U.S. patent number 3,655,964 [Application Number 04/726,928] was granted by the patent office on 1972-04-11 for ionizing radiation apparatus and method for distinguishing between materials in a mixture.
Invention is credited to David Laurie Slight.
United States Patent |
3,655,964 |
Slight |
April 11, 1972 |
IONIZING RADIATION APPARATUS AND METHOD FOR DISTINGUISHING BETWEEN
MATERIALS IN A MIXTURE
Abstract
Materials in a mixture are distinguished for identification or
sorting purposes by subjecting them to ionizing radiation at least
two different energy levels and determining the effects, other than
solely edge effects, of the materials on the two levels of
radiation.
Inventors: |
Slight; David Laurie (North
Mains, Ormiston, East Lothian, SC) |
Family
ID: |
24920619 |
Appl.
No.: |
04/726,928 |
Filed: |
May 6, 1968 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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433705 |
Feb 18, 1965 |
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Current U.S.
Class: |
378/53; 209/640;
250/362; 378/108; 209/589; 209/908; 378/51 |
Current CPC
Class: |
G01N
23/12 (20130101); G01N 23/083 (20130101); Y10S
209/908 (20130101) |
Current International
Class: |
G01N
23/08 (20060101); G01N 23/02 (20060101); G01n
023/12 () |
Field of
Search: |
;250/43.5D,43.5R,51.5,83.3D ;209/111.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Borchelt; Archie R.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application is a continuation-in-part of application
Ser. No. 433,705, filed on Feb. 18, 1965, and now abandoned.
Claims
What is claimed is:
1. A method of identifying pieces of at least one material in a
continuous flow of a mixture comprised of discrete pieces of at
least two different materials, said method comprising establishing
as a standard the ratio of the effects caused by at least one of
the materials on ionizing radiation radiating at each of at least
two levels, said levels being substantially different from and to
one side only of at least a prominent absorption edge of each of
the materials in said mixture, passing the flow of discrete pieces
of said at least two different materials through radiation at least
at said two levels, assessing the ratio of the effect of each piece
of material passing through the radiation on said at least two
levels of radiation, and comparing the assessments with the
standard effect, and thereby identifying at least the pieces of
said at least one material.
2. A method as claimed in claim 1 wherein said radiation comprises
gamma-radiation and wherein said at least two levels of radiation
are obtained by using different sources of gamma-radiation.
3. A method as claimed in claim 1 wherein said mixture includes
first and second materials, said method further comprising sorting
out pieces of said first material from pieces of said second
material using deflecting means responsive to a control signal
produced in accordance with the results of said assessing step for
deflecting pieces of said second material from said continuous
flow.
4. A method as claimed in claim 1 wherein said mixture is radiated
with a beam of ionizing radiation and said assessing step includes
using a plurality of scintillators, arranged at discrete intervals
across the width of said beam, and a plurality of counters
associated with said scintillators, to produce output signals in
accordance with the effect of said mixture on said radiation.
5. A method as claimed in claim 4 further comprising feeding back
said output signals to control the radiation from said sources to
prevent overloading of said scintillators.
6. A method as claimed in claim 5 wherein said output signals are
fed back through an integrator to a power supply for said
sources.
7. A method as claimed in claim 1 wherein said mixture includes
first and second materials, said method further comprising sorting
out pieces of said one material from pieces of said second material
using deflecting means responsive to a control signal derived from
said output signals.
8. A method as claimed in claim 7 further comprising applying said
output signals to a pulse amplifier and two channel pulse height
analyzer to produce first and second signals, applying said first
signal through a first integrator and a first DC amplifier to one
input of a polarized relay and applying said second signal through
a second integrator and second DC amplifier to a second input of
said polarized relay, said relay producing said control signal.
Description
This invention relates to arrangements for and methods of analysing
and/or sorting materials, especially those arrangements or methods
suitable for analysing and/or sorting a mixture of a plurality of
materials. The invention is based upon the fact that most, if not
all, elements have different radiation absorption (and presumably
scattering) coefficients over a range of photon levels. (See, for
example, Cameron, J. F. - "The Use of Radioactive Isotopes in
Non-destructive Testing." Progress in non-destructive testing. Vol.
