US 2928948 A
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Description (OCR text may contain errors)
March 15, 1960 H. l. srLvERsHER LAMINAR RAY RESISTANT MATERIALS Filed May 25. 1955 lll/llllllP-J Ez/o. 3.
, United This invention has to do generally with the shielding against harmful transmission of ray-like emanations of the type produceable from fissionable materials. Primarily the invention is directed in certain of its aspects to improved compositions or combinations of materials for preventing or reducing neutron transmission, or the effects of neutron penetration, and in other and more particular respects, the invention deals with materials and material combinations having for their objective to shield against the transmission of both ray (alpha, beta and gamma ray) as well as neutron transmission.
Speaking first in terms of the last-mentioned objective, the invention contemplates shielding against or minimizing the effects of ray-type radiation by the use of multiple layer or laminated materials, which may employ different metal and resinous plastic materials, all as more particularly dealt with in my copending application Ser. N0. 492,486, tiled March 7, 1955, now U.S. Patent No. 2,858,451 issued October 28, 1958, on Laminat Ray Shielding Materials, together with a material or mixture of materials resistive to neutron transmission, so that the entire composite or combination becomes protective against both ray and neutron transmission or radiation. Before entering into a description of the entire combination or composite, reference preliminarily may be had to those general contemplations of the invention which pertain particularly to the absorption or slowing down of neutron energy.
It is found that certain metals and their compounds serve effectively to produce absorption or slowing down of neutrons of varying kinetic energy produced by the bombardment of direct and secondary radiation. The particular metals contemplated are of the class consisting of boron, cadmium, and lithium. I t appears that the effectiveness of any of these metals, whether in elemental o'r chemically combined form, is due to the presence and distribution of boron, cadmium, or lithium atoms, or mixtures thereof, across the path of the neutron ow to be de-energized. And it will be understood that such distribution of the metal atoms can be present whether the metal be used in elemental form or in chemically combined form. Where it is desired to use the metal chemically combined, generally speaking any of its compounds may be employed, notably inorganic compounds of the metal, including oxides, salts such as the chlorides, sulfates, nitrates, including salts complexed with other metals, and also acids and bases of the metals. Of the named metals, boron and its compounds are preferred, and accordingly in the description to follow reference will be had to the use of boron or its compounds as preferred, though typical of the class. And in further reference to boron, it is found advantageous for many purposes to employ boron in the form of boric acid because of the supplementary beneficial effects uponneutron absorption contributed by the hydrogen atoms in the acid.`
The general effect created by the presence of boron or its compounds in a shield form or ,composition ap-` pears to be that neutrons of high kinetic energy will ICC react with the metal molecules, as well as with hydrogen present therein, and will tend to reach a vstate of thermal equilibrium and to be less likely to ionize or otherwise contaminate the material bombarded. As previously indicated, a shield so composed normally will be employed with a material or combination of materials' used for shielding against alpha, beta and gamma ray transmission or radiation, since in most instances the nature of the total radiation will be inclusive of neutron etects as well as the named rays.
Generally speaking, the invention contemplates incorporating the boron or its compounds in or on a suitable carrier, for which any of various plastics, inclusive Aof thermo-setting resins, are eminently suited by reason of I desirable shielding properties possessed by the resins themselves. Typical plastic resins are the polyethylene, urea formaldehyde, melamine, phenolic, vinyl, and epoxytype thermo-setting resins. As illustrative forms or conditions in which the boron or its compounds may be ap.
plied to or incorporated in a carrier resin, reference may be had to the following: The neutron absorptive metal' persed in an epoxy or other appropriate thermo-setting resin and the resulting compound used to laminate metals or fibers together, as disclosed in my prior application referred to above. Another practice may be to incor-` porate the metal or its compound in a plastic or wax, such as polyethylene or paraffin, by physically mixing or milling, and then applying the composite as a film, layer orlamination, as the circumstances may require.
