Note: Descriptions are shown in the official language in which they were submitted.
1 3 1 q2~6
This invention relates to apparatus and methods for remotely
measuring radiation dose information.
There are a number of situations where radiation dose
information is preferably measured remotely. For example, in the
S treatment of cancers and other diseases where exposure to radiation
is used to kill malignant or otherwise used to treat various types
of diseased tissue, it is currently impossible for the radiologists to
known precisely how much radiation is being administered to the
tissue being treated. The radiologist typically sets the desired
10 radiation level on the radiation generating equipment and then
treats the tissues in a localized manner for a specified period of
time. This approach achieves acceptable results in many cases but
has been found to vary significantly in the amount of applied
radiation dose. Accordingly, there remains a strong need for i)t
15 vivo radiation dosimetry equipment which can provide accurate and
reliable information as to the radiation dose àctually received in
the tissue being treated.
There are also many industrial applications where radiation
dosage or levels are preferably measured for various reasons. In
20 and around nuclear power plants there are portions of equipment
and facilities where radiation levels are sufficiently high that
minimal or no exposure of personnel is allowable without protective
BRI-017 pol 1 ~
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gear. In other applications radiation levels are so high that no
personnel exposure is acceptable under any conditions. In many
of such applications it is desirable to have measurements of
radiation levels on a routine basis.
High levels of radiation are also typica]ly derogatory to
radiation measuring equipment and are often of such significance
that the radiation measuring equipment cannot function accuratel
or reliably in the environment where radiation levels are to be
measured. Accordingly, there is a continuing need for improved
radiation dose measuring systems capable of remotely measuring the
dosages or levels of radiation present. Such radiation measurement
systems also are preferably provided with relatively small replaceable
sensor assemblies which are of minimum effect on the systems
being monitored.
Accordingly, in one aspect the invention proviees
a remotely sensing radiation dose measuring apparatus,
comprising:
at least one luminescent sensor adapted for remote mounting
for exposure to radiation conditions being measured in a remote
2 0 location;
at least one beam generator for producing a stirrlulating beam
with a stimulating beam wavelength spectrum useful for stimulating
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the luminescent sensor to cause a controlled luminescent discharge
from said luminescent sensor wi~h a luminescent discharge
wavelength spectrum;
beam power detection means for measuring the power of the
stimulating beam at least once during an exposure period during
which the stimulating beam is directed upon the luminescent sensor;
beam power control means for rapidly and adjustably
modulating the power output of the stimulating beam to achieve
a desired beam power;
nat least one beam controller for controlling transmission of
the stimulating beam to the luminescent sensor;
at least one remote transmission fiber for conveying the
stimulating beam to the luminescent sensor;
at least one remote transmission fiber for conveying
1 Sluminescent discharge from the luminescent sensor;
at least one luminescent discharge detector for detecting said
luminescent discharge from the luminescent sensor and producing
information indicative of a variable property of said luminescent
discharge which is indicative of the radiation to which the remote
20luminescent sensor has been exposed.
In a further aspect the invnetion provides a remotely
sensing radiation dose measuring apparatus, comprising:
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at least one luminescent sensor adapted for remote mounting
for exposure to radiation conditions being measured in a remote
Iocation;
at least one beam generator for producing a stimulating beam
with a stimulating beam wavelength spectrum which is primarily
shorter than 6 microns and useful for stimulating the luminescent
sensor to cause a controlled luminescent discharge from said
luminescent sensor with a luminescent discharge wavelength
spectrum which is primarily within the visible light wavelength
o spectrum;
at least one beam controller for controlling transmission of
the stimulating beam to the luminescent sensor;
at least one remote transmission fiber for conveying the
stimulating beam to the luminescent sensor and for conveying
luminescent discharge from the luminescent sensor;
at least one luminescent discharge detector for detecting said
luminescent discharge from the luminescent sensor and producing
information indicative of a variable property of said luminescent
discharge which is indicative of the radiation to which the remote
? luminescent sensor has been exposed.
In yet a further aspect the invention provides a
remotely sensing radiation dose measuring apparatus,
comprising:
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a phosphor support;
a Iuminescent phosphor sensor mounted to the phosphor
support;
a transmissive fiber having a distal end connected to the
phosphor support with an end surface of the transmissive fiber
positioned in close proximity to the luminescent phosphor sensor;
at least one - light occluding shield mounted to selectively
exclude ambient light from the transmissive fiber and luminescent
phosphor sensor.
In an alternative aspect the invention provides
a luminescent sensor assembly for use in a probe
assembly of a remotely sensing radiation dose measuring apparatus,
comprising:
a tubular phosphor support having an interior cavity and at
5 least one open end for allowing a transmissive fiber to be extended
thereinto;
a luminescent phosphor sensor mounted to the phosphor
support.
