Apparatus for Measuring Ionizing Radiation

Abstract

An apparatus for measuring ionizing radiation includes a detector having a cathode, an anode, a counting gas between the cathode and the anode for generating gas ionization by ionizing radiation, a voltage source for applying a voltage between the cathode and the anode, and a current measuring device for measuring a detector current between the cathode and the anode. The detector current is generated in the counting gas by the ionizing radiation. The apparatus further includes a setting device, wherein the setting device is configured for independently setting the apparatus into different operating modes depending on the measured detector current, and/or wherein the setting device is configured for independently setting the apparatus into different measurement ranges depending on the measured detector current.

Claims

1. An apparatus for measuring ionizing radiation, comprising: (a) a detector comprising: a cathode, an anode, a counting gas between the cathode and the anode for generating gas ionization by ionizing radiation, a voltage source for applying a voltage between the cathode and the anode, and a current measuring device for measuring a detector current between the cathode and the anode, said detector current being generated in the counting gas by the ionizing radiation; and (b) a setting device, wherein the setting device is configured for independently setting the apparatus into different operating modes depending on the measured detector current, and/or wherein the setting device is configured for independently setting the apparatus into different measurement ranges depending on the measured detector current.

2. The apparatus according to claim 1, wherein the setting device is configured to set the different operating modes and/or the different measurement ranges depending on whether the measured detector current exceeds a first threshold value or falls below a second threshold value.

3. The apparatus according to claim 1, wherein the different operating modes comprise a first operating mode, in which the detector operates with gas gain, and a second operating mode, in which the detector operates without gas gain.

4. The apparatus according to claim 3, wherein in the first operating mode, a first measurement range with high gas gain is settable and further measurement ranges with lower gas gain are settable.

5. The apparatus according to claim 1, wherein switching between different operating modes and/or switching between different measurement ranges are brought about by alteration of the applied voltage between the cathode and the anode.

6. The apparatus according to claim 1, further comprising at least one of: (c) a measurement variable determining device configured to determine a measurement variable on the basis of the measured detector current, and (d) a measurement variable determining device configured to determine a measurement variable, wherein the setting device is configured to monitor the process of determining the measurement variable depending on the measured detector current.

7. The apparatus according to claim 3, wherein the different operating modes comprise a third operating mode, in which the detector operates with gas gain and a measurement variable is determined on the basis of a counting rate of pulses generated by way of the detector.

8. The apparatus according to claim 7, wherein the different operating modes comprise a fourth operating mode, in which the detector operates with gas gain and a measurement variable is determined on the basis of a pulse height spectrum of pulses generated by way of the detector.

9. The apparatus according to claim 1, further comprising: an operating point setting device having a reference source emitting ionizing reference radiation, wherein the operating point setting device is configured to set the applied voltage between the cathode and the anode to an operating point voltage value in such a way that: (i) the detector current measured by the ionizing reference radiation reaches a predefined reference current value, and/or (ii) a property of a pulse height spectrum of pulses generated by way of the detector, said pulse height spectrum being measured by the ionizing reference radiation, reaches a predefined reference spectrum value.

10. The apparatus according to claim 9, further comprising: a settable electronic amplification device configured to effect electronic amplification with an electronic gain value, wherein the operating point setting device for calibrating one or more measurement ranges in the proportional range is configured to: (i) set the electronic amplification with a first electronic gain value and set the applied voltage to a first operating point voltage value for a first measurement range with high gas gain in such a way that the measured detector current reaches the reference current value and/or a suitable property of a reference spectrum is attained, and (ii) set the electronic amplification to further higher electronic gain values relative to the first and set the applied voltages to further lower operating point voltage values relative to the first for further measurement ranges with lower gas gain in such a way that the measured detector current reaches the reference current value and/or a suitable property of a reference spectrum is attained.

11. The apparatus according to claim 10, wherein the reference source comprises sodium-22, iron 55, and/or chlorine 36.

12. The apparatus according to claim 1, further comprising: a controllable alarm signal output device configured to output an alarm signal, wherein the setting device is configured to control the outputting of the alarm signal depending on the measured detector current.

