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1. radiologists and individuals The active detector 24 contains an energy compensated solid state silicon radiation sensitive element and a micro processor to monitor the radiation rate and dose level all housed in a case 26 made of high impact plastic and equipped with a clip 34 for attachment to clothing at various body locations A 3 digit LCD display 28 provides an indication of the dose and or dose rate In addition to recording dose and dose rate the detector 24 provides a dose and dose rate alarm chirper reminder and stay time 20 25 30 35 40 50 55 60 65 4 alarm and dose history In addition to an audible alarm an LED 32 gives a visual indication of the alarm condition With additional reference to FIGS 2 6 the passive detec tor 22 of the illustrated embodiment includes a conventional TLD card 38 and a novel form of holder 40 which is adapted for attachment to the case 26 of the active detector 24 to form a unitary package More particularly the holder 40 includes a base 42 and two rearwardly extending L shape arms 44 that form with the base a socket 46 for slip fitting over the top end of the case 26 The socket 46 has an opening 48 at its top end generally coextensive with the top of the case 26 to permit viewing of the LED 32 and LCD display 28 The opening 48 also permits unobstructed passage of sound emitted through holes 50 FIG 1 from the audible alarm chirper The forward edge of the ope2. The telebox can easily provide multi badging for up to five 5 dosimeters per telebox The telemetry system is designed for two way communication between the telebox and individual units It has heretofore been used for the purpose of wireless monitoring of workers and or entire areas as well as for wireless calibration of dosimeters The telebox transfers data to a base or control station The basic reader interfaces via a serial port to a host computer or other computer for further connectivity to a LAN WAN The smart readers may be connected directly to a LAN WAN with an optional network interface adapter The optional access control software residing on the smart reader provides for networked and stand alone operation These readers may be networked on many standard network platforms The smart reader can function totally indepen dently should the network be unavailable The active detector system provides real time access control enabling supervisory access to entry and exit data personnel records and RWP radiation work permit autho rization information The Dositec Dosi Reader Model 200 is based on a high performance 486 Processor It can provide an access control and or a record keeping system The reader will noi only record data but also will retain it The reader consists of an integrated computer with 120 MB hard disk serial and parallel ports dosimeter receptacle a numeric keypad and or radiation check source The read
3. a holder attachable to the case of the active dosimeter to form therewith a unitary package and at least one non electronic dosimeter element carried by the holder As is preferred the holder is removably attachable to the case and includes a socket for slidably receiving the case According to still another aspect of the invention a radiation monitoring method comprises the steps of using paired active and passive radiation detectors to monitor exposure to a radiation field the active detector providing an output representative of radiation exposure on a real time basis while the passive detector is readable on a delayed basis after exposure to radiation for a period of time to provide an output representative of radiation exposure over such period of time Radiation exposure data derived from one of the detectors may be used to correct or otherwise modify the exposure information derived from the other detector For example data obtained from the passive detec tor may be used to determine radiation energies and mixed field composition which information may then be used to correct the response data of the active detector to obtain a more accurate radiation exposure history The active and passive detectors may be simultaneously calibrated and or have a multi point calibration performed on each According to a further aspect of the invention a radiation monitoring system comprises a plurality of radiation dosim eters each comprising a
4. by its own unique filter which provides different radiation absorption thicknesses to allow dose estimation for various organs in risk The TL elements 77 80 are located in positions designated 1 4 respectively The TLD card is identified by a label with an ID Number appearing in both numeric and barcode formats One comer of the card is notched at 82 to insure proper insertion into the holder and correct orientation when being read in a card reader The illustrated TLD card and filtration corresponds to that of a conventional 8825 Dosimeter the details of which are incorporated herein by reference sold by Harshaw Bicron Radiation Measurement Products Solon Ohio The TL element 79 in position 3 is a thin solid TLD 700 phosphor Lithium 7 enriched fluoride having a preferred thickness of 0 006 inch This element is protected from the environ ment by filter 85 which is a thin aluminized Mylar sheet having a preferred thickness of 0 0015 inch and a density thickness of 17 mg cm The thin aluminized Mylar sheet corresponds to an open window 84 in the holder The response of element 79 provides a basis for shallow dose estimation As a result of the small thickness of element 79 underestimation of shallow dose contribution of low energy beta rays is reduced The small thickness of both the element and filter provide for reduced energy dependent response to low energy beta particles 5 572 027 5 TL elements 77 78 and 80 in positio
