Method and apparatus for determining a fluid density

1. An apparatus, suitable for measuring a property of a fluid, comprising a source of beta particles, a detector capable of detecting beta particles, means to support said source and said detector spaced apart from each other and in contact with said fluid, such that fluid may enter the space between the source and detector and that the source is positioned to emit beta particles towards said detector; wherein said detector comprises a scintillation material in optical communication with a photodetector, and means to physically isolate said photodetector from said fluid.

2. An apparatus according to claim 1 , wherein the photodetector is located within an enclosure, said enclosure being adapted to exclude the ingress of the fluid being measured.

3. An apparatus according to claim 1 wherein said photodetector is separated from the fluid by a fluid-proof seal.

4. An apparatus according to claim 1 , wherein said means to physically isolate said photodetector from said fluid comprises a window of optically conducting material placed between said scintillation material and said photodetector, said optically conducting material being capable of transmitting light from the scintillation detector to the photodetector.

5. An apparatus according to claim 4 , wherein more than one separate window of optically conducting material is provided between said photodetector and said fluid.

6. An apparatus according to claim 4 , wherein said scintillation material and said photodetector are optically coupled to said optically conducting material, said optically coupled material being disposed between said scintillation material and said photodetector.

7. An apparatus according to claim 1 , wherein said scintillation material comprises a scintillation crystal.

8. A method of measuring changes in a physical or chemical property of a hydrocarbon-containing fluid stream using an apparatus according to claim 1 , comprising the steps of installing the apparatus such that said source and detector are within a vessel containing said hydrocarbon fluid and said photodetector is outside said vessel, causing said fluid to flow between the source and detector and calculating changes in the physical or chemical property of the fluid stream from measured changes in the number of beta particles emitted by the source which are detected by the detector.

9. A method according to claim 8 , wherein said property is the bulk density of said fluid.

10. A method according to claim 8 , wherein said fluid comprises a gas and the method detects the presence of liquid in said gas.

11. A method according to claim 8 , wherein a first source and first detector are provided at a first location in contact with the fluid and a reference source and reference detector are provided at a second location in contact with a fluid and said property is calculated from the difference between the beta particles detected by the first detector and the beta particles detected by the reference detector.

12. A method according to claim 11 , wherein the reference source and detector are substantially functionally identical to the first source and detector.

13. A method according to claim 11 , wherein said first location is within a gas stream flowing in a pipeline and the temperature and pressure at said second location are substantially the same as those experienced at said first location.

14. A method according to claim 13 , wherein said second location is in communication with said first location and separated therefrom by a de-mister.

15. A method for measuring a property of a fluid comprising:

(a) providing a source of beta particles and a detector for detecting said beta particles, wherein said source and detector are spaced apart from one another and in contact with said fluid; wherein said source and detector are arranged such that beta particles emitted by said source are capable of being detected by said detector; and wherein said detector comprises a scintillation material in optical communication with a photodetector, and means to physically isolate said photodetector from said fluid;

(b) causing at least a part of said fluid to flow between said source and said detector; and

(c) measuring over a time period the number of beta particles detected by said detector and inferring a change in said property from a change in the number of beta particles detected over said time period.

16. A method according to claim 15 , wherein said property is the bulk density of said fluid.

17. A method according to claim 15 , for measuring the composition of said fluid.

18. A method according to claim 17 , wherein said fluid comprises a gas and the method detects the presence of liquid in said gas.

19. A method according to claim 15 , for measuring the pressure of said fluid.

20. A method according to claim 15 , wherein a first source and first detector are provided at a first location in contact with the fluid and a reference source and reference detector are provided at a second location in contact with a fluid and said property is calculated from the difference between the beta particles detected by the first detector and the beta particles detected by the reference detector.

21. A method according to claim 20 , wherein the reference source and detector are substantially functionally identical to the first source and detector.