FIELD OF THE INVENTION
The present invention is related with an application of a novel method
available to release energy stored in stimulable phosphors, coated in storage phosphor
panels. So the present invention relates to a device essentially providing particular
storage phosphors as composite compounds having the ability to absorb and to store
part of absorbed X-ray and/or UV-ray energy and to emit part of it again under
stimulating forces in form of (visible) detectable light energy. This invention
also relates to a method of recording and reproducing said energy, pattern-wise
where desired, by means of a screen or panel containing such phosphors and built
in in the said device.
BACKGROUND OF THE INVENTION
Well-known in diagnostic imaging is the use of phosphors in the production
of X-ray images. In a conventional radiographic system an X-ray radiographic image
is obtained by X-rays transmitted imagewise through an object and converted into
light of corresponding intensity in a so-called intensifying screen (X-ray conversion
screen) wherein phosphor particles absorb transmitted X-rays and convert them into
visible light and/or ultraviolet radiation. As silver halide grains or crystals,
present in emulsions coated in layers of a silver halide photographic film material
are more sensitive to the thus converted X-ray energy than to direct impact of
X-rays (due to a less effective absorption of those energetic X-rays) the said
conversion is in favour of image formation on the film material.
According to another method of recording and reproducing an X-ray
pattern disclosed e.g. in US-A 3,859,527 a special type of phosphor is used, known
as a photostimulable phosphor, which being incorporated in a panel is exposed to
incident pattern-wise modulated X-rays and as a result thereof temporarily stores
energy contained in the X-ray radiation pattern. At some interval after the exposure,
a beam of visible or infra-red light scans the panel in order to stimulate the
release of stored energy as light that is detected and converted to sequential
electrical signals which can be processed in order to produce a visible image.
For this purpose, the phosphor should store or accumulate as much as possible of
the incident X-ray energy and emit an amount of the stored energy as low as possible
before stimulation by the scanning beam. This form of radiography, wherein use
is made of storage phosphor screens or panels, also called stimulable phosphor
panels or accumulation phosphor panels is called "digital radiography" or "computed
Use of alkali metal halide phosphors in storage screens or panels
is well known in the art of storage phosphor radiology, wherein at least part of
the energy contained in an X-ray pattern is temporarily stored. The high crystal
symmetry of these phosphors makes it possible to provide structured screens and
binderless screens, in favour of image quality. Examples of such alkali metal
phosphor can be found in several documents. In e.g. US-A 5,028,509 a phosphor corresponding
to general formula :
wherein M is Cs or Rb, M' is at least one metal selected from the group consisting
of Li, Na, K, Rb, and Cs, M2+ is at least one metal selected from the
group consisting of Be, Mg, Ca, Sr, Ba, Zn, Cd, Cu and Ni, M3+ is at
least one metal selected from the group Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd,
Tb, Dy, Ho, Er, Tm, Yb, Lu, Al, Ga and In; X, X' and X'' may be the same or different
and each of them represents a halogen atom selected from the group consisting of
F, Br, Cl, I provided that all X' atoms are the same, B is an element selected
from the group consisting of Eu, Tb, Ce, Tm, Dy, Pr, Ho, Nd, Yb, Er, Gd, Lu, Sm,
Y, Tl, Na, Ag, Cu, Mg, Pb, Bi, Mn, and In. 0 ≤ x ≤ 1 and 0 ≤ a ≤ 1
and 0 ≤ b ≤ 0.5 and 0 < d ≤ 0.2
In US-A 5,055,681 a binderless screen comprising the phosphor as
disclosed in US-A 5,028,509 has been disclosed. In US-A 4,806,757 a CsI phosphor
has been disclosed, comprising between 0.0001 to 1 mole % of at least one element
selected from the group consisting of Li, K, Rb, Cu, Au, Be, Mg, Ca, Sr, Ba, Zn,
Cd, Hg, B, Al, Ga, In, Tl, Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm,
Yb, Lu, Si, Ti, Zr, Ge, Sn, Pb, As, Sb and Bi.
Alkali metal halide phosphors performing as desired qualities absorption
characteristics, speed, storage capabilities etc. have been disclosed in EP-A 0
751 200, wherein besides high speed also high chemical stability and low sensitivity
to humidity have been appreciated as well as ability to produce screens comprising
vapour deposited phosphor layers providing high image definition.
The radiation image storage phosphor screen according to that invention
comprises an alkali metal halide phosphor characterized in that said phosphor contains
a dopant selected from the group consisting of Ga1+, Ge2+,
Sn2+, Sb3+ and As3+. In a preferred embodiment
thereof the alkali metal is Cs and/or Rb.
In order to provide a method for recording X-rays following steps
- (i) exposing the photostimulable storage phosphor screen, comprising novel
alkali metal halide phosphors,
- (ii) stimulating said photostimulable screen in order to release the stored
X-ray energy as stimulated light and
- (iii) collecting said stimulated light.
In order to release energy stored by a stimulable phosphor use has
hitherto often been made of optical light sources as mentioned hereinbefore. As
a consequence thereof optical filters are required in order to separate light emitted
by the storage phosphors after stimulation and light originating from the stimulation
source. In order to develop a scan-head in order to scan a plate or panel built-up
with stimulable phosphors in order to release said stored energy, it is recommended
to reduce the volume of such a scan-head to a minimum. Especially when the detector,
collecting said stimulated light is a CCD with Fiber Optic Plate (FOP), the image
plate should be placed in direct contact with this fiber optic plate in order
to obtain a sufficiently good resolution. Presence of any additional intermediate
layer, as e.g. a filter layer, may lay burden thereupon and any measure in order
to simplify the process of reading out a storage phosphor is welcome as well as
any development in form of a practically useful device as a spin-off therefrom.
OBJECTS OF THE INVENTION
Therefore it is an object of the present invention to provide one
or more device(s) offering an easy method in order to stimulate storage phosphors,
wherein said device is essentially provided with panels built up with such storage
It is a further object of the present invention to extrapolate said
method in order to provide practically useful devices as a spin-off thereof.
Any other object will become apparent from the description hereinafter.
