US2188115A - Investigation of materials with neutrons - Google Patents

Description

1940. H. KALLMANN EIAL v 2,188,115

INVESTIGATION OF MATERIALS WITH NEUTRONS Filed March 24, 1938 Eaess CEMENTED me-rremassisted Jan. 23, l

INVESTIGATION OF MA'EEE': ti

NEUTRONS s'ra Germany Application Maren 24, 1938, Serial No. 197,928 In Germany March 25, .1937

The present invention relates to a method and means for investigating materials by means of slowly moving neutrons, and is particularly directed to a method and means for producing a visible image of a beam of neutrons which has passed through the material to be investigated.

Slowly moving neutrons are only slightly absorbed by lead, but are strongly absorbed by wateror hydrogen-containing substances, such 9 as wood or the like. They behave, in this respect, exactly opposite to X-rays. If, therefore, a body composed of difierent substances is transillumi nated by a beam of slowly moving neutrons the intensity distribution of the neutron beam leaving the body is difl 'erent from the intensity distribution in an X-ray beam afterithas penetrated' the same body. If the beam of slowly moving neutrons could be made visible by means 0! a luminous screen or a photosensitive material 0 a; different image would be obtained in the transillumination with slowly moving neutrons than with x-rays, The investigation of substances by means of slowly moving neutrons would be important. thereiore, not only -i'or medical purposes but also for technical investigations. Itv

would be possible, for example, to investigate materials contained in metallic receptacles ii the materials were such as to absorb the neutrons more strongly than they are absorbed by the metallicwalls of the vessel, for example, ii the.materials comprise hydrogen-containing substances.

Slowly moving electrons, however, do not perceptibly excite fluorescent substances, so that inorder to obtain a visible image on a fluorescent screen. for example, of zinc sulfide, it \is neces-' sary to interpose an intermediate reaction. giving rise to particles capable of exciting the fluorescent materials.

It has been round that the production of heavy m particles, such as 1-11 or He particles, which excite fluorescent material much more strongly than neutrons can be efl'ected by associating with the luminous material lithium or boron, or a substance containing atoms oilithium or boron or both. 3 w For example, the fluorescent substance, such as zinc sulfide, is coated in a thin layer onlithium foil. The slowly moving neutrons generate in the lithium i'ast H: particles which cause the fluores- ;6 cent substance to scintillate. In order to render such a fluorescent screen durable, it-is advantageously enclosed between two plates-one of which is transparent and cemented in' an airtight manner between theplates. 7

it Instead of the lithium 'foil, 9. layer of boron.

- or a mixture of boron and lithium, or a substance containing boronor lithium atoms or a mixture" '1 Claims. (01, 250-81) thereof, may be used, and paper coated with amorphous boron'to .which the fluorescent substance is applied may be utilized. Embodiments of the invention are-illustrated in the accompanying (drawing in which Fig. l is a perspective view, with parts broken away, ofpa luminous screen assembly, and

Fig. 21s a perspective view of a modified form oi. the invention. I

In Fig. 1, I is a supporting-film or plate, 2 is 0 r a lithium foil, 3 is a layer of luminous substance and 4 is a transparentplate. i.The edges of the structure are coated with a cement sealing the lithium foil and the luminous substance in an air tight manner between the external plates. 5

In Fig. 2, 5 is a sheet of paper and tie a coating ofamorphous boron and luminous substance. What we claim as new and desire to secure by Letters Patent of the United States is:-

1. Method of forming a visible image of a beam of slowly moving neutrons which comprises causing the beam to impinge on a layer of a,.

- fluorescent substance haying associated therewith a thin layer of a material selected from the group consisting of lithium, boron and-substances containing atoms of at least one'of these. elements. 2. Method of forming a visible image of a beam of slowly moving neutrons which comprises causingthe beam to impinge on a layer of a fluorescent substance-coated on alithium foil.

3. Method of forming a visible image of abeam of slowly moving neutrons which comprises causing the beam to impinge on a layer of a fluorescent substance associated with a layer of amorphous boron.

- 4. A device for forming a visible image of a beam of slowly moving neutrons comprising'ja layer of a fluorescent substance associated with a thin layer of a material selectedfrom the group consisting of lithium, boron and substances containing atoms of at least one of these elements. 40

5. A device for forming a visible image 'of a beam of slowly moving neutrons comprising a layer of a fluorescent substance coatedupon a lithium foil.

6. A device for forming a visible image of a 4 beam of slowly moving'neutrons comprlsinga layer of a fluorescent substance coated upon a lithium foil, the coated foil being enclosed in an 7 air-tight manner between two plates one of which so ERNST KUHNY

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