CA1298698C

CA1298698C - Material for protecting against x-rays and processes for producing this material

Info

Publication number: CA1298698C
Application number: CA000534532A
Authority: CA
Inventors: Michel Puech; Yves Valy; Jean Bourcereau; Jean Duphil; Jean Saint Luce Banchelin
Original assignee: Airbus Group SAS
Current assignee: Airbus Group SAS
Priority date: 1986-04-16
Filing date: 1987-04-13
Publication date: 1992-04-14
Anticipated expiration: 2009-04-14
Also published as: EP0242294B1; DE3770857D1; FR2597651A1; FR2597651B1; ES2023425B3; JPS62250399A; EP0242294A1

Abstract

ABSTRACT OF THE DISCLOSURE
X-ray protection material and process for producing the same. The protection material is formed from a thermosetting or thermoplastic resin matrix containing in the form of a regularly dispersed powder at least one metal and/or one inorganic compound of a metal, the metal having an atomic number at least equal to 47 and the powder only melting at a temperature at least equal to 630°C. The material is applicable in the aerospace field for providing X-ray protection to electronic circuits and optical fibres carried in a craft.

Description

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P~ODUCING THIS ~TERIAL
ACRGROUND OF THE INVENTION
The present invention relates to a material giving protection against X-rays and to various processes for producing this materialr This protective material can be used for protecting a large number of devices which are sensitive to X-rays, such as optical or electronic devicesl as well as persons working in areas exposed to X-rays, such as radiologists.

The invention more specifically applies to providing X-ray protection to integrated circuits and optical fibres used in aeronautical and space fields.

One of the most widely used methods for protecting a random device against X-rays consists of enclosing it in an envelope of pure metal with a high atomic number. The metal and the thickness of the metal sheet are chosen and adapted as a function of the energy of the X-radiation in question and the desired filtering level. This procedure makes it possible to provide effective protection against high X-ray doses, but also against X-rays with a low dose rate.
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Unfortunately the realisation of the metals of greatest interest for this type of protection is difficult and costly. Moreover, the requirements of fixing said protective materials and the ensuring of their non-deterioration with respect to various environmental conditions (climatic, mechanical, ionizing, etc) means that the weight breakdowr of the complete apparatus is great~y increase compared an apparatus not protected against X-rays.

In most cases, the X-ray protection metal sheet cannot be placed directly against all the outer faces of the apparatus due to the often complex profile thereof. In . ~
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9 !3~;9~3 particular, in the case of electronic devices, this complexity of profile is often imposed by thermal dissipation constra~nts.

Consequently the volume defined by the metal protection sheet is greater than the volume of the apparatus to be protected. This leads to an increase in the weight and the overall dimensions of the apparatus r which is ' exacerbated by the mechanical devices which become necessary for maintaining the metal sheet in place (spacers, angles, brackets, screws and bolts, etc).
Moreover, these maintaining or holding devices must be made from the same metal as that of the protection metal sheet, so as not to create "holes" in the X-ray protection.

In certain cases, it is possible to directly make the X-ray protection metal deposit in the desired thickness on the apparatus to be protected either by immersing the latter in a li~uid bath, or by electrolysis.
Unfortunately, these deposition processes are not possible for all metals usable for X-ray protection purposes. Moreover~ the thicknesses which can be deposited for metals lending themselves to these procedures are limited, otherwise the quality of the adhesion of the deposits may be prejudiced.

Moreover, the need to obtain homogeneity of these deposits makes it necessary to operate in successive stages with, in most cases, necessary remachining between the deposits, so that in certain cases the dimensions of the apparatus are respected in the final stage.

Thus, these deposition procedures are limited and lead to a high cost of the X-ray protected apparatus.

In the particular case of protecting against X-rays SP 3004.69 LC

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on-board or embarked electronic components, consideration has been given to a specific protection for each component, which constitutes a further development of the aforementioned known solutions.

5 This specific protection is described in FR-A-2 547 113 filed in the name of the C~mpagnie D'Informatique Militaire, Spatiale et Aeronautique and consists of using several stacked sheets of different materials having different atomic numbers.

As a material having a high atomic number, reference is made to dielectric ceramics t such as barium or neodymium titanate, titanium oxide or a complex, lead-based ceramic. Material with a low atomic number are carbon, aluminium, silicon, alumina and silica.

As a function of the applications and the number of components involved, the increase in the number of individual protections can be more prejudicial from the weight standpoint than an overall protection of all the electronic components Moreover, the technology for producing the various materials constituting the stacks is based on processes used for the production of capacitors and in particular fritting processes. In particular, the process described does not make it possible to obtain an X-ray protection material with a complex shape.

