Dosimeter reading apparatus with optical laser converter

Disclosed is a laser dosimeter reading apparatus having a controllable optical laser converter for providing multiple stimulating laser beams. The convertible laser dosimeter reader can be used to stimulate or otherwise treat dosimeter elements to perform two or more distinct processes on a particular dosimeter element. Additionally, the convertible dosimeter reader can be used to read multiple different types of dosimeter elements contained on a single dosimeter badge, thereby allowing a badge to be read in a multi-stage reading operation in a single dosimeter reader which is preferably automated. The optical laser converter includes a converter block assembly which defines multiple optical pathways therethrough. The convert block assembly is movable between different positions to align the different optical pathways with an incoming laser beam. The output laser beams from the different optical pathways of the converter have differing laser beam characteristics suitable for different types of dosimeters or differing treatment processes. The output beams from the optical pathways are preferably passed through an imaging assembly which images the beams onto the dosimeters being stimulated or for other uses as the laser beam converter may be utilized. The disclosure also includes methods for converting a laser beam and for reading radiation dosimeters.

TECHNICAL FIELD 
The technical field of this invention is radiation dosimeter reading 
apparatus and methods using laser beam optical converters for producing 
multiple types of stimulating beams. 
BACKGROUND OF THE INVENTION 
It is well-known in the art that certain materials called phosphors can be 
irradiated with high energy ionizing radiation, and then subsequently 
stimulated to produce an emission. Thermoluminescent phosphors are 
currently in widespread use in radiation dosimeters used to measure the 
amount of incident radiation to which people, animals, plants and other 
things are exposed. Thermoluminescent dosimeters are widely used by 
workers in the nuclear industries to provide a constant monitor for 
measuring exposure to radiation. 
Phosphors are excited by energetic radiation such as ultraviolet, X-ray, 
gamma, and other forms of radiation. Such ionizing radiation causes 
electrons within the thermoluminescent material to become highly 
energized. The nature of thermoluminescent materials causes these high 
energy electrons to be trapped at relatively stable higher energy levels. 
The electrons stay at these higher energy levels until additional energy, 
usually in the form of heat, is supplied which releases the trapped 
electrons, thereby allowing them to fall back to a lower energy state. The 
return of the electrons to a lower energy state causes a release of energy 
primarily in the form of visible light which is ordinarily termed a 
luminescent emission. 
The use of thermoluminescent phosphors in personnel dosimeters has led to 
demand for a large number of dosimeters which must be read on a routine 
basis in order to monitor exposure of persons or other objects to ionizing 
radiation. Because of the substantial numbers and the relatively slow 
reading techniques currently employed, the job of reading dosimeters 
becomes very time consuming and costly. 
There are four commonly known methods of heating thermoluminescent material 
in order to release the trapped electrons and provide the luminescent 
emission which is measured as an indication of the amount of ionizing 
radiation to which the dosimeter was exposed. The first and most common 
method for heating thermoluminescent phosphors is by contact heating. The 
second method is heating using a hot gas stream which is impinged upon the 
phosphor. The third method uses radiant energy in the form of infrared 
beams which heat the thermoluminescent phosphor. The fourth method uses 
infrared laser beams to provide the necessary heat for luminescent 
emission. 
Novel methods and apparatuses for laser reading of thermoluminescent 
phosphor dosimeters are disclosed in detail in U.S. Pat. Nos. 4,638,163 
and 4,839,518 incorporated by reference hereinabove. One of the inventors 
of this invention and his colleagues have developed laser reading 
techniques and dosimeters, as disclosed in an article entitled "Laser 
Heating In Thermoluminescence Dosimetry," by J. Gasiot, P. Braunlich, and 
J. P. Fillard, Journal of Applied Physics, Vol. 53, No. 7, July 1982. In 
that article, the authors describe how thin layers of thermoluminescent 
phosphors can be precipitated onto glass microscope cover slides and used 
as laser readable dosimeters. Powder layers of the phosphors were in some 
cases coated with a thin film of high temperature polymers. The content of 
said article is hereby incorporated hereinto by reference. 
Laser heating of thermoluminescent phosphors is superior because of the 
greatly decreased heating times and associated increased processing rates 
which are possible. Release of stored luminescent energy within a short 
period of time greatly improves signal-to-noise ratios and thus the 
accuracy of dosimeter measurements. 
It is desirable in the monitoring of radiation dosage to discriminate 
between different types of radiation. In the case of some types of 
radiation it is desirable or necessary to use specific forms of dosimeters 
for detecting and measuring that type of radiation as distinct from other 
types of dosimeters used for detecting other forms of radiation. For 
example, the measurement of gamma radiation can be accomplished using a 
single thermoluminescent dosimeter element which is heated uniformly to a 
desired temperature thus causing a thermoluminescent emission to occur. 
The thermoluminescent emission is measured and the resulting luminescence 
is interpreted and has been found useful as an accurate measurement of the 
amount of ionizing radiation to which the dosimeter was exposed. 
Alternatively, it is possible to heat a large number of small localized 
areas of a dosimeter to identify the approximate number of localized areas 
which have been ionized by the impingement of a heavy charge particle. The 
proportion of areas which have experienced such a heavy charged particle 
event can used as an indication of the amount of heavy particle radiation 
to which a dosimeter has been exposed. Such radiation dose measurement 
techniques are appropriate for radiations such as alpha particles and 
neutrons among others. The methodology of such dose measurement techniques 
is further explained in the incorporated by reference parent application 
Ser. No. 336,015. 
In addition to the heat stimulation of phosphors it is also possible to 
stimulate them with laser beams in a phenomenon call optically stimulated 
luminescence. In optically stimulated luminescence the laser beam is 
directed in an intense beam having high power for very brief periods of 
time. This form of laser stimulation is explained in U.S. Pat. No. 
4,507,562 which is hereby incorporated by reference. 
