Radiation detection

Abstract

A radiation detector is disclosed. The detector comprises a translation device configured to produce a voltage upon receiving incident radiation, and an operable switch configured to transition between a first state and a second state upon triggering by a threshold voltage. The translation device is connected to the switch such that the switch is triggered to transition from the first state to the second state upon the threshold voltage occurring across the translation device. The detector further comprises an interrogation circuit operable to determine whether the switch is in the first state or the second state, thereby determining whether the detector has received a threshold level of radiation associated with the threshold voltage. A system is also disclosed that includes a radiation sensitive device and a radiation detector.

Description

[Technical Field]

[0001] The present invention relates to radiation detectors and systems comprising radiation detectors, and more particularly, but not exclusively, to radiation detectors for use in determining whether a particular threshold limit of radiation exposure has been exceeded for an extended period of time. [Background technology]

[0002] Many systems are known to be damaged by exposure to ionizing radiation, such as alpha, beta, or gamma rays; cosmic radiation, which includes a variety of different types of radiation; or x-rays. Such ionizing radiation can damage electronic components and, in some cases, cause damage to materials. Devices such as cell phones or computers can be vulnerable to radiation damage, and damage to structural materials can have serious consequences for the product if the damage is severe enough to result in structural failure.

[0003] It is desirable to be able to quickly and reliably identify whether a system has been exposed to levels of radiation that could cause damage or malfunction so that appropriate action can be taken before the system is put into use. Summary of the Invention

[0004] According to an aspect of the present invention, there is provided a radiation detector comprising: a conversion device configured to generate a voltage when exposed to incident radiation; a first switch configured to transition between a first state and a second state when triggered by a threshold voltage; wherein the conversion device is connected to the switch such that the switch is triggered to transition from the first state to the second state when the threshold voltage occurs across the conversion device; and an interrogation circuit operable to determine whether the switch is in the first state or the second state, thereby determining whether the detector has received a threshold level of radiation associated with the threshold voltage.

[0005] The switch can be a MEMS switch. MEMS refers to microelectromechanical systems. Such systems have components in the micrometer range. As used herein, MEMS also includes systems with nanometer-sized components, sometimes referred to as NEMS. MEMS switches can be made to be very robust, able to withstand high temperatures, and radiation-resistant.

[0006] The switch may comprise a latch circuit. Alternatively, the switch may comprise a relay circuit.

[0007] The conversion device and switch may be operable without any further power source, and the interrogation circuit, when connected to a power source, may be operable to determine whether the detector received a threshold level of radiation while the interrogation circuit was not connected to power. Not requiring power allows the radiation detector to be used for long periods of time, for example in association with a radiation-sensitive device, and to be interrogated only when the device is to be used. This may be beneficial when the device is to be stored for long periods of time or when it is difficult to provide a power source. A detector that does not require power to operate in this manner, at least until the point at which the interrogation circuit is operated, may be referred to as a passive radiation detector.

[0008] If the switch comprises a latching circuit or a relay, a small amount of power may be required, but this may be provided, for example, using solar power or, if more convenient, using power from the device itself.

[0009] The radiation detector may further include a second switch configured to transition between a first state and a second state when triggered by a threshold voltage, the second switch being connected to the conversion device through the first switch when the first switch is in the second state, and the detector may further include a second interrogation circuit operable to determine whether the second switch is in the first state or the second state. As described in more detail below, such a configuration allows the duration of exposure to radiation to be determined. It should be appreciated that the detector may further include a third switch similarly connected to the second switch, and may also include additional switches. The number of switches may be selected depending on the expected duration of radiation exposure or the duration of radiation exposure desired to be detected.

[0010] The invention extends to an apparatus comprising a plurality of radiation detectors as described above, each of the plurality of radiation detectors may be configured to have a different threshold voltage, or alternatively, each of the plurality of radiation detectors may be configured to have the same threshold voltage.

[0011] The apparatus may further comprise a processor in communication with the interrogation circuit of the or each radiation detector and configured to determine further characteristics of the radiation exposure in response to a switch state determined by the interrogation circuit, The further characteristics may comprise one or more of a duration of exposure to radiation and a type of radiation.

[0012] The invention further extends to a system comprising a radiation detector or device as described above and a radiation sensitive device, the system being configured to alert an operator if the interrogation circuit determines that the radiation detector has received a threshold level of radiation. Alternatively, the system may be configured so that the radiation sensitive device is disabled if the interrogation circuit determines that the radiation detector has received a threshold level of radiation.

[0013] The radiation detector may be located adjacent to the radiation sensitive device, or preferably, the radiation detector may be located outside the radiation sensitive device.

