INTRINSIC AND ACTIVATED A4BX6 SCINTILLATORS

Abstract

Mixed halide scintillation materials of a first general formula A.sub.4B.sub.(1-y)M.sub.yX′.sub.6(1-z)X″.sub.6z and a second general formula A.sub.(4-y)BM.sub.yX′.sub.6(1-z)X″.sub.6z are disclosed. In the general formulas, A is an alkali metal, B is an alkali earth metal, and X′ and X″ are two different halogen atoms. Scintillation materials of the first general formula include a divalent external activator M such as Eu.sup.2+ or Yb.sup.2+ or a trivalent external activator M such as Ce.sup.3+. Scintillation materials of the second general formula include a monovalent external activator M such as In.sup.+, Na.sup.+, or Tl.sup.+ or a trivalent external activator such as Ce.sup.3+.

Claims

1. A scintillator comprising a chemical compound having the chemical formula A.sub.4B.sub.(1-y)M.sub.yX′.sub.6(1-z)X″.sub.6z, wherein 0≦y≦1, 0≦z≦1, A is one of Li, Na, K, Rb, Cs, and In, or any combination thereof, B is one of Mg, Ca, Sr, and Ba, or any combination thereof, M is one of Eu, Yb, and Ce, X′ is one of F, Cl, Br, and I, or any combination thereof, and X″ is different from X′ and is one of F, Cl, Br, and I, or any combination thereof.

2. The scintillator of claim 1, wherein M is one of Eu.sup.2+, Yb.sup.2+, and Ce.sup.3+.

3. The scintillator of claim 1, wherein A is Cs, B is Ca, X′ is I, M is Eu, and z=0.

4. The scintillator of claim 1, wherein A is Cs, B is Ca, X′ is Br, X″ is I, M is Eu, and z=5/6.

5. The scintillator of claim 1, wherein A is Cs, B is Ca, X′ is Br, M is Eu, and z=0.

6. The scintillator of claim 1, wherein A is Cs, B is Sr, X′ is I, M is Eu, and z=0.

7. The scintillator of claim 1, wherein A is K, B is Sr, X′ is I, M is Eu, and z=0.

8. The scintillator of claim 1, wherein A is Cs, B is Ba, X′ is I, M is Eu, and z=0.

9. The scintillator of claim 1, wherein A is a combination of Cs and K, B is Ca, X′ is I, M is Eu, and z=0.

10. The scintillator of claim 1, wherein A is Cs, B is Ca, X′ is I, y=0, and z=0

11. A scintillator comprising a chemical compound having the chemical formula A.sub.(4-y)BM.sub.yX′.sub.6(1-z)X″.sub.6z, wherein 0≦y≦1, 0≦z≦1, A is one of Li, Na, K, Rb, Cs, and In, or any combination thereof, B is one of Mg, Ca, Sr, and Ba, or any combination thereof, M is one of In, Na, Tl, and Ce, X′ is one of F, Cl, Br, and I, or any combination thereof, and X″ is different from X′ and is one of F, Cl, Br, and I, or any combination thereof.

12. The scintillator of claim 11, wherein M is one of In.sup.+, Na.sup.+, Tl.sup.+, and Ce.sup.3−.

13. The scintillator of claim 11, wherein A is Cs, B is Sr, X′ is I, M is In, and z=0.

14. The scintillator of claim 11, wherein A is Cs, B is Sr, X′ is I, M is Ce, and z=0.

15. The scintillator of claim 11, wherein A is Cs, B is Sr, X′ is I, y=0, and z=0.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] FIGS. 1A and 1B show a crystal of an exemplary scintillator.

[0007] FIGS. 2A-2F are graphs showing X-ray excited radioluminescence spectra of scintillator samples.

[0008] FIGS. 3A-3F are graphs showing pulse height spectra of exemplary scintillators.

[0009] FIGS. 4A-4F are graphs showing scintillation decay profiles of exemplary scintillators.

[0010] FIGS. 5A-5D show crystals of exemplary scintillators.

[0011] FIGS. 6A-6D are graphs showing pulse height spectra of exemplary scintillators.

[0012] FIGS. 7A-7C are graphs showing X-ray excited radioluminescence spectra of exemplary scintillators.

