US2500223A

US2500223A - Artificial atomic disintegration

Info

Publication number: US2500223A
Application number: US717292A
Authority: US
Inventors: William H Wells; William E Stephens; William E Shoupp; Robert O Haxby
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1946-12-19
Filing date: 1946-12-19
Publication date: 1950-03-14
Anticipated expiration: 1967-03-14

Description

Match 14, 1950 w. H. WELLS ETAL 2,500,223 ARTIFICIAL ATOMIC DISINTEGRATION Filed Dec. 19, 1946 75 Vacuum Pump WITNESSES: INVENTORS William H Mel/s, Wf lliam E.$1pbens M v William 5. $1701.90 & I;oberI QHzzxb u.

ATTORNE Patented Mar. 14, 1950 UNITED STATES PATENT OFFICE phens, Philadelphia,

and William E. Shoupp,

Wilkinsburg, -Pa., and Robert 0. Haxby, La Fayette, Ind., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application December 19, 1946, Serial No. 717,292

8 Claims. 1

Our invention relates to artificial atomic disintegration, and has particular relation to fission of materials. This application is a continuationin-part of our application Serial No. 339,586 for Artificial atomic disintegration filed June 8, 1940, which has been abandoned. Fission is the division of the atomsof an element into a plurality of sub-atoms of smaller atomic weight. This phenomenon should be distinguished from the atomic disintegration which occurs when the electrons, neutrons, alpha particles or protons are derived from a substance. In the case of fission, the disintegration, of an atom results in two or more sub-atoms of substantial atomic weight. Where atoms are deprived of their component electrical particles by ionization or bombardment, the result is a num ber of electrons, neutrons, alpha particles or protons and a somewhat modified element having atomic weight not far different than the original undisintegrated element.

Since the sub-atoms produced by fission may be radioactive, the phenomenon is of importance to therapy and other fields in which radioactivity is useful. In addition, when fission occurs the intrinsic potential energy of the original atoms is converted into kinetic energy manifested by the motion of the sub-atoms. The kinetic energy may be converted into heat, and thus the energy of fission may be used for power or motive purposes. The conversion of external energy into energy of fission is in itself not highly efiicient if the only conversion considered is that pro, duced by the incident energy. However, fission is accompanied by the emission of radiation and particles which tends to produce further fission, and thus the original incident energy may effect the release of a substantial quantity of energy.

In accordance with the teachings of the prior art, fission is produced by projecting neutrons on the element to be disintegrated.

It is an object of our invention to provide a novel method for producing fission.

Another object of our invention is to produce fission by the projection of radiant energy rather than by particles.

' An incidental object of our invention is to provide a method for efiectively destroying undesired cellular growth.

' In accordance with our invention, fission is produced by projecting gamma rays of certain frequencies on the element to be disintegrated. We have found that the phenomenon is produced to a marked extent by projecting gamma rays, the frequency of which corresponds to radiations having an energy equivalent of the order of 6,000,000 electron volts on the uranium or thorium target. Gamma rays of this frequency may be produced by bombarding calcium fluoride or aluminum fluoride with protons. Our investigations indicate, moreover, that although the radiation mentioned is singularly useful for the purpose of producing fission, gamma rays of some, although not all, other frequencies may be used with results sufiiciently good for some purposes. Most efiective results follow if the gamma rays fall in the range about 6,000,000 or more electron volts.

The novel features that we consider characteristic of our invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of a specific embodiment when read in connection with the accompanying drawing, in which:

Figure 1 is a diagrammatic view showing an embodiment of our invention; and

Figure 2 is a diagrammatic showing of a modified embodiment of a portion of Fig. 1.

The apparatus shown in Fig. 1 comprises a dome-shaped enclosure l within which a chamber 3, projecting from the top of an evacuated cylinder 5, extends. Within the chamber 3 a filamentary cathode 1 of the usual oxide-cathode type and a cooperative anode 9 are mounted. The cathode is heated from a suitable power source II, and a potential is impressed between the anode 9 and cathode I from a second power source l3. The chamber 3 is in communication with the cylinder 5 through a conductive capillary tube I5.

