CA1193371A - Neutron method for elemental analysis independent of bulk density - Google Patents
Neutron method for elemental analysis independent of bulk densityInfo
- Publication number
- CA1193371A CA1193371A CA000402700A CA402700A CA1193371A CA 1193371 A CA1193371 A CA 1193371A CA 000402700 A CA000402700 A CA 000402700A CA 402700 A CA402700 A CA 402700A CA 1193371 A CA1193371 A CA 1193371A
- Authority
- CA
- Canada
- Prior art keywords
- rays
- gamma
- neutron
- measuring apparatus
- source
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
- G01N23/22—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material
- G01N23/221—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material by activation analysis
- G01N23/222—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material by activation analysis using neutron activation analysis [NAA]
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2223/00—Investigating materials by wave or particle radiation
- G01N2223/07—Investigating materials by wave or particle radiation secondary emission
- G01N2223/074—Investigating materials by wave or particle radiation secondary emission activation analysis
- G01N2223/0745—Investigating materials by wave or particle radiation secondary emission activation analysis neutron-gamma activation analysis
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2223/00—Investigating materials by wave or particle radiation
- G01N2223/60—Specific applications or type of materials
- G01N2223/613—Specific applications or type of materials moisture
Landscapes
- Physics & Mathematics (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Analysing Materials By The Use Of Radiation (AREA)
Abstract
ABSTRACT
The invention relates to a measuring apparatus and method for quantitatively measuring the concentration of a first element in a sample containing the first element and other element or elements. The apparatus comprises source yielding neutrons having energy sufficient to produce first .gamma.-rays by neutron inelastic scattering or thermal neutron capture by atoms of the first element and other .gamma.-rays by neutron inelastic scattering or thermal neutron capture by atoms of the other element or elements, detector means adapted to detect the first .gamma.-rays and the other .gamma.-rays, shield means associated with the detector means to reduce the intensity of direct source .gamma.-rays and neutrons, energy analysis means associated with the output of the detector means adapted to distinguish between the first .gamma.-rays and the other .gamma.-rays and calculating means associated with the output of the energy analysis means to calculate the concentration.
The invention relates to a measuring apparatus and method for quantitatively measuring the concentration of a first element in a sample containing the first element and other element or elements. The apparatus comprises source yielding neutrons having energy sufficient to produce first .gamma.-rays by neutron inelastic scattering or thermal neutron capture by atoms of the first element and other .gamma.-rays by neutron inelastic scattering or thermal neutron capture by atoms of the other element or elements, detector means adapted to detect the first .gamma.-rays and the other .gamma.-rays, shield means associated with the detector means to reduce the intensity of direct source .gamma.-rays and neutrons, energy analysis means associated with the output of the detector means adapted to distinguish between the first .gamma.-rays and the other .gamma.-rays and calculating means associated with the output of the energy analysis means to calculate the concentration.
Description
3 ~
The present invention provides an improved apparatus and method of elemental analysis based on the sim~ltaneous measurement of the intensities of two or more neutron-induced Xc' i~
~, y-rays from different elements in a ~sample. These intensities are combined to yield an elemental abundance which is essentially independent of bulk density.
The method is particularly applicable to situations where either (a) one of the elements is of fixed or known concentration or (b) there is known relationship between two of the elements in the sample. Two favourable potential applications of the technique are for the analysis of sulfur in lead sinter feed product and the analysis of moisture in coal or other organic material.
sv/,~
When a~sample is ieradiated with fast neutrons, these neutrons interact with the sample to produce prompt ~-rays mainly by inelastic scatter and thermal neutron capture. As well, thermal neutron capture can lead to the forrnation of an unstable nucleus which emits delayed y-rays. Measurement of the intensity oE these prompt or delayed y-rays can be used for elemental analysis of static bulk samples or for on-line analysis (e.g. of ores on conveyor belts). Work in this field has recently been reviewed by Nargolwalla, S.S. et al., in "Nuclear Metnods in Mineral Exploration and Production", ed. J.G. Morse (Elsevier, Amsterdam, 1977), p.ll3. and Berry, P.F. and Martin, T.C., Adv. Activation Analysis 2 (1972) ~9.
Accurate elemental analysis often requires a me,hod of compensating the y-ray yields for changes in bulk density. Methods of compensation include separate
The present invention provides an improved apparatus and method of elemental analysis based on the sim~ltaneous measurement of the intensities of two or more neutron-induced Xc' i~
~, y-rays from different elements in a ~sample. These intensities are combined to yield an elemental abundance which is essentially independent of bulk density.