[0014] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a diagram of a radiation detector according to a first embodiment of the present invention; [Figure 2] 2 shows further details of the components of the radiation detector of FIG. 1; [Figure 3] FIG. 2 is a diagram of a radiation detector according to a second embodiment of the present invention. [Figure 4] 1 is a diagram of a system including a radiation detector. DETAILED DESCRIPTION OF THE INVENTION

[0016] FIG. 1 is a schematic diagram of a radiation detector 100. Broadly speaking, the radiation detector comprises a conversion device 110, a switch 120, and an interrogation circuit 130. The conversion device operates to convert incident ionizing radiation into an electrical signal. Radiation incident on the conversion device induces a voltage across the conversion device. The switch 120 is connected to the conversion device and is triggered to transition from a first state to a second state when the voltage across the conversion device reaches a threshold level. As the voltage across the conversion device depends on its exposure to radiation, as is known, the threshold voltage will be reached when the conversion device is exposed to a certain threshold radiation level. Thus, the switch is triggered when the threshold radiation exposure level is reached.

[0017] The interrogation circuitry is used to determine whether the switch has been triggered and, from this, whether the device has been exposed to a threshold level of radiation. Typically, in use, the radiation detector is associated with some radiation-sensitive device, such as a computing device or a device having major structural elements fabricated from radiation-sensitive materials, and the interrogation circuitry can be activated when it is desired to operate the device, which may be some time after the actual radiation exposure has occurred. However, radiation detector 100 allows for the determination of whether the device has been exposed to potentially damaging levels of radiation, regardless of whether that level of exposure was recent.

[0018] The conversion device 110 includes a semiconductor pn junction. Ionizing radiation passing through the junction interacts with the semiconductor material to create electron-hole pairs. As is commonly understood, electrons in the junction are biased toward one side of the junction, while holes are biased toward the other side, resulting in a potential difference between the two sides of the junction depending on the number of electron-hole pairs created. Because the number of pairs created depends on the energy of the incident radiation, the resulting voltage can be related to the exposure of the junction to ionizing radiation. The semiconductor material used can be selected depending on the particular type or energy level of ionizing radiation desired to be detected. Furthermore, the dopant and doping level of the semiconductor material can be selected to change the bandgap of the device and, therefore, to exert some control over the device's response to incident ionizing radiation. From this, it should be appreciated that radiation detectors can be modified in several ways to achieve an appropriate response to the type and energy of radiation desired to be detected.

[0019] Many different semiconductor materials can be used, with those with higher bandgaps expected to be more suitable. The band structure and bandgap can be varied through varying the material used, the dopant, and the concentration of the dopant in the semiconductor material. In this example, gallium arsenide is used. Some alternative examples include silicon carbide, gallium nitride, and diamond.

[0020] Switch 120 is a MEMS switch. MEMS should be understood to refer to microelectromechanical systems, or electromechanical systems whose components are sized in the micrometer or nanometer range. Switch 120 is shown in more detail in FIG. 2 and, in this example, is of the type disclosed by Rana et al. in “Nanoelectromechanical relay without pull-in instability for high-temperature non-volatile memory” in Nature Communications (2020) 11:1181. Switches designed for use with non-volatile memory have the desirable property of retaining their switch state when power is removed. Switch 120 comprises an arc-shaped beam 210 with an additional beam 220 extending toward the center of curvature of the arc-shaped beam. The additional beam is secured via a hinge 230. In FIG. 2, switch 120 is shown in its neutral state, with a small gap between either end of arc-shaped beam 210 and the respective terminals 240, 250. Primary gates 260, 270, located inside the arc-shaped beam 210, and auxiliary gates 280, 290, located outside the arc-shaped beam 210, allow an electrostatic voltage to be applied to the arc-shaped beam to bias it toward one or the other of the terminals 240, 250. When a threshold voltage is reached, the beam 210 will contact one of the terminals 240, 250. In the absence of any further applied force to remove the beam from the terminal, such as an opposing voltage, the beam will remain in contact with the terminal. The switch 120 does not require any additional power source to operate. In some cases, it may be desirable to metal-plate the arc-shaped beam and contacts to improve electrical characteristics. According to Rana et al., plating with Cr-Au can also be used to alter the switch characteristics, so that the arc-shaped beam is cold-welded to the contacts once contact is made. In the present application, this provides a very robust means of detecting exposure to threshold radiation levels.

[0021] Figure 1、2 , the conversion device 110 is Gate 280 and Gate 27 to 0 This voltage is connected to terminal 240. Arc beam 210 If the exposure of the conversion device to radiation is sufficient to reach the threshold voltage, Arc beam 210 contacts terminal 240, which closes interrogation circuit 130. At any suitable time later, the state of the interrogation circuit can be detected to determine whether the detector has received a threshold radiation level.