Where admixed with a resinous, waxy or other carrier or binder, the percentage of boron or its compounds may vary depending upon any of various considerations such as the thickness of the shield, layer or lamination, and the degree of neutron shielding required. In general the proportion of metal or its compound may range as high as 50%, and to even higher levels so long as the quantity and properties of the selected resin or other binder are sufficient to integrate the metallic additive in a continuous and ordinarily self-supporting mass; In most instances strength, hardness and rigidity will be imparted to the composite by curing of a thermo-setting resin binder which, if desired, may be reinforced by pigment or vfiller or by glass fabric or fibers.
Referring now to the ray shielding materials or combinations thereof in conjunction with which the abovementioned neutron absorptive materials may be used, it isfound that by reason of their relatively great density, certain metals of the group consisting of lead, uranium, thorium and thallium have a capacity to block ray transmission to a considerable extent by virtue of absorption of the rays. For purposes of further description, lead may be regarded as typical and preferred because of its availability and cost advantages of metals in this class. The completeness of ray blocking by any of these metals, will be dependent upon the nature and concentration of the rays, as well as the total thickness of the metalbarrier in any particulartinstance. It will be understood that for, the purposes of the invention, I may use one or more sheetsA of any of these metals, or combinations thereof, and which may range in thickness fromV about 2/000 inch to 6 inches. Blocking of the'rays by these heavier metals occurs at least partially by absorption in them of some of the ray energy, and gives rise to another phenomena in the nature of a secondary radiationK Patented Mar. 15, 196i?"` In laminated forms the metalk ofsabsorbed. energy. from .themetat Aswill appear, in
dealing.. with the problem of preventing.or..limiting.ray..
transmission, the invention also aims to reduce and minimlze the secondary radiation eects.
The jpresent composite material also employsthe .use i otoneor` moresheets whose thicknesses may. fall in,
about.. the same, range.. of the .thicknesses of ,the heavy. metal, of one onmoreof such metals as copper, aluminum, brass, lithium, and ductile ferrous metals, whose. effect upon therays .striking them. is more. inthe nature, ofdefiection or reflection, as distinguished from blocking.. Aluminum.
by absorption and relatively low reection. maybe regarded as illustrativeofthe metals, in. this second group. Thus in acomposite employing for, exampl e lead, and valuminum sheets, the aluminumservesto reduceby deliectionor reflection of therays, the ray,
energy and concentrationto which the lead is subjected,
and the aluminum serves further to, reduce secondary.
ray emanations from the lead. The aluminum has a comparatively. short half-life, Le the timeduringwhich it will continue to emanate previously absorbed rays..
It-isv preferred to further increase the ray blocking cas, pacity., of the composite and prevent or minimize neu.-
tron transmission by including therein one ormoresheets of; apolymerized resin or plastic material, which generally speaking may beselected from any of the so-called i plastics capable of conforming to such deformation as thecornpositeis to be given in any particular molding o r shaping operation. Typically, the preformed plastic sheet or` sheets, in thicknesseswithin, the meta1 sheet thickness range, may be selected fromsuchresinsas. polyethylene, fluorinated ethylenes, polystyrene and polybutener ThusV when so composed, all. the laminations, metaluand resin, have such ductility as will permit ,them to be shaped and deformed as desired.-
The laminations are bonded together by the us e of..
wherein R represents the divalent radical. of `dihydric:l phenol and "nf is from to 4.v One major difference.
between various resins having this genericiformula is in the (n) value which determines the length oftheimolecule. The more duid the resin theA smaller thel` (n). value. Generally these epoxy resins having a value, for (n) of 2 or more are solid or essentially solid and may require solvent thinning for their use, whereas those having an (n) value of 0 or l are essentially stable fluids. It is these latter lluid epoxy resins which I prefer to use for the purposes of the present invention by reason of the facility possessedby the uid resin for wetting the lead or lead silicate particles, andthe resultant capacity of the resin to permit incorporation therewith of. higher amounts of the lead or lead silicate in dense, andauni- `form distribution. Accordingly, the preferred repoxy resins are those which are normally uid, having an (n) VlUQOf from 0 t0 1, and an ePOXd .equivalei between 70 heapertured wheredesirablefor etecting stronger. bonds;.