The method is particularly applicable to situations where either (a) one of the elements is of fixed or known concentration or (b) there is known relationship between two of the elements in the sample. Two favourable potential applications of the technique are for the analysis of sulfur in lead sinter feed product and the analysis of moisture in coal or other organic material.
sv/,~
When a~sample is ieradiated with fast neutrons, these neutrons interact with the sample to produce prompt ~-rays mainly by inelastic scatter and thermal neutron capture. As well, thermal neutron capture can lead to the forrnation of an unstable nucleus which emits delayed y-rays. Measurement of the intensity oE these prompt or delayed y-rays can be used for elemental analysis of static bulk samples or for on-line analysis (e.g. of ores on conveyor belts). Work in this field has recently been reviewed by Nargolwalla, S.S. et al., in "Nuclear Metnods in Mineral Exploration and Production", ed. J.G. Morse (Elsevier, Amsterdam, 1977), p.ll3. and Berry, P.F. and Martin, T.C., Adv. Activation Analysis 2 (1972) ~9.
Accurate elemental analysis often requires a me,hod of compensating the y-ray yields for changes in bulk density. Methods of compensation include separate
- 2 -measurement oE y-ray transmission,reported by Gozani, ri et al ANL-79-62, 266, and by Holmes~ ~.J. Messenger, A.J., and Miles, J.~., Proc. Australas. Inst. Min. Metal:L. 274 (1980), 17~, separate measurement of "matched" ~-ray back-scatter, defined in United States Patent No. 4,314,1S5 and Sowerby~
B.D., Nuclear Instruments and Methods~ 160 (1979) 173 and normalisation to another peak in the ~-ray spectrum, reported by Stewart R.~ all, ~.W., Martin, J.W., Farrior, ~.L. and Poston, A.M., ~.S. Bureau of Mines Technical Progress Report 74, Jan. 1974 and Hall, A.W., Martin J.W., Stewart R.F. and Poston, A.M., U.S. Bureau of Mines Report BM-RI-8038 (1975).
The work reported by Stewart et al., is the closest in concept to the present invention. This work concerns the development of neutron capture techniques for the on-line bulk analysis of sulfur in coal. The coal was contained within a bin of diameter 1 m and height 4 m and sulfur was measured using the 5.42 MeV thermal neutron capture y-ray from sulfur. One method used for the compensation of variations in moisture and bulk density was to normalise the measured sulfur rray yield to the area under the 2.22 MeV H
capture peak. However this procedure alone will not determine elemental abundance independent of bulk density except over small ranges of variation in moisture and ash.
Variations in these parameters will affect the hydrogen content. For example, ccnsider a coal containing 20 wt. %
ash, 0% moisture and 4 wt. % ~. If moisture increases to 5 wt. ~, the hydrogen content of the sample will increase to approximately 4.5 wt. ~. Also, if ash increases to 25 wt. %, the hydrogen content will drop to about 3.75 wt~ %. In fact, Stewart et alO found that hydrogen normalisation did not improve the accuracy of results.
The above discussion relates mainly to on-line and bulk analysis of samples9 Anot:her application area in which neutron techniques are used for elemental analysis is borehole logging, such as reported by Caldwell; R.L. et al., in "Nuclear Techniques and Mineral Resources", (Proc. Symp.
Vienna, 1977), IAEA, Vienna (1977), p~3D In this area, techniques have been recently developed for the ~eterminaticn of elemental ratios (carbon/oxygen and silicon~calcium) to distinguish oil/water ratios in porous rocks. The technique depends primarily on neutron inelastic scatter. However~ the technique is not used to obtain elemental concentrations.
The measured flux Fi of a prompt y-ray produced by neutron interaction in a sample is given by an equation of the form:
Fi = J~(r)-nl-P-NO Cl (Ai) ai.f(~r)Odv ....(1) where ~(r) = neutron flux r = radial distance from source and detector ni = rumber of y-rays produced per neutron interaction in element i p = bulk density No = Avogadro's number Ci ~ concentration of element i Ai = atomic weight of element i ai = neutron cross section f~r) = function of ~ and r ~ ~= y-ray absorption coefficient~
v = volume considered.
The form of this equation is valid for both neutron inelastic scatter and thermal neutron capture.
To a first approximation the ratio of measured ~(-ray yields Pi and Fj is given by Fi F ( i Ci ai Ajj/(Ni Cj ~j A~ .(2) This equation is accurate for two y-rays of similar energy produced by the same interaction process (i.e. inelastic scatter or neutron capture) but can be subject to errors when the ~-rays are produced by different interaction processes.
As the values of n, ~ and A are known for eLements i and j, the ratio Fi/Fj can be used to deduce Cl if Cj is known. To a good approximation, the result will be independent of bulk density~
In general, it is difficult to determine exact ~-ray yields independent of background and a correlation equation of the following form can be used Ci a where a, b, c are constants The method therefore can be used for the measurement of elemental concentration independent of bulk density where the concentration of one element is known or where the relationship between elemental concentrations are known.
