Electronic Radiation Dosimeter

Abstract

A radiation dosimeter includes a first radiation detector configured to operate in a counting mode, and a second radiation detector configured to operate in a current mode. A processor is configured to calculate a first detected dose of the first radiation detector, a second detected dose of the second radiation detector, and a total dose value using the first detected dose and the second detected dose. An alarm indicates when the total dose value is above a predetermined level.

Claims

1. A radiation dosimeter comprising: a first radiation detector configured to operate in a counting mode; a second radiation detector configured to operate in a current mode; a processor configured to calculate a first detected dose of the first radiation detector and a second detected dose of the second radiation detector, and a total dose value using the first detected dose and the second detected dose; and an alarm to indicate when the total dose value is above a predetermined level.

2. The radiation dosimeter of claim 1, wherein the second detector is a PIN-Diode detector.

3. The radiation dosimeter of claim 2, wherein a dark current component of the PIN diode detector is separated by capacitive coupling.

4. The radiation dosimeter of claim 1, further comprising a first filter positioned on the first detector and a second filter positioned on the second detector.

5. The radiation dosimeter of claim 4, wherein the first and second filters are configured to provide a substantially flat energy response.

6. The radiation dosimeter of claim 1, further comprising a capacitor configured to store a charge generated in the second detector from a radiation pulse.

7. The radiation dosimeter of claim 6, further comprising a resistor and an amplifier; wherein the resistor prevents discharge of a charge from a detector charge stored in the capacitor during radiation pulse ionizing the semiconductor of the amplifier and making the amplifier input conductive.

8. The radiation dosimeter of claim 1, wherein the total dose value is a sum of the first detected dose and the second detected dose.

9. The radiation dosimeter of claim 8, wherein the first detected dose is multiplied by a calibration factor (Sv/count) to form a dose value for continuous radiation, and the second detected dose is added to the dose value for continuous radiation to provide the total dose value.

10. The radiation dosimeter of claim 1, further comprising a third radiation detector configured to operate in a counting mode.

11. A method comprising: operating a first radiation detector in a counting mode; operating a second radiation detector in a current mode; calculating a first detected dose of the first radiation detector and a second detected dose of the second radiation detector, and a total dose value using the first detected dose and the second detected dose; and activating an alarm when the total dose value is above a predetermined level.

12. The method of claim 11, wherein the second detector is a PIN-Diode detector.

13. The method of claim 12, wherein a dark current component of the PIN diode detector is separated by capacitive coupling.

14. The method of claim 11, further comprising a first filter positioned on the first detector and a second filter positioned on the second detector.

15. The method of claim 14, wherein the first and second filters are configured to provide a substantially flat energy response.

16. The method of claim 11, further comprising a capacitor configured to store a charge generated in the second detector from a radiation pulse.

17. The method of claim 16, further comprising a resistor and an amplifier; wherein the resistor prevents discharge of a charge from a detector charge stored in the capacitor during radiation pulse ionizing the semiconductor of the amplifier and making the amplifier input conductive.

18. The method of claim 11, wherein the total dose value is a sum of the first detected dose and the second detected dose.

19. The method of claim 18, wherein the first detected dose is multiplied by a calibration factor (Sv/count) to form a dose value for continuous radiation, and the second detected dose is added to the dose value for continuous radiation to provide the total dose value.

20. The method of claim 11, further comprising a third radiation detector configured to operate in a counting mode.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The foregoing and other features and advantages of the present embodiments will be more fully understood from the following detailed description of illustrative embodiments taken in conjunction with the accompanying drawings in which:

[0021] FIG. 1 is a graph showing detectable dose/pulse values for prior art dosimeters.

[0022] FIG. 2 is a functional block diagram of an electronic personal radiation dosimeter and user including an optional wireless receiver.

[0023] FIG. 3 is a functional block diagram of an embodiment of the electronic personal radiation dosimeter of FIG. 1.

[0024] FIG. 4 is a schematic diagram of an embodiment of a circuit of a radiation dosimeter of FIG. 1.

[0025] FIG. 5 is a schematic diagram of an alternative embodiment of the circuit of FIG. 3.

[0026] FIG. 6 is a graph illustrating the charge of a capacitor of the circuit of FIG. 4.

[0027] FIG. 7 is a schematic diagram of a radiation pulse detector of the dosimeter of FIG. 2, shown with a filter.

