US3809901A - Automatic thermoluminescence dosimetric system with coded card - Google Patents

Abstract

A precision machine is provided which automatically senses the thermoluminescence emanating from a dosimeter which has previously been exposed to radiation, particularly X-rays, gamma rays, electrons and neutrons, wherein the dosimeters are mounted in uniform, rectangular cards adapted to be stacked in a cartridge. The cartridge is horizontally disposed near the top of the machine. A single card is selectively transferred from the cartridge into a vertical gate with a plurality of sequential light locks. Each card is automatically positioned for activation of the dosimeter by contact with a cyclically heated, hot element. After a reading of disseminated luminescence has been made, the cards are automatically discharged from the vertical chute into a receiver where they are serially stacked in another cartridge. Readings with less than 1 percent error can be made reproducibly. A laminated card with at least one aperture adapted to peripherally seal an encapsulated dosimeter is formed by bonding a foraminous, code-adaptable, rigid rectangular sheet of low-Z material with a codedly transparent sheet of low-Z material in light-transmitting registry with particular code-holes of the rigid sheet. The laminated card may be coded to identify the person, circumstances, or location related to its radiation exposure and the identification is printed out, without error, using a ''''parity checking'''' system which permits ''''autocorrection.'''' Alternatively, where the correction cannot be made automatically, the machine stops to permit visual examination of the rejected card. The card is also coded for identifying the type of card and whether or not it is correctly present at any position during its sequential progress through the machine.

Description

United States Patent [191 Szalanczy et al. 7

Inventors: AndrasSzalanczy, Oakwood Village; Erwin F. Shrader, East Cleveland; Bruce M. Shoftner, Shaker Heights; James D. Chamberlain,-Solon, all of Ohio [73] Assignee: Kewanee Oil Company, Bryn Mawr,

[22] Filed: Nov. 30, 1971 I [21] Appl. No.: 203,281

[52] U.S. Cl. .-.250/337,250/369 [51] Int. Cl. H01j 39/00 [58] Field of Search.... 250/71 R, 83 R, 83 PH, I 250/83.3 H

[5 6] References Cited- UNITED STATES PATENTS 3,652,854 3/1972 .Wheeler 2'50/71 R 2,680,816 6/1954 Stern 250/83 PH 3,419,720 l2/l968 Debye et al... 250/83 R 3,348,044 lO/l967 Sanders 250/83 R 3,631,243 l2/l97l Byler 250/7l R Primary Examiner-Harold A. Dixon Attorney, Agent, or Firm--Cain and Lobo [5 7] ABSTRACT A precision machineis provided which automatically 0 AUTO-LOA DER O r451 May 7, 1974 senses the thermoluminescence emanating from a dosimeter which has previously been exposed to radiation, particularly X-rays, gamma rays, electrons and neutrons, wherein the dosimeters are mounted in uniform, rectangular cards adapted to be stacked in a cartridge. The cartridge is horizontally disposed near the top of the machine. A single card is selectively transferred from the cartridge into a vertical gate with a plurality of sequential light locks. Each card is automatically positioned for activation of the dosimeter by contact with a cyclically heated, hot element. After a reading of disseminated luminescence has been made, the cards are automatically discharged from the vertical chute into a receiver where they are, serially stacked in another cartridge. Readings with less than 1 percent error can be made reproducibly.

A laminated card with at least one aperture adapted to peripherally seal an encapsulated dosimeter is formed by bonding a foraminous, code-adaptable, rigid rectangular sheet of low-Z material witha codedly transparent' 'sheet of low-Z material in light-transmitting registry with particular code-holes of the rigid sheet. The laminated card may be coded to identify the person, circumstances, or location related to its radiation exposure and the identification is printed out, without error, using a parity checking system which permits auto-correction. Alternatively, where the correction cannot be made automatically, the machine stops to permit visual examination of the rejected card. 'The card is also coded for identifying the type of card and whether or not it is correctly present at any position during its sequential progress through the machine.

