Method For Measuring Counting Rates Or Measured Variables Dependent On The Counting Rates And Apparatus For Measuring Counting Rates Or Measured Variables Dependent On The Counting Rates

Abstract

A method for measuring counting rates or measured variables dependent on the counting rates for determining a density profile of at least two substances with different densities arranged within a container by using a plurality of detectors is provided. The method includes recording respective gamma rays which have penetrated at least partially through at least one of the substances by using the detectors, and generating a respective counting rate or a respective measured variable dependent on the counting rate only on the basis of respectively recorded gamma rays of which the respective gamma energy is greater than or equal to an energy threshold value, the energy threshold value being a minimum of 0.5 times a Compton energy value of a Compton gap of the gamma rays.

Claims

1. A method for measuring counting rates or measured variables dependent on the counting rates for determining a density profile of at least two substances with different densities arranged within a container by using a plurality of detectors, the method comprising, in each case: recording respective gamma rays which have penetrated at least partially through at least one of the substances by using the plurality of detectors, and generating a respective counting rate or a respective measured variable dependent on the counting rate only on the basis of respectively recorded gamma rays of which the respective gamma energy is greater than or equal to an energy threshold value, the energy threshold value being a minimum of 0.5 times a Compton energy value of a Compton gap of the gamma rays.

2. The method according to claim 1, further comprising: determining the density profile on the basis of the respectively generated counting rates or the respectively generated measured variables.

3. The method according to claim 1, wherein: recording the respective gamma rays comprises generating respective detector signal pulses by using the plurality of detectors, with respective forms of the respectively generated detector signal pulses being dependent on the respective gamma energy levels of the respectively generated gamma rays, and the respective counting rate or the respective measured variable is generated only on the basis of respectively generated detector signal pulses of which the respective forms are equal to or greater than a form threshold value, the form threshold value being dependent on the energy threshold value.

4. The method according to claim 1, wherein at least one of: the plurality of detectors have a detector noise with a noise energy value, and the energy threshold value is a minimum of 2 times the noise energy value, or the energy threshold value is a minimum of equal to the Compton energy value.

5. The method according to claim 1, wherein at least one of: the plurality of detectors are arranged laterally outside a round wall of the container, or the plurality of detectors are arranged vertically one above the other.

6. The method according to claim 5, further comprising: emitting respective gamma rays with a discrete isotope gamma energy into at least one of the substances by using a plurality of radiation sources, wherein the Compton energy value is less than the isotope gamma energy.

7. The method according to claim 6, wherein: the radiation sources are arranged within the container.

8. The method according to claim 6, wherein: each of the plurality of detectors is directed at an assigned radiation source or at a point midway between two assigned radiation sources.

9. The method according to claim 8, wherein: each of the detectors is arranged at a same height as the assigned radiation source or at a same height as the point midway between the two assigned radiation sources.

10. The method according to claim 6, wherein at least one of: each of the plurality of detectors comprises a collimator, and each of the collimators respectively narrows an angle of incidence to the assigned radiation source, or each of the radiation sources comprises a collimator, and each of the collimators respectively narrows an angle of reflection to the assigned detector.

11. The method according to claim 1, each of the plurality of detectors comprises a scintillator for recording respective gamma rays, and each of the scintillators comprises a density of at least 3 g/cm.sup.3.

12. The method according to claim 1, wherein at least one of: the substances comprise at least one of gas, foam, oil, emulsion, water, or sand, the container is an oil-water separator, the substances comprise at least one of hydrocarbon or acid, or the container is a hydrocarbon-acid separator.

13. An apparatus for measuring counting rates or measured variables dependent on the counting rates for determining a density profile of at least two substances with different densities arranged within a container by using a plurality of detectors, the apparatus comprising: the plurality of detectors, wherein each of the plurality of detectors is configured to record respective gamma rays which have penetrated at least partially through at least one of the substances, and a plurality of generating devices, wherein each of the plurality of generating devices is configured to generate a respective counting rate or a respective measured variable dependent on the counting rate only on the basis of respectively recorded gamma rays of which the respective gamma energy is greater than or equal to an energy threshold value, the energy threshold value being a minimum of 0.5 times a Compton energy value of a Compton gap of the gamma rays.