[0028] FIG. 8 is a graph showing the energy response of the radiation pulse detector of FIG. 2.

[0029] FIG. 9 is a graph showing the energy response of the radiation pulse detector of FIG. 7 with the filter.

[0030] FIG. 10 depicts a flow diagram of the calculation of a total dose from the event counting sensor and the charge sensor of FIG. 3.

[0031] The figures referred to above are not drawn necessarily to scale, should be understood to provide a representation of particular embodiments, and are merely conceptual in nature and illustrative of the principles involved. Some features depicted in the drawings have been enlarged or distorted relative to others to facilitate explanation and understanding. The same reference numbers are used in the drawings for similar or identical components and features shown in various alternative embodiments. Radiation dosimeters as disclosed herein would have configurations and components determined, in part, by the intended application and environment in which they are used.

DETAILED DESCRIPTION OF EMBODIMENTS

[0032] Embodiments disclosed herein provide a radiation dosimeter with a first detector that employs counting and a second detector that employs charge integration.

[0033] FIG. 2 provides a simplified illustrative example of a dosimeter 100 that is typically worn on the body of the user 110. Dosimeter 100 may be positioned at various locations on the users' body. For example, a whole body dosimeter may be positioned at the user's breast or belt, a finger dosimeter may be positioned on the user's finger, and an eye dosimeter may be positioned at the user's head. A receiver 130 may receive and/or transmit one or more wireless communications from and to dosimeter 100, and in some embodiments may provide user 110 with real-time information on a radiation dose detected by dosimeter 100 based on the communications received. In some embodiments, receiver 130 may include a smart phone, tablet, other general-purpose wireless-capable device, or any receiver type device known in the field of active dosimetry. The term “close proximity” as used herein in reference to the spatial relationship between dosimeter 100 and user 110, and generally refers to a location within a range where user 110 can unambiguously identify a signal from dosimeter 100 and respond accordingly. For example, an acceptable range may depend on the type and/or intensity of the signal or combination of signals provided by dosimeter 100 such as audible, visual, or mechanical (e.g. vibration) signals. It is to be appreciated that the dosimeter 100 may provide various pieces of information to user 110 including numerical information regarding accumulated dose, current dose rate and various means of instantaneous alarm notification, which may include an optical or visual signal, an audible sounder, and a tactile vibration alarm.

[0034] In certain embodiments, dosimeter 100 may be configured to engage with a base station 140 when not in use by user 110. Embodiments of base station 140 may provide a charging capability for dosimeter 100, as well as a network connection that provides the capability for dosimeter 100 to transmit data to other computing devices via the network and/or receive information such as software updates, detection parameters, security identifiers, etc. In certain embodiments, base station 140 may include a processor or microprocessor as well as data storage elements that may be particularly useful if a consistent network connection is not available.

[0035] An illustrative example of an embodiment of a dosimeter 100 capable of providing a measurement of a user's exposure using at least two sensors is shown in FIG. 3. Dosimeter 100 may include an event counting sensor 307, which may be enabled to measure particular aspects of a radiation field 300, and a charge sensor 309. A first signal processor 317 may process signals from event counting sensor 307, and a second signal processor 319 may process signals from charge sensor 309. Each of first signal processor 317 and second signal processor 319 may include signal processing components known to those of ordinary skill in the art (e.g., amplifiers, comparators, etc.). First signal processor 317 may receive the output from event counting sensor 307 and provide a signal of a detected ionizing event, which signal may then be provided to an event counter 327. Event counter 327 may integrate the number of events, which is equivalent to a dose value. The number of events detected over a period of time (e.g., between approximately 1 ms and approximately 1 second), may also be communicated to a processor 340. It is to be appreciated that such a measurement may be an average of detection events over a unit of time, such as counts per second (“cps”) equivalent to a dose rate.

[0036] In certain embodiments, processor 340 may include one or more processors and/or microprocessors coupled with system memory 341 that includes one or more data storage elements, which may use solid state storage technologies known in the related art. In certain embodiments, processor 340 may employ control logic (e.g. software programs, including program code) stored in system memory 341. The control logic of processor 340, when executed by processor 340, may cause the processor to perform functions described herein. For example, processor 340 may implement software that executes a processing algorithm that receives inputs from event counters 327 and 329, and sends and receives information to/from a user interface 350 of dosimeter 100. In certain embodiments, user interface 350 may include a display (e.g. liquid crystal display, touch screen comprising a graphical user interface (GUI), or other type of display interface known in the related art), and one or more buttons to activate various features of dosimeter 100.