In yet an alternative aspect the invention provides
a method for measuring radiation dose at a remote
location using a remotely sensing sensor probe assembly,
comprising:
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positioning the sensor pro?De in a desired location so that a
luminescent sensor portion of said probe is positioned at a location
for which radiation dose information is desired;
exposing the luminescent sensor portion of the probe to
radiation being measured;
controllably beaming a stimulating beam through a
transmissive fiber in said probe assembly to stimulate the
luminescent sensor portion to emit a luminescent discharge; said
beaming being with a stimulating beam having a stimulating beam
l o wavelength spectrum;
collecting emission from the luminescent discharge and causing
transmission of the luminescent discharge along the transmissive
fiber;
selectively detecting luminescent discharge transmitted along
the transmissive fiber from the remote location of the luminescent
sensor portion;
producing information indicative of a variable property of said
luminescent discharge which is indicative of the radiation to which
the remote luminescent sensor has been exposed.
In a further alternative aspect the invention provides
a method for measuring radiation dose at a remote
location using a remotely sensing sensor probe assembly,
comprising:
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positioning the sensor probe in a desired location so that a
luminescent sensor portion of said probe is positioned at a location
for which radiation dose information is desired;
exposing the luminescent sensor portion of the probe to
radiation being measured;
emitting a stimulating beam from a beam generator which is
capable of modulation to control a power level of the stimulating
beam;
controllably beaming the stimulating beam through a
transmissive fiber in said probe assembly to stimulate the
luminescent sensor portion during a stimulating beam exposure
period to cause emission of any luminescent discharge from the
luminescent sensor portion; said beaming being with a stimulating
beam having a stimulating beam wavelength spectrum;
l S measuring the power level of the stimulating beam at least
once during a stimulating beam exposure period;
modulating the power level of the stimulating beam to
provide a desired stimulating beam power level during the
stimulating beam exposure period;
collecting emission from the luminescent discharge and causing
transmission of the luminescent discharge along the transmissive fiber;
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selectively detecting luminescent discharge transmitted along
the transmissive fiber from the remote location of the luminescent
sensor portion;
producing information indicative of a variable property of said
luminescent discharge which is indicative of the radiation to which
the remote luminescent sensor has been exposed.
Preferred embodiments of the invention are illustrated in the
accompanying drawings which are briefly described below.
Fig. 1 is a combined diagrammatic and plan view showing
the general layout of a preferred remotely sensing radiation dose
measuring apparatus according to this invention.
Fig. 2 is an enlarged sectional view of a preferred form of
remote luminescent sensor assembly used in the apparatus shown
in Fig. 1.
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Fig. 3 is an enlarged sectional view of a preferred form of
remote dosimeter sensor probe assembly used in the apparatus
shown in Fig. 1. The probe assembly of Fig. 3 incorporates the
sensor assembly shown in Fig. 2.
Fig. 4A and 4B are graphs showing an example luminescent
emission using an appara~us according to this invention.
Fig. S is another graph showing an example luminescent
emission.
Fig. 6 is a composite graph showing 4 curves using simi1ar
radiation doses and conditions to indicate the high degree of
repeatability of readings using the novel apparatuses of the
invention.
Fig. 7 is a further graph showing a relatively low radiation
dose whicll was obtained using a device of this invention.
Fig. 1 shows a preEerred remotely sensing radiation dose
measuring apparatus 9 made in accordance with this invention.
Apparatus 9 includes a beam generator, such as laser 10, for
generating and emitting a stimulating beam, such as laser beam 16.
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Laser 10 is powered by a laser power supply 15 which is
advantageously a radio frequency power supply capable of
modulation. Alternatively, silicon controlled rectifiers can be used
to control the total AC power to some types of lasers thus
5 providing the desired modulation of laser beam power. Other
constructions which are otherwise controllable to obtain a desired
laser beam power are also potentially useful in this invention.
Lasers which utilize a DC power supply are also useful in this
invention if appropriately constructed to allow modulation or control
10 of beam power. Beam generator 10 is advantageously a
neodymium yttrium aluminum garnet laser producing a laser
beam 16 which is primarily coherent laser light having a stimulating
beam wavelength spectrum which is narrowly centered about an
approximately 1.32 micron wavelength. Another desirable laser
15 includes a solid state diode laser (not shown). The stimulating
beam generator is preferably capable of producing a beam which
has a wavelength spectrum which is primarily less than 6 microns,
more preferably primarily less than 2 microns. The stimulating
beam wavelength spectrum is preferably different from the
20 wavelength of the luminescent discharge which the stimulating beam
causes, as explained more fully below.