14. The apparatus according to claim 13, further comprising: a determining device configured to determine the density profile on the basis of the respectively generated counting rates or the respectively generated measured variables.

15. The apparatus according to claim 13 further comprising at least one of: a plurality of radiation sources wherein each of the plurality of radiation sources is configured to emit respective gamma rays with a discrete isotope gamma energy into at least one of the substances, the Compton energy value being less than the isotope gamma energy, or the container.

16. The method according to claim 3, wherein the forms comprise at least one of amplitudes, widths, or products of the amplitudes and the widths.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] FIG. 1 shows a longitudinal sectional view of an apparatus according to embodiments of the invention comprising a container.

[0044] FIG. 2 shows a cross-sectional view of the apparatus from FIG. 1 and of a method according to embodiments of the invention.

[0045] FIG. 3 shows a schematic view of the apparatus from FIG. 1 and of the method from FIG. 2.

[0046] FIG. 4 shows a further schematic view of the apparatus from FIG. 1.

[0047] FIG. 5 shows an energy spectrum of gamma rays.

[0048] FIG. 6 shows a further embodiment of the apparatus from FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

[0049] FIGS. 1 to 6 show a method according to an embodiment of the invention and an apparatus 10 according to an embodiment of the invention for measuring counting rates ZR1, ZR2, ZR3, ZR4 for determining a density profile DP of at least two substances ST with different densities DE arranged within a container 20 by using a plurality of detectors 41, 42, 43, 44.

[0050] In detail, the apparatus 10 comprises the container 20, which in the present case is designed as an oil-water separator 21. In this case, the substances ST lie one above the other in a layered manner. The container 20 serves in principle for separating these substances ST. Also depicted in FIG. 1 is a coordinate system, which defines an x axis, y axis and z axis.

[0051] FIGS. 2 and 6 show the container 20 in cross section with the substances ST located in it and a list alongside of the various substances ST. It can be seen here that the container 20 has a round cross section. This is defined by a wall 22.

[0052] The substances ST or the discernible layers in the container 20 are in the present case, from bottom to top or in the z direction, sand (SAND), water (WATER), an emulsion (EMULSION), oil (OIL), foam (FOAM) and gas (GAS). It should be understood that such substances ST are only given by way of example.

[0053] Arranged within the container 20 are a plurality of radiation sources 31, 32, 33, 34 of the apparatus 10, only some of which are schematically denoted here. As shown in FIGS. 2 to 4, the radiation sources 31, 32, 33, 34 are arranged vertically one above the other or in the z direction along an arcuate segment and have in each case, as seen in the radial x direction, a similar distance from the wall 22. Arranged on the right side in relation to the, in particular round, wall 22 or outside the container 20 in the x direction are a plurality of detectors 41, 42, 43, 44 of the apparatus 10, only some of which are schematically denoted here. These are also arranged vertically one above the other or in the z direction along an arcuate segment. Consequently, in a step a) of the method, the detectors 41, 42, 43, 44 may in each case record respective gamma rays GR, which have in each case been emitted by the radiation sources 31, 32, 33, 34 and have penetrated at least partially through the respective substance ST.

[0054] Shown on the right in FIG. 2 is the density profile DP of the substances ST. In this case, the respective density DE of one of the substances ST is indicated over the height LE. It can be seen that, in principle, the density DE increases from top to bottom or counter to the z direction and the substances ST are correspondingly separated.

[0055] FIG. 3 shows in detail mechanisms for the evaluation and an associated schematic signal processing. In this case, only the four detectors 41, 42, 43, 44 already mentioned and the assigned radiation sources 31, 32, 33, 34 are shown, as representative of the total number of detectors and radiation sources.

[0056] By using a plurality of generating devices 71, 72, 73, 74 of the apparatus 10, in a step b) of the method, respective counting rates ZR1, ZR2, ZR3, ZR4 are only generated on the basis of respectively recorded gamma rays GR of which the respective gamma energy GE is equal to or greater than an energy threshold value ETh2, the energy threshold value ETh2 being a minimum of 0.5 times a Compton energy value CE of a Compton gap CG of the gamma rays GR, in particular the recorded gamma rays GR, as shown in FIG. 5.