7 Claims, 16 Drawing Figures DIGITAL-COMPARATOR a v TELETYPE INTERFACE UPPERQJMIT mu 7,1 malul O PATENTEUHAY 71914 MU 5 [IF 6 FROM AUTO LOADER TO AUTO-RECEIVER ATENTED MAY 7 i974 SHEET 8 OF 6 AUTOMATIC THERMOLUMINESCENCE DOSIMETRIC SYSTEM WITH CODED CARD BACKGROUND OF THE INVENTION Radiation is rountinely measured by exposing a thermoluminescent dosimeter to radiation and thereafter measuring the light output of the dosimeter when it is heated. Various thermoluminescent materials are known, the preferred ones being crystalline ionic salts of the alkali metal and alkaline earth metals. Radiation dosimetry utilizing crystal dosimeters, sometimes referred to as chips, is the most widely utilized system for monitoring'the radiation to which persons in an ambience of radiation have been exposed over apreselected time interval, ranging from a few minutes to several weeks.

Conventionally, persons likely to be exposed to radiation carry a dosimeter fixedly mounted in a support such as a card which is subsequently read by being positioned for heat conductive contact with a heated element in a light-tight chamber. The heated dosimeter luminesces and with the aid ofa photo-multiplier tube, generates a reading indicative of the level of radiation to which the dosimeter and the person carrying it has been subjected. It will be apparent where a large number of persons are susceptible to radiation in their working environment, the level of radiation to which each has been subjected must be monitored relatively frequently, and the speed and accuracy with which this can be'done assumes overriding importance.

Machines presently used to read a multiplicity of dosimeter with the degree of accuracy desired are, for the most part, manually operated, and provide a reading on a dosimeter'which must be manually inserted and subsequently retracted after it has been read. The major obstacles to'an accurate automatic machine have been the lack of: a reliable automatic feed mechanism for cards or other dosimeter supports carrying the delicate chips; a reproducibly accurate means of heating the dosimeter orchip; and above all, effective light-locks to preclude light leakage while a reading is taken. Even traces of visible light constitute unacceptable leaks which will give an erroneous reading or which may damage the ultrasensitive photo-multiplier tube. The instant invention effectively overcomes all these obstacles and simultaneously provides readouts even at low radiation levels of about milliroentgens, with less than 1 percent-error and error-free identification of the exposed dosimeter.

SUMMARY OF THE INVENTION A surprisingly accurate, automatic thermoluminescence detection system is provided which utilizes small. rectangular cards suitably coded and adapted to hold in posit-ion at least one, and preferably two, encapsulated crystal dosimeters; a multiplicity of variously coded similar cards are upstandingly stacked in a cartridge which is horizontally disposed near the top of the machine and are selectively transferred into a vertical card holder or chute equipped with sequentially activated floating shutters having low mass which serve both .to position the card and to provide the required light locks; an encapsulated dosimeter positioned to be read is activated by acyclically heated heating element which is pressed into heat-conductive contact with the dosimeter while the heating element is being heated from a relatively low temperature to a temperature of about 280C. and then removed from contact, while the photomultiplier tube records and transmits a read out of the luminescent emission from the dosimeter during a predetermined period of time; the card is identified and thereafter gravitationally discharged from the chute by sequentially operated shutters into an automatic receiver which restacks the cards in another cartridge. The machine is capable of a reading of 5 milliroentgens with less than 1.0 percent error and high reproducibility of results, one of the reasons being the close positioning, less than 2.5 centimeters, of the phototube to the dosimeter being read, which permits a high signal-to-noise ratio. I

A laminated card of a foraminous, code-adaptable rigid sheet of essentially non-luminescent material, on which is superposed a codedly transparent sheet of non-luminescent material in light-transmitting registry with particular code-holes of said foraminous sheet, is adapted to peripherally seal, in at least one aperture in the card, a dosimeter encapsulated in a substantially light permeable synthetic resinous material which is itself essentially non-luminescent.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevation view of the automatic thermoluminescence detector/dosimeter identifier with the Auto-Loader above and the Auto-Receiver below it, an automatic integrating picoammeter, a digital comparator, a teletype interface, and a teletype-writer;

FIG. 2 is a perspective view on an enlarged scale of the laminated card showing the coded transparent sheet;

FIG. 3 is a view of the card on an enlarged scale showing the foraminous code-adaptable rigid sheet;

FIG. 4 is a view of the card on an enlarged scale showing the holes of the codedly transparent sheet in light-transmitting registry with holes of the foraminous, code-adaptable sheet;