The method and apparatus of the invention find special use in the determination of moisture in coal. The most common nuclear method for the measurement of moisture is that based on the slowing down of fast neutrons by hydrogen in the sample, reported in International Atomic Energy Agencyl "Neutron Moisture Gauges", Tech. Report Series No.
B.D., Nuclear Instruments and Methods~ 160 (1979) 173 and normalisation to another peak in the ~-ray spectrum, reported by Stewart R.~ all, ~.W., Martin, J.W., Farrior, ~.L. and Poston, A.M., ~.S. Bureau of Mines Technical Progress Report 74, Jan. 1974 and Hall, A.W., Martin J.W., Stewart R.F. and Poston, A.M., U.S. Bureau of Mines Report BM-RI-8038 (1975).
The work reported by Stewart et al., is the closest in concept to the present invention. This work concerns the development of neutron capture techniques for the on-line bulk analysis of sulfur in coal. The coal was contained within a bin of diameter 1 m and height 4 m and sulfur was measured using the 5.42 MeV thermal neutron capture y-ray from sulfur. One method used for the compensation of variations in moisture and bulk density was to normalise the measured sulfur rray yield to the area under the 2.22 MeV H
capture peak. However this procedure alone will not determine elemental abundance independent of bulk density except over small ranges of variation in moisture and ash.
Variations in these parameters will affect the hydrogen content. For example, ccnsider a coal containing 20 wt. %
ash, 0% moisture and 4 wt. % ~. If moisture increases to 5 wt. ~, the hydrogen content of the sample will increase to approximately 4.5 wt. ~. Also, if ash increases to 25 wt. %, the hydrogen content will drop to about 3.75 wt~ %. In fact, Stewart et alO found that hydrogen normalisation did not improve the accuracy of results.
The above discussion relates mainly to on-line and bulk analysis of samples9 Anot:her application area in which neutron techniques are used for elemental analysis is borehole logging, such as reported by Caldwell; R.L. et al., in "Nuclear Techniques and Mineral Resources", (Proc. Symp.
Vienna, 1977), IAEA, Vienna (1977), p~3D In this area, techniques have been recently developed for the ~eterminaticn of elemental ratios (carbon/oxygen and silicon~calcium) to distinguish oil/water ratios in porous rocks. The technique depends primarily on neutron inelastic scatter. However~ the technique is not used to obtain elemental concentrations.
The measured flux Fi of a prompt y-ray produced by neutron interaction in a sample is given by an equation of the form:
Fi = J~(r)-nl-P-NO Cl (Ai) ai.f(~r)Odv ....(1) where ~(r) = neutron flux r = radial distance from source and detector ni = rumber of y-rays produced per neutron interaction in element i p = bulk density No = Avogadro's number Ci ~ concentration of element i Ai = atomic weight of element i ai = neutron cross section f~r) = function of ~ and r ~ ~= y-ray absorption coefficient~
v = volume considered.
The form of this equation is valid for both neutron inelastic scatter and thermal neutron capture.
To a first approximation the ratio of measured ~(-ray yields Pi and Fj is given by Fi F ( i Ci ai Ajj/(Ni Cj ~j A~ .(2) This equation is accurate for two y-rays of similar energy produced by the same interaction process (i.e. inelastic scatter or neutron capture) but can be subject to errors when the ~-rays are produced by different interaction processes.
As the values of n, ~ and A are known for eLements i and j, the ratio Fi/Fj can be used to deduce Cl if Cj is known. To a good approximation, the result will be independent of bulk density~
In general, it is difficult to determine exact ~-ray yields independent of background and a correlation equation of the following form can be used Ci a where a, b, c are constants The method therefore can be used for the measurement of elemental concentration independent of bulk density where the concentration of one element is known or where the relationship between elemental concentrations are known.
The method and apparatus of the invention find special use in the determination of moisture in coal. The most common nuclear method for the measurement of moisture is that based on the slowing down of fast neutrons by hydrogen in the sample, reported in International Atomic Energy Agencyl "Neutron Moisture Gauges", Tech. Report Series No.
3~
112, IAEA, Vienna, (1970). ~his method is relatively straight forward for many applications provided the results are compensated for bulk density and matrix effects. However a neutron moisture gauge based on this principle is incapable of distinguishing between hydrogen in coal and hydrogen in water. As coal matter contains about 5 wt. % H and as 1 wt. % water contains only Ooll wt. % H, variations in the hydrogen content of coal must be very small for accurate moisture measurements.
One method for the measurement of moisture in bulk coal samples involves the accurate determination of carbon and hydrogen using a neutron gauge and a matched y-ray backscatter gauge, described in U.S. Patent No. 4,314,155, and reported by Sowerby, B.D., Nuclear Instruments and Methods, 160 (1979) 173. However, if carbon and hyd~ogen assays are not required, moisture in coal can be determined with a y ray backscatter gauge using the present method.
