U.S. patent application number 14/635575 was filed with the patent office on 2016-09-08 for nuclide decay discriminator system and method.
This patent application is currently assigned to CANBERRA INDUSTRIES, INC.. The applicant listed for this patent is CANBERRA INDUSTRIES, INC.. Invention is credited to Henrik JADERSTROM, Steve Fisher Jones, Wilhelm Mueller, Mark Vicuna.
Application Number | 20160259069 14/635575 |
Document ID | / |
Family ID | 56611082 |
Filed Date | 2016-09-08 |
United States Patent
Application |
20160259069 |
Kind Code |
A1 |
JADERSTROM; Henrik ; et
al. |
September 8, 2016 |
NUCLIDE DECAY DISCRIMINATOR SYSTEM AND METHOD
Abstract
A nuclide decay discriminator system and method is disclosed.
The system utilizes a digital computing device (DCD) to capture
radiation counts from a radiation detection device (RDD) such as a
photon detector via the use of one or more integrated
analog-to-digital converters (ADC). The radiation count information
is then processed using a recursive procedure in the DCD that
determines the desired nuclide to be evaluated and then defines the
possible nuclide decay transition states. For each possible nuclide
decay state, a recursive permutation of possible state transitions
from this nuclide state is determined using a state permutation
engine (SPE). Combinations of these state transition branches are
linked to form state transition chains each having individual
probabilities associated with the overall state transition chain.
These state transition chain probabilities are applied to the RDD
ADC data to form observed RDD radiation data radiation count
probabilities and displayed in real-time.
Inventors: |
JADERSTROM; Henrik;
(Meriden, CT) ; Vicuna; Mark; (Meriden, CT)
; Mueller; Wilhelm; (Meriden, CT) ; Jones; Steve
Fisher; (Meriden, CT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CANBERRA INDUSTRIES, INC. |
Meriden |
CT |
US |
|
|
Assignee: |
CANBERRA INDUSTRIES, INC.
Meriden
CT
|
Family ID: |
56611082 |
Appl. No.: |
14/635575 |
Filed: |
March 2, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01T 3/001 20130101;
G01T 1/172 20130101; G01T 1/36 20130101 |
International
Class: |
G01T 3/00 20060101
G01T003/00; G01T 1/172 20060101 G01T001/172 |
Claims
1. A nuclide decay discriminator system comprising: (a) radiation
detection device (RDD); (b) analog-to-digital converter (ADC); (c)
digital computing device (DCD); (d) operator interface console
(OIC); (e) real-time display (RTD); (f) nuclide state database
(NSD); (g) transition probability database (TPD); and (h) state
permutation engine (SPE); wherein said RDD is configured to detect
radiation and produce an analog electrical signal corresponding to
the detection of a radiation event; said RDD is configured to
electrically couple said analog electrical signal to said ADC; said
ADC is configured to convert said analog signal to digital
radiation data (DRD) representing the presence of detected
radiation in said RDD; said DCD is configured to count occurrences
of said DRD that are above a predetermined energy detection
threshold (EDT) to produce a radiation detection count (RDC); said
DCD is configured to accept via said OIC a nuclide inspection list
(NIL); said DCD is configured to retrieve nuclide state information
(NSI) from said NSD that defines the possible states of nuclides
within said NIL; said DCD is configured to use said NSI to define
nuclide state branches (NSB) that define transitions between states
listed in said NSI; said DCD is configured to associate a state
transition probability (STP) for each of said NSB by retrieving a
probability associated with said NSB from said TPD; said DCD is
configured to recursively permute said NSB using said SPE to form a
nuclide state chain (NSC) list associated with each of said
nuclides within said NIL; said DCD is configured to compute an
overall nuclide chain probability (NCP) for each said NSC; said DCD
is configured to generate a nuclide probable decay chain (PDC) list
from said NSC by including in said PDC only chains in said NSC
having a NCP above a predetermined threshold; said DCD is
configured to associate a detected energy level in said DRD with
entries in said PDC to produce a detected nuclide decay (DND) list;
said DCD is configured to display said DND list to said RTD for
review by an operator in real-time; and said DCD is configured to
display said RDC associated with entries in said RTD for review by
said operator in real-time.
2. The nuclide decay discriminator system of claim 1 wherein said
RDD comprises a photon detector.
3. The nuclide decay discriminator system of claim 1 wherein said
RDD is configured to detect alpha, beta, and gamma radiation.
4. The nuclide decay discriminator system of claim 1 wherein said
SPE is configured to recursively permute (N+1) total nuclide states
into (N!) nuclide decay chains; wherein: for each of said nuclides
within said NIL, said N represents a count of non-terminal energy
levels in said nuclide within said NIL.
5. The nuclide decay discriminator system of claim 1 wherein said
DCD generates N .times. ( N - 1 ) 2 ##EQU00028## of said NSB for a
nuclide having (N+1) total nuclide states; wherein: for each of
said nuclides within said NIL, said N represents a count of
non-terminal energy levels in said nuclide within said NIL.
6. The nuclide decay discriminator system of claim 1 wherein said
DCD is configured to perform parallel hardware processing of said
DRD with entries in said PDC to produce said DND list.
7. The nuclide decay discriminator system of claim 1 wherein said
DCD uses relative peak sizes of said DRD to identify nuclides using
X-ray--X-ray sum peaks, gamma--X-ray sum peaks, gamma--gamma sum
peaks, and gamma--annihilation photon sum peaks.
8. The nuclide decay discriminator system of claim 1 wherein said
DCD is configured to generate a nuclide probable decay chain (PDC)
list from said NSC by including in said PDC only chains in said NSC
having a NCP above a predetermined threshold by calculating the
minimum efficiency for each nuclide chain, on a point by point
basis, to determine if the nuclide chain has a non-negligible
impact on the coincidence summing factor (COI).
9. The nuclide decay discriminator system of claim 1 wherein said
DCD computes said NCP using a true coincidence summing (TCS)
correction factor (COI) that is calculated from the ratio of the
probability that a photon of the energy of interest is detected
alone by said RDD if said RDD has a non-perfect time resolution and
the probability that a photon is detected by said RDD with a
perfect time resolution C.sub.p with no true coincidence summing
using the formula: C O I = C P - C so - C si C p ##EQU00029##
wherein C.sub.so is the probability that a photon is summed out of
the peak and C.sub.si is the probability that two or more photons
are summed into the peak.
10. The nuclide decay discriminator system of claim 1 wherein said
DCD is configured to calculate sum peaks from a plurality of
photons.
11. A nuclide decay discriminator method comprising: (1) with a
radiation detection device (RDD), detecting radiation and producing
an analog electrical signal corresponding to the detection of a
radiation event; (2) with said RDD, electrically coupling said
analog electrical signal to an analog-to-digital converter (ADC);
(3) with said ADC, converting said analog signal to digital
radiation data (DRD) representing the presence of detected
radiation in said RDD; (4) with a digital computing device (DCD),
counting occurrences of said DRD that are above a predetermined
energy detection threshold (EDT) to produce a radiation detection
count (RDC); (5) with said DCD, accepting via an operator interface
console (OIC) a nuclide inspection list (NIL); (6) with said DCD,
retrieving nuclide state information (NSI) from a nuclide state
database (NSD) that defines the possible states of nuclides within
said NIL; (7) with said DCD, using said NSI to define nuclide state
branches (NSB) that define transitions between states listed in
said NSI; (8) with said DCD, associating a state transition
probability (STP) for each of said NSB by retrieving a probability
associated with said NSB from a transition probability database
(TPD); (9) with said DCD, recursively permuting said NSB using a
state permutation engine (SPE) to form a nuclide state chain (NSC)
list associated with each of said nuclides within said NIL; (10)
with said DCD, computing an overall nuclide chain probability (NCP)
for each said NSC; (11) with said DCD, generating a nuclide
probable decay chain (PDC) list from said NSC by including in said
PDC only chains in said NSC having a NCP above a predetermined
threshold; (12) with said DCD, associating a detected energy level
in said DRD with entries in said PDC to produce a detected nuclide
decay (DND) list; (13) with said DCD, displaying said DND list to a
real-time display (RTD) for review by an operator in real-time; and
(14) with said DCD, displaying said RDC associated with entries in
said RTD for review by said operator in real-time.
12. The nuclide decay discriminator method of claim 11 wherein said
RDD comprises a photon detector.
13. The nuclide decay discriminator method of claim 11 wherein said
RDD is configured to detect alpha, beta, and gamma radiation.
14. The nuclide decay discriminator method of claim 11 wherein said
SPE is configured to recursively permute (N+1) total nuclide states
into (N!) nuclide decay chains; wherein: for each of said nuclides
within said NIL, said N represents a count of non-terminal energy
levels in said nuclide within said NIL.
15. The nuclide decay discriminator method of claim 11 wherein said
DCD generates N .times. ( N - 1 ) 2 ##EQU00030## of said NSB for a
nuclide having (N+1) total nuclide states; wherein: for each of
said nuclides within said NIL, said N represents a count of
non-terminal energy levels in said nuclide within said NIL.
16. The nuclide decay discriminator method of claim 11 wherein said
DCD is configured to perform parallel hardware processing of said
DRD with entries in said PDC to produce said DND list.
17. The nuclide decay discriminator method of claim 11 wherein said
DCD uses relative peak sizes of said DRD to identify nuclides using
X-ray--X-ray sum peaks, gamma--X-ray sum peaks, gamma--gamma sum
peaks, and gamma--annihilation photon sum peaks.
18. The nuclide decay discriminator method of claim 11 wherein said
DCD is configured to generate a nuclide probable decay chain (PDC)
list from said NSC by including in said PDC only chains in said NSC
having a NCP above a predetermined threshold by calculating the
minimum efficiency for each nuclide chain, on a point by point
basis, to determine if the nuclide chain has a non-negligible
impact on the coincidence summing factor (COI).
19. The nuclide decay discriminator method of claim 11 wherein said
DCD computes said NCP using a true coincidence summing (TCS)
correction factor (COI) that is calculated from the ratio of the
probability that a photon of the energy of interest is detected
alone by said RDD if said RDD has a non-perfect time resolution and
the probability that a photon is detected by said RDD with a
perfect time resolution C.sub.p with no true coincidence summing
using the formula: C O I = C P - C so - C si C p ##EQU00031##
wherein C.sub.so is the probability that a photon is summed out of
the peak and C.sub.si is the probability that two or more photons
are summed into the peak.