Within the scope of the protecting persons working in the presence of X-rays, the materials used mainly consist of a charge or filler such as lead, dispersed in an organic binder. Such protective materials- are in particular described in FR-A-2 190 717 filed in the name of Giken, FR-A-2 482 761 filed in the name of A. MAURIN and US
patent 3 622 432 of H.~. PORTER Company.
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These lead-based materials can only be used as X-ray protection materials for radiations having a low dose rate associated with relatively long dose distribution times.

Moreover, in the building field, materials are known for giving protection against neutron and gamma radiation which are formed from a rubber or plastic material containing the powder of a lead, tungsten, barium, cadmium, bismuth or tin salt of a saturated fatty acid.
~0 These materials are particularly described in FR-A-2 027 5l4 filed in the name of F. MARYEN.

The present invention relates to an X-ray protection material making it possible to obviate the aforementioned disadvantages. In particular, this organic protective material which contains a charge or filler makes it possible, compared with the use of a heavy metal sheet, to bring about an improvement as regards weight and overall dimensions, whilst still providing an effective protection against X-radiation with a high dose rate and in particular a dose rate exceeding 10 rad.s.
Moreover, this protective material causes no major production problem and can be used in a larger number of applications than those of the prior art.
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UMMARY OF THE INVENTION
The invention specifically relates to an X-ray protection material, wherein it is formed from a resin matrix containing in the form of a regularly dispersed powder at least one metal and/or at least one inorganic compound of a metal, the powder only melting at a temperature at least equal to 630 C and the metal having an atomic number at least equal to ~7O

The term powder of at least metal and/or at least one inorganic compound of a metal is understood more SP 3004.6 LC

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particularly to mean a powder constituted by a metal and an inorganic compound of said same metal or a different metal.

The expression powder only meltiny at a temperature at least equal to 630 C means that the metals and inorganic compounds present in the powder form in the organic matrix all have a melting point equal to or exceeding 630 C.

The use of a metal with a high atomic number equal to or greater than 47 permits an effective X-ray filtering.

In the case of an intense X-radiation flow rate and for short periods, the filtering thereof leads to a thermal shock phenomenon within the material. These thermal shocks are also linked with the considered energy spectrum. For an equal filtering efficiency, the thermal shock produced in the protection material will be much lower than in the corresponding solid metal. This has a double advantage with respect to the non-deterioration of the inventive X-ray protection material and with respect to the objects to be protected~
, ' It is to avoid undesirable ancillary effects linked with such thermal shocks, such as surface melting of the grains which can lead to the destruction of the protective material, that the inventors have selected materials having a melting point equal to or higher than 630 C.

The dimensions (thicknesses) and efficiency of the X-ray protection material are calculated in the energy range of ~the absorption by the photoelectric effect of the ; 30 material. Within this range and for a given spectrum or energy, the parameters influencing the protection level, i.e. the filtering, are defined so as to offer the same SP 3004.~0 LC

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protection efficiency as a solid metal taken as reference. The efficiency of the filtering of the solid reference metal is expressed in g/cm .

In the case of an X-ray protection material according to the invention, reference is then made to filtering equivalent to n g/cm of the reference metal, n being a function of the required efficiency.

For a particular application without thickness constraint, it is possible to use any one of the protective materials according to the invention. In other applications, as the protection level possible is partly a function of the available thickness for housing the X-ray protection materials, the nature of the powder and its quantity in the resin matrix will be imposed.

For an equal pure metal quantity, the use of a powder regularly distributed in a resin matrix leads to an efficiency loss compared with sheet metal, all other conditions being equal. This efficiency loss is essentially a function of the grain size distribution of the powder and the powder quantity in the organic binder, it being assumed that a homogeneous distribution has been obtained.

The efficiency loss decreases as the powder quantity increases and the grain size is small. To this end, preference is given to a powder having a grain size between 0.5 and 25 ~m. Powder mixing operations remain possible below O.S ~m, but cause much greater difficulties. Above 10 ~um, X-ray protection is no longer effectively assured.

The grain size dispersion value of the powders in the matrix is linked with the means grain size value chosen for the considered application. This dispersion value SP 3004.69 LC

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can be up to five times the mean grain size value.

The grain size parameter guaranteeing the best "cost performance - use" compromise occurs with a powder having a grain size with a mean value of 4 um and with a dispersion coefficient of 2.5. Thus, the powder can advantageously contain gralns having dimensions between 1.6 and 10 ~m.

