Abstract:
Described are mobile phones that incorporate radiation detectors formed using commonly available semiconductor memories. The radiation detectors require little or no additional hardware over what is available in a conventional phone, and can thus be integrated with little expense or packaging modifications. The low cost supports a broad distribution of detectors. Data collected from constellations of detector-equipped mobile phones can be used to locate mislaid or stolen nuclear materials or other potentially dangerous radiation sources. Phone users can be alerted to radiation dangers in their vicinity, and aggregated phone-specific error data can serve as user-specific dosimeters.

Description:
FIELD 
       [0001]    This invention relates to the field of portable radiation detectors, and in particular to inexpensive detectors that are easily integrated into cellular telephones and other types of portable computing devices. 
       BACKGROUND 
       [0002]    Governments and their associated first responders are increasingly interested in protecting their citizenry from exposure to dangerous levels of radiation that might result from accidental or purposeful release of nuclear materials. In a current high-profile example from recent media reports, the United States Department of Homeland Security suspects terrorist organizations of planning to build and explode a so-called “dirty bomb” in the United States. Less newsworthy, but nevertheless troubling, dangerous nuclear materials are commonly lost or stolen. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0003]    The subject matter presented herein is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which: 
           [0004]      FIG. 1  is a block diagram of a cell phone  100  adapted to sense and report soft errors in accordance with one embodiment; 
           [0005]      FIG. 2  is a flowchart  200  depicting the operation of an embodiment of radiation detector  175  of  FIG. 1 ; 
           [0006]      FIG. 3  depicts a system  300  that employs a constellation of cell phones  100  to locate a radiation source  305 ; 
           [0007]      FIG. 4  is a flowchart  400  depicting the operation of host  320  of  FIG. 3  in accordance with one embodiment; and 
           [0008]      FIG. 5  is a block diagram of an iPhone  500 , an Internet-connected multimedia smart phone available from Apple Inc. of Cupertino, Calif. 
       
    
    
     DETAILED DESCRIPTION 
       [0009]    “Soft errors” in electronic circuitry are signals that represent erroneous data, but not due to an error in the design or operation of the circuitry. If detected, a soft error can be corrected by simply restoring the errant signal to the correct state. Soft errors can occur in a broad range of electronic devices, but are most commonly observed in semiconductor memories (e.g., SRAM, DRAM). A memory circuit&#39;s exposure to high-energy particles can induce soft errors or contribute to an increase in soft-error rates. Memories, for example, store information as a plurality of bits that are susceptible to transient state changes caused by high-energy particles. Radioactive contaminants in circuit packaging and cosmic radiation are common sources of these particles, and are consequently causes for soft errors. 
         [0010]    Applicants have employed soft-error detection to innovate an inexpensive radiation detector that can, for example, help locate potentially dangerous radiation sources. Some embodiments use commonly available semiconductor memory that also serves the need of cell-phone applications. The radiation detectors, in some embodiments, thus require little or no additional hardware, and can be integrated into common cell phones without modified packaging. 
         [0011]      FIG. 1  is a block diagram of a mobile phone  100  adapted to sense and report soft errors in accordance with one embodiment. Phone  100  is a “smart phone” portable device in that it supports a range of features beyond simply cellular or satellite communication (e.g., web access, location-based services, multimedia applications etc.). An application/media processor  105  at the heart of phone  100  is typically a single integrated circuit that processes and manages programs stored in a flash memory  110 . Such programs might support, for example, Internet access, e-mail and text messaging, and the display and sharing of still and moving images. Processor  105  supports various user interfaces, including a camera  115  and display  120 . Other interfaces  125  include e.g. a microphone, microphone jack, an infrared port, a Bluetooth wireless port, and a Wi-Fi wireless network connection. Phone  100  may also include a Global Positioning System (“GPS”) receiver  130 . 
         [0012]    Phone  100  includes one or more antennas  135  that are coupled to processor  105  via a respective interface or interfaces  140  in support of e.g. Wi-Fi, Bluetooth, and GPS functionality. Phone  100  additionally includes a conventional baseband processor  145 , supported by flash and DRAM memories  150  and  155 , that executes instructions in support of communication with cell networks ( FIG. 3 ) via a wireless network interface  160  and antenna  165 . Network interface  160  is a cellular front end in this embodiment, and is adapted to communicate with a cellular network via antenna  165 . 