140 land V550,Y the epoxide equivalent beingdefined as.
thefgrains of resin containingl gram equivalent of the epoxide group- TheA araheet 10 .of. relatively dense metal, such as leavdfbondedlv The epoxide resin is curedlby cross linkage or additiompolymerization..with any, of various compoundshaypm ing amino or amide groups. Among the various amino or amide materials useable for the curing of epoxy rcsins are (2,4,6-tri(dimethylaminomethyl) phenol, diethdilinoleic acid) with aliphatic amines such as ethylene diamine. Structurally, such polyamide resins have the formula.
wherein "n,.-may range from Sto l5. Typical of such.. resins is.Polyamide Resin as sold by General Mills, Inc.. Inthe.caseoftheamino reaction, if theamine.. molecule.. contains more. than one amino group, two..
ormoreepoxide. units may be coupled together.
Relative to the curing effects and reactions of the.
aminogroup materials with relation to ythe epoxy resin,
ifcthe, amine molecule contains more than one amino group, two ormore epoxide units may be coupled together. The optimum amount of curing will occur when the epoxide and. amino groups react,.without any of either being left in excess after the reaction 1s completed. Thuslthe proper amount ofany amino or amide group materialto be. used in the curing of the epoxy resin may. In. general the, amide .or amino group. additive. will range between from.
be determined on. a stoichiometric basis.
1/0` to.1/z weight parts` to 1 part of the epoxy resin.
' Where Adesiredfor additional strength and possible.
shear resistance in the bonding resin, the latter may be. reinforced .with such inert materials as glass .or glass.
fibers or. fabrics.
The invention .contemplates further the incorporation ofanyof .the aforementioned metals, heavy salts (e.g..v
lead.monosilicate)` and oxides thereof, or mixtures there-'- of,.-infany of the resinous components of the composite Thus the bonding agent, e.g. epoxy resin,Y
material. may be admixed with up to around 15 weight parts of any of these metals, e.g. lead or aluminum, in powdered form, to. improve the ray blocking or dellecting qualities o f thejresinas such. Also the preformed sheetfplastiey material, e.g. polyethylene, may be composed of the.4 resin cgntaininguuniformly distributed therein any of the. pouwggleredY metals.. in whatever concentration desired so long as they are adequately integrated by the resin.
The inventionwill be further understood by reference,
tothe accompanying drawing wherein I have shown certaintypical and illustrative combinations of the sheet.
materialsin interbonded laminar form. In the drawing:
Fig.i 1 afragmentary section taken through a lami.- mated, composite containing .two dissimilar. metal. sheets r 55 bonded together in directrelation;
Fig, 2 -is a similar view showing the metal sheets in- Sheet;
l-`ig ..3,isY another view showing the metal sheetsV to and'.U
Fig .4 isla view showing a simpler laminated composite. embodying theinvention..
lnFig. l thecomposite. material is. shownto include to a sheet 11 of a deflective metal such as aluminum which in use, may be positioned between sheet and the ray source. The two metal sheets are bonded together by a layer or common coating of a thermo setting bonding plastic 12, such as the epoxy resin which polymerizes as the composite assembly is heated and subjected to whatever pressure desired to urge the sheets together. Ordinarily it is preferred to include also a preformed plastic sheet 13, such as polyethylene, which may surface the composite at one or both sides of the metal sheets 10 and 11. The plastic sheet is bonded thereto at 14 using the same resin employed for bonding the metal sheets together or by mechanical attachment.
In Fig. 2 the lead 15 and aluminum 16 sheets are shown to be indirectly bonded to an inner positioned plastic sheet 17 by the bonding resin indicated at 18. As before, one or both metal sheets may be covered at the outside by plastic sheets 19.
Fig. 3 shows the metal sheets 20 and 21 to contain recesses or holes 22 wherever desirable to form a stronger bond, as with the plastic sheets 23 and 24. Here the bonding resin 2S may contain any of the metals, for example lead or aluminum, in powdered form, uniformly dispersed throughout the resin, for the purpose of minimizing ray transmission through the recesses or openings.