This results in a considerable simplification for the accurate determination of moisture in coal.
In the present preferred method, moisture is determined essentially from deviations in the measured carbon/hydrogen ratio from that of dry coal. From the published assays of 112 Australian black coals, Joint Coal Board/Queensland Coal Board, Australian Black Coals Report, Sept. 1976, the dry coal ratio is 16.45 + 1.78. Deviations in this ratio are much reduced for ccal from a particular seam. A 1 wt. % change in moisture will cause the C/H ratio to change by about 2.8% relativeO
The present invention therefore provides a measuring apparatus for quantitatively measuring the concentration of a S~
first element in a~sample containing said first element and other element or elements, said apparatus comprising a source yielding neutrons having energy sufficient to produce first ~-rays by neutron inelastic scattering or thermal neutron capture by atoms of said first element and other ~-rays by neutron inelastic scattering or thermal neutron capture by atoms of said other element or elements, detector means adapted to detect said first y-rays and said other y-rays, shield means associated with said detector means to reduce the intensity of direct source ~-rays and neutrons, energy analysis means associated with the output of said detector means adapted to distinguish between said first y-rays and said other y-rays and calculating means associated with the output of said energy analysis means to calculate said concentration.
The invention also provides a method for quantitatively measuring the concentration of a first element Sd J~ J
in a~sample containing said first element and other element or elements, said method comprising combining the results of (i~ a measurement of first y-rays generated by neutron inelastic scattering or thermal neutron capture by atoms of said firs element, and (ii) at least one measurement of other ~-rays generated by neutron inelastic scattering or thermal neutron capture by atoms of said other element or elements.
Suitable sources include various (~,n) sources with beryllium targets (e~g. plutonium-238/Be, radium-226/Be, americium-241/Be, plutonium-239/Be, polonium-210/Be~
actinium-227/Be), spontaneous fission sources (e~g.
~ ~¢~
californium-25~) and neutron generators utilising the (d,T) and (d,d~ reactions.
Suitable y-ray detectors include scintillation detectors such as NaI(Tl)~ CsI(Na~ and bismuth germanate and solid state detectors such as ~e(Li) and intrinsic Ge.
Suitable neutron shields contain a thermal neutron absorber such as boron or lithium. They can also contain hydrogen to slow the neutrons to thermal energies. The shield between source and detector is primarily to reduce the flux of source ~-rays reaching the detector. Suitable materials are the high density metals such as tungsten, lead and bismuth.
It is preferred that the signal or signals from the detector are amplified preferably in a pre-amplifier or gain stabilised amplifier before being fed into the energy analyses means (energy analyser). The energy analyser can comprise a hardwired multi-channel analyser (e.g.
Hewlett Packard 5401B, Canberra models 30, 35, 40 or 80, Nuclear Data models 60, 600, 660). Alternatively, it may comprise an analog-to-digital converter (either Wilkinson-type or successive approximation) interfaced to a computer, or it may comprise a series of single channel analysers~
The calculating means is preferably a computer or calculator to calculate the elemental concentration from the measured count rates~ A suitable computer would be the PDP
11/03. The preferred embodiments are described with reference ~o the drawings in which:-Fig. 1 is a cross sectional view of an assembly used in a determination according to the invention;
Fi~. 2 is a pulse-height spectrum obtained using the assembly shown in Fig. l;
Fig. 3(a) shows the net count rate of 2.2~ MeV H
capture ~rays plotted against chemical laboratory moisture;
Fig. 3(b) shows the chemical laboratory moisture plotted against the measured intensity of both 2.22 MeV H
capture y-rays and 4O43 MeV C inelastic scatter Y-rays.
Fig. 4 shows chemical laboratory sulfur plotted against the measure intensity of both 2.23 MeV S inelastic scatter Y-rays and 2.62 MeV Pb inelastic scatter y-rays.
The method was tested by measuring the moisture content of coal samples using the experimental assembly shown in Fig. 1. In this assembly a neutron source 1 (e.g.
38Pu-Be) emits 4.43 MeV y-rays and neutrons, which neutrons follow a path such as 2 in-to a sample 3 (e.g. a coal sample) where they strike atoms of the element being determined at 4 thereby producing y-rays which follow a path such as 5 through a neutron shield 6 to a detector 7 which is shielded from the neutron source 1 by a further shield 8. A
suitable shield 6 is boron trioxide which shields the detector 7 from scattered neutrons whereas tungsten, lead or bismuth would be suitable as shield 8 to shield the detector 7 from the source 1. A suitable detector 7 would be a 150 mm diameter x 100 mm thick NaI(Tl) crystal.
