US2520603A - Method of and means for utilizing charged-particle radiation - Google Patents

Description

Aug 29, 1950 E. G. UNDER METHOD 0F AND MEANS FOR UTILIZING CHARGED-PARTICLE RADIATION Flled Sept 25 1948 INVEITOR Ernes Lmder BY A'L'TORNEY Patented Aug. 29, 1950 METHOD 0F AND MEANS FOR UTILIZING i i CHARGED-PARTICLE RADIATION iii-nentJ G. Linder, Princeton, N. J., 'minor to Radio Corporation ot America, a corporation o! Delaware vApplication September 25, 1948, Serial No. 51,206

f 1s claims. (ci. 111-330) This invention relates to electron sources and beams and more particularly to electron beams and multipliers obtained by secondary electrons emitted upon bombardment by nuclear particles.

It is known that certain isotopes are radioactive and emit nuclear charged particles at known rates over known periods of time and over a range of energy values or levels expressed in electron volts. Some emissions consist of positively charged or alpha particles, others of negatively charged or beta particles and others of both alpha and beta particles.

With the emission of a charged particle from the nucleus of an atom, there occurs a transn mutation of the atom into an atom of another element and this atom may or may not be radioactive and it may or may not be gaseous in form.

It is also known that when certain materials are subjected to nuclear radiation bombardment, electrons around the nuclei of the bombarded atoms are knocked out of their orbits and projected into space. This phenomenon is known as secondary emission. The number oi secondary electrons emitted per bombarding particle depends in general upon the material itself and upon angleof incidence and the velocity of the bombarding particle. In general, the greater the angle of incidence and the less the velocity of the bombarding particle, the greater is the number of secondary emitted electrons.

These secondary emitted electrons usually have relatively low energy values compared with the primary emission values. Their further movements after leaving the bombarded surface depend upon their initial velocities and their initial random direction and upon the electro- `trode ofthe tube and 'with sufilcient energy as to i i cause secondary electron emission. Also phosphorus2 becomes stable after emission and is particularly adapted to high vacuum tube use as its decay products are not gaseous. There are, however, a large number of other suitable radioactive substances that may be used within the scope of the invention.

The instant invention comprises improvements on the methods and systems disclosed and claimed in copending U. S. application Serial No. 49,736 illed September 17, 1948, which basic invention contemplates the use or a source of radio-active material and an'electrode that is secondaryemission responsive to the charged particle radiation thereof, the space between the source and the electrode being under partial vacuum and also subjected to a constant magnetic field and the source and the bombarded electrode being connected to an external load circuit in which is provided an electric potential source to keep the radio-active source electrode (cathode) positive in respect to the bombarded electrode (anode).

The improvement of the instant invention comprises the addition of an electrode maintained at a high positive potential near one end of the bombarded anode to draw the electrons from their trapped paths and project them in the form of a beam or collect them on the third electrode and thus secure electron multiplication. In both cases the ow of electrons may be modulated to obtain amplincation of an electrical modulated source.

Among the objects oi the invention are to provide an improved method of and means for producing electron beams.

Another object of the invention is to produce sources of electrons and collect the electrons.

Another object of the invention is to provide an electron multiplier. j

Another object of the invention is to provide an electron beam and to modulate the beam in accordance with a signal, such as a source of alternating current or a modulated current.

Another object of the invention is to provide a new method and means for causing secondary emission of electrons.

Other objects may be apparent from the disclosure of the invention as hereinafter set forth in detail and from the drawing made a partM hereof in which Figure 1 is a schematic diagram of the said basic invention disclosed in said copending application; Figure 2 is a schematic diagram of the instant invention including a third electrode, such as one near the end of the bombarded electrode; Figure 3 is another schematic diagram of the invention and is similar to Figure 2 except that there is provided a modulated voltage to modulate the electron beam; Figure 4 is a schematic diagram of the invention showing a collector electrode near one end of the bombarded electrode and providing tor modulation for the electron beam; and Figure is similar to Figure 4 except the provided modulation ls accomplished by a grid positioned between the source of the radioactive material and the bombarded electrode.

Similar reference characters are applied to similar elements throughout the drawings.

Referring to Figure 1, which is a schematic diagram of the basic invention disclosed in said pending application, I is a nuclear energy generator tube consisting aof a source oi radioactive material 2 mounted on a conducting support l, the source 2 and the support l acting as one element of the tube I.

This element of the tube will be referred to throughout the specication and claims as the source or radioactive source."

