CA1131808A - Apparatus for measuring the concentrations of elements in a material by the capture gamma method - Google Patents
Apparatus for measuring the concentrations of elements in a material by the capture gamma methodInfo
- Publication number
- CA1131808A CA1131808A CA326,775A CA326775A CA1131808A CA 1131808 A CA1131808 A CA 1131808A CA 326775 A CA326775 A CA 326775A CA 1131808 A CA1131808 A CA 1131808A
- Authority
- CA
- Canada
- Prior art keywords
- detector
- neutron source
- moderator
- neutrons
- cone
- 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
Abstract
ABSTRACT OF THE DISCLOSURE
The invention provides an apparatus for measuring the concen-trations of elements in a material sample by the capture gamma method, said apparatus including a neutron source in the form of an isotope source or a neutron generator, a moderator surroundingthe neutron source and being at least partly consti-tuted by heavy water, a semiconductor detector serving as gamma radiation detector and positioned in the immediate vicinity of the material to be analyzed and in the flux of slow neutrons, so much of the moderator being provided before the detector that this is reached only by a very low number of fast neutrons that have a damaging effect upon the detector.
The material itself can form part of the moderator and also graphite is preferably used as a moderator around said heavy water.
Furthermore; a body of bismuth having the shape of a cone or a double cone is preferably positioned in front of the neutron source so as to absorb gamma radiation and to scatter fast neutrons.
The invention provides an apparatus for measuring the concen-trations of elements in a material sample by the capture gamma method, said apparatus including a neutron source in the form of an isotope source or a neutron generator, a moderator surroundingthe neutron source and being at least partly consti-tuted by heavy water, a semiconductor detector serving as gamma radiation detector and positioned in the immediate vicinity of the material to be analyzed and in the flux of slow neutrons, so much of the moderator being provided before the detector that this is reached only by a very low number of fast neutrons that have a damaging effect upon the detector.
The material itself can form part of the moderator and also graphite is preferably used as a moderator around said heavy water.
Furthermore; a body of bismuth having the shape of a cone or a double cone is preferably positioned in front of the neutron source so as to absorb gamma radiation and to scatter fast neutrons.
Description
~3~
OUTOKUMPU Oy, Outokumpu 7813~1 Apparatus for measuring the concentrations of elements in a material by the capture gamma method ~' :::
The present inven-tion reIates to an apparatus for measuring the concentrations of elements in a material by the capture gamma method, the apparatus comprising a neutron source, , a gamma-radia-tion detector, and a moderator between these two. `
The capture gamma method is known per se. In this method the neutrons travelin~ from a neutron source are allowed to be captured by the atom nuclei of the specimen, whereby energy is released in the form of gamma-radiation. The elements presen-t in the specimen can be identified and their concentra-tions calculated on the basis of the energies and intensities of the yamma~radiation.
The capture gamma method has been studied over`a long period of tlme, and it has been applied by using various neutron sources, such as reactors, neutron generators and isotope sources. The neutrons traveling from the source are fast, and they must be decelerated in a moderator before they cause nuclear reactions which produce capture g~immas. The deceleration is 'best performed in a substance with llghtweight atom nuclel,(hydrogenl. The energles and lntensitles of the gamma-radiatlon generated are detected by gamma-ray slJectroscopy, and -the elements and their ' ' ' -: ' ~:
, .
:~, L8~1~
OUTOKUMPU Oy, Outokumpu 7813~1 Apparatus for measuring the concentrations of elements in a material by the capture gamma method ~' :::
The present inven-tion reIates to an apparatus for measuring the concentrations of elements in a material by the capture gamma method, the apparatus comprising a neutron source, , a gamma-radia-tion detector, and a moderator between these two. `
The capture gamma method is known per se. In this method the neutrons travelin~ from a neutron source are allowed to be captured by the atom nuclei of the specimen, whereby energy is released in the form of gamma-radiation. The elements presen-t in the specimen can be identified and their concentra-tions calculated on the basis of the energies and intensities of the yamma~radiation.
The capture gamma method has been studied over`a long period of tlme, and it has been applied by using various neutron sources, such as reactors, neutron generators and isotope sources. The neutrons traveling from the source are fast, and they must be decelerated in a moderator before they cause nuclear reactions which produce capture g~immas. The deceleration is 'best performed in a substance with llghtweight atom nuclel,(hydrogenl. The energles and lntensitles of the gamma-radiatlon generated are detected by gamma-ray slJectroscopy, and -the elements and their ' ' ' -: ' ~:
, .
:~, L8~1~
- 2 concentr~tions can be determined on the basis oE these energies and intellslties.
The most impor-tant advan-tage of the capture gamma method is that the penetration depth of both neutrons and gamma-radiation is grea-t in the specimen. For example, -the half~value thickness of -the Eeed mix-ture oE a flash-smelting furnace is approx. 6 cm for neutrons and approx. 12 cm for gamma-radia-tion. The half value thickness for neutrons can vary considerably rom one specimen to another. Usually the absorption oE gamrna-radiation is dependent on only the thickness of the specimen. The specimens are usually very coarse-grained. The measuring can also be performed through a thick aluminum plate. The measuring can be performed directly from a process pipe, silo, or conveyor.