         [0013]    Processor  105  and supporting memory  170  are encompassed within a dashed boundary, the contents of which serve as a radiation detector  175  in accordance with one embodiment. The components outside the dashed boundary are conventional and well understood, so a detailed treatment is omitted for brevity. 
         [0014]    Processor  105 , and possibly memory  170 , is modified in accordance with the depicted embodiment in support of soft-error detection and reporting. A combination of hardware and software that realizes a “soft error detection capability” (SEDC)  180  is added to radiation detector  175  such that it utilizes the existing memory arrays within a local memory  170  and the processing core of application processor  105  to perform its detection. An SEDC implementation  180  can be integrated in conjunction with memory  170  or processor  105 , or can be provided on a separate integrated-circuit (IC) device. Wherever located, an SEDC implementation  180  detects soft errors created in memory  170  (or created within cache memory contained within processor  105 ) and reports detected errors to an error-reporting application  185  executing on processor  105  or elsewhere. Similar to SEDC, application  185  can be implemented in hardware or as a program executing on general-purpose hardware. 
         [0015]    Memory  170  can be a single, a plurality of, or multiple types of integrated circuit memory devices, e.g. synchronous dynamic random-access memory (SDRAM), static random-access memory (SRAM), or a mixture of device types. Other types of random-access memory or processor cache memory (not shown) might also be used. Memory  170  may additionally include some measure of storage for redundant information that follows certain algebraic or geometric relations to the stored data to facilitate error detection or correction. When enhanced with such error correction, memory  170 , or a portion thereof, can be selected to be relatively sensitive to soft errors, increasing the utility of the SEDC process, while still providing error-correction codes that compensate the resultant soft errors, and allow normal memory operations to operate undisturbed. 
         [0016]    There are a number of ways to modify the sensitivity of memory  170  to soft errors. In general, soft-error sensitivity is inversely proportional to capacitance and voltage. A parameter Qcrit commonly used to describe a logic circuit&#39;s soft-error sensitivity is therefore a function of capacitance and voltage. Qcrit is a measure of the minimum electrical charge disturbance needed to induce an error. Memory  170  can therefore be designed or selected so provide a relatively low measure of Qcrit to increase soft-error sensitivity. Other variables that can be manipulated to provide a desired degree of radiation sensitivity for a memory device include the types of IC packaging and substrate materials, and the type and geometry of the memory cells. In embodiments in which memory  170  includes an area made more sensitive to high-energy particles, the relative proportion of errors in sensitive area can be used to better identify soft-errors induced by charged particles. For example, read errors uniformly distributed across memory  170  are less likely to result from high-energy particles than read errors concentrated in the area of memory  170  designed with a relatively low Qcrit. 
         [0017]    In some embodiments, error data is recorded on the phone device, in nonvolatile storage (e.g., in flash memory  110 ) before being uploaded to an aggregation server available within the cellular network or via the Internet ( FIG. 3 ). Compounded error data, particularly where the errors are correlated with radiation exposure using data from other devices, can be maintained for a cell-phone user via this aggregation server. The cumulative exposure measure can serve as a personal dosimeter that maintains a measure of the user&#39;s exposure to radiation. The cumulative data is best maintained at the aggregation server, as there could be megabytes of data generated by each user, which would overwhelm the local storage capabilities of the individual user&#39;s smartphone. Further, the aggregation server has access to error information from many detectors, and can thus provide a more aggregate assessment of radiation exposure than a single detector. The aggregation server may consider information from more sophisticated detectors as well. For example, a cell-based detector network can be used to spot problem areas that deserve increased scrutiny. Further study of problem area may yield a better understanding of the threat, if any, and this better information can be used to improve dosimeter data and better calibrate cell-based detectors. 