SUMMARY OF THE INVENTION
A device for measuring a pressure force or changes thereof (directly
or indirectly) applied by a pressure source and for reading out said pressure force,
has been provided as a spin-off from the property of "tribostimulability" of storage
The present invention provides a device as defined in claim 1 and
a method as defined in claim 11.
Because of the proportionality of the emitted light energy with the
applied pressure, the technique is suitable for measuring pressure forces and provides
methods to do so.
Specific features with respect to preferred embodiments of the invention
are disclosed in the dependent claims and further advantages and embodiments of
the present invention will become apparent from the following description and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
DETAILED DESCRIPTION OF THE INVENTION
- Fig. 1 shows an Image Plate essentially consisting of a storage
phosphor plate wherein an "X-ray" image has been stored. By means of a
Knife Edge a pressure force F is performed linewise on the
Image Plate, whereby the stored energy is released and becomes read-out
by a CCD via a Fibre Optic Plate (FOP).
- Fig. 2 shows an Image Plate essentially consisting of a storage
phosphor plate, just as in Fig. 1, wherein an "X-ray" image has been stored.
By means of a continuously rolling roller (opposite to the discontinuous linewise
registration by the Knife Edge as in Fig.1), wherein the said roller linewise
performs a pressure force F on the Image Plate, the stored energy
is released and becomes read-out by a CCD via a Fibre Optic Plate (FOP).
- Fig. 3 shows a Plate carrying a layer having Piezo-electric
Crystals, whereupon and in direct contact with it, the Storage Phosphor
layer is present, said Storage Phosphor layer being covered with a
Transparent plate. The "X-ray" image stored in the Storage Phosphor
layer is read-out after release of stored energy by a pressure force generated
pixelwise by the said Piezo-electric Crystals. As a detector, just as in
Fig. 1 use is made of a CCD,
capturing the pressure as converted and
released energy via a Fibre Optic Plate (FOP).
In this document the term "X-ray" should be understood as "any penetrating
radiation" and includes i.a. radiation originating from a radioisotope (e.g. a
Co60 source), radiation created by an X-ray generator of any type, radiation
and high energy particles created by a high energy radiation generator (e.g. Betatron),
radiation from a sample labelled with a radioisotope as is the case in e.g. autoradiography.
Although composites showing "triboluminescence" are known in literature
as e.g. described in Opto & Laser Europe, issue 61, published April 1999, wherein
it has been established that "composites glow where they crack" and that "Reinforced
polymers that emit red, green or blue light where they fracture could give aircraft
a "skin" that senses damage" as described in a report on the performance of resins
containing light-emitting crystals, nothing has been suggested nor disclosed about
"tribostimulability" of storage phosphors or stimulable phosphors.
It has thus unexpectedly been found that conversion of energy stored in phosphor
composites having energy storage properties, such as the storage phosphors, well-known
in image storage phosphor plates or panels used in diagnostic imaging by X-rays,
is performed by means of a source of pressure energy. This pressure energy is
differing from pressure energy directly generated from an air pressure source,
the determination of which has been described in EP-A 0 558 771, wherein use is
made from luminescent oxygen sensitive pressure sensitive compositions, having
no specific storage properties.
Absence of specific storage properties further becomes clear from
following references, wherein practical applications have been described for phosphors
having triboluminescent properties. So in US-A 5,905,260 a damage sensor has been
disclosed for detecting damage within a structure such as aircraft wings or fuselage,
or a bridge, wherein the sensor comprises a small piece of a triboluminescent
material connected via light guiding fibres or layers to one or more detectors.
As the sensor may be embedded within the structure or mounted on its surface, impact
of objects on the structure causes a physical damage to the triboluminescent material
and such damage causes light emission which is detected and recorded for later
observation. The invention presented in US-A 5,817,945 relates to the field of
strain measurements and more particularly to a system and method of determining
strain and, more particularly, a system including a stimulating light source; a
device for placing stress on an object; a number of local strain gauges attached
to the object; and an image capturing device. A controller, coupled to the stimulating
light source, has a signal that turns on the stimulating light source and the controller
receives a strain signal from each of the local strain gauges located on the object
as a photoluminescent coating is present thereupon, wherein luminescence is dependent
on the strain of the coating and wherein after having been stimulated from the
molecular ground state to the molecular excited state, the photoluminescent probe
molecule quickly decades back to its ground state by radiative or non-radiative
decay. In GB-A 2,232,119 a method of identification and/or security marking ahs
been disclosed which comprises applying to or incorporating into an article one
or more triboluminescent phosphors and wherein a similar article to be tested may
be subsequently subjected to means for stimulating triboluminescence and wherein
emission of triboluminescent radiation serves to identify or confirm the authenticity
of the test article in the fight against crime such as fraud and counterfeiting.
As the triboluminescent phosphors exhibit afterglow or persistance in emission
after removal of the stimulating energy source, the rate of decay of afterglow
with time is characteristic for any particular phosphor so that presence of a
particular phosphor becomes unequivocally proved.