If the specimen bed is sufficiently thick, the detector and the source can be placed on different sides of the specimen, thus creatin~ a yreater distance between them, which is advantageous in terms of protecting the detector. Using a thicker specimen, however, a large portion of the capture gammas have to pass through the entire specimen layer, thereby increasin~
the~Compton background in the spectrum, and it is more advantageous to use a geometry in which the detector and the source are on the same side of the specimen.
According to the literature, the cap-ture gamma method has been used as a continuous-working process only with a scintillation detector. A semi-conductor detector has been used in intermittent measurements in, for example, bore analysis.
This is so because fast electrons damage the semi-conductor detector even in rather small quanti-ties (less than 101 neutrons/cm2). For example, in the analysis of a flash-smelting furnace feed, a better resolution of a semi-conductor detector is, however~ necessary in order to ma]ce distinction between the lines of various substances. Thus, the problem is to obtain a sufficient quant:ity of thermal neutrons in the sample and at the same time to prevent fast neutrons from entering the detector. The de-tectvr must be so close to the specim~n ;
.33~
that the capture gan~a quanta can be detected effectively.
The object of the present invention is to solve the above problem and to provide a measuring apparatus with which capture gamma measuring can be performed on a continuous-working basis and with a high capacity.
According to the present invention, this problem is solved by an apparatus for measuring the concentrations of elements in a material by the capture gamma method, said appara-tus compris-ing a neutron source, a moderator surrounding the neutron source and being at least partly constituted by heavy water, a gamma radiation detector in the form of a semiconductor detector, said detector being positioned close to the material to be measured and in a flux of slow neutrons, there being so much of the moderator between the neutron source and the detector that at most only a ew fast neutrons can reach the detectorO
That which is essential in the invention is the use of heavy water as the moderator to obtain a large flux of slow neutrons in the sample and at the same time so small a flux of fast neutrons that the detector can be placed right next to or inside the speci men. Therebythe gamma-radiation emitted by the specimen can be measured with a high efficiency.
Before describing the invention in detail it is advisable to discuss the principles of the theory underlying the lnvention.
The deceleration and diffusion of the neutrons is a mathematically difficult problem for which a precise solution can be found only by means of a very simple geometry, for exam~le in a case of spherical symmetry. The measuring equipment includes, however, many dif~erent materials and interfaces with various
The most impor-tant advan-tage of the capture gamma method is that the penetration depth of both neutrons and gamma-radiation is grea-t in the specimen. For example, -the half~value thickness of -the Eeed mix-ture oE a flash-smelting furnace is approx. 6 cm for neutrons and approx. 12 cm for gamma-radia-tion. The half value thickness for neutrons can vary considerably rom one specimen to another. Usually the absorption oE gamrna-radiation is dependent on only the thickness of the specimen. The specimens are usually very coarse-grained. The measuring can also be performed through a thick aluminum plate. The measuring can be performed directly from a process pipe, silo, or conveyor.
If the specimen bed is sufficiently thick, the detector and the source can be placed on different sides of the specimen, thus creatin~ a yreater distance between them, which is advantageous in terms of protecting the detector. Using a thicker specimen, however, a large portion of the capture gammas have to pass through the entire specimen layer, thereby increasin~
the~Compton background in the spectrum, and it is more advantageous to use a geometry in which the detector and the source are on the same side of the specimen.
According to the literature, the cap-ture gamma method has been used as a continuous-working process only with a scintillation detector. A semi-conductor detector has been used in intermittent measurements in, for example, bore analysis.
This is so because fast electrons damage the semi-conductor detector even in rather small quanti-ties (less than 101 neutrons/cm2). For example, in the analysis of a flash-smelting furnace feed, a better resolution of a semi-conductor detector is, however~ necessary in order to ma]ce distinction between the lines of various substances. Thus, the problem is to obtain a sufficient quant:ity of thermal neutrons in the sample and at the same time to prevent fast neutrons from entering the detector. The de-tectvr must be so close to the specim~n ;
.33~
that the capture gan~a quanta can be detected effectively.
The object of the present invention is to solve the above problem and to provide a measuring apparatus with which capture gamma measuring can be performed on a continuous-working basis and with a high capacity.
According to the present invention, this problem is solved by an apparatus for measuring the concentrations of elements in a material by the capture gamma method, said appara-tus compris-ing a neutron source, a moderator surrounding the neutron source and being at least partly constituted by heavy water, a gamma radiation detector in the form of a semiconductor detector, said detector being positioned close to the material to be measured and in a flux of slow neutrons, there being so much of the moderator between the neutron source and the detector that at most only a ew fast neutrons can reach the detectorO
That which is essential in the invention is the use of heavy water as the moderator to obtain a large flux of slow neutrons in the sample and at the same time so small a flux of fast neutrons that the detector can be placed right next to or inside the speci men. Therebythe gamma-radiation emitted by the specimen can be measured with a high efficiency.
Before describing the invention in detail it is advisable to discuss the principles of the theory underlying the lnvention.
The deceleration and diffusion of the neutrons is a mathematically difficult problem for which a precise solution can be found only by means of a very simple geometry, for exam~le in a case of spherical symmetry. The measuring equipment includes, however, many dif~erent materials and interfaces with various
-3-:: :
~3~
directions. The simplest solution in this case i5 to use the Monte Carlo method in the calculations, which is based on the knowledge of the laws of probability governing the behavior of an individual neutron in each medium. By following several differ-ent neutron case histories (travel vf a neutron decelerating and changing direction upon impinging against atoms, and finally absorption), an idea of the number and energy distribution of neutrons in various places is gradually obtained.