The other element of tube I is the collector electrode 4, which may be of one oi various shapes, shown in this case as a cylinder of sheet material. This electrode il is secondary-electron emission responsive upon bombardment by the charged particles emitted from source 2. Aluminum has been found to be a suitable material for electrode 4. An external load 5 is connected between source 2 and electrode 4 and in this load circuit is inserted, in series, a source of electrical potential B, the positive pole ofwhich is connected to source 2, that the source 2 is positive in respect to electrode 4. Source 2 and electrode 4 are surrounded by an envelope 1 [made of some nonmagnetic material such as lglass and is adapted to exhaustion to a residual pressure of the order of -3 mm. of Hg or loweriby any conventional means, not shown. 'I'he residual gaseous medium secondary emission electrons from electrode 4, f'

and the electrons produced by gaseous ionization, but principally from the latter.

Referring to Figure 2, there are provided a source of radioactive material 2, an electrode 4 in the form of a cylinder of sheet material, a solenoid 8 and a source of direct current 9. There is also provided an electrode I0, which is also shown in the form of a cylinder of sheet material. This electrode Ill will be referred throughout this specication and the claims as the accelerating electrode. or accelerator. Accelerator I0 is connected to electrode 4 through a high potential electrical source I4. The electrode 4 is connected to the negative pole of electrical source 6, the positive pole of which is connected to source 2, that the source 2 may be biased and maintained positive in respect to electrode 4. Electrode 4 may be grounded as at I2. 'I'he theory upon which the observed amplification of electrons is accomplished by the arrangements disclosed in Figure l, is not fully known but it is believed to be that when the electrode 4 is bombarded'by particles from source 2, and in the absence of a magnetic eld therebetween, a current will flow through the external load, connected, for example, to any suitable collector electrode, not shown, which is responsive to the impingement of the beam Il thereon, as shown in Figs. 4 and 5. Some secondary electrons from electrode 4 will travel to source 2 but, in general, the current through load 5 will be approximately equal to the primary emission current of source 2. When, however, a constant magnetic ileld is impressed in the space between and parallel to the source 2 and the electrode 4, primary and secondary electrons are deected in their paths, the primary electrons striking electrode 4 at oblique 4 angles and thus causing a greaterl secondary -cuit may be grounded as at I2.

emission of electrons than when striking normal to electrode 4 and the secondary electrons being reilected successively by electrode 4, or trapped within the space, until under certain conditions of the magnetic ileld and the pressure of the medium, the paths of the electrons exceed the mean free path for ionization by collision with molecules of the medium and ionization of the medium occurs, making the medium conductive. This results in an enormous increase in current from the copious supply of electrons made available mainly by gas ionization.

Applying this theory to the instant invention, as disclosed in Figure 2, the copious supply of electrons within thespace between the source 2 and electrode 4 are subjected to two forces: (1) the magnetic ileld created by the solenoid 8 which causes the electrons emitted by secondary emission upon bombardment of electrode 4 by the primary electrons of source 2, as well as the electrons emitted upon bombardment of electrode 4 by the secondary emitted electrons, and also electrons produced by gas ionization to follow curved paths as their velocities are spent and (2) the electrostatic field created by the electric source I 4 which sets up a difference of potential between accelerator I0 and electrode 4 and a difference of potential between accelerator I0 and source 2. The electrons are therefore drawn from the space between source 2 and kelectrode 4 and are accelerated in the form of an electron beam, I3.

Referring to Figure 3, the arrangement disclosed therein is similar to that disclosed in Figure 2, except that the magnetic eld is supplied by a permanent magnet I5, on which is disposed the radioactive material 2. Also, in Figure 3, there is included the secondary coil I6 of a transformer, which is connected in series between the biasing electric source 6 and the magnet I5, The negative pole of electric source 6 is connected to the negative pole of electric source I4. The cir- The primary coil I1 of the transformer is connected to a source of electricy potential, either an alternating or a modulated source, such as signal.

In operation, the permanent magnet l5 creates the magnetic field, having a component as shown by arrow H, which deflects the paths of, the primary and secondary electrons to trap them in the space between the sourcel.` and electrode 4, as previously disclosed. 'I'he electrons are also subject to the electrostatic field created by the electrical potential I4 andare accelerated as a beam along the axis of accelerator I0.

It is apparent that a variation of the potential impressed on magnet I5 will vary the' flow of electrons along beam i3. When the potential of source 2 becomes progressively less positive, electrons are repulsedv more and more by the lower electrostatic eld around source 2 and more electrons are available to be drawn into beam I3. Also when the potential of source 2 asaaeos the form of a flat electrode. These elements are mounted in envelope 1. The magnetic iield,

. created by solenoid 8 connected to direct current source 9, is at right angles to the longitudinal axis oi' electrode I8 and electrode 4, as indicated by H.` The magnetic iield and the electrostatic field, created by electric source I4, react on the primary and secondary emission electrons and deflect them along the path I9. As the electrons strike electrode 4, at points `ill, 20, further secondary emission occurs. There is thus created a copious supply of electrons and the lengths of their paths are increased beyond the mean free path for ionization by collision with molecules of the medium, causing gas ionization and the iiow oflarge currents to the collector -plate 2|. Collector 2| is connected to electrode I8 through electric source I4, load 5, the secondary coil I6 oi' a transformer and biasing electric source 6. The drop of potential along load 5 is available i'or use in an outside circuit (not shown) or the current passing through load may be used in load 5 to perform a useful function. Electrode 4,is grounded at I2 as well as the lead between `load 5 and coillli.