Storage phosphors suitable for releasing stored energy by means of
pressure are called "tribostimulable phosphors" in the present invention. Said
tribostimulable phosphors in most general form are alkali metal-halide phosphors
and, more preferably are alkali metal halide phosphors have a composition based
on CsBr, CsCl, KCl and KBr. A more preferred suitable "tribostimulable" phosphor
providing release of stored energy to be read-out under the influence of pressure
energy is CsBr:Eu. The mechanism has also been found to apply to other phosphor
compositions as there are CsBr and CsCl (without further dopant); CsBr:Eu,Gd ;
CsBr:Ga; CsBr:Ca ; CsBr: Sr; CsBr:Gd ; CsBr:CsF ; CsBr:CsOH ; CsBr:Cs2CO3
; CsBr:Cs2SO4 ; CsBr:Ge ; CsBr:Sn ; CsBr:Au ; CsCl:Eu ; CsCl0.5Br0.5:Eu
; CsBr:In; CsBr:Ce ; CsBr:In,Ce ; CsBr:Tb; RbBr:Ga; RbBr:Ga,Li and more in general
terms to all phosphors mentioned in US-A 5,028,509 and in EP-A 0 751 200. Further
interesting storage phosphors are KBr:Cu; KCl:Cu; KCl(1-x)Br(x):Eu, wherein 0<x<1
and KCl(1-x)Br(x):Cu, wherein 0<x<1. KBr:Eu is a particularly preferred pressure
stimulable storage phosphor giving rise to the emission of blue light after having
been pressure stimulated. As a further advantage e.g. versus CsBr:Eu it is much
less moisture sensitive. Moreover from the point of view of dark discharge it is
a very interesting and suitable pressure stimulable phosphor. Methods suitable
for the determination of "tribostimulability" of storage phosphors have been described
in the Examples hereinafter. Phosphors present in samples (normally provided in
supported coated screens or panels, but also in self-supporting panels) suitable
for use in most general form as an essential part of devices according to the present
invention, and pressure meters in particular, clearly show emission of visible
light from the moment that the pressure force applied thereon by a pressure source
is varying the said originally applied pressure force. Variations in pressure force
are thus immediately detected. In a dark room the light emitted from the sample
or screen coated with such a storage phosphor or stimulable phosphor, also called
"tribostimulable" phosphor, by performing a pressure force variation is clearly
observed through an optical filter at the moment that said force variation is applied.
The intensity of the emitted light caused by the pressure force variations is very
much higher than emitted light caused by afterglow. It has e.g. been found also
that the "tribostimulable" crystals are emitting light energy very strongly (with
a high light intensity) when the surface of the crystal has been damaged with a
knife or even with a finger nail. So when the tribostimulable crystal is "cracked"
an intense light pulse is detected. When the tribostimulable storage phosphor
crystal, thus showing "tribostimulability", is not exposed to X-rays or is completely
erased with a light source after stimulation it has clearly been established that
no emitted light is leaving the crystal after application of a pressure force (variation),
wherein the crystal has been damaged or cracked.
It is thus clear that only stored energy, captured after a previous
exposure with ionization radiation (as e.g. X-rays) of a composite storage phosphor
crystal having tribostimulable properties as the crystals presented hereinbefore
is released by pressing, damaging or cracking the said crystal and that the said
released energy is proportional with the applied pressure or pressure variations.
In order to produce a pressure meter the crystal(s) can be placed
permanently on the place where the pressure should be measured. The crystal(s)
should be irradiated before with incident radiation energy having a wavelength
of 350 nm or less; more preferably with UV-rays and/or X-rays in order to provide
an amount of stored energy. The device according to the present invention thus
has a tribostimulable storage phosphor panel which absorbs calibrated amounts of
energy, generated by incident radiation (X-ray and/or UV-radiation) having a wavelength
of 350 nm or less (in order to permit release of (tribo)stimulated light energy
in an amount proportional with the said pressure force and in order to determine
said pressure force in a quantitative way).
This source of energy should preferably be built in the device according
to the present invention in favour of ease to handle, although, for more industrial
applications, depending on the scale whereupon the device should be used, an external
irradiation is more preferred. Especially when X-rays are a more preferred source
of irradiation security measures are required: a device having a chamber, the
walls of which have been covered with lead foils and wherein an X-ray source is
present in order to irradiate a storage phosphor panel should then be constructed.
It is clear that also irradiation with an UV-source requires security measures,
e.g. in form of suitable UV-filters, in order to protect the user and, in particular,
the user's eyes and skin.
As it is easy to measure said amount of irradiation energy it is
easy to calibrate the amount of stored energy in a quantitative way. Once the tribostimulable
storage phosphor is loaded with an amount of stored energy, the energy or radiation
in form of light emitted after stimulation of the said tribostimulable storage
phosphor (present as a single crystal or as crystals coated as self-supporting
screen or panel or coated onto a support) by a pressure source, causing pressure
force variations, is detected with a detector, e.g. a photomultiplier, at the time
and during the time the said pressure force variations are caused by said pressure
source or sources causing said pressure variations. Because the phosphor and the
detector are reacting quickly, short and rapid pressure force variations are detected
in this way. In dedicated applications it is useful to plot the said pressure force
variations as a function of time. As the reaction time of the system is less than
1 µs such a quick detection is superior with respect to detection speed in order
to determine changes in pressure forces.
This technique or method is thus suitable for use in those applications
where a pressure force differing from pressure by air directly in contact with
the panel is present during a very short time, or where quick variations of pressure
forces should be detected . Devices according to the present invention are thus
suitable for use in a lot of applications. Examples thereof are given hereinafter,
without however being exhaustive.
Pressure sources causing variable pressures which are perfectly detectable
by devices according to the present invention thus applying the method of the present
invention are e.g. pressure force variations caused by crashes of cars in accidents,
or even more generally in crashes in traffic (trains, aeroplanes, etc.). During
the crash a short but high force is generated. Measuring this force as a function
of time provides helpful tools in order to develop e.g. safer cars in favour of
security of the driver and of the passengers. Detection as a function of the sites
on the vehicle where crashes appear gives engineers an opportunity to work out
safer constructions for the future in the motor-car industry.
Another example wherein variable pressure sources should be detected
is the pressure force of a bullet when hitting an obstacle or pressure forces caused
by objects flying around after having been thrown away or catapulted into the environment
by an explosion. For the bullets and for the explosives an optimization of the
accuracy of fire can thus be provided, e.g. as a function of distance, etc.. Otherwise
an optimization of hitted materials in order to provide protection against bullets
from fire-arms or against splinters from explosions as, e.g. by safety glass (also
useful for cars), is another valuable application. Testing of materials on ability
to withstand pressures and pressure variations in general is a very useful application
for the device according to the present invention. So materials hitted by acoustic
waves, measurable as pressure waves, e.g. in noise controll, etc. are perfectly
tested and warning signals can be provided when an undesired or even dangerous
level is exceeded.
