DE3025489A1 - METHOD AND DEVICE FOR MEASURING IONIZING RADIATION - Google Patents

Description

3025483

Method and device for measuring ionizing radiation

The present invention relates to a method and apparatus for measuring ionizing radiation.

The system used comprises a measuring device with pulse counting, such as a Geiger-Müller counter (G-M), as a detector Measuring circuit and a display device.

In the present invention, the G-M counter is used to measure radiation is used in a manner that differs from currently known methods in which the number of pulses are measured by the G-M counter per unit of time, with the Number is proportional to the radiation intensity. The present one The measuring system has a number of tile parts which are avoided in the present invention.

Due to the influence of the dead time, the characteristic curve of the counter (pulse frequency as a function of the irradiation rate) is not linear, since the pulse frequency becomes correspondingly lower when the irradiation rate increases. For this reason, linearization must always take place, either with a dedicated linearization circuit or by adapting the scale graduation of the measuring device according to the characteristic curve of the GM counter. In addition, the measuring device must be calibrated at two or more measuring points for the irradiation rate, since the ^m angente of the characteristics of GM counters does not have a constant angle.

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The features of the new invention are set out in the claims set out.

With the present invention, the influence of dead time as a factor influencing linearity can be eliminated will. The G-M counter can be operated linearly over a measuring range of more than 5 powers of ten, what means an extension of the linearity range. Because of the Linearity can be calibrated the measuring device by a single measuring point for the irradiation rate, what the industrial Production of radiation measuring devices is considerably simplified.

The service life of a G-M meter is limited. Both "Known measuring systems is the maximum number of pulses that can be achieved with the counter until the extinguishing gas is used up is and the meter becomes unusable, in the order of magnitude

10
of 10 . The present invention can extend the life of the counter at higher exposure rates.

Theoretically, the invention offers the possibility of being used as a detector to use any gas-filled tube with sufficient gas pressure to trigger an ion "avalanche". With the present Invention, power consumption can be reduced, which is an important factor in terms of operating characteristics the batteries or accumulators used to supply power to portable measuring devices.

There now follows a description of the invention on the basis of a Embodiment, explained in connection with the figures from Figures 1, 2 and 3

Figure 1 is a block diagram of the apparatus of the invention.

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Figure 2 is a timing chart for explaining the operation of the finding.

Figure 3 shows the measurement results obtained with the inventive Device from Figure 1 were achieved.

In Figure 1, the reference numeral 1 is a high voltage source for the supply of operating voltage for the Geiger-Müller counter 2; 3 is a capacitor, 4 is a from the IvTeß circuit 5 operated switch and 6 is a Display device.

In FIG. 2, tL ™ means the voltage on the Geiger-Müller counter, t is the time axis and τ .., tp and t ·, are individual points on this time axis. First consider a case where the measuring circuit 5 closes the switch 4 for a short period of time and then opens it again. The capacitor 3 is not charged, which is why the voltage from the high-voltage source 1 acts fully on the GM counter 2. At the same time as the switch 4 is closed, a timer is started in the measuring circuit. This instant is marked in FIG. 2 with t ₁ .

When the Geiger-Müller counter 2 detects an amount of radiation, ionization occurs in the counter tube and the counter becomes conductive. This point in time is identified in FIG. 2 with ± 2 & ^e ~ .

The electricity generated in this way, that of the high voltage source flows through the GM counter 2 and the capacitor 3 back to the high voltage source, charges the capacitor 3. While in this way the voltage in the capacitor rises,

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accordingly, the voltage on the G-M counter decreases while the voltage from the high voltage source remains the same. At the end of this voltage decrease on the G-M counter, the flow of ions stops by the counter all the way up when the charge on the capacitor has reached a sufficiently high value. If for the capacitor If a low capacitance is chosen, the capacitor can be charged quickly, causing the current pulse to flow through the G-M counter is shortened, resulting in the operational life of the G-M counter increases.