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The laser beam 16 from laser 10 is preferably passed
through a polarizer 118 which causes the beam to be polarized
thus reduc;ng the risk of variations in the beam due to
polarization changes during laser operation. The polarization
S changes cause variations in the reflectance and other optica]
properties which are undesirable. The laser 10 can preferably be
provided with an internal polarization means (not shown) for
polarizing the beam prior to emission from the laser device. The
polarizer is of particular significance when the remote radiation
10 dosimeter 9 is provided with a preferred stimulating beam power
control system which is described below.
The stimulating beam 16 is advantageously directed in a
desired orientation using an adjustable mirror assembly 17. Mirror
assembly 17 is advantageously provided with a two-axis mounting
15 which allows the reflective surface of the mirror to be adjusted
about two orthogonal axes for both up and down, and left and
right orientation adjustments. The mirror assembly 17 is used to
direct the beam 16 to a beam controller which is advantageously
provided in the form of a stimulating beam control shutter 26.
20 Alternatively, it is possible in some cases to use beam generators
which can be accurately turned on and off to achieve the desired
beam control. Other means for controlling the emission or
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communication of the stimulating beam to the luminescent sample
used as the radiation sensor and contained in probe tip 301 are
also possible. The stimulating beam controller, such as shutter 26,
is preferably connected to computer 202 which controls the
5 operation of the shutter and passage of the stimulating beam
therethrough.
Fig. 1 also shows a desirable laser beam power control
subsystem for controlling the power of the laser beam emitted
from the laser 10. The power control subsystem includes a beam
10 splitter 18 which is advantageously positioned to reflect a detector
beam 21 consisting of only a limited portion of the laser
beam 16, for example 1-10%. The power detector l~eam 21 is
directed to a power detector, such as laser power detector 20.
The laser power detector 20 can be either a continuously
15 monitoring power detector or an intermittently monitoring power
detector. A suitable power detector is a pyroelectric detector, such
as a lead-zirconate-t;tanate detector, for example model series 350
manufactured by Barnes Engineering. Such a pyroelectric type of
detector performs best when the detector beam does not impinge
20 upon the detector in a continuous manner. Accordingly, the
detector beam is preferably rendered intermittent by a suitable
beam interrupter, such as rotating chopping wheel 23 shown in
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Fig. 1. The power detector can alternative]y be a continuously
monitoring detector, such as a photodiode when diode lasers are
used. In apparatus including continuously monitoring power
detectors there is no need for a detector beam interrupter.
The beam interrupter preferably is rotated or otherwise
operated to allow measurement of the detector beam power at
least once, preferably more than once, during a stimulating beam
exposure period. This allows adjustment of the laser beam power
during the exposure period to prevent undesirable power deviations
which otherwise occur due to operational variations in the laser.
More preferably a number of power measurements are made by
the power modulation subsystem during the exposure periods used
to stiml~late the luminescent phosphor sensor 305, see Fig. 2.
Such multiple beam power detection measurements allow rnore
accurate beam power to be maintained. The beam power can be
used at a relatively fixed level or varied with time as explained
in u. S. Patent No. 4,825,084.
The power level detected by detector 20 is in the form ot
an electronic output signa] which is appropriately communicated to
computer 202. This is advantageously done using a laser power
signal enhancer circuitry 62 which is used to condition the signal
. and is described in u. s. Paten~ No. 4, 839, 518, issued
BRI-017.P01 7
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June 13, 1989. Other suitable means for
conditioning the detector output signal are also clearly possible.
The electronic signal output from the signal enhancer 62 is
communicated to a suitable analog-to-digital conver~er 200. The
5 resulting digital signal is input to the computer 202 and suitably
interpreted by appropriate software.
The detected power level received by the computer 202 is
compared against preprogrammed operational power parameters
which thus allow an appropriate laser control signal to be
10 determined. The laser control signal either increases, decreases or
continues the existing power output from the beam generator.
Such signal is output to a digital-to-analog converter 206 which
provides an analog signal used to control the modulation circuit 70.
A preferred construction for the mt)dulation circuit 70 is sho- n in
15 said U. S. Patent 4, 839, 5l8 . The
output from the modulation circuit is communicated to the laser
power supply 15 to suitably control the power of stimulating
beam 16. Other alternative means for modulating the laser power
supply 15 may also be appropriate.
It should also be noted that some forms of solid state diode
lasers include an integral power detection and modulation which
serves to maintain the laser beam power at desired levels. Such
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internal power cvntrol systems of a laser may also be appropriate
as power control subsystems in the current invention.
