Radiant energy – Invisible radiant energy responsive electric signalling – Including a radiant energy responsive gas discharge device
Reexamination Certificate
2002-06-04
2003-11-18
Porta, David (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Including a radiant energy responsive gas discharge device
C250S326000
Reexamination Certificate
active
06649916
ABSTRACT:
BACKGROUND OF THE INVENTION
1. The Field of the Invention
This invention is concerned with improvements in and relating to ion detectors and particularly, but not exclusively to detectors in which the detector moves relative to the ion source. Relative movement may arise due to movement of the detector and/or due to movement of the ion source, for instance due to passage of the item carrying the source through the detector.
2. The Relevant Technology
The monitoring of alpha emissions from an item or location is of particular significance during decommissioning, material accounting and a variety of other applications.
The long range detection of alpha emissions, indirectly, through the monitoring of air ions generated by the passage of alpha particles is known. The item believed to be carrying the alpha sources is placed in a container, the container completely enclosing the item so as to exclude ambient ions. The ions generated by alpha particles are attracted to electrode(s) in the detector system and a current arises as a result.
The very small size of this current makes it prone to interference from noise currents arising due to other variables in the system. Movement of the detector electrode relative to the source of the alpha particles causes significant changes in the system capacitance and significant noise currents as a result.
BRIEF SUMMARY OF THE INVENTION
The present invention aims to provide a detector system which is far less prone to noise interference, even where the detector is actively moved relative to the source, for instance when mounted on a vehicular survey system or, for instance, when an elongate item is moved through the detector during monitoring.
According to a first aspect of the invention we provide an instrument for detecting ions originating from a monitored location, the instrument having a body portion and one or more electrodes at an electrical potential relative to the monitored location, and one or more electrically conducting element(s) provided with one or more apertures, the element(s) being provided between the electrode(s) and the monitored location and further comprising means to monitor ions discharged on the electrode(s).
The element(s) are preferably provided with a large number of apertures, for instance greater than 80% of their effective area as apertures. The element may be in the form of a grid. A single metal element is preferred.
The element(s) may be planar. A single continuous element or a plurality of elements may be provided.
The element may be at a different potential to the location, including item, being monitored. The element may be earthed. The element may have an applied potential or an electrostatic potential.
The element may be provided across the full extent of the electrode(s), or at least a substantial part thereof. Preferably the configuration of the element mirrors that of the electrode(s), for instance a planar electrode may be provided together with a planar element or grid.
The element may be provided at a significant separation from the location/item to be monitor, for instance greater than 5 cm, greater than 10 cm and even greater than 20 cm.
Equally the element may be provided in proximity to the location/item to be monitored, for instance less than 5 cm and more preferably less than 1 cm from the closest surface of the item.
The instrument may be provided with a plurality of detection electrodes. The electrode(s) may be provided close to or away from the element. A continuous detector electrode may be used, such as a plate. A discontinuous detector may be used, such as an apertured plate or grid.
Preferably an electrical potential is applied to the electrode(s). An electrical potential may be provided electrostatically. The potential is preferably higher than that applied to the element. The potential of the element may be lower than that of the electrode(s), but higher than that of the location/item. The location/item and element may both be grounded.
The ions may be attracted to the electrode(s) electrostatically by the electric field. Alternatively or additionally air flow within the instrument from the location were ions are generated into proximity with the electrode(s) may be promoted. A fan may be used to promote the movement of ions to the electrode(s).
The electrode(s) may be provided within a continuous enclosure with a closeable opening for introducing the item to be monitored. A support may be provided within the enclosure for the item so as to maximize the surface area in contact with air. Preferably means to promote air flow around the item are provided. Preferably the air flow circulates within the sealed enclosure.
The electrode(s) may be provided within an enclosure which is open to its surroundings on at least a portion of one side. The enclosure may be in the form of a hood with an open side. Such an enclosure is suited to monitoring large areas or surfaces, such as floors and walls. The perimeter of the opening may be provided with a laterally extending flange. The lateral extent of the flange is preferably greater than the gap between the flange and surface. An extent at least 5 times and more preferably 10 times is provided. Preferably the flange is provided around the opening. Preferably a planar flange, opposing the surface to be monitored is provided.
The location to be monitored may be a surface, such as a wall, ceiling or floor, including these of a building, room or vessel; or a surface of a piece of equipment, such as a glove box, tank or vessel. Monitoring of open ground, rubble and soil is possible. The location to be monitored may be material passing the detector on a conveyor system.
The item to be monitored may be a piece of equipment, or a part thereof, such as a pump, pipe, beam, glove box, tool, filter, cable, rod or the like.
The item/location may be placed within the instrument and/or placed against and/or in proximity to the instrument.
Preferably the item/location is electrically grounded.
The item/location may be moved relative to the instrument, for instance a beam on a roller bed or soil on a conveyor belt and/or the instrument may be moved relative to the location/item, for instance a vehicularized instrument moved across a stretch of ground.
The means for monitoring ion discharge preferably comprises current monitoring, and more preferably current measuring means. The means for monitoring ion discharge may comprise means for monitoring the remaining electrostatic potential, such as surface charge monitors.
The current monitoring means is preferably an electrometer, most preferably the electrometer is provided as a floating input electrometer. The electrometer may be provided as a ground referenced electrometer.
An additional detector may be provided in the instrument to detect background ion levels. The additional detector may comprise an electrode and an apertured element. Preferably the additional detector electrode is separated from the electrode by a guard plate.
Preferably an equivalent potential is applied to the electrode and the background electrode. Preferably an equivalent potential is present for the element and the background element.
The ions may originate from the location directly or indirectly. Preferably the ions are generated by alpha particles, most preferably alpha particles emitted from material on or at the location being monitored.
According to a second aspect of the invention we provide a method of detecting ions originating from a monitored location, the method comprising providing one or more electrode(s) at an electrical potential relative to the location so as to attract at least some of the ions to the electrode, and additionally providing one or more electrically conducting element(s) with one or more apertures therein to allow the passage of ions, between the electrode(s) and the monitored location, the discharge of ions on the electrode(s) being monitored.
Other features, options, possibilities and details provided in the first aspect of the invention and/or elsewhere in this document are included in the possibilities for t
Dockray Thomas
Luff Craig Janson
Macarthur Duncan Whittemore
Orr Christopher Henry
British Nuclear Fuels PLC
Porta David
Sung Christine
Workman Nydegger
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