In connection with the present invention, calculations concerning different capture gamma measurement arrangements were carried out by the Monte Carlo method and it was discovered that the use of slightly -3a-~3~8 absorbing decelerating subs-tances (heavy water, graphite~ is essential. The suitable geometries were also discovered, and the test performed showed that the results of simulation calculations were right.
In the detailed description oE the invention below, reference is made to the accompanying drawings, in which Figure 1 depicts curves connected with the explanation of the theory of the invention, Figure 2 depicts various alternatives of the bismuth radiation shield Figure 3 depicts one me~suring arrangement which has proven to be especially advantageous, Figure 4 depicts one measurement arrangement, Figures 5 and 6 depict spectra measured using the apparatus according to the invention, Figure 7 depicts another, slightly modiEied measuring arrangemen-t, Figure 8 depicts the application of the apparatus to the measurement of a slurry.
The results show~ in Figure 1 were obtained by calculating the thermal and the fast flux on the basis of H20 and D20 spheres with a radius of 100 cm. The figure shows that in ~2 the thermal flux drops at the same rate as the fast flux, `
whereas in D20 the diffusion spreads the thermal flux over a larger area without absorption and only leakage outside the sphere begins to reduce the~flux.
The deceleration distance of graphite is greater and the diffusion distance smaller than those of D20, but because of its low price graphite is advantageous to use around D20, and possibly H20 around the graphite. In order to scatter the fast neutrons traveling towards the detector and in order to absorb the gammas of the source, it is advantageous to use a Bi cone between the source and the detector. Bismuth has hardly any interfering capture gammas and it is a heavy material.
. . .
: . ' - :
1~3~
Used Wit}l a semi-conductol cletector, however, bismuth is a very poor decelerator, and it must not extend as far as the detector lest the ~ast neutrons travel to the detec-tor along it. The -table below shows the quantity (n) oE neutrons arriviny at the detector wi-thin a certain time period in arranyements according to Fiyure 2. The ~2 distance does not have a very yreat effect, but a lonyer dis-t-ance is somewhat bet-ter. A
broader initial cone further improves the situation. It scatters the neutrons in a larger space al~gle.
Table 1 A B C C
a lO 20 lO 20 (crn) b - - lO - ~cm) l 50 5O 50 50 (cm) n 147 131 168 113 In Figure 2 reference nurneral 1 indicates the detector, which can be, for example, a semi-conductor detector. Num~3ral 2 indicates the scatteriny cone, which is of bismuth, for example. Around the scatteriny device there is, conically enclosed, heavy water 3. Nurneral 4 indicates the source of radiation.
Heavy water is rather expensive and therefore i-ts quantity;is worth optimizing. The geometry according to Figure 3 has been arrived at as a result oi optimization. In this g~ometry most of the decelerator is graphite instead of heavy water. However, it is advantacJeous to use heavy water on the side facing the detector, since it is essential that the neutrons arriving at the detector have already thermalized. The width of the necessary D2O space has been calculated, and it has been observed that increasing the quantity of D2O beyond approx. 12 llters no lonyer substantially improves the situa-tion.
;
~; In Figure 3 reference numerals 1, 2 and 3 indicate, as above, the detector, the scattering device, and the heavy wa-ter around the scattering device. The neutron source 4 is situated at the apex of the scattering device, numeral 5 indicates the ~::
~ ~ , `~
~3~
grapl~ite, and numeral 6 t~le ma-terial. on which the measuring is performed, sltuated on a ~onveyor, :Eor: example.
The neutron source used in the experiments and calculations is a 252CE-isotope source because it produces the best neu-tron y:ield per activity uni-t, its price is ra-ther advantageous and its neutron spectrum is sof-t. O-ther isotope sources or neutron generators can, of course, also be used.
In -the literature, data concerning -the quan-ti~y of fas-t neutrons tolerated by the detector vary to a rather high degree.
Here 109 n/cm2, which represen-ts a cautious average, has been taken as a starting poin-t. On the basis of simulation, an increase of 15 cm in the distance between the source and the detector decreases the dose of East neutrons to one-ten-tn. The values obtained for the useful life of the detector with -the optimal geometry using different distances were those according to Table 2 for 20 ~g 252Cf:
Table 2 ~ffect of distance on the useful life of detec-tor _ _ and gamma intensity Distallce Usefùl life of detector Relative gamma : : intensity 45 cm 110 days 2.2 55 cm 1.4 years 1.2 :
60 cm 3 years 0.8 65 cm 6.3 years 0 5 Most likely it is`advantageous to use a distance of avprox.
65 cm in the construction, although in -the experiment it was 55 cm. A damaged detector is not unusable but can be repaired by the manufacturer.
The experimental geometry according to Figure A was ob-tained on the basis oE the optimization performed.
In Figure 4, reference numerals 1-6 indica-te the same par-ts as above. Numeral 7 indicates a support device, which keeps the scattering device 2 in the correct position. Numeral 8 indicates . : ,~ . .
~13~
the liquid nitrogen bottle; liquid nitroCJen is used for maintaininy the detector at a low temperature. A hollow has been made in -the specLmen tank 6 for the preamplifier of the detec-tor. I-t should be noted -that this arrangement was made for a laboratory experimen-t and that in practical applications -the arrangement can conslderably differ from this one.
