SU1045195A1 - Well-logging gamma-radiometer - Google Patents

Abstract

Logging GAMMA RADIOMETER / comprising crystal scintillator, a photomultiplier tube (PMT) divider power photomultiplier coupled to the high voltage source PMT power and amplitude discriminator divider by two resistors, whose input is connected to the anode photomultiplier and output via the transmitter and the logging cable connected to a ground receiving device, in order to increase the working frequency while decreasing the device dimensions, a high-resistance resistor was inserted into it, through which the ungrounded s The output of the high-voltage power source of the PMT is connected to the midpoint (L koy divider discriminator.

Description

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SP -Izoreoretenie refers to the discovery of minerals with the help of ionizing beams, namely, rota- tion gamma radiometers. In modern logging gammaradiometers, scintillation detectors of gamma radiation, consisting of crystal scintillation and photoelectronic intelligence, nozteltel, are widely used. The well-known logging gamma radio meter contains a scintillator detector, amplitude discriminator with a constant number and is used by the program. ground receiving device. The downhole part of the radiometer also contains a high-voltage PMT power supply unit l. The high voltage supplying PMT has strict requirements for stability and pulsation coefficient. This is due to the fact that even with insignificant changes in the voltage of a photomultiplier, its amplification factor changes dramatically, and this leads to a change in the energy equivalent of the trigger level of the discriminator. For this reason, the scintillation detector has a plateau of no more than 100-200 V. The closest to the proposed technical essence is a logging gamma radiometer containing a crystal scintillator, a photomultiplier, a photomultiplier power divider connected to a high voltage photomultiplier and a photomultiplier of the photomultiplier , and the amplitude discriminator with a divider setting the threshold for its operation on two resistors, the input-which is connected to the output (anode) of the photomultiplier, and the output is connected through a transmitting device and a logging cable with a ground receiving device. In addition, the power divider of the PMT of this device contains an additional gas stabilitron connected to a part of the high resistance PMT divider, which expands the plateau on the counting characteristic of the detector up to 320 V and thereby increases the operating stability of the gamma radiometer 2, however, the high-voltage gas logging gamma radiometer zener diodes increases its dimensions and reduces reliability of operation, since the parametric 3S1 stabilizer consumes additional power from a high-voltage source and requires for its normal minimum work of increased (at least 20-30%) voltage. The purpose of the invention is to increase reliability while reducing the dimensions of the logging gamma radiometer. The goal is achieved in that a logging gamma radiometer containing a crystal scintillator, a photomultiplier tube, a PMT power divider connected to a high; with a voltage source of power of the PMT, an amplitude -discriminator with a divider setting the threshold for its operation on two resistors, the input of which is connected to the output (anode) of the PMT, and the output through the transmitting device and the logging cable is connected to the ground receiving device, a high-resistance resistor is introduced through which the ungrounded The output of the high-voltage power source of the PMT is connected to the midpoint of the discriminator divider. The energy equivalent of the discriminator actuation level is kept constant over a wide voltage range at the photomultiplier by varying the discriminator response voltage in proportion to the photomultiplier gain factor. For this, the average voltage divider point setting the actuation voltage of the discriminator is additionally connected through a high-resistance resistor with an ungrounded the output of the high voltage power supply unit PMT. In particular, the PMT power divider can serve as a high-resistance resistor (to save power consumption, the latter is not grounded in this case, Fig. -I shows the functionality of the logging gamma radiometer; Fig. 2 shows the counting characteristics of the proposed Gs1Mma radiometer, as well as prototype and analogue. The log gamma radiometer contains scintillator 1 located in the borehole part, photomultiplier 2 with divider 3 of the PMT, high-voltage source 4 of the PMT, divisor discrimination ores on resistors 5 and 6, a high-resistance resistor 7, a discriminator 8 and a transmitting device 9 connected by a logging cable 10 to a ground receiving device 11. The PMT 2 is powered from a stabilized high-voltage source 4 (usually a voltage converter with a rectifier that is powered via logging cable 10 from ground-based current source) At the moments of gamma-quanta entering the volume of the scintillator crystal 1, anode load of the photomultiplier 2 (upper discriminator input 8) gives rise to voltage pulses, amplitude which depends on the energy of the gamma rays and the gain of the photomultiplier, the discriminator 8 performs amplitude selection of the incoming

its pulse input in order to separate the useful signal from the noise of the scintillation detector. A useful signal from the output of the discriminator 8 enters the transmitting device 9 where it is converted into a form convenient for transmission over the logging cable 10 to the earth's surface to the receiving device 11. The latter usually contains a recorder that records the gamma radiation intensity chart as a function of the depth of the well.