5. 250 337 FOREIGN PATENT DOCUMENTS 1134286 5 1989 Japan seesessecsesesesessssensees 250 482 1 NCE A DANN AR TN T US005572027A 11 Patent Number 5 572 027 45 Date of Patent Nov 5 1996 OTHER PUBLICATIONS Campos Investigation of Teflon Electrect Detectors for Beta Dosimetry p 216 Nuclear Instruments and Methods in Physics Research 1986 Dessauer Photographic Neutron Dosimetry to Date Uni versity of Rochester Sep 14 1948 AECD 2278 US Atomic Energy Commission E Casal et al Experimental Comparison of Automatic TLD Readout Systems Radiation Protection Dosimetry vol 30 No 1 pp 23 31 Nuclear Technology Publishing 1990 Dositec Electronic Dosimetry Manual Version 3 1 Section I pp 1 71 Jan 1993 Dosimeter Model L36 Test Results University of Massa chusetts Dositec Facility Publication No 0001 0793 00 Jul 1993 Moscovitch et al Letter to the Editor Nuclear Technology Publishing Radiation Protection Dosimetry vol 42 No 1 pp 57 59 1992 List continued on next page Primary Examiner Constantine Hannaher Assistant Examiner Virgil Orlando Tyler Attorney Agent or Firm Volker R Ulbrich Don W Bul son 57 ABSTRACT A radiation monitoring system and method characterized by the use of paired active and passive radiation detectors to monitor exposure to a radiation field The active detector provides an output representative of radiation exposure on a real time basis w
6. S Patent FIG U S Patent Nov 5 1996 Sheet 2 of 4 5 572 027 FIG 2 U S Patent Nov 5 1996 Sheet 3 of 4 5 572 027 FIG 4 FIG S 38 PRIOR ART U S Patent Nov 5 1996 Sheet 4 of 4 5 572 027 108 00 TLD SYSTEM READERS 4 2 120 5 572 027 1 INTEGRATED DOSIMETER FOR SIMULTANEOUS PASSIVE AND ACTIVE DOSIMETRY The present invention relates generally to radiation dosimetry and more particularly to a novel concept of integrating an active real time dosimeter with a passive delayed readout dosimeter in a unified package BACKGROUND OF THE INVENTION Two major technologies are in use today to monitor radiation exposure from ionizing radiation The technologies are generally categorized as passive or delayed readout dosimetry and active or real time dosimetry Passive dosim eters have included for example TLD based dosimeter elements bubble based dosimeter elements polycarbonate based dosimeter elements photographic film based dosim eter elements indium based dosimeter elements sulphur based dosimeter elements quartz based dosimeter elements or gold based dosimeter elements or the like Active dosim eters have used for example silicon diodes photodiodes GM tubes ionization chambers electrets MOSFETs and DRAMs or the like as the radiation sensitive elements for providing real time monitoring of radiation levels The two different technologies each have advan
7. United States Patent 9 Tawil et al 54 75 73 21 22 51 52 58 56 INTEGRATED DOSIMETER FOR SIMULTANEOUS PASSIVE AND ACTIVE DOSIMETRY Inventors Riad A Tawil Kirtland Ohio Sam S Hsu Farmingham Mass Assignee Saint Gobain Norton Industrial Ceramics Corp Worcester Mass Appl No 371 694 Filed Jan 12 1995 Tnt lo enana kaani GOIT 1 11 GOIT 1 15 GO1J 1 02 US Glo sieccacccctscecchiconscstsssen 250 336 1 250 370 07 250 390 03 250 394 250 378 250 337 250 389 250 482 1 Field of Search 0 000000 250 336 1 370 07 250 390 03 394 361 R 378 389 337 482 1 References Cited U S PATENT DOCUMENTS 2 793 298 7 1954 Landsverk ccssssscssseerseeeees 250 378 4 465 936 8 1984 Ishiguro et al 250 390 03 4 546 251 10 1985 Schaffer 0 0 eessesesessseeseees 250 337 4 642 463 2 1987 Thoms 0 0 eeeeeseeeseseeeseeees 250 336 1 4 876 454 10 1989 Burgess 250 370 14 4 975 589 12 1990 Chamberlain et al 250 484 1 4 999 503 3 1991 Andru oon cseseessesteeeeeseeees 250 482 1 5 004 921 4 1991 Moscovitch 250 390 03 5 055 691 10 1991 Burgess 250 370 07 5 059 801 10 1991 Burgess w 250 370 14 5 065 031 11 1991 Moscovitch csesssesseesees 250 482 1 5 083 028 1 1992 Decossas et al 250 390 03 5 173 609 12 1992 Lacoste et al w 250 370 07 5 177 363 1 1993 Velbeck et al oe eseccseseseeees
8. and the CR39 strip in their respective readers in known manner the dosimeter may be reassembled as above described Detents 93 may be pro vided for releasably engaging in recesses on the back side of the case 26 to aid in retaining the holder on the case When the holder is assembled to the case together they may be considered a housing for containing the active and passive radiation sensitive elements The dosimeter assembly 20 is one component of an overall dosimetry system which further comprises readers for the active and passive detectors 22 and 24 and a processor or processors which interrelate the radiation exposure information read from the detectors and deter mines a quantity of radiation exposure from the radiation 10 15 20 25 30 35 50 55 65 6 information acquired from the detectors such as effective dose type of radiation etc Effective dose as a measure of the type and severity of the measured radiation on the human body may be determined from the response of the detectors through application of appropriate correction algorithms For example a neural network beta gamma dose algorithm as described in copending U S patent application No 08 326 606 may be used to convert the reader output from the TLD dosimeters to deep and shallow dose As will be appreciated by those skilled in the art the active detector may be used to provide radiation readings at a frequency greater than the readings obta