The powder quantity in the binder can be up to 50% by volume of the finished X-ray protection material. As for the grain size, the higher the powder quantity, the more effective the protection. However, a powder quantity exceeding 50% by volume is disadvantageous for a good mechanical strength or behaviour of the material, as well as a good homogeneity thereof. Moreover, the minimum powder quantity making it possible to provide effective protection against X-rays is 25% by volume of the finished protection material.

In the aforementioned range, the higher the powder quantity, the heavier and more rigid the protection material. Consequently the doping rate a function of the ` envisaged application and more particularly a function of the desired flexibility for the protective material.

In the same way, as a function of the desired flexibility for the protective material, it is possible to use a thermoplastic or thermosetting resin. Resins which can be used are polyamides, polyethers, polyesters, phenoplastics or phenolic resins, polyolefins, epoxides, polyimides, silicones and furan resins.

Preference is given to the use of a silicone resin such as a mixture of Rhone Poulenc RTV1502 and RTV141, a ~ phenolic resin, such as bakelite, or a polyether block -~ amide or polyether block ester resin.

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The metal powder dispersed in the organic binder can be powder of silver, antimony, barium, rear earth, tantalum, tungsten, rhenium, iridium, platinum, gold, uranium, hafnium or mixture50f these metals. Preference is given to the use of a silver, tantalum, tungsten or uranium metal powder.

In the same way, the powder constituted by an inorganic compound dispersed in the organic binder can be an oxide, nitride or carbide of a heavy metal, whose atomic number 10 at least equal to 47, or a mixture of these compounds.
Metals entering in the composition of the inorganic compound can be those referred to hereinbefore.
Advantageously, the inorganic compound is an oxide, nitride or carbide of silver, tantalum, tungsten or 15 uranium, when said compound effectively exists.

For a given pure metal, the X-ray filtering efficiency is related to the irradiation spectrum and the energy levels of the electron bands of the reference metal. The energy levels have discontinuities so that, for a given 20 X-radiation energy, a metal A and consequently an inorganic compound of said metal filters more than a metal B and consequently an inorganic compound of the latterr For a different energy, said metal B could filter more than metal A and this also applies with 25 regards to the inorganic compounds of these metals.

Thus, the use of one or more metals and/or one or more inorganic compounds of a metal makes it possible to . optimize the X-ray protection on a very wide energy spectrum. The choice o~ metals and/or inorganic 30 compounds to be mixed takes account of the intended specific use. Moreover, association more particularly takes place of metals and/or compounds having complementary absorption spectra, in order to obtain the desired X-ray protection. Therefore, it is possible to SP 300~.69 LC

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g use a powder containing either barium and hafnium, or tungsten and uranium dioxide (U02) or tantalum and uranium dioxide ~U0 ).

It is also possible to use several metals (e.g. W+Ta) and/or several inorganic compounds having adjacent absorption spectra for supply, cost or metallurgical reasons.

The invention also relates to processes for producing an X-ray protection material of the type defined hereinbefore. All these processes involve a premixing of the resin and the p~wder, followed by polymerization in accordance with the desired shape. The premixing stage makes it possible to obtain a good distribution of the powder in the organic binder and consequently a homogeneity of the opacity of the X-ray protection material.

A first process consists of melting granules of a thermoplastic resin, intimately mixing this melted resin with the powder of at least one metal and/or at least one inorganic compound of a metal, the powder only melting at a temperature at least equal to 630 C and the metal having an atomic number at least equal to 47, extruding the mixture to form granules thereof and polymerizing said granules.

~5 This process has the advantage of simple realisation and gives very good results with respect to the homogeneity ; of the protection material. Bearing in mind the flexibility of the material obtained, it can be used for producing a sheath for protecting a plastic, glass or silica optical fibre or an electrical conductor against the action of X-rays.

The extrusion of the resin - powder mixture can be SP 3004.~9 LC

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--- o--obtained with conventional means and in particular a ~ERNE~ ZSK 30 extruder - granulator.

The thermoplastic resins and powders which can be used are those referred to hereinbefore.

Polymerization is obtained by introducing a catalyst or hardener into the mixture associated with a temperature cycle. The specific form of the finished material can be obtained by injection or compression moulding of known type.

A second production process according to the invention consists of intimately mixing a first powder of a resin and a second powder of at least one metal and/or at least one inorganic compound of a metal, the second powder only melting at a temperature at least equal to 630 C and the metal having an atomic number at least equal to 47, followed by the polymerization of the mixture obtained.

The resin powder has a grain size range between 1 and 50 um, so as to ensure a good distribution of the resin and the filler in the finished material.

This process has the advantage of being usable both with thermoplastic resins and with thermosetting resins. The usable resins and powders are those referred to ~ hereinbefore. In the case of thermosetting resins, ; polymerization can be obtained by heating the mould into which the powders are introduced.

