US2814727A - Device for utilizing high-energy beams of particles - Google Patents

Description

Nov. 26, 1957 K; GUND ErAL 2,814,727

DEVICE FOR UTILIZING HIGH-ENERGY BEAMS OF PARTICLES Filed July 21, 1951 INVENTORS KONRAD GUND HANS BERGER MAX MARTIN SCHEER AND RUDOLF SCHITTENHELM W ATTORNEY United States Patent DEVICE FOR UTILIZENG HIGH-ENERGY BEAMS OF PARTICLES Konrad Gund, Hans Berger, Max Martin Scheer, and Rudolf Schittenhelm, Erlangen, Germany Application July 21, 1951, Serial No. 237,924

Claims priority, application Germany July 24, 1950 12 Claims. (Cl. 250-495) This invention is concerned with adevice for scatteringor widening a high-energy particle radiation by means of scattering foils interposed in the path thereof'wi'thout causing any particular energy loss of the scattered particles (the quality of the scattered particles of the radiation remaining substantially uniform or constant) so as to obtain a widened area for medical irradiation purposes.

It is known to conduct high-energy particles, for example fast electrons, from a generator or electron accelerator tothe outside so as to utilize them for electro medical irradiation purposes. The angle'of divergence of the beam is, inside the generator or accelerator, relatively small and is not appreciably dependent on the energy of the beam. On passing through the exit foil or window of the accelerator, the beam is, however, more or less strongly scattered. The mean angleof' divergence or scattering in such a window is given by the relationship where E is the particle energy, Z the atomic number and N the number of atoms per unit area of the scattering foil. C and C areoonstants. The angle of divergence or scattering therefore is strongly dependent on the beamv energy and decreases with increasing energy.

It is desirable for the medical application. of highenergy corpuscular particle beams, particularly of fast electrons, to obtain larger scattering angles for high energies, in order to make it possible to irradiate large areas homogeneously. The invention therefore provides. a. scattering foil which is interposed in the beam path, such foil being made of a material of high atomic number, preferably higher than the atornic number of the rare earths, and its thickness is so dimensioned in accordance with the formula noted above that the intensity of the X-ray radiation produced in it is relatively small as compared to the intensity of the particle radiation passing therethrough. Putting it in other Words, the thickness of the scattering foil is such that the energy of the corpuscular particles penetrating it remains substantially unaffected. For an electron accelerator of 5 to 15 m. e. v., a mean scattering angle of about may be obtained by disposing in front of the beam exit window of the accelerator a scattering foil of gold or lead, between 5 and 200 1. thick.

It has been proposed, for the purpose of increasing the scattering angle of an electron radiation beam, to associate with the exit foil of an electron accelerator an auxiliary scattering body made of material of low atomic number. Such proposal has been made because of the then prevailing opinion (as indicated, e. g., in the paper of L. S. Skaggs et al., published in Radiology, vol. 50, 1948, page 172), that a considerably increased X-ray radiation would be produced in the scattering foil by using foil material of high atomic number. The total energy loss of the corpuscular particles includes impact and radiation losses. The invention is based upon recognition of the fact that a scattering foil made of material of high atomic number causes less distortion of the energy spectrum, as

compared with foils made of material of low atomic numher and equivalent thickness, i. e.,. a thickness that would produce the same mean scattering angle, due to the lesser relative mean energy losses, and. that this advantage does not entail the: drawback of a considerably increased X-ray production of the radiation. This result is believed due to the fact that the impact losses are in. the thin heavy metal foil very much lower while the radiation losses are negligibly higher as compared with an equivalent light metal foil. The total energy loss of the corpuscular particles is accordingly smaller in the heavy metal foil than in an equivalent foil made of material of low atomic number.v

It is particularly desirable in the medical application of corpuscular radiation tohave available radiation that is as monochromatic. as possible so as to obtain a well defined maximum of the path of the depth dosis; ThlS11Il21X-- imum deteriorates with the broadening or widening: of the energy spectrum of the corpuscular radiation. with the increase of the mean energy loss of the radiation in the scattering body. A. scattering body according to the invention yields at all energies and at all mean scattering angles smaller energy losses and therewith smaller deviations from the favorable depth dosis curves of. monochromatic corpuscular radiation than a scattering. body made of material of low atomic number.

The following, table shows the results in the case of. scattering foils of a thickness equivalent to the foil of. the invention, made respectively of aluminum (Al) and lead (Pb) for obtaining a mean scattering angle of. in-

the appended claims which define what. is believed to be new and desired to have protected by Letters Patent.

The objects indicated above and additional objects andfeatures will appear from the description of. an example of the invention, which is rendered below with reference to the accompanying drawing.