9. bration may be performed at any level from 200 mrem hr to 9 rem hr In addition to the calibration display on the unit the following reports are available a Last calibration data including calibration date dosim eter serial number and calibration numbers b Verification data including dosimeter serial number calibration date dose expected dose measured percent error passing criteria pass or fail signature of the person performing the calibration c Linearity check report including dosimeter serial num ber calibration date and time dose expected dose measured and percent error d Calibration history of the dosimeter including dosim eter serial number calibration date and time and cali bration numbers The following information may be retrieved from the dosimeter and stored by the reader 1 Dosimeter dose from 0 1 mrem to 999 rem 10 15 20 25 30 35 40 45 50 55 65 10 2 Peak dose rate from 1 mrem Hr to 260 rem Hr 3 Dose history 4 Worker s ID dose dose margin dose history of each entry training information entry and exit information etc 5 Dosimeter calibration information The Dositec Software controls access through RWP radiation work permit authorization lists and exposure limits maintained personnel exposure data and maintained dosimeter calibration data all controlled through a Database Management System DBMS running on a computer This system can o
10. ement selected from the group consisting of a TLD based dosimeter element bubble based dosimeter ele ment polycarbonate based dosimeter element photographic film based dosimeter element indium based dosimeter ele ment sulphur based dosimeter element quartz based dosimeter element and gold based dosimeter element or the like The active detector includes at least one radiation sensitive element selected from the group consisting of a silicon diode photodiode GM tube ionization chamber electret MOSFET and DRAM or the like Further in accordance with a preferred embodiment the dosimeter assembly comprises a housing and the active and passive detectors respectively include an electronic radiation 15 20 25 30 35 40 45 50 55 65 2 sensitive element and a TL element within the housing The housing may include a case and a holder removably attached to the case the case containing the electronic radiation sensitive element and the holder containing the TL element A substrate for carrying the TL element is removably carried by the holder and the holder may include one or more filters overlying the TL element or elements According to another aspect of the invention there is provided a conversion device for converting an active dosimeter that provides an output representative of radiation exposure on a real time basis to an integrated active and passive dosimeter assembly The conversion device includes
11. er communicates with the active detector through an infrared interface eliminating the need for external switches and connectors The reader can be used to calibrate either single or multiple dosimeters 5 572 027 9 The base or contro station can scan all units with a period variable from six seconds and up The total number of units the base station can scan is dependent on the scanning frequency for example 1000 units at one minute scanning time or 2000 units at thirty seconds scanning time for example The base station operator has the ability to monitor both the exposure levels and dose rates of all units and is also able to control each dosimeter s alarm settings An individual s Telebox alarm will be automatically activated if he she gets out of detection range of the base station As above indicated the Model L36 dosimeter contains an energy compensated solid state silicon detector and employs a microprocessor to monitor and process data on the radiation rate and dose level The dosimeter s detection circuit features include the following 1 solid state Si detector 2 No high voltage low maintenance 3 energy response within 25 from 60 KeV to 6 2 MeV 4 dose range 0 999 rem with increments of 1 mrem 5 dose rate range 0 260 rem hr with increments of 1 mrem hr 6 linearity from 0 100 rem hr within 10 for both dose and rate 7 field accurate within 10 of the TLD reading in the field 8 dose rate response less t
12. g said case 5 572 027 11 9 A conversion device for converting an active dosimeter that provides an output representative of radiation exposure on a real time basis to an integrated active and passive dosimeter assembly the active dosimeter including a case comprising a holder attachable to said active dosimeter to form a unitary package and at least one non electronic dosimeter element carried by said holder 10 A conversion device as set forth in claim 9 wherein said holder is removably attachable to said case 11 A dosimeter as set forth in claim 9 wherein said holder includes a socket for slidably receiving said case 12 A radiation monitoring method comprising the steps of using paired active and passive radiation detectors in a single assembly to monitor exposure to a radiation field the active detector providing an output representative of radia tion exposure on a real time basis while the passive detector is readable on a delayed basis after exposure to radiation for a period of time to provide an output representative of radiation exposure over said period of time 13 A method as set forth in claim 12 including the step of simultaneously calibrating the active and passive detec tors 14 A method as set forth in claim 12 including the step of performing a multi point calibration on each of said active and passive detectors 15 A radiation monitoring system comprising a plurality of radiation dosimeters each c
