Radiation detector and method

Disclosed is a radiation detector, comprising a chamber or cavity that produces charge carriers when radiation is incident thereon. The chamber is defined in part by a deformable plate along one side of the chamber or cavity; and a rigid plate spaced and electrically insulated from the deformable plate. A charging voltage source is present for applying a voltage to the deformable plate; such that wherein the deformable plate is attracted toward the rigid plate by electrostatic forces when charged by the charging voltage source, and moves away from the rigid plate when charge carriers produced in the chamber or cavity by incident radiation reduce the electrostatic forces between the deformable and rigid plates.

BACKGROUND

The present technology pertains generally to radiation detectors, and more particularly to self indicating or direct reading radiation detectors, and most particularly to radiation detectors with a direct optical visual readout.

2. Description of Related Art

There is a need to monitor exposure to radiation in a variety of work environments, from nuclear reactors to hospitals and other medical facilities. In today's world, there is also the danger of terrorist threats using nuclear material, so military personnel and first responders need to be able to monitor their environments for these materials.

A wide variety of radiation detectors are available. Some are complex and permanently installed in a facility such as a nuclear reactor. Others, such as personal dosimeters, are worn by individuals. Ideally a personal dosimeter will give an immediate indication of the presence of radiation.

Self indicating or direct reading personal dosimeters include electronic personal dosimeters (EPD), quartz fiber dosimeters (QFD), and radiochromic dosimeters (RCD). However, these types of dosimeters have a number of drawbacks. Electronic dosimeters are expensive and require a battery to operate. Quartz fiber dosimeters are difficult to read and have a limited measuring range. Radiochromic dosimeters are not capable of measuring low doses of radiation and are sensitive to ambient UV radiation, temperature, and humidity, and cannot be reused.

Accordingly it is desirable to provide an improved self indicating or direct reading radiation detector and method.

BRIEF SUMMARY

This writing pertains to a radiation detector with a deformable cavity or chamber. More specifically, an aspect of the present technology is a radiation detector, including a conductive plate having a semireflective surface; a conductive plate having a mirrored surface; one of the plates being flexible and the other being rigid; electrically insulating supports separating the flexible and rigid conducting plates, the plates and supports defining and enclosing a chamber therebetween; a switch; a charging voltage source connected across the plates by the switch; wherein the flexible plate is attracted toward the rigid plate by an electrostatic force produced between the plates when the charging voltage source is connected across the plates, and charge carriers produced in the chamber by incident radiation are attracted to the plates and change the electrostatic force between the plates so that the flexible plate moves relative to the rigid plate, and ambient light reflected from the flexible and rigid plates interferes and produces observable color changes as the flexible plate moves relative to the rigid plate.

Another aspect is a radiation detector, including a chamber or cavity that produces charge carriers when radiation is incident thereon; a deformable plate along one side of the chamber or cavity; a rigid plate spaced and electrically insulated from the deformable plate; a charging voltage source for applying a voltage to the deformable plate; wherein the deformable plate is attracted toward the rigid plate by electrostatic forces when charged by the charging voltage source, and moves away from the rigid plate when charge carriers produced in the chamber or cavity by incident radiation reduce the electrostatic forces between the deformable and rigid plates.

A further aspect is a method of detecting radiation, by providing a chamber or cavity that produces charge carriers when radiation is incident thereon; providing a deformable plate along one side of the chamber or cavity; providing a rigid plate spaced and electrically insulated from the deformable plate; applying a voltage to the deformable plate; wherein the deformable plate is attracted toward the rigid plate by electrostatic forces when charged by the applied voltage, and moves away from the rigid plate when charge carriers produced in the chamber or cavity by incident radiation reduce the electrostatic forces between the deformable and rigid plates.

DETAILED DESCRIPTION

Referring more specifically to the drawings, for illustrative purposes the present technology is embodied in the apparatus generally shown inFIG. 1throughFIG. 6. It will be appreciated that the apparatus may vary as to configuration and as to details of the parts, and the method may vary as to specific sequence of steps, without departing from the basic concepts as disclosed herein.

