CA1134070A - Self-powered radiation detector with stranded wire emitter - Google Patents

Abstract

7 45,874 ABSTRACT OF THE DISCLOSURE
An improved flexible self-powered radiation detector wherein the elongated central conductive emitter is formed of a plurality of small diameter stranded wires of the desired emitter material to improve the flexibility of the detector. Insulating means is provided about the stranded emitter, and a thin conductive sheath is provided about the insulating means.

Description

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5,874 ~-SELF-POWERED RAD~A~ION DETECTOR
WITH STRANDED WIRE EMITTER
BACKGROUND OF THE INVENTIO~
The present invention relates to nuclear radia-tion detectors, and more particularly to self-powered ; detectors. An exemplary self-powered de-tector is seen in U.S. 3,872,311. Such devices are termed self-powered in -that a si.gnal is generated by action of incident neutrons passing through an outer conductive collector sheath, through insulating means, to a central conductive emitter.
No applied potential is required for such devices, unlike ionization chamber detectors or the like. A signal is generated be-tween -the emitter and collec-tor electrodes and sensed externally as a func-tion of the differing neutron interactions between the emitter and collector electrodes.
~` Self-powered detectors have been particularly suggested for in-core neutron flux level monitoring. This means the detector must be insertable into a nuclear reactor core, where it typically remains in place, or may be movable to sense the neutron flux at various positions in the core. The detector must be connected via instru-mentation cable to the monitoring station. The self-powered detector must be insertable into the reactor .
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2 L~5, 87~1 vessel within which the core is disposed through instrumen-tating tubing or -thimbles which are sealed through the reactor vessel. The detector has to be inserted or moved through several feet of such tubing which may have several bends in the tubing because of where it is inserted in the reactor vessel, and because of the sealed containment aspect of the vessel.
The typical self-powered detector may have an outside diameter of Erom abou-t 0.080 to 0.150 inch. The cen-tral emit-ter is typically about 0.010 to 0.080 inch in diameter. The emitter wire is typically one of the metals platinum, rhodium, vanadium, cobalt, cerium, osmium or tantalum. These metals are primari~y selected for their neutron interaction properties, bu-t mos~ of the metals which have been used have high tensile strength and hard-ness. An insula-tion means is provided about -the center emitter, and is typically compacted aluminum oxide or magnesium oxide which is about 0.010 to 0.0~0 inch thick.
An outer conductive tubular co:Llector sheath is disposed about the insulation means, and is typically ~nconel steel with a thickness of about 0.025 inch. Inconel is a trade-marked nickel-steel of the International Nickel Co.
The relative diameter of the center emitter and the relative strength and hardness of the emitter material make it difficul-t to flex the detector during insertion and movement of the detector in the instrumenta-tion tubing Any flexing that takes place during insertion may result in breakage or fracture of the emitter portion which could mean electrical discontinuity and failure of the device.

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3 l~5~87 The radiation sensitivity of the detector is a function o the materials used and the relative dimensions of the respecti~e emit-ter and collector. For a given emitter metal the sensitivity of the de-tector increases with increasing emitter diame-ter. Thus, ~or most applica-tions the emitter diameter must be kept large enough to provide the requisite sensitivity, bu-t for a solid rod-like emitter this will limit -the fle~ibility of the assem-bly and make -the emitter subjec-t to breaking when the assembly is flexed during insertion into the reactor. It is therefore desirable to maintain a large emitter dia-meter without making the detector assembly so rigid tha-t insertion through the bent path lead-in tubing is dif:Ei-cult or causes breakage and electrical discontinuity in the emitter cable.
SUMMARY OF THE INVENTION
An improved fle~ible self-powered radiation de-tector is provided by forming t:he emitter of a plurality of small diameter stranded wires of the desired emitter material. The individual wires of the stranded emitter are preferably less than about 0.005 inch in diameter.
The emitter wires are stranded or helically wrapped about a core wire or in a coreless configuration.
BRIEF DESCRIPTION OF THE DRAWINrlS
Figure 1 is a side elevational view in section of ~he self-powered radiation detector of the present invention.
Figure 2 is a section view taken along lines II-II of Figure 1.

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~ 5,874 Figure 3 is a sectional view taken through an alternate embodiment wherein the emitter is formed of a plurality of stranded wires wi-th a single larger core wire and a plurality of smaller diameter wires wound about this core.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The self-powered radiation de-tector 10 of the present invention is seen in detail in Figures 1 and 2 The detect~r 10 comprises an elongated central conductive emitter 12, insulating means 14 about the emitter 12, and a thin generally tubular conductive collector 16 about the insulating means 14.
The emitter 12 is formed of a plurality of stranded, spirally wound, small diameter wires 18 of the selected emitter metal. The individual wires 18 which form the emitter preferably have a diameter of less than about 0.005 inch when the wires 18 are of -the same size, with the overall stranded emitter being from abo-ut 0.020 to 0.080 inch in diameter. The emitter metal is prefera-bly selected from one of the metals platinum, rhodium,vanadium, cobalt, cerium, osmium and tantalum.
The insulating means 14 is -typically compacted finely divided aluminum oxide or magnesium oxlde which is about 0.010 to 0.040 inch thick. The thin collector sheath 16 is typically Inconel steel and is about 0.025 inch thick. I'he overall outside diameter of the detector 10 is from about 0.080 inch to 0.150 inch.
The use of the rela-tively small diameter wires 18 and stranding them to form the emitter permits the 3~7'~

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detector to be relatively Elexib:Le. S-ince the collector sheath is re:latively thin and tubular it has some inheren-t flexibility, and the stranded wire emitter is not as rigid as a larger diame-ter solid rod-like emit-ter.
In another embodimen-t of -the invention seen in cross-section in Figure 3, the emi-tter 22 of the detector 20 comprises a cen-ter core wire 24 with a plurality of smaller diame-ter wires 26 spirally wound or stranded about the center wire. The center wire and plurality of smaller o wires about the center wire are formed of the same emit-ter metal and are in intimate electrical contact. By way of example, the center wire would have a diame-ter of 0.020 inch, and the outer wires have a diameter of 0.005, so that the overall emitter diameter is 0.030 inch. A var-iety of other plural wire configurations can be used in forming the emitter with the desired flexibility and sensitivity. The insulating means 28 is disposed about the emitter 22 and insulates it from the conductive outer collector electrode 30.

Claims (4)

6 45,874 What is claimed is:

1. An improved self-powered radiation detector of the type comprising a neutron absorptive elongated central conductive emitter, insulating means about the emitter, and a thin conductive collector coaxially spaced about the emitter and the insulating means, the improve-ment wherein the emitter is formed of a plurality of stranded wires of the desired conductive emitter material whereby the detector is made relatively flexible.

2. The self-powered radiation detector set forth in claim 1, wherein the stranded emitter wires are of equal diameter and each has a diameter of less than about 0.005 inch per wire.

3. The self-powered radiation detector set forth in claim 1, wherein the emitter wire material is selected from one of platinum, rhodium, vanadium, cobalt, cerium, osmium, and tantalum.

4. The self-powered radiation detector set forth in claim 1, wherein the emitter comprises a center core wire with a plurality of wires stranded about the center core wire.