DETAILED DESCRIPTION

[0013] In some embodiments herein, the compositional formula expression of a scintillator material may contain a colon “:”, wherein the composition of the main scintillation material is indicated on the left side of the colon, and the activator or dopant ion is indicated on the right side of the colon. The atomic percentage of the dopant or activator ion may also be indicated to the right side of the colon. For example, for ternary metal scintillators that comprise an alkali metal and an alkali earth metal, the atomic percentage of a divalent dopant ion (e.g., divalent europium ion) may be expressed in atomic percentage relative to the total amount of dopant and alkali earth metal. Thus, the dopant ion may be a divalent ion that substitutes for a percentage of the divalent alkali earth metal ion in the base (i.e., main or undoped) ternary metal halide composition. For example, K.sub.2BaBr.sub.4:Eu 5% represents a K.sub.2BaBr.sub.4 scintillator material activated by europium, wherein 5 atomic % of the barium is replaced by europium. In some embodiments, the dopant may be a monovalent ion that substitutes for a percentage of the alkali metal ion in the base ternary metal halide composition. Thus, the atomic % of a monovalent dopant may be expressed as the atomic % relative to the total amount of dopant and alkali metal.

[0014] As used herein, chemical ions are typically represented by their chemical element symbols alone (e.g., Eu for europium ion(s) (e.g., Eu.sup.2+) or Na for sodium ion(s) (e.g., Na.sup.+)). Similarly, the terms “alkali metal” and “alkali earth metal” are used herein to refer to an alkali metal ion or ions and an alkali earth metal ion or ions, respectively.

[0015] The present disclosure is directed to a group of newly discovered mixed-halide scintillator compounds. These scintillators are particularly notable for their high light output, useful emission wavelength, low melting point, congruent melting, and practical crystal growth.

[0016] Mixed-halide scintillators according to embodiments of the present disclosure may include two families with the following general exemplary formulas:

A.sub.4B.sub.(1-y)M.sub.yX′.sub.6(1-z)X″.sub.6z   (1)

and

A.sub.(4-y)BM.sub.yX′.sub.6(1-z)X″.sub.6z   (2)

[0017] where 0<y≦1, and

[0018] 0≦z≦1.

[0019] Scintillators belonging to the families represented by formulas (1) and (2) may generally be referred to as A.sub.4BX.sub.6 scintillators.

[0020] In the formula (1), M may include either a divalent external activator (such as europium (Eu) or ytterbium (Yb)) or a trivalent external activator (such as cerium (Ce)); A may include an alkali metal (such as Li, Na, K, Rb, Cs, In, or any combination thereof); B may include an alkali earth metal (such as Mg, Ca, Sr, Ba, or any combination thereof); and X′ and X″ are two different halogen atoms (such as F, Cl, Br, I, or any combination thereof).

[0021] In the formula (2), M may include a monovalent external activator (such as indium (In), sodium (Na), or thallium (Tl)) or a trivalent external activator (such as cerium (Ce)); A may include an alkali metal (such as Li, Na, K, Rb, Cs, In, or any combination thereof); B may include an alkali earth metal (such as Mg, Ca, Sr, Ba, or any combination thereof); and X′ and X″ are two different halogen atoms (such as F, Cl, Br, I, or any combination thereof).

[0022] The compounds of formulas (1) and (2) may form excellent scintillators. These new scintillators may be suitable for radiation detection applications including medical imaging, homeland security, high energy physics experiments, and geophysical exploration. As mentioned above, these scintillators are particularly notable for their high light output, useful emission wavelength, low melting point, congruent melting, and practical crystal growth.

[0023] Embodiments of methods for making the mixed-halide scintillators according to formulas (1) and (2) will now be described. In these embodiments, anhydrous high purity (e.g., at least 4N-purity) raw materials from Sigma-Aldrich were mixed in stoichiometric ratio according to the chemical formulas of the respective compounds and loaded into clean quartz ampoules. The mixing and loading were done inside a dry glove box with moisture and oxygen content of less than 0.01 ppm. The starting materials were subsequently dried in the quartz ampoules under 10.sup.−6 torr vacuum at 200° C. for 4 hours, cooled down to room temperature, and sealed inside of the quartz ampoules under vacuum with a hydrogen torch.