A further useful example is the detection of the force and variations
thereof as a function of a load transported by a truck or trailer. When one or
more detectors are put on the load, and more preferably, at one or more edges thereof,
the trucker can be warned by signals sent by the detector(s) to the cabin, e.g.
on a display giving an optical signal or, more preferably by an acoustic signal
in order to warn the driver when the load is moving during transport before hitting
the wall of the truck or trailer or before causing desequilibrium of the load and
danger to be canted or tilted.
So quite a lot of other applications where pressure variations can
be detected are available, as e.g. when providing security systems to houses against
break-in, any change from a system in equilibrium or balanced system to undesired
unbalanced situations. Still another example, without being exhaustive, is the
force created by the vibrations of earth tremors, e.g. as a warning signal for
future earth-quakes, vulcan eruptions and the like, thus providing warning signals
for geographic and geological scientists. Analysis of vibration patterns (shock
waves, acoustic waves,etc. causing detectable pressure variations) would provide
those scientists with useful data in order to predict the time, site and intensity
of threatening disasters caused by such natural phenomena and would give the authorities
time to organize evacuations if required. Because of the short reaction times of
this technique, as already mentioned herinbefore, vibrations having high frequencies
are detectable and frequency spectra of pressure variations analyzed. Otherwise
making use of such a technique provides detectability of noises caused e.g. vibrations
in production processes which are very sensitive thereto, as e.g. in coating processes,
wherever required as in production of coatings, in the photographic industry, in
chips production as e.g. in microelectronic applications, in astronomy where high
stability of e.g. telescopes is required, thus requiring high stability from the
buildings wherein such apparatus are mounted, and in all machines and devices
requiring high quality equilibrium situations, as in cybernetics, fault finding
techniques, fault-find apparatus, in scientific apparatus in laboratories, in barometers
as a special application of pressure meter expressing changes in atmospheric air
pressure, wherein said changes are not the result of direct interaction of air
with the phosphor plate or panel having tribostimulable storage phosphors but where
the said air pressure differences have already been converted into fluctuating
mechanical forces, etc..
The pressure meter device described hereinbefore comprising a "tribostimulable"
phosphor crystal, present in a coated (self-supporting or supported) layer of a
panel, screen or plate as an essential element which has been described hereinbefore,
according to the present invention comprises, as part of a housing wherein said
device is built-in, in order,
- a tribostimulable storage phosphor panel as a storage medium for absorbing
energy, and more preferably calibrated amounts of energy, generated by incident
radiation energy having a wavelength of 350 nm or less, and more preferably having
an X-ray and/or UV-radiation source, and, adjacent thereto,
- transmission means permitting to apply a pressure force and variations thereof
onto said tribostimulable storage phosphor panel by means of said pressure source,
thereby stimulating said tribostimulable storage phosphor panel in order to release
stimulated light energy, preferably in an amount proportional with the said pressure
Whereas the device according to the present invention, in one embodiment,
permits pressure force or pressure force variations to be applied directly onto
said tribostimulable storage phosphor panel, in another embodiment a pressure force
or variations thereof are indirectly performed by means of transporting or transmission
means, thereby stimulating said tribostimulable storage phosphor panel in order
to release tribostimulated light energy.
According to the present invention the device comprising capturing
means captures energy released from the tribostimulated phosphor sheet or panel
in an amount proportional with the said pressure force.
According to the present invention the device wherein said panel,
said capturing and said detecting means are built-in in a housing is thus available
as a pressure meter device.
In the device according to the present invention preferred transmission
means (of the pressure forces and variations thereof) are provided by a mechanical,
an electrical, an electronical, a hydraulic or a pneumatic system wherein differences
in air pressure energy have already been converted into mechanical pressure energy,
thus differing from direct pressure energy on the panel by air or gas molecules
in more general terms, without however being limited thereto.
In the embodiment wherein the mechanical system is used a crystal
is pressed between two plates. One of those plates is connected by means of a stick
(preferably a metal stick or a stick made of composite materials) with the pressure
source. When using a hydraulic system, a liquid is preferably pressing a plate
to the crystal instead of being in direct contact therewith. When the tribostimulable
phosphor is hygroscopic, like most of those phosphors are, except from those mentioned
hereinbefore wherefore direct contact is principally possible, the said phosphor
is not placed into the liquid. Using a pneumatic system, a gas is pressing a plate
to the crystal, but positioning the tribostimulable phosphor directly into the
gas is not excluded. When doing so the pressure of the gas is detected through
a transparent area of the tube.
In one embodiment said means providing transport or transmission
of the pressure forces and variations thereof is an electrical or an electronical
system wherein a piezo-electric crystal is converting an electrical signal into
pressure energy. In another embodiment said device according to the present invention
wherein said means providing transport or transmission of the pressure forces
and variations thereof is an electrical system, said transmission means permits
pixelwise detection of variations in electrical signals performed by means of at
least one layer of piezo-electrical crystals as a source of pressure energy.
When said piezo-electrical crystal is in contact with a stimulable
phosphor crystal the thus generated pressure force or pressure force variation
is detected in form of light energy emitted from the phosphor crystal by pressure
stimulation. Arranging the piezo-electrical crystals in one row or array provides
measuring pressure and pressure variations in one dimension, i.a. linewise. Providing
more arrays of piezo-electrical crystals as a source of pressure energy makes available
detection of pressure energies and variations thereof in two dimensions and, in
accordance with the present invention, the device provides an image. In this application
however it is not the purpose to provide a radiological image, although this is
principally possible e.g. by "activation" of the pixel-wise arranged piezo-electrical
crystals by pixel-wise generating electrical pulses from digitally stored information
(e.g. captured from X-ray images obtained by CT-techniques, echography, CRT's,
laser sources, acoustic signals etc.). The stability of any light source or any
acoustic energy source (required e.g. when accurate and well-known amounts of energy
should be added as in medical therapies or in micro-electronics and/or measured
as in digitizing techniques, speech technology, etc.) can thus be analyzed very
quickly with a high accuracy and even in quantitative way after calibration of
the measuring device.