The equipment available Eor the experiments included a Ge(Li) detector ~volume 110 cm3, effectiveness 21.8 %) and a da-ta machine sys-tem coupled -to it. The results were obtained in -the form of a listing on punch -tape and a plotter. The source was 1 ~g 252Cf. The measuring period was 100 min and the speclmens were Ni and Cu concentrates. ~he concentrations of the principal components of the concentrates are given in Table 3.
Table 3 Concentrations of the principal components of the concentrates Ni Cu S Fe SiO2 % % % % %
Ni concentrate 5.52 3.40 23.3 29.8 24.9 Cu concentrate 0.21 24.8 29.6 29.8 8.3 In addition, background~measurements were performed by~
replacing the specimen with a boric acid solution having a reflection capacity to thermal neutrons approximately equal to that of the specimen. The geometry for the measuring is~shown in Figure 4. Furthermore, the geometry was varied so that the empty space surrounding the detector between the sample and the moderator was filled wlth specimen and in other cases graphite pieces were fitted as reflectors around the detector. In addition experiments were performed on the effects on the spectrum of a thin Cd plate placed to protect the detector.
The relatively great height of the apparatus shown in Figure 4 is due to the fact that the graphite was in standard-leng-th bars ~: -The program used for the processing of the spectrum was a program called Vipunen developed in the Department of Physics, University of Helsinkl. On the basis of international testing :~:
:
~3~ 8 this is a very {Jood progr;lln for processlncJ -the spec-trum.
The progralll detects the pea]cs, calibrates -the energies, det~rmines the background, and calcu]ates the area of the peaks and their error values. The lis-ting gave, in addition to the spectrum, a table of -the pealcs and -their parame-ters.
The mos-t important peaks of the various subs-tances were used in estimating the error caused by pulse statistics:
Fe: 7.646 MeV and 7.632 MeV wi-th escape peaks S: 5.420 Mev with escape peaks~ 3.221 MeV, 2.931 MeV and 2.380 MeV
Cu: 7.915 MeV and 7.306 MeV with escape peaks Ni: 8.999 MeV and 3.535 MeV wi-th escape peaks Si: 4.934 MeV and 3.539 MeV.
The results ob-tained wi-th Ni concentrate are shown in the table below.
Table 4 Sourcel~g 252Cf, measuring period 100 min Ni concentrate relative absolute error % errol %
S 4.1 0.96 Fe 1.~ 0.54 Cu 9.0 0.31 Ni 4.5 0.25 SiO2 11.5 2.9 ~ .
Corresponding resul-ts would be obtained by using 10 ~g/10 min or 20 ~g/5 min. By quadrupling the time, the error could be ~ reduced by one half.
:: :
Figures 5 and 6 show parts of the spectrum of Ni concentrate.
:::: :
The capture gammas and ac-tivation peaks produced by the structure material of the detector could be elimina-ted using a Cd shield. Some neutron absorber other than Cd could worsen the peak-background ratio to a lesser degree. The quantity of ::
.
.
.- . . , ~ :.:
, , . ' , ' : ~ ~
. . .
8~
capture gammas obtained from ~he specimen was reduced by 1.7 when uslng a Ccl shield.
Finally, Figure 7 shows how a measuring apparatus according to the invention could be positioned for the measuring of, for example, material 6 being conveyed on a Reedler conveyor. The geometry is the same as -that shown in Figures 3 and 4, but it has been reversed.
It is evident that the yeometry can be varied in many ways without deviating from -the idea of the invention, which is using heavy water as moderator. If, for example, the material to be studied is a flow of material in a pipe, e.g. a slurry, it also works as a moderator itself. The detactor can be placed in the slurry, in which case the arrangement will be similar to that shown in Figure 8. In this case the specimen to be studied, i.e. slurry 6, flows in a pipe and the detector is ir~ the middle of the pipe. Naturally, several other alternatives are also possible.
::~
::
,~
. . ~ . -- . . : .
: ' , - ~ ' :
~3~
directions. The simplest solution in this case i5 to use the Monte Carlo method in the calculations, which is based on the knowledge of the laws of probability governing the behavior of an individual neutron in each medium. By following several differ-ent neutron case histories (travel vf a neutron decelerating and changing direction upon impinging against atoms, and finally absorption), an idea of the number and energy distribution of neutrons in various places is gradually obtained.
In connection with the present invention, calculations concerning different capture gamma measurement arrangements were carried out by the Monte Carlo method and it was discovered that the use of slightly -3a-~3~8 absorbing decelerating subs-tances (heavy water, graphite~ is essential. The suitable geometries were also discovered, and the test performed showed that the results of simulation calculations were right.
In the detailed description oE the invention below, reference is made to the accompanying drawings, in which Figure 1 depicts curves connected with the explanation of the theory of the invention, Figure 2 depicts various alternatives of the bismuth radiation shield Figure 3 depicts one me~suring arrangement which has proven to be especially advantageous, Figure 4 depicts one measurement arrangement, Figures 5 and 6 depict spectra measured using the apparatus according to the invention, Figure 7 depicts another, slightly modiEied measuring arrangemen-t, Figure 8 depicts the application of the apparatus to the measurement of a slurry.