[0024] A single-zone furnace may be used to melt and synthesize compounds of formulas (1) and (2), but it is to be appreciated that other furnaces, including without limitation a two-zone transparent furnace and a three-zone vertical Bridgman furnace, may be used. Synthesis techniques including without limitation, Bridgman method, electronic dynamic gradient method, Czochralski method, micro-pulling down method, thin film deposition, melt-freezing, and ceramic hot pressing may be used to produce the final product in poly-crystal, single crystal, thin film, or ceramic forms.

[0025] According to an embodiment, a single zone clamshell furnace was used to melt and synthesize 4-gram samples of compounds of the formula (1). For each sample, the melt and synthesis temperature was raised to 20° C. above the highest melting point of the starting materials used. The temperature was held for 7 hours and cooled down to room temperature in 7 hours. The ampoule was inverted and the procedure above was repeated to encourage complete mixing and reacting of all starting materials. This resulted in polycrystalline samples with analogous physical, optical, and scintillation properties of corresponding grown single crystals. The scintillation properties of one such sample, Cs.sub.4CaI.sub.6:Eu 4%, are included in Table I below. Table I also includes scintillation properties of exemplary rapid melt-freeze samples of compounds of the formula (1). It is to be appreciated that the results shown in Table I may be improved by optimizing the crystal growth protocols.

TABLE-US-00001 TABLE I Light Energy Yield Radioluminescence Resolution Scintillation Composition (ph/MeV) peak (nm) (%) Decay (ns) Cs.sub.4CaI.sub.6: ~50,000 474 3.6 1,600 (92%), Grown Eu 4% 500 crystal Cs.sub.4CaBrI.sub.5: ~35,017 469 1150 (75%), Rapid melt- Eu 4% 3000 freeze sample Cs.sub.4CaBr.sub.6: ~14,298 459 1310 (58%), Rapid melt- Eu 4% 3700 freeze sample Cs.sub.4SrI.sub.6: ~37,300 468 n/a 1900 Rapid melt- Eu 4% freeze sample K.sub.4SrI.sub.6: ~48,880 455 n/a 1600 (80%), Rapid melt- Eu 4% 870 freeze sample Cs.sub.4BaI.sub.6: ~28,180 460 n/a 1200 (56%), Rapid melt- Eu 4% 5900 freeze sample

[0026] To allow for the observation of melting, nucleation, and evolution of the interface shape of an exemplary Cs.sub.4CaI.sub.6:Eu 4% scintillator, a 17-mm Bridgman crystal growth of the exemplary Cs.sub.4CaI.sub.6:Eu 4% scintillator was carried out in a two-zone transparent furnace. The resulting crystal is shown in FIGS. 1A and 1B. In FIG. 1A, the crystal growth of the Cs.sub.4CaI.sub.6:Eu 4% scintillator in the ampoule is shown. FIG. 1B shows on the left a 10×10×10 mm.sup.3 sample and on the right a 5×5×5 mm.sup.3 sample of the exemplary Cs.sub.4CaI.sub.6:Eu 4% scintillator.

[0027] FIGS. 2A-2F are graphs showing X-ray excited radioluminescence spectra corresponding to the exemplary scintillators in Table I. Radioluminescence spectra were measured at room temperature under continuous irradiation from an X-ray generator model CMX003 (at 32 kV and 0.1 mA). A model PI Acton Spectra Pro SP-2155 monochromator was used to record the spectra. The single-peak emission observed in the radioluminescence spectra shown in the FIGS. 2A-2F may be solely attributed to characteristic emission of Eu.sup.2+ 5d to 4f transitions, which shows that Eu.sup.2+ enters the lattice in divalent form. The energy of Eu.sup.2+ 5d-4f excited states is described by P. Dorenbos in “Energy of the First 4f.sup.7-4f.sup.65d Transition of Eu.sup.2+ in Inorganic Compounds,” Journal of Luminescence, 2003, 104, 239-260 and luminescence from this excited state is reported by D. H. Gahane, et al., in “Luminescence of Eu.sup.2+ in Some Iodides,” Optical Materials, 2009, 32, 18-21.

