Radiant energy – Invisible radiant energy responsive electric signalling – Including a radiant energy responsive gas discharge device
Reexamination Certificate
1999-05-07
2001-12-04
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Including a radiant energy responsive gas discharge device
C250S370010, C250S374000
Reexamination Certificate
active
06326626
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention concerns, improvements in and relating to alpha and/or beta particle detection in small spaces, particularly but not exclusively through the detection of Ions produced by the passage of alpha and/or beta particles through a medium such as air.
2. Present State of the Art
Direct detection of alpha particles emitted into air is only possible if the detector is presented very close to the source. Alpha particles decay over a range of 4 to 5 cm and as a consequence are not directly detectable beyond that range.
Techniques have been developed in which the ions generated by the passage of the alpha particles over this range are detected at a remote location so as to give an indication of the level of contamination present. These techniques rely upon as much of the ions generated as possible being detected as the number of ions, and hence signal currents involved, are very small.
In many applications, the effective path of the alpha particles from the source is shortened by a collision between the alpha particle and an opposing surface. Such occasions occur in narrow diameter pipes, for instance, as well as in confined locations on the surfaces of pieces of apparatus, such as heat exchange surfaces on motors and the like, as well as elsewhere. The effective path of the alpha particles in such situations is so short that very few ions are actually generated before the alpha particle loses its energy through collision with further surfaces. Existing techniques for detecting these ions face problems in such circumstances due to the small number of ions generated.
Due to their high energies the length of the path over which beta particles decay in media such as air is far longer. As a consequence even in relatively large sized pipes and the like relatively few ions are generated through unit of path length and the effective path is shortened by a collision between the beta particle and opposing surface. As a consequence of the low number of ions generated beta particle monitoring using ions detection has not been pursued.
BRIEF SUMMARY AND OBJECTS OF THE INVENTION
The present invention aims to provide a method and apparatus whereby the number of ions generated is substantially increased for shorter path lengths. As a consequence of the increased number of ions generated, successful detection in more confined and smaller spaces can be implemented.
According to a first aspect of the invention we provide a system for monitoring alpha and/or beta emitting sources on an item or location, the item or location being in contact with a medium, alpha and/or beta emissions generating ions in the medium, the system comprising an instrument having a detecting chamber, the detecting chamber being provided with one or more electrodes for discharging and/or collecting ions, the instrument further being provided with means to monitor ions discharged on the electrode(s), the system being provided with means for moving the medium from in proximity to with the item or location to the detecting chamber, the system being provided with means for increasing the pressure of the fluid above atmospheric pressure.
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.
Preferably the item is mounted or supported so as to maximise the surface area exposed, for instance to the airflow.
The item or location may be introduced within the detecting chamber.
The item or location may be monitored in-situ. The item or location may be connected to the detecting chamber by fluid conveying means, such as a pipe or conduit. The conveying means may be temporarily connected to the item or location. The conveying means may be provided as a part of the instrument. The conveying means, item or location and detecting chamber may define a closed circuit.
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 may comprise an elongate chamber. The detecting chamber may have a circular or rectilinear cross-section. The detecting chamber may be provided with an inlet and an outlet, the electrodes being provided between the inlet and the outlet. The inlet and/or outlet may connect to the surrounding environment for the instrument, for instance to give an open circuit instrument. The inlet and/or outlet may connect the instrument to the item or location, for instance through intermediate medium conveying means, for instance to give a closed circuit.
Preferably means are provided within the system to remove extraneous ions and/or particulate matter. The ions and/or particles may be removed by a filter. The filter may be provided downstream of the electrodes. The filter may, for instance be provided at the end of the fluid conveying means leading to the item or location. A filter is preferably provided in this way in a sealed system. The filter may be provided between the inlet from the surrounding environment and the detecting chamber. The filter may be provided between the detecting chamber and the outlet to the surrounding environment.
The detecting chamber may be openable to introduce or remove an item or location, for instance for an open circuit. The detecting chamber may comprise a sealable chamber, for instance for a closed circuit. The seal may be broken to make the chamber accessible to introduce and/or remove an item to be monitored.
Preferably the item or location is positioned upstream in the fluid flow relative to the electrodes, where fluid flow is used to move the ions.
The instrument may be provided with a single electrode. The instrument may be provided with a charged element or plate, such as an electret.
Preferably the apparatus comprises a plurality of electrodes, the electrodes being spaced from one another. The electrodes may be configured with a first outer electrode and a second outer electrode and none or one or more intermediate electrodes provided there between.
The electrodes are preferably arranged parallel to the direction of airflow. Preferably the airflow passes through the spacing between the electrodes.
One or more, and preferably all, of the electrodes may be planar. Preferably the electrodes are provided parallel to one another. Preferably the electrodes are provided in opposition, for instance, an outer electrode being opposed by one electrode, an intermediate electrode being opposed by two electrodes. The spacing between the electrodes is preferably the same between each pair of opposing electrodes. The spacing between the outer electrodes and the detector chamber is preferably the same as between opposing electrodes.
The electrodes may be continuous, such as a plate, or discontinuous, such as a grid.
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 charged plate or element, such as from an electret.
Potentials of between 10V and 1000V may be provided.
The means for monitoring ions discharged 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 all the 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.
The means for moving the fluid may be a fan. Preferably the electrodes are provided between the fluid moving means and the item or location. The fan may be of controllable, and preferably of variable,
Dockray Thomas
Luff Craig Janson
Macarthur Duncan Whittemore
Orr Christopher Henry
British Nuclear Fuels PLC
Gabor Otilia
Hannaher Constantine
Workman & Nydegger & Seeley
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