The technology is an apparatus and method for detecting radiation in which a microelectromechanical structure (MEMS) is used to provide the readout. In one embodiment the radiation detector is configured as an interferometric modulator in which visually observed change in color indicates exposure. In a basic embodiment, the structure has two electrically conductive plates electrically insulated and separated from each other by a micromechanical spring, and the space between the plates is filled with gas. The plates are charged to different electric potentials, creating an electrostatic force between the plates, which pulls one plate closer to the other. Ionizing radiation interacts with the gas, producing electric charges, which change the electric potential on the plates, which causes a change in the electrostatic force and the distance between the plates. This change in distance between the plates can be detected optically as a result of interferometric effects. An incident light beam on the two plates is reflected and constructively or destructively interferes, depending on the plate separation. This constructive or destructive interference results in an easily observable change in color of the reflected light. To detect nonionizing radiation, a photoemitter material is placed on one of the plates. In an alternate embodiment, the two plate structure is adjacent a much larger cavity in which the radiation produces charge carriers. Again, the charge carriers produced by the radiation, either by interacting with a gas or with a photoemissive material, change the charge on the plates, thereby changing the plate separation, and allowing a visual or other readout.

FIG. 1shows an interferometric modulator radiation detector10of the invention. The detector10is based on a microelectromechanical structure12formed of two spaced conductive plates14,16separated by electrically insulating supports18. The plates14,16and supports18define and enclose a chamber or cavity20which is filled with a gas22. Top plate14is a flexible conductive plate with a semireflective surface. Bottom plate16is a rigid conductive plate with a mirrored surface. An incident light beam24will be partly reflected from plate14as beam26and partly transmitted therethrough to plate16where it will be reflected as beam28. Beam28may be produced by multiple reflections from plate16as shown (by back reflections from the bottom of plate14), depending on the size of structure12and the angle of incidence of beam24. Beams26and28may constructively or destructively interfere, depending on the spacing between plates14,16. Incident light beam24is just ambient light, e.g. sunlight or interior lighting. Structure12is basically a Fabry-Perot interferometer or etalon where light beams reflected from two surfaces interfere. Top plate14may be formed of or include an optical thin film stack on its bottom surface to optically enhance the properties of the interferometer, e.g. by controlling reflectivity of particular wavelengths.

As shown inFIG. 1, a charging voltage source30is connected across plates14,16through a micromechanical or other switch32. Switch32is controlled by a switch control voltage source34. As shown inFIG. 1, switch32is open, so no voltage is applied to plates14,16. Thus structure12is in a first or open state.

FIG. 2shows the radiation detector10of the invention with switch32closed by applying a voltage from switch control voltage source34. Switch control voltage source34applies a sequence of very short pulses to switch32so that switch32is closed for only a short time, and then opens. The voltage from charging voltage source30has now been applied across the plates14,16, creating an electrostatic force between the plates14,16. Since plate14is flexible, it is pulled down toward plate16, thereby changing the distance between plates14,16. Since the path length between the reflected beams26,28from plates14,16respectively has changed, the interference effects have also changed, which can be observed directly as a change in the color of the reflected light. The electrostatic force pulls plate14against the spring force provided by the flexible material, to a position where the forces are balanced. Structure12is now in a second or closed state. WhileFIGS. 1-2show partly reflective top plate14as flexible and reflective bottom plate16as rigid, the partly reflective top plate14may be rigid and the reflective bottom plate16may be flexible, as shown inFIG. 3A. InFIG. 3AMEMS structure12is shown in the second or closed state with bottom plate16attracted towards top plate14; the first or open state of plate16is shown by the dashed lines.

As also shown inFIG. 2, incident radiation36interacts with the gas22in chamber20and produces charge carriers38which are attracted to the plates14,16. The resultant change in charge on plates14,16changes the electrostatic force between plates14,16, allowing plate14to move to a different position, e.g. back from the second or closed state to the first or open state. This again changes the spacing between the plates so the interference effects change. The resultant color change is an indicator of the presence of radiation. The next voltage source pulse then fully charges the plates again so they return back to the second or closed state again, and the operation repeats as more radiation is incident thereon.

The basic structure12is similar in some respects to the interferometric modulator (imod) invented by Mark W. Miles, e.g. see U.S. Pat. Nos. 5,835,255; 6,040,937; and 7,995,265. The imods disclosed therein form pixels for electronic display devices, creating various colors by interference of reflected light by electronically addressing the individual imods and changing the voltages thereto to control the colors of each pixel to form the desired image.

