The corresponding frequency gives the velocity v. The pioneering work of Wien and Thomson stimulated many other scientists to experiment with canal rays and to improve the techniques of mass spectrometry.
Wien's interest was focussed more on the physics of canal rays. For many years, canal rays generated in discharge tubes became the most important source of ions. Not only ions of different filling gases were studied but also ions of material evaporated inside the discharge tube or produced by sputtering.
The canal rays were generally guided through narrow capillaries and apertures into the observation tube. He employed this method to study the interaction of canal rays with various gases. In the following, the development of mass spectrometry based on canal rays will be briefly described. Soon, the visual observation of the patch at the back wall of the obervation tube was replaced by photography, - the photo film was sometimes mounted on the inside of the tube.
Two corresponding pictures taken with a parabola-image spectrograph are shown in Fig. The spots of the bended rays are remarkably sharp indicating a narrow velocity range of the particles.
Wien was surprised that a carbon spot was not observable, - although the fill gas was CO 2. Retschinsky [16] studied the formation of ions in gas mixtures. As can be noticed in Figs. Small amounts of mercury vapor enhance the intensity of the various oxygen ions. Supposedly, these intensity variations are associated with the different electron affinities of the gases.
In order to detections of canal rays bended by crossed electric and magnetic fields, Wien [17] used small thermocouples, which were warmed by the impacting particle beam. Measuring the thermovoltage as a function of the magnetic field strength, Wien obtained the "Energiekurve" of the canal rays, i. Thomson [18] had already analysed the bended canal rays by means of the 'transported electricity'.
He mounted at the position of the observation screen a Faraday cup behind a fine slit. By changing the magnetic field strength he obtained enhanced cup currents, whenever the beam of a certain ion passed the slit.
An instrument equipped with such a Faraday cup is sketched in Fig. This was built by Dempster [19] in Substances of interest were evaporated from a glowing wire spiral K. After deflection, the canal rays penetrated the Faraday cup through a parabolically formed slit F. By means of an improved parabola-image spectrograph, Thomson discovered in , amongst destillates of liquid air, particles having the atomic weight 22 u, which he first considered as a new gas.
Later, it turned out that the corresponding mass line was associated with an isotope of Neon. This was the first identification of an isotope. The mass spectrum of methane presented in Fig. Concerning mass resolution, a big step forward was the double focussing spectrograph of Aston, which is explained in Fig. This instrument also utilizes evaporation of probes inside the discharge tube. The canal rays produced in the right tube of the instrument pass through a small hole in the cathode and a narrow slit in front of the deflection plates, - the latter being the entrance slit of the spectrometer.
After traversing the bending magnetic field, which is perpendicular to the electric field, the rays impact onto the photographic film.
This film can be turned away to allow visual observation of the canal-ray patch on a Willemit screen through the window F. The instrument of Aston compensated the wide energy dispersion in the electric field by the contrary dispersion in the magnetic field.
Double focussing requires a certain arrangement of ion source, bending fields and detection device. The functional dependence of the spectrometer parameters has been derived, for instance, by Wien in his handbook [2]. With Aston's instrument, the mass spectrometry of canal rays had reached a culminating point. It seems that, up to , canal rays were plainly the general source of ions.
Further improvements of mass resolution required ion sources with more homogeneous ion energies than canal rays can provide.
A way out of this dilemma was to apply evaporation of the material of interest leading to a thermal energy spectrum and then to accelerate the thermally generated ions.
One of the first spectrometers using such ion sources was that of Dempster [21]. He managed to use only magnetic bending. Goldstein had discovered canal rays by the light they emitted when travelling through gases and by the fluorescent patch they produced on the wall of the discharge tube.
The study of this light indeed made a major contribution to the understanding of canal rays and how they reacted with matter. It provided information on the nature of the excited atoms. An extremely important discovery made by Stark in [22] was that of the Doppler shift.
In addition to the unshifted lines, broad stripes appeared in the direction of the longer wavelengths which corresponded to the atoms moving towards the observer see in Fig. The Doppler shift allowed the observer to differentiate moving canal ray ions and neutral particles from static gas atoms excited by canal rays. Wien thus examined the question of whether the light was emitted by charged or uncharged atoms or molecules.