In light of these differing approaches for measuring gamma radiation versus 
heavy particle radiation, and other differing laser dosimeter reading 
techniques, it has not been practical to include dosimeters on a single 
badge having differing stimulating laser beam requirements and accordingly 
some forms of radiation have not been monitored. It has further not been 
possible to use a single laser dosimeter reader to stimulate radiation 
dosimeters having distinct beam requirements. Accordingly, there has been 
a need in the art for laser dosimeter reading equipment which can read 
multiple types of radiation dosimeters having differing stimulating beam 
requirements using a single laser source.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The following disclosure of the invention is submitted in furtherance with 
the constitutional purpose of the Patent Laws "to promote the progress of 
science and useful arts" (Article 1, Section 8). 
FIG. 1 shows a portion of a preferred laser dosimeter or phosphor reading 
apparatus 9 according to this invention. Dosimeter reading apparatus 9 is 
similar in construction to the phosphor reading apparatuses described in 
the incorporated by reference U.S. Pat. No. 4,839,518, specifically at 
pages 8-33 and associated FIGS. 
Dosimeter reader 9 includes a laser beam source means 10 which generates a 
suitable laser beam 16 for use in stimulating the particular type of 
phosphor or other radiation sensing and storing material used to detect 
the radiation dose. The laser beam source 10 can be a laser, such as a 
wave guide or non-wave guide laser of desired stimulating frequency or 
wavelength. When the dosimeter being read uses a thermoluminescent 
phosphor a suitable type of laser is preferably an infrared carbon dioxide 
(CO.sub.2) laser having an approximate wavelength of 10 micrometers. Other 
lasers having beams in the infrared and visible ranges of the 
electromagnetic spectrum can alternatively be used. When the dosimeter 
dose storage material or phosphor is of a type suited for optically 
stimulated luminescent emission then a higher frequency laser, such as a 
neodymium yttrium aluminum garnet laser (Nd:YAG) laser or dye laser having 
an approximate wavelength of 1 micrometer is preferably used as laser 
source 10. Lasers having wavelengths of 0.1-1 micron are alternatively 
possible, as are other lasers providing beams in the ultraviolet range of 
the electromagnetic spectrum. Optically stimulated luminescence and the 
reading of phosphors using optically stimulated luminescence is explained 
in greater detail in U.S. Pat. No. 4,507,562, entitled "Methods For 
Rapidly Stimulating Luminescent Phosphors and Recovering Information 
Therefrom", issued Mar. 26, 1985 which is hereby incorporated into this 
document by reference in its entirety. 
Laser source 10 advantageously includes a laser head 12 having a laser 
cavity 11, and preferably a laser cooling and temperature stabilization 
unit 13. Cooling and stabilization unit 13 helps to maintain the laser 
beam 16 within an acceptable range of frequency or wavelength output. 
Laser head 12 is powered by an electronic laser power supply 15. Laser 
head 12 and laser power supply 15 are preferably selected to allow 
modulation of the laser power output. The preferred modulation is pulse 
width modulation at radio frequencies as explained in greater detail in 
the incorporated U.S. patent application Ser. No. 882,953 now U.S. Pat. 
No. 4,839,518. A suitable laser is Model B48-1-115 from Synrad, Inc., 
having a modulation frequency of 30 kHz. 
The preferred laser source includes suitable means for providing a fixed 
orientation polarized laser beam 16. The polarizer or other equivalent 
polarization means is preferably incorporated into the laser source, but 
can alternatively be provided in the form of an initial optical polarizing 
element 118 which is not incorporated into the laser. Fixed polarization 
is desired because the mirrors and other optical elements typically have 
some variations in reflectance or other optical properties which vary 
dependent upon the polarization orientation of the laser beam 16. 
The emitted laser beam 16 is advantageously directed using any desired 
mirror arrangement as the particular arrangement of the dosimeter reader 
suggests or requires. FIG. 1 shows an arrangement utilizing two mirrors 17 
and 30. The mirrors are most preferably gold coated copper mirrors having 
a flat reflective surface. 
FIG. 1 also shows a beam splitter 18 which allows most of the laser beam to 
continue therethrough, but reflects a detector beam 21. The beam splitter 
18 can advantageously be a zinc selenide window having anti-reflection 
coating on one side. The uncoated face is used to reflect the detector 
beam 21. The beam splitter is preferably made with non-parallel faces to 
prevent coincident interfering reflections from being directed to a laser 
power detector 20 from both faces of the beam splitter. 
Detector beam 21 is directed through a beam interrupter, such as a chopping 
wheel 23 with one or more apertures 24, and then to the laser power 
detector 20. The chopping wheel or other beam interrupter is needed when 
the laser power detector performs better with an intermittent detector 
beam. When laser power detectors are used which can continuously monitor 
the beam, then no beam interrupter is needed. A preferred type of laser 
power detector is a pyroelectric detector having a lead zirconate titanate 
detector element available from Barnes Engineering, Div. of EDO 
Corporation, Model 350-2. Such a pyroelectric detector is preferably used 
with a beam interrupter. An alternative arrangement and type of laser 
power detector is also shown in connection with FIG. 2 and is described 
below. 
The laser power detector produces an electronic output signal which is 
communicated to a laser power signal enhancer 62 to improve the signal's 
characteristics. The resulting enhanced signal is communicated to an 
analog-to-digital (A/D) converter 200 which produces a digital signal 
representative of the laser power level at particular measurement points 
in time, dependent upon the output signal of the laser power detector and 
the frequency rate at which the A/D converter scans it's input signal from 
the laser power signal enhancer 62. 
The digital laser power signal from A/D converter 200 is communicated to a 
computer or other digital controller 202. The computer preferably stores 
information indicative of the laser power with time. Computer 202 also 
processes the digital laser power signal from converter 200 relative to a 
desired and adjustable laser power level which is programmed into the 
computer. The comparison of the measured laser power level against the 
predetermined laser power level target produces a power control output 
signal which is suitably processed, such as through a digital-to-analog 
converter 206. Converter 206 provides an analog laser power control signal 
which is communicated to a modulation circuit 70. Modulation circuit 70 
outputs a modulation signal which is communicated to laser power supply 15 
in order to control the power of the laser beam 16 output from laser 
source 10. 
