WO1989002087A1

WO1989002087A1 - Device for measuring ionizing radiation

Info

Publication number: WO1989002087A1
Application number: PCT/FI1988/000138
Authority: WO
Inventors: Kauko Tanskanen
Original assignee: Kauko Tanskanen
Priority date: 1987-09-01
Filing date: 1988-08-30
Publication date: 1989-03-09
Also published as: FI873781A0; FI81454B; FI81454C; FI873781A; AU2306988A

Abstract

The object of the invention is a device for measuring of ionizing radiation, to which device belong a high voltage source (1), a radiation detector (2), favourably a Geiger-Muller tube, in which the radiation quantum together with the voltage generates an ionic current and the radiation detector becomes conductive, detecting instruments (9) for indication of the ionic current, and a with the cathode side of the radiation detector connected voltage source (4), which is arranged to conduct to the radiation detector a counter voltage, which quenches the ionic current. The present devices are complicated and it is not possible to measure with the help of them a continuously ionizing radiation. In a device in accordance with the invention the voltage source and the radiation detector are connected with the earth with one coupling (6) and to the device belongs a with the coupling and with the detecting instruments of the ionic current connected controlling apparatus (8), which is arranged to open the coupling, when a radiation quantum hits the radiation detector, whereat the voltage is conducted to the cathode of the radiation detector to act as a quenching voltage.

Description

DEVICE FOR MEASURING IONIZING RADIATION

The object for the invention is a device for measuring of ionizing radiation, to which device belong a high voltage source, a with the voltage source connected radiation de¬ tector, favourably a Geiger-Muller tube, where the radi- ation quantum together with the voltage causes an ionic current and the radiation detector becomes conductive, de¬ tecting instruments (9) for indication of the ionic cur¬ rent, a voltage source connected with the cathode side of the radiation detector, which is arranged to conduct to the radiation detector a counter voltage, which quenches the ionic current-

Radiation detectors and in particular G-M tubes are used for indication of ionizing radiation particularly the elec- tromagnetic and particle radiation generated at the de¬ gradation of a radioactive substance. The radiation detec¬ tors operating on the impulse principle have a gas-filled radiation detector tube, in which the gas is under press¬ ure. On the anode side is conducted the high voltage and when the radiation quantum hitting the tube generates an ionic current, the tube becomes conductive. The radiation is measured by measuring the number of pulses per time unit coming from the tube, which is proportional to the intensity of the radiation to be measured. The quenching gas in the radiation detector tubes is quenching after the elapse of a certain period of time the ionic current. This time is called the dead time of the G-M tube, during which the tube is unable to react to a possibly, arriving new quantum of radiation. The dead time is growing in importance when the speed of irradiation is increasing, whereat the radiation detection impulses received per time unit do not indicate the the change in irradiation speed in a depend¬ able way. Additionally, the quenching gas of the G-M tube is consumed in use and the tube is not operable anymore when the quenching gas has been consumed. In the US-patent 3 185 847 a device has been presented, in which into the radiation detector a counter voltage is conducted, that quenches the ionic current by lowering the anode voltage below the "ignition voltage" of the G-M tube. The device presented in the patent is complicated to its structure and for instance voltage levels are needed at least four. In addition the G-M tube is in operation only part-time and the device does not measure the radi¬ ation all the time.

The purpose of the invention is to bring forth a device for measuring of ionizing radiation, by means of which the frequency behaviour of the radiation detector tube, in particular the G-M tube, is improved, the operational life of the G-M tube is prolonged and the continuous ob¬ servability of the from it obtained radiation detecting impulses particularly in the high radiation speeds is made better and the obstruction of the tu-be is avoided. Additionally the aim of the invention is to bring forward a device, that is simple to its structure and dependable.

The purpose with the invention is reached by a device, which is characterized by it, what has been presented in the patent claims.

In the device in accordance with the invention the voltage source and the radiation detector are connected with the earth with at least one coupling and to the device belongs a controlling apparatus connected with the coupling and the detecting instruments for the ionic current, which is arranged to open the coupling when the radiation quantum hits the radiation detector , whereat the voltage is con¬ ducted to the cathode of the radiation detector to act as a quenching voltage. Hereat immediately when the radi- ation quantum has arrived in the tube causing an ionic current a counter voltage is generated and the tube returns to a non-conductive state and is ready to receive the fol- lowing radiation quantum. When applying the method the con¬ sumption of the quenching gas is decreasing in an efficient way and it is possible to increase the natural impulse fre¬ quency of the tube. The obstruction of the tube in the high radiation speeds is prevented and the maximum frequency for the tube can be determined in advance. When operating above the maximal frequency the impulse frequency is con¬ stant and such a presently common situation, that the tube is in a continuous conductive state, cannot occur. This is of importance then, when the operation takes place in the overloading range of the tube and an indication from the measuring device of a radiation field above its range of measurement is expected. When the G-M- tube is continuously in a state of conductivity, it is destroyed quickly.

