Patent Number: 
Section: claims

1. An observation instrument inside a thick-walled radiation shielded cell, wherein the instrument is arranged to be capable of extending inside a cavity passing through a wall of the cell, the instrument comprising two separate modules:a first module of the instrument comprising a biological protection shield, a camera for acquiring images of zones situated in the cell; anda travel mechanism for moving the camera between a retracted position to which the camera is retracted into the cavity and a deployed position for observing the inside of the cell, the travel mechanism being coupled to the camera and including an actuator for causing the camera to move between the retracted position and the deployed position; anda second module of the instrument comprising a dome that is substantially transparent to rays or radiation and that is arranged to be capable of receiving the camera therein when the camera is in the deployed position for observation;each of the two modules including a mutual bearing face, the two modules being capable of being put into mutual contact via their respective mutual bearing faces when the modules are engaged in the cavity,the camera being arranged between the dome and the shield, and being secured to the shield via the travel mechanismthe dome being provided at a first end of the instrumentthe actuator causing the camera to move between the retracted position away from the dome and the deployed position in which the camera extends inside the dome,the travel mechanism being arranged between the dome and the shield, andthe dome being separate from the camera, from travel mechanism, and from the shield of the instrument. 2. An instrument according to claim 1, wherein the dome is secured to a tubular sleeve fitted with two O-rings and is arranged to slide in a tubular bushing lining the cavity, the O-rings being arranged to be in contact with the bushing. 3. An instrument according to claim 1, wherein the dome comprises a substantially hemispherical wall. 4. An instrument according to claim 3, wherein the wall is made of a plastics material, in particular of polycarbonate. 5. An instrument according to claim 1, wherein the travel mechanism comprises:a first actuator for causing the sensor to move in translation along the longitudinal axis of the instrument;a second actuator for causing the sensor to move in turning about the longitudinal axis; anda third actuator for causing the sensor to move in pivoting about an axis that is substantially orthogonal to the longitudinal axis. 6. An instrument according to claim 1, wherein the camera includes a controlled or automatic focusing lens with a motor-driven zoom function. 7. An instrument according to claim 1, wherein the camera includes a motor-driven zoom function. 8. A cell including a wall pierced by a cavity and an instrument according to claim 1 that extends inside the cavity. 9. A cell according to claim 8, wherein the wall of the cell includes an abutment that is movable between a stop position in which the abutment prevents the dome from being expelled into the cell, and a release position in which the abutment allows the dome to be expelled into the cell. 10. An observation instrument for observing the inside of a thick-walled radiation shielded cell, wherein the instrument is arranged to be capable of extending inside a cavity passing through a wall of the cell, the instrument comprising two separate modules:a first module of the instrument comprising:a biological protection shield;a gamma ray detector for measuring gamma rays emitted in zones situated in the cell; anda travel mechanism for moving the detector between a retracted position in which the detector is retracted into the cavity and a deployed position for observing the inside of the cell, the travel mechanism being coupled to the detector and including an actuator for causing the detector to move between the retracted position and the deployed position; anda second module of the instrument comprising a dome that is substantially transparent to rays or radiation and that is arranged to be capable of sliding in the cavity, which dome is capable of receiving the detector therein when the detector is in the deployed position for observation;each of the two modules including a mutual bearing face, the two modules being capable of being put into mutual contact via their respective mutual bearing faces when the modules are engaged in the cavity,the detector being arranged between the dome and the shield and being secured to the shield via the travel mechanism,the dome being provided at a first end of the instrument,the actuator causing the detector to move between the retracted position away from the dome and the deployed position in which the detector extends inside the dome,the travel mechanism being arranged between the dome and the shield, andthe dome being separate from the detector, from the travel mechanism, and from the shield of the instrument. 11. An instrument according to claim 10, wherein the dome is secured to a tubular sleeve fitted with two O-rings and is arranged to slide in a tubular bushing (31) lining the cavity, the O-rings being arranged to be in contact with the bushing. 12. An instrument according to claim 10 wherein the dome comprises a substantially hemispherical wall. 13. An instrument according to claim 12, wherein the wall is made of a plastics material, in particular of polycarbonate. 14. An instrument according to claim 10, wherein the travel mechanism comprises:a first actuator for causing the detector to move in translation along the longitudinal axis of the instrument;a second actuator for causing the detector to move in turning about the longitudinal axis; anda third actuator for causing the detector to move in pivoting about an axis that is substantially orthogonal to the longitudinal axis. 15. A cell including a wall pierced by a cavity and an instrument according to claim 10 that extends inside the cavity. 16. A cell according to claim 15, wherein the wall of the cell includes an abutment that is movable between a stop position in which the abutment prevents the dome from being expelled into the cell, and a release position in which the abutment allows the dome to be expelled into the cell.