         [0018]      FIG. 2  is a flowchart  200  depicting the operation of an embodiment of radiation detector  175  of  FIG. 1 . The process begins at step  205  when phone  100  is powered on and consequently undergoes a power-on-reset (POR) operation to ready the phone for operation. Next, an initialization process associated with SEDC  180  writes a “test pattern” into a portion of memory  170  (step  210 ). This can be readily done by a software application simply by initializing a large static array (e.g., a 1 MB array). The specific test pattern can be selected to facilitate soft error detection. For example, if memory  170  is more susceptible to radiation-induced upsets that change stored levels representative of a logic one to levels representative of a logic zero than vice versa, then the test pattern could be all ones. In that case an error could be detected by simply reading the pattern back periodically and counting the number of zeroes. In other embodiments the test pattern written after power up or subsequently can be any data and instructions the application or baseband processors happen to be executing. Though not shown, the initialization process associated with SEDC  180  may immediately read back the test pattern to ensure it was written properly. Write verification prevents SEDC  180  from later interpreting a write error as a soft error. 
         [0019]    Once the test pattern has been initialized and is resident in memory, the overall SEDC process next moves to a low-power “sleep” mode (step  215 ) in which the test pattern is retained but the software is otherwise quiescent. Upon waking (step  220 ), an error-checking process associated with SEDC  180  reads back the test pattern (step  225 ) and checks it for errors. Per decision  230 , if there are no errors, the overall SEDC process returns to the low-power sleep state. If there are errors but these do not rise above some predefined or dynamic error threshold, decision  235  returns the process to step  210  for the initialization process to re-initialize the test pattern. If the errors do exceed the threshold (and the threshold could very well be “more than zero errors”), then the error checking process records error information, such as a value representative of the number of soft-errors detected within memory  170  (step  245 ). When the error checking process records the error result (e.g., within non-volatile storage on the smartphone device), it may augment the error information with a time stamp and/or location information from e.g. GPS  130  of  FIG. 1  to correlate the error signal or signals with a time and position. Alternatively, the error checking process may record all error results, even the “no errors detected” results, along with a time stamp and/or location information. In other embodiments the radiation detector can identify its location by triangulating with neighboring cellular antennas, or the cellular network that includes the antennas can similarly locate the detector. 
         [0020]    When the overall SEDC process determines that it has error information to report (e.g., the number of locally stored error events exceeds some threshold), an error reporting process  185  associated with SEDC  180  determines whether a connection exists for reporting the information to the aggregation server (decision  250 ). When a connection is available, the error reporting process  185  “uploads” the locally stored error data and any associated location or time information (step  255 ) to the host system and returns to step  210  to await the arrival of new errors. Reported error information  260  can be conveyed to the host via e.g. cellular front end  165  or some other network resource. Optionally, the smartphone may secure the data transmission to the aggregation server as well as verify its authenticity via common network communication protocols such as HTTPS. Where GPS location data is unavailable, as where the phone lacks the requisite receiver or is positioned where GPS reception is lacking, the phone&#39;s cell network may provide location-based information directly to the aggregation server (e.g., the cellular network may include a service that replies to requests from the aggregation server, as to where a specific client was during a particular time period associated with a recorded time stamp). Once the error reporting process uploads its data to the aggregation server, the error information can be deleted from the smartphone itself (step  265 ). 
         [0021]    The presence of soft errors detected by this process may not indicate a danger, as soft errors can result from innocuous sources. The embodiment of  FIGS. 1 and 2  thus elects not to alert the user of cell phone  100  of any errors. Other embodiments of the SEDC process could very well involve user-alerts, perhaps generated in conjunction with the aggregation server. As shown in  FIG. 3 , the aggregation server preferably has access to error data from many cell phones, and has location information that may help a specific cell phone  100  distinguish between false alarms and serious threats. For example, the host might send a warning notice to cell phone  100  only if other phones in the same general area exhibit anomalously high soft-error rates, or the host may elect not to warn the cell-phone user of radiation upsets that commonly occur at the reported levels in a dentist&#39;s office (where X-rays are routinely taken) or that are occurring widely due to e.g. sun-spot activity. In the embodiments shown, the SEDC process thus awaits an emission reporting signal, such as a radiation warning, from the aggregation server (decision  270 ) before sending an alert (e.g. a display message  275 ) to the user. The alert message may identify the area of danger, direct the user to a safe area, or otherwise assist the user. 
