GB1572989A

GB1572989A - Method of manufacturing sealed sources of ionizing radiation

Info

Publication number: GB1572989A
Application number: GB2317178A
Authority: GB
Original assignee: Commissariat a lEnergie Atomique CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 1977-07-05
Filing date: 1978-05-26
Publication date: 1980-08-13
Also published as: FR2397047B2; FR2397047A2; CH623163A5

Abstract

This process consists in: - depositing on a substrate (1) consisting of a metal a thin active layer (3) of a radio element, called first layer, - subjecting the substrate thus coated to an oxidation treatment so as to obtain on the first layer (3) an inactive layer (5) of an oxide of the said metal, called second layer, - depositing a layer of varnish (9) on the said second, inactive layer (5). Application to the production of sealed sources of ionising radiations. <IMAGE>

Description

(54) IMPROVEMENTS TO THE METHOD OF MANUFACTURING SEALED SOURCES OF IONIZING RADIATION (71) We, COMMISSARIAT A L'ENERGIE ATOMIQUE, an organisation created in France by Ordinance No.45-2563 of 18th October 1945, of 31/33, rue de la Federation, 75015 Paris, France, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to improvements to the method of manufacturing sealed sources of ionizing radiation as described and claimed in our British Patent Specification No. 1,487,358 filed on the 13th December 1974.

The aforementioned patent relates to a method of obtaining sealed radioactive sources for use in devices which may undergo considerable increases in temperature and may be subjected to corrosive media.

The method of obtaining a source according to the aforementioned patent is characterised in that a thin active layer of a radioelement is deposited on to a metal substrate and the thus-coated substrate is oxidized to obtain an inert coating comprising an inactive protective layer of oxide on the active layer, the oxide being of the aforementioned metal.

According to the parent patent, the substrate metal can be e.g. nickel and the active layer can be an oxide of a radio-element emitting a, ss, y or X-rays and/or neutrons, the thickness of the active layer usually being between 1 A and 0.1 ,u.

However, the method according to the parent patent cannot be used to obtain sealed radioactive sources having high resistance to corrosion and abrasion but having sufficient ionizing power.

The present invention relates to a method of obtaining sealed ionizing radiation sources which obviates the aforementioned disadvantage.

According to the invention the method of manufacturing a sealed source of ionizing radiation according to Patent No. 1,487,358 is characterised by the additional step of despositing a layer of varnish on the inactive protective layer of oxide.

Thus, the aforementioned method has the advantage of giving a source which is very strong owing to the composite natureof the protective coating comprising the inactive layer of an oxide of the metal and the layer of varnish, and owing to the slipperiness of the outer coating surface.

Thus, the method can be used to obtain sources which can be subjected to various cleaning operations without risk of losing their non-contaminating character.

In a first variant of the method according to the invention, a layer of enamel is deposited on the inactive layer of oxide before depositing the layer of varnish.

According to a second variant, a layer of a metal oxide is deposited on the inactive layer of oxide before depositing the layer of varnish.

According to the invention the thickness of the protective coating (i.e. the inactive layer of metal oxide, the layer of varnish and if required, a layer of enamel or metal oxide) is chosen so that a coating is sufficiently thick for the sealed source not to be contaminated but is sufficiently thin for the emerging radiation not to be excessively attenuated. Preferably the thickness of the coating is between 2 and 10 CL in the case of a source emitting a rays and between 5 and 50 CL in the case of a source emitting ss, ry or X-rays and/or neutrons.

The thickness of the inactive oxide layer can be adjusted by suitably adjusting the time for oxidising the substrate coated with the active layer under the preferential conditions given in the parent patent, the time varying from 1 to 24 hours. When a layer of enamel followed by a layer of varnish is to be deposited on the second layer, the thickness of the second layer is preferably between 0.5 and 5 EL for a source emitting a radiation, and between 5 and 50 it for a source emitting p, 7 or X radiation and/or neutrons.