20. The nuclide decay discriminator method of claim 11 wherein said
DCD is configured to calculate sum peaks from a plurality of
photons.
21. A tangible non-transitory computer usable medium having
computer-readable program code means embodied thereon comprising a
nuclide decay discriminator method comprising: (1) with a radiation
detection device (RDD), detecting radiation and producing an analog
electrical signal corresponding to the detection of a radiation
event; (2) with said RDD, electrically coupling said analog
electrical signal to an analog-to-digital converter (ADC); (3) with
said ADC, converting said analog signal to digital radiation data
(DRD) representing the presence of detected radiation in said RDD;
(4) with a digital computing device (DCD), counting occurrences of
said DRD that are above a predetermined energy detection threshold
(EDT) to produce a radiation detection count (RDC); (5) with said
DCD, accepting via an operator interface console (OIC) a nuclide
inspection list (NIL); (6) with said DCD, retrieving nuclide state
information (NSI) from a nuclide state database (NSD) that defines
the possible states of nuclides within said NIL; (7) with said DCD,
using said NSI to define nuclide state branches (NSB) that define
transitions between states listed in said NSI; (8) with said DCD,
associating a state transition probability (STP) for each of said
NSB by retrieving a probability associated with said NSB from a
transition probability database (TPD); (9) with said DCD,
recursively permuting said NSB using a state permutation engine
(SPE) to form a nuclide state chain (NSC) list associated with each
of said nuclides within said NIL; (10) with said DCD, computing an
overall nuclide chain probability (NCP) for each said NSC; (11)
with said DCD, generating a nuclide probable decay chain (PDC) list
from said NSC by including in said PDC only chains in said NSC
having a NCP above a predetermined threshold; (12) with said DCD,
associating a detected energy level in said DRD with entries in
said PDC to produce a detected nuclide decay (DND) list; (13) with
said DCD, displaying said DND list to a real-time display (RTD) for
review by an operator in real-time; and (14) with said DCD,
displaying said RDC associated with entries in said RTD for review
by said operator in real-time.
22. The computer usable medium of claim 21 wherein said RDD
comprises a photon detector.
23. The computer usable medium of claim 21 wherein said RDD is
configured to detect alpha, beta, and gamma radiation.
24. The computer usable medium of claim 21 wherein said SPE is
configured to recursively permute (N+1) total nuclide states into
(N!) nuclide decay chains; wherein: for each of said nuclides
within said NIL, said N represents a count of non-terminal energy
levels in said nuclide within said NIL.
25. The computer usable medium of claim 21 wherein said DCD
generates N .times. ( N - 1 ) 2 ##EQU00032## of said NSB for a
nuclide having (N+1) total nuclide states; wherein: for each of
said nuclides within said NIL, said N represents a count of
non-terminal energy levels in said nuclide within said NIL.
26. The computer usable medium of claim 21 wherein said DCD is
configured to perform parallel hardware processing of said DRD with
entries in said PDC to produce said DND list.
27. The computer usable medium of claim 21 wherein said DCD uses
relative peak sizes of said DRD to identify nuclides using
X-ray--X-ray sum peaks, gamma--X-ray sum peaks, and
gamma--annihilation photon sum peaks.
28. The computer usable medium of claim 21 wherein said DCD is
configured to generate a nuclide probable decay chain (PDC) list
from said NSC by including in said PDC only chains in said NSC
having a NCP above a predetermined threshold by calculating the
minimum efficiency for each nuclide chain, on a point by point
basis, to determine if the nuclide chain has a non-negligible
impact on the coincidence summing factor (COI).
29. The computer usable medium of claim 21 wherein said DCD
computes said NCP using a true coincidence summing (TCS) correction
factor (COI) that is calculated from the ratio of the probability
that a photon of the energy of interest is detected alone by said
RDD if said RDD has a non-perfect time resolution and the
probability that a photon is detected by said RDD with a perfect
time resolution C.sub.p with no true coincidence summing using the
formula: C O I = C P - C so - C si C p ##EQU00033## wherein
C.sub.so is the probability that a photon is summed out of the peak
and C.sub.si is the probability that two or more photons are summed
into the peak.
30. The computer usable medium of claim 21 wherein said DCD is
configured to calculate sum peaks from a plurality of photons.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] Not Applicable
PARTIAL WAIVER OF COPYRIGHT
[0002] All of the material in this patent application is subject to
copyright protection under the copyright laws of the United States
and of other countries. As of the first effective filing date of
the present application, this material is protected as unpublished
material.
[0003] However, permission to copy this material is hereby granted
to the extent that the copyright owner has no objection to the
facsimile reproduction by anyone of the patent documentation or
patent disclosure, as it appears in the United States Patent and
Trademark Office patent file or records, but otherwise reserves all
copyright rights whatsoever.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0004] Not Applicable
REFERENCE TO A MICROFICHE APPENDIX
[0005] Not Applicable
BACKGROUND
[0006] 1. Field of the Invention
[0007] The present invention generally relates to radionuclide
spectroscopy analysis using radiation detectors, and more
specifically, to correcting the true coincidence summing (TCS) and
calculating total efficiency during spectroscopy analysis of
radionuclides undergoing cascading gamma or X-ray emissions. The
present invention may have application to contexts in which
discriminating multiple simultaneous nuclide decays is desired.
[0008] 2. Prior Art and Background of the Invention
[0009] Radioactive decay of a parent nuclide to the ground state of
its daughter often results in the emission of several gamma ray
photons in a cascade sequence. In some types of decay modes such as
Electron Capture (EC) or transitions such as Internal Conversion
(IC), X-rays are emitted in conjunction with the cascading gamma
rays. During such an event if two photons with different energies
are emitted in a cascade, and they are detected within the
resolving time of the detector system, the two photons are said to
be detected in true coincidence. The detector accumulates the sum
total of the energy deposited by these two photons. If a photon
deposits its full energy--and would normally be in the Full Energy
Peak (FEP)--then any extra energy deposited from the second photon
will remove the initial photon from the Full Energy Peak (FEP). As
a result, events are lost from the Full Energy Peak (FEP) of the
gamma-ray of interest. Such a loss is known as a "summing-out."
Conversely, partial energy depositions from two cascading photons
could add up and result in an extra count in the Full Energy Peak
(FEP) of a gamma ray of interest. Such a gain in counts is known as
"summing-in" when there is full energy deposition. If either of
these events occurs, then activity determination based on the
normal measurement of the FEP efficiency will be in error unless a
correction is made.
[0010] Summing-in leads to an increase of an observable peak area,
whereas summing-out leads to a decrease of an observable peak area.
The total true coincidence summing effect (COI) with respect to a
gamma line of interest (denoted with subscript "A") of a
radionuclide under consideration is:
COI.sub.A=(1-L.sub.A.sup..gamma.-.gamma.-L.sub.A.sup..gamma.-X,511)(1+S.-
sub.A.sup..gamma.-.gamma.)(1+S.sub.A.sup..gamma.-X,51) (1)
where L.sub.A.sup..gamma.-.gamma. and S.sub.A.sup..gamma.-.gamma.
are the loss and gain probability due to coincidence between decay
gamma-rays, and L.sub.A.sup..gamma.-X,511 and
S.sub.A.sup..gamma.-X,511 are the loss and gain probability due to
coincidence between decay gamma-rays and X-rays, and 511 keV
annihilation photon. These probabilities are the sum of the partial
probabilities calculated for individual decay chains involving the
gamma line of interest:
L A = i = 1 N L A , i ( 2 ) S A = j = 1 M S A , j ( 3 )
##EQU00001##
[0011] The computation of L.sub.A.sup..gamma.-.gamma. and
S.sub.A.sup..gamma..gamma. is well known and described in U.S. Pat.
No. 6,225,634; the present invention extends the concept to include
coincidence corrections for X-rays and gamma-rays, and the 511 keV
photons and gamma-rays, e.g. computation of
L.sub.A.sup..gamma.-X,511.
[0012] It is therefore necessary to correct the FEP efficiency for
true coincidence effects. Various methods have been developed to
deal with these "summing-in" and "summing-out" events. However,
such methods fail to properly compensate FEP efficiency for true
coincidence effects and are known to be problematic for this
reason.
[0013] To compute the summing-in and summing-out probability, L.
Moens et al. [J. Radioanal. Nucl. Chem. 70 (1982) 539] suggested
the use of gamma-ray intensities and derived the mathematical
formulae for practically important cases for gamma-ray true
coincidence summing correction. F. De Corte [The
k.sub.0-Standardization Method: A Move to the Optimization of
Reactor Neutron Activation Analysis, Agrege thesis,
Rijksuniversitiet Gent, 1987] updated the approach by Moens, and
extended it for the cases of gamma-KX (EC) and gamma-KX (IC) true
coincidences, but only for a single decay chain.
[0014] V. Kolotov et al. [J. Radioanal. Nucl. Chem. 233 (1998) 95;
U.S. Pat. No. 6,225,634] implemented Moen's approach in Canberra
Industries, Inc.'s Genie-2000 spectroscopy analysis software
product. The implementation is based on the mapping of the
efficiencies in the space around the detector. In Kolotov's method,
the total sample efficiency is computed by knowing the Full Energy
Peak (FEP) efficiency and the intrinsic Peak-to-Total (P/T) ratio.
The method assumes that the introduction of a sample does not
affect the P/T ratio for voluminous sources. The true coincidence
correction factor at a gamma ray of interest can be obtained by
numerical integration of the correction factors for volume elements
that are small enough for the efficiencies to be considered
constant within them. Furthermore, the software code only corrects
for true coincidence summing between decay gamma-rays, and not
between gamma and X-ray or 511 keV photons as in the present
invention.
[0015] M. Blaauw [Nucl. Inst. Meth. Phys. Res., A332 (1993) 493]
suggested a self-validating calibration method for simultaneous
computation of the true coincidence effect and activity in the case
of a highly efficient point source. Together with S. Gelsema,
Blaauw [Nucl. Inst. Meth. Phys. Res., A505 (2003) 3111 introduced a
third efficiency curve to account for the variation of the detector
efficiency over the source volume due to self-attenuation and
scattering in the sample. M. Blaauw and Gelsema's method is
implemented in Ortec's GAMMAVISION.RTM. spectroscopy analysis
software product. However, the cascade summing correction results
for radionuclides prone to gamma-X ray coincidences is marginal
from the published data in the literature ("The evaluation of true
coincidence effect on CTBTO-type sample geometry", The 2003 IEEE
Nuclear Science Symposium and Medical Imaging Conference, Portland,
Oreg., Oct. 19-25, 2003].
