave-length 1216A was excited in the residual gas by the canal ray beam when the pressure was as low as ${10}^{\ensuremath{-}4}$ mm of Hg. Any characteristic radiation from the target excited by canal ray impact is too small to be measured.

Based on fully kinetic model using drift-Maxwellian distributions and taking into account the transverse electrostatic field (TEF), it is shown that the current-filamentation instability (CFI) grows unexpectedly with the plasma temperature. The growth is attributed to the decreasing of the TEF as the plasma becomes hot. In the low-temperature plasma regime where the TEF is strong, it is identified that the TEF can dominate over the thermal pressure in suppressing the CFI. Since the TEF originates from the temperature difference between the beam and the plasma, the plasma temperature plays a significant role for the development of the CFI and the quasistatic magnetic fields in a hot-beam warm-plasma system. Particle-in-cell simulations verify the above results.

We investigate how the presence of a transverse electrostatic field influences the propagation properties of guided electron waves in coupled-quantum-well waveguides. The basis eigenstates of electrons in the uncoupled quantum well in the presence of a transverse electric field are calculated by using the Airy-function approach and the transfer-matrix method. By decomposing the eigenfunctions of electrons in the coupled double quantum wells in terms of the basis eigenfunctions of the individual wells, the expression for the mode-amplitude functions (MAF) for various bare states in the wells is presented. By setting up appropriate initial boundary conditions one can simulate different electron-injection conditions for the system and study how the electron waves evolve among the various states. By varying the bias, different configurations of electron-state structure can be formed. When a pair of matching states are produced in the wells, the electron-wave transfer takes place mainly between these matching bare states. The particular patterns of the transfer depend on the injection conditions and the energy of the incident electron. The variation of the magnitude of the MAF's can have a sinusoidal-like oscillation or the profile of a rapid decay (growth) from unity (zero) to a plateau imposed upon a small-amplitude oscillation. When all the bare states are mismatched the transfer of electron waves may still occur between two states with close energy levels in the channels. We also show the influence of multimodes on the variation of the magnitude of MAF. This leads to some oscillations imposed on the original sinusoidal-like function and causes incomplete transfer between pairs of states in the channels. Therefore, the pattern of the electron-wave transfer in channels may be controlled and modified by applying a transverse electrostatic field in the coupled-quantum-well waveguide.

In 1886, Goldstein observed that when the cathode in a vacuum tube was pierced with holes, the electrical discharge did not stop at the cathode; behind the cathode, beams of light could be seen streaming through the holes in the way represented in fig. 1. He ascribed these pencils of light to rays passing through the holes into the gas behind the cathode; and from their association with the channels through the cathode he called these rays Kanalstrahlen. The colour of the light behind the cathode depends upon the gas in the tube: with air the light is yellowish, with hydrogen rose colour, with neon the gorgeous neon red, the effects with this gas being exceedingly striking. The rays produce phosphorescence when they strike against the walls of the tube; they also affect a photographic plate. Goldstein could not detect any deflection when a permanent magnet was held near the rays. In 1898, however, W. Wien, by the use of very powerful magnetic fields, deflected these rays and showed that some of them were positively charged; by measuring the electric and magnetic deflections he proved that the masses of the particles in these rays were comparable with the masses of atoms of hydrogen, and thus were more than a thousand times the mass of a particle in the cathode ray. The composition of these positive rays is much more complex than that of the cathode rays, for whereas the particles in the cathode rays are all of the same kind, there are in the positive rays many different kinds of particles. We can, however, by the following method sort these particles out, determine what kind of particles are present, and the velocities with which they are moving. Suppose that a pencil of these rays is moving parallel to the axis of x, striking a plane at right angles to their path at the point O; if before they reach the plane they are acted on by an electric force parallel to the axis of y, the spot where a particle strikes the plane will be deflected parallel to y through a distance y given by the equation y = e/mv2 A, where e, m, v, are respectively the charge, mass, and velocity of the particle, and A a constant depending upon the strength of the electric field and the length of path of the particle, but quite independent of e, m, or v.