Pulses from a NaI(Tl) detector in the neutron assembly were amplified using a gain stabilised amplifier 9 and fed into a Hewlett-Packard 5401B multichannel analyser 10. Count rates and backgrounds were determined by setting windows in the pulse height spectra. A typical pulse-height s~ectrum is shown in Fiy. 3. ~lemental concentration was calculated from the measured count rates by ~D~ 11/03 computer 11.
The source and detector may also be located on opposite sides vf the sample when the sample under analysis is of substantially uniform ~hickness.
In figure 2 curves B and C represent 10 and S0 times magnification, compared with curve A. Peak 19 represents 1.78 ~eV Si, 20 represents ~.22 MeV H, 21 represents 3.92 MeV
C escape and 22 represents 4.43 MeV CO The 3.92 MeV
peak results from the escape of one 0.511 MeV annihilation y-ray from the interaction of a 4.43 ~leV C y-ray in the detector.
Fig~ 3(a) shows the net count rate of 2.22 MeV H
capture y-rays plotted against chemical laboratory moisture.
These results were obtained using one coal sample with added water and in which the bulk density was deliberately varied by compaction. The 2.22 ~eV count rate shows a very poor correlation with moisture. ~lowever if moisture is correlated with the measured intensities of both the 2.22 MeV H capture Y-ray and the 4.43 MeV C inelastic scatter y-ray using equation (3), the moisture can be determined to within 0.36 wt. ~ as shown in Fig. 3(b). No improvement in accuracy is obtained using the combination neutron and Y-ray backscatter method, UDS. Patent No. 4,314,155 and Sowerby9 B.D., Nuclear Instruments and Methods, 160, (1~79) 173.
The method can be used for the measurement of moisture in any organic material such as agricultural products (e.g. wool, cotton~ wheat) for which the dry C/H
337~
ratio is fairly constant.
The method and apparatus of the invention also find use in the analysis of sulfur in lead smelter samples. In many lead smelter plants, lead concentrate is treated in a sinter machine prior to smeltincl in a blast furnace. The sinter machine converts lead sulfide to lead oxide and creates a lump size suitable for the blast furnace. There is a lot of interest in on-line sulfur determination particularly of sinter feed to permit better control of sinter machinesO
This application is ideally suited to the present technique as the concentration of lead remains constant to within about 5~ relative. The energies of the prominent inelastic scatter ~-rays from sulfur (2.23 MeV) and lead (2.62 MeV) are sufficiently similar for equation (2) to be an accurate approximation.
The method has been tested usiny nine samples of Mount Isa sinter feed, product and returns on a neutron assembly similar to that shown in Fig. 1. The results in Fig. 4 show that sulfur can be determined to within 0.24 wt. ~ using the intensitities of 2.23 and 2.62 MeV
~-rays. For comparison the rms deviation between sulfur content and 2.23 MeV yield alone was 0.6 wt. ~. The rms deviation between sulfur and 2.23 MeV intensity together with ~ray backscatter UDS. Patent No. 4,314,155 was 0~5 wt~ % S.
An alternative analysis method is also possible using the 5.42 MeV neutron capture ~-ray from sulfur.
112, IAEA, Vienna, (1970). ~his method is relatively straight forward for many applications provided the results are compensated for bulk density and matrix effects. However a neutron moisture gauge based on this principle is incapable of distinguishing between hydrogen in coal and hydrogen in water. As coal matter contains about 5 wt. % H and as 1 wt. % water contains only Ooll wt. % H, variations in the hydrogen content of coal must be very small for accurate moisture measurements.
One method for the measurement of moisture in bulk coal samples involves the accurate determination of carbon and hydrogen using a neutron gauge and a matched y-ray backscatter gauge, described in U.S. Patent No. 4,314,155, and reported by Sowerby, B.D., Nuclear Instruments and Methods, 160 (1979) 173. However, if carbon and hyd~ogen assays are not required, moisture in coal can be determined with a y ray backscatter gauge using the present method.
This results in a considerable simplification for the accurate determination of moisture in coal.
In the present preferred method, moisture is determined essentially from deviations in the measured carbon/hydrogen ratio from that of dry coal. From the published assays of 112 Australian black coals, Joint Coal Board/Queensland Coal Board, Australian Black Coals Report, Sept. 1976, the dry coal ratio is 16.45 + 1.78. Deviations in this ratio are much reduced for ccal from a particular seam. A 1 wt. % change in moisture will cause the C/H ratio to change by about 2.8% relativeO
The present invention therefore provides a measuring apparatus for quantitatively measuring the concentration of a S~
first element in a~sample containing said first element and other element or elements, said apparatus comprising a source yielding neutrons having energy sufficient to produce first ~-rays by neutron inelastic scattering or thermal neutron capture by atoms of said first element and other ~-rays by neutron inelastic scattering or thermal neutron capture by atoms of said other element or elements, detector means adapted to detect said first y-rays and said other y-rays, shield means associated with said detector means to reduce the intensity of direct source ~-rays and neutrons, energy analysis means associated with the output of said detector means adapted to distinguish between said first y-rays and said other y-rays and calculating means associated with the output of said energy analysis means to calculate said concentration.