In a particular embodiment the device according to the present invention,
more particularly the device having a layer of piezo-electrical crystals pixelwise
performing pressure on the said storage phosphor panel in order to read-out said
tribostimulable storage phosphor panel imagewise by direct contact between said
piezo-electrical crystals and said storage phosphor panel is provided with means
in order to apply an electrical field on said piezo-electrical crystals by row
and column electrodes, provided at both sides of said layer and mounted perpendicularly
to each other, coupled to a voltage source adapted for applying an electrical
potential to each of said electrodes separately.
Otherwise the device according to the present invention provides,
in a particularly preferred embodiment, an imagewise pattern corresponding with
e.g. a stiffness pattern or a relief pattern of a test material: sites where less
stiffness is measured give rise to less deformation of the piezo electrical crystal,
thus without creating a high pressure, opposite to sites showing a higher degree
of stiffness. In praxis in this application the tribostimulable storage phosphor
plate or panel is uniformly exposed with X-ray or UV-light in order to get accumulation
of equal amounts of stored energy over the whole panel.
So the device according to the present invention thus provides, in
a particularly preferred embodiment, an imagewise pattern corresponding with a
stiffness or a relief pattern of a test material.
As in the case of pixel-wise stimulation of tribo-stimulable phosphor
crystals a differing pressure from one to another pixel is detectable, an image
is generated. The image thus obtained is an image which is illustrative for e.g.
the uniformity of a flat surface or coating of a material, of differences in the
stiffness of e.g. a cardboard, a collar, a joint, etc., or every material having
a profile with respect to pressure or whatever a physical (wave pattern, able to
be transformed into pressure or able to cause pressure waves as e.g. acoustic waves
as example of longitudinal waves, as also caused by oscillating springs or strings)
or electrical property convertable to pressure signals.
Two-dimensional relief profiles or patterns thus obtained by those
particular devices and variations thereupon, making use of the method of providing
pressure measurements, according to the present invention opens perspectives with
respect to applications in the domain of surface quality controll of (composite)
materials, research related with surface sciences, colloid surface sciences, thermographic
properties (heat conductivity, expansion of materials caused thereby), hardening
(chemical - as cross-linking processes - and physical - as phase transitions),
orientation of crystals - also liquid crystals -as a function of external magnetic
(e.g. microwaves, causing thermal effects and expansion of materials) and/or electrical
According to the present invention a device is thus provided offering
pixelwise detection (in one or in two dimensions) of variations in pressure or
electrical signals by means of at least one layer of piezo-electrical crystals
as a source of pressure energy. According to the present invention a device is
provided wherein pressure is applied linewise (in one dimension) by means of a
knife-edge or (in two dimensions) by means of a roller as a source of pressure
energy (applying pressure and pressure variations). Said knife-edge and said roller
are, according to an embodiment of the device of the present invention, present
as mechanical means transporting pressure energy and in a particular embodiment
in said device according to the present invention, transmission means provided
by said mechanical system proceed by means of a knife-edge or a roller.
The device according to the present invention having as an essential
element a tribostimulable storage phosphor plate or panel thus comprises a alkali-halide
phosphor as a tribostimulable phosphor in the most general form. More preferably
the said tribostimulable phosphor present in the device according to the present
invention has a composition comprising at least one of CsBr, CsCl, RbBr, KCl or
KBr. In a still more preferred embodiment said composition further comprises a
dopant selected from the group consisting of Eu, Gd, Ga, Ca, Sr, Ge, Sn, Au, In,
Tl, Sb, Tb and Ce or a combination thereof. Said dopant(s) is(are) present in an
amount of from 500 up to 50000 p.p.m. or in an amount of from 0.1 up to 5 % by
In the device according to the present invention energy stored in
a tribostimulable phosphor is thus converted (in part) by means of a source of
pressure energy differing from direct air pressure energy. Converting energy stored
in a tribostimulable phosphor panel or plate thus comprises the steps of
- (a) storing energy in a stimulable phosphor of a screen or panel comprising
one or more layers comprising stimulable phosphors;
- (b) converting said energy to emission energy by means of said source of pressure
- (c) detecting said energy.
Step (a) is required-as the storage phosphor should be loaded with
an amount of energy (exceeding a minimum level, preferably a well-known and well-defined
amount of energy) in order to get pressure stimulability.
The device according to the present invention is provided with capturing
means as has already been set forth, wherein said capturing means capture energy
released from the tribostimulated phosphor sheet or panel in an amount proportional
with the said pressure force. The device according to the present invention in
one embodiment provides the tribostimulated light to be detected as a signal by
capturing means and brought to a photomultiplier where the said signal is further
processed. In a preferred embodiment said capturing means represent at least one
line of optical fibers.
Further according to the present invention the device provides said
detectable signal become a processed signal stored in an electronic memory. In
a preferred embodiment said device is provided with a DSP(digital signal processing)-chip
as a very suitable electronic memory, wherein said processed signal is stored.
The device according to the present invention further comprises detecting means
selected from the group consisting of a CCD, a photo-multiplier and a photodiode-array.
In a preferred embodiment said CCD, photomultiplier or photodiode-array is in indirect
contact with the storage panel by means of a fiber optic plate and in a particularly
preferred embodiment said indirect contact is realized by means of a fiber optic
plate or by means of an array of focusing cells or lenses.
The device according to the present invention in a preferred embodiment
comprises a panel, a capturing means and a detecting means, built-in in a housing
as a pressure meter device.
The device according to the present invention in a particular embodiment
further contains as outermost layers covering the tribostimulable storage panel
- at its largest sides a layer, present at one or both of said largest sides,
wherein said layer is a filter layer absorbing energy which should not be detected
during exposure (in order to avoid deterioration of the calibrated amount of energy
added to the storage phosphor panel);
- at surrounding edges around the layers, a surrounding layer, wherein said layer
is an optical filter layer transmitting exclusively energy released by said tribostimulable
storage phosphor panel after tribostimulation.
