Patent Number: 
Section: claims

1. A tagged excavation element including:an excavation element body; anda tagging device securable to the excavation element body;characterized in that the tagging device includes a radioactive source,wherein the excavation element is a shroud or a tooth of an excavation bucket. 2. The tagged excavation element of claim 1 in which the tagging device is in the form of a sealed radioactive source. 3. The tagged excavation element of claim 2 in which the sealed radioactive source comprises a radioactive material encapsulated in a sealed metal housing. 4. The tagged excavation element of claim 3 in which the sealed metal housing is locatable inside an aperture provided in the excavation element. 5. The tagged excavation element of claim 1 in which the radioactive source has a half-life of between 40 days and 150 days. 6. The tagged excavation element of claim 5 in which the radioactive source has a half-life of between 80 days and 90 days. 7. The tagged excavation element of claim 1 in which the radioactive source is a radioactive metal. 8. The tagged excavation element of claim 1 in which the radioactive source emits gamma radiation at an energy level between 300 keV and 2000 keV. 9. The tagged excavation element of claim 8 in which the radioactive source emits gamma radiation at an energy level between 850 keV and 1500 keV. 10. The tagged excavation element of any one of the preceding claims in which the radioactive source is selected from the group including scandium (Sc), tantalum (Ta), terbium (Tb) and antimony (Sb). 11. The tagged excavation element of any one claims 1 to 9 in which the radioactive source is a radioisotope of the element scandium (Sc), scandium 46 (46Sc). 12. A method of manufacturing a tagged excavation element, the method including the steps of:providing an excavation element body;providing a tagging device including a radioactive source; andsecuring the tagging device to the excavation element body,wherein the excavation element is a shroud or a tooth of an excavation bucket. 13. The method of claim 12 in which the tagging device is in the form of a sealed radioactive source. 14. The method of claim 13 in which the sealed radioactive source comprises a radioactive material encapsulated in a sealed metal housing. 15. The method of claim 14 in which the sealed metal housing is locatable inside an aperture provided in the excavation element. 16. The method of claim 12 in which the radioactive source has a half-life of between 40 days and 150 days. 17. The method of claim 16 in which the radioactive source has a half-life of between 80 days and 90 days. 18. The method of claim 12 in which the radioactive source is a radioactive metal. 19. The method of claim 12 in which the radioactive source emits gamma radiation at an energy level between 300 keV and 2000 keV. 20. The method of claim 19 in which the radioactive source emits gamma radiation at an energy level between 850 keV and 1500 keV. 21. The method of any one of claims 12 to 20 in which the radioactive source is selected from the group including scandium (Sc), tantalum (Ta), terbium (Tb) and antimony (Sb). 22. The method of any one of claims 12 to 20 in which the radioactive source is a radioisotope of the element scandium (Sc), scandium 46 (46Sc). 23. A method of detecting the displacement of an excavation element, the method including the steps of:providing an excavation element tagged with a tagging device including a radioactive source, the excavation element comprising a shroud or a tooth of an excavation bucket;providing a radiation detector; anddetecting a change in radiation when the excavation element is displaced relative to the radiation detector. 24. The method of claim 23 in which the radiation detector is mounted on part of a structure to which the excavation element is secured, and in which the radiation detector detects a reduction in radioactivity when the excavation element is displaced away from the structure. 25. The method of claim 24 in which the structure is the body of an excavation apparatus. 26. The method of claim 25 in which one or multiple radiation detectors are provided on the excavation apparatus. 27. The method of 25 in which the radiation detector is mounted on a structure at one or more locations adjacent a route along which excavated material is displaced, and in which the radiation detector detects an increase in radioactivity when the excavation element is displaced together with the excavated material. 28. The method of claim 27 in which the structure is a gantry past which the excavated material is displaced.