METHOD FOR PRODUCING NEUTRON CONVERTERS

Abstract

The present invention relates to a method for producing a neutron converter from boron carbide or a boron film on a neutron transparent metal substrate. The neutron transparent metal substrate is polished in a first step by fine grinding and coated in a further step by means of sputtering with boron carbide or a boron film. An adhesion promoting layer is optionally applied between the metal substrate and below the boron or boron carbide layer. The coatings obtained have a high homogeneity in layer thickness, chemical composition and isotope ratio as well as a low level of impurities such as oxygen or nitrogen.

Claims

1. A method for producing neutron converts, wherein a neutron transparent metal substrate of aluminium or an aluminium alloy is polished in a first step by fine grinding and coated in a second step by sputtering with boron carbide.

2. The method according to claim 1, characterised in that the fine grinding takes place using grinding papers.

3. The method according to claim 2, characterised in that grinding papers of a grain in the range of from 1000-2500 are used.

4. The method according to claim 2, characterised in that the fine grinding additionally takes place using a grinding liquid.

5. The method according to claim 4, characterised in that the grinding liquid is selected from the group consisting of acetone, an alcohol and water.

6. The method according to claim 5, characterised in that ethanol is used as alcohol.

7. The method according to claim 1, characterised in that the neutron transparent metal substrate consists of aluminium or a titanium-aluminium alloy.

8. (canceled)

9. The method according to claim 1, characterised in that B.sub.4C enriched with .sup.10B is used as boron carbide for coating.

10. The method according to claim 8, characterised in that the boron carbide has 95% .sup.10B.

11. (canceled)

12. (canceled)

Description

DETAILED DESCRIPTION

[0019] According to the invention a metal substrate is polished in a first step and coated in a further step by means of sputtering with boron carbide or a boron film.

[0020] The fine grinding preferably takes place using grinding papers but can also be carried out using a polishing paste—an emulsion of metal dust, grinding liquid and grinding paper grains. During grinding, the upper material layers are removed using sandpaper grains (SiC, Al.sub.2O.sub.3, diamond or CBN). The grain or grade of the grinding paper or grinding paste used is preferably in the range of from 800 to 2500, wherein the term “polishing” is used in the case of finer grains or grades. The metallographic polishing process is based, like grinding, on the cutting removal effect of the polishing media, but the abrasion is somewhat lower than the case with grinding, as very fine grains are used.

[0021] The metal substrate is preferably initially finely grinded in successive steps using grinding papers and/or grinding pastes with increasingly fine grain and then polished.

[0022] SiC or Al.sub.2O.sub.3 papers or pastes are preferably used for fine grinding.

[0023] When using a grinding paper the fine grinding preferably takes place also using a grinding liquid as wet grinding. The grinding liquid is preferably selected from the group consisting of acetone, an alcohol such as methanol, ethanol, propanol or butanol, and water. Ethanol or water is preferably used as a grinding liquid. Even when using a polishing paste, the grinding liquid is preferably selected from the group consisting of acetone, an alcohol such as methanol, ethanol, propanol or butanol, and water.

[0024] The metal substrate is neutron transparent and is preferably selected from the group consisting of aluminum or an aluminum alloy such as a titanium-aluminum alloy.

[0025] After the fine grinding the metal substrate is preferably rinsed. Subsequently the polished and possibly rinsed metal substrate can be coated with an adhesion promoting layer such as a titanium layer. The adhesion promoting layer is preferably produced by sputtering. However, the pre-treatment achieves an adhesion between the converter layer and metal substrate which renders an adhesion promoting layer unnecessary in most cases.

[0026] Finally, the metal substrate is coated by means of sputtering with boron carbide or with boron film. B4C enriched with 10B is preferably used as boron carbide. The coating can be carried out with or without an adhesion promoter such as titanium. The layer thickness of the coating is preferably in the range of from 100 nm to 10 μm, more preferably 250 nm to 5 μm, most preferably 500 nm to 3 μm.

[0027] The sputtering both of the adhesion promoting layer and also of the converter layer is preferably carried out with solid magnetron sputtering sources, wherein the substrates are moved relative to the cathodes in order to produce a large-area homogeneous coating. The particle flow is preferably horizontally orientated in order to minimize contamination on the substrate and the sputter target. The coating rates are preferably in the range of from 0.1 to 1.0 nm/s. The coating preferably takes place under an argon pressure which can be as low as 1 μbar. Further details concerning coatings and methods, in particular magnetron sputtering, can be found in Milton Ohring, Materials Science of Thin Films, Academic Press, London 1992, to which reference is made here in full.

[0028] By applying the method according to the invention neutron converters can be produced with an even coating area of up to several square meters, such as in the range of from 1 to 100 m2. The layers produced in trials on metal substrates with a coating area of from 0.5 to 1.0 m2 were characterized by means of a specially developed test detector. High quantum efficiencies could be detected.

[0029] The coatings obtained have a high homogeneity in layer thickness, chemical composition and isotope ratio as well as a low level of impurities such as oxygen or nitrogen. Surprisingly, the coatings produced according to the invention have a good adhesion to thin sheets of aluminum or an aluminum alloy, even with large-area or thick coatings of up to 5 μm.