US2575134A

US2575134A - Radioactive source

Info

Publication number: US2575134A
Application number: US199465A
Authority: US
Inventors: Warner W Schultz; Eugene P Kozorlz
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1950-12-06
Filing date: 1950-12-06
Publication date: 1951-11-13
Anticipated expiration: 1968-11-13

Description

lrwentfo: warnerwchulbz, Eu ene P Kozoriz,

His Attorney.

RADIOACTIVE SOURCE Filed Dec. 6, 1950 W. W. SCHULTZ ET AL Nov. 13, 1951 v Patented Nov. 13, 1951 y1de;applications"forradioactive sourceseXist in'bthvmedicineand industry-,filmt heretofore 'e tfis lfan''obj'ect' fof-f this f-invention; therefore;Y to rovd-n'ewland improved means.'v for housing a -I'irsoure'e oradioactivity.

Anptheiob'ject ofthis inventionis tdprovide a structionzand i'ow in expense.

Afurtnereobject" ofi this inventionfisto :provide aaradi'o'a'ctive sourceih'avin'g aiphysicalib'alirie of uc'i'ent Jstrength'15o-safely contain the radioacagentA usefuluradiation. @In 'accordance' withi this invention, afdeposit of A.. radioactive "material placed on aflat 'surface offer-'supporting block -formed -of a `substancei lsuch as metalfor resinous materialfeig., fiberglass f. -r llaminate,v which is :not readily broken down: by

.fprolongedbombardment from radioactive matet P-rials. "f1-he nat surface and the radioactive-layer v a are -coveredby-r a `thinfsheet of sealing -material,

lwsnhasv-.micaftransparent to the spectrum of'- adiationfrom thehradioativematerial, the sheet iff di s eal-ingfmateri-ai being bonded t0 the-fiat surface by a thin layer oran-adhesive agent such as aspolyepoxide Vresin` or-a low melting glass composition. Ther supporting-block With its-radio v@active sur-face andA thin covering sheet is placed a ma casing-made `of some material, such asfor "example, stainless steel, capable offwithstanding H prolonged bombardment from nuclear particles land is bonded therein by a layer of adhesive. The

v --fcasm`g has-anaperture or Window over theerado- 'fctiveportion of the surfacetopermitthe radiaionsto escapei For furtherfsafety, thisrst'casmgimaybe placed Within a'similarsecond casing. the fsecondror outercasing #hasr a1 windowieon.

inentof `the leaks', they absorbthe softe'rilradiaive'inateral yetthinfenough to. permit thelp'as- @in housing-f forting: block v2 "contains" an material is deposited in solution within the con`" bardment from radioactive materials; more speciiically, these other resins frequently become friable or turn into powder. The qualities of the polyepoxide resins which make them particularly desirable in this application are that they have no volatile by-products on condensation or polymerization; they have no initial solvents; they setiat room temperatures and have a reasonably fast room cure, for example, 4 hours at 70 F. Other preferred adhesive or bonding agents are low melting glass compositions. To be satisfacnes of moat 3. Then, the solution is evaporated,

leaving radioactive layer 5.' During the 'evapo-4 ration process, chimney I3 can be fitted intomoatf 3 to prevent the spread of radioactivity tolother parts of supporting block 2. Other methods ofdepositing radioactive layer 5 may, of course, be used. Electroplating would be one such method. However, for electroplating to be used, block 2 must be constructed oi?r a conducting material. If electroplating is employed to deposit radioactive layer 5, moat 3 can be eliminated from surface 4, since there is then no evaporation process to oifer. contamination to surrounding areas.-

To continue with the method ofconstructing housing I, once radioactive layer 5 is deposited on the portion of surface 4 enclosed by moat 3, a very thin sheet 6 of material is placed over and bonded to surface 4. Sheet 6 must be of such a type that it forms a sealing layer transparent to the useful spectrum of radiation from radioactive layer 5. In the preferred embodiment of this invention, sheet 6 is a sheet .of mica but other materials may be employed.V

y Thepurpose of sheet 6, as placed over surface 4, is to serve as a barrier to hold radioactive layer 5 thereon, since the'escape of any part of layer 5 would present -a serious health hazard. The sheet of material-must be keptextremely thin where alpha, beta or beta-gammafemitters are employed, in order that the alpha or beta. particels will not be absorbed. For low energy gamma or X-ray emitters, the same requirement also exists. `Since mica can be split into extremely thin sheets, sometimes even only a few molecules thick, it is an excellent material for coated with adhesive layer 6a. Sheet 6 is then pressed on surface 4, moat 3 actingV as a trap vfor any radioactive material that is squeezed sideways, thus further preventing contamination of any other parts of block 2. The bonding agent not only holds sheet 6 in place, but also by mixing with radioactive layer 5 tends to prevent any movement therein. This is important in that if sheet 6 should be punctured, only the small'bit of radioactive material directly underneath 'the puncture may escape, nor matter in what position housing I is placed.