[0016] The GammaVision.RTM. product requires a geometry specific
source based calibration that is both time consuming and expensive.
Further, the performance of GammaVision.RTM. for radionuclides
prone to gamma-X ray true coincidences summing is marginal, and
there is no data available to verify the performance for gamma-511
keV true coincidence effects. Moreover, GammaVision.RTM. requires
source-based calibrations for true coincidence summing correction,
which can be both time consuming and very costly, and the cascade
summing correction results are heavily dependent on the
radionuclides in the calibration source and source geometry.
[0017] Kolotov's method uses a simple intrinsic P/T efficiency
ratio calibration to estimate the total efficiency in a volume
source. However, this can be used to correct for gamma-gamma true
coincidence losses or gains, by utilizing P/T efficiency ratios
that are maintained invariant throughout a voluminous source. This
approach may introduce a higher uncertainty in the computed true
coincidence correction factors. Using this method also requires the
use of radioactive sources to determine the P/T efficiency
calibration, which is then used to compute the total
efficiency.
[0018] To date the true coincidence summing correction due to
coincidence between gamma and X-rays or gamma and annihilation
photons (or 511 keV) has not been adequately considered. Previous
cascade summing correction inventions do not rigorously treat the
gamma-KX ray and gamma-511 keV true coincidence summing analysis as
does the present invention. Alternate methods can be employed using
Monte Carlo codes such as MCNP-CP (Berlizov, A. N., MCNP-CP--A
Correlated Particle Radiation Source Extension of a General Purpose
Monte Carlo N-Particle Transport Code, Applied Modeling and
Computations in Nuclear Science. Semkow, T. M., et al., Eds. ACS
Symposium Series 945. American Chemical Society, Washington, D.C.,
2006, p. 183-194.) and GEANT (Nuclear Instruments & Methods in
Physics Research, A 506 (2003) 250-303.). MCNP-CP and GEANT may be
used to compute true coincidence summing effects that involve
gamma-X rays (and gamma-511 keV photons) true coincidence. However,
neither MCNP-CP nor GEANT are commonly available and both typically
require exceedingly long computational times making such use
impractical for other than academic settings.
[0019] Accordingly, a need exists for a method for efficiently
computing the true coincidence summing correction factors between
gamma-KX ray and gamma-511 keV events. Further, a need exists for a
method of computing the voxelized total efficiency with gamma-ray
buildup correction directly from a mathematical model to improve
accuracy of the true coincidence correction factor for voluminous
sources. The present invention satisfies these needs and others as
demonstrated in the detailed description below.
BACKGROUND INFORMATION
[0020] Many nuclides emit more than one photon from a single decay.
The time between the emissions are much shorter than the resolving
time of the detectors used to detect the photons. There is a
possibility that the detector will detect more than one photon from
the decay which will change the number counts in the Full Energy
Peaks (FEP) and therefore also the activity determined of the
nuclide. This phenomenon is called true coincidence summing
(TCS).
[0021] The prior art teaches a system and method for TCS correction
and has been described in various patents (See H. Zhu, et al., TRUE
COINCIDENCE SUMMING CORRECTION AND TOTAL EFFICIENCY COMPUTATION FOR
RADIONUCLIDE SPECTROSCOPY ANALYSIS, U.S. Pat. No. 8,227,761; and V.
Kolotov, V. Atrashkevich, TRUE COINCIDENCE SUMMING CORRECTION FOR
RADIATION DETECTORS, U.S. Pat. No. 6,225,634; each hereby
incorporated by reference).
[0022] The finite energy resolution of the detector makes it
possible that some energies emitted are indistinguishable to the
radiation detector and there are currently no prior art systems or
methodologies that accurately discriminate nuclide decay in these
circumstances. The extra peaks created by the summing of two or
more photons in the decay makes nuclide identification more
complicated and error prone in all prior art system
configurations.
DEFICIENCIES IN THE PRIOR ART
[0023] Current methods for True Coincidence Summing (TCS)
Corrections are approaches found in products such as Genie-2000
V3.3 (see H. Zhu et al., "True coincidence summing correction and
total efficiency computation for radionuclide spectroscopy
analysis", U.S. Pat. No. 8,227,761; V. Kolotov, V. Atrashkevich,
"True coincidence summing correction for radiation detectors", U.S.
Pat. No. 6,225,634; L. Moens, et al., J. Radioanal. Nucl. Chem. 70
(1982) 539; F. De Corte, The k0-Standardization Method: A Move to
the Optimization of Reactor Neutron Activation Analysis, Habil.
Thesis, University of Gent, Belgium, 1987), the algorithms in
Ortec's GammaVision V7 (see M. Blaauw, Nucl. Inst. Meth. Phys.
Res., A332 (1993) 493; M. Blaauw, Nucl. Inst. Meth. Phys. Res.,
A505 (2003) 311; R. Keyser, "The evaluation of true coincidence
effect on CTBTO-type sample geometry", The 2003 IEEE Nuclear
Science Symposium and Medical Imaging Conference, Portland, Oreg.,
Oct. 19-25, 2003), GESPECOR (see D. Arnold and O. Sima, Applied
Radiation and Isotopes 60 (2004) 167), EFFTRAN (see T. Vidmar et
al., Applied Radiation and Isotopes 69 (2011) 908), and software
using Monte Carlo methods (e.g. GEANT (see S. Agostinelli et al.,
Nucl. Inst. Meth. Phys. Res., A506 (2003) 250) and MCNP-CP (see A.
N. Berlizov, Applied Modeling and Computations in Nuclear Science,
chapter 13 183-194 ACS Symposium Series, Vol. 945, (2006)).
[0024] The simplified treatment of the decay used in prior art
systems such as the Genie-2000 V3.3 makes it impossible to
correctly treat complex decays where the decays branch out and
later merge to the same level. Other systems such as the
GammaVision V7 needs a geometry specific source based calibration
that is both time consuming and expensive. Also, from the published
data in the literature, the performance of GammaVision V7 for
radionuclides prone to gamma-X ray true coincidences summing is
marginal, and there is no data available to verify the performance
for gamma-511 keV true coincidence effects. Monte Carlo computer
codes such as MCNP-CP and GEANT can be used to compute true
coincidence summing effects that involve gamma-X rays (and
gamma-511 keV photons) for any complexity of the decay, but
obtaining an appropriate result requires very long computational
times.
[0025] While some of the prior art may teach some solutions to
several of these problems, the core deficiencies in the prior art
systems relating to TCS correction have not been addressed.
OBJECTIVES OF THE INVENTION
[0026] Accordingly, the objectives of the present invention are
(among others) to circumvent the deficiencies in the prior art and
affect the following objectives: [0027] (1) Provide for a nuclide
decay discriminator system and method that accurately corrects for
emissions among all possible decay chains. [0028] (2) Provide for a
nuclide decay discriminator system and method that uses all the
possible decay chains that have probability of more than a
threshold value and discard decay chains that have negligible
impact on the TCS correction factor. [0029] (3) Provide for a
nuclide decay discriminator system and method that uses all decay
chains that contribute to the correction factor to make the TCS
applicable to all types of decays. [0030] (4) Provide for a nuclide
decay discriminator system and method that uses a minimum
efficiency for each chain, on a point by point basis, to determine
if the chain has a non-negligible impact on the coincidence summing
factor. [0031] (5) Provide for a nuclide decay discriminator system
and method that is able to predict the relative peak size of peaks
that are summed into but does not have transition energy in the
decay schema. [0032] (6) Provide for a nuclide decay discriminator
system and method that uses relative peak sizes to identify the
nuclides using X-ray--X-ray sum peaks, gamma--X-ray sum peaks,
gamma--gamma sum peaks, and gamma--annihilation photon sum peaks.
[0033] (7) Provide for a nuclide decay discriminator system and
method that calculates sum peaks from more than two photons with no
upper limit on how many photons that can be used. [0034] (8)
Provide for a nuclide decay discriminator system and method that
sums in correction factors that can be calculated from transitions
in any decay chain with transitions that do not have to be from
successive levels nor do they have to start from the same level as
the gamma ray of interest. [0035] (9) Provide for a nuclide decay
discriminator system and method that uses timing information from a
multi-channel analyzer or other electronics to break chains that
have half-lives longer than the time it takes for the electronics
to read the pulse information from the radiation detector. [0036]
(10) Provide for a nuclide decay discriminator system and method
that uses the energy resolution of the detector to determine how
close in energy the sum of two photons have to be for the analysis
not to be able to distinguish between the two peaks when looking
for potential sum peaks. [0037] (11) Provide for a nuclide decay
discriminator system and method that is able to treat
indistinguishable energies (energies close enough so that it is not
possible to distinguish between them) which are emitted in the same
decay. [0038] (12) Provide for a nuclide decay discriminator system
and method that is capable of correcting for complex decays that
prior art systems could not provide correct results for by
considering all possible ways that the nuclide can decay and using
the probability of the decay chain and the peak and total
efficiencies to discard decay chains that have negligible impact on
the correction factor.
[0039] While these objectives should not be understood to limit the
teachings of the present invention, in general these objectives are
achieved in part or in whole by the disclosed invention that is
discussed in the following sections. One skilled in the art will no
doubt be able to select aspects of the present invention as
disclosed to affect any combination of the objectives described
above.
BRIEF SUMMARY OF THE INVENTION
[0040] The present invention addresses several of the deficiencies
in the prior art in the following manner. The systems and methods
in this formulation extend upon the disclosure in U.S. Pat. No.
8,277,761 by storing and accessing the nuclear data in a novel way
to allow additional correlations to be computed that were
previously not possible.
[0041] The present invention improvement/extension of the prior art
system/method described herein is capable of correcting for complex
decays that the prior art is incapable of obtaining a correct
answer and achieves this advantage by considering all possible ways
that the nuclide can decay. It uses the probability of the nuclide
decay chain and the peak and total efficiencies to discard nuclide
decay chains that have a negligible impact on the correction
factor.