In .ne aforementioned case, the thickness of the enamel and varnish layers is between 2 and 4 CL for an a source and between 5 and 50 IL for a p, x, 7 and/or neutron source.

According to the present invention: the varnish is preferably based on ethoxyline resins, preferably having a high molecular weight, the enamel is preferably based on metal oxides, having a composition chosen to obtain the desired coefficient of expansion and the desired vitrification temperature.

The mixture of oxides comprises silica, borate, alumina, magnesia, alkali-metal oxides and inter alia oxides of cobalt, nickel and copper.

The metal oxide is preferably an oxide of a metal identical with the metal constituting the substrate.

According to the invention, a layer of enamel is deposited by spraying an enamel suspension in a suitable solvent and then by vitrifying it by raising the coated substrate to a temperature such that the substrate no longer continues to be oxidised.

The layer of varnish is deposited by spraying a mixture comprising an ethyoxyline resin, a solidifying agent and suitable adjuvants.

The present invention also relates to a sealed radioactive source comprising the following in succession: a metal substrate, an active layer of a radio-element and a protective layer comprising an inactive layer of a metal oxide constituting the substrate and a layer of varnish.

According to the invention, the protective coating also preferably comprises a layer of enamel or a layer of a metal oxide between the inactive layer of a metal oxide constituting the substrate and the layer of varnish. A highly resistant embodiment of the invention can emit a, ss, 7 or X radiation and/or neutrons. The radio-elements used can be plutonium 238, curium 244, americium 241, californium 252 or strontium 90.

The following description relates to an example of manufacturing a sealed radioactive source according to the present invention, the example being given by way of example only. The description refers to the accompanying drawings, in which: Figure 1 is a sectional view of a source of a radiation according to the invention, the source being more particularly adapted for use in a device for eliminating static charges, and In Figure 2, curves C1 - C4, in the case of various sources, give the number N of particles leaving the sources (ordinate) and the energy E in MeV of the particles (abscissa), curve C1 referring to the source in Figure 1, curve C2 referring to a source comprising a layer of plutonium 238 oxide, a layer of nickel oxide and an enamel layer, curve C3 relating to a source comprising a layer of plutonium 238 oxide and a layer of nickel oxide, and curve C4 relating to a source comprising an unprotected deposit of plutonium 238 or americium 241 radioisotope.

Figure 1 shows an a source intended more particularly for a static electricity eliminator as described in our French Patent Application No. 77-20586 filed on the 5th July 1977 for "A device for eliminating static charges".

It is in the form of a parallelepiped. The source is obtained as follows: An active layer of plutonium 238 oxide between 1 A and 0.1 it thick is deposited on a nickel substrate 1 approximately 1 mm thick by evaporation in vacuo or cathode sputtering.

The substrate 1 coated with the active layer 3 is placed in a furnace and oxidised at high temperature (900 to 1300"C) in an atmosphere containing oxygen, e.g. air. The oxidation time is adjusted to obtain a nickel oxide layer 5 3 IL thick.

After the oxidation treatment, a layer 7 of enamel comprising metal oxides 1 IL thick is deposited by sputtering on the nickel oxide layer 5. The substrate coated with layers 5 and 7 is heated to between 750 and 900"C for 10 minutes so as to vitrify the enamel layer 7.

Next, a layer 9 of varnish 3 Er. thick is deposited on the enamel layer 7. The varnish layer is deposited by sputtering a mixture containing (a) an ethoxyline resin which, solubilized with suitable adjuvants, is sold under the name DER 669 by Messrs. DOW CHEMICAL and (b) a solidifying agent based on isocyanates sold under the name DESMODUR by Messrs. BAYER.

The resulting a source has an activity of 2 millicuries.

As curve C1 shows, the energy E of the particles leaving the source obtained in the aforementioned manner is between 3 and 4.8 MeV, whereas the energy of particles (curve C4) from an a source formed from a bare deposit of plutonium 238 or americium 241 is approximately 5.5 MeV.

