SU341088A1 - METHOD FOR CALIBRATING RADIO ISIZING MEASURING INSTRUMENTS - Google Patents

Description

The invention relates to radioisotopic instrumentation, in particular, to methods for measuring coating thicknesses, and can be used to calibrate radioisotope devices containing a decade measurement counter, for measuring the counting rate of a detector in the form of a digital readout directly in units of the measured parameter, for example, in microns.

Various designs of radioisotope devices are known, by means of which the measured parameter is determined by the number of detector pulses counted by the measuring crossover device for a certain time, using calibration graphs to convert the number of pulses into units of the measured parameter. The possibility of calibration in these devices is not provided. The need to use calibration curves is a significant disadvantage of these instruments.

The purpose of the invention is to obtain the value of the monitored parameter in digital form.

The goal is achieved by the fact that according to the proposed calibration method, an auxiliary (background) beta or gamma radiation flux is used, which in certain ratios is measured together with the working flux from the monitored material. At that, the readout of the monitored parameter is obtained on indicator digital lamps of a decade counting device, registering the total count rate of two streams. FIG. Figure 1 shows the block diagram of the beta thickness gauge of the coatings, which allows the proposed calibration method to be implemented; pas figs. 2 shows schematically one of the options for the construction of a beta-thickness gauge sensor for coatings with an adjustable working flux of back scattered beta radiation and an adjustable auxiliary flux; pas figs. Figures 3, 4, 5, and 6 show variations of sensor designs that use different methods to form and regulate the auxiliary flow.

The proposed method is based on the use of known functionalities of the intensity of the flux of backscattered beta radiation from the thickness n of the atomic number of the scattering material. Nd backscattered beta radiation or d-coated base can be expressed as:

 (Woo -) (1 - e-),

(1) MJO is the backscattered flux from the coating layer, the thickness of which is greater than the saturation thickness for backscattering; Y is the absorption coefficient of the scattered radiation, depending on the energy of the beta spectrum and conditional registration. The proposed method can be used in a range of coating thicknesses where a linear dependence of the back scattered beta radiation flux on thickness occurs. In the linear measurement area with small tolpi1, the relation (1) irides is (l + 03ouf), I / 7 ttOKp 1) where ZQ and ZnoKp are effective atomic numbers for OCHOBF materials, respectively, and coatings; k is a coefficient characterizing the sensitivity to the atomic number of the scattering material (it is practically possible to accomplish the words when k lies in the range of 0.3-2). The linear range corresponds to the thickness of the coverings from O to 0, lrfi, where d is the saturation thickness for back scattered beta rays. For example, with a source, the linear range extends to thicknesses of about 30 M & ICM. In the linear range, the variation in the counting rate of AL with a change in the thickness of the coating by the value of Ac remains constant, due to the atomic omosomes of the substrate and coating, the beta spectrum energy, the spectral characteristics of the detector, and the intensity of the workflow. For measuring the thickness of coatings for each combination of materials, axes and coats using standards of known thickness, use adjusting controls to set the intensity of the workflow such that the increase in the number of pulses during the measurement time / with an increase in the thickness of the coating of Arf satisfies the condition (4) where t - an integer corresponding to the decade on the measuring device. In this case, with a change in the thickness of the coating d, the recorded counting rate changes in a decisive ratio. Since the choice of the magnitude of the measurement time / in practice may be limited, in a number of cases the detector pulses are first advisable to apply to the preliminary recalculation unit and then to the measuring counter. Taking into account the preliminary number of counted pulses, the correlation is DL., - 10 ™ -АЙ. (5) The use of a preliminary recalculation with a coefficient expands the possibilities of applying the proposed calibration method with a limited number of possible discrete values of the measurement time t. The calibration method is applicable to coating materials with 2pcr - approx. After setting the thickness gauge according to conditions (4) or (5), it is necessary to ensure that the number of counted pulses from the base material is uncoated. Compensation is carried out by smoothly measuring the intensity of the auxiliary (background) gamma-beta beta stream in such a way that the total count rate corresponds to the condition 0 L t n –W ki kz where L / F is the count rate due to the all-flow; k is the preliminary conversion factor for the auxiliary detector pulses (in the case of one detector or one preliminary conversion unit); oc is an integer (1, 2, 3); m-fa is an indicator corresponding to the highest measuring decade of a recalculation device; n is an integer indicating the number of overruns of the highest measuring decade of the scaler. An indication of the provision of condition (6) during the paste thickness of a thickness gauge is the appearance of a bullet readout during the measurement time for significant decade of the measurement scaler. Thus, the proposed method for calibrating beta thickness gauges of coatings is reduced to performing the following tuning operations in turn. First, with the help of two standards with a known thickness of coatings, the decimal growth of the counting rate from the working flow is established according to conditions (4) or (6). An uncoated backing material can be used as one of the standards, and a sample with a known coating thickness can be used as the other. For calibration of thickness gauges, equivalent standards made of some other material or with a different coating can also be used, in terms of backscatter characteristics corresponding to two known thicknesses of the coating material to be measured. At the same time, the intensity of the auxiliary flow must be maintained at a constant (desirable minimum) level. Then, by summing the change in the intensity of the complementary stream, the sums are set at a level corresponding to the compensation condition or the condition of complete overflow of significant decades (usually).