13. The apparatus according to claim 1, wherein the cathode is configured to be at ground potential during operation, and the anode is configured to be at a positive potential relative to ground potential during operation.

14. The apparatus according to claim 3, wherein in the second operating mode, a counting wire is the cathode and a counting tube wall is the anode.

15. The apparatus according to claim 1, wherein the cathode partly or completely is made of carbon fibers, and/or the detector comprises a cylindrical counting tube or a large-area counter.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0086] FIG. 1 shows an apparatus according to an embodiment of the invention for measuring ionizing radiation.

[0087] FIG. 2A shows a cross section of a cylindrical counting tube of a detector of the apparatus from FIG. 1.

[0088] FIG. 2B shows a cross section of a large-area counter of a detector of the apparatus from FIG. 1.

[0089] FIG. 3 shows a block diagram of the apparatus from FIG. 1.

[0090] FIG. 4 shows current-voltage characteristic curves of the apparatus from FIG. 1 for various dose powers.

[0091] FIG. 5 shows a spectrum of heights of detector current pulses measured by means of the apparatus from FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

[0092] FIGS. 1 to 3 show an apparatus 1 for measuring ionizing radiation IS. The apparatus 1 comprises a detector 2 and an operating mode setting device 7. The detector 2 comprises a cathode device 3, an anode device 4, a counting gas ZG, a voltage source 5 and a current measuring device 6. The counting gas ZG is situated and/or is spatially arranged and/or configured between the cathode device 3 and the anode device 4 for generating free charge carriers FL by gas ionization by the ionizing radiation IS. The voltage source 5 is configured for applying a voltage U5 between the cathode device 3 and the anode device 4. The current measuring device 6 is configured for measuring a detector current 16 between the cathode device 3 and the anode device 4. The operating mode setting device 7 is configured for independently setting the apparatus 1 into one of the operating modes B1, B2, B3 or B4 depending on the measured detector current 16 in the event of predefined limit values being exceeded or undershot, optionally with hysteresis.

[0093] Furthermore, the voltage source 5 is a settable voltage source for applying a settable voltage U5 between the cathode device 3 and the anode device 4.

[0094] Moreover, the operating mode setting device is configured for independently setting the voltage source to different voltage values in accordance with different gas gains depending on the measured detector current, as shown in FIG. 4.

[0095] FIG. 4 shows three voltage values for ionization chamber range (U51), low (U52b) and high (U52a) gas gain. The voltage value U51 is such, in particular minimal, that the apparatus 1 without gas gain is within the ionization chamber range. In detail, the voltage U51 is in a range of 200 volts (V) to 400 V. The voltage value U52b is such that the apparatus with a low gas gain is in the proportional range. The voltage value U52a is such, in particular maximal, that the apparatus with a higher gas gain is in the proportional range. In particular, the voltage value U52b is lower than the voltage value U52a such that the lower gas gain is lower than the higher gas gain by a factor of 5-20, in particular 10. In detail, the voltage values U52b, U52a are in a range of 1000 V to 2000 V. The gas gain is in a range of up to 100 000. In alternative exemplary embodiments, there may be two voltage values or a plurality of voltage values, in particular with at least two voltage values between the minimum voltage value without gas gain in the ionization chamber range and the voltage value with maximum gas gain in the proportional range.

[0096] The apparatus 1 further comprises a determining device 8, as shown in FIG. 3. The determining device 8 is configured for determining a property EG of the ionizing radiation IS on the basis of the measured detector current 16.

[0097] Moreover, the apparatus 1 comprises a current pulse measuring device 9. The current pulse measuring device 9 is configured for measuring heights H6 with a downstream integral discriminator for measuring a counting rate Z6 of signal current pulses IP6 based on detector current pulses IP6 between the cathode device 3 and the anode device 4.

[0098] In addition, the determining device 8 is configured for determining an, in particular the, property EG of the ionizing radiation IS on the basis of the measured counting rate Z6 and/or a spectrum SP of the measured heights H6 of the signal current pulses IP6.