2. p.91 (1959)).
Proposals have been made heretofore for apparatus to determine the
composition and thickness of a layer of material by use of X-rays
and these proposals have in fact been particularly suited to
control of composition of material in production in continuous
flow. The proposals have, however, relied upon use of radiation
radiating at two energy levels, one just above and the other just
below the absorption edge of the element being monitored; it is
another limitation that the proposals have been capable of
monitoring only one element. Furthermore, use of the absorption
edge effect places a further limitation on thickness of the layer
being monitored and only thin sheets of materials, such as metal or
plastics, films or foils, or paint films on standard bases are
capable of being monitored by this known apparatus.
There is a demand for apparatus that is capable of providing rapid
identification or analysis and such like of mixtures of discrete
lumps of materials of differing sizes and compositions and it is an
object of the present invention to provide such an apparatus.
It is a particular feature of use of the present invention,
therefore, that discrimination may be effected between different
materials in spite of their being of different thicknesses and
masses.
An arrangement for analysing and/or sorting a mixture of two or
more materials in accordance with the invention comprises means for
subjecting said materials to radiant energy at or including a
plurality of energy levels, means responsive to the effects of said
materials upon said radiation at two or more different energy
levels and means under the influence or control of said responsive
means, for indicating the composition of at least one of said
materials and/or for identifying and/or discriminating between
and/or sorting at least some of the said different materials in
dependence upon the response of said responsive means at said two
or more energy levels. The radiant energy may be substantially
continuous over the whole range of the said energy levels and
response at the required different levels may be derived from
analysis of the response of said responsive means to said
continuous range of radiant energy. Alternatively the radiant
energy may be derived from sources of different gamma-radiations,
the number of different radiations being at least equal to the
number of different materials to be analyzed and/or separated out;
it may be possible to obtain the requisite number of different
radiations from a single source of gamma-radiation, emitting in a
plurality of modes.
Signals from the responsive means may be passed to means for
subjecting them to analysis at each of the said plurality of
levels, said energy level analysis means being adapted to pass
their signals of analysis to means for submitting the same to
comparison with standard signals, whereby one or more of the
materials may be identified and/or sorted or it, or their,
composition(s) indicated.
In accordance with a feature of the invention an arrangement for
monitoring and/or determining the composition of a mixture of
materials in substantially homogeneous form, such as for process
control, comprises means for subjecting said mixture in motion, or
in turn, to radiant energy at or including a plurality of energy
levels, means responsive to the effects of said materials upon said
radiation at two or more different levels, the number of levels
depending upon the number of discrete materials in the mixture the
composition of which it is desired to monitor and/or determine,
means adapted to compare said effects on said responsive means at
the said two or more energy levels with similar effects caused by
materials of standard composition and means sensitive to said
response for indicating coincidence with and/or departures from
said standard.
In accordance with yet another feature of the invention an
arrangement for sorting one or more materials from a mixture with
one or more other materials having different response(s) to the
incidence of ionising radiation, comprises means for providing a
beam of radiant energy at or including a plurality of energy
levels, means for causing said mixture to pass through said beam,
means for detecting the response of said different materials to the
effects of incidence of two or more of said levels of radiant
energy, means for comparing the response of their effects at the
two different levels or more with standard responses or their
effects at the respective levels, diverting means in the path of
said materials after passing through said beam being provided under
the control of signals from said comparison means for said
responsive means, for diverting the or those material(s) for which
there is coincidence with (or departure from) standard response for
that particular material selected. The said diverting means may
comprise electro-mechanically controlled keys adapted to be
operated in accordance with signals from said comparison means to
divert or let pass certain of the different materials depending
upon the information supplied by the comparison means concerning
said materials. If two or more materials are to be separated from
each other and from one or more other materials, a plurality of
sets of said diverting means may be arranged in series, the
different sets being adapted to operate in accordance with the
signals derived from said comparison means for different materials
in said mixture, whereby said different materials may be segregated
from each other by operation of one or other of said diverting
means.
