Methods for evaluating gamma detectors and gamma detector instrument response, particularly for use in investigation emissions from spent nuclear fuel rods

A method of investigating the response of an instrument to gamma emissions using a gamma source package, the method comprising:

• providing a source package on one side of a collimator including an aperture and providing a detector on the other side of the collimator relative to the source package, the collimator and detector positions defining an operating axis for the instrument;
• moving the position of the source package relative to the collimator with the response of the detector being measured for two or more of those different positions of the source package, the gamma emissions which generate the measured response passing through a single aperture in the collimator to reach the detector;
• the aperture in the collimator having a first dimension measured in a first direction perpendicular to the operating axis;
• and
• the source package comprising one or more individual gamma emitting sources provided in a container, during a measurement of response at a position, the individual source(s) having a maximum extent in the first direction, the maximum extent, during at least 10 seconds of use, being two or more times the first dimension of the aperture in that first direction.

A method of investigating the response of an instrument for investigating gamma emissions from a fuel rod using a gamma source package, the method comprising:

• providing a source package on one side of a collimator, the source package being provided within a location, relative to the collimator, that receives a fuel rod during investigation, the collimator including an aperture;
• providing a detector on the other side of the collimator relative to the source package, the collimator and detector positions defining an operating axis for the instrument;
• moving the position of the source package relative to the collimator with the response of the detector being measured for two or more of those different positions of the source package;
• the aperture in the collimator having a first dimension measured in a first direction perpendicular to the operating axis;
• and
• the source package comprising one or more individual gamma emitting sources provided in a container, in use the individual source(s) having a maximum overall extent in the first direction, the maximum overall extent, during at least 10 seconds of use, being two or more times the first dimension of the collimator in that first direction.

A method of investigating the response of an instrument for investigating gamma emissions from fuel rods to gamma emissions using a source package, the method comprising:

• providing a source package on one side of a collimator, the source package being provided within a location, relative to the collimator, that receives a fuel rod during investigation of a fuel rod, the collimator including a single aperture, the aperture in the collimator having a first dimension measured in a first direction perpendicular to the operating axis;
• providing a detector on the other side of the collimator relative to the source package, the collimator and detector positions defining an operating axis for the instrument;
• and
• moving the position of the source package relative to the collimator substantially along a direction, the direction lying perpendicular to the operating axis and to the direction of the first dimension, the response of the detector being measured for two or more of those different positions of the source package;
• the source package comprising one or more individual gamma emitting sources provided in a container, in use the individual source(s) having a maximum extent in the first direction, the maximum extent, during at least 10 seconds of use, being two or more times the first dimension of the aperture in that first direction, such that unquantifiable movement of the source along the direction of the first dimension does not affect the emissions of the source package measured by the detector.