Fig. 1 also shows that the remote radiation measuring
apparatus 9 incl-udes a light-tight enclosure 350 having a
S surrounding case wall 351 which is used to exclude ambient light
from the interior 352 of the enclosure. The stimulating beam 16
enters the enclosure 350 via a filtering window 355. Window 355
is preferably a long-wavelength passing window which filters out
relatively shorter wavelength ambient light. For example, the
window 355 passes approximately 80% or more of the laser
beam 16 while filtering approximately 90% or more of the ambient
and laser generated light having wavelengths shorter than
approximately 700 nanometers. The relatively small amounts of
shorter wavelength laser generated non-coherent light which infiltrate
15 the filtering window 355 are also reduced by including a ditfuse
light baffle 360. The difEuse light baffle has a series of washer-
shaped baffles 361 arranged to provide an aligned beam
passageway 362 therethrough. The interior of the baffle is
absorbing of the diffuse non-coherent light thus attenuating that
20 component of the beam and passing the coherent laser light.
The stimulating beam 16 is also advantageously passed
through a focusing lens 370. Focusing lens 370 is preferably
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mounted to the case 350 on an adjustable mount 371 to allow
adjustment of the lens relative to the beam and other components
of measuring apparatus 9. The stimulating beam passing through
the focusing lens is focused onto the proximal end 381 of an
5 intermediate optical fiber 380. The proximal end of the
intermediate transmission fiber 380 is advantageously held in a 5-
axis positioner 382 which allows tilting about either of two
orthogonal axes which are transverse to the beam, and further
allows 3-dimensional positioning of the proximal end of the fiber
10 to allow maximum transmission of the stimulating beam into the
intermediate transmission fiber 380.
As shown, apparatus 9 also includes a selectively reflective
mirror 385. Dichroic mirror 385 is impinged by the stimulating
beam 16 on its upstream face 385a and selectively passes the
15 relatively longer wavelength of the stimulating beam. This allows
the stimulating beam to be focused onto the proximal end of the
transmissive fiber 380 for communication through the transmissive
fiber system to the luminescent sensor 305.
The relatively shorter wavelength visible emission from the
20 luminescent sensor is also emitted from the proximal end 381 of
the intermediate fiber 380, but in the form of a diverging
beam 383 which is reflected from the downstream face 385b and
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toward an emission beam focusing lens 390. The emission beam
focusing lens 390 is mounted in a lens tube 391 which is held by
a mounting bracket 392 and fasteners 393. The mounting bracket
secures the emission beam focusing lens assembly to the case, or
5 more preferably, to an adjustable positioning device 394, such as
an X-Y positîoning table 396. The focused emission beam 384
from lens 390 is directed to the luminescent emission detector 45.
In certain forms of the apparatus built in accordance with
this invention the emission beam is preferably passed through a
10 filter which is selective to pass the relevant emission wavelength
spectrum to the detector 45. Such a filter is shown as filter 398
positioned to filter the focused emission beam from focusing
lens 390. A variety of suitable spectral filters are commercially
available for typical emission spectra from thermoluminescent
15 phosphors appropriately used in this invention. It may also be
advantageous in certain embodiments to include an emission beam
controller, such as emission beam shutter 397. Emission beam
shutter 397 controls the transmission of the emission beam 391 to
emission detector 45 for use in certain methods of this invention
20 as are explained in greater detail below.
Emission detector 45 can be of a variety of types dependent
upon the particular requirements of the luminescent emission being
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measured. Detector 45 as shown is advantageously a
photomultiplier tube, well-known in the art of light detection. The
detector 45 produces an electronic output signal which is
communicated to appropriate equipment, such as a luminescent
5 emission signal processing and memory unit 52. Alternatively, the
general purpose or other computer 202 can receive the emission
detector signal and appropriately store or route the signal for
recordation in various manners, preferably in digital form for
subsequent analysis. As shown, Fig. 1 indicates that the memory
unit 52 is connected to the computer 202 for receiving information
therefrom concerning timing and power of the stimulating beam.
Other relevant data may also similarly be recorded to provide an
integrated data record of the dose measuring operations. The
control system can also be used to appropriately anneal the
15 luminescent sensor and record the sampling time between annealing
and stimulated emission to thereby allow measurement of the level
of radiation over the relevant sampling period.
Radiation measuring apparatus 9 includes the various
components described above which make up the base unit. Fig. 1
20 further shows that apparatus 9 includes a remote unit which is a
probe assembly 300. Probe assembly 300 is for remotely sensing
radiation dose or level information and allowing the sensed
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information to be remotely read from the luminescent sensor
contained in probe assembly head 301. Probe head 301 is formed
at the distal end of the detachable probe assembly 300. Probe
assembly 300 is connected at its proximal end to an optically
5 transmissive coupling 302 which allows transmission between the
outer end of intermediate fiber 380 and the proximal end of
probe fiber 310. The optically transmissive coupling 302 can be
of various types which are commercially available. The coupling
must be selected to allow transmission of both the stimulating
10 beam spectrum and the luminescent emission spectrum between the
intermediate and probe fibers.