FIG. 5 is a cross-section view of the card approximately along the line 55 in FIGS. .3 and 4 showing the position of the encapsulated dosimeter;

FIG. 6' is a side elevation of the detector/dosimeter identifier;

FIG. 7 is a front elevation of the sub front plate shown full scale along the line 7--7 in FIG. 6, in the direction of the arrows;

FIG. 8 is a rear elevation view of the door assembly shown full scale along the line 8-8 in FIG. 6, in the direction of the arrows;

FIG. 9.is a side elevation section approximately along the line 9-9 in FIG. 8;

scale of the door assembly along the line 12-12 in FIG. 8;

FIG. 13 is a rear elevation view on an enlarged scale showing the spring-biased heating element assembly in heat-conductive contact with an encapsulated dosimeter;

FIG. 14 is a plan section view on an enlarged scale of the heating element assembly along the line 14-14 in FIG. 13;

FIG. 15 is a side elevation section detailed on an enlarged scale to show actuation of the heating element assembly into heat conductive contact with the encapsulated dosimeter;

FIG. 16 is a rear partial section view of an enlarged scale of the cartridge mounted on the auto-loader, along the line l6l6 in FIG. 6.

PREFERRED EMBODIMENT OF THE INVENTION The instant detector/dosimeter identifier is most conveniently used for fast and accurate readouts of a large number of cards in conjunction with an automatic integrating pico ammeter, a teletypewriter, a teletypewirter interface or, optionally, a dual-pin strip-chart recorder. The electronics for sensing the luminescence of a heated dosimeter and transmitting the sensed light to a recording means is old and forms no part of the instant invention.

Referring now to FIGS. 1 and 6, the detector and the dosimeter identifier shown generally at 10 carries an automatic loader, also referred to as an auto-loader 11, upon which is horizontally disposed a card cartridge 12 in which a multiplicity of single cards 13 are upstandingly stacked prior to being read. Beneath the detector-dosimeter identifier 10 is disposed an automatic receiver, also called an auto-receiver 14, into which each card 13 is fallingly discharged and serially upstandingly stacked in another card cartridge 12 demounta bly disposed upon the auto-receiver 14. A front panel l5 is fitted with appropriate controls for obtaining the reading on either one or both of the dosimeters, displaying the temperature history to which each dosimeter is subjected, and for otherwise operating the detector-dosimeter identifier to give the desired information. Immediately behind the front panel 15 is a door assembly with integral card holder 16, to be described more fully hereinafter, swingably disposed and precisely alignable with a sub-front plate assembly 17 behind which is a temperature stabilized photomultiplier tube. The instant detector-dosimeter identifier 10 is also equipped with a card identifier and a decoder, a built-in reference light source, a temperature recorder output, a display for a faulty card, electrical circuits for sequencing the cards, logic for predetermined operations of the machine, and the like, all of which are only incidentally related to the instant invention.

Referring now to FIG. 6, the auto-loader 11 is equipped with means for selectively ejecting downwards an individual card 13. from the upstanding stack of cards in the card cartridge 12, all of which cards are pressingly biased against the auto-loader l1. Ejection of each individual card is effected by a metal finger 61 operated by a snap-type clutch in the auto-loader 11 which ejects a single card downwardly into the uppermost opening 20 of the door assembly 16 disposed beneath it. Biasing means which maintains the stack of cards pressed against the rear plate 62 is conveniently provided by tension lines 63 on either side of the rear plate 62 which is adapted to exert pressure on the pres sure plate 28 of the card cartridge 12. The tension lines 63 may be secured on a drum within the auto-loader 11. Alternatively, the tension lines 63 may be tension springs suitably disposed within the auto-loader 11.