[0037] Dosimeter 100 may also include a wireless device 360, which may include a radio element and a wireless antenna. Wireless device 360 may communicate with receiver 130 via any wireless technology known to those of ordinary skill in the related art and may depend, at least in part, on various criteria. The criteria may include, but is not limited to, range of transmission, data security, power requirements, physical dimension of radio and/or antenna, 1-way or 2-way communication, or other criteria. For example, direct device to device communication can be achieved using what is generally referred to as “Bluetooth” technology, which has become a standard for exchanging data over short distances using short-wavelength UHF radio waves. Alternatively, wireless device 360 may communicate with receiver 130 via an intermediate device. Some examples of communication intermediate using intermediate devices include Wi-Fi communicating via wireless router devices, and cellular based communications utilizing cellular communication points supported by a telecommunications provider (e.g. a text-based standard for communication (also referred to as “short message service” (SMS)).

[0038] Various components of dosimeter 100 may receive power from a power source 370, which may include one or more batteries that in some embodiments may be rechargeable. Dosimeter 100 may also include an alarm device 380, which may include one or more of a speaker interface for audible communication (e.g. an alert message or alarm), visual alarm indicators (e.g., lights), and/or tactile alarm indicators.

[0039] In the described embodiments, each of event counting sensor 307 and charge sensor 309 may be enabled to detect one or more of gamma radiation, beta radiation, neutron radiation, and x-ray-radiation. The specific sensor technology may depend, at least in part, on the type(s) of radiation that the embodiment of dosimeter 100 is designed to measure. For example, charge sensor 309 may include a photodiode with a “PIN diode detector” capable of measuring at least gamma radiation and x-ray radiation.

[0040] FIG. 4 illustrates exemplary circuits used for dosimeter 100, and includes a first branch 400 associated with a counting sensor 307, and a second branch 402 associated with charge sensor 309, each of which may be connected to processor 340. Counting sensor 307 is a conventional counting sensor, which includes a first PIN diode D1 adjacent a resistor R11 and a capacitor C11. The signal from diode D1 passes through an amplifier A1, positioned in parallel with a parallel resistor R12 and capacitor C12 circuit. The amplified signal is sent to a coupling element including a capacitor C13 and a resistor R13, and on to a first comparator CP1, from which the signal passes to processor 340. Each photon ionizing at PIN diode D1 is captured as a pulse and counted as a single event in this conventional branch. Such a conventional counter is configured to measure or count short pulses, e.g., pulses of between approximately 1 ms and approximately 10 ms. However, at high dose rates such a conventional counter can get saturated and may no longer be effective. As illustrated here, first branch 400 includes a single first diode D1. It is to be appreciated that in other embodiments, one or more additional first diodes D1 may be employed as additional counting devices.

[0041] Second branch 402, which is associated with charge sensor 309, includes a second PIN diode D2. Ionizing radiation will create electron hole pairs in the intrinsic zone of PIN diode D2, which causes current flowing through PIN diode D2 and a charging capacitor C1 positioned in parallel with resistor R1. The signal may pass through a resistor R5 and an amplifier A2, with amplification defined by resistors R3 and R4. A coupling RC element of a capacitor C2 and a resistor R2 is positioned between amplifier A2 and a comparator CP2. An input 410 to an analog-to-digital converter (“ADC”) of processor 340 is also illustrated.

[0042] It is to be appreciated that during a radiation flash itself no semiconductor functionality (i.e., amplifier A2 and comparator CP2) is needed because at high radiation intensities, silicon amplifiers become conductive and no amplification takes place. Amplifier A2 and comparator CP2 will recover around 10 μs after a radiation pulse, and a readout of the charge stored in capacitor C1 can begin by cyclically (e.g., every 10 μs) reading the analog value at the amplifier output, integrate these values and use the integral as an equivalent of the stored charge of capacitor C1. Integration of the voltage of capacitor C1 may be stopped if the voltage falls below the threshold voltage of comparator CP2. It is to be appreciated that rather than have comparator CP2 start and stop the ADC conversions, the ADC could run continuously and integration starts/stops at according values. But this would not allow the controller to sleep and power consumption of the system would be high.