[0042] The finite energy resolution of a radiation detector makes
it possible that some energies emitted are indistinguishable to the
detector and present invention methods are able to correctly treat
this both for summing out and summing-in. The extra peaks created
by summing of two or more photons in the decay makes nuclide
identification more complicated and error prone. The present
invention incorporates methods capable of predicting the energy and
peak area of these extra sum peaks. This information is to be used
by the nuclide identification system and method to distinguish
radiation sources that were previously indistinguishable with prior
art systems.
BRIEF DESCRIPTION OF THE DRAWINGS
[0043] For a fuller understanding of the advantages provided by the
invention, reference should be made to the following detailed
description together with the accompanying drawings wherein:
[0044] FIG. 1 illustrates a block diagram depicting a general
system overview of a preferred exemplary invention embodiment;
[0045] FIG. 2 illustrates a typical nuclide decay characteristic
depicting a number of energy branch states;
[0046] FIG. 3 illustrates a typical radiation detector and
associated sample having multiple nuclide sources;
[0047] FIG. 4 illustrates a flowchart depicting a method overview
of a preferred exemplary invention embodiment;
[0048] FIG. 5 illustrates a generic nuclide and associated
states;
[0049] FIG. 6 illustrates a generic nuclide and associated branch
energies;
[0050] FIG. 7 illustrates a generic nuclide and associated nuclide
chains;
[0051] FIG. 8 illustrates a generic nuclide and associated nuclide
chain probabilities;
[0052] FIG. 9 illustrates a flowchart depicting a presently
preferred invention embodiment method implementing a data
definition method;
[0053] FIG. 10 illustrates a data structure associated with the
flowchart of FIG. 9;
[0054] FIG. 11 illustrates a flowchart depicting a presently
preferred invention embodiment method implementing a nuclide
inspection list (NIL) definition method;
[0055] FIG. 12 illustrates a data structure associated with the
flowchart of FIG. 11;
[0056] FIG. 13 illustrates a flowchart depicting a presently
preferred invention embodiment method implementing a nuclide branch
list (NBL) definition method;
[0057] FIG. 14 illustrates a data structure associated with the
flowchart of FIG. 13;
[0058] FIG. 15 illustrates a flowchart depicting a presently
preferred invention embodiment method implementing a nuclide chain
list (NCL) definition method;
[0059] FIG. 16 illustrates a data structure associated with the
flowchart of FIG. 15;
[0060] FIG. 17 illustrates a flowchart depicting a presently
preferred invention embodiment method implementing a nuclide chain
probability list (NPL) definition method;
[0061] FIG. 18 illustrates a data structure associated with the
flowchart of FIG. 17;
[0062] FIG. 19 illustrates an overview block diagram depicting a
preferred invention system embodiment incorporating parallel energy
matching of real-time radiation data with a dynamically generated
nuclide chain list;
[0063] FIG. 20 illustrates a detail block diagram depicting a
preferred invention system embodiment incorporating parallel energy
matching of real-time radiation data with a dynamically generated
nuclide chain list;
[0064] FIG. 21 illustrates an overview flowchart depicting an
operational overview of the present invention;
[0065] FIG. 22 illustrates a flowchart depicting an exemplary
method for selecting which chains to include in the true
coincidence summing correction factor;
[0066] FIG. 23 illustrates a flowchart depicting an exemplary
method for finding the sum within an energy chain;
[0067] FIG. 24 illustrates a flowchart depicting an exemplary
method for calculating the TCS correction factor from the
pre-generated decay chains;
[0068] FIG. 25 illustrates a flowchart depicting the present
invention teachings as applied to the implementation of a nuclide
decay discriminator for .sup.60Co decay;
[0069] FIG. 26 illustrates a general overview of .sup.60Co
decay;
[0070] FIG. 27 illustrates a detail overview of .sup.60Co
decay;
[0071] FIG. 28 illustrates a table of final states and branching
ratios for the decay of .sup.60Co;
[0072] FIG. 29 illustrates a table of the transitions in .sup.60Ni
from .sup.60Co decays;
[0073] FIG. 30 illustrates a table of possible chains in .sup.60Co
decay to .sup.60Ni;
[0074] FIG. 31 illustrates a table of K-X-Ray data for .sup.60Co;
and
[0075] FIG. 32 illustrates a table of peak and total efficiencies
for the involved .sup.60Co energies for two point sources and for
the sample.
DESCRIPTION OF THE PRESENTLY PREFERRED EXEMPLARY EMBODIMENTS
[0076] While the present invention is susceptible of embodiment in
many different forms, there is shown in the drawings and will
herein be described a variety of detailed preferred embodiments of
the invention with the understanding that the present disclosure is
to be considered as an exemplification of the principles of the
invention and is not intended to limit the broad aspect of the
invention to the embodiment(s) illustrated.
[0077] The numerous innovative teachings of the present application
will be described with particular reference to the presently
preferred embodiment, wherein these innovative teachings are
advantageously applied to the particular problems of a NUCLIDE
DECAY DISCRIMINATOR SYSTEM AND METHOD. However, it should be
understood that this embodiment is only one example of the many
advantageous uses of the innovative teachings herein. In general,
statements made in the specification of the present application do
not necessarily limit any of the various claimed inventions.
Moreover, some statements may apply to some inventive features but
not to others.
Parallel Processing
[0078] The present invention anticipates situations in which the
system as described herein may incorporate parallel processing to
simultaneously process incoming data from the radiation detectors
in real-time to discriminate a variety of nuclides that may be
present in a radiation sample.
System Overview (0100)
[0079] An overview of the present invention system functionality is
depicted in FIG. 1 (0100) wherein a radiation source (0101)
positioned within a radiation source container (0102) emits
radiation via nuclide decay to the nuclide decay discriminator
system (NDD) (0110). The NDD (0110) comprises special purpose
hardware that integrates a digital computing device (DCD) (0111)
executing software retrieved from a computer readable medium (0112)
and incorporating local digital memory (0113), fixed media storage
(0114), and a real-time display device (0115). This DCD (0111)
incorporates memory (0113) and fixed media storage (0114) to
collect data from one or more high speed analog-to-digital
converter (ADC) (0116) modules that read information from photon
detectors (0117, 0118, 0119) positioned to detect emitted radiation
from the radiation source (0101).
[0080] A real-time display device (0115) may be incorporated within
the system to communicate identified nuclides to a user and/or
permit modification of radiation detection parameters associated
with the photon detectors (0117, 0118, 0119) and associated
specialized ADC data capture electronics (0116). The photon
detectors (0117, 0118, 0119) may be configured to detect a variety
of radiation types including alpha, beta, and/or gamma radiation.
Various analysis processes associated with the collection and
discrimination of data from the special purpose radiation detection
hardware interfaces (0117, 0118, 0119) and ADC data capture
electronics (0116) serve to permit both collection and
discrimination of nuclide decay information from the radiation
source (0101).
[0081] Within this context the system utilizes a state permutation
engine (SPE) (0121) comprising hardware that allows chains of
nuclide decay branches to be recursively permuted and compared in
parallel to incoming real-time radiation data from the photon
detectors (0117, 0118, 0119) via the ADCs (0116). Within this
context the system utilizes a nuclide state database (NSB) (0122)
that defines various nuclide states and their energies and a
nuclide transition database (NTD) (0123) that defines the branch
energies associated with various nuclide states. Information in
these databases (0122, 0123) is used by the nuclide state
permutation engine (SPE) (0121) that first determines the branch
energies (0124) associated with a given nuclide under inspection
and then determines probabilities associated with these branches
(0125). This information is then used as a basis to recursively
permute all combinations of nuclide state transitions to form
nuclide chains (0126) with associated transition energies and
probabilities. This recursive permuted nuclide chain list (0126) is
then sifted to eliminate low probability chain transitions and
compared in real-time with incoming data from the photon detectors
(0117, 0118, 0119) via the high speed analog-to-digital converters
(0116) integrated within the DCD (0111). Correction factors
associated with the nuclide chains (0126) are applied to the
incoming radiation data to form true coincidence sum counts for the
measured radiation data.
[0082] The real-time display (0115) in the system permits an
operator to select specific nuclides (or groups of nuclides) to be
grouped as a nuclide inspection list (NIL) for parallel evaluation
by the DCD (0111) and SPE (0121) and also permits real-time-display
of measured radiation events. As the system is designed to operate
in a real-time context, the computations and analysis of the DCD
(0111) and SPE (0121) must meet stringent processing delay
requirements which preclude substitution of their functionality by
human effort or thought processes. As an example, it should be
noted that the SPE (0121) is required to determine (N!) nuclide
decay chains for a nuclide having (N+1) energy states. This
precludes human analysis for this application as this information
must be applied to incoming radiation data from the photon
detectors (0117, 0118, 0119) in parallel as the data is collected
to produce a real-time display of the corrected radiation count
information.
Nuclide Decay Overview (0200)
[0083] FIG. 2 (0200) depicts a generic decay chain wherein a parent
nuclide decays to its daughter nuclide through Electron Capture
decay or Positron decay. The sequence begins when a parent nuclide
(0210) transitions to an excited state of its daughter nuclide
through Electron capture decay or Positron decay, possibly
releasing an x-ray or two annihilation photons. The excited
daughter nucleus in this depiction undergoes up to five sequential
transition events (0211, 0212, 0213, 0214, 0215, 0216) releasing
several gamma and x-ray photons along the way.
Exemplary Radiation Detector (0300)
[0084] FIG. 3 (0300) depicts a general cross-section view of a
sample matrix (0301) to be assayed by an HPGe detector (0302) using
the present invention system and method described herein. In this
example, the sample consists of three radioactive source layers
(RSL #1 through #3), a sealed container (0301), and air inside and
outside of the container. An air gap also exists between the sample
(0301) and the detector (0302).
Method Overview (0400)
[0085] An exemplary present invention overview method can be
generally described in the flowchart of FIG. 4 (0400) as
incorporating the following steps: [0086] (1) defining possible
nuclide decay states for each nuclide of interest (0401); [0087]
(2) defining possible state branch transitions between the various
nuclide decay states for each nuclide decay state (0402); [0088]
(3) defining branch transition probability for every possible state
branch transition (0403); [0089] (4) permuting possible state
branch transitions recursively to define all nuclide decay chains
for every possible state branch transition (0404); [0090] (5)
define nuclide chain transition probability for each permuted
nuclide decay chain (0405); [0091] (6) selecting and/or inspecting
the next nuclide chain probability for each permuted nuclide decay
chain (0406); [0092] (7) determining if a nuclide chain likely to
occur, and if not, proceeding to step (9) (0407); [0093] (8) adding
the nuclide chain to the true coincidence summing (TCS) analysis
queue (0408); [0094] (9) determining if the nuclide chain
inspection is complete, and if not, proceeding to step (6) (0409);
[0095] (10) applying the TCS nuclide chain probability queue to
real-time measured radiation sample data and displaying the result
to an operator in real-time (0410); [0096] (11) optionally
proceeding to step (1) to analyze additional nuclides (0411); and
[0097] (12) terminating the nuclide decay discriminator method
(0412).