WHAT WE CLAIM IS: 1. A method of manufacturing a sealed source of ionizing radiation according to any one of Claims 1 to 6 of the parent Patent No.

1,487,358, characterised in that the method comprises the additional step of depositing a layer of varnish on the inactive protective layer of oxide.

2. A method according to Claim 1, characterised in that a layer of enamel is deposited on the inactive protective layer of oxide before depositing the layer of varnish.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. deposited on the second layer, the thickness of the second layer is preferably between 0.5 and 5 EL for a source emitting a radiation, and between 5 and 50 it for a source emitting p, 7 or X radiation and/or neutrons. In .ne aforementioned case, the thickness of the enamel and varnish layers is between 2 and 4 CL for an a source and between 5 and 50 IL for a p, x, 7 and/or neutron source. According to the present invention: the varnish is preferably based on ethoxyline resins, preferably having a high molecular weight, the enamel is preferably based on metal oxides, having a composition chosen to obtain the desired coefficient of expansion and the desired vitrification temperature. The mixture of oxides comprises silica, borate, alumina, magnesia, alkali-metal oxides and inter alia oxides of cobalt, nickel and copper. The metal oxide is preferably an oxide of a metal identical with the metal constituting the substrate. According to the invention, a layer of enamel is deposited by spraying an enamel suspension in a suitable solvent and then by vitrifying it by raising the coated substrate to a temperature such that the substrate no longer continues to be oxidised. The layer of varnish is deposited by spraying a mixture comprising an ethyoxyline resin, a solidifying agent and suitable adjuvants. The present invention also relates to a sealed radioactive source comprising the following in succession: a metal substrate, an active layer of a radio-element and a protective layer comprising an inactive layer of a metal oxide constituting the substrate and a layer of varnish. According to the invention, the protective coating also preferably comprises a layer of enamel or a layer of a metal oxide between the inactive layer of a metal oxide constituting the substrate and the layer of varnish. A highly resistant embodiment of the invention can emit a, ss, 7 or X radiation and/or neutrons. The radio-elements used can be plutonium 238, curium 244, americium 241, californium 252 or strontium 90. The following description relates to an example of manufacturing a sealed radioactive source according to the present invention, the example being given by way of example only. The description refers to the accompanying drawings, in which: Figure 1 is a sectional view of a source of a radiation according to the invention, the source being more particularly adapted for use in a device for eliminating static charges, and In Figure 2, curves C1 - C4, in the case of various sources, give the number N of particles leaving the sources (ordinate) and the energy E in MeV of the particles (abscissa), curve C1 referring to the source in Figure 1, curve C2 referring to a source comprising a layer of plutonium 238 oxide, a layer of nickel oxide and an enamel layer, curve C3 relating to a source comprising a layer of plutonium 238 oxide and a layer of nickel oxide, and curve C4 relating to a source comprising an unprotected deposit of plutonium 238 or americium 241 radioisotope. Figure 1 shows an a source intended more particularly for a static electricity eliminator as described in our French Patent Application No. 77-20586 filed on the 5th July 1977 for "A device for eliminating static charges". It is in the form of a parallelepiped. The source is obtained as follows: An active layer of plutonium 238 oxide between 1 A and 0.1 it thick is deposited on a nickel substrate 1 approximately 1 mm thick by evaporation in vacuo or cathode sputtering. The substrate 1 coated with the active layer 3 is placed in a furnace and oxidised at high temperature (900 to 1300"C) in an atmosphere containing oxygen, e.g. air. The oxidation time is adjusted to obtain a nickel oxide layer 5 3 IL thick. After the oxidation treatment, a layer 7 of enamel comprising metal oxides 1 IL thick is deposited by sputtering on the nickel oxide layer 5. The substrate coated with layers 5 and 7 is heated to between 750 and 900"C for 10 minutes so as to vitrify the enamel layer 7. Next, a layer 9 of varnish 3 Er. thick is deposited on the enamel layer 7. The varnish layer is deposited by sputtering a mixture containing (a) an ethoxyline resin which, solubilized with suitable adjuvants, is sold under the name DER 669 by Messrs. DOW CHEMICAL and (b) a solidifying agent based on isocyanates sold under the name DESMODUR by Messrs. BAYER. The resulting a source has an activity of 2 millicuries. As curve C1 shows, the energy E of the particles leaving the source obtained in the aforementioned manner is between 3 and 4.8 MeV, whereas the energy of particles (curve C4) from an a source formed from a bare deposit of plutonium 238 or americium 241 is approximately 5.5 MeV. WHAT WE CLAIM IS: 1. A method of manufacturing a sealed source of ionizing radiation according to any one of Claims 1 to 6 of the parent Patent No.