This method of depositing radioactive layer 5 within the connes of moat 3 and then bonding it in place with adhesive layer 6a under sheet 6 prevents, as far as possible, the escape of radioactive material in both the construction and use of Housing I. A presently preferred adhesive or bonding agent is a resin of the polyep'oxide class. By a polyepoxide resin it is meant any one of the class of thermosetting resins capable of form ing large macromolecules, i. e., resins whichare capable of becoming highly cross-linked upon polymerization. It is'preferable to use'a highly cross-linked resin because most other'resinsvlose their physical properties more readily under bomtory, a glass composition must be capable, when liquid; v'of wetting both surface 4 and sheet 6.y It

- should also have a'coefhcient of expansion, when solidiiied, in therorder of those of surface 4 and sheet 6 so that appreciable physical stresses will sion-resistant, such as stainless steel, is about the Abest material which can be used for casings l and 9. ,Howeven although casings l and Bare preferably metallic their compositionis not necessarily restricted to metal. There fare a number of non-metallic substances which can stand prolonged bombardment from radioactive materials, and casings which will give satisfactory results can= be formed from those non-metallicl sub- Y stances. For example, casings'formed of plastics can be substituted for Ythe metallic casings, il' desired. i

Casings 9 and II and block 2 together cut oiI almost all radiations except those in the desired direction, and, due to the double casing constructionyit is almost impossible for radiation leaks to develop, unless housing I is severely damaged bysome meanasuch as rough handling.

S- For some applications, only one casing may ybe necessary, while in still other' applications more than two casings may be desirable. t This iny vention is not to be construed as restricted -to a structure having two casings; one casing or a plurality of casings contained one within Yan-YAY other may be employed as necessary, theinnermost casing, of course, containing the supporting block, the sheet of sealing material and the radioactive deposit contained therebetween.

, While there has been described what, at present, is considered to be the preferred embodiand modications as fall within the true spirit from said deposit ofradioactive material; `ailayerk ,y

of adhesive bonding said sheet of sealing material to said surface; a casing formed of material capable of standing prolonged bombardment from radioactive material containing' said snpporting block, said sheet of sealing material and said deposit of radioactive material bonded therebetween and having an aperture positioned over said deposit of radioactive material; and a layer of adhesive bonding said supporting block and said sheet of sealing material to said casing.

2. A radioactive source comprising a supporting block formed of a material not readily broken down by prolonged bombardment from radioactive materials and provided with a at surface containing an endless moat;a deposit of radioactive material on the portion of said flat surface surrounded by said moat; a sheet of sealing material coveringsaid surface and said deposit of radioactive material thereon to form a sealing layer transpartent to the spectrum of radiation from said deposit of radioactive material; a layer of adhesive bonding said sheet of sealing material to said surface; a plurality of casings formed of material capable of standing prolonged bombardment from radioactive materials and contained one within another, the innermost of said casings containing said supporting block, said sheet of sealing material and said deposit of radioactive material contained therebetween, said casings having concentric apertures positioned over said deposit of radioactive material; layers of adhesive bonding said casings to each other, and a layer of adhesive bonding said block and said sheet of material to said innermost casing.

3. A radioactive source comprising a block of resin-bonded fiberglass laminate provided with a flat surface containing an endless moat; a deposit of radioactive material on the portion of said flat surface surrounded by said moat; a sheet of mica covering said surface and said deposit of radioactive material thereon; a layer of a polyepoxide resin bonding said sheet of mica to said surface; an inner casing and outer casing both formed of material capable of standing prolonged bombardment from radioactive materials, said outer casing containing said inner casing and said inner casing containing said block, said sheet of mica and said deposit of radioactive material contained therebetween, said casings having concentric apertures positioned'over said radioactive deposit; a layer of a polyepoxide resin bonding said block and said sheet of mica to said inner casing; and a layer of a polyepoxide resin bonding said inner casing to said outer casing.

WARNER W. SCHULTZ. EUGENE P. KOZORIZ.

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

UNITED STATES PATENTS Number Name Date 2,405,026 Feuer et al July 30, 1946 2,476,644 Wallhausen et al. July 19, 1949 2,479,882 Wallhausen et al. Aug. 23, 1949 FOREIGN PATENTS Number Country Date 467,924 Great Britain June 25, 1937

Claims

1. A RADIOACTIVE SOURCE COMPRISING A SUPPORTING BLOCK FORMED OF A MATERIAL NOT READILY BROKEN DOWN BY PROLONGED BOMBARDMENT FROM RADIOACTIVE MATERIALS AND PROVIDED WITH A FLAT SURFACE; A DEPOSIT OF A RADIOACTIVE MATERIAL ON A PORTION OF SAID FLAT SURFACE; A THIN SHEET OF SEALING MATERIAL COVERING SAID SURFACE AND SAID DEPOSIT OF RADIOACTIVE MATERIAL THEREON TO FORM A SEALING LAYER TRANSPARENT TO THE SEPECTRUM OF RADIATION FROM SAID DEPOSIT OF RADIOACTIVE MATERIAL; A LAYER OF ADHESIVE BONDING SAID SHEET OF SEALING MATERIAL TO SAID SURFACE; A CASING FORMED OF MATERIAL CAPABLE OF STANDING PROLONGED BOMBARDMENT FROM RADIOACTIVE MATERIAL CONTAINING SAID SUPPORTING BLOCK, SAID SHEET OF SEALING MATERIAL AND SAID DEPOSIT OF RADIOACTIVE MATERIAL BONDED THEREBETWEEN AND HAVING AN APERTURE POSITIONED OVER SAID DEPOSIT OF RADIOACTIVE MATERIAL; AND A LAYER OF ADHESIVE BONDING SAID SUPPORTING BLOCK AND SAID SHEET SEALING MATERIAL TO SAID CASING.