In the following the invention is explained more in detail by referring to the attached drawing, which presents one coupling principle of a device in accordance with the in¬ vention .

To the device presented on the figure belong a high voltage source 1, a G-M tube 2, on the anode side 10 of which the high voltage source is connected, a low voltage source 4, which is connected with the cathode side 3 of the G-M tube , detecting instruments 9 for indication of the ionic cur¬ rent and a controlling apparatus 8. Between the high voltage source and the G-M tube is placed an anode resistance 11. Between the cathode of the G-M tube and the earth has been placed the coupling 6. Between the voltage source 4 and the cathode is placed an inductance 5 and a diode 12. The inductance is connected with the earth through the inter¬ mediation of the coupling 7. The controlling apparatus 8 is connected with the anode of the G-M tube and between the anode and the controlling apparatus is placed a con- denser 13. The controlling apparatus is connected with the couplings 6, 7 and is arranged to control their function. The detecting instruments of the impulses are connected with the controlling apparatus and they are as such known conditioning and display instruments.

When introducing the device into operation high voltage is conducted from the high voltage source 1 to the G-M tube 2 through the anode resistance 11. The cathode side 3 of the G-M tube is in contact with the earth when the couplings 6 and 7 are in the closed-position. When a radi- ation quantum hits the G-M tube an ionic current is gen¬ erated in the tube, which short circuits the G-M tube. On the anode side this is observed as a negative drop of the voltage, which is intermediated through the condenser 13 to the controlling apparatus 8 of the couplings. The controlling apparatus opens immediately the coupling 6 and the coupling 7, which controls the earth contact of the inductance 5. The opening of the coupling causes a quick cut-off of the current from the inductance, which again for its part generates an induction voltage, which is directed through the diode 12 to the cathode side.

When the coupling 6 is also in the open-position remains on the cathode the voltage formed by the inductance. The voltage exerting influence over the G-M tube is now lesser than is required for keeping up of the ionic current and in the G-M tube generated ionic current is quenched quicker than solely by the influence of the quenching gas. The controlling apparatus of the couplings is closing the coupl¬ ings after a suitable elapse of time, whereat the G-M tube is ready to receive a new radiation quantum. With the de- tecting instruments the number of impulses is measured and the measuring results are written out.

The invention is not limited to the application presented, but it can vary inside" the frames of the patent claims.

Claims

PATENT CLAIMS

1. Device for measuring of ionizing radiation, to which device belong a high voltage source (1), with the voltage source connected radiation detector (2), favourably a Gei- ger-Muller tube, in which the radiation quantum together with the voltage generates an ionic current and the radi¬ ation detector (2) becomes conductive, detecting instru¬ ments (9) for indication of the ionic current, and with the cathode side of the radiation detector connected volt¬ age source (4), which is arranged to conduct into the radi- ation detector a counter voltage, which quenches the ionic current, c h a r a c t e r i z e d in, that the volt¬ age source and the radiation detector are connected with the earth with at least one coupling (6) and, that to the device belongs a with the coupling (6) and with the detect- ing instruments of the ionic current connected controlling apparatus (8), which is arranged to open the coupling (6), when a radiation quantum hits the radiation detector (2), whereat the voltage is conducted to the cathode of the radiation detector to act as a quenching voltage.

2. Device in accordance with the patent claim 1, c h a r a c t e r i z e d in, that to the device belongs a with the radiation detector (2) and with the voltage source (4) coupled inductance (5), which inductance and the radiation detector are connected with the earth with at least one coupling (6).

3. Device in accordance with the patent claim 2, c h a r a c t e r i z e d in, that to the device belongs a coupling (6) for connecting of the radiation detector (2) and a coupling (7) for connecting of the inductance (5) with the earth, when the couplings (6, 7) are in the closed-position and, that the controlling apparatus (8) is arranged to open the couplings (6, 7), when a radiation impulse is entering the radiation detector, whereat an in¬ duction voltage is created, which is arranged to be con¬ ducted to the cathode of -the radiation detector.