Abstract:
A dosimeter includes a radiation detector and a display. The radiation detector outputs a signal indicative of an instantaneous radiation level. The dosimeter determines and displays a percent of limit (POL) value and/or a time to limit (TTL) value. The POL value indicates a ratio of an accumulated exposure to an exposure threshold. The TTL value indicates an amount of time estimated until the accumulated exposure exceeds the exposure threshold. The display may includes information indicative of both the POL parameter and the TTL parameter. The display may also display the instantaneous radiation level and/or a graphical representation of the instantaneous exposure level. The graphical representation might include a set of LED&#39;s arranged in a line wherein the number of activated LED&#39;s indicates the instantaneous exposure level. The display might also indicate a scale associated with the set of LED&#39;s. The dosimeter might include a switch to select one of multiple operational modes where the POL parameter and the TTL parameter are determined in part by the operational mode.

Description:
BACKGROUND 
       [0001]    1. Field of Invention 
         [0002]    The invention relates to radiological instruments and, more particularly, to radiological instruments used by security, fire-fighting and explosive ordnance disposal personnel to monitor and control radiation doses to which such personnel are exposed. 
         [0003]    2. Description of Related Art 
         [0004]    The term “radiation” as used herein refers to any type of ionizing radiation of various energies and intensity. The term “dirty bomb” relates to an explosive device that contains any type of radioactive isotope. The term “radiological instrument” as used herein refers to any instrument that measures the intensity of a radiation field in units of exposure, absorbed dose, dose-equivalent, or any other units that can be related to a dose limit prescribed for personnel. 
         [0005]    Radiological instruments are used in medicine, industry, and research for dosimetry, imaging, and for homeland security applications. Personnel tasked with responding to radiological emergencies, including actual or suspected dirty bombs, use a wide assortment of radiological instruments capable of detecting and measuring various types of radiation over a wide range of radiation intensities. For homeland security purposes, radiological instruments have been issued to security, fire-fighting, explosive ordnance disposal, and other response personnel and agencies. 
         [0006]    The most basic radiological instruments display only the current radiation dose-rate. Most modern instruments also function as a dosimeter, integrating the dose-rate to record and display the accumulated dose. See, e.g., commercially distributed dosimeters including the MGP DMC 2000S model of electronic dosimeter from Arrow-Tech, Inc. Dose and dose-rates are typically displayed using prefixes such as “m” for milli or “u” for micro. Users of radiological instruments maintain their radiation doses within prescribed dose limits by calculating the fraction of the dose limit they have received and how much time they have before the dose limit will be reached. Properly performing these calculations requires familiarity with radiological units and prefixes and the mathematical formulas involved. 
         [0007]    Personnel entering radiation fields usually have radiation dose limits prescribed by appropriate authorities to ensure the radiation dose received will not inappropriately endanger their health and safety. The dose limits depend on the situation. For example, the dose limits for lifesaving activities are typically greater than those for normal operations. Still higher dose limits can be established for dire emergency situations. 
         [0008]    Personnel must know the dose limit applicable to their situation. Receiving more radiation than the prescribed limit endangers the health and safety could be endangered. On the other, if response personnel are overly cautious and unnecessarily refrain from entering or remaining in radiation fields, their ability to perform their response functions could be diminished. 
         [0009]    Some procedures for disarming dirty bombs call for rotating explosive ordnance disposal technicians to ensure each technician&#39;s dose remains within prescribed limits. The disarming activities may be completed in discrete stages, with the rotation of the technicians preferably occurring only at the completion of a stage. At the end of each stage the technicians need to know how much time they before they will reach their dose limit to know if they should begin the next stage or rotate out. 
         [0010]    Some procedures for disarming dirty bombs call for first measuring radiation levels around the device and using the measured levels to determine an acceptable stay-time for the explosive ordnance disposal technicians. During the disarming of the device, the technician may move into higher radiation fields than were measured during the survey or may increase the radiation levels by disassembling the device. This could result in the technicians exceeding their radiation dose limits. 