Referring now to FIGS. 2, 3, 4 and 5, the card 13 is made of a thin, foraminously code-adaptable, relatively rigid sheet 33 of essentially non-luminescent material, referred was a low-Z material, such as aluminum having a thickness of about 0.005 to 0.020 inch,'which has upturned edges 18 adapted to snugly accommodate a superposed, rectangular, codedly transparent sheet 19 which is adhesively bonded to the aluminum to form a laminate. The dimensions of the card are preferably about 1 3/16 inch X l 1 1/16 inch. Near one side of the laminate card, as viewed when stood on its shorter side, are provided two apertures 21 the centersof which are in a line parallel to the longer axis of the rectangle. In each aperture is peripherally, sealingly mounted a thermoluminescent dosimeter 22 encapsulated in a suitable material transparent to light disseminated by the dosimeter and which will not interfere with the readout of the dosimeter. Such a material may be a synthetic resinous material, preferably polytetrafluoroethylene (PTFE), about 3 mil. thick. Optionally, an inert, nonluminescent filler may be used within the capsule formed by the PTFE, to position the dosimeter. Each dosimeter 22 is a substantially rectangular chip having dimensions approximately 0.32 cm X 0.32 cm. and a thickness of about 0.08 cm. The encapsulated chips 22 are centered within the apertures, the centers of which are approximately 2.5 cm. apart.

Any thermoluminescent material may be sealed into the apertures of the card, but the ionic salts of the alkali and alkaline earth metals are preferred. Most preferred is an extrudate oflithium fluoride ribbon which is comminuted to the desired size. It will be apparent that a single dosimeter may be used ratherthan two. Twin dosimeters are preferred to permit averaging of two readings on two separate dosimeters for the sake of safety and accuracy; also, to permit the measurement of total beta and gamma radiation and, separately, the beta'radiation alone. Typically, such a breakdown of readings of radiation is done by shielding one dosimeter from the beta radiation. I

In the lower portion of the aluminum sheet is provided a plurality of code-adaptable perforations 23- in a rectangular grid pattern and three additional cardcheck perforations 24, all of the perforations being standard for all cards. The perforations are provided in the aluminum sheet prior to lamination with a codedly transparent rectangular sheet 19 of low-Z material which is snugly positioned by the upturned edges 18 of the aluminum sheet 33. The rectangular, codedly transparent sheet 19 is normally of a conventional photographic film which has been exposed so as to have infrared light-permeable spots corresponding to particular perforations in the aluminum sheet in accordance with a preselected code. This is conveniently done by using a master board with a grid pattern of perforations, behind which board are bulbs corresponding to the grid pattern 23 of perforations in the aluminum sheet. Particular bulbs in the grid pattern are lighted for coding each card, and an exposure is made of each identification pattern. When the film is developed, it is cut into the appropriate rectangular sheet sizes 19 and adhesively bonded to the aluminum sheet 33 so as to superpose transparent spots on the coded sheet of film in light-transparent registry with corresponding perforations in the aluminum sheet 33. The preferred grid pattern for coding each card incorporates a double parity check system such as is well known to those skilled in the art, by which a-single error in sensing the presence or absence of any light-permeable spot may be automatically recognized and corrected and by which any double error may be recognized. V

In addition to the grid pattern on the master board corresponding to perforations 32, there are also included three bulbs corresponding to perforations 24, linearly disposed along the edge of a card opposite to the dosimeters, referred to as card-check perforations because they serve to identify the type of the card. The card-check holes 24 are also referred to as location-check" holes since theyserve an ancillary function. Thus, when. a card is correctly presented in the vertical chute in the first position on the knife-shutter 71 light sensors 51 recognize the card as being one which has mounted therein a single dosimeter, or twin dosimeters, or none. If the card has no dosimeter, the card may require, the machine to make a calibration check or a check of background illumination, or both. Additionally, the card-check holes may identify the card as a fneutron card" or gamma card" which requires reading both dosimeters, one of which is screened, and normalizing the read-out. If no card arrives at the first position all light tube sensors are on;

on the other hand, if a card arrives in an inverted posi-,

tion, all light pipes or sensors are off indicating an incorrectly presented card. However, if for example, only the center hole of the perforations 24 is in lighttransmitting registry, it may indicate that the card is a twin-dosimeter card, and that it has arrivedat the first position in correct orientation.

The light tubes or sensors 52 and 53 register the pressure ofa card when each is off, that is, when an opaque portion of the card interrupts the light beam. Appropriate card-check light-permeable spots corresponding to at least one of the perforations 24 are provided on the film by the exposure technique described hereinabove. Instead of photographic film, any suitably low-Z material which does not interfere with the readout of the do simeter may be used, and any preselected, codedly transparent format may be obtained by puncturing the material for light transmitting in registry with particular holes of the rigid aluminum sheet.