[0098] This general method may be modified heavily depending on a
number of factors, with rearrangement and/or addition/deletion of
steps anticipated by the scope of the present invention.
Integration of this and other preferred exemplary embodiment
methods in conjunction with a variety of preferred exemplary
embodiment systems described herein is anticipated by the overall
scope of the present invention.
Nuclide State Energy Levels (0500)
[0099] As generally depicted in FIG. 5 (0500), the nuclide state
database (NSD) as inspected by the SPE generally defines the
various states of nuclide decay (0501, 0502, 0508, 0509) starting
from an initial state S[0] and ending in a final state S[N]. For
each nuclide having (N+1) total states, there will be N
non-terminal energy states.
Nuclide State Branching Energy (0600)
[0100] As generally depicted in FIG. 6 (0600), the nuclide
transition database (NTD) as inspected by the SPE generally defines
the various branch energy transitions (0611, 0621, 0622, 0623,
0631, 0641) between nuclide states (0601, 0602, 0608, 0609)
starting from an initial state S[0] and ending in a final state
S[N]. For each nuclide having (N+1) total states, there will be
N(N-1)/2 potential nuclide branches.
Nuclide State Chains (0700)
[0101] These branch transitions depicted in FIG. 6 (0600) are
assembled by the SPE and used to form nuclide chains as generally
depicted in FIG. 7 (0700). The SPE recursively permutes the
branches depicted in FIG. 6 (0600) to form nuclide chains (0710,
0720, 0730, 0740) between the various nuclide decay states (0701,
0702, 0708, 0709). For each nuclide having (N+1) total states,
there will be (N!) potential nuclide chains.
Nuclide State Chain Probabilities (0800)
[0102] These nuclide decay chains depicted in FIG. 7 (0700) may be
processed by the SPE to form nuclide chain probabilities as
generally depicted in FIG. 8 (0800). The SPE recursively permutes
the branches depicted in FIG. 6 (0600) to form nuclide chain
probabilities (0810, 0820, 0830, 0840). For each nuclide having
(N+1) total states, there will be (N!) potential nuclide chain
probabilities.
[0103] Each chain will have associated branch energies associated
with the decays between states within a given chain. These
branching energies are used by the SPE as a comparison against
measured radiation detection levels to form correction factors for
measured radiation based on the probabilities of decay within a
given nuclide decay chain.
Overview of SPE Functions (0900)-(1800)
[0104] A general overview of the functionality of the SPE is
depicted in the flowchart of FIG. 9 (0900) and involves the
following steps: [0105] (1) Defining the nuclide inspection list
(NIL) (0901); [0106] (2) Defining the nuclide state energy branch
list (NBL) (0902); [0107] (3) Defining the nuclide chain list (NCL)
(0903); [0108] (4) Defining the nuclide chain probability (NCP)
(0904); [0109] (5) Collecting radiation samples from the radiation
detection device (RDD) (0905); [0110] (6) Match the energy levels
in the RDD to NCL energies to generate a TCS list (0906); [0111]
(7) Applying the correction values in the TCS list to measured
radiation values in real-time (0907); and [0112] (8) Displaying
corrected radiation counts in real-time to an operator display
interface and proceeding to step (5) to collect more radiation
samples (0908).
[0113] This general method may be modified heavily depending on a
number of factors, with rearrangement and/or addition/deletion of
steps anticipated by the scope of the present invention.
Integration of this and other preferred exemplary embodiment
methods in conjunction with a variety of preferred exemplary
embodiment systems described herein is anticipated by the overall
scope of the present invention.
[0114] The generalized data structure associated with this method
is provided in FIG. 10 (1000). Corresponding operational
sub-modules referenced in FIG. 9 (0900) are provided in FIG. 11
(1100), FIG. 13 (1300), FIG. 15 (1500), and FIG. 17 (1700) with
corresponding data structures created by these operational blocks
depicted in FIG. 12 (1200), FIG. 14 (1400), FIG. 16 (1600), and
FIG. 18 (1800). As depicted in FIG. 7 (0700) and FIG. 8 (0800), the
potential number of nuclide decay chains is of order (N!) and thus
the data structures represented in these figures (1000, 1200, 1400,
1600, 1800) may be quite large to account for the recursive
permutations of nuclide branches and their associated energies and
probabilities. As data is gathered from the radiation detectors,
the TCS list is dynamically generated from the overall NIL data
structure that is created based on measured energy levels and
transition probabilities. This TCS list is then applied to the
measured data from the radiation detectors to form a real-time
count result that is displayed to an operator console.
[0115] It should be noted that the recursive nuclide chain
permutation depicted in FIG. 15 (1500) and FIG. 16 (1600) may be
performed in a variety of ways depending on hardware
implementation. Indexes may be iterated at each level of the
nuclide branch list or a fully recursive procedure may be
implemented. In either case, the resulting NCL is a list of nuclide
chains each having an associated list of branch energy
references.
Real-Time Processing (1900)-(2000)
Parallel Energy Matching Logic (1900)
[0116] As discussed previously, the present invention targets
real-time analysis of measured radiation data from a variety of
radiation detection devices (RDD). As generally depicted in FIG. 19
(1900) in these scenarios the radiation source (1901) within the
radiation source container (1902) emits radiation that is detected
with one or more RDDs (1911, 1912, 1919) that are interfaced to a
high speed ADC array (1920) that converts incoming analog detector
information to digital. This digital data is streamed in real-time
to FIFO memories (1931, 1932, 1939) for processing by DCD parallel
energy matching logic (1940). This parallel matching logic (1940)
compares in real-time the energy levels retrieved from the FIFOs
(1931) with the nuclide chain list (NCL) (1950) previously
generated by the state permutation engine (SPE) (1960) with input
from the nuclide state database (NSD) (1961) and the nuclide
transition database (NTD) (1962). The SPE (1960) in this context
dynamically builds the NCL (1950) under real-time control of an
operator configuration console (1970). Energy matches between the
NCL (1950) and the FIFO data (1931, 1932, 1939) by the matching
logic (1940) are presented on a display in real-time (1980). This
real-time display (1980) may be integrated within or separate from
the operator configuration console (1970).
Matching Logic Detail (2000)
[0117] Additional detail of the DCD matching logic is depicted in
FIG. 20 (2000) wherein the FIFOs (2031, 2032, 2039) is accepted by
a FIFO data entry module (2030) and compared to NCL chain entry
(2051) nuclide chain energy data (2052) by matching logic (2041)
that compares the two entries to within a matching threshold
register (2042) value. If the match logic (2041) is successful,
this enables further processing is executed by a threshold logic
(2043) function that compares a probability threshold (2071)
against that from the NCL probability (2053). If the chain
probability (2053) is above the probability threshold (2071), TCS
processing logic (2081) is activated against the FIFO data to
produce a real-time presentation of RDD data.
Theory of Operation (2100)-(2400)
Overview
[0118] An overview of the theory of operation may be seen in the
flowchart of FIG. 21 (2100) wherein the major operational loop
consists of the following steps: [0119] (1) Enter nuclides IDs for
inspection via an operator interface console (2101); [0120] (2)
Parsing nuclear data and generating nuclide chains (2102); [0121]
(3) Generate TCS chains for nuclide evaluation (2103); (4)
Calculating and applying TCS corrections for measured real-time
radiation detector energies (2104); [0122] (5) Displaying corrected
radiation counts in real-time to an operator interface console
(2105) and proceeding to step (1) or step (4).
[0123] This general operational loop may be heavily modified
depending on a number of factors, with rearrangement and/or
addition/deletion of steps anticipated by the scope of the present
invention. Integration of this and other preferred exemplary
embodiment methods in conjunction with a variety of preferred
exemplary embodiment systems described herein is anticipated by the
overall scope of the present invention.
Multi-Photon Decay
[0124] Many radioactive nuclides emit more than one photon when
they decay. These photons can either be gamma rays from the
transitions in the daughter, X-rays from internal conversion, or
electron capture or annihilation photons from positrons. When two
or more photons are emitted within a time that is shorter than the
resolution time of the detector they cannot be distinguished and
will be summed by the detector. This is called True Coincidence
Summing (TCS) because they are coincidences from the same initial
decay. This will change the number of counts in the peaks and hence
the activity determined from the spectrum. There are two categories
of true cascade summing: [0125] SUMMING OUT which is when the Full
Energy Peak (FEP) is detected from a gamma ray and some energy is
detected from any of the other photons emitted from the decay; and
[0126] SUMMING IN when two or more photons depositing their full
energies in the detector sum up to the Full Energy Peak (FEP) of
another gamma ray and no energy is deposited from any other photons
in the decay.
[0127] The first category reduces the number of counts in the Full
Energy Peak (FEP) and the second category increases the number of
counts in the Full Energy Peak (FEP).
Detailed Theory Description
[0128] While the present invention method may have a number of
variations, the theory of operation of the basic invention process
steps are described as follows. The first step is to parse nuclear
structure data (e.g., as described in J. K. Tuli, EVALUATED NUCLEAR
STRUCTURE DATA FILE (ENSDF), BNL-NCS-51655-01/02-Rev (2001); herein
incorporated by reference) and generate all possible permutations
of decay chains for the nuclide. Using the nuclide data it is
possible to calculate the probability that the nuclide decays
through the chain using the equation
P = .beta. i = 1 n b i ( 4 ) ##EQU00002##
where .beta. is the probability that the nuclide decays to the
highest excited state in the chain and b.sub.i is the branching
ratio of the i-th transition in the chain. The probability of the
chain is the upper limit of the contribution to the coincidence
summing correction factor and if the probability of the chain,
normalized to the total probability of the transition of interest,
is lower than a threshold value, the chain is discarded. If the
probability is larger than the threshold, the chain is added to the
list of chains for the energy of interest. The selection is
repeated for all energies for which the coincidence summing
correction is to be calculated as depicted in the general flowchart
of FIG. 22 (2200).