         [0011]    During radiological emergencies and practice exercises emergency response personnel have misinterpreted their radiological instrument&#39;s readings, improperly calculated the time remaining until they will reach their dose limit, or used improper dose limits for the situation. These failures are unsurprising since emergency responders are generally unfamiliar with radiological units and prefixes and have never encountered measurable radiation fields. 
         [0012]    There are many radiological instruments developed or presented, including those covered by the reference patents. All of the existing radiological instruments display the radiation dose-rate or accumulated dose in terms of radiological units. This invention provides a unique approach by displaying the radiation dose-rate and accumulated radiation dose in terms of their operational significance rather than as radiological units. This invention will increase the ability of response personnel to safely and effectively respond to radiological emergencies. 
       SUMMARY 
       [0013]    In one aspect, a dosimeter includes a radiation detector and a display. The radiation detector outputs a signal indicative of an instantaneous radiation level. The dosimeter determines and displays a percent of limit (POL) value and/or a time to limit (TTL) value. The POL value indicates a ratio of an accumulated exposure to an exposure threshold. The TTL value indicates an amount of time estimated until the accumulated exposure exceeds the exposure threshold. The display may includes information indicative of both the POL parameter and the TTL parameter. The display may also display the instantaneous radiation level and/or a graphical representation of the instantaneous exposure level. The graphical representation might include a set of LED&#39;s arranged in a line wherein the number of activated LED&#39;s indicates the instantaneous exposure level. The display might also indicate a scale associated with the set of LED&#39;s. The dosimeter might include a switch to select one of multiple operational modes, e.g., emergency mode, normal mode, disaster mode, where the POL parameter and the TTL parameter are determined in part by the operational mode. 
         [0014]    In another aspect, a radiation monitoring service includes providing a dosimeter having a radiation detector and a display. The radiation detector outputs a signal indicative of an instantaneous radiation level. The dosimeter determines and displays a percent of limit (POL) value and/or a time to limit (TTL) value. The POL value indicates a ratio of an accumulated exposure to an exposure threshold. The TTL value indicates an amount of time estimated until the accumulated exposure exceeds the exposure threshold. The display may includes information indicative of both the POL parameter and the TTL parameter. The display may also display the instantaneous radiation level and/or a graphical representation of the instantaneous exposure level. The graphical representation might include a set of LED&#39;s arranged in a line wherein the number of activated LED&#39;s indicates the instantaneous exposure level. The display might also indicate a scale associated with the set of LED&#39;s. The dosimeter might include a switch to select one of multiple operational modes, e.g., emergency mode, normal mode, disaster mode, where the POL parameter and the TTL parameter are determined in part by the operational mode. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    Aspects of one or more embodiments are illustrated, by way of example and not limited by the accompanying drawings, in which like references indicate similar elements, and in which: 
           [0016]      FIG. 1  is a block diagram of selected elements of an embodiment of a detection device; 
           [0017]      FIG. 2  is a conceptual representation of selected modules stored or embedded in a storage medium of the detection device of  FIG. 1 ; 
           [0018]      FIG. 3  is an exemplary illustration of an embodiment of a display element of the detection device of  FIG. 1 ; 
           [0019]      FIG. 4  is a flow diagram of an exemplary implementation of a method of operation for the detection device of  FIG. 1 ; and 
           [0020]      FIG. 5  is a flow diagram showing details of an exemplary implementation of a detect and display module of the method of operation of  FIG. 5 ; 
       
    
    
       [0021]    Although aspects of the one or more exemplary embodiments illustrated are described in detail herein, the depiction and description of these aspects does no limit the invention to the particular embodiment disclosed. To the contrary, the claims are intended to encompass, for example, all equivalent and alternative aspects and embodiments that would occur to one of ordinary skill in the art having the benefit of this disclosure. 
         [0022]    Elements in the drawings may be presented for simplicity and clarity and may not been drawn to scale. For example, the dimensions of some of the elements in the drawings may be exaggerated relative to other elements to clarify or improve the understanding of the embodiments of the present invention. Block diagrams and flow diagrams may include only selected elements of a depicted embodiment. 