The results show~ in Figure 1 were obtained by calculating the thermal and the fast flux on the basis of H20 and D20 spheres with a radius of 100 cm. The figure shows that in ~2 the thermal flux drops at the same rate as the fast flux, `
whereas in D20 the diffusion spreads the thermal flux over a larger area without absorption and only leakage outside the sphere begins to reduce the~flux.
The deceleration distance of graphite is greater and the diffusion distance smaller than those of D20, but because of its low price graphite is advantageous to use around D20, and possibly H20 around the graphite. In order to scatter the fast neutrons traveling towards the detector and in order to absorb the gammas of the source, it is advantageous to use a Bi cone between the source and the detector. Bismuth has hardly any interfering capture gammas and it is a heavy material.
. . .
: . ' - :
1~3~
Used Wit}l a semi-conductol cletector, however, bismuth is a very poor decelerator, and it must not extend as far as the detector lest the ~ast neutrons travel to the detec-tor along it. The -table below shows the quantity (n) oE neutrons arriviny at the detector wi-thin a certain time period in arranyements according to Fiyure 2. The ~2 distance does not have a very yreat effect, but a lonyer dis-t-ance is somewhat bet-ter. A
broader initial cone further improves the situation. It scatters the neutrons in a larger space al~gle.
Table 1 A B C C
a lO 20 lO 20 (crn) b - - lO - ~cm) l 50 5O 50 50 (cm) n 147 131 168 113 In Figure 2 reference nurneral 1 indicates the detector, which can be, for example, a semi-conductor detector. Num~3ral 2 indicates the scatteriny cone, which is of bismuth, for example. Around the scatteriny device there is, conically enclosed, heavy water 3. Nurneral 4 indicates the source of radiation.
Heavy water is rather expensive and therefore i-ts quantity;is worth optimizing. The geometry according to Figure 3 has been arrived at as a result oi optimization. In this g~ometry most of the decelerator is graphite instead of heavy water. However, it is advantacJeous to use heavy water on the side facing the detector, since it is essential that the neutrons arriving at the detector have already thermalized. The width of the necessary D2O space has been calculated, and it has been observed that increasing the quantity of D2O beyond approx. 12 llters no lonyer substantially improves the situa-tion.
;
~; In Figure 3 reference numerals 1, 2 and 3 indicate, as above, the detector, the scattering device, and the heavy wa-ter around the scattering device. The neutron source 4 is situated at the apex of the scattering device, numeral 5 indicates the ~::
~ ~ , `~
~3~
grapl~ite, and numeral 6 t~le ma-terial. on which the measuring is performed, sltuated on a ~onveyor, :Eor: example.
The neutron source used in the experiments and calculations is a 252CE-isotope source because it produces the best neu-tron y:ield per activity uni-t, its price is ra-ther advantageous and its neutron spectrum is sof-t. O-ther isotope sources or neutron generators can, of course, also be used.
In -the literature, data concerning -the quan-ti~y of fas-t neutrons tolerated by the detector vary to a rather high degree.
Here 109 n/cm2, which represen-ts a cautious average, has been taken as a starting poin-t. On the basis of simulation, an increase of 15 cm in the distance between the source and the detector decreases the dose of East neutrons to one-ten-tn. The values obtained for the useful life of the detector with -the optimal geometry using different distances were those according to Table 2 for 20 ~g 252Cf:
Table 2 ~ffect of distance on the useful life of detec-tor _ _ and gamma intensity Distallce Usefùl life of detector Relative gamma : : intensity 45 cm 110 days 2.2 55 cm 1.4 years 1.2 :
60 cm 3 years 0.8 65 cm 6.3 years 0 5 Most likely it is`advantageous to use a distance of avprox.
65 cm in the construction, although in -the experiment it was 55 cm. A damaged detector is not unusable but can be repaired by the manufacturer.
The experimental geometry according to Figure A was ob-tained on the basis oE the optimization performed.
In Figure 4, reference numerals 1-6 indica-te the same par-ts as above. Numeral 7 indicates a support device, which keeps the scattering device 2 in the correct position. Numeral 8 indicates . : ,~ . .
~13~
the liquid nitrogen bottle; liquid nitroCJen is used for maintaininy the detector at a low temperature. A hollow has been made in -the specLmen tank 6 for the preamplifier of the detec-tor. I-t should be noted -that this arrangement was made for a laboratory experimen-t and that in practical applications -the arrangement can conslderably differ from this one.
The equipment available Eor the experiments included a Ge(Li) detector ~volume 110 cm3, effectiveness 21.8 %) and a da-ta machine sys-tem coupled -to it. The results were obtained in -the form of a listing on punch -tape and a plotter. The source was 1 ~g 252Cf. The measuring period was 100 min and the speclmens were Ni and Cu concentrates. ~he concentrations of the principal components of the concentrates are given in Table 3.
Table 3 Concentrations of the principal components of the concentrates Ni Cu S Fe SiO2 % % % % %
Ni concentrate 5.52 3.40 23.3 29.8 24.9 Cu concentrate 0.21 24.8 29.6 29.8 8.3 In addition, background~measurements were performed by~
replacing the specimen with a boric acid solution having a reflection capacity to thermal neutrons approximately equal to that of the specimen. The geometry for the measuring is~shown in Figure 4. Furthermore, the geometry was varied so that the empty space surrounding the detector between the sample and the moderator was filled wlth specimen and in other cases graphite pieces were fitted as reflectors around the detector. In addition experiments were performed on the effects on the spectrum of a thin Cd plate placed to protect the detector.