The laser power modulation and control system just described allows the 
instantaneous power level of the laser beam to remain at a desired level. 
The desired laser power level can remain constant or vary during the 
heating or other reading or stimulating cycle to best stimulate and 
extract the dose exposure information. 
As shown, laser beam 16 is controlled by an exposure shutter 26 which is 
downstream from the beam splitter 18. Alternatively, exposure can be 
controlled by turning the laser source on and off. Any exposure shutter 
can be of a variety of types, and is preferably provided with an 
electrically controlled shutter actuator to enable computer 202 to control 
the shutter and resulting exposure of the dosimeters to the laser beam. 
The reflected laser beam 16a from the shutter when closed is preferably 
dissipated in any suitable beam dump 28. The controlled laser beam emitted 
from the shutter when open is supplied directly to remaining parts of the 
system or beamed against the second mirror 30 to provide the desired 
position, orientation and adjustment capability. 
FIG. 2 shows additional portions of the preferred dosimeter reading 
apparatus 9 according to this invention as adapted to carry out the novel 
methods of the invention. FIG. 2 indicates that the shutter controlled 
laser beam is preferably passed through a short focal length focusing lens 
301 which directs the beam toward an optional aperture means 302. Lens 301 
is advantageously constructed of zinc selenide with an anti-reflective 
coating when transmitting the approximately 10 micron wavelength laser 
beam used in the thermoluminescent dosimeter reading applications among 
those contemplated by this invention. Focusing lens 301 preferably 
converges the beam to a focal point from which the beam diverges toward 
any aperture means. Aperture means 302 is a non-transmissive plate having 
preferably one opening or aperture which can be of suitable configuration, 
such as a circular hole (as shown), circular annular ring (not shown), or 
other suitable configurations. Aperture means 302 is included to reduce 
the amount of the laser power and/or to minimize the beam size. 
FIG. 3 shows an alternative form of dosimeter reader 9a which is very 
similar to the embodiment of FIG. 2 with the addition of an optical 
equalizer means 31 in the form of a reflective optical channel 34. The 
laser beam is directed into the channel through lens 32 which diverges the 
beam into the channel. In the channel the beam is reflected and equalized. 
The beam emitted from the channel is of more uniform laser power density 
and can be used for dosimeters not requiring very small laser beam 
focusing. 
Referring to either FIG. 2 or FIG. 3, the beam emitted from the aperture 
302 or equalizer 31 is preferably directed onto a dosimeter being read, 
such as dosimeter 330, using a suitable beam imaging subsystem 304. The 
imaging subsystem can be arranged in various ways. As shown, imaging 
subsystem 304 includes a first imaging lens 305 which receives the beam 
emitted from any aperture means 302 or equalizer 31. Lens 305 is 
preferably selected to receive the diverging beam and refract the beam to 
provide preferably parallel beam rays. The substantially parallel or other 
suitable beam from lens 305 is reflected from an imaging mirror 308. The 
reflected beam from mirror 308 is advantageously passed through a second 
imaging lens 309 which focuses the beam for appropriate beam size as the 
beam impinges on the dosimeter 330. 
The dosimeter reader can also be adapted to accommodate a laser power 
detector 320 and related components near the beam imaging subsystem. Such 
laser power detector functions in substitution to laser power detector 20 
or in addition thereto to provide increased potential for accurate laser 
power control. Laser power detector 320 receives and measures the 
intensity of a partially reflected detector beam 16b which is split from 
the main laser beam by beam splitter 318. Beam splitter 318 is similar to 
beam splitter 18 described above. Laser power detector 320 is shown as a 
laser power detector which can continuously monitor without the need for a 
beam interrupter, such as chopping wheel 23. A suitable type of continuous 
laser power detector is a photoconductor, such as a mercury cadmium 
telluride photoconductor. A suitable commercially available model is made 
by ElectroOptical Systems, Inc., Model MCT10TE1. Other suitable 
photoconductors may also be appropriate for use in dosimeter reading 
apparatus made in accordance with this invention. 
FIGS. 2 and 3 show that dosimeter readers 9 and 9a also preferably include 
an emission detection subsystem 350. Emission detection subsystem 350 
preferably includes an emission collection means such as reflective 
emission collector and conduit 351 which is adjacent the dosimeter 330. 
Although FIGS. 2 and 3 show the dosimeter spaced downwardly for 
diagrammatic ease of illustration, in preferred arrangements the dosimeter 
will be positioned close to the collector 351 to increase the sensitivity 
of the dosimeter reader. Emission collector 351 includes or is immediately 
adjacent to a specimen opening 352 which allows the stimulating beam to 
pass to the dosimeter, and allows the emitted energy from the dosimeter to 
be concentrated and conveyed to a suitable emission detector 355. The 
emission collector 351 is preferably reflectively coated along interior 
surfaces, and advantageously formed as a semi-cylindrical conduit with the 
curved side upward as shown in FIG. 2. The area below the beam splitter 
318 is advantageously formed as an ellipsoidal reflector which directs the 
reflected luminescent emission from the dosimeter longitudinally along the 
semi-cylindrical collector 351 toward emission detector 355. 
Emission detector 355 is advantageously a photomultiplier tube which 
provides an output signal indicative of the luminescent emission made by 
dosimeter 330 with time. A variety of suitable photomultipliers are 
potentially of use in dosimeter readers according to this invention. Other 
alternative detectors can also be used as needed for the particular type 
of dosimeter or other radiation sampling device which is being stimulated 
to emit energy indicative of the level of radiation exposure experienced. 
The output from the photomultiplier or other emission detector is 
preferably output to an emission signal processing and memory unit 52 
which can provide signal amplification, digitalization, visual display, 
and/or transformation into a suitable form of permanent data storage. It 
is desirable that the output signal with time be carefully recorded in the 
preferred dosimeter reading apparatus according to this invention. Many, 
if not all, of the functions of unit 52 can be performed on either a 
discrete processor unit or using suitable programming and computer 202. If 
discretely processed the output from unit 52 is communicated to computer 
202 for processing or vice versa to allow integration of the stimulation 
and emission information. 