In accordance with another feature of the invention a method of
analysing and/or sorting a mixture of two or more materials having
different response to the incidence of ionizing radiation from each
other, comprises subjecting said materials to radiant energy at or
including a plurality of energy levels, assessing the effects of
said materials upon said radiation at two or more different energy
levels, said two or more different energy levels being chosen to
give different responses of at least one or some of said materials,
and by comparison of said assessment with known responses of each
said material or selected material, identifying the composition of
the said one or more materials or causing said one or more
materials to be separated from the remainder.
Since the invention relies, in effect, upon comparison of
absorption coefficients at the different energy levels, it is clear
that absorption edges are to be avoided and that energy levels must
be chosen so as both to lie to one side or the other of any
prominent edge of the materials under examination. The spectrum of
energy levels used for the present proposals must not span the
absorption edge of any of the elements concerned.
The energy links should be chosen such that the bandwidth of the
detection means is sufficiently far removed from any absorption
edge as not to impair the required accuracy of the final analysis.
Generally speaking the greater the accuracy required, the further
should the energy limits be from the absorption edge.
In order that the invention may be clearly understood, some
embodiments thereof in different forms will now be described by way
of examples with reference to the accompanying drawings.
In FIG. 1 of the drawings is sown in diagrammatic form an apparatus
for separating out one material from a mixture with another
material, such as, for instance, flint form a chalk/flint mixture
so as to leave a substantially flint-free chalk.
FIG. 2 illustrates, also diagrammatically, a suitable arrangement
of X-ray beam generator, conveyor and detection system for use in
recording, or monitoring, the flow of a mixture of solids,
while
FIG. 3 is an indication of an apparatus that would be suitable for
use with a flow of powder or slurry, wherein the composition of the
powder or slurry may be monitored or recorded.
FIG. 4 is a block diagram of apparatus suitable for analysing or
sorting a plurality of more than three materials from a mixture
with one or more further materials.
Referring now to FIG. 1, a mixture that may contain two or more
different materials M.sub.1 and M.sub.2 is fed by a conveyor 1 so
as to fall across an X-ray beam which is emitted by an X-ray tube
in housing 2 through a collimator 3. The collimator provides a thin
beam that is broad enough to span the width of the conveyor.
Various forms of beam generator are described in British Pat. No.
984,232 and it is possible that the generator could be pulsative.
It is necessary to ensure that the radiant energy emanating from
the collimator covers at least two energy levels, the absorption of
which by one material to be sorted out of the mixture is such that
the ratio of the response to the detectors at the two energy levels
in the presence of the one material is appreciably different from
the ratio in the presence of the other or any of the other
materials.
A number of scintillators 4 are arranged at discrete intervals
across the width of the beam and these are normally exposed to the
beam; each scintillator is associated with a scintillation counter
5 in known manner but, if desired, these scintillators and counters
may be replaced by proportional counters and as will be seen later,
the beam may be controlled to prevent overloading of the
scintillators.
The signals from each counter are fed to a pulse analyser 6 which
includes a pulse amplifier and the pulses are divided into two
pulse height channels A, B. Each channel feeds an integrator 7A,
7B, such as a diode pump integrator, and a D.C. amplifier 8A, 8B.
Integration is arranged to be effective over timed periods, these
being triggered by a start/stop timer 9 and the outputs are fed to
a polarized relay 10, or the equivalent.
A control signal is taken from one of the channels A, B, from the
pulse height analyser through a feed back control integrator 11 to
the power supply 14 to control the current in the X-ray tube in
such a way that the tube current is reduced for a high count rate
and increased for a low count rate - this means in fact that the
tube current may be reduced to zero, for example, for air and that
the tube current will be low for a thin piece of material and
increased for a thick piece of material and in this way the
detection system is not overloaded.
The relay 10 may be arranged to operate about a balance point such
that the presence in the radiant beam of a piece of the material to
be sorted out will cause the relay to operated to energise an
electromechanical, or a pneumatic actuator 11, through an amplifier
12 if required, so as to prevent the appropriate finger 13 of a
separator from deflecting when a piece of the particular material
strikes it. The result of that operation of the relay will
therefore be to divert the one material from the general stream of
falling materials, other materials simply deflecting to allow
passage of the material(s). Reference may be had to the
specification and drawings accompanying U.S. Pat. No. 3,209,910 for
further details of conveyor and diverting mechanisms.
