METHOD FOR CALIBRATING A RADIOMETRIC DENSITY MEASURING DEVICE

Abstract

A method for calibrating a radiometric device for determining and/or monitoring the density of a medium located in a container includes: determining the count rate of the radioactive radiation after it has passed through the empty container on the basis of the activity of the transmitting unit; determining the measured count rate of the radioactive radiation after it has passed through the container when a calibration medium of known density is located in the container; determining the mass attenuation coefficient according to the formula μ=−(ln(N/N.sub.0))/(ρ.sub.1D), where D is a beam path of the radioactive radiation or inner diameter of the container, and ρ.sub.1 is density of the calibration medium; and calculating a calibration curve representing the dependence of the density of the medium on the count rate of the measured radiation intensity after the radiation has passed through the container.

Claims

1. A method for calibrating a radiometric device for determining and/or monitoring the density of a medium within a container, the method comprising: providing: a transmitting unit configured to emit radioactive radiation of a predefined intensity; a receiving unit configured to receive the radiation emitted by the transmitting unit after the radiation has passed through the medium; and a control/evaluation unit configured to determine a density of the medium within the container based on a radiation intensity measured by the receiving unit; determining a count rate of the radiation after passing through the container when empty based on an activity of the transmitting unit; determining a count rate of the radiation after passing through the container when a calibration medium of known density is within the container; determining a mass attenuation coefficient defined as:
μ=−(ln(N/N.sub.0))/(ρ.sub.1D), wherein D is a beam path of the radiation or an inner dimension of the container, ρ.sub.1 is the density of the calibration medium, N.sub.0 is the count rate of the measured radiation after passing through the empty container, and N is the count rate of the measured radiation after passing through the calibration medium; and calculating a calibration curve representing a dependence of the density of the medium on the count rate of the measured radiation intensity after the radiation has passed through the container.

2. The method of claim 1, wherein the count rate of the radiation after passing through the empty container is determined according to the formula:
N.sub.0=(P.Math.K.Math.B)/(F.sub.a.Math.F.sub.s), where F.sub.a is a square distance factor between the transmitting unit and the receiving unit, F.sub.s is an attenuation factor that depends at least on a wall of the container and an isotope of the transmitting unit, P is the activity of the transmitting unit, K is an isotope-dependent correction factor, and B is a correction factor for a conversion of a pulse rate to the count rate of the measured radiation after passing through the empty container.

3. The method of claim 2, wherein the attenuation factor F.sub.s is calculated according to the formula:
F.sub.s=e.sup.a.Math.q, wherein a is an isotope-dependent attenuation coefficient, q is a thickness of the wall of the container measured in steel equivalents, wherein a steel equivalent is defined as a density of the wall of the container relative to a density of steel.

4. The method of claim 1, wherein water is the calibration medium.

5. The method of claim 1, wherein the transmitting unit and the receiving unit are positioned relative to one another such that the container is irradiated perpendicular to a longitudinal axis of the container, obliquely to the longitudinal axis of the container, or parallel to the longitudinal axis of the container.

6. The method of claim 5, wherein the receiving unit is configured and positioned such that sensitive components of the receiving unit are irradiated by the radiation.

7. The method of claim 1, wherein the container a pipeline, and wherein the transmitting unit and the receiving unit are fastened to the pipeline on opposing surface regions of the pipeline.

8. The method of claim 7, wherein the receiving unit is configured and positioned such that sensitive components of the receiving unit are irradiated by the radiation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present disclosure is explained in greater detail with reference to the following drawings, FIGS. 1 and 2. In the figures:

[0029] FIG. 1 shows a schematic diagram of an arrangement for radiometrically determining the density of a medium; and

[0030] FIG. 2 shows a schematic diagram of a graph which visualizes the dependence of the count rate on the density.

DETAILED DESCRIPTION

[0031] FIG. 1 shows a schematic diagram of an arrangement for radiometrically determining the density of a medium 6 located in a container 1, here a pipeline with a wall 2. The transmitting unit 3, with the gamma source, and the receiving unit 4 are arranged on opposite surface regions of the pipeline 1. Both components 3, 4 are fastened to the outside of the pipeline 1 via a clamping mechanism, which is not shown separately in FIG. 1.

[0032] The encapsulation of the gamma source by the surrounding housing is designed such that the gamma radiation exits from the transmitting unit 3 only in the region of the exit face A. The gamma radiation irradiates the container 1 with the medium 6 therein, the density p of which is to be determined, on the indicated beam path SP. The gamma radiation weakened by interaction with the container wall and/or the medium 6 is received by the receiving unit 4. The evaluation unit 7 determines the density of the medium 6 located in the container 1 on the basis of the intensity or the count rate of the receiving unit 4. Corresponding radiometric density measuring arrangements are offered and sold by the applicant. As already mentioned above, the arrangement of the transmitting unit 3 and the receiving unit 4 relative to the container 1 can be configured differently.

[0033] FIG. 2 shows a schematic diagram of a graph which visualizes the dependence of the count rate N as a function of the density p of the medium 6. The attenuation of gamma radiation on the beam path SP by a medium 6 can be described by the Beer-Lambert law, and thus follows an e function. The attenuation F corresponds to the ratio of the count rate of the gamma radiation after passing through the medium 6 to the count rate N.sub.0 of the gamma radiation emitted by the gamma source through the exit opening A. The count rate N is indicated in counts (number of events) per second (c/sec).

[0034] In FIG. 2, the count rate is plotted against the density. At maximum density ρ.sub.max the medium 6, the count rate N.sub.min approximately zero; at minimum density ρ.sub.min he count rate N.sub.max substantially equal to the count rate N.sub.0 of the gamma radiation emitted by the gamma source. The following mathematical relationship applies:

[00001]$\frac{N_{\min }}{N_{\max }}=e^{-\mu .Math.D.Math.\left({\rho }_{\max }+{\rho }_{\min }\right)}$

[0035] The count rate N.sub.0 is determined according to the present disclosure on the basis of the activity of the transmitting unit 3, only a further count rate N of a medium 6 with a defined density ρ.sub.1 has to be determined. Then the mass attenuation coefficient μ can be determined, and the exemplary calibration curve shown in FIG. 2 can be calculated.

[0036] In order to illustrate the calculation of the count rate N.sub.0, an example of a calculation will be shown below. By way of example, a transmission unit 3 with a Cs137 gamma source is used which has a correction factor K of 95.95 μSv.Math.m2/(h.Math.GBq), an activity P of 0.13 GBq and an isotope-dependent attenuation coefficient a of 0.048. The receiving unit 4 has a correction factor B of 1350 h/(s.Math.μSv).

[0037] For a wall 2 of the steel container 1 having a thickness of 9.3 mm and a density of steel of 7890 kg/m3, an attenuation factor of F.sub.s=e.sup.aq=2.4 results. The distance between the transmitting unit 3 and the receiving unit 4 is 0.45 m, resulting in a distance factor of F.sub.a=(0.45 m).sup.2=0.2 m.sup.2. This results in a dose rate F.sub.i of 25.5 μSv/h and thus a count rate N.sub.0 of 34479 l/s.