The cylinder 5 is made up of a stack of insulating rings I! separated by conducting toroidal disks is. From opposite sides of each of the disks l9, fan-shaped conducting arms 2| extend radially. Conducting rings 23 are secured to the arms in such manner that they extend coaxial with the insulating rings. The insulating rings are preferably composed of porcleain and are sealed by compression to the disks l9 in such manner that the cylinder 5 is vacuum-tight.

The capillary tube 15 opens into a cup-shaped conductor 25, the rim of which is co-extensive with the conducting rings 23. The cylinder 5 is closed by another cup-shaped conductor 21,

of the same diameter as the insulating rings II.

The latter cup-shaped conductor 21 is open at the center and a cylindrical conducting tube 29 extends from the opening. The tube 29- is in communication with a prism-shaped chamber 3|, from the lower end of which a closed conducting cup-shaped pocket 33 extends eccentrically. A target 35, which is preferably fluorine but may for many practical purposes be calcium fluoride (CaF-i) or aluminum fluoride (AlFs), or any fluorine containing substance, is disposed in 50 the pocket 33.

Where ifluorine is to constitute the target it may be contained within a chamber having thin walls of aluminum or some substance which produces none, or few, neutrons when bombarded by hydrogen, as described below in the path of the ions.

The cylinder and the regions with which it communicates are first evacuated. With the evacuating equipment continuously in operation, hydrogen is supplied to the chamber "31 at a pressure preferably of the order of from to 10- millimeters of mercury. The potential I3 produces a discharge between the anode 9 and the cathode l, ionizing the hydrogen in the chamber.v

A high potential is .impressed between the capillary tube .and the :cup .21 of the cylinder .5, maintaining the capillary tube 15 electrically negative relative to the cup -21. The hydrogen ions are under the influence of the axial field thus produced along the cylinder 5 and are projected along the cylinder. The relative dimensions of the capillary tube 5.5 and the cylinder 5, and the rate of evacuation are preferably such that the pressure in the cylinder 5 isof the order of .trom l0 to 10- millimeters of mercury. In accordance with a preferred practice of our invention, the potential impressed along the cylinderb lies .between 2-and.3.2 million volts. The ion current is .of the order of .5 microampere. To distribute the potential uniformly along the axis of the tube, the toroidal :disks l9 are each provided with a pointed conductor 3'! which extends perpendicular to its surface towards the adjacent disk. -The corona discharge between the conductors 3-! and the adjacent disks efiects a substantially uniform distribution of potential along the cylinder 5.

The ionized hydrogen atoms which are projected along the cylinder 5 are principally of three types. molecule made up of two atoms of hydrogen, and an ionized molecule made up of three atoms of hydrogen. The ionized hydrogen atom having the smallest mass has the highest velocity and is capable of transferring the most energy per atom to the target 35. To facilitate computation, it is desirable that only the ionized atoms impinge on the target. For this reason a magnet-39 encircles the tube 29 near the lower end with its poles extending on opposite sides of the tube. The magnet produces afield perpendicular to the plane determined by the :axis of the cylinder 5 and the line between the center of the target and the center-of the field of the magnet. The ionized atoms are deflected towards the target 35 by the magnetic fiel'd and the two-atom and three-atom molecules are absorbed in the wall of the chamber M. The ions impinge on the target -35 and produce gamma rays having an energy eqnivalentof 6,000,000 electron volts.

Below the pocket 33 an ionizing chamber 4! is disposed. Within the chamber 44 a disk 43 of uranium or thorium is disposed. The gamma rays emitted from the target 35 impinge on the disk 43 and produce fission. The fission maybe measured by the extent of the ionization produced within the chamber M. For this purpose an electrode d5 extends into the chamber. The electrode is connected to an indicating .ins-trtb ment M, such as an cscillograph, through suitable amplifying equipment 40. Certain of the sub-atoms produced by the gamma rays are -re leased from the disk 43 and produce substantial ionization within the chamber. The ionization may be detected because it is of an abrupt char- There is a single atom, anionized 4 acter and is manifested by the flow of a current impulse through the electrode 45, which is indicated on the instrument 41.