The upturned edges 18 of the aluminum sheet 33 enhance the rigidity of the laminate,accurately position the sheet of codedly transparent film, and provide a relatively wide surface both to guide the card through the vertical chute and to enable the card to be selectively ejected from the cartridge 12 by the auto-loader l l and to commence its individual, sequentially staged passage through the door assembly.

FIG. 6 is a side elevation of the detector/dosimeter identifier which shows a view of a card cartridge 12 which has a channel section 25 adapted to snugly accommodate a multiciplicity of cards in an upstanding stack. FIG. 16 is a rear partial section view on an enlarged scale of the cartridge 12 mounted on the autoloader 11 along the line 16-16 in FIG. 6. An end plate 26 and a mounting plate 27 are provided at each end of the cartridge. A pressure plate 28 is slidably disposed in the channel 25 to exert sufficient pressure on the upstanding stack, with the aid of biasing means 63 actuated from the auto-loader 11, to maintain the cards pressed against the rear plate 62 of the auto-loader 11. Additionally, friction clips may be disposed on the horizontal ridges 37 which protrude inwardly in the channel 25, which clips aid in biasing the pressure plate 28 when the cartridge is used with the auto-receiver 12. The mounting plate 27 of the cartridge is adapted to be demountably disposed on the rear plate 62 of the autoloader so as to ejectably present the upstanding stack of cards to the, metal finger 61, which selectively'ejects individual cards into the uppermost opening 20 of the door assembly 16, the aluminum sheet of the laminated card being nearest to the photomultipliertube. The cards 13 are stacked in the cartridge 12 on the shorter end of the rectangle so as to present the cards in the door assembly in the correct position. If the door assembly were designed to accommodate cards in a different position, the cards could be stacked in the cartridge to accommodate such adesign.

The mounting plate 27 of the cartridge is equally adapted to be demountably disposed on the rear plate 64 of I the auto-receiver. When a cartridge 12 is mounted on the auto-receiver, snap-type spring clips 65, which are not used when the cartridge is mounted on the auto-loader 11, are snapped into operative position. The spring clips 65 are provided with angular planar faces which slope inwardly to the longitudinal axis tor-actuated lever (not shown) the motor being actuated on signal from an infrared light pipe which determines whether a card has been delivered to the auto receiver for stacking. It is possible to operate the instant detector/identifier without the auto-receiver, and to do so, a discharge chute is provided which discharges the cards, after they are read, when the auto receiver is not used.

The door assembly 16 shown in FIGS. 6, 7 and 8 has a card holder or vertical chute trimmedby oppositely disposed guides 29, integral with the inside face of the door 30, through which chute the cards 13 are individually sequentially staged, presented for readout by the phototube, identified and discharged. A single card 13 enters the uppermost opening 20of the door assembly, having been ejected downwards by the auto-loader 11, and is slidingly accommodated by the chute. The card comes to rest on a first knife-shutter 71, structurally similar to other knife-shutters referred to hereinafter and shown in detail in FIG. 10. The knife-shutter 71 is fioatingly disposed on the end of a rod 31, which is retractably disposed through the door 30 near the top, and is preferably spring-biased by a spring 32 to block the path of a card and solenoid-actuated for retraction. The solenoid coacts with the end of the rod 31 protruding through the door to retract the knife-shutter 71 from itsnormally closed position. Sincethe solenoids must be small so as not to affect the operation of the phototube, it is necessary that the mass of the knifeshutter assemblies be sufficiently low without sacrificpreferably also solenoid-operated, is disposed immediately below the first knife-shutter to stop the card at a As soon as the card is dropped from its first position into its second position on the second knife-shutter 72, the first knife-shutter 71 is closed by being thrust into snug engagement into a first slot 81 in the sub-front plate assembly 17. The knife-shutters are planar, flexible, and relatively thin, having a thickness in the range of from about 0.010 to 0.020 inch. The floating knifeshutter, preferably disposed on a pin 34 at the end of the rod, finds the opposite slot and snugly fits into it. The slot 81 is only slightly wider than the first knifeshutter, with a'clearance of about 0.005 inch, and it is imperative that there be no difficulty in fitting the shutter into the slot or the shutter will snap. When the first knife-shutter 71 is closed, it forms a light-lock to prevent any extraneous light from damaging the sensitive phototube. With the knife-shutter 71 ina closed position, the second knife-shutter 72 is then retracted and it permits the card to fall on a third knife-shutter 73, the sole function of which is to position the card for reading the first dosimeter, i.e., the lowerof the two dosimeters. As soon as the card 13 is dropped from its second position, the second knife-shutter 72 is closed by being thrust into a second slot 82, disposed in the sub-front plate assembly 17, which slot is adaptedto snugly accommodate the second knife-shutter 72 in light-locking engagement.