Fig. 3 shows the probe head 301 in sectional view and
enlarged. The probe head is advantageously mounted upon the
distal end of the probe assembly. The probe assembly includes
15 the probe transmission fiber 310 which is preferably a single fiber
between a distal end 311 and a proximal end at the probe side
fitting of the transmissive coupling 302. The transmissive probe
fiber can be constructed of relatively economical, widely available
optical fibers when stimulating beams of wavelengths shorter than
20 2 microns are used. Examples of suitable fibers include fused
si!ica fibers having a central core of approximately 600 microns
diameter and having a doped silica cladding, such as Superguide-
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G 600 available from Fiberguide Industries. When stimulating
beams of wavelengths of 2-6 microns are used it is much more
costly and difficult to find acceptable fibers and couplings.
Sapphire fibers are capable of transmitting in this range but are
S very expensive. The selected optically transmissive fiber is
preferably transmissive to both the stimulating beam and the
luminescent emission wavelength spectrum so that a single fiber can
be used. Since most thermoluminescent phosphors luminesce with
visible or near visible emission spectra this requirement is typically
10 more easily accommodated than the infrared or near infrared
wavelengths of the stimulating beam. The probe fiber is
preferably provided with a an outer sheath 312 which is opaque
or otherwise occlusive to ambient light which might render
unreliable the transmitted luminescent emission being transmitted
S through the probe fiber. The probe sheath can advantageously be
made of a heat-shrinkable polymer, such as heat-shrinkable Teflon
tubing. The sheath is mounted coaxially over the fiber and then
the fiber and sheath assembly are heated to shrink the sheath into
tight contact over the exterior of the fiber. This construction
20 provides a durable and flexible probe shaft which can be bent to
radii of approximately S centimeters.
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The probe assembly is also preferably provided with an end
cap 314 which is advantageously detachable to allow installation and
replacement of a sensor assembly 330, shown in isolation in Fig. 2.
Alternatively, the end cap can be integral with the probe sheath.
5 The end cap is made of a suitable protective layer, such as from
a synthetic polymer, for example Teflon. The end cap is shaped
with a rounded end to facilitate insertion of the probe tip into
a cavity, opening or other relatively small aperture. The end cap
has an opening 315 which receives the probe fiber and protective
10 sheath therein, preferably to form a friction fit maintaining the end
cap in position on the distal end of the probe assembly. This
overlapping joint between the end cap and the probe-fiber sheath
prevents ambient light from infiltrating at the joint therebetween.
The exclusion of light can be even more apporpriately accomplished
15 using an intergral probe sheath and end cap (not shown).
Fig. 2 shows a preferred detachable and replaceable
luminescent sensor assembly 330 according to this invention. The
sensor assembly includes a phosphor sample or sensor element
support 331. The phosphor support 331 is advantageously tubular
20 and appropriately shaped in cross-section to receive the distal
end 311 of the probe fiber 310. As shown the tubular phosphor
support is cylindrical and hollow to receive a cylindrical fiber end.
BRl-017.P01 15
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The inside diameter of the tubular phosphor support is preferably
slightly larger than the outside diameter of the transmissive
fiber 310 to thereby provide a spaced annular relationship. The
annular space 335 between the engaged tubular phosphor support
S and probe fiber provides thermal isolation between these two parts
which reduces heat transfer from the phosphor support during
heating of a thermoluminescent phosphor sensor element or
sample 305.
The luminescent sample or sensor 305 is preferably bonded
10 to the phosphor support within the interior of the tubular member
and is thus supported about its periphery to reduce heat transfer
to the support. Reduced heat transfer reduces the laser power
required and the heating time. The peripheral support of the
sensor is advantageously done at or near the distal end of the
15 tubular phosphor support member 331. The phosphor support can
be constructed of a variety of suitable materials such as quartz,
glass, fused silica, high temperature plastics and others.
The phosphor can be a solid piece of suitable phosphor
crystal or a matrix of particulate and binder which is bonded
20 substantially according to the teachings contained in U. S. Patent
No. 4,825,084 and as described in further alternatives
indicated in U. S. Patent No. 4,999,504,
13RI-017.P01 16
1 31 q206
issued March 12, 1991. For example, the phosphor
material and a heat fusible glass can be mixed with a printing
vehicle and deposited within the end of a small glass tube having
an interior diameter of approximately 0.8-1.0 millimeter. The
S phosphor material used in the luminescent sensor can be selected
from a variety of suitable phosphors, particularly thermolumin~scent
phosphors such as CaSOs:Mn and others described in U.S. Patent
No. 4,825,084. The deposited phosphor and binder are heated to
volatilize the printing vehicle and subsequently heated to soften the
10 glass binder thus causing wetting between the binder and phosphor
support. After cooling the softened glass binder fuses to both the
phosphor particles and the support tube. Other alternative means
for holding the luminescent phosphor sensor in location are also
possible.
