RU2646542C1 - Scintillational gamma spectrometer - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: invention relates to scintillation γspectrometers, more precisely to energy spectrometers based on scintillators NaI:Tl, CsI:Tl, CsI:Na, LaCl₃:Ce and others, characterized by multicomponent light flashes with a strong dependence of the fluorescence time constants on the crystal temperature. To exclude the influence of this dependence on the spectrometer speed, over a wide temperature range, spectrometer composition, detector pulse processor of which may contain a shortening circuit with pole compensation by zero, is added with additional similar shortening circuits with constant time on the input side in pairs equal to the time constants of the exponential components of the primary electric pulse to be shortened at the output of the photosensor optically articulated with the scintillator, time constants on the output side of said circuits are chosen to be larger than the decay time constant of the nearest faster component to prevent the formation of an ejection of opposite polarity, and the time constants on the input side of the shortening circuits tuned to the exponential components of the primary signal, automatically change when the operating temperature changes in accordance with the laws of temperature variation of the scintillator fluorescence components.

EFFECT: exclusion of the effect on the spectrometer speed.

1 cl, 13 dwg

Description

The present invention relates to the field of scintillation γ-spectrometers, more specifically to energy spectrometers based on scintillators NaI: Tl, CsI: Tl, CsI: Na, LaCl ₃ : Ce and others characterized by multicomponent light flashes.

The principle of operation of any scintillation γ-spectrometer is to convert the energies of gamma rays absorbed in the scintillator into relatively short light flashes with a proportional number of photons; collecting scintillation photons on the sensitive surface of photosensors that convert light pulses into electrical current pulses; amplification and conversion of current pulses into proportional voltage pulses, tight reference of the spectrometer base line to zero (elimination of drift and fluctuations of the initial level); giving detector pulses a given shape (using an analog or digital driver); identification and rejection of pulses whose amplitudes are distorted by mutual overlapping in time and correction of miscalculations (correction of dead time); converting the amplitudes of the selected pulses into digital codes, sorting these codes and constructing the instrumental energy spectra of the measured emissions; compensation of temperature variations of the scintillator light output. The peaks in the instrumental spectrum reflect the energies of the detected gamma quanta, and their areas reflect the nuclide content in the sample.

Classical scintillation γ-spectrometer (Fig. 1) [Belousov M.R. et al. Portable scintillation gamma-ray spectrometer STARK-01. Analytics and control V. 15 (2011) No. 4. from. 429-438] contains: a detecting module 1, consisting of optically connected inorganic scintillator (most often NaI: T1) and a vacuum photoelectron multiplier (PMT), as well as a high voltage photomultiplier power supply (High voltage source) and a scintillator temperature sensor (for use with temperature stabilization of the spectrometer scale); linear amplifier 2; a processor for detector pulses 3, including a differentiation circuit with "compensation of the pole zero" (P-Z-differentiator); Base-line stabilizer, two or three sections of active integrators, analogue-to-digital convenor (ADC), timing device for timing spectrometric pulses (Timing circuit), Pile-up inspector and corrector for the dead time corrector; controller with interface 4 (Controller & Interface) for controlling the processor of detector pulses and two-way communication with a computer.

The structures of scintillation spectrometers may slightly differ from those shown in FIG. 1. So instead of a vacuum photomultiplier tube (PMT), semiconductor photosensors can be used - silicon photodiodes (PhD), avalanche photodiodes (APhD) or silicon photomultipliers (SiPM). PhDs do not have an internal gain in the number of formed charge carriers (electrons and holes), and the gain in APhD is in the range of 50-100 times (for PMT and SiPM, the gain can reach 10 ⁶ times). If PhD or APhD is used instead of PMT, then a low-noise charge-sensitive preamplifier (ChA) is included between the output of the photosensor and the input of the linear amplifier to compensate for the absence or small self-amplification of these photosensors. The use of ChA in other cases is extremely undesirable, because Due to the long edges of the pulses generated during the integration of the current pulse by the charge-sensitive preamplifier, accurate timing to them is always difficult.

Scintillation flashes have the form of one or the sum of several exponentially decaying in time with a steep (0.1 ÷ 10 ns) front and a relatively slow decline [Akimov Yu.K. Photonic radiation registration methods. Dubna: JINR, 2014. 323 pp.]. The decay time constant of a light flash is called the scintillator decay time constant τ _d . For practical inorganic scintillators, τ _d lies in the range from 15 ns to several microseconds.