[0129] The selection of sum-in chains to an energy of interest
starts from the chains left after the low probability chains have
been excluded. Each chain is searched for permutations of two or
more photons; gamma, X-rays or annihilation photons that can add up
to the energy of interest within a tolerance. This tolerance is
adjusted based on the detector resolution. A sum-in chain is
created if the sum of the energies are within the tolerance of the
energy of interest; otherwise the next permutation is checked.
After all the permutations are exhausted for a particular chain,
the next chain is run through. This is repeated for all energies of
interest as depicted in the general flowchart of FIG. 23
(2300).
[0130] When all chains summing-in to an energy in decay have been
determined the chains are again searched for all combinations of
two or more photons in a decay that have an emission probability
higher than a threshold value. These chains are stored as sum-in to
pure sum peaks. The information for the pure sum peaks are added to
the nuclide fingerprint during the nuclide identification
process.
[0131] Once all the sum-out and sum-in chains have been found, they
can be stored for use later in their current form, converted into
source code to be compiled so the TCS correction factor
calculations can use parallel processing techniques, or calculate
the TCS correction factors for the nuclide.
[0132] The TCS correction factor (COI), is calculated from the
ratio of the probability that a photon of the energy of interest is
detected alone by the detector if the detector has a non-perfect
time resolution and the probability that a photon is detected by a
detector with a perfect time resolution C.sub.p, i.e, there is no
true coincidence summing:
COI = C P - C so + C si C p ( 5 ) ##EQU00003##
where C.sub.so is the probability that a photon is summed out of
the peak and C.sub.si is the probability that two or more photons
are summed into the peak.
[0133] C.sub.p can, for a transition that occurs in n chains be
expressed as
C p = c p i n P i ( 6 ) ##EQU00004##
Where c is the gamma emission probability for the transition.
[0134] The probability P.sub..gamma.j that a photon .gamma..sub.j
is detected together with another photon from the same decay chain
is
P .gamma. j = c j pj [ 1 - .PI. i = 1 i .noteq. j n ( 1 - ti ) ] (
7 ) ##EQU00005##
where c.sub.j is the gamma emission probability for the transition,
.epsilon..sub.pj is the Full Energy Peak (FEP) efficiency for
.gamma..sub.j and .epsilon..sub.ti is the probability that any
energy is detected by the detector for the i-th transition (see M.
Blaauw, Nucl. Inst. Meth. Phys. Res., A332 (1993) 493 and S.
Agostinelli et al., Nucl. Inst. Meth. Phys. Res., A506 (2003) 250;
both documents included herein by reference). Co, the total
probability for all chains can be calculated by summing Equation
(7) and multiplying it with the probability that the chain occurs
for all chains containing .gamma..sub.j.
[0135] The probability that m photons deposit their full energy and
no other photons in that decay chain deposits any energy
P.sub..gamma..gamma. in the detector is given by
P .gamma..gamma. = [ .PI. j m ( c j pj ) ] [ 1 - .PI. i = 1 i
.noteq. j n ( 1 - ti ) ] ( 8 ) ##EQU00006##
(See M. Blaauw, Nucl. Inst. Meth. Phys. Res., A332 (1993) 493,
herein incorporated by reference). Csi is calculated by summing all
summing-in chains multiplied by the probability that the chain
occurs, summing-in to .gamma..sub.j.
[0136] From Equations (6)-(8) it can be seen that the Full Energy
Peak (FEP) and total efficiencies are needed to calculate the
correction, these quantities are the only quantities that are not
known a priori. For volume sources, the peak and total efficiencies
are needed for many points, and the correction factor is calculated
by integrating over all source points in the sample.
[0137] For each chain it is possible to determine the minimum peak
and/or total efficiency needed for the chain to have a
non-negligible contribution to the correction factor.
[0138] For summing-in, Equation (8), it is enough if the
probability of the chain multiplied by c.epsilon..sub.p (where c is
the gamma emission probability) for any of the photons summing-in
to the energy of interest, is below a threshold value to be able to
discard the chain for the source point.
[0139] For summing-out, Equation (7), it is required that the
probability of the chain multiplied by at for all photons, except
the photon of interest, are below the threshold for the chain to be
discarded.
[0140] For the cases where m photons are emitted in the same decay
with indistinguishable energies, the energy resolution of the
detector is not good enough to distinguish between the energies,
and the photons are emitted in the same decay Equations (6)
becomes
C p = j n c j pj i n P i ( 9 ) ##EQU00007##
where n in this case is the number of chains where containing
photons with indistinguishable energies.
[0141] The probability that one of the indistinguishable photons j
and k were detected together with the any energy deposited from the
other transitions in the decay P.sub..gamma.j is
P .gamma. j = c j j [ 1 - ( 1 - ( tk - c k pk ) ) ] .PI. i = 1 i
.noteq. j , k n ( 1 - ti ) + c k pk [ 1 - ( 1 - ( tj - pj ) ) .PI.
i = 1 i .noteq. j , k n ( 1 - ti ) ] + c j pj c k pk [ 1 - .PI. i =
1 i .noteq. j , k n ( 1 - ti ) ] ( 10 ) ##EQU00008##
Equation (10) can also be generalized to more than two
indistinguishable photons.
[0142] For voluminous sources integration it is necessary to
integrate the TCS correction factors from source points in the
entire volume. (See V. Kolotov and V. Atrashkevich, TRUE
COINCIDENCE SUMMING CORRECTION FOR RADIATION DETECTORS, U.S. Pat.
No. 6,225,634 or L. Moens, et al., J. Radioanal. Nucl. Chem. 70
(1982) 539 herein incorporated by reference) derived how to do this
for volumes where the point sources have equal weight. This can be
extended to point sources with different weights. Weighted source
points can be used for, but not limited to, non-uniform source
distributions. For example, the activity concentration or density
may vary over the source volume. Following the same derivation as
described in V. Kolotov, V. Atrashkevich, "True coincidence summing
correction for radiation detectors", U.S. Pat. No. 6,225,634
(herein incorporated by reference), the activity determined from a
point source can be expressed as
A = N p .gamma. ( 11 ) ##EQU00009##
where N.sub.p is the counts in the Full Energy Peak (FEP), e is the
peak efficiency and .gamma. is the intensity of the gamma line. If
the source is split up into n sub-sources the activity contribution
from the i-th source with weight w.sub.i can be written as
A i = N p w i i .gamma. j n w j ( 12 ) ##EQU00010##
[0143] The count rate contribution from the i-th sub-source is
then
N.sub.p,i=A.sub.i.epsilon..sub.i.gamma. (13)
Inserting Equation (12) into Equation (13) yields
N p , i = N p w i i j = 1 n w j ( 14 ) ##EQU00011##
[0144] If the count rate from the .gamma.-ray is suffering from
true coincidence summing, the observed peak count rate becomes
N p , i , o = N p w i i COI i j = 1 n w j ( 15 ) ##EQU00012##
where COI.sub.i is the true coincidence summing correction factor
of the i-th subsample. The observed peak count rate can be
calculated by summing over all sub-sources as follows:
N p , o = i = 1 n N p i w i COI i j = 1 n w j = N p j = 1 n w j [ i
= 1 n i w i COI i ] ( 16 ) ##EQU00013##
[0145] The true coincidence summing correction factor for the whole
sample COI then becomes
COI = N p N p , o = j = 1 n w j i = 1 n i w i COI i ( 17 )
##EQU00014##
The flowchart depicted in FIG. 24 (2400) summarizes the calculation
of the TCS correction factors.
True Coincidence Summing Example for .sup.60Co
Overview (2500)
[0146] The present invention will now be described in terms of an
example in which the true coincidence summing techniques are
applied to a .sup.60Co nuclide decay discrimination scenario. FIG.
25 (2500) depicts the basic flowchart of operations required to
perform this example and includes the following steps: [0147] (1)
Initializing thresholds for Abundance, SummingOutProbability, and
PureSumPeak (2501); [0148] (2) Defining possible nuclide decay
states for Co-60 (2502); [0149] (3) Defining nuclide decay branches
(2503); [0150] (4) Retrieving terminal branching ratios from the
NTD transition database (2504); [0151] (5) Calculating nuclide
decay branch probabilities (2505); [0152] (6) Permuting the decay
branches to form nuclide decay chains (2506); [0153] (7) Collecting
K-X-Ray Data (2507); [0154] (8) Selecting the next nuclide chain
for processing (2508); [0155] (9) determining if I.gamma.[k] is
below the abundance threshold, and if so, proceeding to step (11)
(2509); [0156] (10) Calculating peak and total energies for
measured real-time radiation data using nuclide chain probabilities
(2510); [0157] (11) Incrementing the nuclide chain counter (k=k+1)
(2511); [0158] (12) Determining if the nuclide chain counter is
less than or equal to the number of nuclide chains, and if so,
proceeding to step (8) (2512); and [0159] (13) terminating the
nuclide decay discriminator method (2513). These steps are further
detailed below.
.sup.60Co Decay
[0160] FIG. 26 (2600) shows a (simplified) decay scheme of
.sup.60Co and 60mCo. The main R-decay transitions are shown. The
probability for population of the middle energy level of 2.1 MeV by
.beta.-decay is 0.0022%, with a maximum energy of 665.26 keV.
Energy transfers between the three levels generate six different
gamma-ray energies. As depicted in FIG. 26 (2600) the two important
ones are marked.
[0161] 60mCo is a nuclear isomer of .sup.60Co with a half-life of
10.467 minutes. It decays by internal transition to .sup.60Co,
emitting 58.6 keV gamma rays, or with a low probability (0.22%) by
3-decay into .sup.60Ni.
[0162] Cobalt-60 (.sup.60Co) decays by .beta..sup.- emission to an
excited state in .sup.60Ni which decays by photon emission to the
stable ground state.
TCS Correction Factor Operational Parameters
[0163] This section describes how the True Coincidence Summing
(TCS) correction factor is calculated using the method described
herein for a volumetric source that can be represented as two point
sources with weight 1. The following thresholds are used in this
example: [0164] ABUNDANCE THRESHOLD (10E-3)--The minimum ratio of
I.gamma. and the maximum gamma intensity for any transition for
which the TCS correction is calculated for; [0165] SUMMING OUT
PROBABILITY THRESHOLD (10E-6)--The minimum probability for a chain
to be used in the calculation of the sum-out probability; and
[0166] PURE SUM PEAK (1E-3)--The minimum probability for a chain to
be used in the search for pure sum peaks.