A number of fission reactions are produced 5 when gamma rays impinge. on the uranium or the thorium. One characteristic reaction may be expressed as follows:

Gamma ray+U235+Xel37+Sr95+3 neutrons+ 200,000,000 electron volts.

In accordance with this reaction, uranium of atomic weight 238 when irradiated with gamma rays produces xenon of atomic weight 137, strontium of atomic weight 95, 3 neutrons of atomic weight 1, and 200,000,000 electron volts of energy. In addition, gamma rays are also emitted, first, because the xenon and the strontium are radioactive, and, second, because the reaction itself results in gamma rays. If sufiicient neutrons and gamma rays are produced, they may in the end convert substantial nuclear potential energy into kinetic energy. The foregoing reaction .is not the only one which takes place. It is given only for the purpose of example.

Use of .a target '35 consisting of the element fluorine results in irradiating the uranium or thorium target 63 with gamma rays unaccompanied by neutrons. When calcium fluoride targets are used, .a vfew neutrons are mixed with the gamma rays .but we have demonstrated by careful tests that these .play no perceptible part in causing fission-of the uranium or thorium, but that the later is, in our apparatus, produced by the gamma rays. However, even these neutrons from the calcium fluoride or aluminum .fiuoride targets may be .prevented .from striking the uranium or thorium by the arrangement shown in Fig. '2. In that arrangement -a block of paraffin 5| is interposed between the target 35 and the work substance 4.3, and the lower face of the parafiin is faced with a layer 52 of cadmium sufiiciently thick to remove all neutrons. The gamma rays .pass this cadmium layer and the work substance 43 is thus bombarded by a pure stream of gamma radiation.

Experiment has .shown that the fission crosssection of uraniumior gamma rays from fluorine is 3.5i0.8 10 cm. and that of thorium is 59 l.7:0.6 1-0- -cm. while the corresponding figures for neutrons are about 1,000 times greater. These fission cross-sections are proportional with the probability that emission of one gamma ray quantum, in the one case, or emission of a neutron, in the other case, will produce fission in a centimeter cube of the corresponding substance positioned one meter .from the radiating source. The probability that a neutron will produce fission, is accordingly, considerably higher than an the probability that a gamma ray quantum will do so, and the neutrons swamp the effect of gamma radiation where both are present in force. This doubtless explains why Fermi in an article Artificial radioactivity produced by neutron bombardment, Proceedings of the Royal Society of London, .September 1934, page 484, states that his experiments showed that he produced fission of uranium by means of neutrons, although he recognized that the uranium was being bom barded by a mixture of neutrons with gamma radiation. Fermi stated that his test showed it to be most unlikely that the observed effects :are

in any way connected with this gamma radiation. Fermis stated "results seem not to be in conflict with our discoveries as to the --efiect on uranium of a stream of gamma radiation substantially free from neutrons capable of producing fission.

Because of the ionization which is produced in the practice of our invention, it is peculiarly adapted for destroying undesired cellular growth. In the practice of this aspect of our invention, uranium or thorium compounds are injected in, in the region adjacent to or in the region encircling the cellular growth. The injected region is then subject to gamma rays from the target 25. The ionization and radiation resulting from the fission destroys the growth.

While we have described hydrogen ions, or protons, as the agency for producing gamma rays, other means of generating such rays may be used for many purposes; for example, electrons of over 6,000,000 electron volts energy incident upon such a target as tungsten will produce the gamma rays.

Certain further information connected with our invention appears in our article Photofission of uranium and thorium, beginning at page 5'7 of volume 59, and our letter of similar title on page 92 of volume 58 of the Physical Review, Second Series, published by the American Institute of Physics.

Although we have shown and described certain specific embodiments of our invention, we are fully aware that many modifications thereof are possible. Our invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

We claim as our invention:

1. A method of causing fission which comprises the step of subjecting a member of the group consisting of uranium and thorium to a bombarding stream consisting only of gamma rays having an energy of above 6,000,000 electron Volts.