13. han 5 seconds 9 neutron response less than 1 10 fast recovery for radiation overrange 7 times faster than specified in the IEC 45B 1991 Standard and 11 minimum dose retrievable by the reader is 0 1 mrem The detector dosimeter is equipped with a programmable alarm indicated by a bright red LED equipped with a curved light guide for easy visibility from wide angles The loud ness of the audible alarm is 85 95 dBA 30 cm The set point for dose alarm is from 1 mrem to 999 rem with increments of 1 mrem the dose rate alarm can be set from 1 mrem hr to 65 rem hr with increments of 1 mrem Hr The dosimeter will also uniquely identify 4 12 4 and full scale 4 Level dose alarm The chirp rate is adjustable to the following values 0 1 2 4 8 16 32 64 128 and 256 mrem per chirp The user may also set a reminder time alarm from 0 1 minute to 32 hours and a stay time alarm from 1 minute to 32 hours The memory in the Model L36 dosimeter will record 0 01 mrem as the minimum measurement dose which can be retrieved by the reader The memory also records the peak dose rate and the dose history of up to 240 data intervals with programmable time for each data interval from 0 1 minute to 32 hours It also stores the following operating data dosim eter serial number calibration numbers and alarm settings The Model L36 dosimeter may be calibrated by using either a standard Dositec reader or a computer with Dositec calibration software The cali
14. hile the passive detector is readable on a delayed basis after exposure to radiation for a period of time to provide an output representative of radiation exposure over said period of time Respective readers are provided for extracting the radiation exposure information from the detectors as is a processor which determines a quantity of radiation exposure from the radiation information extracted from the detectors The processor corrects radiation expo sure data derived from one of the detectors using radiation exposure data derived from the other of the detectors 17 Claims 4 Drawing Sheets 5 572 027 Page 2 OTHER PUBLICATIONS Kramer et al Software to Maintain Dosimeter Chain of Custody and Health Physics Records Harshaw Bicron Radiation Measurement Products Jul 11 15 1993 Moscovitch Dose Algorithms for Personal Thermolumines cence Dosimetry Nuclear Techology Publishing Radiation Protection Dosimetry vol 47 No 1 4 pp 373 380 1993 Moscovitch et al A TLD System Based on Gas Heating With Linear Time Temperature Profile Nuclear Technology Publishing Radiation Protection Dosimetry vol 34 No 1 4 pp 361 364 1990 Duftschmid et al Automated TLD Systems What Can We Expect From The Market Today Nuclear Technology Pub lishing Radiation Protection Dosimetry vol 34 No 1 4 pp 339 343 1990 Dositec Electronic Dosimetry System User s Manual Jan 1993 5 572 027 Sheet 1 of 4 Nov 5 1996 U
15. ined from the passive detector This provides an exposure history between passive detector readings as may be useful for a variety of reasons such as real time access control Also the active detector functions as a real time indicator and may warn of high radiation levels and or exposures Presently known active detectors heretofore have had some inherent shortcomings For example many commer cially available electronic dosimeters overestimate low energy Gamma rays and underestimate Beta particles in a radiation field consisting of a mixture of Betas and Gammas Also electronic dosimeters have generally had difficulty accurately reporting mixtures of Gamma rays X rays and Beta particles The paired passive detector enables retroactive correction for these shortcomings of the active detector For example radiation energies and field mixtures can be more accurately determined from the radiation exposure information acquired from the passive detector With this information an appropriate algorithm may be applied to the data derived from the active dosimeter to correct same As a result either detector might be selected as the dosimeter of record for compliance purposes Another advantage is that one detector provides a check for the other detector there is added assurance that the information reported is accurate The doses reported by the detectors may be compared to determine if a problem exists The detectors may be independently or