The invention also provides a method for quantitatively measuring the concentration of a first element Sd J~ J
in a~sample containing said first element and other element or elements, said method comprising combining the results of (i~ a measurement of first y-rays generated by neutron inelastic scattering or thermal neutron capture by atoms of said firs element, and (ii) at least one measurement of other ~-rays generated by neutron inelastic scattering or thermal neutron capture by atoms of said other element or elements.
Suitable sources include various (~,n) sources with beryllium targets (e~g. plutonium-238/Be, radium-226/Be, americium-241/Be, plutonium-239/Be, polonium-210/Be~
actinium-227/Be), spontaneous fission sources (e~g.
~ ~¢~
californium-25~) and neutron generators utilising the (d,T) and (d,d~ reactions.
Suitable y-ray detectors include scintillation detectors such as NaI(Tl)~ CsI(Na~ and bismuth germanate and solid state detectors such as ~e(Li) and intrinsic Ge.
Suitable neutron shields contain a thermal neutron absorber such as boron or lithium. They can also contain hydrogen to slow the neutrons to thermal energies. The shield between source and detector is primarily to reduce the flux of source ~-rays reaching the detector. Suitable materials are the high density metals such as tungsten, lead and bismuth.
It is preferred that the signal or signals from the detector are amplified preferably in a pre-amplifier or gain stabilised amplifier before being fed into the energy analyses means (energy analyser). The energy analyser can comprise a hardwired multi-channel analyser (e.g.
Hewlett Packard 5401B, Canberra models 30, 35, 40 or 80, Nuclear Data models 60, 600, 660). Alternatively, it may comprise an analog-to-digital converter (either Wilkinson-type or successive approximation) interfaced to a computer, or it may comprise a series of single channel analysers~
The calculating means is preferably a computer or calculator to calculate the elemental concentration from the measured count rates~ A suitable computer would be the PDP
11/03. The preferred embodiments are described with reference ~o the drawings in which:-Fig. 1 is a cross sectional view of an assembly used in a determination according to the invention;
Fi~. 2 is a pulse-height spectrum obtained using the assembly shown in Fig. l;
Fig. 3(a) shows the net count rate of 2.2~ MeV H
capture ~rays plotted against chemical laboratory moisture;
Fig. 3(b) shows the chemical laboratory moisture plotted against the measured intensity of both 2.22 MeV H
capture y-rays and 4O43 MeV C inelastic scatter Y-rays.
Fig. 4 shows chemical laboratory sulfur plotted against the measure intensity of both 2.23 MeV S inelastic scatter Y-rays and 2.62 MeV Pb inelastic scatter y-rays.
The method was tested by measuring the moisture content of coal samples using the experimental assembly shown in Fig. 1. In this assembly a neutron source 1 (e.g.
38Pu-Be) emits 4.43 MeV y-rays and neutrons, which neutrons follow a path such as 2 in-to a sample 3 (e.g. a coal sample) where they strike atoms of the element being determined at 4 thereby producing y-rays which follow a path such as 5 through a neutron shield 6 to a detector 7 which is shielded from the neutron source 1 by a further shield 8. A
suitable shield 6 is boron trioxide which shields the detector 7 from scattered neutrons whereas tungsten, lead or bismuth would be suitable as shield 8 to shield the detector 7 from the source 1. A suitable detector 7 would be a 150 mm diameter x 100 mm thick NaI(Tl) crystal.
Pulses from a NaI(Tl) detector in the neutron assembly were amplified using a gain stabilised amplifier 9 and fed into a Hewlett-Packard 5401B multichannel analyser 10. Count rates and backgrounds were determined by setting windows in the pulse height spectra. A typical pulse-height s~ectrum is shown in Fiy. 3. ~lemental concentration was calculated from the measured count rates by ~D~ 11/03 computer 11.
The source and detector may also be located on opposite sides vf the sample when the sample under analysis is of substantially uniform ~hickness.
In figure 2 curves B and C represent 10 and S0 times magnification, compared with curve A. Peak 19 represents 1.78 ~eV Si, 20 represents ~.22 MeV H, 21 represents 3.92 MeV
C escape and 22 represents 4.43 MeV CO The 3.92 MeV
peak results from the escape of one 0.511 MeV annihilation y-ray from the interaction of a 4.43 ~leV C y-ray in the detector.
Fig~ 3(a) shows the net count rate of 2.22 MeV H
capture y-rays plotted against chemical laboratory moisture.