[0028] FIG. 2A shows the exemplary Cs.sub.4CaI.sub.6:Eu 4% scintillator having a single peak centered at 474 nm. FIG. 2B shows the exemplary Cs.sub.4CaBrI.sub.5:Eu 4% scintillator having a single peak centered at 469 nm. FIG. 2C shows the exemplary Cs.sub.4CaBr.sub.6:Eu 4% scintillator having a single peak centered at 459 nm. FIG. 2D shows the exemplary Cs.sub.4SrI.sub.6:Eu 4% scintillator having a single peak centered at 468 nm. FIG. 2E shows the exemplary K.sub.4SrI.sub.6:Eu 4% scintillator having a single peak centered at 455 nm. FIG. 2F shows the exemplary Cs.sub.4BaI.sub.6:Eu 4% scintillator having a single peak centered at 460 nm.

[0029] FIGS. 3A-3F are graphs showing pulse height spectra corresponding to the exemplary scintillators in Table I. Scintillation light yield of the exemplary scintillators was measured using a Hamamatsu H3177-50 photomultiplier tube (PMT). Gamma-ray energy spectra and energy resolution were recorded using a .sup.137Cs as excitation source. The exemplary scintillators were placed in a quartz container filled with mineral oil to protect them from moisture during the measurement. The mineral oil also served as optical coupling between the quartz container and the PMT such that scintillation light generated in the scintillators would transmit to the PMT for measurement. A Spectralon hemispherical dome was used as a reflector to improve the scintillation light collection into the PMT and a shaping time of 10 μs was used to ensure the complete integration of the light pulse. The photopeaks were fitted with a Gaussian function to determine the centroid of the peak. The conversion from the number of measured photoelectrons to the number of photon per unit of γ-ray energy (i.e., ph/MeV) emitted by a scintillator, i.e., the scintillator's light yield, was accomplished by convolving the quantum efficiency of the PMT as a function of wavelength (measured by Hamamatsu, the manufacturer of the PMT) with the emission spectrum of the scintillator.

[0030] In FIG. 3A, the pulse height spectrum of the exemplary Cs.sub.4CaI.sub.6:Eu 4% scintillator (crystal dimensions: 2×2×2 mm.sup.3) under .sup.137Cs excitation is shown to exhibit a light yield of 50,000 ph/MeV and an energy resolution of 3.6% at 662 keV. FIGS. 3B-3F show pulse height spectra of the exemplary Cs.sub.4CaBrI.sub.5:Eu 4%, Cs.sub.4CaBr.sub.6:Eu 4%, Cs.sub.4SrI.sub.6:Eu 4%, K.sub.4SrI.sub.6:Eu 4%, and Cs.sub.4BaI.sub.6:Eu 4% scintillators, respectively, under .sup.137Cs excitation at 662 keV.

[0031] FIGS. 4A-4F are graphs showing scintillation decay profiles, corresponding to the exemplary scintillators in Table I. Scintillation decay time was recorded using a .sup.137Cs source and the time-correlated single photon counting technique described by L. M. Bollinger, et al., in “Measurement of Time Dependence of Scintillation Intensity by a Delayed-Coincidence Method,” The Review of Scientific Instruments, 1961, 32, 1044-1050. The decay profiles are fitted with exponential decay functions.

[0032] FIG. 4A shows the scintillation decay profile of the exemplary Cs.sub.4CaI.sub.6:Eu 4% scintillator, fitted with a two-component exponential decay function having a primary component lasting 1600 ns and accounting for 92% of the total light output and a second component lasting 500 ns and accounting for the remaining light. Similarly, FIGS. 4B-4F show scintillation decay profiles of the exemplary Cs.sub.4CaBrI.sub.5:Eu 4%, Cs.sub.4CaBr.sub.6:Eu 4%, Cs.sub.4SrI.sub.6:Eu 4%, K.sub.4SrI.sub.6:Eu 4%, and Cs.sub.4BaI.sub.6:Eu 4% scintillators, fitted with a two-component exponential decay functions.

[0033] According to another embodiment, three exemplary crystals of scintillators of the formula (1) (Cs.sub.4SrI.sub.6:Eu 4%, Cs.sub.3KCaI.sub.6:Eu 0.5% and Cs.sub.3KSrI.sub.6:Eu 0.5%) were grown by the vertical Bridgman-Stockbarger technique using a two-zone transparent furnace. At least 4N-purity raw materials were mixed and loaded into quartz ampoules in a dry glove box with moisture and oxygen content of less than 0.01 ppm. The starting materials were subsequently dried in the quartz ampoules under 10.sup.−6 torr vacuum at 200° C. A pre-synthesis stage was carried out by reacting the starting materials at 20° C. above the melting points of all the components for 12 hours and then allowed to cool to room temperature over a 10-hour period. The resulting exemplary Cs.sub.4SrI.sub.6:Eu 4%, Cs.sub.3KCaI.sub.6:Eu 0.5% and Cs.sub.3KSrI.sub.6:Eu 0.5% crystals are shown in FIGS. 5A-5C, respectively.