The gamma radiometer contains a compensating circuit on a high-resistance resistor 7, which provides tracking of the threshold of the discriminator 8 for the voltage of the PMT and, therefore, the gain of the PMT.

Indeed, in a certain range of variation of the power of the photomultiplier, the voltage and the gain of the photomultiplier K can be approximated :: with sufficient accuracy for our case linear dependence on U

To a + no,. (1) where a, b are the approximation coefficients depending on the parameters of the photomultiplier and the chosen range of approximation

In order to keep the energy equivalent value unchanged, the discrimination damage in the range of possible changes U is necessary and sufficient

 : (a -i-bU), (2) where Ug is the tripping voltage of the discriminator;

c is the coefficient depending on the chosen energy equivalent of the level of discrimination;

m with with A;

P with - in

Resistors 5-7 serve to derive Eq. (2). It is recommended to set the energy equivalent of the actuation level of the discriminator according to the rudimentary method of adjusting the resistance of resistor 5 at the minimum value U (selecting the coefficient rm)) and adjusting the resistance of the resistor b at the maximum value II (choosing the coefficient p). The adjustment is made several times by the method of consecutive proximity.

SRI.

In order to save power consumption o: high-voltage power source 4 as a high-resistance resistor 7 can be used

PMT divider 3. In this case, its upper circuit is not grounded and is connected at the midpoint of the Divider on resistors 5 and 6, and resistor 7 is excluded from the circuit. 5 Use to select n

The resistor circuit of the high impedance PMT power divider makes it difficult to adjust its resistance.

10 After replacing the PMT, it may be necessary to re-select the resistance of resistors 5 and 6.

The device’s capabilities are illustrated by its counting characteristic.

5 detector (curve 12 in Fig. 2).

It was removed using a N a D (TP) crystal with dimensions of mm and a photomultiplier tube of the type of an FEU-74A photoelectric multiplier. Iso0-top 137 C5, shielded from detec- tors, was used as a source of gamma radiation. torus stylish sheet thickness 10 mm. The energy equivalent of the discriminator trigger level, composition. 50 keV is set at 1250 in resistor 5 and at 1550 V in resistor 6. In comparison with the counting characteristics of detectors of known radiometers (curves 13 and 14), in the proposed device

0 The plateau is 2-3 times larger and is 500-600 V.

The energy equivalent of the discriminator response level of about 50 keV is located in the energy

5, between the PMT noise (which reaches 15 keV at 150-C) and the useful signal. In this case, the departure of the energy equivalent of the discrimination level fJg as due to the inaccuracy of the linear approximation (not

more than + 20%), and due to the temperature instability of the threshold of the discriminator due to the instability of the low-voltage power source of the discriminator (up to + 30%) does not impair the operation of the detector.

The presence of a plateau of 15–20% of the supply voltage of the photomultiplier allows in the proposed gamma radio meter to perform a high-voltage power source of the photomultiplier without parametric stabilization of high voltage, which significantly reduces its dimensions and improves reliability of operation. The device can be used in ground, in particular, in field radiometric equipment.

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Claims (1)

A GAMMA RADIOMETER, comprising a crystal scintillator, a photomultiplier tube (PMT), a PMT power divider connected to a high-voltage PMT power supply, and an amplitude discriminator, a divider with two resistors, the input of which is connected by an PMT anode, and the output is through a transmission device and a wireline cable coupled to the receiver ground, of t lichayusch.iysya in that, in order to increase reliability of operation while reducing device dimensions, it introduced high impedance resistor through which the output ungrounded _β Vysokovo tnogo source pi <g Thaniah photomultipliers connected to a midpoint divider discriminator. SU „1045195