The relatively great height of the apparatus shown in Figure 4 is due to the fact that the graphite was in standard-leng-th bars ~: -The program used for the processing of the spectrum was a program called Vipunen developed in the Department of Physics, University of Helsinkl. On the basis of international testing :~:
:
~3~ 8 this is a very {Jood progr;lln for processlncJ -the spec-trum.
The progralll detects the pea]cs, calibrates -the energies, det~rmines the background, and calcu]ates the area of the peaks and their error values. The lis-ting gave, in addition to the spectrum, a table of -the pealcs and -their parame-ters.
The mos-t important peaks of the various subs-tances were used in estimating the error caused by pulse statistics:
Fe: 7.646 MeV and 7.632 MeV wi-th escape peaks S: 5.420 Mev with escape peaks~ 3.221 MeV, 2.931 MeV and 2.380 MeV
Cu: 7.915 MeV and 7.306 MeV with escape peaks Ni: 8.999 MeV and 3.535 MeV wi-th escape peaks Si: 4.934 MeV and 3.539 MeV.
The results ob-tained wi-th Ni concentrate are shown in the table below.
Table 4 Sourcel~g 252Cf, measuring period 100 min Ni concentrate relative absolute error % errol %
S 4.1 0.96 Fe 1.~ 0.54 Cu 9.0 0.31 Ni 4.5 0.25 SiO2 11.5 2.9 ~ .
Corresponding resul-ts would be obtained by using 10 ~g/10 min or 20 ~g/5 min. By quadrupling the time, the error could be ~ reduced by one half.
:: :
Figures 5 and 6 show parts of the spectrum of Ni concentrate.
:::: :
The capture gammas and ac-tivation peaks produced by the structure material of the detector could be elimina-ted using a Cd shield. Some neutron absorber other than Cd could worsen the peak-background ratio to a lesser degree. The quantity of ::
.
.
.- . . , ~ :.:
, , . ' , ' : ~ ~
. . .
8~
capture gammas obtained from ~he specimen was reduced by 1.7 when uslng a Ccl shield.
Finally, Figure 7 shows how a measuring apparatus according to the invention could be positioned for the measuring of, for example, material 6 being conveyed on a Reedler conveyor. The geometry is the same as -that shown in Figures 3 and 4, but it has been reversed.
It is evident that the yeometry can be varied in many ways without deviating from -the idea of the invention, which is using heavy water as moderator. If, for example, the material to be studied is a flow of material in a pipe, e.g. a slurry, it also works as a moderator itself. The detactor can be placed in the slurry, in which case the arrangement will be similar to that shown in Figure 8. In this case the specimen to be studied, i.e. slurry 6, flows in a pipe and the detector is ir~ the middle of the pipe. Naturally, several other alternatives are also possible.
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Claims (16)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An apparatus for measuring the concentrations of elements in a material by the capture gamma method, said apparatus compris-ing a neutron source, a moderator surrounding the neutron source and being at least partly constituted by heavy water, a gamma radiation detector in the form of a semiconductor detector, said detector being positioned close to the material to be measured and in a flux of slow neutrons, there being so much of the moderator between the neutron source and the detector that at most only a few fast neutrons can reach the detector.
2. An apparatus according to claim 1, wherein part of the moderator is graphite.
3. Apparatus according to claim 2 wherein the graphite is situated around the heavy water.
4. An apparatus according to claim 1 or 2, further compris-ing as moderator substance ordinary water.
5. An apparatus according to claim 1, wherein a heavy sub-stance which absorbs neutrons only slightly is placed between the neutron source and the detector to absorb gamma-radiation and to scatter fast neutrons.
6. An apparatus according to claim 5, wherein the scatter-ing substance has the shape of a cone, the neutron source being situated in the vicinity of the cone apex, and the base of the cone facing the detector.
7. An apparatus according to claim 5, wherein the distance between the scattering substance and the semiconductor detector in heavy water is at least about 10 cm.
8. Apparatus according to claim 5 wherein the heavy sub-stance is bismuth.
9. Apparatus according to claim 5 wherein the scattering substance has the shape of two cones in succession, the neutron source being situated in the vicinity of the apex of one of the cones, and the base of the other cone facing the detector.
10. An apparatus according to claim 1, wherein the intensity of the neutron source is about 5.10 neutrons/s, the distance between the neutron source and the detector is at least about 45 cm, this distance increasing by about 15 cm when the intensity increases by one decade.
11. Apparatus according to claim 10 Further comprising as moderator substance ordinary water.
12. An apparatus according to claim 1, wherein the intensity of the neutron source is about 5.10 neutrons/s, the distance between the neutron source and the detector is at least about 45 cm, this distance increasing by about 15 cm when the intensity increases by one decade, and wherein the heavy water has been arranged around the neutron source, substantially in the form of a truncated cone, the neutron source being situated at the narrow end of the cone and the detector being situated at the wider end of the cone.
13. Apparatus according to claim 12 further comprising as moderator substance ordinary water.
14. An apparatus according to claim 1, wherein the material to be studied flows in a pipe, the detector being positioned in-side the pipe in the flowing material, which itself partly serves as a moderator.