FIGS. 2 and 3 also show that dosimeter reading apparatus 9 and 9a 
preferably includes a suitable dosimeter holding and positioning means 
370. Dosimeter positioner 370 is advantageously an X--Y positioning device 
constructed to allow automated control of the X and Y positioning 
coordinates. Positioner 370 includes two Y direction slide bars 372 which 
allow the Y positioning stage 374 to move back and forth in the Y 
direction. A suitable Y direction drive is included such as the Y drive 
375. Y drive 375 includes a threaded receptacle 376 on the Y positioning 
stage. A lead screw 377 is threadably received in the receptacle 376. A 
lead screw motor 378 is mounted to the frame 371 and is used to turn the 
lead screw thus causing the Y stage to slide on the slide bars 372. Motor 
378 is preferably a highly accurate stepper motor. Optionally, an encoder 
can be incorporated into the motor and used to detect the motor position 
and produce a feedback position signal indicating the position of the 
stage. 
Dosimeter positioner 370 similarly includes an X positioning stage 380. X 
positioning stage 380 is slidably mounted on two X direction slide bars 
382 which are secured to the Y stage 374 in a manner allowing the motion 
of X stage 380. The X stage 380 also preferably includes a threaded 
receptacle 386 which receives an X lead screw 387. A further stepper motor 
388 turns lead screw 387 thus driving the X stage in the same manner as 
the Y stage, except in an orthogonal direction. 
The X stage can also advantageously be provided with one or more dosimeter 
or other sample holding devices 390 to secure the dosimeter in position. 
The dosimeter positioning means 370 functions as a holder for the 
dosimeter 330, and is further adapted to include the lateral restraints or 
holders 390. The lateral dosimeter holders engage the dosimeter applying 
downward force in a spring clip arrangement which serves to restrain the 
dosimeter against inadvertent dislodgment. A variety of means for holding 
the dosimeters are possible, including application of a vacuum to the 
lower surfaces of the dosimeter through holes in the X stage (not shown). 
The dosimeter positioning arrangement and construction allows the dosimeter 
330 to be moved relative to the focused laser beam point 16d to heat, 
optically stimulate, or otherwise stimulate the dosimeter phosphor or 
other suitable dose storage material. The drive motors 378 and 388 are 
preferably controlled by computer 202 so that automated movement of the 
dosimeter positioning device can be accomplished. This allows effective 
scanning of the dosimeter by the stimulating beam and other types of 
relative positioning to be accomplished in order to practice the novel 
methods of this invention as explained more fully hereinafter. 
FIGS. 4 and 5 diagrammatically show a preferred laser beam converter 
apparatus 400 adapted for use in a radiation dosimeter badge reading 
application. Laser beam converter 400 is positioned adjacent to the X--Y 
positioner and dosimeter holder 370 described above and similar reference 
numerals are used. The laser converter 400 includes a frame 451. The frame 
mounts a converter block 402 using a shaft 403. The converter block is 
connected to a converter block drive gear 404. Converter block drive gear 
404 is turned through a limited arc of approximately 180.degree. by a 
stepper motor 407 using output pinion gear 408 which meshes with the drive 
gear. 
The optical laser converter 400 defines two different optical pathways for 
the incoming laser beam 16. The first optical path 410 is shown aligned to 
receive and transmit the incoming laser beam 16 in FIG. 4. The second 
optical pathway 420 is shown aligned to receive and transmit the incoming 
laser beam 16 in FIG. 5. Both optical pathways 410 and 420 are defined by 
passageways formed through the converter block 402. 
The first optical pathway 410 includes a lens 432 which is similar to lens 
32 described hereinabove. Lens 432 disperse the incoming laser beam 16 
into a reflectively lined optical equalizer channel 431a formed in an 
optical equalizer insert 431. The optical equalizer 431 is mounted within 
the first passageway 411 formed in the converter block 402. A spacer tube 
412 is used to hold the lens 432 in position against a shoulder 413 formed 
along the incoming face of the converter block adjacent to the first 
passageway incoming opening 414. The equalized laser beam emits from the 
emission end of the optical equalizer, which is the left end as shown in 
FIG. 4. The equalized output laser beam passes through an outlet passage 
418 formed in the gear 404. The output beam then advantageously enters an 
imaging block section 460 which is preferably used in the optical laser 
converter 400. 
FIG. 5 shows the converter block rotated 180.degree. relative to FIG. 4, 
thus bringing the second optical pathway 420 into alignment with the 
incoming laser beam 16. The second optical pathway is arranged through a 
second passageway 421 formed through the converter block 402. The incoming 
laser beam 16 is first passed through a beam splitting mirror 422 which 
partially reflects a secondary laser beam 423 downwardly and into a cavity 
424 which serves as a beam dump to dissipate the energy of the secondary 
laser beam. The beam splitter 422 serves to reduce the amount of power 
contained in the laser beam which is output from the second optical 
pathway 420. 
The reduced power laser beam transmitted through the beam splitter 422 is 
passed to a lens 425 which serves as an initial element in the imaging of 
the laser beam when it is transmitted through the second optical pathway 
420. This second pathway converter lens 425 is held in position by a 
mounting tube 435. Second pathway converter lens 425 also serves in 
conjunction with an aperture to a power reduction capacity by focusing and 
dispersing the beam which it outputs for diminution by the aperture. The 
output beam from the second optical pathway is passed through or about 
power reducing aperture 426 which is advantageously mounted as near the 
imaging lens 461 as practicable, such as at the emission side of the 
passageway 427 formed through the gear 404. FIG. 5A shows that the power 
reducing aperture 426 can advantageously be formed by positioning a small 
circular occlusive element 428 within the passage 427, such as by using 
small circular holder 426a which mounts supporting wires 429 which suspend 
the occlusive element 428. This aperture construction reduces the laser 
beam power further by occluding the center, most power portion of the 
laser beam. It works in addition to the power reduction by the beam 
splitter 422, and is independent with respect thereto. 