16. is a front view of the front wall plate of the holder FIG 7 is an end view of the front wall plate FIG 8 is a diagrammatic view of a radiation dosimetry system according to the invention DETAILED DESCRIPTION Referring now in detail to the drawings an exemplary dosimeter assembly according to the invention is indicated generally by reference numeral 20 in FIG 1 The dosimeter assembly 20 comprises a passive detcetor 22 and an active detector 24 As is preferred the passive detector and active detector are physically connected together as a unitary package The active demeanor provides an output represen tative of radiation exposure on a real time basis whereas the passive detector is readable on a delayed basis after expo sure for a period of time to provide an output representative of radiation exposure over such period of time The passive detector may be used for primary dose reporting while the active detector may be used for real time dose reporting access control and or as a backup In the illustrated embodiment the active detector 24 is a conventional electronic dosimeter More particularly the demeanor 24 is an active real time electronic Model L36 dosimeter the details of which are hereby incorporated herein by reference available from Dositec Inc of Framingham MA The Model L36 dosimeter is accurate reliable rugged lightweight and designed for nuclear power plants nuclear facilities hospitals dentists schools
17. ive detector includes at least one radiation sensitive element selected from the group consisting of a TLD based dosim eter element bubbie based dosimeter element polycarbon ate based dosimeter element photographic film based dosimeter element indium based dosimeter element sul phur based dosimeter element quartz based dosimeter ele ment and gold based dosimeter element 3 A dosimeter as set forth in claim 1 wherein said active detector includes at least one radiation sensitive element selected from the group consisting of a silicon diode pho todiode GM tube ionization chamber electret MOSFET and DRAM 4 A dosimeter as set forth in claim 1 comprising a housing said active detector including an electronic radia tion sensitive element within said housing and said passive detector includes a TL element within said housing 5 A dosimeter as set forth in claim 4 wherein said housing includes a case and a holder removably attached to said case said case containing said electronic radiation sensitive element and said holder containing said TL ele ment 6 A dosimeter as set forth in claim 5 including within said holder a substrate for carrying said TL element and said substrate being removable from said holder 7 A dosimeter as set forth in claim 6 wherein said holder includes a filter element overlying said TL element 8 A dosimeter as set forth in claim 5 wherein said holder includes a pocket for slidably receivin
18. megabyte capacity 640 kilobyte RAM two diskette drives a Math Coprocessor color graphics monitor and an IBM compat ible printer The system may be controlled by Network Aware Har shaw Radiation Evaluation and Management System NETREMS software available from Harshaw Bicron Radiation Measurement Products The NETREMS software is available for several Harshaw readers With the reader set in remote mode NETREMS takes complete and automatic control of the instrument providing powerful data handling capabilities including reader and field card calibration and automatic application of element correction coefficients to field card readings automatic TTP selection data storage selection and summarization computerized glow curve deconvolution and data exporting in a variety of formats 10 15 20 25 40 45 50 55 60 65 8 The software also provides a common interface from the various readers to a central computer system Results of read operations including glow curves and computed data are displayed on a display In addition the following instrument variables are continuously updated and displayed on a results screen at all times type of reading card ID active TIP number and name date and time of last card read current date and time read cycle phase air temperature for both channels high voltage value for both channels nitro gen flow rate and supply temperature As TL material is read by the photo
19. multiplier tube in the above identified TLD Reader the output is expressed in nanocoulombs The reader calibration factor RCF converts this output to the dosimetric units in which the reader is calibrated such as rem This simple conversion however often is inadequate for determining the effect of the mea sured radiation on the human body especially considering the effects of different types of radiation at varying depths of human tissue By using a variety of TL materials and placing the TL material behind different filters as described above the relative TL response of the materials can be evaluated to determine the type as well as the severity of the radiation and thus estimate its effect on the body These values are derived by processing the reader generated data through an algorithm developed by analyzing exposures to known radiation fields A number of such algorithms have been developed and are commercially available for environmen tal extremity and whole body dose estimation The EPD system in the illustrated exemplary system is composed of one or more conventional readers 120 Two different types of readers Model 200B and Model 200 basic and smart are available from Dositec Inc each being adaptable to a variety of networking concepts Dositec Inc also provides DOSISYS dosimetry system software A Dositec Telemetry System includes teleboxes that use an infrared interface for communication with the Model L36 dosimeters