These results were obtained using one coal sample with added water and in which the bulk density was deliberately varied by compaction. The 2.22 ~eV count rate shows a very poor correlation with moisture. ~lowever if moisture is correlated with the measured intensities of both the 2.22 MeV H capture Y-ray and the 4.43 MeV C inelastic scatter y-ray using equation (3), the moisture can be determined to within 0.36 wt. ~ as shown in Fig. 3(b). No improvement in accuracy is obtained using the combination neutron and Y-ray backscatter method, UDS. Patent No. 4,314,155 and Sowerby9 B.D., Nuclear Instruments and Methods, 160, (1~79) 173.
The method can be used for the measurement of moisture in any organic material such as agricultural products (e.g. wool, cotton~ wheat) for which the dry C/H
337~
ratio is fairly constant.
The method and apparatus of the invention also find use in the analysis of sulfur in lead smelter samples. In many lead smelter plants, lead concentrate is treated in a sinter machine prior to smeltincl in a blast furnace. The sinter machine converts lead sulfide to lead oxide and creates a lump size suitable for the blast furnace. There is a lot of interest in on-line sulfur determination particularly of sinter feed to permit better control of sinter machinesO
This application is ideally suited to the present technique as the concentration of lead remains constant to within about 5~ relative. The energies of the prominent inelastic scatter ~-rays from sulfur (2.23 MeV) and lead (2.62 MeV) are sufficiently similar for equation (2) to be an accurate approximation.
The method has been tested usiny nine samples of Mount Isa sinter feed, product and returns on a neutron assembly similar to that shown in Fig. 1. The results in Fig. 4 show that sulfur can be determined to within 0.24 wt. ~ using the intensitities of 2.23 and 2.62 MeV
~-rays. For comparison the rms deviation between sulfur content and 2.23 MeV yield alone was 0.6 wt. ~. The rms deviation between sulfur and 2.23 MeV intensity together with ~ray backscatter UDS. Patent No. 4,314,155 was 0~5 wt~ % S.
An alternative analysis method is also possible using the 5.42 MeV neutron capture ~-ray from sulfur.
Claims (12)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS;
1. Measuring apparatus for quantitatively measuring the concentration of a first element in a solid sample con-taining said first element and other element or elements, said apparatus comprising a source yielding neutrons having energy sufficient to produce first .gamma.-rays by neutron inelastic scattering or thermal neutron capture by atoms of said first element and other .gamma.-rays by neutron inelastic scattering or thermal neutron capture by atoms of said other element or elements, detector means adapted to detect said first .gamma.-rays and said other .gamma.-rays, shield means associated with said detector means to reduce the intensity of direct source .gamma.-rays and neutrons, energy analysis means associated with the output of said detector means adapted to distinguish between said first .gamma.-rays and said other .gamma.-rays and calculating means associated with the output of said energy analysis means to calculate said concentration.
2. The measuring apparatus as defined in claim 1, wherein said source is selected from an (.alpha., n) source with a beryllium target, a spontaneous fission source and a neutron generator utilising the (d,T) and (d,d) reactions.
3. The measuring apparatus as defined in claim 2, wherein said (.alpha.,n) source is selected from 238Pu/Be, 226Ra/Be, 241Am/Be, 239Pu/Be, 210Po/Be and 227Ac/Be.
4. The measuring apparatus as defined in claim 2, wherein said spontaneous fission source is 252Cf.
5. The measuring apparatus as defined in claim 1, wherein said detector means is a scintillation detector or a solid state detector.
6. The measuring apparatus as defined in claim 5, wherein said scintillation detector is selected from NaI(Tl), CsI(Tl), CsI(Na) and bismuth germanate.
7. The measuring apparatus as defined in claim 5 wherein said solid state detector is Ge(Li) or intrisic germanium .
8. The measuring apparatus as defined in claim 1, wherein said energy analysis means is selected from a multi-channel analyser, an analog to digital converter and a plurality of single channel analysers.
9. A method for quantitatively measuring the concentration of a first element in a solid sample containing said first element and other element or elements, said method comprising combining the results of (i) a measurement of first .gamma.-rays generated by neutron inelastic scattering or thermal neutron capture by atoms of said first element, and (ii) at least one measurement of other .gamma.-rays generated by neutron inelastic scattering or thermal neutron capture by atoms of said other element or elements.
10. The method as defined in claim 9, wherein said sample is coal and said first element is hydrogen or sulfur.
11. The method as defined in claim 10, wherein the measurement of hydrogen content is used to quantitatively determine moisture content.