15. An apparatus according to claim 1, wherein the neutron source is an isotope source.
16. An apparatus according to claim 1, wherein the neutron source is a neutron generator.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FI781381 | 1978-05-04 | ||
| FI781381A FI56904C (en) | 1978-05-04 | 1978-05-04 | PROCEDURE FOR MAINTENANCE OF GROUND HEMES AND HARD MATERIAL ENLIGGES INFAONGNINGSGAMMAMODODEN |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1131808A true CA1131808A (en) | 1982-09-14 |
Family
ID=8511681
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA326,775A Expired CA1131808A (en) | 1978-05-04 | 1979-05-02 | Apparatus for measuring the concentrations of elements in a material by the capture gamma method |
Country Status (15)
| Country | Link |
|---|---|
| US (1) | US4278885A (en) |
| JP (1) | JPS54149697A (en) |
| AU (1) | AU515642B2 (en) |
| CA (1) | CA1131808A (en) |
| DE (1) | DE2917473C2 (en) |
| ES (1) | ES480742A1 (en) |
| FI (1) | FI56904C (en) |
| FR (1) | FR2425066A1 (en) |
| GB (1) | GB2020421B (en) |
| PL (1) | PL122043B1 (en) |
| SE (1) | SE440696B (en) |
| SU (1) | SU1291033A3 (en) |
| YU (1) | YU41862B (en) |
| ZA (1) | ZA792076B (en) |
| ZM (1) | ZM3779A1 (en) |
Families Citing this family (35)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4365154A (en) * | 1980-03-06 | 1982-12-21 | Texaco Inc. | Detection of impurities in a fluid containing free gas using nuclear techniques |
| US4464330A (en) * | 1982-05-13 | 1984-08-07 | The United States Of America As Represented By The Department Of Energy | Apparatus for irradiating a continuously flowing stream of fluid |
| US4483817A (en) * | 1983-01-31 | 1984-11-20 | The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration | Method and apparatus for mapping the distribution of chemical elements in an extended medium |
| US4590377A (en) * | 1984-06-11 | 1986-05-20 | Irt Corporation | In situ isotopic meat grader |
| GB8523060D0 (en) * | 1985-09-18 | 1985-10-23 | Cogent Ltd | Coal analysis |
| FR2588085B1 (en) * | 1985-10-02 | 1987-10-30 | Commissariat Energie Atomique | FISSILE MATERIAL DETECTION DEVICE |
| FR2588969B1 (en) * | 1985-10-18 | 1988-02-26 | Commissariat Energie Atomique | DEVICE FOR DETECTION OF EXPLOSIVE EXAMPLES |
| AU600461B2 (en) * | 1985-12-31 | 1990-08-16 | Commonwealth Scientific And Industrial Research Organisation | Neutron and gamma-ray moisture assay |
| US4851687A (en) * | 1987-01-13 | 1989-07-25 | Scientific Innovations, Inc. | Detection of nitrogen in explosives |
| US4822552A (en) * | 1987-02-25 | 1989-04-18 | Westinghouse Electric Corp. | Method and apparatus for passively gamma scanning a nuclear fuel rod |
| US5153439A (en) * | 1987-05-26 | 1992-10-06 | Science Applications International Corporation | Multi-sensor explosive detection system using an articifical neural system |
| FR2641867B1 (en) * | 1989-01-13 | 1991-03-08 | Commissariat Energie Atomique | METHOD AND DEVICE FOR DETECTION OF SUBSTANCES AND PARTICULARLY EXPLOSIVES, BY NEUTRONIC IRRADIATION THEREOF |
| FR2652651B1 (en) * | 1989-10-03 | 1991-12-13 | Commissariat Energie Atomique | SYSTEM FOR DETECTION OF SUBSTANCES AND IN PARTICULAR EXPLOSIVES, BY NEUTRONIC IRRADIATION THEREOF. |
| US5098640A (en) * | 1990-01-10 | 1992-03-24 | Science Applications International Corporation | Apparatus and method for detecting contraband using fast neutron activation |
| US5076993A (en) * | 1990-01-12 | 1991-12-31 | Science Applications International Corporation | Contraband detection system using direct imaging pulsed fast neutrons |
| US5133901A (en) * | 1991-03-01 | 1992-07-28 | Westinghouse Electric Corp. | System and method for on-line monitoring and control of heavy metal contamination in soil washing process |
| US5539788A (en) * | 1992-10-08 | 1996-07-23 | Westinghouse Electric Corporation | Prompt gamma neutron activation analysis system |
| US5412206A (en) * | 1994-02-18 | 1995-05-02 | Westinghouse Electric Company | Method and apparatus for determining the depth of a gamma emitting element beneath the surface |
| US5781602A (en) * | 1996-05-17 | 1998-07-14 | Westinghouse Electric Corporation | PGNAA system for non-invasively inspecting RPV weld metal in situ, to determine the presence and amount of trace embrittlement-enhancing element |
| US20030165212A1 (en) * | 1998-02-18 | 2003-09-04 | Maglich Bogdan C. | Method and apparatus for detecting, locating, and analyzing chemical compounds using subatomic particle activation |