The flow of electrons between electrode I8 and electrode 4 may be modulated in the same manner as disclosed in connection with Figure 3. The secondary coil I6 of a transformer, connected to electrode I8, will impress upon electrode I8 electrostatic potentials in accordance with the a1- ternations or the modulations of currents ilowing through the primary coil I'I of the transformer. The potentials on electrode I8 are biased by electrical source 6 connected between coil I6 and the electrode I8.

`The disclosure in Figure 5 is similar to that in Figure 4, except that the modulation is accomplished by inserting a, grid 22 between the source 2 and electrode 4. Grid 22 is connected Ito the secondary coil I6 of the transformer, the

other end of the coil being connected to the collector 2I through load 5 and electric source I4.

The primary coil I'I of the transformer is connected to the source of the modulated current or signal. The electrode I8 is connected through biasing electric source 6 grounded at I2 and to collector 2I through load 5 and electric source I4. Electrode 4 is grounded at I2.

It is apparent that grid 22 will affect the disposition of electrons in the space between electrode I8 and electrode 4, when an alternating or modmaung potential is napressed upon the grid ondary particles to a magnetic field to deflect said source lparticles against said material at oblique angles and to deiiect said secondary particles successively against said material to provide i'urther secondary emission particles and to extendthe paths of said secondary particles bepositive. the electro- 6 yond the mean free path for ionization by collision with the molecules ot the medium to provide further particles, and impressing on said medium an electrostatic eld to accelerate said particles into a beam.

2. The method of utilizing a source of radioactive charged-particle radiation for creating and collecting an electron beam comprising: exposing to said radiation a secondary-emission charged-particle radiation responsive material in a confined gaseous medium. subjecting said source and secondary particles to a magnetic iield to deect said source particles against said material at oblique angles and to deiiect said secondary particles successively against said material to provide further secondary emission particles and to extend the paths of said secondary particles beyond the mean free path for ionization by collision with the molecules of the medium to provide further particles, impressing on said medium an electrostatic field to accelerate said particles into a beam, and collecting said particles in said beam.

3. The method of utilizing a source of radioactive charged-particle radiation for creating and utilizing an electron beam comprising: exposing to said radiation a secondary-emission electron radiation responsive material in a coniined gaseous medium, subjecting said source particles and said electrons to a magnetic field to deiiect said source particles against said material at oblique angles and to deflect said electrons successively against said material to provide further secondary emission electrons and to extend the paths of said electrons beyond the mean free path for ionization by collision with the molecules of the medium to provide further electrons, impressing on said medium an electrostatic field to accelerate said particles into a beam, collecting said electrons in said beam, and utilizing the currents produced by the iiow of said electrons.

4. The method of utilizing a source of radioactive charged-particle radiation for creating and controlling an electron beam comprising: exposing to said radiation a secondary-emission electron radiation responsive material in a coniined gaseous medium, subjecting said source particles and said electrons to a magnetic field to deiiect said source particles against said material at oblique angles and to deiiect said electrons successively against said material to provide further secondary emission electrons and to extend the paths of said electrons beyond the mean free path for ionization by collision with the molecules of the medium to provide further electrons, impressing on said medium an electrostatic iield to accelerate said particles into a beam, and varying the electrostatic potential of said source to cause variations in the density of said electrons in said beam.

5. Apparatus for creating a charged-particle beam including: a radioactive source providing charged-particle emission, means disposed in a region adjacent said source that are secondaryemission charged-particle radiation responsive to said source, said source and said responsive means y being disposed in a coniined gaseous medium, means for impressing a magnetic eld on said source particles to deflect said source particles against said responsive means at oblique angles and to deflect said secondary particles successively against said material to provide further secondary emission particles and to extend the 7 paths of said secondary particles beyond the mean free path for ionization by collision with the molecules of the medium to provide further secondary charged particles, and means for accelerating said particles into a particle beam.

6. Apparatus for creating and collectingv a charged-particle beam including: a radioactive source providing charged-particle emission, means disposed in a region adjacent said source that are secondary-emission charged-particle radiation responsive to said source, said source and said responsive means being disposed -in a confined gaseous medium. means for impressing tial source connected between said radioactive source and said responsive electrode.