As a result of such a calibration, when measuring an unknown coating thickness, the set of digits in (t-1-1) decade of a measuring recalculation device corresponds to tens of units of thickness, in t decade - units of thickness, in (t-1) decade - tenth fractions of units, etc. For each combination of base and coating materials, a different set of standards is required for calibration. Measurement results are obtained in the form of a digital readout directly in units of thickness or surface density.

In the beta thickness gauge, the beta-emission working flow is recorded by the detector /, the pulses of which through the shaper 2 and the pre-recalculation unit 5 arrive at the input of the ten-decade metering measuring device 4. The auxiliary (primary) flow is recorded by the detector 5, the pulses of which are fed through the shaper 6 and the preliminary and recalculate 7 to the common input of the metering device 4. The device shown in FIG. A measuring meter has a duration of six decades, of which three older decades, in which thousands, tens of thousands of hours, and hundreds of thousands of pulses are recorded, are measuring or meaningful. After the thickness gauge has been calibrated, the numbers in these decades show the tenth fractions, units and tens of units of the coating thickness, for example, in microns (for decadalities, the measurement readout corresponds to 16.3 microns. The display of numbers in the first decades, measuring units, tens and hundreds of pulses may be absent altogether, as the numbers in these decades more reflect the fluctuating nature of radioactive radiation.

Registration of the auxiliary (background) radiation flux can be carried out using a separate detector or working detector 1; in the latter case, the need for blocks 5, 6 and 7 is eliminated. To create an auxiliary (background) flux, you can also use either a separate radiation source or a working beta radiation source. Numerous design variants of sensors are possible to create adjustable flows. For example, a change in the intensity of a work flow can be accomplished by one of the following methods: by changing the distance from the source to the material being monitored while maintaining the distance from the material to the detector; changing the distance from the material to the detector when the distance from the source to the detector is constant; covering the sensitive surface of the detector with an impenetrable shutter or various filters; a change in the discrimination level of the pulses, if a spectrometric type detector is used; using magnetic fields, deflection, their (5ta-particles, etc.