In order to determine in a quantitative way stored amounts of radiation
energy originating from radiation having a wavelength of 350 nm or less, following
method is very suitable as method according to the present invention, said method
comprising the steps of :
- i) providing a device as described hereinbefore;
- ii) irradiating said device by incident radiation in such a way that the said
tribostimulable storage panel is exposed with a calibrated amount of energy, generated
by incident radiation having a wavelength of 350 nm or less;
- iii) reading out said storage phosphor panel by provoking stimulation of said
tribostimulable storage phosphors by a source of pressure force;
- iv) digitally detecting energy released from said tribostimulable storage phosphor
panel by a detector;
- v) erasing stored rest energy.
In a preferred embodiment of the present invention a method is provided
to absorb or capture energy and reproduce quantitatively said energy originating
from a pressure source by the device according to the present invention described
hereinbefore, wherein said method comprises the steps of
wherein said phosphor is stimulated by pressure emanating from a pixel-wise driven
- i) exposing the tribostimulable storage phosphor to a calibrated amount of
penetrating radiation having a wavelength of 350 nm or less (X-rays and/or UV-rays),
- ii) storing the said calibrated amount of energy from said penetrating radiation
in said storage phosphor,
- iii) releasing at least part of said stored energy as tribostimulated light
by stimulating said phosphor with energy generated by a source of pressure force
In another preferred embodiment according to the present invention
a method is provided of measuring a pressure force generated by making use of following
further storing said digitally detected energy (as e.g. individual digital data)
in an electronic memory;
- i) absorbing and storing incident radiation energy originating from radiation
having a wavelength or 350 nm or less (in a particular embodiment from radiation
having a wavelength of 254 nm, corresponding with a mercury vapour lamp)
wherein said panel is covered with an optical filter absorbing radiation having
a wavelength of 350 nm or more;
- ii) reading out said storage phosphor having pressure stimulating ability by
adding stimulating energy to the said storage panel by means of pressure or energy
convertable to pressure,
- iii) (digitally) detecting energy released from said storage phosphor panel
by a detector as digitally detected energy,
plotting said data (from those digital measurements showing pressure
variations) as a function of time, and
erasing stored rest energy in the storage panel by means of energy
from a light source (capable to discharge any energy stored as rest energy in the
panel), a heat source or a pressure source.
According to the present invention methods have thus been provided,
as described hereinbefore, wherein said phosphor is stimulated by pressure emanating
in one or in two dimensions from a source of pressure energy.
In a particular embodiment according to the present invention a method
for monitoring a dose of penetrating radiation absorbed by an object is provided,
said method comprising the steps of
- (a) providing said object with a device for absorbing penetrating radiation,
including a tribostimulable storage phosphor for storing energy from said penetrating
- (b) at predetermined intervals coupling said tribostimulable storage phosphor
to a source of pressure, activating said source of pressure in such a way as to
cause said tribostimulable storage phosphor to emit an amount of fluorescent light
proportional with an amount of stored energy;
- (c) reading said amount of fluorescent light and converting it in an electric
signal value or values;
- (d) storing electric signal value(s) obtained at said predetermined intervals
and processing them in order to evaluate a total amount of radiation absorbed by
- (e) comparing said total amount with a predefined threshold value in order
to obtain a figure as a difference of values, and
- (f) displaying said figure on a (decentralized) display.
Apart from the method of the present invention as set forth, this
method of monitoring a dose is characterised by the steps of coupling said tribostimulable
storage phosphor to a source of pressure, activating said source of pressure in
such a way as to cause said tribostimulable storage phosphor to emit an amount
of fluorescent light proportional with an amount of stored energy; reading said
amount of fluorescent light and converting it in an electric signal value or values;
storing electric signal value(s) obtained at said predetermined intervals and processing
them in order to evaluate a total amount of radiation absorbed by said object;
comparing said total amount with a predefined threshold value in order to obtain
a figure as a difference of values, and displaying said figure on a (decentralized)
The alkali metal phosphors used in tribostimulable phosphor panels
of devices according to the present invention can be produced according to any
way known in the art, starting from phosphor precursors, e.g. oxides, carbonates,
sulfonates, halides, phosphates, nitrates, oxalates, lactates, acetylacetonates,
malonates, phthalates, alkoxides, phenoxides or ethylenediamine derivatives of
the metalions that are to be incorporated in the phosphor. These phosphor precursors
are mixed in the appropriate stoechiometric proportions and are then heated for
a given time. After cooling, the sintered block of phosphor is milled into fine
phosphor particles. The milling operation continues until phosphor particles with
the appropriate average particle size and size distribution are obtained. During
the preparation of the phosphor any known flux materials can be added to the reaction
mixture. Flux materials useful for use in the preparation of the phosphors according
to the invention are e.g. halides, metasilicates of alkali metals or alkaline earth
A very useful and preferred method for the preparation of alkali
metal phosphors suitable for use in tribostimulable phosphor panels of devices
according to the present invention can be found in Research Disclosure Volume 358,
Februari 1994 p 93 item 35841. Another useful method can be found in US-A 5,154,360.
The average grain size of said alkali metal-phosphors is preferably
in the range of 2 to 25 µm, more preferably in the range of 3 to 15 µm.
The alkali metal phosphors for use in the method of the present invention
are beneficially used in order to form a radiation image storage screen or panel.
A storage panel or screen comprising such a phosphor for use in the present invention
comprises in its method for use the steps of
- i) exposing a tribostimulable storage phosphor screen,
- ii) stimulating said tribostimulable screen in order to release the stored
(high energetic X-ray, UV-ray..) energy as stimulated radiation (in form of visible)
- iii) collecting said stimulated light.
It is possible to use the alkali metal phosphors suitable for use
in stimulable phosphor panels of devices according to the present invention either
alone or mixed with one or more other phosphors. Mixtures of alkali metal phosphors
and other tribostimulable storage phosphors can be useful but also for dual energy
applications this may be applied, e.g. mixing tribostimulable phosphors with radiation
stimulable phosphors (stimulable by a laser emitting light source between 500
and 1000 nm as e.g. an Ar gas ion laser (514 nm), a frequency double NdYAG laser
(532 nm), a He-Ne laser (632 nm), a diode laser emitting at 680 nm, a GaAs laser
emitting at 835 nm, etc.), provided that the relative amounts of both types of
stimulable phosphors and their relative absorption capacity of high energetic X-rays
and/or UV-rays can be calculated in order to know the relative amounts of stored
energy by said both types when calibration and/or precise knowledge of emitted
energy is required.