The most important characteristic of the spectrometer is the energy resolution, defined as the width of the peak of the total absorption of γ-rays with energy E _γ at half height (Full Width on Half Maximum - FWHM), as well as the relative energy resolution η = FWHM / E _γ . It is customary to characterize and compare scintillation γ-spectrometers by relative energy resolution on the ¹³⁷ Cs source line with an energy E _γ = 662 keV. The energy resolution of a scintillation spectrometer with PMT and SiPM has two main components [Moszynski M. et al. Temperature dependences of LaBr3 (Ce), LaCl3 (Ce) and NaI (T1) scintillators. Nucl. Instr. & Meth. in Phys. Res. A 568 (2006) 739-751]: intrinsic energy resolution η _int (inhomogeneities of the scintillation crystal) and statistical component η _st (probabilistic nature of the conversion of γ-quantum energies to the number of charge carriers). The total energy resolution η _{tot is} obtained by quadratic summation of these components:

The first component (η _int ) is determined by the material of the scintillator crystal and the technology of its growth. The second, and predominant, statistical component largely depends on how the electronic path of the spectrometer is built. The value of η _st is given by formula (2):

where N is the number of primary carriers of electric charge (photoelectrons).

where LY is the scintillator light output, i.e. the number of emitted light photons per 1 keV of energy of the absorbed γ-quantum or charged particle (LY≈35 for NaI: T1); QE is the quantum efficiency of the PMT photocathode or SiPM crystal (QE = 0.25 ÷ 0.43 for Hamamatsu photomultipliers in the region of emission wavelengths NaI.T1).

In ionizing radiation energy spectrometers, the electric quantity linearly related to the γ-quantum energy absorbed in the detector’s working substance is the pulse amplitude of the optimal shape (from the point of view of light collection and speed), measured using an analog-to-digital converter (ADC). The relative amplitude fluctuations at the ADC input will be the smaller, the more photons of light flashes and, accordingly, the primary electrons of the photosensor contribute to the formation of these amplitudes. Therefore, the first requirement for the generated pulses is the time T _peak for them to reach the amplitude (peak) value so that the scintillation flares decay to this level, for example, 5–10% (collection of 95–90% of photons).

The second requirement for the generated pulses follows from the statistical nature of the distribution of γ-quanta or charged particles in time and the need to use a spectrometer in intense radiation fields. The higher the radiation intensity (the number of γ-quanta per unit time) and the longer the generated pulses, the more probable their mutual overlap in time and, consequently, the distortion of their amplitudes. The most important spectrometer parameter characterizing its speed is microscopic dead time T _D [O. Ignatiev. Comparison of the capabilities of analog and digital x-ray spectrometers with semiconductor detectors. Analytics and Control (2006) No. 3-4, p. 223-232]. It is defined as the sum of the minimum possible time intervals between the moments of occurrence of a given spectrometric pulse, the previous and the next, at which there is no distortion due to overlapping amplitude V _{max of} this pulse. For an ideally designed spectrometer with time-invariant signal generation, T _{D is} simply equal to the sum of the times of reaching the maximum T _peak and the pulse decay T _F , i.e. the total duration T _{w of the} generated detector signal (Fig. 2). The duration of the decaying part of the generated detector pulses T _{F is} usually measured as the time from the maximum T _peak to the level of 1% or 0.1% V _max .

The dependence of the rate of accumulation of the amplitude codes R _o “cleaned” from the imposition of pulses on the intensity R _{i of the} γ-quanta detected by the scintillator is given by formula (4):

In FIG. Figure 3 shows dependence (4) for a spectrometer with a NaI: T1 scintillator under the conditions: τ _d = 225 ns; T _peak = 5.92 _τd ; T _w ≈16τ _d (quasi-Gaussian formation on 3 active integrators with τ _int = τ _d ). Note that with increasing statistical load at the spectrometer input above R _i ≥R _max , the spectrum accumulation rate decreases due to a decrease in the number of spectrometric pulses that are not distorted by mutual overlapping.