[0099] In detail, a property is the spectrum SP, which is a frequency HK of the measured heights H6, in particular of height values of the heights H6, as a function of the measured heights H6, as shown in FIG. 5.

[0100] In alternative exemplary embodiments, it may be sufficient if the determining device can be configured either for determination on the basis of the measured detector current or on the basis of the measured counting rate and/or the spectrum of the measured heights of the detector current pulses. In particular, the apparatus need not or may not comprise the current pulse measuring device.

[0101] In detail, in the exemplary embodiment shown, the operating mode setting device 7 is configured for independently setting the determining device 8 for determining the property EG of the ionizing radiation IS in the operating modes B1 and B2 on the basis of the measured detector current 16 and in the operating modes B3 and B4 on the basis of the measured counting rate Z6 and/or the spectrum SP of the measured heights H6 of the detector current pulses IP6 depending on the measured detector current 16.

[0102] In detail, there are four operating modes B1, B2, B3, B4 in the exemplary embodiment shown.

[0103] The operating mode B1 operates with gas gain with different gain factors in the proportional range for example in the case of the voltage values U52a or U52b and the property EG (e.g. dose power) is determined on the basis of the measured detector current 16.

[0104] The operating mode B2 operates without gas gain in the ionization chamber range, in particular in the case of the voltage value U51, and the property EG is determined on the basis of the measured detector current 16.

[0105] The operating mode B3 operates with the higher gas gain in the proportional range, in particular in the case of the voltage value U52a, and the property EG is determined on the basis of the measured counting rate Z6 of the detector current pulses IP6.

[0106] The operating mode B4 operates with the higher gas gain in the proportional range, in particular in the case of the voltage value U52a, and the property EG is determined on the basis of the spectrum SP of the measured heights H6 of the detector current pulses IP6.

[0107] In alternative exemplary embodiments, the apparatus, in particular the detector, need not have all the operating modes or need not be configured for all the operating modes or need not be able to be operated in all the operating modes.

[0108] The operating mode B1 operates in differently calibrated measurement ranges Ma, Mb or further ranges. If the active operating mode is for example B1, Ma (maximum sensitivity), then the apparatus can automatically switch into the measurement ranges B1, Mb . . . or into the operating mode B2.

[0109] If, in a further exemplary embodiment, the chosen operating mode is B3 or B4, then the apparatus can automatically switch into one of the measurement ranges of the operating mode B1 in the event of a predefined limit value of the detector current pulses being reached, and into the operating mode B2 in the case of even higher detector current.

[0110] Furthermore, the operating modes B2 or insensitive measurement ranges of the operating mode B1 are suitable for high radiation intensities, in particular pulsed ionizing radiation IS, but the operating modes B3, B4 are not suitable. In particular, by comparison with the operating modes B3, B4, the operating mode B2 can enable a measurement of radiation intensities higher by two orders of magnitude or a factor of 100. At low radiation intensities, in particular in the case of non-pulsed ionizing radiation IS, the operating modes B3, B4 have the highest measurement sensitivity.

[0111] Moreover, in the exemplary embodiment shown, the determining device 8 is configured for comparing the measured counting rate Z6 and/or the spectrum SP of the measured heights H6 of the detector current pulses IP6 with the measured detector current 16 and for determining the property EG (e.g. dose power) of the ionizing radiation IS on the basis of the comparison.

[0112] In alternative exemplary embodiments, the determining device need not or may not be configured for comparing and for determining on the basis of the comparison.

[0113] The apparatus 1 further comprises an operating point setting device 10 having a reference source 11, which emits ionizing reference radiation ISR, as shown in FIGS. 1 and 3.

[0114] In detail, the operating point setting device 10 is configured for independently setting the voltage source 5, in particular the voltage U5, to an operating point voltage value U5R in such a way that the detector current 16 measured by the ionizing reference radiation ISR reaches a predefined reference current volume I6R, in particular during operation with gas gain, in particular during proportional range operation, as shown in FIG. 4.