The optical laser converter 400 also advantageously includes the imaging 
block 460 which appropriately directs and images the laser beams output 
from the converter block first and second optical pathways 410 and 420. 
The imaging system included in imaging block 460 advantageously includes a 
first imaging block lens 461 which receives the diverging first and second 
output laser beams from the first and second optical pathways. The first 
imaging block lens 461 renders the enlarged output laser beams into 
parallel ray beam formations. The parallel ray beams are then reflected 
from the front inside surface of a surface coated mirror 463. Mirror 463 
is held in position by a retainer 464 which is fastened to the frame 
structure 451 using fasteners (not shown). The reflected beam from imaging 
mirror 463 is directed to a second imaging lens 467 which focuses the 
first or second output laser beams onto the dosimeter 330. 
As FIG. 4 indicates the first stimulating beam output after passage of the 
laser beam through the first optical pathway produces a relatively larger 
heating beam. The optical equalizing channel 431a is preferably square in 
cross-section thus producing an imaged stimulating beam which is about 2-4 
millimeters along each side and substantially square as shown on the 
dosimeter 330. This beam can be used to heat dosimeters to cause 
thermoluminescent or other emissions to occur as is well-known in the art. 
The large beam can also be used to laser anneal dosimeters by providing a 
relatively uniform, equalized, laser beam. The power level of the 
stimulating beam can also be adjusted as explained hereinabove to a 
desired laser power level, which in the case of annealing operations can 
be relatively low power. 
FIG. 5 indicates that the second stimulating beam output after passage of 
the laser beam through the second optical pathway produces a very small 
highly focused beam which is preferably less than 100 microns is diameter. 
The stimulating beam is preferably approximately 3-10 wavelengths of the 
infrared laser beam in diameter, approximately 30-100 microns in diameter. 
This very small stimulating laser beam can thus be used to heat very 
small, localized regions of a dosimeter to perform radiation dosimetry by 
counting differentially ionized sample areas from heavy charged particle 
events as explained in the co-pending incorporated by reference parent 
application, Ser. No. 336,015. 
FIGS. 4 and 5 further show an output beam splitter 478 which produces a 
secondary output beam directed at an output beam detector 479. Dectector 
479 can be similar to laser power detector 20 described hereinabove, or an 
alternative detector for alternative purposes. The use of an output beam 
detector allows more accurate monitoring of the actual laser beam power 
used to stimulate the dosimeters. 
FIG. 6 shows a preferred form of dosimeter reading apparatus 100 according 
to this invention. Dosimeter reading apparatus 100 includes a front panel 
101 which includes a digital display 102 and printer 103. The display 102 
displays operational commands and dose exposure information. The printer 
can print dose exposure information. Two ventilation covers 104 and 105 
are shown covering an exhaust vent and fan intake, respectively. A 
dosimeter read cycle activation switch 106 is pushed to start the reading 
cycle. A printer control switch 107 is used to control operation of an 
auxiliary, external printer or plotter 402 (FIG. 16) which can be used to 
print the dose information displayed by display 102 and luminescent glow 
curves measured in producing the dose information. A power on-off switch 
108 is also mounted on the front panel, as is an hour meter 109 which 
indicates total operational time. 
The front panel also mounts a power cord 120 for providing 120volt a-c 
power to the reader. An electrical connector 122 includes electrical 
conductors which are appropriately connected to key signal and circuit 
components for use in diagnosing electrical system problems which might 
develop in the reader. The electrical connector also serves as an 
electronic signal port for connecting an external computer to the reader 
for programming the reader and to advantageously serve as an external data 
storage 401 (FIG. 16), either in addition to or in substitution of data 
storage mounted on the reader 100. A signal output connector 123 is 
provided to transmit glow curve and dose information signals to the 
auxiliary printer or plotter 402 (FIG. 16). A fuse receptacle 124 and 
spare fuse receptacle 125 are also shown. 
Handles 130 and 131 are mounted to the front panel to aid in disassembly of 
the unit. The reading apparatus is advantageously provided with a rugged 
fiberglass and nickel shielded case 140. Case 140 mounts carrying handles 
141 and 142. The case also includes six (6) heavy duty over-center luggage 
type fasteners 145 which clip over and hold a case cover (not shown) which 
covers the front panel 101. 
The left part of the dosimeter reader as shown in FIG. 6 includes a 
dosimeter badge reading compartment 150 which is covered by a reading 
compartment front panel 151 which can be removed. The reading compartment 
front panel is normally installed and forms a cover over the light and 
dust tight reading compartment 150. The reading compartment is shown with 
cover 151 removed in FIG. 9, which will be described in greater detail 
below. 
FIGS. 6 and 7 show that the dosimeter reader includes a dosimeter infeed 
mechanism 160. The dosimeter badge infeed mechanism 160 is advantageously 
provided in the form of a sliding dosimeter badge holder 161. The sliding 
dosimeter badge holder 161 includes a slide framework 168. The slide 
framework is mounted by slide tracks 162 (FIG. 8) which are mounted on the 
inside of the cover 151 in a well-known fashion to form a slideway 181. 
The sliding dosimeter holder further includes a dosimeter badge receptacle 
163 which is mounted on the slide framework 168. The dosimeter badge 
receptacle is shaped to receive an irregularly shaped dosimeter badge (not 
shown) in a unique manner so that the badge can only be fully accepted 
into the receptacle 163 when the badge is properly oriented. 
The sliding dosimeter badge holder further advantageously includes a handle 
165. The handle 165 is integral or rigidly connected with slide framework 
168. Adjacent to the handle is a flange 167 which acts as a stop when the 
slide is fully inserted and further serves as a dust and light seal which 
covers the slide receiving opening 180. 