To cite a specific example of the invention in reference to Fig. 2, lead sheet 15, aluminum sheet 16 and plastic sheets 19 each may be around M; inch in thickness, and are bonded together by polymerization of about 100 parts of an epoxy resin (e.g. Shell Epon 8221") and about parts of meta phenylene diamine. The laminations are placed together as illustrated in a heated press or mold, and the resin cured at a temperature of about 280 F. A post cure at 350 F. will give optimum physical and structural properties.
The described embodiments of the invention in Figs. 1 to 3, may be supplemented for the purposes of neutron absorption, in any of various manners. For example, in Fig. 1 any or all of the epoxy resin laminations 12 and 14, and any or all of the laminations 18 in Fig. 2, and any or all of the laminations 25 in Fig. 3, may be supplemented by incorporating in the resin up to 50% or more of boron or boron compound, preferably boric acid, which may be uniformly distributed in finely divided form by admixture with the resin in an uncured state. The specific example given above pertaining to Fig. 2, is to be construed accordingly. Alternately, or in addition, the. neutron absorptive metal or its compounds, may be similarly incorporated in either or both the surface layers 13 of Fig. 1, 19 of Fig. 2, and 24 of Fig. 3.
In Fig. 4, I show a further variational form of the invention in which bonded to a lead sheet 26 is a. resinous lamination 27, composed typically of a thermally cured epoxy resin. Dispersed in the latter may be any ofY the neutron absorptive metals or their compounds, as previously described. Fig. 4 is illustrative of the further possibility of surface coating a layer or rheet, cr layer composite, with uniformly distributed atoms of the neutron absorptive metal, whether in the elemental state or chemically combined. Thus, for example, to the resin layer 27 may be applied a coating 28 which for example may be cadmium electroplated on a resi-.1 lamination 27 rendered conductive by loading with carbon and graphite, or the coating 28 may be applied in the form of a paint composed essentially of neutron absorptive atoms, typically as cadmium, boron or boric acid, in a resinous binder which may be thermally cured to hardness.
l. An integrated laminous shielding material comprising a first layer of ray-blocking metal of the group consisting of lead, uranium, thorium and thallium, and a second layer comprising an organic resin carrying a uniformerly distributed neutron absorbent of the group consisting of boron, cadmium and an inorganic compound of boron, cadmium and lithium.
2. A shielding material as defined by claim 1, in which said resin is a thermally hardened thermosetting resin.
3. A shielding material as defined by claim 1, in which said first layer is lead and said resin is a thermally hardened thermosetting resin bonded thereto.
4. A shielding material as defined by claim 1, in which said neutron absorbent is an inorganic compound of boron bonded to the first layer by said resin.
5. For use in ray shielding, the combination comprising a first layer of ray-blocking material of the group consisting of lead, uranium', thorium and thallium, a second layer of ray refiective metal of the group consisting of copper, aluminum, brass and ductile ferrous metals, a neutron absorbent of the group consisting of boron, cadmium and lithium uniformly distributed coextensively with common areas of said first and second layers, and an organic resinous carrier for said absorbent.
6. The combination as dened in claim 5, in which said resinous carrier is a heat hardened thermosetting resin.
7. The combination as defined in claim 5, in which said absorbent is uniformly distributed in a third layer comprising a thermosetting resin and said first layer is lead.
8. For use in ray shielding, an integrated laminar combination comprising a first layer of ray-blocking material of the group consisting of lead, uranium, thorium and thallium, a second layer of ray reflective metal of the group consisting of copper, aluminum, brass and ductile ferrous metals, and a third intermediate layer comprising a thermosetting resin containing a uniformly distributed inorganic compound of boron.
9. For use in ray shielding, an integrated laminate comprising a first layer of lead, a second layer of aluminum, and a third intermediate layer bonded to said first and second layers and comprising a thermosetting resin containing a uniformly distributed inorganic compound of boron.
' References Cited in the file of this patent UNITED STATES PATENTS