         [0022]    In some embodiments the SEDC process does not warn the user responsive to all emission reporting signals, but may e.g. aggregate the results from multiple emission reporting signals and alert the user only when the aggregate measure exceeds a predetermined threshold. A user interface to the aggregate measure can also be provided to allow the phone to serve as a convenient personal dosimeter. In other embodiments each emission reporting signal indicates that high-energy particle emissions in the user&#39;s vicinity are at or above a dangerous level and the user&#39;s phone accordingly alerts the user immediately to the perceived threat. 
         [0023]      FIG. 3  depicts a system  300  that employs a constellation of mobile phones  100  to locate a radiation source  305 . In this embodiment, a widely dispersed collection of phones  100  reports error information via a cell network  310 , which includes a distributed collection of cellular antennas  312  (though not shown, cell network  310  is commonly connected to a public switched telephone network). In other embodiments, the mobile devices may use satellite or short-range wireless networking (e.g., WiFi, Bluetooth, ZigBee, etc.) to interconnect their users. An aggregation server  315 , shown as data aggregation and error-reporting storage at a host site  320 , may be coupled to the wireless network via e.g. the Internet  325  or some other suitable connection. System  300  additionally supports web-based observation  330  of error reporting for e.g. cell-phone users, law-enforcement, government agencies or the general public. Garnering data from a large number of phones allows processes associated with the aggregation server to map radiation patterns, identify movement of radioactive materials, and issue warnings when needed, and otherwise publish helpful information relating the position and movement of radiation sources. System  300  forms a radiation monitoring network similar to RadNet now under development at Lawrence Livermore national Laboratory, but as the entire SEDC process can be implemented in software installable by the end-user, adding this capability to cell phone  100  is expected to be smaller and less expensive in our technique than in techniques which exhibit similar functionality and include other forms of radiation detectors. 
         [0024]      FIG. 4  is a flowchart  400  depicting the operation of aggregation server  320  of  FIG. 3  in accordance with one embodiment. Flowchart  400  is depicted as a “for-loop” that begins with receipt of error data (step  405 ) from one of the phone devices  100 . The error data and corresponding time and location information is recorded in a database along with other similar data from other phone devices (step  410 ). Error data may be sorted by time and location to reduce false positives (step  415 ). If the collective error information for a given location indicates a probable radiation hazard (decision  420 ), in step  425  a public safety alert process associated with aggregation server  320  reports the problem and location information ( 430 ) to some pre-designated authority, such as the local fire department or other first-responders. 
         [0025]    Depending upon such factors as the severity of the perceived danger and the possibility of panic, aggregation server  320  may elect to alert users to the problem (decision  435 ). If an alert is to be sent (step  440 ), the alert  445  may be limited to users in the area of exposure or may extend to other users who are near or are expected to enter the area of exposure. User&#39;s driving toward the scene of a nuclear spill might, for example, be directed around the accident via a report  445  identifying the location of the spill. Report  445  is not limited to participating phones, but can also be sent to e.g. GPS receivers or traffic reporting services to direct traffic away from hazards. 
         [0026]      FIG. 5  is a block diagram of an iPhone  500 , an Internet-connected multimedia smart phone available from Apple Inc. of Cupertino, Calif. Phone  500  may be adapted for use as a radiation detector in accordance with one embodiment with little or no hardware modifications. In one embodiment, for example, an iPhone can be configured for use as a radiation detector using a software application downloaded over the Internet. Phone  100  is one of many readily available platforms easily adapted for use as a radiation detector. Phone  500  and its constituent components are well understood by those of skill in the art. A brief description of the phone systems and subsystems is provided for context. 
         [0027]    Phone  500  includes two processors, a communications processor  505  and an application/media processor  510 , that are interconnected by a pair of serial interfaces I 2 C (for Inter-Integrated Circuit) and UART (for Universal Asynchronous Receiver/Transmitter). Communications processor  505 , sometimes called a baseband processor, supports widely used wireless communication protocols, GPRS/GSM, EDGE, 802.11, and Bluetooth, and is coupled to a respective set of antennas  520  for this purpose. The GPRS/GSM block, part of the cellular front end, can be adapted to support different cellular communication standards in other embodiments. Phones in accordance with still other embodiments communicate via networks other than cellular networks, in which case the function of the cellular front end is provided by a different form of wireless network interface. 