Synchrobetatron coupling in a storage ring with transverse electrostatic fields

THE technic of high voltage generators and high voltage discharge tubes for the production of penetrating x-rays has been successfully applied to nuclear physics. In fact, generators for one million volts and more, designed to produce x-rays by accelerating electrons (the usual way), can be used to accelerate positive particles merely by reversing the tension. Positive particles may be produced by voltages of the order of 50 kv. in tubes not essentially different from the good old gas tubes, the positive ions emerging through a hole in the cathode. These positive ions (canal rays) are protons if the gas in the discharge tube is hydrogen, deutons in the case of heavy hydrogen, and α-particles in the case of helium. The acceleration of the positive particles takes place in a tube which shows, as we shall see in more detail later on, a great analogy with a high voltage x-ray tube. At the other hand, the results of nuclear physics have stimulated further development of high voltage technic. Generators for voltages of many millions of volts have been designed. The first interesting nuclear reaction by means of high voltage was performed by Cockcroft and Walton in 1932 (1). The lithium nucleus was split up into two helium nuclei or α-particles by means of protons accelerated with a voltage of some hundreds of kilovolts. It was shown later that this reaction is possible with voltages as low as 10 kv. (2, 3); but the output increases rapidly with the voltage, as is the case for most nuclear reactions. Moreover, many reactions cannot be expected to take place below certain minimum voltages. So, for instance, may a beryllium nucleus be split up by x-rays or γ-rays equivalent to one and a half million volts as a minimum value. At voltages of little over one million volts (1 mv.) a very interesting phenomenon appears: a gamma quantum is transformed into a pair of particles, a positron and an electron. The production of x-rays (γ-rays) of one million volts becomes extremely efficient, the output at one million volts being equivalent to more than 1 kg. of radium at 1 ma. tube current. A short description of a high voltage generator developed by the author, given at the American Congress of Radiology in 1933, has been published (4). This generator has been further developed up to a voltage of four million volts. A full description has been published recently (5). The article contains also a brief critical survey of the other methods to produce fast particles with and without high voltages. Figure 1 shows a generator of two million volts to earth, being the negative half of a four-million-volts set at the Eindhoven laboratories. Figure 2 shows a one and a quarter million volts generator delivered to, and in use for many months now at, the Cavendish Laboratory, Cambridge. For further details we refer to the paper mentioned above (4) and proceed to describe—(a) A million-volt x-ray or γ-ray tube of the sealed-off type; (b) A high voltage neutron tube.

IN a paper published during the War the late Lord Rayleigh reported some new experiments about the hydrogen spectrum, indicating a duration of Balmer lines of more than 10-5 sec., which is roughly one thousand times greater than the values calculated from quantum mechanics and experimental results with positive rays. The method consists in producing a strong luminosity induced by a powerful condenser discharge in an electrodeless glass tube. Each discharge produces a jet of luminosity, squirting out of the electric field by thermal expansion into a side tube where the decay of the Balmer lines is observed and measured1.

J. J. THOMSON1 discovered the triatomic molecule of hydrogen by the positive ray parabolic method. It was later confirmed by Dempster2, Duane and Wendt3, and several others. Its occurrence is very frequently noted in discharge tubes, but the optimum conditions are not well defined. While investigating the Doppler effect in hydrogen positive rays, using a Wien type of discharge tube, maximum Doppler displacements corresponding to H3+ molecules in the discharge space were observed. The accompanying graph gives the maximum Doppler displacements recorded in the HI´ line of the Balmer series. A Steinheil three-prism glass spectrograph was used at two different dispersions, namely, 7.6 A. and 27.2 A. per mm. in the HI´ region.

Summary Doppler effect in Hγ, Hδ and Hϵ lines in the hydrogen positive rays was studied at discharge potentials between 0·5 kv. and 4·0 kv. H+ 3 and Hi+ 1 particles were found to predominate between 0·5 kv. and 2·5 kv., while H+ 2 were negligibly small in that region. Above 2·5 kv., however, H+ 3 could not be traced while H+ 1 and H+ 3 were present. The pressure corresponding to the discharge potential 2·5 kv. was 0.09 ram. The results are discussed in relation to the findings of Smith and Hornwell. The observations support the view that H+ 2 molecule is the primary particle which dissociates into H+ 3 and H+ 1 at high pressures. The above work was carried out in the Positive Ray Section of the Department of Physics, Benares Hindu University, and the author expresses his grateful thanks to Dr. B. Dasannacharya for his interest in the progress of the investigation.

In view of the extremely important results obtained by Sir E. Rutherford and others from a study of the scattering of α -rays, it seemed worth while to investigate the scattering of particles moving with smaller velocities such as occur in the positive rays. The most interesting, because the simplest, are the rays of positively charged hydrogen atoms, which presumably consist simply of a nuclear particle, or proton. The experiments described in this paper were made in some cases with these rays, in others with the positively charged hydrogen molecules, systems consisting of two protons and one electron. The scattering medium was in all cases hydrogen gas. This was chosen largely for convenience, as the experimental arrangement is considerably simplified if the same gas is used to produce the rays and to scatter them, and also because, with the exception of helium, the molecule of hydrogen is the simplest known, and there seemed more hope of obtaining results which could be given a definite theoretical interpretation. The general scheme of experiment was to produce the rays in a discharge tube, analyse them by magnetic and electric fields in the ordinary way, cut off all except those of the kind required by a slotted diaphragm, pass the remainder through a chamber containing the scattering gas, and receive them in a Faraday cylinder arranged behind a slit of variable width. The experiment consisted in finding how the charge received by the Faraday cylinder varied with the width of the slit, when this was made wider than the geometrical “shadow” of the slot in the diaphragm. Any rays lying outside this “shadow” must have been scattered.