[0115] In addition, the operating point setting device 10 is configured for independently setting the voltage source 5, in particular the voltage U5, to an, in particular the, operating point voltage value U5R in such a way that a property of a, in particular the, spectrum SP of the heights H6 of the detector current pulses IP6, said heights being measured by the ionizing reference radiation, reaches a predefined reference spectrum value, in particular during operation with gas gain, in particular during proportional range operation, as shown in FIG. 5.

[0116] In detail, FIG. 5 qualitatively shows the pulse height spectrum SP that results e.g. with a radionuclide with the correct operating point voltage value U5. In the exemplary embodiment shown, for the purpose of correctly setting the operating point voltage value U5R, the voltage U5 is altered or varied such that the spectrum components A1 and A2, in particular the integrals over parts of the spectrum SP, assuming that the spectrum form is always the same, yield a previously defined ratio, the predefined reference spectrum value EGSR: A2/(A1+A2)=constant=EGS. The threshold TH1 separates undesired interference and noise components (below A1). The energetically higher threshold TH2 separates the upper signal component A2. In alternative exemplary embodiments, the property of the spectrum can be a position of an unambiguous maximum in the spectrum, the threshold TH2 in FIG. 5.

[0117] In alternative exemplary embodiments, it may be sufficient if the operating point setting device can be configured either for setting in such a way that the measured ionization current and/or signal current reach(es) the predefined reference current value, or for setting in such a way that the property of the spectrum of the measured heights of the ionization current pulses and/or signal current pulses reaches the predefined reference spectrum value.

[0118] Moreover, the apparatus 1 comprises a settable electronic amplification device 15, 15, as shown in FIG. 3. The electronic amplification device 15, 15 is configured for amplifying the detector current 16 and/or the detector current pulses IP6 with a settable gain value VW. The operating point setting device 10 is configured for independently setting the amplification device 15, 15 to a first gain value VWa and for independently setting the voltage source 5, in particular the voltage value U52a, to a first operating point voltage value U5Ra for attaining the reference current value I6R and/or the reference spectrum value EGSR in the case of the first gain value VWa. Furthermore, the operating point setting device 10 is configured for independently setting the amplification device 15, 15 to a second gain value VWb, higher than the first, and for independently setting the voltage source 5, in particular the voltage value U52b, to a second operating point voltage value U5Rb, lower than the first, for attaining the reference current value I6R and/or the reference spectrum value EGSR in the case of the second gain value VWb.

[0119] In particular, the first gain value VWa is lower than the second gain value VWb by a factor of 5-20, in particular 10. In alternative exemplary embodiments, there may be at least three gain values and correspondingly at least three operating point voltage values.

[0120] In detail the following equation can hold true: (primary ionization current with reference source)(gas gain)(electronic gain)=reference current value. Generally, the following equation can hold true: (ionization current)(gas gain)(electronic gain)=detector current. The same can correspondingly hold true in the case of the spectrum of the measured heights of the detector current pulses, in particular wherein, instead of the current, it is possible to use for example the integral over the spectrum with regard to the pulse heights.

[0121] Furthermore, the reference source 11 comprises for example Na-22 and/or Fe-55 and/or Cl-36, as shown in FIG. 1.

[0122] Moreover, the apparatus 1 is configured for a defined detector-reference source geometry. In detail, the detector 2 comprises a probe 22 comprising the cathode device 3, the anode device 4 and the counting gas ZG. The apparatus 1 comprises a housing 20 having an opening 21 for inserting the probe 22. The reference source 11 is arranged spatially behind the opening 21.

[0123] After the probe 22 has been removed or withdrawn from the opening 21, the actual or normal measurement, as described above, can begin or be continued.

[0124] In detail, the apparatus 1 comprises a microcontroller, wherein the microcontroller comprises a part of the operating mode setting device 7, a part of the determining device 8 and a part of the operating point setting device 10. In other words, the operating mode setting device 7, the determining device 8 and the operating point setting device 10 are accommodated besides other setting devices in the microcontroller device.

[0125] The apparatus 1 further comprises a drivable alarm signal output device 12. The alarm signal output device 12 is configured for outputting an, in particular acoustic and/or optical, alarm signal AS. The operating mode setting device 7 is configured for independently driving the alarm signal output device 12 for outputting the alarm signal AS depending on the measured detector current 16.