       DETAILED DESCRIPTION 
       [0023]    In one aspect, a dosimeter including a radiation detector or display is described. The dosimeter is suitable for use by first responder to the scene of an emergency or disaster. The radiation detector is preferably operable to output a signal indicative of a radiation level. The dosimeter is preferably operable to determine and display a percent-of-limit (POL) value, a time-to-limit (TTL) value, or both. The POL value reflects a ratio of a user&#39;s accumulated exposure to an exposure threshold. The accumulated exposure value may represent the cumulative amount of radiation to which the user has been exposed. The exposure threshold may represent a threshold level of radiation beyond which exposure to the user may be hazardous. The user might, for example, be a first responder to the scene of a disaster or other emergency. 
         [0024]    Turning now to the drawings,  FIG. 1  depicts selected elements of an embodiment of a dosimeter device  100 . Device  100  as depicted includes a processing module  101 , a radiation detector  120 , and a display  110 . In other embodiments, radiation detector  120  may be an external unit that is not part of device  100 . The depicted implementation of processing module  101  includes processing logic  102  and storage  104  that is accessible to processing logic  102 . Processing logic  102  may represent one or more integrated circuits including, for example, a commercially distributed microprocessor, microcontroller, embedded controller, or the like. Processing logic  102  may also include a field programmable gate array or other form of programmable hardware. Storage  104  may include persistent or non-volatile storage such as a flash memory or other form of programmable read only memory. Storage  104  may also include nonvolatile storage such as an array of static or dynamic random access memory. In some implementations, for example, a non volatile portion of storage  104  may include software code that is executable by processing logic  102 . 
         [0025]    Radiation detector  120  is preferably operable to detect and measure levels of radioactive energy, represented by reference numeral  122 , emanating for a radioactive source  121  in proximity to device  100 . Detector  120  is preferably operable to produce an analog or digital signal, referred to herein as radiation signal  125 , that is indicative of the detected level of radiation. In some embodiments, detector  120  may further include an accumulation or integration module (not depicted) that is operable to determine a cumulative amount of radiation detected during a specific time interval. In other embodiments, radiation accumulation or integration functionality is delegated to processing module  101 . An accumulator may, for example, be implemented as hardware within processing logic  102 , software code within storage  104 , or a combination thereof. 
         [0026]    In the depicted implementation of device  100 , processing module  101  communicates with display  110 . The depicted embodiment of display  110  includes an instantaneous display module  130  and a “to-limit” display module  140 . As its name implies, instantaneous display module  130  preferably displays instantaneous levels of radiation detected by radiation detector  120 . As discussed in greater detail below, the “to-limit”: display module  140  preferably displays one or more parameters that indicate directly, without further calculation or manipulation by the user, how close the user is to exceeding a limit or threshold value of exposure. 
         [0027]    As depicted in  FIG. 1 , processing module  102  receives radiation signal  125  from radiation detector  120 . Radiation signal  125  may be an analog or digital signal provided over a serial or parallel communication link. The communication link may be wireless or wired. In any event, processing module  101  receives radiation signal  125  and uses radiation signal  125  to provide one or more signals, including instantaneous signal  105  and to-limit signal  107  to display  110 . 
         [0028]    In embodiments where radiation signal  125  is an analog signal, processing logic  102  preferably includes analog-to-digital (A/D) circuitry capable of converting radiation signal  125  to a digital signal for further processing. In other cases, A/D circuitry is incorporated within radiation detector  120  and radiation signal  125  is a digital signal. In either case, radiation signal  125  is preferably indicative of the instantaneous level of radiation in proximity to radiation detector  120 . Radiation signal  125  may also be indicative, in some embodiments, of other measures of radiation levels. For example, radiation detector  120  may be operable to produce a radiation signal  125  indicative of a time-averaged level or radiation over a specified duration. As another example, radiation detector  120  may be operable to produce, as part of radiation signal  125 , information indicative of an accumulated level of radiation over a specified duration. In other implementations desirable for lower cost, radiation signal  125  produced by radiation detector  120  may simply be an analog signal that indicates the instantaneous level of radiation. 
         [0029]    Where radiation detector  120  merely indicates instantaneous radiation levels, processing module  101  is operable to accumulate radiation signal  125  to determine an accumulated measure of exposure for specific period of time. Device  101  may include a reset button  103  that is operable to clear or initiate the accumulated value and thereby start an accumulation period. As suggested previously, the radiation accumulation functionality of processing module  101  may be implemented with hardware in processing logic  102 , software in storage  104 , or a combination thereof. 