Various gases, including air, at various pressures may be used in the detector10. However, as plate14is attracted to plate16, the chamber volume decreases and the gas pressure increases, increasing the spring force on plate14. To avoid this interference, structure12may be enclosed in a hermetic enclosure or housing40and plate14may contain perforations or small apertures42therein. The chamber20and enclosure40may then be filled with gas22and constant pressure in chamber20may be maintained as plate14moves closer or farther from plate16.

While a particular application of the detector of the invention is to detect harmful ionizing radiation such as x-rays, gamma rays, alpha particles and beta particles, the detector of the invention can be used to detect non-ionizing radiation from other parts of the electromagnetic spectrum and even to neutron detection. Ionizing radiation interacts directly with the gas in the cavity to directly produce charge carriers (or it may interact with detector materials to produce secondary electrons). If the radiation to be detected is non-ionizing, e.g. visible or UV light, then a thin layer44of a photoemitter material may be placed over plate16, as shown inFIG. 3B(or on plate14or supports18). Layer44is sufficiently thin that it does not change the reflective properties of plate16. When non-ionizing radiation is incident on layer44, layer44will emit photoelectrons that are then attracted to one of the plates and produce the desired effect. Similarly, to detect neutrons, layer44will be made of a neutron absorbing photoemissive material, e.g. a material containing boron or lithium such as plastic with boron nitride or polyethylene with lithium nitride. In this case, charged alpha particles will be produced. Thus the detector of the invention is broadly a radiation detector for all types of radiation, including non-ionizing radiation as well as ionizing radiation.

As described, one embodiment of the detector of the invention operates between two states, representing two positions of top plate14relative to bottom plate16. In another embodiment of the invention, different integrated doses of radiation produce different amounts of total charge, which create different changes in the original electrostatic forces that allow the plate14to be in a continuum of positions, with corresponding color changes that reflect the total integrated radiation dose.

FIG. 4shows an optional contact50positioned so that when plate14returns to its first or open state (represented by the dashed lines), contact50will contact plate14and recharge plate14, i.e. apply charging voltage from voltage source30. In this embodiment, switch control voltage source34initially closes switch32which remains closed so that charging voltage source30remains connected to contact50. As soon as the voltage from source30is applied to plate14, plate14is attracted toward plate16(i.e. to its closed position as shown), thereby breaking contact with contact50. When radiation3ocauses plate14to return to its original open position, plate14again makes contact with contact50, becoming charged again, and the detector operation repeats. Each time that plate14contacts contact50and a voltage is applied, the voltage pulse may be counted by a register51connected to contact50. Each detected pulse is the result of radiation having been detected, and the measured pulse rate is a measure of the radiation flux.

An array52of individual detectors54,56,58is shown inFIG. 5. While three are shown, any number may be used. In one embodiment, all the individual detectors in the array are the same and small in size. A plurality of identical, small, individual detectors have been combined into an array to produce a sufficiently large array that can be easily observed so that the color variation indicating exposure to radiation can be recognized. Individual detectors may be designed for particular types of radiation, or for different levels of radiation, so that a more complete picture of the radiation environment may be provided. Each detector will produce a color change when it is impinged on by the particular type of radiation or the particular radiation level for which it is designed. The properties of each individual detector can be adjusted to suit the detection requirements for the type and level of radiation by adjusting the size and the materials used in its construction. The array would then be made up of subarrays of individual detectors, i.e. each detector54,56,58may in turn be formed of a subarray similar to array52. Different subarrays would change color when certain types of radiation are encountered or as progressively higher doses or levels of radiation are encountered.

A larger detector60is shown inFIG. 6, where a large detection volume is provided by a chamber or cavity62formed between a bottom plate64and a first top plate66and the interferometer structure is formed between the first conductive top plate66having a mirrored top surface and a semireflective rigid second conductive top plate68. The first top plate66is electrically insulated from the conductive exterior housing70by insulators72and is supported by springs74. Plate66is charged to an electric potential by connecting a voltage source76via a switch78controlled by a switch control voltage source80. Following the initial charging step the first top plate66is attracted to the second top plate68due to the electrostatic force between the two surfaces that are in close proximity from each other. The electrostatic force between the first top plate66and the bottom plate64is insignificant due to the large distance between the plates66and64. Radiation produces charge carriers in the large chamber or cavity62, and these charge carriers change the charge on first top plate66. As the electrostatic force between the first and the second top plates66,68changes due to radiation causing a decrease in the potential of the first top plate66, the distance between the first and the second top plates66,68changes, which causes a color change in the reflected light through the interferometer formed between the first and the second top plates66,68.