| US6144032A (en) * | 1998-05-07 | 2000-11-07 | Gazdzinski; Robert F. | Method and apparatus for measuring the condition of degradable components |
| US6791089B1 (en) * | 1999-03-29 | 2004-09-14 | Bechtel Bwxt Idaho, Llc | PINS chemical identification software |
| WO2005088245A1 (en) * | 2004-03-11 | 2005-09-22 | Hienergy Technologies, Inc. | Method and apparatus for measuring wall thickness of a vessel |
| US7847260B2 (en) | 2005-02-04 | 2010-12-07 | Dan Inbar | Nuclear threat detection |
| US7820977B2 (en) | 2005-02-04 | 2010-10-26 | Steve Beer | Methods and apparatus for improved gamma spectra generation |
| US8173970B2 (en) | 2005-02-04 | 2012-05-08 | Dan Inbar | Detection of nuclear materials |
| US9859972B2 (en) | 2014-02-17 | 2018-01-02 | Ubiqomm Llc | Broadband access to mobile platforms using drone/UAV background |
| US9479964B2 (en) | 2014-04-17 | 2016-10-25 | Ubiqomm Llc | Methods and apparatus for mitigating fading in a broadband access system using drone/UAV platforms |
| US9614608B2 (en) | 2014-07-14 | 2017-04-04 | Ubiqomm Llc | Antenna beam management and gateway design for broadband access using unmanned aerial vehicle (UAV) platforms |
| US9571180B2 (en) | 2014-10-16 | 2017-02-14 | Ubiqomm Llc | Unmanned aerial vehicle (UAV) beam forming and pointing toward ground coverage area cells for broadband access |
| US9712228B2 (en) | 2014-11-06 | 2017-07-18 | Ubiqomm Llc | Beam forming and pointing in a network of unmanned aerial vehicles (UAVs) for broadband access |
| US9590720B2 (en) | 2015-05-13 | 2017-03-07 | Ubiqomm Llc | Ground terminal and gateway beam pointing toward an unmanned aerial vehicle (UAV) for network access |
| US9660718B2 (en) | 2015-05-13 | 2017-05-23 | Ubiqomm, LLC | Ground terminal and UAV beam pointing in an unmanned aerial vehicle (UAV) for network access |
| US10321461B2 (en) | 2016-05-06 | 2019-06-11 | Bridgewest Finance Llc | Unmanned aerial vehicle (UAV) beam pointing and data rate optimization for high throughput broadband access |
| US10313686B2 (en) | 2016-09-20 | 2019-06-04 | Gopro, Inc. | Apparatus and methods for compressing video content using adaptive projection selection |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2938119A (en) * | 1956-10-08 | 1960-05-24 | Texaco Inc | Radioactivity analysis |
| US3234387A (en) * | 1962-01-03 | 1966-02-08 | Gen Electric | Apparatus for identifying materials by activation analysis |
| US3746871A (en) * | 1970-12-02 | 1973-07-17 | Union Carbide Corp | Method of determining the presence and amount of vanadium in an earth formation |
| US3723727A (en) * | 1971-06-30 | 1973-03-27 | Atomic Energy Commission | In-situ neutron activation |
-
1978
- 1978-05-04 FI FI781381A patent/FI56904C/en not_active IP Right Cessation
-
1979
- 1979-04-16 ZM ZM37/79A patent/ZM3779A1/en unknown
- 1979-04-30 ZA ZA792076A patent/ZA792076B/en unknown
- 1979-04-30 DE DE2917473A patent/DE2917473C2/en not_active Expired
- 1979-05-01 GB GB7915162A patent/GB2020421B/en not_active Expired
- 1979-05-01 AU AU46614/79A patent/AU515642B2/en not_active Ceased
- 1979-05-02 US US06/035,245 patent/US4278885A/en not_active Expired - Lifetime
- 1979-05-02 CA CA326,775A patent/CA1131808A/en not_active Expired
- 1979-05-03 ES ES480742A patent/ES480742A1/en not_active Expired
- 1979-05-03 SE SE7903869A patent/SE440696B/en not_active IP Right Cessation
- 1979-05-03 FR FR7911812A patent/FR2425066A1/en active Granted
- 1979-05-03 PL PL1979215343A patent/PL122043B1/en unknown
- 1979-05-03 SU SU792777201A patent/SU1291033A3/en active
- 1979-05-04 JP JP5414379A patent/JPS54149697A/en active Granted
- 1979-05-04 YU YU1057/79A patent/YU41862B/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| DE2917473C2 (en) | 1983-11-03 |
| AU4661479A (en) | 1979-11-08 |
| PL215343A1 (en) | 1980-02-11 |
| FR2425066A1 (en) | 1979-11-30 |
| YU41862B (en) | 1988-02-29 |
| SU1291033A3 (en) | 1987-02-15 |
| ZA792076B (en) | 1980-06-25 |
| AU515642B2 (en) | 1981-04-16 |
| FI56904C (en) | 1980-04-10 |
| FI56904B (en) | 1979-12-31 |
| DE2917473A1 (en) | 1979-11-08 |
| JPS6149618B2 (en) | 1986-10-30 |
| ZM3779A1 (en) | 1979-11-21 |
| YU105779A (en) | 1982-06-30 |
| ES480742A1 (en) | 1979-12-01 |
| GB2020421B (en) | 1982-09-22 |
| GB2020421A (en) | 1979-11-14 |
| SE440696B (en) | 1985-08-12 |
| SE7903869L (en) | 1979-11-05 |
| PL122043B1 (en) | 1982-06-30 |
| FI781381A (en) | 1979-11-05 |
| JPS54149697A (en) | 1979-11-24 |
| US4278885A (en) | 1981-07-14 |
| FR2425066B1 (en) | 1982-03-05 |
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