The storage screen or panels used in devices according to the present
invention can be prepared by vacuum deposition of tribostimulable phosphors on
a support, yielding a panel or screen. Substantially no binder is then required.
It is also possible to prepare panels by electro-depositing the tribostimulable
phosphors onto the support also yielding a screen or panel comprising substantially
no binder. A very suitable method for electro-depositing tribostimulable phosphors
for use in a device according to the present invention has e.g. been disclosed
in US-A 5,296,117.
The storage screen or panel is either self-supporting or is coated
on a support, whether or not comprising a binder in both cases.
Any binder known in the art can be used to form a screen or panel
comprising a tribostimulable phosphor for use in the device according to the present
invention. Suitable binders are, e.g., gelatin, polysaccharides such as dextran,
gum arabic, and synthetic polymers such as polyvinyl butyral, polyvinyl acetate,
nitrocellulose, ethylcellulose, vinylidene chloride-vinyl chloride copolymer,
polyalkyl (meth)acrylate, vinyl chloride-vinyl acetate copolymer, polyurethane,
cellulose acetate, cellulose acetate butyrate, polyvinyl alcohol, polystyrene,
polyester, etc. These and other useful binders are disclosed e.g. in US-A's 2,502,529;
2,887,379; 3,617,285; 3,300,310; 3,300,311 and 3,743,833. A mixture of two or
more of these binders may be used, e.g., a mixture of polyethyl acrylate and cellulose
acetobutyrate. Weight ratios of phosphor to binder are generally within the range
of from 50:50 to 99:1, preferably from 80:20 to 99:1. Preferably a self-supporting
or supported layer of tribostimulable phosphor particles according to the present
invention comprises said particles dispersed in a binding medium and a protective
coating thereover characterized in that the binding medium substantially consists
of one or more hydrogenated styrene-diene block copolymers, having a saturated
rubber block, as rubbery and/or elastomeric polymers. The polymer can be represented
by the formula A-B-A (tri-block) or by the formula A-B (di-block), wherein A represents
styrene and B represents the hydrogenated diene block e.g. ethylene-butylene or
ethylene-propylene. Further the ratio by volume of phoshor to binding medium is
preferably more than 70/30 and still more preferably more than 85/15.
By said hydrogenated diene copolymers, for use as rubbery and/or
elastomeric polymers, the phosphor layer has improved elasticity of the screen,
high protection against mechanical damage and thus high ease of manipulation and
allows high pigment to binder ratio without getting deteriorated by ageing after
frequent reuse. Particularly suitable thermoplastic rubbers, used as block-copolymeric
binders in phosphor screens in accordance with this invention are the KRATON-G
rubbers, KRATON being a trade mark name from SHELL. KRATON-G thermoplastic rubber
polymers are a unique class of rubbers designed for use without vulcanisation.
In the published report KR.G.2.1 (INTERACT/7641/2m/1186 GP KRA/ENG) wherein a description
of KRATON-G rubbers is given, the KRATON-G 1600 series rubbers are presented as
block copolymers in which the elastomeric midblock of the molecule is a saturated
olefin rubber. KRATON-G 1600 series rubbers are described to possess excellent
resistance to degradation by oxygen, ozone and UV light and they also have high
cohesive strength and retain their structural integrity at elevated temperatures.
The coating weight of tribostimulable phosphor particles can be adapted
to the desired energy of the storage screen or panel to be captured, but preferably
a coating weight between 5 and 250 mg/cm2, most preferably between 20
and 175 mg/cm2, is used.
A stimulable storage screen or panel for use in a device according
to the present invention can be prepared by the following manufacturing process.
The tribostimulable phosphor layer can be applied to the support by any coating
procedure, making use of solvents for the binder of the phosphor containing layer
as well as of useful dispersing agents, useful plasticizers, useful fillers and
subbing or interlayer layer compositions that have been described in extenso in
EP-A 0 510 753. Tribostimulable phosphor particles are mixed with the dissolved
rubbery polymer, in a suitable mixing ratio to prepare a dispersion. Said dispersion
is uniformly applied to a substrate by a known coating technique, e.g. doctor blade
coating, roll coating, gravure coating or wire bar coating, and dried to form
a phosphor layer. In the preparation of a tribostimulable storage screen, one or
more additional layers are occasionally provided between the support and the phosphor
containing layer, having subbing- or interlayer compositions, in order to improve
the bonding between the support and the phosphor layer, or to improve the sensitivity
of the screen or the sharpness and resolution of an image provided thereby. For
instance, a subbing layer or an adhesive layer may be provided by coating polymer
material, e.g., gelatin, a polyester cross-linked by a reaction with a tri-isocyanate
or a polyester with only terminal hydroxyl groups, the chain length of which has
been increased by the reaction of said terminal hydroxyl groups and a di-isocyanate,
over the surface of the support on the phosphor layer side. Said subbing layer
may contain also modified thermoplastic acrylic resins such as those described
above to improve the adhesion properties of the subbing layers. After applying
the coating dispersion onto the support, the coating dispersion is heated slowly
to dryness so as to complete the formation of a phosphor layer. In order to remove
as much as possible entrapped air in the phosphor coating composition it can be
subjected to an ultrasonic treatment before coating. Another method to reduce the
amount of entrapped air consists in a compression method as has been described
in EP-A 0 393 662, wherein the said compression is preferably carried out at a
temperature not lower than the softening point or melting point of the rubbery
binder to improve the phosphor packing density in the dried layer. In order to
avoid electrostatic discharges during manufacture of the screen, especially during
the coating procedure, conductive compounds can be added to the phosphor/binder
mixture or the support can be provided with a conductive layer (lateral resistance
< 1012 W/square) on that side of the support opposite to the side
to be coated with the phosphor/binder mixture.