In doing so, he studied the light decomposed in spectral lines and emitted from deflectable and non-deflectable rays and found, for example, that the Balmer series of hydrogen came from the neutral atoms and the spark-line of oxygen from the ions. Wien carried out numerous other experiments on light emission; three shall be briefly described in the following section. Firstly, Wien [24] used the Doppler effect for measuring the absolute energy of light associated with a single spectral line emitted by canal rays.
As it is sketched in Fig. This light was observed behind the cathode in direction of the canal rays and compared with the radiation of a black-body having the same intensity and the same wavelength. Applying the radiation laws, the integral radiation energy was calculated, which accounts for the number of emitted photons. This leads to the number of exciting atomic collisions and subsequently to the cross section for excitation or emission, respectively, of the H b light.
Regarding the atomic excitations by collisions as a statistical process, Wien developed a theory using the mean free path as the basic parameter. He also employed the concepts of mean free path and cross section to charge exchange processes, i. Such processes were indicated by the fact that a certain fraction of the canal rays experienced a smaller deflection than pure ion beams. Wien noticed charge exchange first, when canal rays passed through two subsequent regions with magnetic fields: the first field did not influence the neutral component of the rays.
This component, however, turned out to be partially charged, when passing through the second field. Obviously, originally neutral particles were ionized on their way between the two magnets. He recognized that charge exchange depended strongly on the pressure in the observation tube and that also negatively charged particles were formed.
It was used, for instance, to fill the two tubes with different gases or to remove water vapor from the canal rays. In order to prove his theory of collision statistics, Wien built the apparatus shown in Fig. Behind the cathode, the canal rays fly first through the capillary separating discharge and observation area and pass then a series of deflection plates, which remove successively the charged particles from the canal rays. Loading the condensers one after the other, the relative number of particles moving in the straight canal-ray beam was measured by means of a thermocouple T.
Thus, it was possible to determine the ratio of charged to neutral particles behind the last loaded condenser. Provided that the velocity of the canal rays remains constant over the series of condensers, this ratio should be independent of the number of loaded condensers. It turned out that reliable results were obtainable only with canal rays being generated in very pure gases with a very narrow velocity distribution.
By this method, Wien determined, for instance, the mean free path of hydrogen atoms for charge exchange in 0. He got a value of 0. Such results were compared with radii deduced from Bohr's atom model. Stark performed numerous optical experiments on canal rays. One of his peculiar findings was that the light of some spectral lines is observable beyond the sharp border of a canal-ray bundle. His interpretation of this phenomenon was that due to thermal motion some gas atoms escape from the bundle still emitting light with decreasing intensity.
This did not happen to all spectral lines. An example for decreasing light emission are the lines of the Balmer series. Wien [27] tried to measure the decay constant for these Balmer lines. He let the canal rays penetrate the observation tube through a short, little capillary.
The observation tube was evacuated to the lowest possible pressure; this means only a few atomic collisions occurred in the expanding plume. The canal ray bundle was then visible only over a short distance as seen in Fig. The light of this short gleaming strip was split into spectral lines and then used to make a photograph of the strip.
A wedge-shaped absorber in front of this slit had weakened the light exponentially over the length of the slit. By tuning the intensity and the exponential decrease of the comparative light, Wien was able to determine the decay constant of the light emitted from the atoms streaming with a certain velocity into the observation tube. The velocity was measured with help of the Doppler effect. For the light of the Balmer series he obtained a decay constant of 6.
This corresponds to In , Stark [28] made another important discovery concerning light emission of canal rays: he found that many spectral lines - in particular those of hydrogen - split, when the light emitting gas is located in a static electric field. As an example, Fig. Two series of polarized lines are seen, - one polarized parallel P to the field direction, the second one perpendicular S. One year after Stark's discovery, Wien [30] tried to prove if the splitting of spectral lines observed in static electric fields occurs in the same way also, when the light emitting atoms move in a magnetic field.
Such an effect is predicted by Maxwell's theory taking into account the relativity principle: the field strength affecting an atom moving with velocity in the magnetic field with c the velocity of light.