         [0030]    As depicted in  FIG. 1 , processing logic  102  provides instantaneous signal  105 , which is indicative of the instantaneous radiation level, to instantaneous display module  130  of display  110 . Processing logic  102  as depicted further provides a to-limit signal  107  to a to-limit module  140  of display unit  110 . Whereas instantaneous signal  105  may be derived from radiation signal  125  with little, if any, processing by processing module  101 , to-limit signal  107  is preferably indicative of radiation values that cannot be derived by processing module  101  without information in addition to the instantaneous radiation level. 
         [0031]    In preferred embodiments, for example, processing module  101  is operable to provide a to-limit signal  107  that indicates an estimate of the time remaining until the user&#39;s accumulated exposure exceeds a specified exposure threshold, i.e., the TTL value. As another example, processing module  101  is operable to provide a to-limit signal  107  that indicates a ratio of the user&#39;s accumulated exposure to the exposure threshold, i.e., the POL value. In both of these examples, information in addition to radiation signal  125  is required to derive the appropriate signal. 
         [0032]    More specifically, processing module  101  derives the exemplary to-limit values referred to above by first accumulating, or integrating over time, radiation signal  125  to produce a cumulative exposure value. Processing module  101  may then retrieve an exposure threshold from storage  104 . Processing module  101  then computes the POL value as the ratio of the accumulated exposure to the retrieved exposure threshold. To determine a TTL value, processing module  101  must first determine an estimate of the expected level of exposure. The expected level of exposure might, as an example, represent the average value of exposure experienced during a specified time interval. Other techniques or models for estimating the expected level of exposure may be used as well. The TTL value may then be determined by dividing the difference between the exposure threshold and the accumulated exposure by the estimate of the expected exposure level. 
         [0033]    Device  100  may incorporate two or more sets of exposure thresholds for a give user where one set of exposure threshold is used in a less critical environment and another set is used for a more critical environment. In addition, device  100  may incorporate different sets of limits for individuals having different characteristics. As an example, different sets of limits may be selected depending on the user&#39;s age, weight, gender, or other characteristic, health status including, for example, whether the user is pregnant. In other embodiments, the radiation limit for a given situation or environment is uniform without regard to the user&#39;s characteristics. 
         [0034]    Referring now to  FIG. 2 , a conceptual representation of selected functional modules that may be included in processing module  101  is presented. Each of the modules  202  through  210  in the depicted representation may be implemented as software where the software includes instructions, executable by processing module  101 , stored in a computer readable medium such as storage  104 . As depicted in  FIG. 2 , storage  104  of device  100  may includes an accumulated dose module, a POL module  204 , a TTL module  206 , a set of programmable parameters  208 , and an expected exposure level module  210 . 
         [0035]    Accumulated dose module  202  preferably includes code that, when executed, effectively integrates the radiation signal  125  over time to produce an estimate of a cumulative value of radiation exposure. Predicted exposure level module  210  preferably includes code that when executed produces a value representing a predicting level of radiation exposure. The predicted level of exposure may be derived, for example, as the average value of instantaneous exposure experienced during a specific time interval. Predicted exposure level module  210  may also employ other formulae or functions for predicting the exposure level. 
         [0036]    POL module  204  includes software code that, when executed, is operable to retrieve an appropriate exposure threshold from programmable parameters  208  and to retrieve from accumulated dose module  202  the cumulative exposure value. POL module  204  then divides the cumulative dose value by the exposure threshold to determine the percentage of a threshold level radiation that a user has experienced. TTL module  206  preferably includes code that when executed determines how much time a user has until the user&#39;s exposure exceeds a specified threshold. In one embodiment, for example, TTL module  206  first determines the difference between the exposure threshold and the cumulative exposure value provided by accumulated dose module  202 . This difference is then divided by the predicted level of exposure to derive a TTL value. 