         [0028]    Processor  510  is at the heart of the phone, and includes support for a number of input/output devices in addition to what is provided by the communications processor. An analog package  525  includes an accelerometer, a touch sensor, a proximity sensor, and a photosensor. The accelerometer allows the application processor to sense changes in phone orientation, the touch sensor supports the user interface, the proximity sensor senses e.g. that the phone is near or far from the user&#39;s cheek or the difference between a cheek and a fingertip, and the photosensor provides a measure of ambient light for e.g. adjusting display backlighting. Other useful input comes from a GPS receiver  530 , plugs/slots  535  that support memory cards and a USB port, and a camera  540 . Other sensors, such as a microphone, are not shown. User output is provided by an LCD display  545  and, though not shown, a speaker, headphone jack, and a motor supporting a vibrating alert. 
         [0029]    Processor  510  includes two sub-processors, a general purpose ARM (Advanced RISC Machine) core  550  and a media processor  555  dedicated to the efficient processing of audio and video data. A memory device or module (multiple memory die)  560  stores instructions and data for processor  510 . Memory  560  is implemented using e.g. synchronous dynamic random access memory (SDRAM). 
         [0030]    Phone  500  is programmed, in accordance with one embodiment, to execute an application  565  that detects and reports soft errors in memory  560 . In one embodiment the hardware in phone  500  is unchanged to support error detection, and application  565  follows the process outlined in flowchart  200  of  FIG. 2 . The details of that implementation are not repeated here. In other embodiments phone  500  may be modified to increase the soft-error rate, and thus to provide more sensitivity to hazardous particle detection. Memory  560  may be modified as noted previously to increase soft-error sensitivity, in which case application  565  can implement error correction to offset memory errors with processor gain. Alternatively, memory  560  can includes a portion, such as an additional die or a portion of a die, that is dedicated for use in soft-error detection. Memory  560  would thus be divided into application space  570  in support of communication and media processing and an array  575  that defines an error-detection space to receive sense patterns for soft-error monitoring. In some embodiments memory  560  includes SEDC hardware that reports errors to processor  510  by e.g. writing to a register. The portion of array  575  used to store the sense pattern need not be contiguous memory cells. Finally, in some embodiments, the error-detection array  575  may be a “read/reset only” portion of memory which can only be read and initialized, but not written to. In such an embodiment, the only means of creating a “bit flip” (e.g., turning a stored logic-1 into a logic-0, or vice-versa) is a soft-memory error. Even malicious software running on the same hardware could not inject memory errors into the array  575  in this embodiment. 
         [0031]    In the foregoing description and in the accompanying drawings, specific terminology and drawing symbols are set forth to provide a thorough understanding of the present invention. In some instances, the terminology and symbols may imply specific details that are not required to practice the invention. For example, the cell phones discussed above are “smart phones” that support many services in addition to the standard voice functions. Radiation detectors in accordance with other embodiments can be incorporated into relatively simple cell phones with relatively minor hardware, software, or firmware modifications. Portable computing devices other than phones, such as palm-top and lap-top computers, can be equipped as detailed herein to serve as radiation detectors and reporting devices. 
         [0032]    While the present invention has been described in connection with specific embodiments, variations of these embodiments will be obvious to those of ordinary skill in the art. Moreover, some components are shown directly connected to one another while others are shown connected via intermediate components. In each instance the method of interconnection, or “coupling,” establishes some desired electrical communication between two or more circuit nodes, or terminals. Such coupling may often be accomplished using a number of circuit configurations, as will be understood by those of skill in the art. Therefore, the spirit and scope of the appended claims should not be limited to the foregoing description. In U.S. applications, only those claims specifically reciting “means for” or “step for” should be construed in the manner required under the sixth paragraph of 35 U.S.C. Section 112.