According to the invention, a third production process consists of dispersing in a liquid resin a powder of at least one metal and/or at least one inorganic compound of a metal. The powder only melting at a temperature at least equal to 630 C and the metal having an atomic number at least equal to 47 and then polymerizing the ;' SP 3004.69 LC

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thus fllled resin.

: This proces~ is particularly sultable ln the case of thermosetting resins, such as silicones. This process can in particular be used for coverlng a protective box, particularly for electronic devices. This covering of the box is ensured by in particular hot potting, the filled liquid resin being ~ntroduced into the mould by injection.

The metal powders or inorganic compounds of a metal used advantageously have a purity exceeding 99.9% in order to permit a homogeneity of the opacity to X-rays~

DESCRIPTION OF EXEMPLIFIED E~BODIMENTS
Other features and adv~ntages of the invention can be better qathered from the study of the following examples of materials and processes for the production thereof.

In a refractory material container are melted at a temperature of 220 C granules of a resin marketed under the reference PA11 by A~l 'HEM. This resin is a thermoplastic polyamide resin, whose polymerization i5 obtained by cooling to ambient temperatureO

To this melted resin is added powdered tungsten representing 30~ by volume of the finished product. This powder has an average grain size of 4 ~m and a dispersion of 2.5. The purity of the tungsten is 99.9~. This mixture is int~oduced into a WERNER~ ZSK30 extruder granulator, in order to obtain diameter 3 to 5 mm mixture granules, which can be polymerized into a random form.

These mixture granules are in particular introduced into a mould containing a box, which i5 intended to contain electronic circuits and which is to be protected against SP 3004.Ç9 LC

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X-rays. The thickne~s of the protected coverlng i8 dependent on the desired X-ray flltering efficiency and the energy spectrum of these rays can be adapted ln each case. However, a thickness of 1O5 mm may be adequate in most cases.

The covering of the box is obtained by potting by in~ection or compression of the X-ray protection materlal on the box to be protected located in the mould.

Under the same operating condltions, an X-ray protective material is produced with PA11 resin containing 6% by volume of tungsten and 24% by volume of uranium dioxide (U02), the W and U02 powders have a grain size of 4 ~m and a dispersion of 2.5. The material, obtained by injection potting on a box, makes it possible to provide an effective protection against X-rays with energy levels of 4 to 70 KeV. A thickness exceeding 2 mm of said material is adequate to ensure that the electronic circuits in the box are effectively protected.

Under the same conditlons as in example 1 was produced an X-ray protection material formed from a RHONE-POULENC
DINYL resin containing 30g by volume of a 99~ pure tungsten powder. This resin is a polyether block amide of a thermoplastic type. The average grain size of this powder ~s 4 ~m and the dispersion coefficient is 2~5.
25 This material was used for covering optical fibres with silica and the external diamete~ of the fibre sheathing was 2.5 mm.

A similar material can be obtained by replacing the DINYL
resin by the HYTREL~ resin of DUPONT de NEMOURS, the latter being a thermoplastic polyether block ester.

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~:9~ 8 ~ 13 EXAMPL~ 5 An X-ray protection material was produced from a silicone matri~ (RTV1502 + RTV141) containing a tungsten powder at a rate of 40% by volume of the finished material. The tungsten powder has the same characteristics as defined hereinbefore. The material obtained is flexible and has an elongation at break exceeding 50%. This material is particularly suitable for coating electrical conductors or optical fibres, bearing in mind the flexibility thereof.

In the various examples given hereinbefore, the homogeneity of the opacity of the X-ray protection material was checked by a microdensitometric analysis of a negative of the part obtained in X-radiography~ The fineness of the measurement reaches dimensions of 2x5 ~m.

It is found that the material obtained according to the invention have a distribution of the opacity values within the opacity distribution of the equivalent protection of the pure metal taken as a reference as a function of the metallurgical state (surface state, planeity, scratches, edge effect) of the sample of said metal, all other things being equal.

When the resin matrix of the protective material according to the invention is a thermoplastic resin, said material will be mainly used as a covering material. It could be used for covering a rigid box or a flat or curved panel made from a plastic material or a metal, an electrical conductor or an optical conductor made from plastic or glass. In such an application, the resin used must have an expansion coefficient compatible with that of the material constituting the surface to be covered.
In the case of an inventive protective material, the latter could be directly produced in the form of a box or protective panel, which could be rigid or flexible as a SP 3004.69 LC

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function of the resin used.

The material according to the invention is used wherever a random device has to be protected against X-rays and more particularly under severe climatic and mechanical conditions.