[0057] In detail, in step a), the detectors 41, 42, 43, 44 in each case generate respective detector signal pulses DI1, DI2, DI3, DI4, with respective forms, in particular amplitudes IA1, IA2, IA3, IA4, of the respectively generated detector signal pulses DI1, DI2, DI3, DI4 being dependent on the respective gamma energy levels GE of the respective gamma rays GR, in particular recorded gamma rays GR. In this case, in particular respective forms, in particular amplitudes IA1, IA2, IA3, IA4, of the respectively generated detector signal pulses DI1, DI2, DI3, DI4 are evaluated. The respective forms, in particular the respective amplitudes IA1, IA2, IA3, IA4, are in each case compared with a respective form threshold value ATh2, the form threshold value ATh2 being dependent on the energy threshold value ETh2. The respective counting rates ZR1, ZR2, ZR3, ZR4 are only generated and evaluated on the basis of respectively generated detector signal pulses DI1, DI2, DI3, DI4 or events of which the respective forms, in particular their respective amplitudes IA1, IA2, IA3, IA4, are greater than or equal to the form threshold value ATh2.

[0058] In the present case, the energy threshold value ETh2 is equal to the Compton energy value CE of the Compton gap CG of the gamma rays GR used, that is to say the gamma rays GR emitted by the radiation sources 31, 32, 33, 34.

[0059] On the basis of the counting rates ZR1, ZR2, ZR3, ZR4, the density profile DP is subsequently determined in a step c) of the method by a determining device 80 of the apparatus 10.

[0060] As a result, a respective density DE between the respective radiation source 31, 32, 33, 34 and the respective detector 41, 42, 43, 44 can be advantageously determined, since almost exclusively unscattered gamma rays GR are evaluated. Crosstalk effects are thereby avoided.

[0061] The effect of crosstalk is shown in FIG. 3. Depicted there, specifically by a respective solid line, are respective gamma rays GR which run directly horizontally from the respective radiation source 31, 32, 33, 34 to the respective detector 41, 42, 43, 44. Also depicted however, by dashed lines, are radiation profiles of gamma rays GR that represent crosstalk. Such gamma rays GR are typically undesired for the evaluation, since they have been scattered and typically have not only penetrated through one substance ST. Consequently, they do not contribute to reliable density determination. This effect is particularly strong in the case of round geometries, but also occurs in the case of other geometries.

[0062] FIG. 4 shows part of the apparatus 10, the specific mechanisms for the evaluation no longer being represented. The detectors 41, 42, 43, 44 comprise respective collimators 51, 52, 53, 54, which ensure that an angle of incidence or recording angle EW of the respective detector 41, 42, 43, 44 is narrowed, in particular to the respectively assigned radiation source 31, 32, 33, 34. In addition, the radiation sources 31, 32, 33, 34 comprise respective collimators 81, 82, 83, 84, which ensure that an angle of reflection AW of the respective radiation source 31, 32, 33, 34 is narrowed, in particular to the respectively assigned detector 41, 42, 43, 44. Although this allows crosstalk effects to be reduced, they cannot be avoided completely, as can be easily seen for example from a possible profile, depicted by dashed lines, of a multiply scattered gamma ray or gamma quant GR.

[0063] The respective angle of incidence is in this case represented by the reference sign EW, specifically by way of example in the case of the lowermost detector 41. The respective angle of reflection is in this case represented by the reference sign AW, specifically by way of example in the case of the uppermost radiation source 34.

[0064] The detectors 41, 42, 43, 44 comprise in each case a scintillator 61, 62, 63, 64 for recording respective gamma rays GR, in particular which respond to incident gamma rays GR by giving off respective flashes of light. These flashes of light are then typically intensified by photomultipliers and correspondingly evaluated. The scintillators 61, 62, 63, 64 may have a density of a minimum of 3 g/cm.sup.3 and/or a maximum of 20 g/cm.sup.3. As shown, the scintillators 61, 62, 63, 64 may partially or completely consist for example of an element with a high atomic number Z, in particular greater than or equal to 31, it being possible for example for BiGeO, LaBr, CsI, LuYSiO, CdWO or GdAlGaO to be used.

[0065] FIG. 5 shows a typical energy spectrum that is detected by one of the detectors 31, 32, 33, 34. On the horizontal axis, the respective energy GE of the gamma rays GR is indicated here in the unit keV, on the vertical axis the respective counting rate ZR is indicated for each energy level or energy channel.