FIGS. 6 and 7 further show a dosimeter badge opening and closing actuator 
289. In FIG. 6 the actuator is in the badge closed position awaiting 
insertion of a badge. In FIG. 7 the actuator lever has been rotated 
counterclockwise. The lever 289 is connected through the front panel 151 
to an interior first link 292. The first link 292 is connected to a slide 
bar 293 which slides as a result of the pivotal action of link 292. The 
slide bar is mechanically coupled with a dosimeter badge assembly, 
disassembly and positioning chuck 200, shown in phantom in FIGS. 12 and 
15. 
FIG. 8 shows a top view of the dosimeter badge reader 100 with the case 
removed and portions broken away. In particular the light and dust tight 
reading compartment 150 is shown opened at the left of the machine. FIG. 8 
shows a laser 10a which emits a laser beam 16a. The laser beam 16a is 
partially reflected from a beam splitter 18a. FIG. 11 shows in elevational 
view that the beam splitter 18a directs the detector laser beam 21a 
downwardly at angle through a detector beam focusing lens 147 which 
focuses the beam at the plane of the chopping wheel 148. The detector beam 
is then intermittently passed by the rotating chopping wheel 148 having a 
plurality of apertures 149. The chopping wheel is turned by a motor 146 
via shaft 146a. The intermittent passage of the detector beam impinges 
upon the laser power detector 20a, such as described above. The detector 
20a provides a laser power signal which is used to provide control of the 
laser power at desired, potentially time variable, power levels. 
The portion of laser beam 16a which passes through the beam splitter 18a is 
redirected by a mirror 30a which is advantageously adjustable. The 
reflected laser beam from mirror 30a is directed through an 
anti-reflective coated germanium window 156. The window transmits the 
laser beam and blocks visible light from entering the reading compartment 
150. The laser beam is received by an optical laser converter 500 which is 
similar in construction to laser converter 400 described above in 
connection with FIGS. 4 and 5. The laser converter directs the output 
stimulating beams in a rightward direction as shown in FIG. 8 to the 
dosimeter badge holding chuck assembly 200. As shown in FIG. 8, the chuck 
assembly 200 is positioned to engage a newly loaded dosimeter in the slide 
dosimeter infeed loader 160. FIG. 15 shows the movement of the chuck which 
places the dosimeters in position for reading as shown in FIG. 12 in 
phantom. Additional description of the chuck head positioning mechanism 
will be made below with reference to FIGS. 9, 10, and 15. 
FIGS. 12-14 show a further preferred optical laser converter 500 according 
to this invention. Laser converter 500 includes a frame 551 having spaced 
apart upright frame members 551a and 551b. Frame side panels 551c extend 
between the upright frame members along both sides. The frame 551 supports 
a converter block assembly 502 which is advantageously made in two parts 
502a and 502b. The converter block assembly 502 is mounted for limited, 
approximately 180.degree., arcuate travel upon the converter block 
assembly mounting shaft 503 using bearings 503a. 
The converter block assembly 502 is rotated back and forth using a stepper 
motor 507 which drives the assembly through a double reduction gear set 
consisting of first pinion gear 508, idler gear 568, second idler pinion 
569 and main converter gear 504. The secondary part of the converter block 
502a is provided with limit switch activation extensions 581 and 582 which 
engage a limit switch assembly 583 having two limit switches to thus 
control the automatic back and forth operation controlled by computer 202. 
FIG. 13 shows the converter block assembly aligned with the first optical 
pathway 510 positioned to receive the incoming laser beam 16a through an 
inlet opening 546 formed through frame member 551a. The incoming beam is 
passed through a first lens 532 which disperses the incoming laser beam 
into an optical equalizer 531 having reflective channel walls 531a. The 
lens is held in position using a mounting tube 567 held within the first 
passageway 511 formed through the converter block 502. The emission end of 
the optical equalizer 531 is toward a first imaging lens 561 forming a 
part of the imaging block assembly 560 described below. 
The second optical pathway 520 is through a second passageway 521 formed 
through the converter block assembly 502. When the converter block is 
driven via gear 504 into a position wherein the passage 521 aligns with 
opening 546, then the incoming laser beam 16a will pass through the second 
optical pathway 520. The second optical pathway includes a lens 525 held 
in position by a tube mount 535 and a shoulder formed on the walls of 
passageway 521. The second optical pathway lens 525 disperses the incoming 
laser beam on to the first imaging lens 561. An aperture assembly 528 
similar to aperture assembly 428 shown in FIG. 5A is included to reduce 
the power of the output laser emitted by the second optical pathway when 
it is positioned to transmit the beam. 
The imaging subassembly 560 is similar to imaging subassembly 460 described 
hereinabove. It includes a surface mirror 563 which is mounted using a 
mounting piece 564. The output laser beams transmitted by imaging lens 561 
are refracted to form generally more parallel rays which reflect from the 
mirror surface as explained in connection with FIGS. 4 and 5. The 
reflected partially imaged output laser beams are directed through the 
second imaging lens 567 which focuses the output beams as they pass 
through an emission collection assembly 590. 
The light collection assembly 590 includes a laser beam passageway 591 
which communicates the first and second stimulating output laser beams 
from the imaging assembly through an opening 592 formed in an emission 
collection reflector 593. The stimulating laser beams then pass through a 
dosimeter exposure opening 594 shown most clearly in FIG. 14. The opening 
is adjacent to the dosimeters held by the dosimeter badge chuck 200 (see 
in FIG. 12). The opening 594 is formed through both an interior mirror 
element 595 and a supporting cover piece 596. The cover piece 596 mounts 
the mirror element 595 and reflector 593 to the light collection assembly 
base member 597. 
The emission collection reflector 593 is preferably made with a lower end 
which is ellipsoidal near the lower end adjacent to the opening 594. The 
ellipsoidal end 593a (see FIG. 12) reflects the visible light or other 
luminescent emission upwardly along the reflector as viewed in FIGS. 12 
and 14. The emission is thus directed to the emission detector 350 which 
is advantageously a photomultiplier tube. A filter 353 is advantageously 
included between the end of the light collecting reflector 593 and the 
detector 350 to filter out wavelengths of light longer or different than 
the desired emission spectrum being measured. The emission collection 
chamber formed within the reflector is advantageously purged with 
compressed air to help exclude dust and smoke. 