         [0037]    The POL value and the TTL value are then provided to display  110  of device  100  to generate a display that includes either the POL value, the TTL value, or both. Referring to  FIG. 3 , for example, an exemplary display device  110  suitable for use in device  100  is depicted. The depicted display  110  includes a mode indicator  302 , a mode selector  304 , an instantaneous gauge  306 , an instantaneous range indicator  308 , and an instantaneous exposure level window  310 . In addition, the depicted embodiment of display  110  includes a POL window  320  and a TTL window  330 . 
         [0038]    Instantaneous gauge  306  as depicted includes a set of LED&#39;s or other visually detectable elements where each illuminated element represents an additional quantum of radiation exposure. The amount of exposure represented by each element in gauge  306  is indicated in range indicator  308 , while the actual exposure level is indicated in window  310 . The mode indicator  302  indicates the application or environment in which device  100  is being used. The available modes may includes a set of modes representing various levels of emergency or disaster. In the depicted embodiment, the mode is hand selectable using mode selector  304 . In some embodiments, the various modes correspond to various exposure thresholds such that, for example, a first mode corresponds to a first exposure threshold while a second mode corresponds to a second threshold. The ability to accommodate multiple modes of operation beneficially enables the use of a first set of exposure thresholds during an event characterizable as relatively low risk or low damage and to use a second set of exposure thresholds during a relatively higher risk or higher damage. 
         [0039]    Turning now to  FIG. 4 , a flow diagram depicted an embodiment of a method  400  for detecting radiation. In some embodiments, the functionality represented by method  400  is implemented as software stored, for example, in storage  104 . In the depicted embodiment of method  400 , device  100  monitors (block  402 ) for a triggering event to initiate operation. The triggering event could be a power on sequence, an indication of a reset by the user, including, as an example, the activation of reset button  103 , a change of mode by the user, or the like. Upon detecting a triggering event (block  404 ), method  400  proceeds. 
         [0040]    In block  406 , method  400  identifies the setting indicated in mode indicator  302  and retrieves (block  408 ) exposure thresholds and/or other limits and parameters applicable to the indicated mode. After retrieving the applicable exposure thresholds, the depicted implementation of method  400  includes retrieving an accumulated radiation value for the user. This embodiment is suitable for use in which a user may be removed from the radiation causing environment for a period of time. If the period is less than a specified minimum, it may be desirable to maintain any previous exposure, in which case, the previous exposure is accounted for by retrieving the accumulated radiation value applicable to the user. After retrieving exposure thresholds and prior exposure data, method  400  calls (block  420 ) a detect and display module. 
         [0041]    Referring to  FIG. 5 , the depicted embodiment of detect and display module  420  includes activating (block  502 ) the instantaneous display module to display the instantaneous levels of radiation to the user. Detect and display module  420  as depicted further includes maintaining data (block  504 ) that indicates the accumulated radiation level and maintaining (block  506 ) data regarding the instantaneous radiation dose level. The accumulated radiation value may be determined by integrating the instantaneous signal over time or implementing a digital approximation of integration. The maintenance of radiation dose level may be used to make a meaningful prediction of expected radiation dose level. 
         [0042]    Detect and display module  420  as depicted further includes determining (block  508 ) the POL and determining (block  510 ) the TTL. The determined POL and TTL are then displayed (block  520 ). Although  FIG. 3  and  FIG. 5  described the determination of the POL value and the TTL value, other embodiments may use just one of these parameters. 
         [0043]    Returning to  FIG. 4 , method  400  resumes operation after calling module  420  by monitoring (block  422 ) for a termination event. The termination event may be a power off, reset, or other user initiated event. Alternatively, a terminating event might be communicated wirelessly in embodiments where device  100  includes, for example, a wireless transceiver. If no terminating event is detected, method  400  returns to block  420  and re-executes the detect and display module  420 . If a terminating event is detected, method  400  stores the user&#39;s accumulated exposure values in storage for possible future use if or when the user later enters the same environment or a different radiation emitting environment. 
         [0044]    Those of ordinary skill in the field of radiation hazards and radiation monitoring will appreciate that an apparatus and associated technique for monitoring and reporting radiation exposure using time to limit or percent of limit parameters has been disclosed. The implementations and embodiments depicted in the drawings and described in the accompanying text are exemplary, but not exhaustive, of the scope of embodiments covered by the following claims.