In the embodiment of the sensor shown in FIG. 2, the workflow (shown by flat lines) is created by a beta radiation source 8, which is iomed in collimator 9 with a working channel 10. Beta radiation flux reflected from the material // with a coating 12. mounted on a table (diaphragm).

enters detector 14. A detector / 5 is placed in front of the detector 14 on the path of the backscattered beta radiation to increase the sensitivity. The intensity of the workflow is controlled by changing the distance between

material and detector due to the rotation of the table-diaphragm 13 in the sensor body 16. The intensity of the working flow can also be changed and the cover of the sensitive surface of the detector impermeable screen / 7. The auxiliary beta-radiation flux is formed using a special scatterer 18. Part of the beta-radiation from source 8 through the second channel 19 in the collimator .9 hits the scatterer 18 and after

The reflector is registered by the working detector 14. In order to increase the backscatter coefficient, the surface of the diffuser 18 is made of a material with a large Z.

The intensity of the auxiliary flux (shown by the dotted line) is adjusted by changing the distance from the source to the diffusor. Geiger-Muller counters, a scintillation counter, or a semiconductor detector can be used as a detector.

With the help of one source, two controlled flows are formed, the working and the supporting ones, which are then recorded.

one common detector.

In the design of the sensor shown in FIG. 3, the auxiliary beta-ray flux is formed using the spreader 18, onto which a portion of the beta radiation falls, output and its 1 through the working channel 10. The intensity of the flow is adjusted by shifting the diffuser in the direction of the source-coated material. In the presence of a divider in the outgoing zone

through the collimator of the beta-radiation flux and the detector, the working flux of beta-radiation, dispersed from the coated material, and a small constant part of the auxiliary flux, dispersed by the table (diffuser / 8 extended), which is made of material with a small Z, enter the detector. As the diffuser / 8 moves to the outgoing beam zone, the intensity of the auxiliary stream increases.

FIG. Figure 4 shows a variant of the sensor design in which an auxiliary stream is formed due to the bremsstrahlung radiation of the beta radiation source 8 penetrating through the walls of the collimator 9. The brake radiation from the beta radiation emitter and the walls of the collimator. The bremsstrahlung flux is recorded by the working detector 14 at the same time as the beta radiation flux. The intensity of the bremsstrahlung current is controlled by not moving the protective wedge-shaped screen 20 with a micrometer screw 21. This sensor option is more useful in cases where a source of hard beta radiation is used, for example.

In the embodiment of the sensor shown in FIG. 5, the auxiliary stream is formed by a radioactive source (beta or gamma-) 22 or 23 and recorded by the working detector 14. The intensity of the auxiliary stream can be adjusted by changing the distance from source 22 to detector 14, or by blocking a portion of the radiation flux from source 23 by shutter 24 .

FIG. 6 shows a variant of the sensor in which the auxiliary stream is formed using a separate beta or gamma radiation source 23 detected by a separate detector 25. The intensity of the auxiliary stream is adjusted by moving the shutter 24 overlapping part of the incident stream to the detector 25. The adjustment can also be made by changing the distance of the source 23 of the detector 25. The pulses from the detector 25 to apply either to the driver 2 and the conversion unit 3, or to a separate driver 5 and the conversion unit 6 (Fig. 1). The first case is advisable to use when the working detector 14 and the auxiliary 25 are of the same type. When using a separate driver 5 and conversion unit 6 with a sufficiently large conversion factor, the fluctuations in the pulse count rate of the auxiliary flow can be significantly smoothed. Other options are also possible for forming and adjusting the auxiliary flux of radioactive radiation, which serves to calibrate the coating thickness gauge.

Subject invention

A method for calibrating radioisotope measuring instruments, for example, beta-thickness gauges of coatings, containing as a secondary measuring instrument a decade scaler, consisting in establishing a correspondence between the values of the scaler and the values

controlled parameter of reference samples of the material, characterized in that, in order to obtain the value of the controlled parameter in digital form, the regulating workflow of ionizing radiation establishes a decimal increment of the counting rate for a certain period of time when the value of the monitored material parameter is changed by one and then the introduction of an auxiliary ionizing radiation flux establishes a total count rate such that, in significant decades, Device according VILS zero reading when the whole multiplicity overflow decades for the same

time interval for the selected value of the controlled parameter.

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