[0167] The decay of .sup.60Co used in this example can be seen in
FIG. 27 (2700). The main decay branch is to the third excited state
with a small fraction decaying to the first excited state. The two
most common photon emissions are the 1173 keV and 1332 keV gamma
rays. The nuclear data needed for the method are summarized in
tables provided in FIG. 28 (2800) and FIG. 29 (2900).
Nuclide Transition Branching Ratio
[0168] The branching ratio for a transition can be calculated
from
P i = I .gamma. , i ( 1 + .alpha. ) j I .gamma. , j ( 1 + .alpha. )
, ( 18 ) ##EQU00015##
where I.sub.y,i is the gamma intensity from the i-th state and the
.alpha. is the internal conversion coefficient and the summation is
done over all transitions originating from the same state as
Transition i.
[0169] Combining the nuclear data it is possible to build the decay
chains listed in the table depicted in FIG. 30 (3000).
[0170] The K-X-ray data is summarized in the table depicted in FIG.
31 (3100). K-X-ray florescence yield a .omega..sub.k value of
0.406.
[0171] From the table depicted in FIG. 29 (2900) it can be seen
that the I.sub.y is below the ABUNDANCE THRESHOLD for Transitions
1, 2, 5, and 6 and the TCS correction factor is only to be
calculated for Transitions 3 and 4.
[0172] The peak and total efficiencies for all energies of interest
for the two point sources that can be used to represent the
volumetric source is listed in the table depicted in FIG. 32
(3200).
Transition 3
[0173] Transition 3 is present in chains number 3 and 5. The
probability that a photon from Transition 3 deposits its full
energy in the detector is
C p = ( .beta. 3 - P 3 P 4 + .beta. 1 - P 3 ) p , 3 1 + .alpha. 3 =
0.9998 p , 3 ( 19 ) ##EQU00016##
where .epsilon..sub.p,3 is the Full Energy Peak (FEP) efficiency of
the photon emitted from Transition 3.
[0174] The probability to observe the photon from Transition 3
together with any other photon is
C so = .beta. 3 - P 3 P 4 p , 3 1 + .alpha. 3 [ 1 - ( 1 - 4 ) ] =
0.9986 p , 3 4 where ( 20 ) 4 = 4 , t + .alpha. k 4 i b i i , t 1 +
.alpha. 4 ( 21 ) ##EQU00017##
and b.sub.i is the emission probability of the i-th K-X-ray and
.epsilon..sub.i,t is the total efficiency of the i-th K-X-ray.
Since there is only one photon emitted in chain 5 there is no
summing out contribution from it.
[0175] Checking the sum of all the combinations of transition
energies and x-ray energies reveals that the sum of Transition 1
and 2 are within the sum tolerance and the summing-in probability
can be expressed as
C si = .beta. 3 - P 1 P 2 P 4 p , 1 p , 2 1 + .alpha. 3 [ 1 - ( 1 -
4 ) ] = 0.0000653 p , 1 p , 2 4 ( 22 ) ##EQU00018##
[0176] The TCS correction factor for Transition 3 can then be
expressed as
C O I = C P - C so - C si C p ( 23 ) ##EQU00019##
[0177] Applying the efficiencies for the two point sources in to
Equation (23) gives the COI factors 0.874 and 0.919 for the two
point sources and combining them using the equation
C O I = p j w j i p , i w i C O I i ( 24 ) ##EQU00020##
gives the total COI factor as 0.893.
Transition 4
[0178] Transition 4 is present in chain number 1 and 3. However the
probability that chain 1 occurs is below the SUMMING OUT
PROBABILITY THRESHOLD and its contribution to the COI factor can be
neglected. The probability that a photon from Transition 4 deposits
its full energy in the detector is
C p = .beta. 3 - P 3 P 4 p , 4 1 + .alpha. 4 = 0.9986 p , 4 ( 25 )
##EQU00021##
where .epsilon..sub.p,4 is the Full Energy Peak (FEP) efficiency of
the photon emitted from Transition 4.
[0179] The probability to observe the photon from Transition 4
together with any other photon is
C so = .beta. 3 - P 3 P 4 p , 4 1 + .alpha. 4 [ 1 - ( 1 - 3 ) ] =
0.9986 p , 4 3 ( 26 ) ##EQU00022##
No combination of transition energies or K-X-ray energies adds up
to the energy of Transition 4 within the sum tolerance.
[0180] The TCS correction factor for Transition 4 can then be
expressed as
C O I i = C P - C so C p . ( 27 ) ##EQU00023##
[0181] Applying the efficiencies for the two point sources in to
Equation (2727) gives the COI factors 0.869 and 0.915 for the two
point sources and combining them using the equation
C O I = j w j i i w i C O I i ( 28 ) ##EQU00024##
gives the total COI factor as 0.886.
Pure Sum Peaks
[0182] Combining the transition energies and K-X-ray energies (for
the chains that have higher probability than the minimum sum
probability) and having a sum that is not within the sum tolerance
of a Transition that have a COI factor is calculated for reveals
that the only pure sum peak that survives is the sum of Transitions
3 and 4. Although the sum is within the sum tolerance for
Transition 6 the low I.sub..gamma. causes this peak to be regarded
as a pure sum peak.
[0183] The probability that Transitions 3 and 4 both emit photons
and the full energy is deposited by both photons is
P 3 , 4 = .beta. 3 - P 3 P 4 p , 3 p , 4 ( 1 + .alpha. 3 ) ( 1 +
.alpha. 4 ) ( 29 ) ##EQU00025##
Applying the peak efficiencies for the two point sources the
probability is 0.000951 and 0.000396 for the two point sources
respectively.
[0184] Combining the two probabilities using the equation
P sum = i P 3 , 4 , i w i j w j = 0.000673 ( 30 ) ##EQU00026##
yields the probability that a count is registered in the peak at
2505 keV per decay of .sup.60Co.
SUMMARY
[0185] The above discussion describes how the TCS correction
factors and the pure sum peak probabilities are calculated with the
recursive true coincidence summing correction system/method
implemented within various embodiments of the present
invention.
Typical Application Context
[0186] While a variety of application contexts for the present
invention are anticipated, some are preferred. One such preferred
application context is in radiation safeguard measurement equipment
that is generally categorized into three groups: [0187] Portable
equipment; [0188] Attended in-situ (or installed) equipment; and
[0189] Unattended installed equipment.
[0190] Portable equipment is carried or shipped for a single
inspection while in-situ equipment is installed permanently at a
facility. Unattended equipment is installed in a facility and
operates continually to monitor movement of nuclear material in the
absence of inspection personnel. Both the attended in-situ and
unattended installed equipment often serve a dual purpose function
because they are used by the inspection agency for international
safeguards and the member state for domestic safeguards.
[0191] Within these application contexts, several known portable
radiation detection systems include the U-Pu InSpector, the IMCA,
and the JSR-14 systems. All of these prior art systems combine
automatic control of acquisition electronics and rapid analysis
with an integrated software package for ease of use. The U-Pu
InSpector incorporates the MGA code used by the IAEA and Euratom
for plutonium analysis. The IMCA complies with IAEA PMCN and PMCG
procedures for uranium analysis. The JSR-14 is a portable neutron
coincidence counter that complies with the IAEA neutron counting
procedures.
[0192] The gamma spectrometry systems described above are used to
determine the isotopic abundances of the special nuclear materials.
When the isotopic information is combined with the results from a
neutron coincidence counter, it is possible to establish the total
special nuclear material content of the sample for safeguard
accountability purposes. A calorimeter measures the heat output of
the sample and can also be used in conjunction with the isotopic
measurement results to determine the total special nuclear material
mass for accountability purposes. There are several situations
where a calorimeter is preferable to a neutron coincidence counter
for this purpose.
[0193] The present invention may in some preferred embodiments be
integrated within these existing radiation detection systems to
improve the overall detection and nuclide discrimination
capabilities of these systems.
System Summary
[0194] The present invention system anticipates a wide variety of
variations in the basic theme of construction, but can be
generalized as a nuclide decay discriminator system comprising:
[0195] (a) radiation detection device (RDD); [0196] (b)
analog-to-digital converter (ADC); [0197] (c) digital computing
device (DCD); [0198] (d) operator interface console (OIC); [0199]
(e) real-time display (RTD); [0200] (f) nuclide state database
(NSD); [0201] (g) transition probability database (TPD); and [0202]
(h) state permutation engine (SPE); [0203] wherein [0204] the RDD
is configured to detect radiation and produce an analog electrical
signal corresponding to the detection of a radiation event; [0205]
the RDD is configured to electrically couple the analog electrical
signal to the ADC; [0206] the ADC is configured to convert the
analog signal to digital radiation data (DRD) representing the
presence of detected radiation in the RDD; [0207] the DCD is
configured to count occurrences of the DRD that are above a
predetermined energy detection threshold (EDT) to produce a
radiation detection count (RDC); [0208] the DCD is configured to
accept via the OIC a nuclide inspection list (NIL); [0209] the DCD
is configured to retrieve nuclide state information (NSI) from the
NSD that defines the possible states of nuclides within the NIL;
[0210] the DCD is configured to use the NSI to define nuclide state
branches (NSB) that define transitions between states listed in the
NSI; [0211] the DCD is configured to associate a state transition
probability (STP) for each of the NSB by retrieving a probability
associated with the NSB from the TPD; [0212] the DCD is configured
to recursively permute the NSB using the SPE to form a nuclide
state chain (NSC) list associated with each of the nuclides within
the NIL; [0213] the DCD is configured to compute an overall nuclide
chain probability (NCP) for each NSC; [0214] the DCD is configured
to generate a nuclide probable decay chain (PDC) list from the NSC
by including in the PDC only chains in the NSC having a NCP above a
predetermined threshold; [0215] the DCD is configured to associate
a detected energy level in the DRD with entries in the PDC to
produce a detected nuclide decay (DND) list; [0216] the DCD is
configured to display the DND list to the RTD for review by an
operator in real-time; and [0217] the DCD is configured to display
the RDC associated with entries in the RTD for review by the
operator in real-time.
[0218] This general system summary may be augmented by the various
elements described herein to produce a wide variety of invention
embodiments consistent with this overall design description.