A variety of chuck assemblies or other dosimeter holding and positioning 
mechanisms can be used in the dosimeter badge reading apparatus made in 
accordance with this invention. Rotatable tables with extendible chuck 
mounting heads (not shown), or a large variety of translational stage 
chuck positioners can be used. FIGS. 9, 10 and 15 show one suitable form 
of chuck positioner 300 used in the reading apparatus 100. The chuck 
positioner 300 includes a carrier plate 301 to which the chuck assembly 
200 is mounted securely, such as by securing fasteners (not shown) through 
mounting holes in the chuck assembly 200. The carrier plate 301 is mounted 
to upper and lower mounting plates 232 and 233 which are pivotally mounted 
to a U-shaped piece 304 using upper and lower bearings 305 and 306. The 
carrier plate 301 and mounting plates 232 and 233 form a chuck mounting 
head 234 pivotally mounted on the U-shaped bracket. The U-shaped bracket 
is supported on the X stage frame piece 380' which slides along X stage 
slide rods 382' with adjustment of the X--Y positioner 370'. The X stage 
piece 380' moves the chuck mounting head along a path which retracts the 
chuck from the dosimeter engaged position shown in solid line in FIG. 15 
and moves it rearwardly, as indicated by the intermediate position and 
fully retracted reading position, both shown in FIG. 15 in phantom lines. 
The chuck positioner 300 further advantageously includes a translational 
stage camming mechanism 310 which includes a track assembly 312 having a 
first guide track 313 and a second guide track 314 shown in FIG. 15. The 
upper mounting plate of the chuck head assembly mounts a set of follower 
bearings 316 and 317 which extend upwardly and are received within the 
tracks 313 and 314, respectively, as the X positioner stage retracts the 
chuck head rearwardly relative to the track assembly 312 which is mounted 
in a fixed position relative to X-stage motion. This arrangement causes 
the chuck assembly mounting head 234 to pivot and reorient the dosimeter 
badge chuck assembly 200 into dosimeter badge reading position shown at 
the left in FIG. 15, which is at approximately a right angle to the 
orientation of the chuck mounting head when extended into the dosimeter 
badge engaging position shown in solid line at the right in FIG. 15. 
The X--Y positioner 370' is shown most clearly in FIGS. 9 and 10. It 
includes vertical guide rods 372' and horizontal guide rods 382'. The 
vertical Y stage guide rods 372' mount linear bearings 372a and the 
horizontal X stage guide rods mount linear bearing 382a. The horizontal 
motion of the positioner is driven by a horizontal motion stepper motor 
388' which drives a screw shaft 387' and follower assembly 386'. The 
horizontal position of the positioner is detected by an X position encoder 
388a which is connected to the end of the screw shaft and produces an 
electronic signal representative of the S position which is communicated 
to the computer 202. The X positioning stage 380' also includes an X 
position limit switch 379. 
A similar arrangement is used to vertically position the Y stage of the 
X--Y positioner which mounts the X stage slide rods 382' upon which the X 
stage and chuck mounting head are mounted. The Y stage includes a slidably 
mounted stage piece 374' to which the X stage is mounted. The Y stage is 
driven by a stepper motor 378' via a lead screw 377' and screw follower 
assembly 376'. Y position encoder 378a provides an electronic signal 
indicative of the position of the Y stage. A Y position limit switch 389 
is also advantageously included. 
FIG. 15 shows the basic operation which both translates and rotates the 
chuck 200 as the chuck is moved from the badge engaging position into a 
reading position shown at the left in phantom in FIG. 15. This positions 
the dosimeter being held with the interior face outwardly adjacent to 
opening 594. The stimulating laser beams impinge upon the dosimeter 
elements causing an emission which is collected by the emission collector 
assembly and detected by photomultiplier tube 350. 
Although description has been made of one type of positioner for the 
dosimeter badge chuck assembly, the invention is not to be construed as 
requiring any particular form of positioner for the chuck assembly and a 
variety of robotic arms, X--Y positioners, rotational positioners and 
others are alternatively possible. 
A small radioactive light source 980 is also preferably mounted on the X 
stage 380' for use as a calibrating light detected by detector 350 when 
the source 980 is properly positioned. An incandescent spot 981 can also 
be included for heating by the laser or other stimulating beam to 
incandescence also for calibrating the detection of emissions. A 
protection plate 983 is further shown for covering the laser emission and 
detection opening (not shown). 
FIG. 16 shows a preferred form of control system which can be used to 
operate the parts of dosimeter reader 100 relevant to the present 
invention. The control system includes an on-board computer 202. The 
computer receives information from the X and Y encoders 376 and 386 and 
produces signals which drive the X and Y stepper motors 373 and 383 to 
desired positions. Data storage is coordinated through the computer to a 
data storage unit 401. The computer can also drive an internal or external 
printer 402 which prints dose exposure related emission information in a 
variety of forms as desired. The computer receives the emission 
information from the emission detector 350. Laser optics unit 340 is 
preferably adjustable and controlled to provide two different types of 
stimulating laser beams to read different types of dosimeters mounted on a 
suitable badge. The X and Y position limit swiches 379 and 389 are also 
connected to computer 202 to indicate full travel of the positioning 
stages. The computer 202 is preferably programmed to provide automatic 
operation of the dosimeter badge reader. Badge actuator limit switches 297 
and 298 are also connected to computer 202. 
The invention further includes novel methods for reading and stimulating 
dosimeters and dosimeter badges. In a first embodiment the invention 
includes methods which use two different stimulating laser beams to treat 
one or more dosimeters. The method advantageously includes positioning a 
dosimeter in a reading position wherein the dosimeter is appropriately 
located for receiving a stimulating beam or beams. An incoming laser beam 
16a is preferably converted into a desired stimulating laser beam such as 
by passing the incoming beam through an optical laser converter to produce 
a stimulating laser beam. For example, the incoming laser beam can be 
converted by positioning the laser converter block 502 with the second 
optical pathway 520 positioned to receive the incoming laser beam. The 
incoming laser beam is then passed through the converter second optical 
pathway 520 to produce the focused second stimulating beam. The dosimeter 
is then stimulated such as by impinging the second stimulating laser beam 
upon the dosimeter. In a preferred form of the invention the second 
stimulating beam is impinged upon numerous localized areas of a dosimeter. 