[0022] The radiation detector 100 can be used, for example, to determine whether a system has been exposed to cosmic radiation during transport. Electronic devices can be sensitive to cosmic radiation, and in some cases, exposure to even a single ionizing particle of sufficient energy can cause a system containing such equipment to malfunction. For example, silicon-based devices are susceptible to damage or soft errors when exposed to cosmic radiation or high-energy secondary particles. This can be particularly problematic for aircraft systems or systems transported by aircraft, because cosmic radiation incidence is more frequent at higher altitudes. It can also be problematic for systems stored for long periods of time, where the risk of exposure increases simply as a result of the length of time the system is stored.

[0023] The radiation detector 100 can be incorporated into such a system, allowing a determination to be made after transportation or storage regarding whether the system is safe for use or the likely risk of malfunction as a result of exposure to space radiation. A system 400 including the radiation detector 100 is illustrated in FIG. 4. The radiation detector 100 is positioned adjacent to a target processor 420 in the system, so that the detector 100 is exposed to approximately the same level of radiation as the target processor. As shown in this embodiment, the detector 100 can be placed on top of the target processor, oriented to face the expected direction of incident radiation, so that any radiation reaching the processor is most likely to have passed through the detector 100. Generally, it will be desirable to place the detector 100 outside the target processor, since if the detector were placed inside, damaging radiation could be absorbed by the target processor or the detector could be shielded to some extent from radiation exposure. In some examples, the conversion material can extend to cover all or at least a substantial portion of the target processor. In such cases, the conversion material can be formed like an umbrella that covers the target processor. In this way, any trigger event can be directly related to ionizing radiation incident on the target processor, rather than being inferred from proximity.

[0024] Use of radiation detector 100 eliminates any need to monitor radiation throughout transport or for extended periods of time while the system is in storage. Several radiation detectors can be incorporated into the system, each configured to detect the same radiation type and energy to increase confidence in the determined radiation exposure levels.

[0025] When the system is ready for use, after transportation and / or storage, an interrogation circuit is operated to determine whether the radiation detector has been exposed to a threshold level of radiation. If it is determined that the detector has been exposed to or above the threshold level of radiation, the system may be configured to automatically take action without additional operator input by determining through the interrogation circuit that a switch has been triggered. For example, the system may alert the operator via an alarm. Alternatively, for example, in the case of a safety-critical system, the system may automatically shut down, or the system may perform a memory reconfiguration or check or other diagnostic to ensure proper functioning.

[0026] Several radiation detectors similar to radiation detector 100 but using different conversion materials in the conversion device can be combined in a system to better characterize the type of radiation to which the system was exposed. Different conversion materials respond differently to incident radiation of different types and energies, and switch 120 can be configured to trigger at different voltages. Thus, for example, a system can include a first detector and a second detector. The first detector can be configured to trigger at a first threshold voltage, and the second detector can be configured to trigger at a second, higher threshold voltage. If, upon interrogation of the radiation detectors, it is determined that the first detector was triggered but the second detector was not, it can be inferred that the system's exposure to radiation was between the level associated with the first threshold voltage and the level associated with the second threshold voltage.

[0027] Alternatively, the first detector can be configured to be sensitive to a first type of ionizing radiation, such as beta particles, but not to a second type of ionizing radiation, such as gamma radiation, and the second detector can be configured to be sensitive to the second type of radiation but not to the first type of radiation. In this way, it can be determined whether the system was exposed to the first type of radiation but not to the second type of radiation, the second type of radiation but not to the first type of radiation, both types of radiation, or neither type of radiation. This information can be used to infer whether the system was exposed to cosmic radiation. Typically, cosmic radiation can be expected to include beta particles but not gamma radiation. From this, it can be inferred, for example, that the system was exposed to a radiation source other than cosmic radiation.

[0028] To ensure reliability in the results of determining whether a system has been exposed to radiation, multiple detectors can be used in the system. The detectors can be located at different points on the system, especially if the system is susceptible to radiation damage over a large portion of its area, or they can be packaged in a single device.

[0029] A system including multiple radiation detectors may further include a processor in communication with each of the multiple radiation detectors. The processor may be, for example, a standard computer or a specially designed microprocessor. The processor is programmed to operate each of the interrogation circuits of the radiation detectors and, for example, to provide an output to a user indicating which of the radiation detectors has been triggered or to provide further information for inferring which radiation detector has been triggered.