Method Summary
[0219] The present invention method anticipates a wide variety of
variations in the basic theme of implementation, but can be
generalized as a nuclide decay discriminator method comprising:
[0220] (1) with a radiation detection device (RDD), detecting
radiation and producing an analog electrical signal corresponding
to the detection of a radiation event; [0221] (1) with the RDD,
electrically coupling the analog electrical signal to an
analog-to-digital converter (ADC); [0222] (2) with the ADC,
converting the analog signal to digital radiation data (DRD)
representing the presence of detected radiation in the RDD; [0223]
(3) with a digital computing device (DCD), counting occurrences of
the DRD that are above a predetermined energy detection threshold
(EDT) to produce a radiation detection count (RDC); [0224] (4) with
the DCD, accepting via an operator interface console (OIC) a
nuclide inspection list (NIL); [0225] (5) with the DCD, retrieving
nuclide state information (NSI) from a nuclide state database (NSD)
that defines the possible states of nuclides within the NIL; [0226]
(6) with the DCD, using the NSI to define nuclide state branches
(NSB) that define transitions between states listed in the NSI;
[0227] (7) with the DCD, associating a state transition probability
(STP) for each of the NSB by retrieving a probability associated
with the NSB from a transition probability database (TPD); [0228]
(8) with the DCD, recursively permuting the NSB using a state
permutation engine (SPE) to form a nuclide state chain (NSC) list
associated with each of the nuclides within the NIL; [0229] (9)
with the DCD, computing an overall nuclide chain probability (NCP)
for each NSC; [0230] (10) with the DCD, generating a nuclide
probable decay chain (PDC) list from the NSC by including in the
PDC only chains in the NSC having a NCP above a predetermined
threshold; [0231] (11) with the DCD, associating a detected energy
level in the DRD with entries in the PDC to produce a detected
nuclide decay (DND) list; [0232] (12) with the DCD, displaying the
DND list to a real-time display (RTD) for review by an operator in
real-time; and [0233] (13) with the DCD, displaying the RDC
associated with entries in the RTD for review by the operator in
real-time.
[0234] This general method summary may be augmented by the various
elements described herein to produce a wide variety of invention
embodiments consistent with this overall design description.
System/Method Variations
[0235] The present invention anticipates a wide variety of
variations in the basic theme of construction. The examples
presented previously do not represent the entire scope of possible
usages. They are meant to cite a few of the almost limitless
possibilities.
[0236] This basic system and method may be augmented with a variety
of ancillary embodiments, including but not limited to: [0237] An
embodiment wherein the RDD comprises a photon detector. [0238] An
embodiment wherein the RDD is configured to detect alpha, beta, and
gamma radiation. [0239] An embodiment wherein the SPE is configured
to recursively permute (N+1) total nuclide states into (N!) nuclide
decay chains. [0240] An embodiment wherein the DCD generates
N(N-1)/2 of the NSB for a nuclide having (N+1) total nuclide
states. [0241] An embodiment wherein the DCD is configured to
perform parallel hardware processing of the DRD with entries in the
PDC to produce the DND list. [0242] An embodiment wherein the DCD
uses relative peak sizes of the DRD to identify nuclides using
X-ray--X-ray sum peaks, gamma--X-ray sum peaks, gamma--gamma sum
peaks, and gamma--annihilation photon sum peaks. [0243] An
embodiment wherein the DCD is configured to generate a nuclide
probable decay chain (PDC) list from the NSC by including in the
PDC only chains in the NSC having a NCP above a predetermined
threshold by calculating the minimum efficiency for each nuclide
chain, on a point by point basis, to determine if the nuclide chain
has a non-negligible impact on the coincidence summing factor
(COI). [0244] An embodiment wherein the DCD computes the NCP using
a true coincidence summing (TCS) correction factor (COI) that is
calculated from the ratio of the probability that a photon of the
energy of interest is detected alone by the RDD if the RDD has a
non-perfect time resolution and the probability that a photon is
detected by the RDD with a perfect time resolution C.sub.p with no
true coincidence summing using the formula:
[0244] C O I = C P - C so - C si C p ##EQU00027## wherein C.sub.so
is the probability that a photon is summed out of the peak and
C.sub.si is the probability that two or more photons are summed
into the peak. [0245] An embodiment wherein the DCD is configured
to calculate sum peaks from a plurality of photons.
[0246] One skilled in the art will recognize that other embodiments
are possible based on combinations of elements taught within the
above invention description.
Generalized Computer Usable Medium
[0247] In various alternate embodiments, the present invention may
be implemented as a computer program product for use with a
computerized computing system. Those skilled in the art will
readily appreciate that programs defining the functions defined by
the present invention can be written in any appropriate programming
language and delivered to a computer in many forms, including but
not limited to: (a) information permanently stored on non-writeable
storage media (e.g., read-only memory devices such as ROMs or
CD-ROM disks); (b) information alterably stored on writeable
storage media (e.g., floppy disks, thumb drives, and hard drives);
and/or (c) information conveyed to a computer through communication
media, such as a local area network, a telephone network, or a
public network such as the Internet. When carrying computer
readable instructions that implement the present invention methods,
such computer readable media represent alternate embodiments of the
present invention.
[0248] As generally illustrated herein, the present invention
system embodiments can incorporate a variety of computer readable
media that comprise computer usable medium having computer readable
code means embodied therein. One skilled in the art will recognize
that the software associated with the various processes described
herein can be embodied in a wide variety of computer accessible
media from which the software is loaded and activated. Pursuant to
In re Beauregard, 35 USPQ2d 1383 (U.S. Pat. No. 5,710,578), the
present invention anticipates and includes this type of computer
readable media within the scope of the invention. Pursuant to In re
Nuijten, 500 F.3d 1346 (Fed. Cir. 2007) (U.S. patent application
Ser. No. 09/211,928), the present invention scope is limited to
computer readable media wherein the media is both tangible and
non-transitory.
CONCLUSION
[0249] A nuclide decay discriminator system and method has been
disclosed. The system utilizes a digital computing device (DCD) to
capture radiation counts from a radiation detection device (RDD)
such as a photon detector via the use of one or more integrated
analog-to-digital converters (ADC). The radiation count information
is then processed using a recursive procedure in the DCD that
determines the desired nuclide to be evaluated and then defines the
possible nuclide decay transition states. For each possible nuclide
decay state, a recursive permutation of possible state transitions
from this nuclide state is determined using a state permutation
engine (SPE). Combinations of these state transition branches are
linked to form state transition chains each having individual
probabilities associated with the overall state transition chain.
These state transition chain probabilities are applied to the RDD
ADC data to form observed RDD radiation data radiation count
probabilities and displayed in real-time.
DOCUMENTS INCLUDED BY REFERENCE
[0250] The following documents are included herein by reference:
[0251] H. Zhu, et al., TRUE COINCIDENCE SUMMING CORRECTION AND
TOTAL EFFICIENCY COMPUTATION FOR RADIONUCLIDE SPECTROSCOPY
ANALYSIS, U.S. Pat. No. 8,227,761. [0252] V. Kolotov, V.
Atrashkevich, TRUE COINCIDENCE SUMMING CORRECTION FOR RADIATION
DETECTORS, U.S. Pat. No. 6,225,634. [0253] L. Moens, et al., J.
Radioanal. Nucl. Chem. 70 (1982) 539. [0254] F. De Corte, The
k0-Standardization Method: A Move to the Optimization of Reactor
Neutron Activation Analysis, Habil. Thesis, University of Gent,
Belgium, 1987. [0255] M. Blaauw, Nucl. Inst. Meth. Phys. Res., A332
(1993) 493. [0256] M. Blaauw, Nucl. Inst. Meth. Phys. Res., A505
(2003) 311. [0257] R. Keyser, "The evaluation of true coincidence
effect on CTBTO-type sample geometry", The 2003 IEEE Nuclear
Science Symposium and Medical Imaging Conference, Portland, Oreg.,
Oct. 19-25, 2003. [0258] D. Arnold and O. Sima, Applied Radiation
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CLAIMS INTERPRETATION
[0263] The following rules apply when interpreting the CLAIMS of
the present invention: [0264] The CLAIM PREAMBLE should be
considered as limiting the scope of the claimed invention. [0265]
"WHEREIN" clauses should be considered as limiting the scope of the
claimed invention. [0266] "WHEREBY" clauses should be considered as
limiting the scope of the claimed invention. [0267] "ADAPTED TO"
clauses should be considered as limiting the scope of the claimed
invention. [0268] "ADAPTED FOR" clauses should be considered as
limiting the scope of the claimed invention. [0269] The term
"MEANS" specifically invokes the means-plus-function claims
limitation recited in 35 U.S.C. .sctn.112(f) and such claim shall
be construed to cover the corresponding structure, material, or
acts described in the specification and equivalents thereof. [0270]
The phrase "MEANS FOR" specifically invokes the means-plus-function
claims limitation recited in 35 U.S.C. .sctn.112(f) and such claim
shall be construed to cover the corresponding structure, material,
or acts described in the specification and equivalents thereof.
[0271] The phrase "STEP FOR" specifically invokes the
step-plus-function claims limitation recited in 35 U.S.C.
.sctn.112(f) and such claim shall be construed to cover the
corresponding structure, material, or acts described in the
specification and equivalents thereof. [0272] The phrase "AND/OR"
in the context of an expression "X and/or Y" should be interpreted
to define the set of "(X and Y)" in union with the set "(X or Y)"
as interpreted by Ex Parte Gross (USPTO Patent Trial and Appeal
Board, Appeal 2011-004811, Ser. No. 11/565,411, ("`and/or` covers
embodiments having element A alone, B alone, or elements A and B
taken together"). [0273] The claims presented herein are to be
interpreted in light of the specification and drawings presented
herein with sufficiently narrow scope such as to not preempt any
abstract idea. [0274] The claims presented herein are to be
interpreted in light of the specification and drawings presented
herein with sufficiently narrow scope such as to not preclude every
application of any idea. [0275] The claims presented herein are to
be interpreted in light of the specification and drawings presented
herein with sufficiently narrow scope such as to preclude any basic
mental process that could be performed entirely in the human mind.
[0276] The claims presented herein are to be interpreted in light
of the specification and drawings presented herein with
sufficiently narrow scope such as to preclude any process that
could be performed entirely by human manual effort.
* * * * *