The sensor assembly 330 is also advantageously provided with
an absorbing element or layer 337 which is preferably in direct
physical contact with the luminescent sensor 30S. The absorbing
layer is particularly advantageous when the wavelength of the
stimulating beam is not efficiently absorbed by the sensor element
~() or other formation. The absorber layer can be selected from a
variety of materials which are highly absorbing of the stimulating
beam wavelength. For example, 3M brand ECP-~00 solar
BRI-017.P01 17
1 31 q206
absorber coating can be used to increase the efficiency of
absorbing 1.32 micron wavelength laser light from the YAG laser
described above. Other suitable absorbing coatings can also be
used. Alternatively, binders can be selected which are inherently
S good absorbers of the stimulating beam when the stimulating and
emission spectra are sufficiently distinct.
The luminescent sensor assembly further advantageously
includes a fiber connection fitting 338 which can be a suitably
sized piece of heat-shrinkable Teflon tubing. The connection fitting
advantageously has a phosphor support section 338a which is about
the tubular phosphor support 331, and a probe shaft section 338b
which is about the fiber 310 when installed as shown in Fig. 3.
The inside diameter of the shaft section is preferably slightly
smaller than the outside diameter of the probe shaft to provide
an interference fit which is accommodated by the plastic material
used to form the fit. This construction holds the sensor assembly
in fixed relationship on the end of the probe shaft without the
need for complex fittings, thus maintaining the size very small,
approximately less than 2 millimeters outside diameter.
The invention further includes novel methods for measuring
radiation at a remo~e location using a remotely sensing probe
assembly. The methods include positioning the probe 300 with the
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sensor containing head 301 in a desired position for obtaining the
radiation measurement. The very small size of probes possible
using the present invention allow the precise monitoring of
radiation within tumors during treatment or at other specific
5 locations of interest. The properly placed luminescent sensor 305
is then exposed to the radiation being measured. For example,
the radiation therapy could be administered using whatever radiation
treatment which is appropriate thereby exposing the luminescent
sensor to the radiation during a radiation exposure or measurement
10 period.
After the desired radiation exposure period, the remote
sensor 305 is read. The reading of sensor 305 is advantageously
accomplished by controllably beaming a stimulating beam to the
luminescent sensor phosphor deposit 305. The stimulating beam is
15 emitted from the laser beam generator 10 and directed by
mirror 17 to shutter 26. The shutter controls the passage of the
stimulating beam therethrough. When shutter 26 is open the
stimulating beam passes through the long wavelength passing
window 355 and into the confined and darkened interior of the
20 case 350. The stimulating beam is further improved by passage
through the diffuse light baffle 360 which further reduces non-
coherent beam components which pass through window 355. The
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stimulating beam 16 then is preferably focused onto the
transmissive fiber system which communicates the stimulating beam
to the Illminescent sensor 305. The stimulating beam preferably
is transmitted by at least one intermediate transmission fiber 380
S thus allowing the probe 300 to more conveniently be constructed
for detachment from the base portion of the device. The
stimulating beam is then communicated by optically transmissive
coupling 302 to the flexible probe 300 wherein the beam is
transmitted along the transmissive fiber 310 from the proximal end
l O thereof to the distal end thereof.
The stimulating beam 16 is preferably controlled during the
exposure of the luminescent sensor to provide desired stimulating
beam power. The stimulating beam can be contro]led to provide
a relatively constant beam power, or beam power can be profiled
lS over time to help minimize incandescence or to achieve other
desired operational characteristics. The power control is preferably
automatically performed by the computer 202 which is
preprogrammed to open shutter 26 and to begin a preprogrammed
beam power schedule for the desired exposure period or periods.
20 During the exposure period the laser power detector 20 receives
at least one and preferably a number of bursts of detector
beam 21. The detected power of the stimulating beam is
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communicated to the computer where the measured level is
compared against the preprogrammed desired power level. I he
computer then provides a control signal to the modulation
circuit 70 to control the power of the stimulating beam as desired
S and preprogrammed.
The stimulating beam communicated through the transmissive
fiber system emits from the distal end 311 of fiber 310 and is
beamed to the luminescent sensor 305, preferably across a narrow
thermally isolating gap 313 of approximately 0.1-1 millimeter, more
preferably approximately 0.5 millimeter. The stimulating beam thus
stimulates the luminescent phosphor sensor, such as by directly
heating the sensor or associated beam absorbing material 337, such
as when a thermoluminescent phosphor is used. The heating or
other stimulating process causes the luminescent sensor to emit a
luminescent discharge which because of the close proximity is
collected and transmitted into the distal end of the transmissive
fiber 310. The luminescent discharge is transmitted through the
transmissive fiber conduit system including fibers 310 and 380
through coupling 302.