The methods are advantageously further defined to include detecting an 
emission or emissions from the dosimeter as a result of treatment by the 
stimulating beam. When the dosimeter is stimulated numerous times by the 
stimulating beam the resulting numerous emission phenomenon are detected. 
The detected emissions are then preferably recorded. 
The novel method further advantageously includes converting the laser beam 
to produce a different laser beam having differing laser beam 
characteristics. The converting step is advantageously accomplished by 
moving portions of a laser beam converter, such as converter block 502 
into a position wherein the incoming laser beam passes through the first 
optical pathway 510 to produce a subsequent stimulating laser beam, such 
as the first stimulating laser beam, having laser beam characteristics 
which are different from the previous stimulating beam, such as the second 
laser beam characteristics. For example a dosimeter read to measure 
ionization at numerous discrete locations using the focused second laser 
beam can subsequently be treated by the relatively larger, equalized first 
stimulating laser beam to anneal the dosimeter prior to reuse. Emission 
from the dosimeter during such an annealing step can optionally be 
detected to monitor the annealing process. It is also possible to use a 
pre-reading annealing process to remove relatively unreliable luminescent 
energy which is unstable and luminesces at a lower stimulation 
temperature. 
In other embodiments of the novel methods of this invention processes are 
provided for reading multiple types of dosimeters contained on a single 
dosimeter badge using a multiple step treatment process and at least two 
differing types of stimulating laser beams which have differing 
characteristics. The differing stimulating laser beams are advantageously 
produced by converting an incoming laser beam using at least one optical 
laser converter which is adjustable to provide two differing output beams, 
preferably using at least one optical pathway which changes the 
characteristics of an incoming laser beam in at least one of two possible 
positions of the laser converter. More preferably, the optical laser 
converter transforms the incoming laser beam into two different output 
stimulating laser beams each of which is optically changed to provide 
differing desired laser beam characteristics. 
The novel methods can be defined to include positioning a first dosimeter 
in a reading position, such as by moving the dosimeter held in a dosimeter 
badge in a desired position aligned to receive a stimulating laser beam 
such as the first stimulating beam produced by passing the incoming laser 
beam through the first optical pathway 510. The methods can also be 
defined to include moving at least a movable portion of the optical laser 
converter to provide an optical pathway which produces the desired 
stimulating beam characteristics. For example, the laser converter block 
502 is positioned with the first optical pathway aligned to receive the 
incoming laser beam. The optical pathway can provide means for changing or 
converting the incoming laser beam to produce a changed beam with desired 
laser beam characteristics, such as by equalizing the incoming beam by 
passing it through the first optical beam pathway 510 to produce an 
equalized first stimulating laser beam having a more uniform 
cross-sectional laser power profile than the incoming laser beam. The 
first optical pathway can further advantageously provide a converted beam 
having a square cross-sectional beam shape, such as by passing the beam 
through an equalizing channel having a square beam shape. Alternatively, 
the channel can have other cross-sectional shapes to provide a beam 
pattern which matches the shape of the dosimeter being treated. 
The novel methods further include stimulating or otherwise treating the 
first dosimeter with a first stimulating beam having the desired first 
stimulating beam characteristics. This is advantageously accomplished by 
beaming the stimulating laser beam onto the first dosimeter which has been 
positioned in the appropriate first dosimeter reading position. 
The novel methods further advantageously include converting the incoming 
laser beam into a desired second stimulating laser beam. This is 
advantageously accomplished by moving at least portions of an adjustable 
laser beam converter, such as by rotating the converter block assembly 502 
to align the second optical pathway with the incoming laser beam 16a. The 
incoming laser beam is preferably converted by the second optical pathway 
to produce a second stimulating laser beam having desired treatment 
properties for a second dosimeter carried on a dosimeter badge. The second 
dosimeter is placed in appropriate position for receiving the second 
stimulating laser beam, such as by positioning the second dosimeter in a 
second dosimeter reading position which can be the same or different from 
the first dosimeter reading position. In preferred embodiments the first 
and second dosimeter reading positions are approximately along the same 
stimulating beam axis emitted through the opening 594. The first and 
second dosimeter reading positions can vary in longitudinal position, but 
are more preferably as close to the opening 594 as practicable to increase 
the emission collection efficiency of the reader, thereby increasing 
minimum dose sensitivity. 
The methods further include stimulating or otherwise treating the second 
dosimeter with the second stimulating laser beam. The emission produced by 
the treatment of the second dosimeter is preferably detected, such as by 
detecting the emission with the photomultiplier 350. The emission can be 
collected, such as by using the ellipsoidal reflector 593 or other 
otherwise collecting and conveying the emission from the dosimeter to the 
emission detector. The emission information is preferably recorded and 
used to produce an indication of radiation dose to which the dosimeter was 
exposed. 
Although the novel methods described above have been presented in the 
context of the preferred dosimeter reading apparatus having two optical 
pathways, it should further be appreciated that other multiple optical 
pathway converters having more than two pathways, and reading and 
stimulating processes having more than two steps or which include more 
than two dosimeters are also included in this invention. 
The apparatus according to this invention are constructed by appropriately 
forming the various components indicated above from suitable materials, 
such as metals and synthetic polymers, to serve the desired function. The 
components are fabricated in traditional manners using such materials and 
assembled into the indicated structures. 
In compliance with the statute, the invention has been described in 
language more or less specific as to structural features. It is to be 
understood, however, that the invention is not limited to the specific 
features shown, since the means and construction herein disclosed comprise 
a preferred form of putting the invention into effect. The invention is, 
therefore, claimed in any of its forms or modifications within the proper 
scope of the appended claims appropriately interpreted in accordance with 
the doctrine of equivalents.