[0066] At low energy levels, initially electronic noise is evident, lying below another energy threshold value ETh1. The noise ends at the noise energy value NE.

[0067] In the exemplary embodiment shown, when using cesium-137 (Cs 137) for the radiation sources 31, 32, 33, 34, the Compton gap CG, in which the counting rate ZR becomes virtually zero, is arranged between approximately 450 keV and 600 keV. In the middle of this Compton gap CG is the Compton energy value CE, which in the present case is equal to the energy threshold value ETh2. Above it is a peak with a distinct maximum for a discrete isotope gamma energy IGE of the emitted gamma rays GR from the radiation sources 31, 32, 33, 34. In other words: the Compton energy value CE is less than the isotope gamma energy IGE. In alternative exemplary embodiments, the detectors may in each case comprise a scintillator, in particular an organic scintillator, by way of which a detected energy spectrum comprises or has a less distinct peak or no peak for a discrete isotope gamma energy. To put it another way: a significant frequency, in particular counting rate, may end with the Compton gap.

[0068] If the other energy threshold value ETh1 were used in the exemplary embodiment shown, it would detect all of the gamma rays GR that lie at or above the noise threshold. This may lead to the undesired effects already described further above, since in particular gamma rays GR that have been multiply scattered and have passed through layers that are not to be measured at all are also detected. If, on the other hand, the energy threshold value ETh2, which is in particular a minimum of 2 times the noise energy value NE, is used, only evaluated are the unscattered gamma rays GR which have typically only passed horizontally through one substance ST, for example with the arrangement described with respect to FIGS. 2 to 4. These typically have the full energy of the radiation sources 31, 32, 33, 34, which for example when using cesium-137 has a value of 662 keV. With this selection, for example supported by the use of collimators 51, 52, 53, 54, 81, 82, 83, 84, gamma rays or gamma quants GR that have arrived at one of the detectors 41, 42, 43, 44 after at least one scattering are also filtered out, so that in any event there is a good assignment in each case between the radiation sources 31, 32, 33, 34 and the detectors 41, 42, 43, 44. This makes a significantly improved measurement result possible, which in turn makes it possible that an installation can be operated much closer to the design limit, without for example in case of the oil-water separator 21 running the risk of untreated oil leaking out into the waste water.

[0069] The properties of Compton scattering are known in principle, so that the energy loss of the gamma rays GR can be directly attributed to a scattering angle. However, this conversely also allows scatterings that have only taken place at a small angle, and consequently have not yet put at risk the respective assignment of radiation sources 31, 32, 33, 34 and detectors 41, 42, 43, 44, to continue to be permitted. This is possible by not setting the measurement threshold directly below the peak with maximum energy, but further below that. The further down the threshold can be brought, the more scattered gamma rays GR are detected. This provides a way of adjustment between allowed crosstalk (=measuring accuracy) and counting rate efficiency. The solution according to embodiments of the invention can therefore be optimized and adapted according to the application.

[0070] Since the gamma rays or gamma quants GR in the respective scintillators 61, 62, 63, 64 are detected both by way of the photo effect and by way of the Compton scattering, it may be that even gamma rays GR with full energy IGE could only deposit a fraction of the energy IGE in the respective scintillator 61, 62, 63, 64. As a result, they would be falsely detected as gamma rays GR with too low energy. This effect can be countered by using the detector material with a high density, in particular with elements with a high atomic number Z. Then the photo effect outweighs the Compton scattering, whereby the full energy, in particular IGE, is detected. The low counting rate efficiency can also be compensated by increasing the source activity. Often, however, it may also be sufficient to increase the averaging time, since the processes in separators do not in any case proceed quickly.

[0071] FIG. 6 shows another alternative configuration of the container 20 with the radiation sources 31, 32, 33, 34 and detectors 41, 42, 43, 44. As a difference from the embodiment of FIGS. 2 to 4, the detectors 41, 42, 43, 44 are no longer directed here in each case at an assigned radiation source 31, 32, 33, 34, in particular arranged at the same height in the z direction as the associated radiation source 31, 32, 33, 34, but are rather directed at a point between, in particular midway between, two assigned radiation sources 31, 32, 33, 34, in particular arranged at the same height in the direction z as the point between the two assigned radiation sources 31, 32, 33, 34, or offset thereto as seen in the z direction.