While the interferometric detectors10ofFIGS. 1-2are small and suitable for personal dosimetry, detector60can be large and is suitable for applications such as inside nuclear reactors. In such a harsh environment, visual readout using ambient light may not be possible. Different readout techniques can be used. Electrical contact readout such as shown inFIG. 4may be used. Capacitive measurements could be used. A light source could be positioned to reflect a beam off the top surface of plate66to determine the position of plate66.

The technology includes a method for detecting radiation by positioning a chamber formed between two conductive plates electrically insulated from each other and containing a gas to receive ionizing radiation or containing a vacuum with one of the plates having a photoemissive surface to receive nonionizing radiation. The top plate is formed of a conductive material with a semireflective surface. The bottom plate is formed of a conductive material with a mirrored surface. The top plate is flexible and the bottom plate is rigid, or vice versa. A charging voltage is applied across the plates. The charging voltage creates an electrostatic force between the plates which operates against the spring force of the flexible plate to draw the flexible plate toward the rigid plate to a position where the forces balance. An incident light beam is directed at the plates so that it is partly reflected from the top plate and partly transmitted therethrough to the bottom plate where it will be reflected. Charge carriers produced by ionizing radiation or by photoemissive material for non-ionizing radiation are attracted to the plates and change the electrostatic force so that the gap spacing between the plates changes. The change in position of the plates results in interference effects in the reflected beam that changes the color of the reflected beam, which may be visually observed or otherwise detected.

This technology also includes a method of detecting radiation by providing a chamber or cavity between a bottom plate and a first top plate. The chamber or cavity contains a gas (to detect ionizing radiation) or a vacuum and a surface formed of photoemissive material (to detect non-ionizing radiation). An interferometric structure is formed between the first top plate and a spaced second top plate. The first top plate is formed of a flexible conductive material and has a reflective top surface and is electrically insulated from the bottom plate and the second top plate. The second top plate is formed of a rigid conductive material and has a semireflective surface. The chamber or cavity is positioned to receive incident radiation which produces charge carriers. The first top plate is charged by a charging voltage source, and is attracted to the second top plate by electrostatic forces. When charge carriers are formed in the chamber or cavity by incident radiation, the charge carriers are attracted to the first top plate and change the electrostatic force between the first and second top plates, resulting in a change in the distance between the first and second top plates. This change is measured by any suitable technique and indicates the presence of radiation.

The invention thus provides a radiation detector for a wide spectrum of radiation that has an immediate color change visual readout. The detector is small and rugged. Since it does not include any electronic parts, but is made of a mechanical structure with a mechanical switch (the power supplies can be remote and connected by cables), the detector can be placed in a high radiation environment.

All elements, parts and steps described herein are preferably included. It is to be understood that any of these elements, parts and steps may be replaced by other elements, parts and steps or deleted altogether as will be obvious to those skilled in the art.

In some depth, this writing presents the following. An apparatus and method for detecting radiation provides a visually observed change in color indicating exposure. The detector is based on an interferometric modulator in which a microelectromechanical structure (MEMS) is used to detect the radiation. In a basic embodiment, the structure has two electrically conductive plates electrically insulated and separated from each other by a micromechanical spring, and the space between the plates is filled with gas or contains a photoemissive surface. The plates are charged to different electric potentials, creating an electrostatic force between the plates, which pulls one plate closer to the other. The radiation interacts with the gas or photoemissive surface, producing electric charges, which change the electric potential on the plates, which causes a change in the electrostatic force and the distance between the plates. This change in distance between the plates can be detected optically as a result of interferometric effects. Ambient light incident on the two plates is reflected and constructively or destructively interferes, depending on the plate separation. This constructive or destructive interference results in an easily observable change in color of the reflected light. In an alternate embodiment, a similar interferometric modulator is positioned adjacent to a larger chamber in which incident radiation produces charge carriers that affect the position of the flexible plate.

CONCEPTS

This writing presents at least the following concepts.

a chamber or cavity that produces charge carriers when radiation is incident thereon;

a deformable plate along one side of the chamber or cavity;

a rigid plate spaced and electrically insulated from the deformable plate;

a charging voltage source for applying a voltage to the deformable plate;

wherein the deformable plate is attracted toward the rigid plate by electrostatic forces when charged by the charging voltage source, and moves away from the rigid plate when charge carriers produced in the chamber or cavity by incident radiation reduce the electrostatic forces between the deformable and rigid plates.