12. The method as defined in claim 9 wherein said sample is lead sinter feed and said first element is sulfur.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| AUPE8790 | 1981-05-11 | ||
| AU879081 | 1981-05-11 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1193371A true CA1193371A (en) | 1985-09-10 |
Family
ID=3699510
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000402700A Expired CA1193371A (en) | 1981-05-11 | 1982-05-11 | Neutron method for elemental analysis independent of bulk density |
Country Status (4)
| Country | Link |
|---|---|
| JP (1) | JPS5832150A (en) |
| AU (1) | AU8343182A (en) |
| CA (1) | CA1193371A (en) |
| GB (1) | GB2100421A (en) |
Families Citing this family (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0415968Y2 (en) * | 1985-10-18 | 1992-04-09 | ||
| AU708990B2 (en) * | 1994-06-09 | 1999-08-19 | Commonwealth Scientific And Industrial Research Organisation | Determination of pre-reduction degree in iron ore materials |
| AUPP083097A0 (en) * | 1997-12-10 | 1998-01-08 | Commonwealth Scientific And Industrial Research Organisation | An improved bulk material analyser for on-conveyor belt analysis |
| US7112783B2 (en) * | 2003-09-08 | 2006-09-26 | Schlumberger Technology Corporation | Neutron measurement method for determining porosity of a formation surrounding a borehole |
| US7511266B1 (en) * | 2006-12-06 | 2009-03-31 | Bothner Ronald E | Irradiated formation tool (IFT) apparatus and method |
| USD957385S1 (en) | 2007-08-31 | 2022-07-12 | Apple Inc. | Electronic device |
| USD602015S1 (en) | 2008-04-07 | 2009-10-13 | Apple Inc. | Electronic device |
| CN101603930B (en) * | 2009-07-16 | 2011-12-07 | 江苏广兆科技有限责任公司 | Neutron source mechanism of device for detecting compositions of coal on conveying belt in real time |
| CN102608141A (en) * | 2012-03-23 | 2012-07-25 | 南京龙源环保有限公司 | On-line analysis device of pulsed neutron coal element content and proximate analysis indexes |
| WO2015019170A1 (en) * | 2013-08-09 | 2015-02-12 | Vetco Gray Scandinavia As | Method and device for detecting deposited material |
| CN112326708B (en) * | 2020-10-20 | 2023-10-24 | 汪金龙 | Human tissue density and element composition reconstruction algorithm based on instantaneous gamma spectrum |
-
1981
- 1981-05-11 AU AU83431/82A patent/AU8343182A/en not_active Abandoned
-
1982
- 1982-05-11 CA CA000402700A patent/CA1193371A/en not_active Expired
- 1982-05-11 JP JP57077634A patent/JPS5832150A/en active Pending
- 1982-05-11 GB GB213662A patent/GB2100421A/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5832150A (en) | 1983-02-25 |
| AU8343182A (en) | 1982-11-18 |
| GB2100421A (en) | 1982-12-22 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US4090074A (en) | Analysis of coal | |
| US4884288A (en) | Neutron and gamma-ray moisture assay | |
| US3889112A (en) | Method and apparatus for measuring the concentration of water, iron and aluminum in iron ore by neutron radiation | |
| US4314155A (en) | Method and apparatus for elemental analysis employing combination of neutron inelastic scattering and γ ray scattering | |
| CA1157169A (en) | Annihilation radiation analysis | |
| US4566114A (en) | X- and γ-Ray techniques for determination of the ash content of coal | |
| CN101349660A (en) | On-line analysis detection method of mine material iron ore grade | |
| CA1193371A (en) | Neutron method for elemental analysis independent of bulk density | |
| Borsaru et al. | Application of PGNAA for bulk coal samples in a 4π geometry | |
| CA1158783A (en) | Method for determining the solids weight fraction of a slurry | |
| Sowerby et al. | Development of nuclear techniques for on-line analysis in the coal industry | |
| CA1165018A (en) | Analysis of coal | |
| JPH06103279B2 (en) | Component analysis method | |
| AU600461B2 (en) | Neutron and gamma-ray moisture assay | |
| El-Bahi et al. | Application of neutron activation analysis technique for gold estimation in mines in southern Egypt | |
| Holmes et al. | Grade determination of iron ore using pair production | |
| Charbucinski | A universal gamma-gamma method for simultaneous determination of rock and ore properties | |
| Borsaru et al. | Determination of aluminium in bulk coal samples by neutron activation analysis | |
| Hall et al. | Precision tests of neutron sulfur meter in coal preparation plant | |
| CA1126414A (en) | COMBINATION NEUTRON AND .gamma. RAY METHOD OF ELEMENTAL ANALYSIS | |
| Baron et al. | Potential of Nuclear Techniques for On-Line Bulk Analysis in the Mineral Industry | |
| Sowerby | Combination neutron and γ ray method of elemental analysis | |
| Lim et al. | On-belt analysis of ash in coal | |
| Sowerby | Prompt neutron-gamma methods | |
| Brodzinski et al. | Californium-252 in situ activation and photon detection techniques for uranium ore deposit evaluation |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |