Patent Number: 
Section: claims

1. A method for producing a radioisotope, comprising:irradiating a given volume of radioisotope precursor fluid contained in a hermetic cell of a target, using a beam of particles of given beam current intensity (I) which is produced by a particle accelerator;cooling said target using a given cooling power; andmeasuring the internal pressure (P) inside said hermetic cell, wherein:during irradiation, the internal pressure (P) inside said hermetic cell is allowed to freely evolve within a first pressure tolerance range, wherein said first pressure tolerance range is determined as a function of different parameters having an influence on the evolution during irradiation of the internal pressure inside said hermetic cell, said parameters comprising, for a given target, a given beam of particles and a given radioisotope precursor fluid, the given volume of the radioisotope precursor fluid contained in said hermetic cell, the given cooling power used for cooling said target and the given beam current intensity (I); andirradiation is interrupted or its intensity reduced when the internal pressure (P) in said hermetic cell moves out of said first internal pressure tolerance range,wherein a curve P=f(I) is defined giving the internal pressure (P) of said hermetic cell at different beam current intensities (I), for a given volume of radioisotope precursor fluid and a given cooling power used for cooling said target;said first internal pressure tolerance range has a lower pressure and an upper pressure limit defined for said given beam current intensity (I) based on said curve P=f(I);said lower limit of internal pressure is defined so that it is lower than the pressure value inferred from said curve P=f(I) for said given beam current intensity (I); andsaid upper limit of internal pressure is a pressure between the pressure value inferred from said curve P=f(I) for said given beam current intensity and a nominal pressure value (Pmax) of said hermetic cell, said nominal pressure value (Pmax) being the maximum operating pressure for which said hermetic cell has been designed. 2. The method according to claim 1 wherein said upper limit of internal pressure in said first internal pressure tolerance range is lower by at least 20% than said nominal pressure value (Pmax) of said hermetic cell. 3. The method according to claim 1 wherein said upper limit of internal pressure in said first internal pressure tolerance range is between 5 and 10 bars higher than the pressure value inferred from said curve P=f(I) for said given beam current intensity (I) and its ceiling is a pressure value (P2) that is lower than said nominal pressure value (Pmax) of said hermetic cell. 4. The method according to claim 1 wherein a control device triggers an alarm when the internal pressure (P) in said hermetic cell moves out of a second internal pressure tolerance range defined as a function of different parameters having an influence on changes in internal pressure in said hermetic cell during irradiation, said second tolerance range being included within said first tolerance range. 5. The method according to claim 4 wherein:said second internal pressure tolerance range has a lower pressure limit and a higher pressure limit defined on the basis of said curve P=f(I);said lower pressure limit of said second tolerance range is defined so that it is lower than the pressure value inferred from said curve P=f(I) for the given beam current intensity (I) whilst remaining higher than said lower pressure limit of said first internal pressure tolerance range; andsaid upper pressure limit of said second internal pressure tolerance range is defined so that it is higher than the pressure value inferred from said curve P=f(I) for the given beam current intensity (I) whilst remaining lower than said upper pressure limit of said first internal tolerance range. 6. The method according to claim 1 wherein, when the internal pressure (P) in said hermetic cell exceeds an upper limit of internal pressure fixed inside said first internal pressure tolerance range, the beam current is decreased. 7. The method according to claim 1 wherein the given volume of the radioisotope precursor fluid contained in said hermetic cell is optimised experimentally for a range of envisaged beam currents. 8. The method according to claim 1 wherein said radioisotope precursor is a precursor of 11C, 13N, 15O or 18F. 9. An installation for implementing the method according to claim 1, comprising:a target with a hermetic cell capable of containing a given volume of precursor fluid, said hermetic cell being designed to withstand a nominal pressure (Pmax);a particle accelerator capable of producing and directing a beam of accelerated particles of a given beam current intensity (I) onto said target and of irradiating a given volume of the radioisotope precursor fluid contained in the hermetic cell of the target;a system to monitor the internal pressure (P) inside said hermetic cell;a cooling device configured to cool said target using a given cooling power;a control device programmed to interrupt or reduce said beam of particles when the internal pressure (P) inside said hermetic cell moves out of a first internal pressure tolerance range determined as a function of different parameters having an influence on changes in internal pressure in said hermetic cell during irradiation, said parameters comprising, for a given target, a given beam of particles and a given radioisotope precursor fluid, the given volume of the radioisotope precursor fluid contained in said hermetic cell, the given cooling power used for cooling said target and the given beam current intensity (I),wherein the control device is programmed with a curve P=f(I) giving the internal pressure (P) of said hermetic cell at different beam current intensities (I), for a given volume of radioisotope precursor fluid and a given cooling power used for cooling said target, and said curve P=f(I) is used by said control device to define said first internal pressure tolerance range as a function of beam current intensity (I),said first internal pressure tolerance range has a lower pressure and an upper pressure limit defined for said given beam current intensity (I) based on said curve P=f(I),said lower limit of internal pressure is defined so that it is lower than the pressure value inferred from said curve P=f(I) for said given beam current intensity (I), andsaid upper limit of internal pressure is a pressure between the pressure value inferred from said curve P=f(I) for said given beam current intensity and a nominal pressure value (Pmax) of said hermetic cell, said nominal pressure value (Pmax) being the maximum operating pressure for which said hermetic cell has been designed. 10. The installation according to claim 9 wherein said control device is programmed to trigger an alarm when the internal pressure in said hermetic cell lies outside a second range included within said first internal pressure tolerance range. 11. The installation according to claim 9 wherein said control device is programmed to cause a reduction in the intensity of the beam current when the internal pressure (P) in said hermetic cell exceeds an upper limit of internal pressure included in said first internal pressure tolerance range. 12. The method according to claim 1, wherein said lower limit of internal pressure is defined so that it is 5-20% lower than the pressure value inferred from said curve P=f(I) for said given beam current intensity (I). 13. The method according to claim 5, wherein said lower pressure limit of said second tolerance range is defined so that it is at least 2% lower than the pressure value inferred from said curve P=f(I) for the given beam current intensity (I) whilst remaining higher than said lower pressure limit of said first internal pressure tolerance range. 14. A method for producing a radioisotope, comprising:irradiating a volume of radioisotope precursor fluid contained in a hermetic cell of a target, using a beam of particles of given current intensity which is produced by a particle accelerator;cooling said target; andmeasuring the internal pressure inside said hermetic cell;wherein:a curve P=f(I) is determined giving the internal pressure (P) of the hermetic cell at different beam current intensities (I), for a given volume of radioisotope precursor fluid and a given power used for cooling said target;a first internal pressure tolerance range has a lower pressure limit and upper pressure limit defined for said given beam current intensity (I) on the basis of said curve P=f(I);a second internal pressure tolerance range has a lower pressure limit and a higher pressure limit defined for said given beam current intensity (I) on the basis of said curve P=f(I);said lower pressure limit of said second internal pressure tolerance range is defined so that it is lower than the pressure value inferred from said curve P=f(I) for the given beam current intensity (I) whilst remaining higher than said lower pressure limit of said first tolerance range;said upper pressure limit of said second tolerance range is defined so that it is higher than the pressure value inferred from said curve P=f(I) for the given beam current intensity (I) whilst remaining lower than said upper pressure limit of said first internal tolerance range;said irradiation is interrupted or its intensity reduced when the internal pressure (P) in said hermetic cell moves out of said first internal pressure tolerance range; anda control device triggers an alarm when the internal pressure (P) in said hermetic cell moves out of said second internal pressure tolerance range.