Radiant energy – Invisible radiant energy responsive electric signalling – Methods
Reexamination Certificate
2002-03-27
2004-10-19
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Methods
C250S363040
Reexamination Certificate
active
06806475
ABSTRACT:
This invention concerns improvements in and relating to methods and apparatus for investigating emissions, particularly, but not exclusively in relation to gamma emissions.
During a number of tasks involving radioactive materials it is desirable to be able to accurately determine the position and level of radioactive materials within an environment. The environment may be a room or vessel in which operations involving radioactive material have been conducted and/or situations where decommissioning is required. To enable efficient decommissioning and/or to ensure man access under appropriate conditions to such environments accurate level and positional information is needed.
It is known to use a collimated gamma detector of the type referred to in EP 0542561 or WO 98/52071 to investigate gamma contamination. To achieve information about the sources of radiation the detector is collimated to give a conical field of view, with apex angle of less than 10°. This necessitates a significant length for the collimator. Furthermore, as the counts arising from the field of view must be very much higher than those penetrating the collimator from other directions to ensure meaningful measurements, the collimator must present a substantial thickness of material, 50 mm or more, around the detector. As a consequence the collimator alone has a substantial mass, 40 kg. The physical dimensions and properties necessary to achieve successful operation thus impair or prohibit the use of such instruments in locations for which access is limited, by the size of available entrance apertures for instance. Specific new entries to such locations are thus needed in such prior art systems or limited information on the radioactive materials must be tolerated.
The present invention has amongst its aims to provide an instrument which is capable of introduction into environments for which access is awkward or impaired. The present invention has amongst its aims to provide accurate and detailed information. The present invention has amongst its aims to operate and be capable of achieving such results in a practical time period.
According to a first aspect of the invention we provide a method of investigating emissions from radioactive sources in an environment, the method comprising:
providing an instrument, the instrument having a detector assembly, the detector assembly including a detector, preferably a single detector, which generates a signal in response to a detected emission, the detector being provided with a greater level of shielding against emissions in one or more directions than in one or more other directions to define the field of view of the environment for the detector, and a moveable shielding component which is moveable relative to the field of view;
introducing the detector assembly of the instrument into the environment;
obtaining a signal count and/or count rate from the detector with at least a part of the environment with the field of view, the moveable shield being out of the field of view, the result forming the reference count and/or reference count rate for that given field of view;
obtaining a signal count and/or count rate from the detector for the given field of view, with a part of the given field of view occluded by the moveable shielding component, the result forming the partially occluded view's count and/or count rate for that given field of view with that given part occluded;
for a given occluded part of a given field of view, the reference count and partially occluded view count and/or reference count rate and partially occluded view count rate being considered against one another to provide information about the emissions arising from the given field of view.
The first aspect of the invention may include any of the features, options or possibilities set out elsewhere in this document including the second aspect of the invention.
The first aspect of the invention may particularly include obtaining a signal count and/or count rate from the detector with at least part of the environment within the field of view, the moveable shielding component being out of the field of view; moving at least part of the detector assembly to place at least another part of the environment within the field of view and obtaining a signal count and/or count rate from the detector for that field of view, the moveable shielding component being out of that field of view; considering the counts and/or count rates obtained from the two or more different fields of view and selecting one or more areas of the environment for further investigation; the reference count and/or reference count rate being obtained for at least part of a selected area of the environment.
According to a second aspect of the invention we provide a method of investigating emissions from radioactive sources in an environment, the method comprising:
providing an instrument, the instrument having a detector assembly, the detector assembly including a detector which generates a signal in response to a detected emission, the detector being provided with a greater level of shielding against emissions in one or more directions than in one or more other directions to define the field of view of the environment for the detector, and a moveable shielding component which is moveable relative to the field of view;
introducing at least the detector assembly of the instrument into the environment;
obtaining a signal count and/or count rate from the detector with at least part of the environment within the field of view, the moveable shielding component being out of the field of view;
moving at least part of the detector assembly to place at least another part of the environment within the field of view and obtaining a signal count and/or count rate from the detector for that field of view, the moveable shielding component being out of that field of view;
considering the counts and/or count rates obtained for the two or more different fields of view and selecting one or more areas of the environment for further investigation;
obtaining a signal count and/or count rate from the detector with at least a part of a selected area of the environment within the field of view, the moveable shield being out of the given field of view, the result forming the reference count and/or reference count rate for that given field of view;
obtaining a signal count and/or count rate from the detector for the given field of view, with a part of the given field of view occluded by the moveable shielding component, the result forming the partially occluded view count and/or count rate for that given field of view with that given part occluded;
for a given field of view and a given part occluded, the reference count and partially occluded view count and/or reference count rate and partially occluded view count rate being considered against one another to provide information about the emissions arising from the given field of view.
The first and/or other aspects of the invention may include any of the features, options or possibilities set out elsewhere in this document, and in particular in the following statements.
Preferably the method of investigating emissions is a method for determining the position of one or more radioactive sources in an environment which generate emissions and/or a method for determining the level of emissions arising from one or more radioactive sources in an environment. The method may achieve one or both of these measurements for at least part of a field of view, preferably all, with the detector in a fixed position relative to the environment during the measurement. The method may achieve one or both of these measurements by using a single field of view for the instrument. The method may achieve one or both of these measurements by occluding a non-converging, preferably diverging part of the field of view. The method may achieve one or both of these measurements by occluding a single part of the field of view of the instrument for each partially occluded view count and/or count rate obtained.
The emissions may be alpha and/or beta and
Hughes Karl Anthony
Lightfoot John Adrian
Beyer Weaver & Thomas LLP
British Nuclear Fuels PLC
Gabor Otilia
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