The luminescent emission is emitted from the proximal end
of the intermediate fiber 380 in a diverging beam 383 which is
selectively detected to measure the amount, intensity or other
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characteristic of the luminescent discharge from the remote
luminescent sensor. The luminescent emission beam is
advantageously directed to the luminescent detector 45 using
dichroic mirror 385. The emission beam 383 is also advantageously
S focused using lens 390 to increase the intensity of the beam
directed to detector 45. Emission beam 383 is also advantageously
filtered to help remove any spurious light, such as might come
from the stimulating beam 16. This filtering and selection is
advantageously accomplished by both the selective reflectivity of the
lO mirror and passing the emission beam through filter 398 prior to
detection by detector 45.
In a further novel process according to this invention the
stimulating beam is made intermittent during the reading period of
the remote sensor such as by controlling the shutter 26. The
15 intermittent stimulating beam exposure periods are complementary
with stim~llating beam non-exposure periods during which the
shutter 26 is closed or the stimulating beam is turned off if the
beam is controlled by turning the beam generator on and off.
The novel methods further involve selectively detecting the
20 luminescent emission from the remote luminescent sensor during the
non-exposure periods. The detecting of the luminescent emission
is thus intermittent and performed during luminescent emission
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.i 1 31 q206
detection periods. The luminescent emission detection periods are
controlled by the emission detection shutter 397 or using other
suitable means for controlling impingement of the luminescent
beam 383 onto the detector 45. The luminescen~ detection periods
5 are preferably complementary, asynchronous and directly out of
phase with the stimulating beam exposure periods. Alternatively,
the luminescent emission detection periods can be asynchronous and
shorter than the non-exposure periods. This method for stimulating
and reading the remote sensor allows the effects of the stimulating
10 beam to be minimized with regard to possible interference with
detection of the luminescent discharge from the remote sensor.
This beneficial aspect of the method is increasingly important as
the wavelength spectra of the stimulating beam and luminescent
emission become closer or overlapping.
The intermittent stimulating and detection can advantageously
be accomplished using complementary exposure and detection periods
of approximately 0.1-100 milliseconds. Total reading times for
sensors stimulated with laser beams are in the range 0-5 seconds,
more typically 100 milliseconds - 2 seconds. The lengths of the
20 exposure and detection periods are preferably adjusted to allow
five (5) or more detection periods during the luminescent discharge
period from the sensor which occurs during the reading of the
sRI-0l7 Pl)] 23
~lq;2~6
sensor. ~Iore preferably, the periods are adjusted to allow a
minimum of fifty (50) periods to be performed during the
luminescent discharge period. The total nurnber of emission readings
taken during the reading period will typically be in the range 50-
500, more preferably 50-200. The emission detection periods are
typically shorter in duration than the stimulating exposure periods.
For example the stimulating beam can be provided in intermittent
pulses of approximately 1-10 milliseconds duration, and the detector
can be provided with the luminescent emission beam during periods
of 0.2-2 milliseconds. When relatively short periods are provided,
the stimulating beam control and the emission detector control may
no longer be adequately handled by mechanical shutters. Such
embodiments may more appropriately include chopping wheels which
are suitahly synchronized, or alternatively, suitable electronic controls
can be used, such as with a diode laser.
The emission sensed by the emission detector is preferably
translated into an electronic output signal which is communicated
to the luminescent emission signal processing and memory unit 52.
Therein the signal is appropriately conditioned and stored,
preferably in digital form, to achieve a record of the emission.
The emission information directly from the emission detector or as
stored in the memory unit 52, is then available for analysis to
BRI-017.pO1 24
1 31 9206
produce information which is indicative of a vari~ble property of
the luminescent discharge which is indicative of the radiation to
which the remote luminescent sensor has been exposed. The
maximum intensity of the luminescent emission has been found
useful in determining the radiation dose to which the sensor has
been exposed over time since the sensor was previously read, or
read and annealed. Other information indicated by the emission
signal may also be useful such as the integral of the emission
intensity or other quantities derivable from the intensity.
Alternatively, the emission detector may detect additional aspects of
the emission other than intensity and such characteristics of the
emission may be sufficiently related to the dose or level of
radiation so as to allow calibration and thus determination using
such alternative emission detection parameters. The apparatus 9
and associated detected emission information is preferably calibrated
by comparing the characteristic intensity or other detected parameter
from the remote sensor for various exposures to known radiation
levels or dosage quantities. The calibrated instrument can then be
used to test unknown radiation levels or dosages.
The apparatus 9 can also be used to prepare the
sensor 305 for additional dose measuring procedures. This
preparation can occur automatically as a result of the reading of
sRI.0l7.Pol 25
1 3 1 q20~
the sensor by stimulation with the stimulating beam to release the
stored luminescent energy. Alternatively, the operation of the
apparatus may require a specific annealing procedure to provide
increased accuracy for the next radiation sensing and reading cycle.