[0030] A radiation detector 300 according to an embodiment of the present invention is illustrated schematically in FIG. 3. Detector 300 is similar to detector 100, except that detector 300 includes multiple switches 320, 330, 340, and 350. Switches 320, 330, 340, and 350 may each be the same type as switch 120. Like detector 100, detector 300 includes a translation device 110. Translation device 310 may be the same as translation device 110, and like detector 100, translation device 310 is connected to switch 320 such that a threshold voltage across translation device 310 triggers switch 320 to transition from a first state to a second state. In this embodiment, the first state of switch 320 is an open state, and the second state is a closed state. In the closed state, a voltage is dropped across the translation device. The closed state also connects switch 330 to the translation device. Thus, when the threshold voltage is again reached across the translation device, switch 330 is triggered to transition from its first open state to its second closed state. This causes the voltage across the translation device to drop again, and switch 340 is connected to the translation device. Switches 340 and 350 are similarly connected to the translation device, with switch 340 being triggered the first time the threshold voltage is reached after switch 330 is triggered, and switch 350 being triggered the second time the threshold voltage is reached after switch 330 is triggered.

[0031] The radiation detector 300 also includes four interrogation circuits 360. Each interrogation circuit 360 is associated with one of the switches 320, 330, 340, 350 and operates as described above with respect to the radiation detector 100 so that a determination of the state of each switch can be made when necessary. The interrogation circuits are connected to a processor 370 operable to determine the state of the switches. The processor may be further operable to determine further characteristics of the radiation exposure, such as the duration of the exposure, depending on the number of switches that are in a second state.

[0032] Detector 300 provides an indication of the duration of exposure to radiation above the threshold level through the number of switches that are triggered to transition to the second state. For example, if only one of the switches is triggered, the duration of exposure will be relatively short. If all of the switches are triggered, the duration of exposure will be relatively long. It will be further recognized that detector 300 can include more than four switches as described above to enable the detector to provide information about longer exposures. Also, depending on the application, it may be desirable to vary the threshold voltages of the switches in detector 300. For example, a first threshold voltage may be relatively high so that only high-energy incidents trigger the detector, while the remaining switches may have relatively lower threshold voltages to determine the duration of exposure.

[0033] While several specific embodiments of the present invention have been described above, those skilled in the art will recognize that variations and modifications to those embodiments are possible. For example, while the use of MEMS switches has been described above, it should be recognized that many of the advantages of the present invention can be achieved using any switch that can be triggered with a predetermined voltage to transition from a first state to a second state, provided that the switch remains in the second state for an extended period of time or indefinitely without further operator input. Preferably, therefore, the switch is nonvolatile. The switch is also preferably radiation-hard. Radiation-hard switches are not damaged by exposure to ionizing radiation and are unlikely to change state as a result of exposure to ionizing radiation. For example, many different types of low-energy relay circuits can be used to trigger larger switches, or latch circuits can be used. It may also be possible to use magnetoresistive RAM, other types of radiation-hard nonvolatile RAM, or radiation-hard FLASH® memory. Such switches may require a power supply to operate. However, power requirements are expected to be low and therefore relatively easy to provide for long durations, for example, using a power supply included in the radiation-sensitive device or using an additional power source such as solar power.

[0034] Moreover, while various combinations of radiation detectors, such as radiation detector 100 and radiation detector 300, have been described above, it should be noted that other uses of detector combinations are possible. Detectors may be combined in several ways, for example, with different types of detectors arranged in combination to enable logical calculations related to the properties of the radiation. Different types of detectors may comprise conversion materials with different doping characteristics, switches with different threshold voltages, or conversion materials of different sizes, or a combination of some or all of these variations. Detectors of the same or different types may also be logically combined to create a voting system to more reliably determine whether exposure to a particular level of radiation has occurred.

[0035] It should be further appreciated that other components may be included in the radiation detector circuit depending on the particular application for which the detector is to be used. For example, in some cases, it may be desirable to include a capacitor between the conversion device and the switch. The capacitor acts to smooth out any sudden fluctuations so that, for example, voltage spikes caused by intense but short bursts of radiation do not trigger the switch. A higher capacitance will have a greater smoothing effect. The capacitor will likely be bleed-resistant, allowing its charge to be bleed-off.

