Method for Operating a Radiometric Measuring Device, and Radiometric Measuring Device

Abstract

A radiometric measuring device has a counting tube having an anode and a cathode, and is configured to determine a measurement variable depending on properties of ionizing radiation that impinges on the counting tube. In a first measurement mode, a constant first voltage is set between anode and cathode such that the counting tube operates as a proportional counting tube, and the measurement variable is determined depending on a current flowing between anode and cathode. In a second measurement mode, the current flowing between anode and cathode is controlled to a current setpoint value, wherein the voltage between anode and cathode serves as a manipulated variable of the current control, and the measurement variable is determined depending on the voltage between anode and cathode. In a third measurement mode, a constant second voltage is set between anode and cathode such that the counting tube operates as an ionization chamber, and the measurement variable is determined depending on the current flowing between anode and cathode. Either the first, second, or third measurement mode is activated depending on the current flowing between anode and cathode and/or depending on the voltage between anode and cathode.

Claims

1. A method for operating a radiometric measuring device, wherein the radiometric measuring device comprises a counting tube having an anode and a cathode, and wherein the radiometric measuring device is configured to determine a measurement variable depending on properties of ionizing radiation that impinges on the counting tube, wherein the method comprises the steps of: (i) in a first measurement mode, setting a constant first voltage between anode and cathode such that the counting tube operates as a proportional counting tube, and determining the measurement variable depending on a current flowing between the anode and the cathode; (ii) in a second measurement mode, controlling the current flowing between the anode and the cathode to a current setpoint value, wherein the voltage between the anode and the cathode serves as a manipulated variable of the current control, and determining the measurement variable depending on the voltage between anode and cathode; and (iii) in a third measurement mode, setting a constant second voltage between the anode and the cathode such that the counting tube operates as an ionization chamber, and determining the measurement variable depending on the current flowing between the anode and the cathode; and activating either the first measurement mode, the second measurement mode or the third measurement mode depending on the current flowing between the anode and the cathode and/or depending on the voltage between the anode and the cathode.

2. The method according to claim 1, wherein the counting tube operates as a proportional counting tube in the second measurement mode.

3. The method according to claim 1, wherein proceeding from the activated first measurement mode, the second measurement mode is activated as soon as the current flowing between the anode and the cathode exceeds a current threshold value.

4. The method according to claim 3, wherein the current setpoint value is chosen on the basis of the current threshold value.

5. The method according to claim 4, wherein the current setpoint value and the current threshold value are chosen to be identical.

6. The method according to claim 1, wherein proceeding from the activated second measurement mode, the third measurement mode is activated as soon as the voltage between the anode and the cathode falls below a voltage threshold value.

7. The method according to claim 1, wherein the measurement variable is a dose power.

8. A radiometric measuring device, comprising: a counting tube having an anode and a cathode; a drivable voltage generating unit configured to generate a settable voltage between the anode and the cathode; and a control unit configured to drive the voltage generating unit and to detect a current flowing between the anode and the cathode, wherein the control unit is configured to drive the radiometric measuring device so as to carry out the acts of: (i) in a first measurement mode, setting a constant first voltage between anode and cathode such that the counting tube operates as a proportional counting tube, and determining the measurement variable depending on a current flowing between the anode and the cathode; (ii) in a second measurement mode, controlling the current flowing between the anode and the cathode to a current setpoint value, wherein the voltage between the anode and the cathode serves as a manipulated variable of the current control, and determining the measurement variable depending on the voltage between anode and cathode; and (iii) in a third measurement mode, setting a constant second voltage between the anode and the cathode such that the counting tube operates as an ionization chamber, and determining the measurement variable depending on the current flowing between the anode and the cathode; and activating either the first measurement mode, the second measurement mode or the third measurement mode depending on the current flowing between the anode and the cathode and/or depending on the voltage between the anode and the cathode.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] FIG. 1 schematically shows a radiometric measuring device.

[0033] FIG. 2 schematically shows a gain as a function of a voltage and a current in logarithmic representation.

DETAILED DESCRIPTION OF THE DRAWINGS

[0034] FIG. 1 shows a radiometric measuring device 1 comprising a counting tube 2. The counting tube 2 comprises an anode 3 and a cathode 4 in a conventional manner.

[0035] The radiometric measuring device 1 further comprises a drivable voltage generating unit 6 configured to generate a settable (high) voltage UHV between anode 3 and cathode 4. In this respect, reference should also be made to the relevant technical literature.

[0036] The radiometric measuring device 1 further comprises a control unit 7 configured to drive the voltage generating unit 6 for generating a desired voltage UHV and to detect a current im flowing between anode 3 and cathode 4 and the generated voltage UHV.

[0037] The radiometric measuring device 1 is configured to determine a measurement variable, for example in the form of a dose power, depending on properties of ionizing radiation 5 that impinges on the counting tube 2. The properties of the ionizing radiation 5 can be the intensity of the ionizing radiation 5.

[0038] The measuring method carried out by means of the radiometric measuring device 1 will be explained in greater detail with reference to FIG. 2.

[0039] FIG. 2 schematically shows, in a three-dimensional coordinate system, a gain G (plotted logarithmically) as a function of the (counting tube) voltage UHV and the (counting tube) current im.

[0040] FIG. 2 shows by way of example the dose-power-dependent trajectory or path according to the invention on the gain characteristic curve, beginning with a low dose power at the operating point AP1 on the left in the direction of increasing dose powers at the operating point AP1 on the right, then with further increasing dose power in the direction of operating point AP2, then with even further increasing dose power in the direction of AP3 and finally with even further increasing dose power from the operating point AP3 in the direction of increasing currents im.

[0041] In a first measurement mode M1 between the operating points AP1, a constant voltage UHV between anode 3 and cathode 4 is set in such a way that the counting tube 2 operates as a proportional counting tube. For this case, the measurement variable is ascertained depending on the current im flowing between anode 3 and cathode 4.

[0042] In a second measurement mode M2 between the operating points AP1 and AP2, the current im flowing between anode 3 and cathode 4 is controlled to a current setpoint value, wherein the voltage UHV between anode 3 and cathode 4 serves as a manipulated variable of the current control. For this case, the measurement variable is ascertained depending on the voltage UHV between anode 3 and cathode 4.

[0043] In a third measurement mode M3 beginning with the operating point AP3, a constant voltage UHV between anode 3 and cathode 4 is set in such a way that the counting tube 2 operates as an ionization chamber. The measurement variable is then determined depending on the current im flowing between anode 3 and cathode 4.

[0044] The first measurement mode M1, the second measurement mode M2 or the third measurement mode M3 is selected depending on the current im flowing between anode 3 and cathode 4 and/or depending on the voltage UHV between anode 3 and cathode 4.

[0045] At the operating point AP1, the voltage UHV is kept constant and the current im is measured. As soon as a specific, previously defined current im is reached, it is fixed and the voltage UHV is reduced until the operating point AP2 is reached. A switchover to the operating point AP3 is then made. The latter lies at the ionization chamber plateau. The uninterrupted joining of the measurement range between AP2 and AP3 can be achieved by suitable adaptation of the electronic gain. At the operating point AP3, once again the voltage UHV is fixed and the current im is measured.

[0046] The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.