2. The method of producing fission of a substance drawn from the group consisting of uranium and thorium, which comprises projecting protons with an energy of substantially three million electron volts on a calcium fluoride target, and subjecting said substance to gamma rays of at least six million electron volts emitted by said target.

3. The method of producing fission of a substance drawn from the group consisting of uranium and thorium, which comprises projecting protons with an energy of substantially three million electron volts on a target consisting of a material drawn from the group consisting of calcium fluoride and aluminum fluoride, and subjecting said substance to the resultant gamma rays of an energy of at least six million electron volts emitted by said target.

4. The method of producing fission of a substance drawn from the group consisting of uranium and thorium, which comprises projecting electrically-charged particles, drawn from the group which consists of electrons and protons, on a target consisting of a material from the group which consists of calcium fluoride, aluminum fluoride and tungsten, with an energy sufficient to cause said target to emit gamma rays of an energy of at least six million electron volts and subjecting said subject to said gamma rays.

5. The method of producing fission of a substance drawn from the group consisting of uranium and thorium, which comprises projecting protons with an energy of substantially three million electron volts on an aluminum fluoride target and subjecting said substance to the resultant gamma rays of an energy of at least six million electron volts emitted by said target.

6. The method of producing a fission of a substance drawn from the group consisting of uranium and thorium, which comprises projecting protons with an energy of substantially three million electron volts on a calcium fluoride target and subjecting said substance to the resultant gamma rays of an energy of at least six million electron volts emitted by said target after passing said rays through a filter which comprises a layer containing hydrogen and a layer containing calcium.

7. The method of producing a fission of a substance drawn from the group consisting of uranium and thorium, which comprises projecting protons with an energy of substantially three million electron volts on a calcium fluoride target and subjecting said substance to the resultant gamma rays of an energy of at least six million electron volts emitted by said target after passing said rays through a filter which comprises a layer containing paraflin and a layer containing calcium.

8. The method of producing fission of a substance drawn from the group consisting of uranium and thorium, which comprises projecting protons with an energy of substantially three million electron volts on a target consisting of material drawn from the group which consists of calcium fluoride and aluminum fluoride, and subjecting said substance to the resultant gamma rays of an energy of at least six million electron volts emitted by said target after passing said rays through a filter comprising a layer containing hydrogen and a layer containing calcium. WILLIAM H. WELLS. WILLIAM E. STEPHENS. WILLIAM E. SHOUPP. ROBERT O. HAXBY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 917,191 Trivelli Apr. 6, 1909 2,206,634 Fermi et al July 2, 1940 FOREIGN PATENTS Number Country Date 314,427 Great Britain Dec. 1, 1930 440,023 Great Britain Dec. 12, 1935 OTHER REFERENCES Herb et al., Physical Review, vol. 51, No. 9, pp. 691-608, May 1, 1937.

Roberts et al., Physical Review, vol. 55, pp. 416-417 (1939).

Delsasso et al., Physical Review, vol. 51, page 527 (1937).

Bohr et al., Physical Review, vol. 56, pp. 449-450 (1939).

Physical Review, pp. 284-286, Aug. 1, 1939.

Review Physical Chemistry, Japan, vol. 13, pp. -150 (1939). Proceedings of the Royal Society of London, vol. 146, pp. 483-500, Sept. 1934.

Claims

4. THE METHOD OF PRODUCING FISSION OF A SUBSTANCE DRAWN FROM THE GROUP CONSISTING OF URANIUM AND THORIUM, WHICH COMPRISES PROJECTING ELECTRICALLY-CHARGED PARTICLES, DRAWN FROM THE GROUP WHICH CONSISTS OF ELECTRONS AND PROTONS, ON A TARGET CONSISTING OF A MATERIAL FORM THE GROUP WHICH CONSISTS OF CALCIUM FLUORIDE, ALUMINUM FLUORIDE AND TUNGSTEN, WITH AN ENERGY SUF-