10. Apparatus for creating and controlling an electron beam including: a radioactive source providing charged-particle emission, an electrode disposed in a region adjacent said source that is Usecondary-emission electron radiation responsive to said source. the said source and said electrode being disposed in a confined gaseous medium, a solenoid energized from a direct current electrical y source disposed adjacent said radioactive source a magnetic field on said source particles to de'- e fiect said source particles against said responsive means at oblique angles and to deflect said secondary particles successively against said material to provide further secondary emission particles and to extend the paths of said secondary particles beyond the mean free path for ionization by collision with the molecules of the medium to provide further secondary charged particles, means for accelerating said particles into a particle beam and collecting said particles.

7. Apparatus for creating and controlling an electron beam including: a radioactive source providing charged-particle emission, means disposed in a region adjacent said source that are secondary-emission electron radiation responsive to said source. said source and said responsive means being disposed in a confined gaseous medium. means for impressing a magnetic field on said source radiation particles to deflect said particles at oblique angles against said responsive means and to deflect said electrons successively against said responsive means to provide further secondary electrons and to extend' the paths of said electrons beyond the mean free path for ionization by collision with the molecules of the medium to provide further electrons. means for accelerating said particles into an electron beam. and means for varying the electrostatic potential of said source.

8. Apparatus for creating an electron beam including: a radioactive source providing chargedparticle emission, an electrode disposed in a region adjacent said source that is secondaryemission electron radiation responsive'to said source, the said source and said electrode being disposed in a confined gaseous medium, a solenoid energized from a direct current electrical source disposed adjacent said radioactive source and said electrode, an accelerating electrode disposed adjacent said responsive electrode, an electrical potential source connected between said accelerating electrode and said responsive electrode, and a biasing electrical potential source connected between said accelerating electrode and said responsive electrode, and a biasing electrical potential source connected between said radioactive source and said responsive electrode.

9. Apparatus for creating and controlling an electron beam including: a radioactive source providing charged-particle emission, an electrode disposed in 'a region adjacent said source that is secondary-emission electron radiation responsive to said source, the said source and said electrode being disposed in a confined gaseous medium, a. solenoid energized from a direct current lelectrical source disposed adjacent said radioactive source and said electrode, an accelerating electrode disposed adjacent said responsive electrode, a collecting potential source connected be'- tween said 'accelerating electrode and said responsive electrode, and a biasing electrical potenand said electrode, an accelerating electrode disposed adjacent said responsive electrode, an electrical potential source connected between said accelerating electrode and said responsive electrode, a biasing electrical potential source, and a transformer the primary of which is connected to a source of alternating current and the secondary of which is connected in series with said biasing source between said radioactive source and said responsive electrode.

11. Apparatus forlcreating and controlling an electron beam including: a radioactive source providing charged-particle emission, an electrode disposed in a region adjacent said source that is secondary-emission electron radiation responsive to said source, the said source and said electrode being disposed in a confined gaseous medium, a permanent magnet disposed adjacent said radioactive source and said electrode, an accelerating electrode disposed adjacent said responsive electrode, an electrical potential source connected between said accelerating electrode and said responsive electrode, a biasing electrical potential source, and a transformer the primary of which is -connected to a source of alternating current and the secondary of which is connected in series with said biasing source between said radioactive source and said responsive electron.

12. Apparatus for creating and controlling an electron beam l including: an electrode and a radioactive source mountedw thereon providing charged-particle emission, a second electrode that is Secondary emission electron radiation responsive to said source and disposed in a region adjacent said source electrode, the said source electrode and said responsive electrode being disposed in a confined gaseous medium, a solenoid energized from a direct current electrical source disposed adjacent said radioactive source and said electrode, an accelerating and collecting electrode disposed adjacent said responsive electrodes and said source, an accelerating electrical potential source, a load, a transformer and a biasing electrical potential source, accelerating source, the load, the secondary coil of the transformer and the biasing source being connected in series with each other and between said collecting electrode and said radioactive source electrode, the primary of said transformer being connected to a source of alternating current.

13. Apparatus for creating and controlling an electron beam including: an electrode and a radioactive source mounted thereon providing charged-particle emission, an electrode disposed in a region adjacent said source that is second ary-emission electron radiation responsive to said source, the said source electrode and said responsive electrode being disposed in a confined gaseous medium, a solenoid energized from a direct current electrical source disposed adjacent said radioactive source and said responsive electrode. an accelerating and collecting electrode disposed adjacent said source and said responsive electrodes, an electrical potential source, a load,

a,sao,cos 9 10 and a biasing electrical potential source. the elec- REFERENCES CITED ma smn' the 10nd' and the biasing source The following references are of record in the `being connected in series with each other and me of this patent:

between said source electrode and said collecting electrode, a grid disposed between said source 5 UNITED STATES PATENTS electrode and said responsive electrode, and a Number Name Date transformer the primary of which is connected 2,372,328 Labin Mar. 27, 1945 to a source of alternating current and the secondary of which is connected between said biasing source and said grid. lo

ERNEST G. LINDER.

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