The card 13 is now resting on the third knife-shutter 73 in a reading position to permit the lower dosimeter 22 to be read. If there was only one dosimeter on a card, it would be apparent that the third knife-shutter 73 would be unnecessary. After the lower dosimeter 22 is read, as will be explained hereinafter, the card is dropped into a fourth position on a fourth knife-shutter 74, which is similar to and directly below the first and second knife-shutters, and is positioned so as to locate the card in position for reading the second or upper dosimeter 22. The third light-tube 53 permits a check for the location of the position of the card. In this fourth position of the card, for readout of the upper dosimeter, the third knife-shutter 73 remains retracted. After the second or upper dosimeter is read, the fourth knifeshutter 74 is retracted to permit the card to fall on a fifth knife-shutter 75, whereupon the fourth knifeshutter 74 is immediately closed in the same manner as the preceding knife-shutters, by being fitted into lightlocking engagement into an oppositely disposed third slot 83 in the sub-front plate assembly. On the fifth position the card is identified, or where identification is frustrated, the machine is stopped, indicating an incorrect identification on the card. From the fifth position on the fifth knife-shutter 75, the card is then fallingly discharged into the auto-receiver l4, and the fifth knife-shutter 75 is thrust into light-locking engagement with a fourth slot 84 and returned to its normally closed position.

A calibrating knife-shutter 70 is provided next to but outside of the vertical chute defined by the oppositely disposed guides 29. The

calibrating knife-shutter assembly is retractably disposedhorizontally within the door assembly, as are the other knife-shutter assemblies, but is positioned so that the knife-shutter is vertically disposed. Like the other light-locking shutters, an oppositely disposed vertical slot is provided in the sub-front assembly plate into which the calibrating knife-shutter 70 may be fitted in light-locking engagement. The function of the calibrating knife-shutter 70 is to provide a light-lock against the calibrating light 40, and it is retracted when the phototube is to be calibrated. An infrared screen 42 is provided at the fifth position to screen out all but the infrared radiation from an incandescent light source. The function of the infrared screen is to permit identification readout of the card with infrared light, thus avoiding subjecting the phototube to the possibility ofa light leak in the visible spectrum.

The entire door assembly 16 with the integral card holder is swingably disposed on pivots 41 which areaccommodated in close-clearance holes 43 at the top and bottom of the door assembly. When the door assembly is closed for readout of cards, additional locating bolts 44 are used to precisely position the door assembly against the sub-plate assembly 14 so that the slots for the knife-shutters are precisely oppositely disposed to them.

The heating element assembly, shown generally at 39 in a phantom position in FIG. 8 and in detail in the enlarged views of FIGS. 13 and 14, is dismountably disposed on the door assembly 16 so as to enable the heating element 35 to be thrust into heat-conductive contact with an encapsulated dosimeter 22 which is presented for readout. The heating element 35 is a rectangular piece of chrome molyalloy adapted to be heated to a specific temperature, about 280C., which is monitored and maintained with a thermocouple and related controlling equipment. The temperature to which the heating element is heated will depend upon the characteristicof the dosimeter which may require heating to a temperature in the range from about 250 to 450C. Twin flexible strips 45 are bridged by the heating element 35. Immediately behind the heating element 35 is an insulating end cap 46 adapted to engage a thrust rod 47 ofa solenoid. An end-cap 50 is provided on the heating element assembly which snugly engages the thrust rod 47 to accurately position the heating element 35 upon the encapsulated dosimeter. The thrust rod 47 is disposed through the door assembly l6 and is actuated by the solenoid on that side. Leads 48 bring electric current to the heating element. The ends of the flexible strips 45 opposite the end carrying the heating element are fixedly disposed upon the door so as to make the heating element 35 resiliently reciprocable into and out of heat-conductive contact with a dosimeter to be read.