[0126] Furthermore, the cathode device 3 is configured to be at ground potential EGND during operation, or the cathode device 3 is at ground potential EGND during operation, as shown in FIG. 3. The anode device 4 is configured to be at a positive potential PLUS relative to ground potential EGND during operation, or the anode device 4 is at the positive potential PLUS during operation.

[0127] In detail, the circuit parts enclosed by a dashed border are at the positive potential PLUS during operation. In particular, the detector current 16 is tapped off at the positive potential level. The decoupling of the ionization current pulses IP6 at the positive potential level is effected by way of a capacitive coupling.

[0128] Moreover, the cathode device 3 partly or completely consists of carbon fibers CF.

[0129] In detail, the cathode device 3 has a wall thickness T3 of 0.1 millimeter (mm) to 2 mm, in particular 1.5 mm.

[0130] In one development of the invention, the detector comprises, in particular either, a cylindrical counting tube 13, as shown in FIG. 2a, or a large-area counter 14, as shown in FIG. 2b.

[0131] In detail, the cathode device 3 spatially surrounds the anode device 4.

[0132] The cylindrical counting tube 13 further comprises just a single anode wire 4. The large-area counter 14 comprises a plurality of anode wires 4, in particular electrically connected in parallel and arranged such that they run parallel. In particular, the anode wire/anode wires 4 has/have, in particular in each case, a diameter D4 of 40 micrometers (m) to 80 m, in particular 60 m. Additionally or alternatively, the anode wire/anode wires 4 consists/consist, in particular in each case, partly or completely of tungsten.

[0133] In detail, the cylindrical counting tube 13 is closed at both end sides. Furthermore, in the case of the cylindrical counting tube 13, the cathode device 3 is configured in a cylindrical fashion. In particular, the cylindrical counting tube 13 or the cathode device 3 has a diameter D3 of 15 mm to 35 mm, in particular 25 mm. Additionally or alternatively, the cathode device 13 is the tube wall. The anode wire 4 is situated or is clamped in the longitudinal axis or center axis of the cylinder and is led out of the counting tube 13 at one end through an insulator, in particular ceramic. Isobutane, for example, is suitable as counting gas ZG.

[0134] In particular, the cylindrical counting tube 13 can be used for dose power measurement for gamma and/or X-ray radiation.

[0135] In detail, the apparatus 1 for dose power measurement for gamma and/or X-ray radiation is configured to be operated in all four operating modes.

[0136] In detail, the large-area counter 14 comprises three planes, a middle one of the three planes being shown in FIG. 2b. A front one of the three planes is formed by a very thin window composed of metallized plastic film, in particular for a gas flow counter, or titanium, in particular for a gastight counter having a permanent gas filling. The inner side of the window is grounded. The middle one of the three planes is formed by the plurality of anode wires 4. A rear one of the three planes is formed by an electrically conductive back wall, which is likewise grounded. In particular, the active detector area is hundreds of square centimeters.

[0137] In particular, the large-area counter 14 can be used for measuring radioactive contaminations of surfaces or persons, for example with hand-foot monitors or whole-body monitors.

[0138] In detail, the apparatus 3 in accordance with FIG. 2b for surface contamination measurement is configured to be operated in the operating mode B3, in particular single-pulse counting. In addition, the apparatus 3 for contamination measurement is configured to be changed over from the operating mode B3 to the operating mode(s) B1 or B2 and/or to output the alarm signal AS in the event of the current limit value being reached or exceeded by the measured detector current 16.

[0139] In particular, an operating point voltage setting, as described above, need not or may not be carried out. The operating point setting is carried out here by way of the recording of a plateau curve.

[0140] As made clear by the exemplary embodiments shown and explained above, the invention provides an advantageous apparatus for measuring ionizing radiation which has improved properties compared with the prior art, in particular enables a simple and thus cost-effective construction and at the same time, in particular flexible and/or safe, operation depending on the ionizing radiation.

[0141] 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.