In the drawing, numeral 1 indicates the electron exit window of an electron generator or accelerator. Closely in front of the window is disposed the chainlike member 2 which comprises links forming the new scattering foils made of different materials and/ or of varying thickness. This chainlike member may be wound from the reel 4 to the reel 5, and vice versa, by operating the actuating member or knob 3 coupled with a suitable stepping or setting switch, for selectively interposing the different scattering foils in the path of the electron beam. The scattering foil, which is at any time interposed in the beam path, is indicated on the scale 7 by the pointer 6 coacting with the knob 3. The equivalent thicknesses of the successive scattering foils are preferably in a fixed mutual relationship which may be on the order of about 2:3.

The new device permits satisfactory homogeneous irradiation of all practically occurring areas, within a large energy range, under most favorable conditions.

We claim:

1. In combination with apparatus for producing a beam of electrically charged particles to form a high energy electron radiation for medical irradiation of biologic bodies, a device for increasing the angle of divergence of said beam of charged particles, said device comprising means for disposing a foil in the path of said beam, said charged particles passing through said foil, said foil being made of material of an atomic number higher than that of rare earths, the thickness of said foil being such as to cause the X-ray intensity produced within said foil by said charged particles passing therethrough to be low as compared with the intensity of said particles.

2. The device in the combination as set forth in claim 1, wherein said accelerator produces an electron radiation on the order of 5 to 15 m. e. v., said scattering foil consisting of gold and having a thickness on the order of 5 (O 200/1.

3. The device in the combination as set forth in claim 1, wherein said accelerator produces an electron radiation on the order of 5 to 15 m. e. v., said scattering foil consisting of lead and having a thickness on the order of 5 to 200,4!

4. The device in the combination as set forth in claim 1, comprising a plurality of dilferent scattering foils, and means for selectively disposing said foils in the path of said particle beam.

5. The device in the combination as set forth in claim 1, comprising a plurality of exchangeable scattering foils made of diiferent materials of the class of gold and lead, respectively.

6. The device in the combination as defined in claim 1, comprising a chainlike member having links forming a plurality of scattering foils, and means for moving said chainlike member to dispose said foils selectively in the particle beam path close to the beam exit Window of said accelerator.

7. Apparatus for medical application of high-energy particle radiation comprising an electron accelerator having an exit window for projecting a particle beam, a pair of reels and an endless drive member which interconnects said reels, a chainlike link member having its ends anchored on the respective reels, the links of said chainlike member forming scattering foils, a guide for said scattering foils disposed in front of said exit window, an actuating member for rotating one of said reels to impart through the medium of said endless drive member rotation to the other reel for the purpose of moving said chainlike member to dispose said scattering foils selectively in front of said window in the path of said particle beam, means coacting with one of said reels for indicating the scattering foil Which is at any time position-ed in the path of said particle beam, said scattering foils being made of material of high atomic number exceeding that of the rare earths and being of a thickness which is so dimensioned that the intensity of X-ray radiation produced therein is less than the intensity of the particle radiation passing therethrough.

8. The structure and coaction of elements as set forth in claim 7, wherein said scattering foils are of varying material of the class of gold and lead, respectively.

9. The structure and coaction of elements as set forth in claim 7, wherein said scattering foils are of varying thickness on the order of 5 to 200;1..

10. Apparatus for medical application of high-energy particle radiation comprising an electron accelerator for producing an electron radiation on the order of 5 to 1 m. e. v. and having an exit window for projecting the electron particle beam, a pair of reels and an endless drive which interconnects said reels, a chainlike link member having its ends anchored on the respective reels, the links of said chainlike member forming scattering foils, a guide for said scattering foils disposed in front of said exit window, an actuating member for rotating one of said reels to impart through the medium of said endless drive rotation to the other reel for the purpose of moving said scattering foils to dispose such foils selectively in front of said window in the path of said particle beam, said scattering foils being made of material of high atomic number exceeding that of the rare earths and being of a thickness on the order of 5 to 200 to produce a mean scattering angle of the beam which is on the order of about 10.

11. The device in the combination as set forth in claim 1, comprising means for disposing said foil outside of said accelerator.

12. The device in the combination as set forth in claim 1, wherein the thickness of said foil is less than that of a foil made of identical material which would cause scattering of said charged particles with a mean scattering angle of 10.

References Cited in the file of this patent UNITED STATES PATENTS 2,094,103 Horsley et al. Sept. 28, 1937 2,139,098 Raney Dec. 6, 1938 2,485,470 Baker Oct. 18, 1949 2,496,218 Kieifer Jan. 31, 1950 2,517,260 Van de Graafi et al. Aug. 1, 1950 2,545,958 Kerst Mar. 20, 1951 2,559,526 Van de Graafi July 3, 1951

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