Thus if the material fed by the conveyor 1 is a mixture of chalk
with flints, the separating apparatus can be made to operate so
that flint is the material which causes locking of the appropriate
separating fingers so that the flint is taken out of the stream of
chalk.
It will be understood that if desired a plurality of detector banks
and/or of sorting layers may be provided.
The apparatus shown in FIG. 2 would be associated with a pulse
height analyzer in this way and integrators similar to those shown
in the arrangement of FIG. 1, but the signals from the integrators
may be arranged to feed a recorder or some similar device so that
the composition of the flow of materials may be monitored or
recorded. In FIG. 3, the conveyor for solid materials in FIG. 2 is
replaced by a rectangular section duct through which a liquid
slurry or airborne powder may be directed and the composition of
the powder or slurry can be recorded, monitored or analysed as will
be evident. In the arrangements of both FIG. 2 and FIG. 3 the
signal derived from the detectors will be backed off to a certain
extent because of the presence of the conveyor belt or the
ducting.
It will be understood that each scintillation counter channel will
be associated with its own anaylser circuit and that, therefore,
each finger of the separator in the arrangement of FIG. 1 will be
under the control of its appropriate counter through the particular
circuits associated therewith. It will also be evident that there
is no limit to the number of counters arranged across the width of
the conveyor; and also that the width of the conveyor need not be
restricted, though some difficulty may be encountered with the
spread of a single source of X-rays and it may be necessary to
provide more than one source, though such sources will essentially
be similar. In addition the smaller the scintillator and counter
assembly, the more sensitive may the arrangement be made to size of
material but the complication of the system will increase as the
number of counters is increased, since each will need to have its
own analysing system for control of separators or for monitoring
etc.
Referring now to FIG. 4, a system is illustrated that can be used
for identifying and/or analysing a multiplicity of materials. Here
again it will be understood that the parts of the apparatus
illustrated are only typical and that provision will need to be
made for similar parts for each counter involved. A plurality of
gamma-ray sources 20 are arranged to direct the beam of gamma rays
on to counters 21 which may be of the scintillation or proportional
type. As discussed above, the X-ray source described hereinbefore
can be replaced by a number of gamma-ray sources or by a single
source of gamma-radiation emitting in a plurality of modes. There
are many gamma-ray sources on the market and all one needs to do is
to consult a list from a supplier and choose the sources best
suited to the particular materials to be examined. It is clear that
sources whose half-lives are very short are unacceptable but having
decided upon the particular sources and bearing this limitation in
mind, one need only to determine in a well-known manner the
appropriate quantity of each source necessary to provide a signal
of appropriate strength. The output pulses from each counter are
fed to a linear amplifier 22 and the signal is divided into two
sets of different pulse heights which are fed to analysers 23A and
23B; each set is subsequently integrated in diode pump integrators
24A and 24B at least until a statistical significance is
established and the resulting signals are fed into a simple form of
analogue computer 25. In the computer it may be arranged, for
instance, that the times taken to charge standard capacitors to
preset voltages may be established and a signal proportional to the
ratio of these times for the two channels is fed to a store 26 of
information on each type of material or object or the signal may be
compared with standard ratios and the material or object thereby
identified or analysed.
Thus each counter operates to provide packets of information
concerning each object or piece of material that passes between it
and the radiation sources; and these packets of information are
analysed and eventually provide the means of identifying the
particular object or pieces of material. If analyses of objects or
the pieces of the material are required to be obtained by such a
means, it is almost essential that they should be homogeneous, but
such requirement will depend to a large extent upon the accuracy
with which the apparatus is required to work. It will be seen that
if the material consists of a plurality of constituent parts, it is
necessary that the number of levels of radiant energy, and
therefore the number of channels of pulse heights, should be at
least equal to the number of said constituents. The computer may
then function, if necessary, to provide an indication of the
quantity of each constituent present in a flow of material, or on a
continuous basis. Alternatively, the apparatus may be used to
search for particular materials or constituents and to signal their
presence; the apparatus may even measure the quantity or quantities
present.
Another application of apparatus similar to that illustrated in
FIG. 4, is to separate out a mixture of more than two components.