Concept 2. The radiation detector of Concept 1 wherein the deformable and rigid plates form an interferometric modulator.

Concept 3. The radiation detector of Concept 1 or 2 wherein the deformable and rigid plates are positioned adjacent to one side of the chamber or cavity with the deformable plate being the closest to the chamber or cavity.

Concept 4. The radiation detector of Concept 3 wherein the chamber or cavity is much larger than the volume between the deformable and rigid plates.

Concept 5. The radiation detector of Concept 4 further comprising a bottom plate positioned at the opposed side of the chamber or cavity from the deformable and rigid plates.

Concept 6. The radiation detector of Concept 5 further comprising a switch connecting the charging voltage source between the deformable plate and the bottom plate.

Concept 7. The radiation detector of Concept 1 or 2 wherein the chamber or cavity is between the deformable and rigid plates.

Concept 8. The radiation detector of Concept 1 or 2 further comprising a gas filling the chamber or cavity to produce charge carriers from ionizing radiation or a photoemissive surface in the chamber or cavity to produce charge carriers from non-ionizing radiation.

a conductive plate having a semireflective surface;

a conductive plate having a mirrored surface;

one of the plates being flexible and the other being rigid;

electrically insulating supports separating the flexible and rigid conducting plates, the plates and supports defining and enclosing a chamber therebetween;

a switch;

a charging voltage source connected across the plates by the switch;

wherein the flexible plate is attracted toward the rigid plate by an electrostatic force produced between the plates when the charging voltage source is connected across the plates, and charge carriers produced in the chamber by incident radiation are attracted to the plates and change the electrostatic force between the plates so that the flexible plate moves relative to the rigid plate, and ambient light reflected from the flexible and rigid plates interferes and produces observable color changes as the flexible plate moves relative to the rigid plate.

Concept 10. The radiation detector of Concept 9 further comprising a gas filling the chamber, the gas producing charge carriers when ionizing radiation is incident thereon.

Concept 11. The radiation detector of Concept 9 further comprising a vacuum in the chamber and a layer of photoemissive material formed on a surface in the chamber, the photoemissive material producing charge carriers when non-ionizing radiation is incident thereon.

Concept 12. The radiation detector of Concept 9, 10 or 11 further comprising a switch control voltage source connected to the switch.

Concept 13. The radiation detector of Concept 12 wherein the switch control voltage source comprises a pulsed voltage source for momentarily closing the switch.

Concept 14. The radiation detector of Concept 9, 10 or 11 further comprising an electrical contact connected to the switch and making contact with the flexible plate when the flexible plate is in a first or uncharged position, the charging voltage source being applied to the flexible plate through the electrical contact, the flexible plate breaking contact when the flexible plate is in a second or charged position, whereby the flexible plate is recharged by making contact with the electrical contact when radiation induced charge carriers cause the flexible plate to return to the first position from the second position.

Concept 15. The radiation detector of Concept 10 further comprising a much larger housing surrounding the chamber, and filled with the same gas.

Concept 16. The radiation detector of Concept 15 further comprising a plurality of perforations or apertures formed in the flexible plate.

Concept 17. A method of detecting radiation, comprising:

providing a chamber or cavity that produces charge carriers when radiation is incident thereon;

providing a deformable plate along one side of the chamber or cavity;

providing a rigid plate spaced and electrically insulated from the deformable plate;

applying a voltage to the deformable plate;

wherein the deformable plate is attracted toward the rigid plate by electrostatic forces when charged by the applied voltage, and moves away from the rigid plate when charge carriers produced in the chamber or cavity by incident radiation reduce the electrostatic forces between the deformable and rigid plates.

Concept 18. The method of Concept 17 further comprising positioning the deformable and rigid plates adjacent to one side of the chamber or cavity with the deformable plate being the closest to the chamber or cavity.

Concept 19. The method of Concept 18 further comprising forming the chamber or cavity with a much larger volume than between the deformable and rigid plates.

Concept 20. The method of Concept 17 further comprising forming the chamber or cavity between the deformable and rigid plates.

Concept 21. The method of Concept 17, 18, 19 or 20 further comprising filling the chamber or cavity with a gas to produce charge carriers from ionizing radiation.

Concept 22. The method of Concept 17, 18, 19 or 20 further comprising placing a photoemissive surface in the chamber or cavity to produce charge carriers from non-ionizing radiation.