20. ng a density thickness of 463 mg cm The variation with energy of the photon attenuation characteristics of the tin filter element located in position 4 gives the dosimeter the ability to act as an energy spectrometer for intermediate energy photons The illustrated dosimeter assembly preferably also includes a neutron sensitive element 90 FIG 1 in the form of a strip of CR39 or other polycarbonate material The CR39 strip 90 may be conveniently sandwiched between the TLD card and the case 26 of the active detector when the holder is slipped over the case 26 The above described holder is particularly suited for converting an existing active dosimeter to an integrated passive active dosimeter assembly However those skilled in the art will readily appreciate that the detectors may be otherwise integrated together such as by incorporation into a common case If the passive detector component of the dosimeter assembly employs a TLD card such as that above described then preferably the case has a removable cover preferably tamperproof for permitting removal of the TLD card and or any other passive detector element for reading the TLD card and or any other passive detector element For reading of the radiation sensitive elements of the passive detector 22 in the illustrated embodiment the holder may be slipped off the case 26 of the active detector 24 to permit removal of the TLD card 38 and CR39 strip 90 After reading of the TLD card
21. ning 48 is bounded by an inwardly projecting lip 54 Figure 4 which functions as a stop to prevent the holder from being tele scoped too far over the case 26 so as not to overlie the radiation sensitive element of the active detector located in the lower region of the case 26 The inturned ends of the L shape arms 44 define therebetween a slot 58 accommo dating the clip 34 when the holder is slid over the case 26 The holder is made of durable tissue equivalent ABS plastic The base 42 includes a rectangular shape pocket 62 sized to accommodate the TLD card 38 FIG 5 One corner of the pocket is beveled to form a key 64 for proper orienting of the card in the pocket the card can only fit one way in the pocket The pocket may be circumscribed by an annular gasket not shown for sealing against the front wall of the case 26 of the active detector The bottom of the pocket 62 is formed by a front wall 68 of the holder base 42 The front wall may be formed by a separate plate secured as by a suitable bonding agent in a recess 70 in a border portion 72 of the holder base The front wall includes a window and or various filters for respective radiation sensitive elements of the TLD card 38 As shown in FIG 5 the TLD card 38 consists of four LiF Mg Ti thermoluminescence TL elements 77 80 of different thick nesses and compositions mounted in known manner between two Teflon PTFE sheets on an aluminum sub strate Each TL element is covered
22. ns 1 2 and 4 respectively each are a thicker TLD 700 phosphor having a preferred thickness of 0 015 inch Element 78 is covered by filter 86 to provide a basis for deep dose estimation The filter 86 has a density thickness substantially greater than 250 mg cm and preferably 1000 mg cm 0 040 inch thick ABS and 0 162 inch thick PTFE to minimize the contribu tion of high energy beta rays Sr Y to the deep dose response and to provide tissue equivalent absorption thick ness as close as possible to the actual depth in tissue where deep dose estimation is desired This results in smaller correction factors to be applied to the response of the TL element in position 2 when the deep dose index is estimated Reference may be had to U S Pat No 4 975 589 for further details said patent hereby being incorporated herein by reference Element 77 is covered by filter 87 including a copper filter element The variation with energy of the photon attenuation characteristics of the copper filter element located in posi tion 1 gives the dosimeter the ability to act as an energy spectrometer for low energy photons The filter covering the element 77 is composed of 0 091 inch ABS plastic having a density thickness of 240 mg cm and 0 004 inch thick copper having a density thickness of 91 mg cm TL element 80 in position 4 is covered by 0 091 thick ABS plastic having a density thickness of 240 mg cm and a 0 004 inch thick tin filter element 25 havi
23. omprising a passive detector and an active detector physically connected together as a unitary package said active detector providing an output representative of radiation exposure on areal time basis and said passive detector being readable on a delayed basis after exposure to radiation for a period of time to provide an 20 25 30 12 output representative of radiation exposure over said period of time respective readers for extracting the radiation expo sure information from said detectors and a processor which determines a quantity of radiation exposure from the radia tion information extracted from the detectors said processor modifying radiation exposure data derived from one of said detectors using radiation exposure data derived from the other of said detectors 16 A radiation monitoring system as set forth in claim 15 including an electronic memory for storing incremental radiation exposure information provided by said active detector at intervals over said period of time said reader for Said active detector extracts the incremental radiation infor mation from said active detector for providing a history of readings over said period of time and said processor modi fies the radiation exposure history using the radiation expo sure data derived from said passive detector 17 A radiation dosimeter comprising a housing at least one nonelectronic radiation sensitive element carried by said housing and readable on a dela