If necessary, after coating the phosphor/binder mixture the conductive
layer on the side of the support opposite to the phosphor/binder mixture layer,
may be covered by a plastic sheet or web material. After formation of the phosphor
layer, a protective layer is generally provided on top of the phosphor layer. The
protective coating composition can be applied as described e.g. in US-A 4,059,768.
In a preferred embodiment the protective coating composition is applied by a rotary
screen printing device as has been described in detail in EP-A 510 753. The top
coat is preferably formed by applying a radiation curable coating on top of the
phosphor layer. When radiation-curing is carried out with ultraviolet radiation
(UV), a photoinitiator is present in the coating composition to serve as a catalyst
to initiate the polymerization of the monomers and their optional cross-linking
with the pre-polymers resulting in curing of the coated protective layer composition.
To the radiation-curable coating composition there may be added a
storage stabilizer, a colorant, and other additives, and then dissolved or dispersed
therein to prepare the coating liquid for the protective layer. Examples of colorants
that can be used in the protective layer include MAKROLEX ROT EG, MAKROLEX ROT
GS and MAKROLEX ROT E2G. MAKROLEX is a registered tradename of Bayer AG, Leverkusen,
Germany. A variety of other optional compounds can be included in the radiation-curable
coating composition of the present storage article such as compounds suitable for
reducing static electrical charge accumulation, plasticizers, matting agents,
lubricants, de-foamers and the like as has been described in the EP-A 0 510 753.
In said document a description has also been given of the apparatus and methods
for curing. The edges of the screen may be reinforced by covering the edges (side
surfaces) with a polymer material being formed essentially from a moisture-hardened
polymer composition prepared according to EP-A 0 541 146. An other very useful
way to reinforce of the edges of a screen or panel use in the device according
to the present invention, is to coat the edges with a polymeric composition comprising
polyvinylacetate, crotonic acid and isocyanates. Preferably a copolymer of vinylacetate
and crotonic acid (e.g. MOWILITH CT5, a trade name of Hoechst AG, Frankfurt, Germany)
is used in combination with isocyanates.
Support materials for tribostimulable storage screens suitable for
use in devices in accordance with the present invention include cardboard, plastic
films such as films of cellulose acetate, polyvinyl chloride, polyvinyl acetate,
polyacrylonitrile, polystyrene, polyester, polyethylene terephthalate, polyamide,
polyimide, cellulose triacetate and polycarbonate; metal sheets such as aluminum
foil and aluminum alloy foil; ordinary papers; baryta paper; resin-coated papers;
pigment papers containing titanium dioxide or the like; and papers sized with polyvinyl
alcohol or the like. A plastic film preferably employed as support material includes
e.g. polyethylene terephthalate, clear or blue coloured or black coloured (e.g.,
LUMIRROR C, type X30, (trade name) supplied by Toray Industries, Tokyo, Japan),
polyethylene terephthalate filled with TiO2 or with BaSO4.
Metals as e.g. aluminum, bismuth and the like may be deposited e.g. by vaporization
techniques to get a polyester support having radiation-reflective properties. These
supports may have thicknesses which may differ depending on the material of the
support, and may generally be between 60 and 1000 µm, more preferably between
80 and 500 µm from the standpoint of handling or mountability in the device according
to the present invention.
A screen or panel comprising a tribostimulable phosphor useful in
devices according to the present invention may carry an antistatic layer either
on top of a protective layer or on the side of the support opposite to the side
carrying said phosphor. Said antistatic layer may comprises inorganic antistatic
agents, e.g. metal oxides as disclosed in e.g. EP-A 0 579 016 as well as organic
antistatic agents (polyethylene oxides, poly(ethylenedioxy-thiophene) as disclosed
in e.g. EP-A 0 440 957.
While the present invention will hereinafter be described in connection
with preferred embodiments thereof, it will be understood that it is not intended
to limit the invention to those embodiments.
1. DETERMINATION OF "TRIBOSTIMULABILITY" PROPERTIES OF THE PHOSPHORS
In order to determine whether or not the phosphor was showing tribostimulable
properties, the phosphor was exposed to X-rays (200 kV, 10 mA) without filtering
in dark with a dose of about 10 mGray. The phosphor crystal having two flat parallel
surfaces was placed on a table.
With an optical filter BG39(3mm) of Schott the crystal was pressed
manually between the table and the optical filter.
Because the experiment was performed in a dark room, the emitted
light was seen through the optical filter at the moment that a pressure force was
The intensity of the emitted light caused by the pressure force was
very much higher than the emitted light caused by afterglow. It was also found
that the crystals are emitting strongly when the surface of the crystal was damaged
with e.g. a knife or even with a finger nail.
When the crystal was cracked, an intense light pulse was detected.
When the crystal was not exposed to X-ray or its energy levels were
completely erased with a light source, no emitted light was found after carrying
out the same experiments wherein a pressure force was applied to the crystal, wherein
the crystal was damaged or cracked.
From these experiments it became clear that only stored energy, captured
after a previous exposure with ionization radiation (as e.g. X-rays) of a composite
storage phosphor crystal suitable for use in the method of the present invention
was released by pressing, damaging or cracking the said crystal.
2. "TRIBOSTIMULABILITY" PROPERTIES OF PHOSPHORS FOR USE IN "PRESSURE METERS"
In order to make a "pressure meter" a pressure stimulable crystal,
also called "tribostimulable crystal", was placed permanently on the site where
the pressure should be measured.
The said crystal was irradiated beforehand with a well-known amount
of energy, generated from UV- or X-rays in order to get a known amount of stored
After the said exposure the emitted light was detected with a photomultiplier
while releasing the known stored energy under the influence of an external pressure
Because the storage phosphor and the detector were reacting quickly,
shortly and rapidly changing pressures were detected and pressure was plotted as
a function of time.
As the reaction time of the "tribostimulable phosphor-photomultiplier"
("TSP-PMP") system was less than 1 µs it was shown that the said system was useful
as a "pressure meter" as no other system has hitherto been known to provide such
a speed in determining such small pressure force changements.
Having described in detail preferred embodiments of the current invention,
it will now be apparent to those skilled in the art that numerous modifications
can be made therein without departing from the scope of the invention as defined
in the appending claims.