Radiant energy – Invisible radiant energy responsive electric signalling – Including a radiant energy responsive gas discharge device
Reexamination Certificate
1999-05-07
2001-12-18
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Including a radiant energy responsive gas discharge device
C250S380000, C250S394000, C250S376000
Reexamination Certificate
active
06331707
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention concerns improvements in and relating to item monitoring, particularly but not exclusively to the monitoring of alpha contamination on large items.
2. Present State of the Art
Direct monitoring of the alpha contamination is only possible using detectors presented very close to the actual source of the alpha particles due to their limited range. Techniques have been developed whereby the ions generated by the passage of alpha particles through air can be detected at long range so as to evaluate the alpha contamination present.
Systems using the principal of long range alpha detection have been developed whereby air is drawn through a filter into a chamber, passes the item under investigation, passes on to a detection unit and subsequently exits the apparatus through an outlet filter. Such systems are relatively complicated as filtration of the feed air is necessary to avoid the introduction of ions from the ambient environment into the chamber and filtration of the outlet flow is necessary to avoid contamination being spread from the item into the environment.
BRIEF SUMMARY AND OBJECTS OF THE INVENTION
The present invention aims to provide a simpler, more cost effective method for monitoring items for alpha contamination, amongst other forms, without the need for an inflow and outflow of air.
According to a first aspect of the invention we provide an instrument for monitoring alpha and/or beta emitting sources on an item/location, the item/location being in contact with a medium, alpha and/or beta emissions generating ions in the medium, the instrument having a detecting chamber, the detecting chamber being provided with one or more electrodes in contact with the medium for discharging and/or collecting ions, a potential being applied to the electrode(s) to electrostatically attract ions thereto, the instrument further being provided with means to monitor ions discharged on one or more of the electrode(s), the detecting chamber comprising a sealable chamber.
The item(s) to be monitored may be or include tools, pipes, pumps, filters, cables, beams, rods and the like. The locations may include surfaces in general, such as floors, walls, ceilings, soil, rubble, material on a conveyor, and include parts of, or surfaces of items, such as glove boxes, tanks, vessels and the like.
The item or location may be introduced to within the detecting chamber. The detecting chamber may be introduced to around the item or location. The item or location may be monitored in-situ, for instance still mounted on a floor Alpha impermeable and/or beta impermeable and preferably gamma impermeable shielding may be provided to cover non-desired items or non-desired locations within the detecting chamber.
The item may be suspended within the detector chamber, for instance by hanging. The item may be mounted on a support, such as a grid, to maximize the surface area of the item exposed for detection.
The medium may be a fluid, such as a liquid, but is preferably a gas. The gas may be a mixture, such as air, or may be in substantially single gas form, such as argon.
The detecting chamber is preferably electrically conducting. The detecting chamber may comprise an elongate chamber. The detecting chamber may have a circular or rectilinear cross-section. The detecting chamber may be openable to introduce or remove an item or location. Preferably the chamber is completely sealed relative to its environment in use.
The instrument may be provided with a single electrode. Preferably the electrode extends over a substantial part of at least one wall of the chamber. The instrument may be provided with a charge element or disc, such as an electret. One or more, and preferably all, of the electrodes may be planar. The electrodes may be continuous, such as a plate, or discontinuous, such as a grid. A grid, preferably spaced from the adjoining wall of the chamber is preferred.
An applied, preferably externally generated, potential may be employed. The electrical potential is preferably provided by an external power source. An electrostatic potential may be employed, for instance from a charge element or disc, such as from an electret.
Potentials of between 10V and 1000V may be provided.
The means for monitoring ions discharged and/or collected on the electrode(s) may comprise electrostatic charge monitoring means. More preferably the means for monitoring ions discharged on the electrode(s) comprise current indicating means and more preferably current measuring means. Preferably a single current measuring means is used. Preferably the combined current of a plurality of the electrodes, such as alternate electrodes connected to the current measuring means is measured. An electrometer, such as a ground referenced electrometer or floating electrometer may be used for this purpose.
Means, such as a fan, may be provided for moving the fluid within the chamber. The fluid is preferably moved to promote even distribution of the ions within the chamber. The speed and/or position of the fan may be variable and/or controllable.
The detecting chamber may be provided at an elevated pressure relative to atmospheric.
According to a second aspect of the invention we provide a method for monitoring alpha and/or beta emitting sources on an item/location, the method comprising providing the item/location in a detecting chamber, contacting the item/location with a medium, alpha and/or beta emissions generating ions in the medium, the detecting chamber being provided with one or more electrodes for discharging ions, the electrode(s) contacting the medium, applying an electrical potential to one or more of the electrodes to electrostatically attract ions thereto, the method further comprising monitoring ions discharged on the electrode(s), the item/location being sealed within the detector chamber.
The method may include the passage of a period of time, after the item/location is provided, and after the chamber is sealed, before the electrical potential is applied. The delay may be provided to enable an equilibrium level of ions within the chamber to be reached.
The method may include promoting the mixing of the medium within the chamber. The mixing of the medium may be promoted by a fan and/or the internal configuration of the chamber, for instance through baffles.
The second aspect of the invention includes the features, options and possibilities set out elsewhere in this application, including the steps necessary to implement them.
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Dockray Thomas
Luff Craig Janson
Macarthur Duncan Whittemore
Orr Christopher Henry
British Nuclear Fuels PLC
Hannaher Constantine
Israel Andrew
Workman & Nydegger & Seeley
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