24. orked over a wide area 5 572 027 7 network WAN 106 to provide connectivity to a host or records management system 108 The system preferably is programmed to provide seamless integration of data from both the passive TLD system and the active EPD system Preferably there is provided long term record management of the dose obtained from the TLD system which may be the dose of record and integration of daily readings from the active electronic dosimetry system This ensures timely response to operational needs and complete record keeping for regulatory requirements Dose records and raw data preferably are maintained to support tracking and reporting of personnel and dose information important to a health physicist or manager This availability of information lends itself readily to ad hoc queries and reports The TLD system 102 in the illustrated exemplary system is composed of one or more conventional Model 6600 readers 112 that are available from Harshaw Bicron Radia tion Measurement Products a division of SaintGobain Norton Industrial Ceramics Corporation located in Solon Ohio The Model 6600 reader is capable of automatically reading both whole body and environmental TLD cards A Model 6600E reader gives the additional capability of reading extremity dosimeters The software which controls the reader and stores its output may be resident on a network such as a local area network or in this example on a computer associated with
25. passive detector and an active detector physically connected together as a unitary package The active detector provides an output representative of radiation exposure on a real time basis and the passive detector is readable on a delayed basis after exposure to radiation for a period of time to provide an output repre sentative of radiation exposure over the period of time Respective readers are provided for extracting the radiation exposure information from the detectors as is a processor which determines a quantity of radiation exposure from the radiation information extracted from the detectors The processor corrects or otherwise modifies radiation exposure data derived from one of the detectors using radiation exposure data derived from the other of the detectors In a preferred embodiment the radiation monitoring sys tem includes an electronic memory for storing the incre mental radiation exposure information provided by the active detector at intervals over said period of time The reader for the active detector extracts the incremental radia tion information from the active detector for providing a history of readings over the period of time and said pro cessor modifies or otherwise corrects the radiation exposure history using the radiation exposure data derived from the passive detector According to yet another aspect of the invention a radiation dosimeter assembly comprises a housing at least one non electronic radiation
26. perate stand alone can be networked with other PCs to share a common database and can be interfaced to a host which can control the content of the DBMS with changes or additions to personnel or RWP data Calibration software allows simultaneous calibration of multiple dosimeters using a batch calibration program and calibration of a single dosimeter using a auto timing cali bration program The software adjusts the dosimeter s cali bration numbers and updates the system calibration files The software also allows display and printout of the cali bration information Although the invention has been shown and described with respect to a certain preferred embodiment equivalent alterations and modifications will no doubt occur to others skilled in the art upon the reading and understanding of this specification The present invention includes all such equivalent alterations and modifications and is limited only by the scope of the following claims What is claimed is 1 A radiation dosimeter comprising a passive detector and an active detector physically connected together as a unitary package said active detector providing an output representative of radiation exposure on a real time basis and said passive detector being readable on a delayed basis after exposure to radiation for a period of time to provide an output representative of radiation exposure over said period of time 2 A dosimeter as set forth in claim 1 wherein said pass
27. sensitive element carried by the housing and readable on a delayed basis after exposure to radiation for a period of time to provide an output repre 5 572 027 3 sentative of radiation exposure over such period of time at least one electronic radiation sensitive element carried by the housing for providing an output representative of radia tion exposure on a real time basis and an electronic circuit responsive to the output of the electronic radiation sensitive element for producing an alarm if the output of the electronic radiation sensitive element satisfies a predetermined criteria The foregoing and other features are hereinafter described and particularly pointed out in the claims the following description and the annexed drawings setting forth in detail an illustrative embodiment of the invention this being indicative however of but one of the various ways in which the principles of the invention may be employed BRIEF DESCRIPTION OF THE DRAWINGS FIG 1 is an exploded perspective view of an active passive dosimeter assembly according to the invention the assembly including an active detector and a passive detector FIG 2 is a top plan view of a holder for the passive demeanor with a front wall plate exploded away from the base of the holder FIG 3 is a front view of the base of the holder FIG 4 is a sectional view of the holder asked along the line 4 4 of FIG 3 FIG 5 is a plan view of a TLD card FIG 6