5 The annealing is easily accomplished by stimulating the luminescent
sensor material 305 using the stimulating beam. The annealing can
be preprogrammed for a desired beam intensity and exposure
period to heat or otherwise stimulate the phosphor to release any
residual luminescent energy which may rema;n from the prior
10 exposure and reading cycle. The annealed sensor is then ready
-for additional sensing and reading operations for an indefinite
lifetime dependent upon the useful service life of the luminescent
phosphor, transmissive fibers and other components of the probe
and remaining components making up the base portion of the
15 remote radiation sensing apparatus.
EXAMPLE I
A C-95 YAG-MAX laser modified for 1.32 micron photon
emission was purchased from CVI Laser Corporation. This laser
is water cooled and pumped by two 750 watt tungsten halogen
20 lamps. The laser was operated in the multi-transverse mode to
maximize power output at approximately 1.2 watts. The stimulating
beam shutter was an electro-mechanical shutter from Uniblitz. The
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long wave pass filter was from Corion Corp. model LG-840 which
eliminates most light below 0.8 micron wavelength, and transmittance
of about 90% above 0.95 micron. The stimulating beam focusing
lens had an effective focal length of approximately 58 millimeters.
S The mirror for selectively passing the stimulating beam and
reflecting the luminescent emission was a Corion Corp. cold mirror
model HT-700-F, which was positioned at 45 from the beam axis.
This mirror has a transmittance of about 90% above 0.75 micron
wavelength while reflecting about 95% below 0.68 micron
wavelength. The proximal end of the intermediate fiber was
provided with a modified SMA fiber optic in-line adaptor which
allowed the end of the fiber to protrude slightly from the adaptor.
The luminescent emission from the end of the intermediate fiber
emits in a diverging cone of approximately 40. The cone o~
emission light reflected off the cold mirror to a 21 millimeter
effective focal length condensing lens which produces a spot of
about 5 millimeters for detection by a Hamamatsu R1635
photomultiplier tube having a 10 millimeter bi-alkali photocathode
and 8 dynode stages.
The transmissive fibers were Superguide-G 600 as described
above. The probe shaft including the fiber and shea~h had a
diameter of approximately 1.8 millime~ers. The phosphor support
BRI-017.pO1 27
1 31 9206
was a small pyrex tube approximately 5 millimeters long and
having 0.8 millimeter inside diameter and 1.0 millimeter outside
diameter. The luminescent phosphor was CaS~ Mn which was
mixed with Corning * frit glass No. 7555 and Electro-Science
Laboratory vehicle No. 414 in proportions of 4:2:3, respectively.
The mixture was applied to the end of the glass tube and the
tube was placed on a TFE sheet on end to make the layer even
and to allow the applied mixture to dry. The dried tube with
phosphor sensor layer was inspected and extraneous material
removed from about the tube. The tube and dried layer was
then heated to melt the frit glass binder. Multiple sensor
assemblies were made with resulting luminescent layers ranging in
thickness between 0.005 inch and 0.010 inch (127-254 microns).
The sensor support assemblies were held in place by approximately
0.75 millimeter inside diameter shrink fit Teflon connectors on the
probe shaft. The probe head was capped with an opague end
cap made of Teflon having a rnaximum diameter of 2.3 millimeters.
The resulting system was tested and found to provide
approximately 0.35 watts at the sensor, approximately 30% of the
power delivered by the laser. Sensor assemblies were exposed to
3 rad using l37Cs. Fig. 4A shows a waveform oscilloscope scan
of the luminescent emission produced by heating the sensor over
*Trade Mark
BRI-017.P01 2g
1 3 1 9206
an exposure and reading period of approximately 1 second. The
shutter opened at the start of the horizontal axis and closed about
20 milliseconds from the right margin of the graph where the
signal drops. Fig. 4B shows the data of Fig. 4~ after analysis
5 using a nine point averaging to smooth the curve. Laser power
output was measured at 1.16 Watt.
EXAMPLE 2
Fig. 5 shows a similar experimental run as described above
in Example 1 using a 10 rad 137CS gamma dose. Laser output
0 was measured at 1.35 Watt.
EXAMPLE 3
Fig. 6 shows a plurality of experimental runs as described
above in Example 1 using 3 rad 137CS gamma exposure with laser
output measured at 1.16 for 3 of the curves and 1.09 for the
15 remaining curve. This Fig. indicates the high degree of
repeatability of the results from a prototype device.
EXAMPLE 4
Fig. 7 shows a minimum response obtained using 100 millirad
of 137CS gamma exposure and laser power of 1.14 Watt.
sRI -017 Pol 29