Thermocouple leads 49 from the heating element 35 transmit the temperature to a controler which is adapted to maintain the heating element at a predetermined temperature. Controls are provided to maintain the heating element in heat-conductive contact with the encapsulated dosimeter for a preselected period of time in the range from 10 to about seconds, with a provision for heating the dosimeter continuously for an extended period of time up to several hours if so desired. An inert gas purge, usually a nitrogen purge is maintained around the encapsulated dosimeter while it position.

9 is heated and cooled. The amount of inert gas flow may be varied, but sufficient gas is used to permit reproducible readings.

FIG. 7 is a view along the line 7-7 in FIG. 6 in the direction of the arrows, which shows a front view of the sub-front plate assembly 17 and details of the slots 80-84 which snugly accommodate the knife-shutters to form light-locks.

FIG. 8.is a view along the line 8-8 is FIG. 6 in the direction of the arrows, which shows the vertical chute, the knife-shutters 71-75 all in theirnormal position for reading the lower dosimeter of the card. After the lower dosimeter is read the knife-shutter 73 is retracted and the upper dosimeter is positioned for reading when the card comes to rest on knife-shutter 74. If only the upper dosimeter on each card is to be read, the knifeshutter 73 is maintained in its retracted position.

FIG. 9 is a side elevation section on an enlarged scale approximately along the line 9-9 in FIG. 8 to show details of the solenoid-actuated knife-shutters mounted in the door assembly 16, and light pipes to determine the position of a card as it is sequentially dropped from one position to a subsequent lower position. Details of a knife-shutter in FIG. 10 show the normal position in light-locking engagement with a slot in the sub-front plate assembly and a phantom-position of the knifeshutter in its retracted position.

The shutter 73 which positions the lower dosimeter for reading is seen in FIG. 11 which also shows the positions of the heating element in heating position and in the retracted cooling position (phantom view). It is seen that no light-locking slot is necessary to accommodate the knife-shutter 73 which only positions the lower dosimeter. The calibrating light may beused when required by retracting the knife-shutter 70. As shown in FIG. 11, the calibrating,knife-shutter is in its normal FIG. 12 is a plan section view on an enlarged scale along the line 12-12 in FIG. 8, and shows the mirror 54 which reflects light on to the infrared screen 42 through which only infrared light passes. It is this light which is effective to correctly identify the code-holes in the card. For example, where a code-hole is accidentally blocked, as for example by a particle of dirt or foreign matter, the parity checking system permits the instrument to recognize this fact, and automatically record the correct identification. If however, two holes are blocked, the parity checking system is unable to correctly identify the identification on the card and the machine stops. The operator can then remove the card and visually read the correct number, printed on the card, which corresponds to the proper coding. Thus, the rejected card is properly identifiable.

It will be apparent that electrical circuitry is required to transmit the reading of the dosimeter to the-integrating pico ammeter, which relays the level of the reading to a digital comparator which in turn transmits the information in suitable terms for print-out by a teletypewriter. The electrical circuitry by which the foregoing signals are adapted to be recorded are old and form no part of the instant invention.

We claim:

1. In an automatic thermoluminescent dosimetric system comprising a detector-dosimeter identifier, means for measuring light output, and means for presenting the readings obtained in said detector-dosimeter identifier, the improvement consisting of automatic loading means disposed above said detector-dosimeter identifier comprising means for selectively ejecting a single card from a multiplicity of cards upstandingly stacked in a card-holding cartridge, into a vertical chute integral with a door-assembly removably disposed in abutting relationship with a sub-front assembly disposed in front of a photosensing'means in said eter to a predetermined temperature for a preselected amount of time by contacting said encapsulated dosimeter in heat-conducting relationship and means for retracting a knife-shutter upon which said card is resting, after said dosimeter is read, so as to permit said card,

after it is identified, to be fallingly discharged from said chute under the action of gravity.

'2. The apparatus of claim 1 including logic to permit at least thermoluminescent dosimeters or chips to be read sequentially, to bypass one and readthe other, or to read one and, depending upon a predetermined level of its reading, to bypass the other. I

3. The apparatus of claim 1, including means for receiving said fallingly discharged cards and sequentially stacking them in a. cartridge disposed below said machine.