3. A method according to Claim 1,

characterised in that a layer of metal oxide is deposited on the inactive protective layer before depositing the layer of varnish.

4. A method according to any of Claims 1 to 3, characterised in that the varnish is based on ethoxyline resins.

5. A method according to Claim 2, characterised in that the enamel is based on metal oxides.

6. A method according to Claim 3, characterised in that the metal oxide is an oxide of the metal constituting the substrate.

7. A method according to any of Claims 1 to 6, characterised in that the layer of varnish is deposited by spraying a mixture comprising an ethoxyline resin, a solidifying agent and adjuvants.

8. A method according to any of Claims 2 to 7, characterised in that the enamel layer is deposited by spraying a suspension of enamel and then vatrifying it.

9. A source of sealed ionizing radiation obtained by the method according to any of Claims 1 to 8, characterised in that it comprises the following in succession: a metal substrate, an active layer of a radio-element and a protective layer comprising an inactive layer of a metal oxide constituting the substrate and a layer of varnish.

10. A source according to Claim 9, characterised in that the protective coating comprises an enamel layer between the layer of varnish and the inactive layer of metal oxide comprising the substrate.

11. A source according to Claim 9, characterised in that the protective coating comprises a layer of a metal oxide between the layer of varnish and the inactive layer of metal oxide comprising the substrate.

12. A source according to any of Claims 9 to 11, characterised in that it emits a radiation.

13. A source according to any of Claims 9 to 11, characterised in that it emits p radiation.

14. A source according to any of Claims 9 to 11, characterised in that it emits y and X radiation.

15. A source according to any of Claims 9 to 11, characterised in that it emits neutrons.

16. A source according to any of Claims 9 to 14, characterised in that the radioelement is plutonium 238.

17. A source according to any of Claims 9 to 14, characterised in that the radioelement is curium 244.

18. A source according to any of Claims 9 to 14, characterised in that the radioelement is californium 252.

19. A source according to any of Claims 9 to 14, characterised in that the radioelement is strontium 90.

20. A source according to any of Claims 9 to 14, characterised in that the radioelement is americium 241.

21. A source according to any of Claims 9 to 20, characterised in that the substrate is of nickel.

22. A source according to any of Claims 9 to 21, characterised in that the thickness of the layer of radio-isotope is between 1 A and 0.1 CL.

23. A source according to any of Claims 9 to 11, characterised in that it emits a radiation and the thickness of the protective coating is between 2 and 10 IL

24. A source according to Claim 10, characterised in that it emits a radiation and the thickness of the inactive layer of a metal oxide constituting the substrate is between 0.5 and 5 CL.

25. A source according to Claim 10, characterised in that it emits a radiation and the thickness of the enamel layer is between 0.5 and 4 .

26. A source according to Claim 10, characterised in that it emits a radiation and the thickness of the layer of varnish is between 2 and 4 IL

27. A method of manufacturing a sealed source of ionizing radiation according to Claim 1, said method being substantially as described with reference to the accompanying drawings.

28. A source of sealed ionizing radiation obtained by the method of Claim 27, said source being substantially as described with reference to and as illustrated in the accompanying drawings.