28. simultaneously calibrated Simultaneous calibration ensures that the responses from each detector and at the calibration energy agree within a prescribed percentage To eliminate or reduce the energy dependence of the selected radiation sensitive devices multipoint calibration preferably is performed The calibration data may be stored in tabular form and applied real time or in a delayed step to correct for the energy dependence The foregoing data corrections modifications and com parisons may be implemented by a suitably programmed computer integrated into an overall dosimetry system The system processor typically a suitably programmed digital computer computers or network of computers with associated peripherals may be used to record and report radiation exposure information from both the active and passive detectors and further to analyze the information to provide meaningful information to the radiation monitoring agent The processor also may be used to track employee demographic data as well as the data acquired from the active and passive detectors Through appropriate program ming an organization s internal and external dosimetry reporting requirements can be met An example of one possible dosimetry system configu ration is illustrated in FIG 8 The illustrated system gen erally indicated by reference numeral 100 comprises one or more TLD systems 102 and one or more electronic personal dosimeter EPD systems 104 netw
29. tages and drawbacks not associated with the other For example TLD thermoluminescence dosimetry can be used to satisfy strict performance requirements demanded by various govern mental bodies or other entities that cannot be fully met by active dosimeters presently available in the marketplace On the other hand TLD does not lend itself to real time monitoring of radiation whereas as active dosimeters are commonly used today as indicators to provide a warning when radiation exposure exceeds a prescribed level SUMMARY OF THE INVENTION The present invention uniquely integrates passive and active radiation monitoring technologies to provide a dosim eter method and system and components thereof that provide advantages exceeding the sum of those afforded by the technologies individually A radiation monitoring system and method according to the invention are characterized by the use of paired active and passive radiation detectors to monitor exposure to a radiation field The active detector provides an output representative of radiation exposure on a real time basis while the passive detector is readable on a delayed basis after exposure to radiation for a period of time to provide an output representative of radiation exposure over said period of time In a preferred embodiment the passive detector and active detector are physically connected together as a unitary package The passive detector includes at least one radiation sensitive el
30. the reader One reader and its computer along with application software for managing acquisition analysis of collected data and dose calculation make a single fully integrated workstation Each worksta tion can process up to 200 whole body or environmental cards or 400 extremity dosimeters in the Model 6600E without operator attention while performing a number of real time quality checks on the operation to ensure the integrity of the data Critical operating values may be constantly updated and displayed during data acquisition In addition to online QC testing an offline QA system may include electronic self testing and reporting against user set standards and calibration of the reader and each TL element as is conventional Each of these activities may be docu mented by a printed report Any number of TLD workstations may be connected to a local area network LAN or WAN Workstations can share data such as element correction coefficients ECCs and store data directly on the file server or host for further processing or storage The TLD workstations may be net worked on many platforms such as Novell DEC DECNET 0S 2 Lan Manager and UNIX server Should the LAN or WAN be disabled the workstations preferably should be able to function independently until the network has been restored A typical computer configuration for the worksta tion is an IBM compatible with the following minimum requirements hard disk drive of at least 100
31. yed basis after exposure to radiation for a period of time to provide an output repre sentative of radiation exposure over said period of time at least one electronic radiation sensitive element carried by said housing for providing an output representative of radia tion exposure on a real time basis and an electronic circuit responsive to the output of said electronic radiation sensitive element for producing an alarm if the output of said elec tronic radiation sensitive element satisfies a predetermined criteria
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