4. The apparatus of claim 1, wherein the knife shutters are programmed to be sequentially operated to permit reading of a single dosimeter, or a programmable combination of plural dosimeters, in a, light-locked zone.

5. The apparatus of claim 4, whereinsaid knife shutters are solenoid-actuated spring-biased .T-shaped members, the arms of which represent a flexible knife shutter, having a thickness in the range from 0.0l00.063 in., loosely disposed on the end of the bar of the T so as to permit said knife shutter to find and accommodate itself within a snugly embracing slot oppositely disposed thereto, to effect a light lock.

6. The apparatus of claim 1 wherein said card is identified by infrared radiation codedly transmitted through preselected locations in a grid pattern on said card adapted to identify said card with a parity checking system.

7. The apparatus of claim 1 wherein said encapsulated dosimeter is positioned for reading at a distance less than 2.5 cm from the face of said sensing phototube.

Andras Szalanezy, Erwin F. Shrader, Bruce M. Shofiner, and

James D. Chamberlain Application having been made by Andras Szalanczy, Erwin F. Shrader, Bruce M. Shoffner, and James D. Chamberlain, the inventors named in the patent above identified, and Kewanee Oil Company, Bryn Mawr, Pa., a corporation of Delaware, the assignee, for the issuance of a certificate under the provisions of Title 35, Section 256, of the United States Code, adding the name of Francis Morgan Cox as a joint inventor, and a showing and proof of facts satisfying the requirements of the said section having been submitted, it is this 30th day of September 197 5, certified that the name of the said Francis Morgan Cox is hereby added to the said patent as a joint inventor with the said Andras Szalanezy, Erwin F. Shrader, Bruce M. Shoifner, and James D. Chamberlain.

FRED W. SHERLING, Associate Solicitor.

Claims (7)

1. In an automatic thermoluminescent dosimetric system comprising a detector-dosimeter identifier, means for measuring light output, and means for presenting the readings obtained in said detector-dosimeter identifier, the improvement consisting of automatic loading means disposed above said detector-dosimeter identifier comprising means for selectively ejecting a single card from a multiplicity of cards upstandingly stacked in a cardholding cartridge, into a vertical chute integral with a door assembly removably disposed in abutting relationship with a subfront assembly disposed in front of a photosensing means in said detector-dosimeter identifier, at least four automatically actuated, sequentially staged knife shutters disposed in vertically spaced-apart relation within said door assembly and adapted to be fitted in light-locking engagement around a reading zone, means for positioning said card within said reading zone to present a dosimeter in heating position, a cyclically heated heating element reciprocably disposed within said door assembly to heat an encapsulated thermoluminescent dosimeter to a predetermined temperature for a preselected amount of time by contacting said encapsulated dosimeter in heat-conducting relationship and means for retracting a knife-shutter upon which said card is resting, after said dosimeter is read, so as to permit said card, after it is identified, to be fallingly discharged from said chute under the action of gravity.

2. The apparatus of claim 1, including logic to permit at least thermoluminescent dosimeters or chips to be read sequentially, to bypass one and read the other, or to read one and, depending upon a predetermined level of its reading, to bypass the other.

3. The apparatus of claim 1, including means for receiving said fallingly discharged cards and sequentially stacking them in a cartridge disposed below said machine.

4. The apparatus of claim 1, wherein the knife shutters are programmed to be sequentially operated to permit reading of a single dosimeter, or a programmable combination of plural dosimeters, in a light-locked zone.

5. The apparatus of claim 4, wherein said knife shutters are solenoid-actuated spring-biased T-shaped members, the arms of which represent a flexible knife shutter, having a thickness in the range from 0.010-0.063 in., loosely disposed on the end of the bar of the T so as to permit said knife shutter to find and accommodate itself within a snugly embracing slot oppositely disposed thereto, to effect a light lock.

6. The apparatus of claim 1 wherein said Card is identified by infrared radiation codedly transmitted through preselected locations in a grid pattern on said card adapted to identify said card with a parity checking system.

7. The apparatus of claim 1 wherein said encapsulated dosimeter is positioned for reading at a distance less than 2.5 cm from the face of said sensing phototube.

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