[0034] In particular, FIG. 5A shows on the left a 15-mm diameter single Cs.sub.4SrI.sub.6:Eu 4% crystal in an ampoule under ambient light, and on the right a 5-mm thick specimen of the Cs.sub.4SrI.sub.6:Eu 4% crystal under ambient light. Shown in FIG. 5B on the left is an 8-mm diameter bare single Cs.sub.3KCaI.sub.6:Eu 0.5% crystal under ambient light, and on the right is an 8-mm diameter by 2-mm thick slab of the Cs.sub.3KCaI.sub.6:Eu 0.5% crystal under ambient light. An 8-mm diameter bare single Cs.sub.3KSrI.sub.6:Eu 0.5% crystal under ambient light is shown on the left of FIG. 5C, and an 8-mm diameter by 2-mm thick slab of the Cs.sub.3KSrI.sub.6:Eu 0.5% crystal under ambient light is shown on the right of FIG. 5C.

[0035] According to yet another embodiment, two exemplary crystals of scintillators of the formula (2) (Cs.sub.4SrI.sub.6:In 4% and Cs.sub.4SrI.sub.6:Ce 4%) and two exemplary crystals of undoped scintillators (Cs.sub.4SrI.sub.6 and Cs.sub.4CaI.sub.6) were formed by rapid synthesis. These crystals were obtained by reacting the raw materials at 20° C. above the melting points of all the components for 12 hours and then allowed to cool to room temperature over a 10-hour period. The resulting Cs.sub.4SrI.sub.6:In 4%, undoped Cs.sub.4SrI.sub.6, and Cs.sub.4SrI.sub.6:Ce 4% crystals under ultraviolet (UV) excitation are shown in FIG. 5D, from top to bottom respectively. The undoped Cs.sub.4CaI.sub.6 crystal is not shown.

[0036] FIGS. 6A-6D are graphs showing pulse height spectra of the exemplary Cs.sub.4SrI.sub.6:Eu 4%, Cs.sub.3KCaI.sub.6:Eu 0.5%, Cs.sub.3KSrI.sub.6:Eu 0.5%, and undoped Cs.sub.4CaI.sub.6 scintillator crystals, respectively. The scintillation light yield was measured by coupling each exemplary scintillator crystal to a Hamamatsu 82059 PMT. The single photoelectron technique was used to measure the number of photons per unit of y-ray energy (i.e., ph/MeV) emitted by each exemplary scintillator crystal. The energy resolution for each crystal was measured using a Hamamatsu R6231-100 PMT. Each crystal was placed in a quartz container filled with mineral oil to protect them from moisture during the measurements. The mineral oil also served as optical coupling between the quartz container and the PMT. A Spectralon hemispherical diffuse reflector dome and a shaping time of 10 μs were used.

[0037] FIG. 6A shows the pulse height spectrum of the exemplary Cs.sub.4SrI.sub.6:Eu 4% scintillator (crystal dimensions: 2×2×2 mm.sup.3) under .sup.137Cs excitation, exhibiting a light yield of 60,000 ph/MeV and an energy resolution of 3.3% at 662 keV. FIG. 6B shows the pulse height spectrum of the exemplary Cs.sub.3KCaI.sub.6:Eu 0.5% scintillator under .sup.137Cs excitation, exhibiting a light yield of 21,300 ph/MeV and an energy resolution of 4.77% at 662 keV. FIG. 6C shows the pulse height spectrum of the exemplary Cs.sub.3KSrI.sub.6:Eu 0.5% scintillator under .sup.137Cs excitation, exhibiting a light yield of 23,500 ph/MeV and an energy resolution of 5.50% at 662 keV. The pulse height spectra in FIGS. 6A-6C are fitted with a Gaussian function to determine the centroid of the peak. FIG. 6D shows the pulse height spectrum of the exemplary undoped Cs.sub.4CaI.sub.6 scintillator under .sup.137Cs excitation, exhibiting a light yield of 25,000 ph/MeV and an energy resolution of 12% at 662 keV