More specifically, the invention applies when minimum mass or weight conditions are required. Thus, the material according to the invention leads to advantages as regards weight, overall dimensions and manufacturing costs compared with a solid material sheet, in the case of equivalent filtering efficiency. Thus, the material according to the invention could be advantageously used for protecting electronic equipment on board an aircraft.

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Claims

-1. An X-ray protection solid material consisting essentially of a polymerized resin matrix made of at least one organic resin and having embedded therein 25 to 50% by volume of an inorganic powder selected from the group consisting essentially of :
a) - a mixture of metals, each of said metals having a melt temperature of at least 630°C and an atomic number of at least 47 ; and b) - a mixture of at least one metal and at least one inorganic metal compound, each of said metals and metals of said inorganic metal compound having melt temperature of a least 630°C and an atomic number of at least 47.
-2. An X-ray protection solid material consisting essentially of a polymerized resin matrix made of at least one organic resin and having embedded therein 25 to 50% by volume of an inorganic powder selected from the group consisting essentially of :
a) - a mixture of metals, each of said metals having a melt temperature of at least 630°C and an atomic number of at least 47, said mixture including at least two metals having complementary X-absorption spectra ; and b) - a mixture of at least one metal and at least one inorganic metal compound, each of said metals and metals of said inorganic metal compound having a melt temperature of a least 630°C and an atomic number of at least 47, said mixture including at least one metal and inorganic metal compound having complementary X-absorption spectra.
-3. The material of claim 1 or 2, further characterized in that said organic resin comprises at least one thermoplastic or thermosetting resin.
-4. The material of claim 1 or 2, further SP 3004.69 LC

characterized in that said powder has a grain size ranging from about 0.5 to 25 µm.
5. The material of claim 1 or 2, further characterized in that said powder has a grain size ranging from about 1.6 to 10 µm.
-6. The material of claim 1, further characterized in that said powder consists essentially of at least one metal and at least one inorganic metal compound having complementary X-absorption spectra.
-7. The material of claim 6, further characterized in that said metal is selected from the group consisting of silver, tantalum, tungsten, barium, hafnium and uranium powders.
-8. The material of claim 6, further characterized in that said inorganic metal compound is selected from the group consisting of metal oxide, nitride and carbide powders.
-9. The material of claim 6, further characterized in that said inorganic metal compound powder is selected from the group consisting of silver, tantalum, tungsten and uranium compounds.
-10. The material of claim 6, further characterized in that said inorganic metal compound is uranium dioxide.
-11. The material of claim 1 or 2, further characterized in that said powder consits essentially of tungsten and uranium dioxide.
-12. The material of claim 1 or 2, further characterized in that said powder consists essentially of tantalum and uranium dioxide.
-13. The material of claim 1, further characterized in that said powder consists essentially of at least two metals having complementary X-absorption spectra.
-14. The material of claim 13, further SP 3004,69 LC

characterized in that said metal powder is selected from the group consiting of silver, tantalum, tungsten, barium, hafnium and uranium powders.
-15. The material of claim 13, further characterized in that the metal powder is a mixture of barium and hafnium powders.
-16. A process for producing an X-ray protection solid material comprising intimately mixing a first powder of at least one organic resin and a second powder of an inorganic powder selected from the group consisting of :
a) - a mixture of metals, each of said metals having a melt temperature of at least 630°C and an atomic number of at least 47 ; and b) - a mixture of at least one metal and at least one inorganic metal compound, each of said metals and metals of said inorganic metal compound having a melt temperature of a least 630°C and an atomic number of at least 47 ; and polymerizing the mixture obtained.
-17. A process for producing an X-ray protection solid material comprising melting granules of at least one organic resin, intimately mixing said melted resin with a powder of an inorganic powder selected from the group consisting of :
a) - a mixture of metals, each of said metals having a melt temperature of at least 630°C and an atomic number of at least 47 ; and b) - a mixture of at least one metal and at least one inorganic metal compound, each of said metals and metals of said inorganic metal compound having a melt temperature of a least 630°C and an atomic number of at least 47 ; and extruding the mixture to form granules thereof and polymerizing said mixture granules.

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-18. A process for producing an X-ray protection solid material comprising dispersing in a liquid resin a powder of an inorganic powder selected from the group consisting of :
a) - a mixture of metals, each of said metals having a melt temperature of at least 630°C and an atomic number of at least 47 ; and b) - a mixture of at least one metal and at least one inorganic metal compound, each of said metals and metals of said inorganic metal compound having a melt temperature of a least 630°C and an atomic number of at least 47 ; and polymerizing said charged liquid resin.

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