The measuring circuit 5 detects the ionization in the G-M counter, For example, by detecting the current or the voltage on the capacitor 3 If ionization occurs at time tp, the timer is stopped by the measuring circuit, whereby the capacitor remains charged. The voltage of the G-M counter is below the ignition voltage, whereby the G-M counter cannot detect any radiation. The clock registers now the time interval tp- t .., which is used here as a waiting time tw referred to as. The waiting time (or the mean value over several consecutive waiting times) is reversed proportional to the rate of exposure acting on the G-M counter; therefore the reciprocal of the waiting time is, viz 1 / tw, directly proportional to the irradiation rate. In practice, because of the random occurrence of radiation for a statistically reliable result measured the waiting time for several pulses and determined their mean value tw. After a certain time td, which is referred to here as dead time, the measuring circuit 5 briefly closes the switch 4, whereby the capacitor 3 is discharged. The G-M counter is energized again and the above-described measuring process is repeated themselves. This point in time is marked in FIG. 2 with t ^. The dead time td is represented by the time interval t ·, - tp. Its length is determined electrically by the measuring circuit 5, and it is longer than the dead time of the G-M counter.

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As the exposure rate increases, that from the G-M counter approaches determined pulse rate the value i / td, the lower is than the pulse frequency that could be detected with previously known measurement methods. Because of this, extends the operational life of the G-M meter and reduces the power consumption from the high voltage source. Since the charging of the capacitor interrupts the ionization in the G-M counter, the G-M counter does not need a self-erasing function to have.

In the previously known measuring methods, the dead time of the G-M counter caused a non-linear characteristic curve of the radiation rate compared to the pulse frequency and represented an upper limit for the usable measuring range of the counter.

According to the present invention, the dead time has no influence on the measurement results, because instead of the pulse frequency Waiting time tw is measured. It follows from this that 1 / tw is directly proportional to the irradiation rate and the measuring range can therefore be extended to larger radiation rates. Curve 1 in Figure 3 shows 1 / tw as a puncture of the irradiation rate, measured with the device from FIG. 1. The characteristic curve of a G-M counter is shown in the same diagram for comparison purposes drawn, according to the manufacturer's instructions (curve 2), and related to scale so that the Points for an irradiation rate of 1 mR / h on both curves coincide.

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Claims (2)

/1. A method for measurement of ionizing radiation in a system that comprises the following components: a as a "serving detector G ^ strength Yüller-counter or any gas-filled and serving for Im.pulszah.lung" detector, an electrical Iv'eßschaltung, a Power supply for the: "Detector u / ii a device for displaying the irradiation rate, the irradiation or dose, characterized in that the electronic Kess circuit reduces the voltage of the detector below the extinguishing saving immediately after the plague of an ionization caused by a quantity of radiation in the detector and after the dead time of the system, which is electronically determined so that it lasts longer than the dead time of the detector, the "detector reconnects to the normal operating voltage; and in order to measure the ionizing radiation, the mean time is measured from the moment when the voltage is connected to the detector to the moment when the ionizing radiation causes a new ionization in the "detector, the mean time being proportional to the intensity of the ionization beam is ¹ . 030064/0895 Bayerische Vereinsbank Munich, account no. 882495 (BLZ 700202 70) Deutsche Bank Munich, account no. 82/08050 (BLZ 70070010) Post office in Munich, account no. 163397-802 (bank code 70010080) 2. Apparatus for performing the method according to claim 1, characterized by the following components: a high voltage source (1), a radiation detector designed for pulsed operation (2), such as a Geiger-Müller counter, and a capacitor (3) connected to each other in the order mentioned are connected in series; a switch (4)> which is parallel to the capacitor; a measuring circuit (5), which the time duration between the detected radiation pulses and also the switch for a short time after each detected pulse closes with a certain time delay; and a display device (6) connected to the measuring circuit is. 030064/0895