[0038] FIGS. 7A-7C are graphs showing X-ray excited radioluminescence spectra of the exemplary Cs.sub.4SrI.sub.6:Eu 4%, Cs.sub.3KCaI.sub.6:Eu 0.5%, Cs.sub.3KSrI.sub.6:Eu 0.5%, Cs.sub.4SrI.sub.6:In 4%, Cs.sub.4SrI.sub.6:Ce 4%, undoped Cs.sub.4SrI.sub.6, and undoped Cs.sub.4CaI.sub.6 scintillators. The radioluminescence spectra were acquired at room temperature under continuous 30-keV X-ray irradiation. The emission spectra were recorded with a 150 mm focal length monochromator over a wavelength range of 200 to 800 nm.

[0039] FIG. 7A shows the radioluminescence spectra of the exemplary Cs.sub.4SrI.sub.6:Eu 4%, Cs.sub.3KCaI.sub.6:Eu 0.5%, and Cs.sub.3KSrI.sub.6:Eu 0.5% scintillators having single peaks at 469 nm, 464 nm, and 463 nm, respectively. FIG. 7A also includes the radioluminescence spectrum of an exemplary Cs.sub.4CaI.sub.6:Eu 4% scintillator having a single peak at 473 nm. FIG. 7B shows the radioluminescence spectra of the exemplary Cs.sub.4SrI.sub.6:In 4% and Cs.sub.4SrI.sub.6:Ce 4% scintillators. FIG. 7C shows the radioluminescence spectra of the exemplary undoped Cs.sub.4SrI.sub.6 and undoped Cs.sub.4CaI.sub.6 scintillators.

[0040] It shall be appreciated that the disclosure may be not limited to the described embodiments, and that any number of scenarios and embodiments in which conflicting appointments exist may be resolved.

[0041] Although the disclosure has been described with reference to several exemplary embodiments, it shall be understood that the words that have been used are words of description and illustration, rather than words of limitation. Changes may be made within the purview of the appended claims, as presently stated and as amended, without departing from the scope and spirit of the disclosure in its aspects. Although the disclosure has been described with reference to particular examples, means, and embodiments, the disclosure may be not intended to be limited to the particulars disclosed; rather the disclosure extends to all functionally equivalent structures, methods, and uses such as are within the scope of the appended claims.

[0042] The illustrations of the examples and embodiments described herein are intended to provide a general understanding of the various embodiments, and many other examples and embodiments may be apparent to those of skill in the art upon reviewing the disclosure. Other embodiments may be utilized and derived from the disclosure, such that structural and logical substitutions and changes may be made without departing from the scope of the disclosure. Additionally, the illustrations are merely representational and may not be drawn to scale. Certain proportions within the illustrations may be exaggerated, while other proportions may be minimized. Accordingly, the disclosure and the figures are to be regarded as illustrative rather than restrictive.

[0043] One or more examples or embodiments of the disclosure may be referred to herein, individually and/or collectively, by the term “disclosure” merely for convenience and without intending to voluntarily limit the scope of this application to any particular disclosure or inventive concept. Moreover, although specific examples and embodiments have been illustrated and described herein, it should be appreciated that any subsequent arrangement designed to achieve the same or similar purpose may be substituted for the specific examples or embodiments shown. This disclosure may be intended to cover any and all subsequent adaptations or variations of various examples and embodiments. Combinations of the above examples and embodiments, and other examples and embodiments not specifically described herein, will be apparent to those of skill in the art upon reviewing the description.

[0044] In addition, in the foregoing Detailed Description, various features may be grouped together or described in a single embodiment for the purpose of streamlining the disclosure. This disclosure may be not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter may be directed to less than all of the features of any of the disclosed embodiments. Thus, the following claims are incorporated into the Detailed Description, with each claim standing on its own as defining separately claimed subject matter.

[0045] The above disclosed subject matter shall be considered illustrative, and not restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments which fall within the true spirit and scope of the present disclosure. Thus, to the maximum extent allowed by law, the scope of the present disclosure may be to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description.