[0036] Finally, it should be expressly understood that any feature described above in connection with any one embodiment may be used alone or in combination with other features described, and may also be used in combination with one or more features of any other embodiment or in any combination with any other embodiment. The inventions described in the claims of the present application as originally filed are set forth below. [C1] 1. A radiation detector comprising: (a) a conversion device configured to generate a voltage when exposed to incident radiation; (b) a first switch configured to transition between a first state and a second state when triggered by a threshold voltage; wherein the translation device is connected to the switch such that the switch is triggered to transition from the first state to the second state when the threshold voltage occurs across the translation device; (c) an interrogation circuit operable to determine whether the switch is in the first state or the second state, thereby determining whether the detector has received a threshold level of radiation associated with the threshold voltage; A radiation detector comprising: [C2] The radiation detector of C1, wherein the switch is a MEMS switch. [C3] The radiation detector of C1, wherein the switch comprises a latch circuit. [C4] The radiation detector of C1, wherein the switch comprises a relay circuit. [C5] A radiation detector as described in any one of C1 to C4, wherein the conversion device and the switch are operable without any further power source, and the interrogation circuit, when connected to a power source, is operable to determine whether the detector received radiation at the threshold level while the interrogation circuit was not connected to power. [C6] A radiation detector according to any one of claims C1 to C5, comprising a second switch configured to transition between a first state and a second state when triggered by a threshold voltage, the second switch being connected to the conversion device via the first switch when the first switch is in the second state, and the detector further comprising a second inquiry circuit operable to determine whether the second switch is in the first state or the second state. [C7] An apparatus comprising a plurality of radiation detectors according to any one of C1 to C6. [C8] The apparatus of C7, wherein each of the plurality of radiation detectors is configured to have a different threshold voltage. [C9] An apparatus as described in any one of C6 to C8, further comprising a processor in communication with the interrogation circuitry of the or each radiation detector and configured to determine further characteristics of the radiation exposure in response to the switch state determined by the interrogation circuitry. [C10] The apparatus of C9, wherein the further characteristics comprise one or more of a duration of exposure to radiation and a type of radiation. [C11] A system comprising the radiation detector of any one of C1 to C6 or the device of any one of C7 to C10 and a radiation sensitive device, wherein the system is configured to alert an operator if the interrogation circuit determines that the radiation detector has received the threshold level of radiation. [C12] A system comprising the radiation detector of any one of C1 to C6 or the device of any one of C1 to C7 and a radiation sensitive device, wherein the system is configured such that if the interrogation circuit determines that the radiation detector has received radiation at the threshold level, the radiation sensitive device is disabled. [C13] The system of C11 or 12, wherein the radiation detector is positioned adjacent to the radiation sensitive device.

Claims

1. 1. A radiation detector comprising: (a) a conversion device configured to generate a voltage when exposed to incident radiation; (b) a first MEMS switch configured to transition between a first state and a second state when triggered by a threshold voltage; wherein the translation device is connected to the first MEMS switch such that when the threshold voltage occurs across the translation device, the first MEMS switch is triggered to transition from the first state to the second state; (c) an interrogation circuit operable to determine whether the first MEMS switch is in the first state or the second state, thereby determining whether the radiation detector has received a threshold level of radiation associated with the threshold voltage; and A radiation detector comprising:

2. 2. The radiation detector of claim 1, wherein the conversion device and the first MEMS switch are operable without any further power source, and the interrogation circuit, when connected to a power source, is operable to determine whether the radiation detector received the threshold level of radiation while the interrogation circuit was not connected to power.

3. 2. The radiation detector of claim 1, comprising: a second MEMS switch configured to transition between a first state and a second state when triggered by a threshold voltage, the second MEMS switch being connected to the translation device via the first MEMS switch when the first MEMS switch is in the second state; and the radiation detector further comprising: a second interrogation circuit operable to determine whether the second MEMS switch is in the first state or the second state.

4. An apparatus comprising a plurality of radiation detectors according to claim 1.

5. The apparatus of claim 4 , wherein each of the plurality of radiation detectors is configured to have a different threshold voltage.

6. An apparatus as described in any one of claims 4 to 5, further comprising a processor in communication with the interrogation circuit of the or each radiation detector and configured to determine further characteristics of radiation exposure depending on the state of the first MEMS switch determined by the interrogation circuit.

7. The apparatus of claim 6 , wherein the further characteristics comprise one or more of a duration of exposure to radiation and a type of radiation.

8. 10. A system comprising the radiation detector of claim 1 or the apparatus of claim 4 and a radiation sensitive device, the system being configured to alert an operator if the interrogation circuit determines that the radiation detector has received the threshold level of radiation.

9. 10. A system comprising the radiation detector of claim 1 or the device of claim 4 and a radiation sensitive device, the system being configured such that if the interrogation circuit determines that the radiation detector has received the threshold level of radiation, the radiation sensitive device is disabled.

10. The system of claim 8 , wherein the radiation detector is positioned adjacent to the radiation sensitive device.

11. The system of claim 9 , wherein the radiation detector is positioned adjacent to the radiation sensitive device.

Images