Thus sorting apparatus may be similar to that shown in FIG. 1, but
the number of separators may be increased to equal the number of
components to be taken out of a mixture. The additional separators,
which may each comprise a plurality of controlled fingers in the
same way as a separator in FIG. 1, will be arranged in series, one
vertically below the next. The computer will then assess the pulses
from each counter as pieces of the mixture pass through the beam
and, by means of gating techniques, in well-known manner, will
provide discriminating signals which will cause locking of the
appropriate finger(s) of the particular separator for diverting the
material subjected to the particular scrutiny. The finger thus
locked will ensure that the particular piece of material is
directed from the flow at the correct stage.
It will be observed teat, using the above techniques, mixtures may
be fed over a broad front, or a narrow one, as desired. Of course,
if only a small through-put is required, it may be arranged that
each piece of the mixture passes through the same part of the
radiation and only one counter, and associated gear, need be
provided. Of course if the source is of variable amplitude the
apparatus can be arranged to be set at the most advantageous levels
for any of a whole variety of constituents. By providing for
working over a wide enough spectrum of energy levels, any
particular material may be scrutinised for the presence of selected
constituents.
It would appear that an advantageous range of energy levels in
which apparatus or a method in accordance with the invention is
approximately 10 - 100 KeV.
It is to be understood that the scope of the present invention is
not confined to those embodiments in which it is arranged that the
materials of the mixture shall traverse the radiation beam
completely. Indeed, where the detection system is arranged to
detect effects due to scatter of the radiation falling upon the
materials, it may be necessary, and even desirable, that the
materials shall pass through only a part of the beam thickness,
that is to say, for example, merely into the path of the radiant
energy.
To understand the operation of the apparatus or the method of the
invention, it is necessary to take the basic equation for X-ray (or
other radiation) absorption by a material. This is
I = I.sub.0 e.sup.- x
where I = intensity emergent from the material,
I.sub.0 = intensity incident upon the material
.mu. = absorption coefficient of material and
x = thickness of the material and it is known that .mu. for a
particular material is not constant but varies with the energy
level of the radiation.
Therefore, where a substantially constant composition of mixture is
passed through the apparatus, measurement of the emergent intensity
of the radiation at two energy levels by means of the detector,
amplifier and analyser results in the establishment of two signals
to be passed to the computer:- i.e. proportional to
I.sub.1 = I.sub.01 e .sup.- 1.sup. x
1. I.sub.2 = I.sub.02 e 2. The computer may solve equation 1 for x
using .mu..sub.1 for the "normal" mixture at that energy level, and
that value of x is then substituted in equation 2 which is solved
for .mu..sub.2. If this value of .mu..sub.2 is the same as the
absorption coefficient of the normal mixture at that energy level,
the mixture under test is normal, and if not, the mixture is other
than normal. Thus the output of the computer may be used either to
record the abnormality or to correct it. It should be noted that
the computer calculation is independent of the flow thickness.
Where, in another application of the invention, it is desired to
identify, in respect of its composition and irrespective of its
thickness, each object in a mixture of objects composed of, say, a
number of materials whose absorption coefficient .mu. is known for
particular levels, the same measurements are taken as for the fist
application and the computer then solves the simultaneous equations
in the same way except that if the final comparison of .mu..sub.2
does not tally, the computer recalculates using a different value
of .mu..sub.1 corresponding to a different material. When equality
of .mu..sub.2 is achieved the material is identified and its
thickness has also been calculated, and this information can be
used, for example in keeping records, in quality control or in
separation.
Where in a third application of the invention, it is desired to
find the proportion of each of two or more known materials in a
mixture, measurements are made at two or more energy levels, the
number of energy levels being equal to the number of materials. The
simultaneous equations resulting are solved by the computer and the
proportions of the various materials provided.
It will be appreciated that the response of the various parts of
the circuits described may readily be made sufficiently rapid that
all of the conditions described above for functioning of the
apparatus may be satisfied during the time taken for a piece of
material of smallest effective size to fall under gravity through a
beam of comparable thickness. In consequence apparatus in
accordance with the invention may be made to be very versatile in
application.
* * * * *