[0043] By decoupling the output of amplifier A2 from the ADC input 410 by capacitor C2, the temperature dependent dark current of the PIN diode D2 is suppressed. The time constant of the coupling RC element R2*C2 is chosen large enough that the effect on amplitude reduction is negligible. Practical values are between approximately 10 ms and approximately 1000 ms. Because all accelerator and X-Ray flash devices have a huge pause to pulse ratio, a DC loading of the ADC input 410 will not occur. Baseline restoring techniques may be applied if required.

[0044] An alternative embodiment of a circuit for second branch 402 is illustrated in FIG. 5, and uses a negative bias voltage. In this embodiment, the time constant of the coupling RC element C1*R4 may be between approximately 100 μs and approximately 1000 μs, and the the time constant of the coupling RC element R3*C2 may be between approximately 10 ms and approximately 1000 ms.

[0045] A graph illustrating the voltage at capacitor C1 of second branch 402 is seen in FIG. 6. The area under the curve 510 is equivalent to the dose of radiation received at PIN diode D2. This exemplary graph represents a typical electrical pulse at capacitor C1 from a 0.1 μs radiation pulse of a typical X-ray flash device at a 1 m distance in a main beam (30 v dose) for a typical 7 mm.sup.2 low cost PIN diode and capacitance of 400 pF for capacitor C1 and an R value of 1 Mohm, with a bias voltage of 10V. The integral (area below the line) of the ADC converted voltages of capacitor C1 may be multiplied by a calibration factor (Sv/summed Bits) to form the radiation pulse value. The counts from event counting sensor 307 may be summed together and multiplied by a calibration factor (Sv/count) to form the dose value for continuous radiation, and the radiation pulse value may then be added to the count value to provide a total dose value.

[0046] An alternative embodiment of a PIN diode D2′ of second branch 402 is illustrated in FIG. 7. In this embodiment, a filter 420 partially covers a detector 422 of PIN-diode D2′. Filter 420 may include a first shield 424 including an opening or aperture 426, which exposes a portion of detector 422. First shield 424 may be formed of a medium Z material, such as copper, for example. Filter 420 may also include a second shield 428 including an opening or aperture 430, which exposes a portion of detector 422. Second shield 428 may be formed of a high Z material, such as tin, for example. Filter 420 may serve to smooth the energy response of PIN diode D2, as illustrated in FIGS. 8-9, which show the relative response of a non-filtered PIN diode D2 (FIG. 8) and the relative response of a filtered Diode D2 (FIG. 9). It is to be appreciated that a filter may also be used with first PIN diode D1.

[0047] A method 600 of utilizing dosimeter 100 with counting sensor 307 and charging sensor 309 is illustrated in FIG. 10. At step 610, event counter 327 of event counting sensor 307 is read for each selected time interval. At step 620, the event counter dose (C) is calculated by multiplying the count sensitivity by the number of counts. At step 630, the total detector charge deposited on capacitor C1 is determined for a radiation pulse. At step 640, the radiation pulse dose (P) is calculated by multiplying the charge sensitivity by the charge of the radiation pulse. At step 650, the total dose from both detectors is calculated by adding the event counter dose (C) to the radiation pulse dose (P). At step 660, the dose and dose rate values are provided to the user at user interface 350 of dosimeter 100. At step 670, alarms are provided to dosimeter 100 via alarm device 380 when predetermined threshold values are exceeded.

[0048] Those having skill in the art, with the knowledge gained from the present disclosure, will recognize that various changes can be made to the disclosed apparatuses and methods in attaining these and other advantages, without departing from the scope of the present invention. As such, it should be understood that the features described herein are susceptible to modification, alteration, changes, or substitution. For example, it is expressly intended that all combinations of those elements and/or steps which perform substantially the same function, in substantially the same way, to achieve the same results are within the scope of the invention. Substitutions of elements from one described embodiment to another are also fully intended and contemplated. The specific embodiments illustrated and described herein are for illustrative purposes only, and not limiting of the invention as set forth in the appended claims. Other embodiments will be evident to those of skill in the art. It should be understood that the foregoing description is provided for clarity only and is merely exemplary. The spirit and scope of the present invention are not limited to the above examples, but are encompassed by the following claims.