The corresponding splitting was compared by Wien with the splitting caused in a static Coulomb field. The canal rays used by him had a velocity of 0. Therefore, Wien could compare his splitting with results obtained by Stark.
The canal rays generated in the discharge tube R fly through the capillary C fixed between the poles of an electromagnet. The canal-ray light emerging from a slit in the capillary is examined through a central hole drilled in one of the magnet poles by means of an optical spectrograph. This means, the direction of observation is perpendicular to the velocity of the canal rays and parallel to the magnetic field and therefore transversal to the electrodynamic field as in case of the experiments performed with the electrostatic field.
In order to allow observation of the two differently polarized components, the light passes a lime spar. Wien investigates the H g and the H b lines of hydrogen. The splitting was in fact hardly visible, - probably due to the broad velocity distribution of the hydrogen atoms, - but the width of the patch agreed well with values published by Stark, who applied a static electric field, and also with theoretically expected values. Two years later , Wien succeeded to observe also the actual splitting of the component, which is polarized perpendicularly to the field.
Two splitted lines are seen in Fig. This was one of Wien's most beautiful and smartest experiments. Polished metals became rough after the tube had been in use for a certain period. This erosion of the cathode surface has an important effect on the composition of the canal rays, as the sputtered material mixes itself with the rays. Canal rays in the observation area also cause a sputtering of the material they collide with. The amount eroded could be calculated by weighing the cathode, for example.
Wien did not carry out any experiments on sputtering himself. The various experiments all showed that the sputtered amount is proportional to the voltage of the cathode fall, i. A dependence such as this corresponds to the sputtering energy dependency observed today of metals in the keV range.
Less explicit was the dependency of the atomic numbers and masses of the ions and irradiated metals. A comparison with yields won through application of our contemporary sputtering theory shows that the yields measured then were considerably more dependent on atomic numbers and masses than the sputtering theory would expect. Answer to Question. Dr Manju Sen Jan 16, Canal rays or positive rays are those which contain positive ions and are positively charged.
These positive ions are called protons. Cathode rays are those which contain negative ions and are negatively charged. These negative ions are called electrons. But magnitude of charge in cathode rays is always Upvote 9. Tushar rathore Feb 06, Canal rays means abode rays. It have positively shell it gain energy and from higher to lower shell it looses the energy.
Upvote 3. Harsh Singhal Feb 15, Upvote 2. The answer which i am giving is shortest and bestCanal rays are the rays which are coming from anode and are positively charged Cathode rays are the rays which are coming from catjode and are negatively charged.
After the electrons reach the anode, they travel through the anode wire to the power supply and back to the cathode, so cathode rays carry electric current through the tube. In , Michael Faraday passed a current through a rarefied air-filled glass tube and noticed a strange light arc with its beginning at the cathode negative electrode and its end almost at the anode positive electrode. These were called Crookes tubes. Faraday had been the first to notice a dark space just in front of the cathode, where there was no luminescence.
This came to be called the cathode dark space, Faraday dark space, or Crookes dark space. Crookes found that as he pumped more air out of the tubes, the Faraday dark space spread down the tube from the cathode toward the anode, until the tube was totally dark. But at the anode positive end of the tube, the glass of the tube itself began to glow. What was happening was that as more air was pumped from the tubes, the electrons could travel farther, on average, before they struck a gas atom. By the time the tube was dark, most of the electrons could travel in straight lines from the cathode to the anode end of the tube without a collision.
With no obstructions, these low mass particles were accelerated to high velocities by the voltage between the electrodes. These were the cathode rays.
When they reached the anode end of the tube, they were traveling so fast that, although they were attracted to it, they often flew past the anode and struck the back wall of the tube. When they struck atoms in the glass wall, they excited their orbital electrons to higher energy levels, causing them to fluoresce. Later researchers painted the inside back wall with fluorescent chemicals such as zinc sulfide, to make the glow more visible.
Cathode rays themselves are invisible, but this accidental fluorescence allowed researchers to notice that objects in the tube in front of the cathode, such as the anode, cast sharp-edged shadows on the glowing back wall.
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