Thus, the properties of the scintillation γ-spectrometer will be optimal in terms of energy resolution and speed if the generated detector pulses reach a maximum at t = T _peak after the scintillation burst decays to the level of 5 ÷ 10%, and the decay time T _F satisfies the condition ( 5):

These requirements are quite easily satisfied in practice, if there is one scintillator flashing constant τ _d that is stable enough when the temperature changes. A spectrometer with the structure of FIG. 1 is intended for use in these conditions - scintillators LaBr ₃ : Ce and YAlO ₃ : Ce, used in [Belousov M.R. et al. Portable scintillation gamma-ray spectrometer STARK-01. Analytics and control V.15 (2011) No. 4. from. 429-438; Belousov M.R. et al. Scintillation spectrometer SBL-1 for the x-ray densitometer of radioactive technological solutions. Analytics and Control V. 17 (2013) No. 1, P. 21-26] indeed have one stable emission constant τ _d (16 ns for LaBr ₃ : Ce and 25 ns for YAlO ₃ : Ce).

Many of the scintillators used in commercial spectrometers, for example, NaI: T1, CsI: T1, LaCl ₃ : Ce, and others, have two or more emission components. A characteristic feature is that the slower the highlighting component, the more its time constant depends on temperature. Let us consider the properties of a spectrometer with the oldest and most widely used NaI: T1 scintillator under conditions of a wide range of changes in the ambient temperature.

Until relatively recently, it was generally accepted that the NaI: T1 scintillator has one stable emission time constant τ _d = 230 ns [Knoll GF Radiation Detection and Measurement. 3-rd Edition. New York, 1999 John Wiley & Sons, Inc. 802 p .; Akimov Yu.K. Photonic radiation registration methods. Dubna: JINR, 2014. 323 pp.]. Accordingly, when designing spectrometers with this scintillator, their structure and settings were created based on this value of τ _d [Drndarevic V. et al. Amplifier with time-invariant trapezoidal shaping and shape-sensitive pileup rejector for high-rate spectroscopy. IEEE Trans, on Nucl. See. (1989) v. 36, No. 1, p. 1326-1329; Dudin SV et al. A fast signal processor for Nal (TI) detectors. Nucl. Instr. and Meth. in Phys. Res. A 352 (1995) 610-613]. In the first work, the statistical load at the input R _i ≥3 × 10 ⁵ 1 / s at T _peak ≈345 ns T _D ≈575 ns was achieved, and in the second, R _i ≥10 ⁶ 1 / s at T _peak ≈225 ns T _D ≈1250 ns.

In the work [Moszynski M. et al. Temperature dependences of LaBr3 (Ce), LaCl3 (Ce) and NaI (T1) scintillators. Nucl. Instr. & Meth. in Phys. Res. A 568 (2006) 739-751] showed that the scintillator NaI: T1 is characterized by at least two emission components with very strong temperature dependences of their parameters. In FIG. 4 shows the temperature dependences of the intensities, and in FIG. 5 - constants of flashing time. From the above dependencies, the conclusions follow:

1. When constructing a high-speed spectrometer, it is necessary to take into account the slow emission component. Its contribution to the light flash energy at room temperature is about 20%, and the time constant τ _{ds is} almost 5 times greater than the time constant of the main, fast component, τ _df ≈225 ns.

2. The influence of the slow component increases with decreasing temperature below room temperature.

The real shape of the photocathode current pulse for the NaI.T1 scintillator (without taking into account statistical fluctuations and without taking into account the ultrafast component, the presence of which is not confirmed by other works) is shown in FIG. 6. The time dependence of the number of emitted light photons (formed in the material of the electron photocathode) normalized to unity is also given, which makes it possible to estimate the required value of T _peak , at which 90 or 95% of the flash photons will contribute to the value V _{max of the} generated detector pulse. From the graph of the time dependence of the number of emitted photons, we can conclude that the moment of measurement of the amplitude must satisfy condition (6):

The signal obtained after integrating the photosensor current pulse with 3 active integrators (sometimes limited to 2) with an integration constant τ _int = τ _df = 225 ns is shown in FIG. 7. The parameters of this pulse are as follows: T _peak = 1.22τ _ds ; T _w ≈T _D = 4,5τ _ds ; T _w / T _peak ≈ 3.68 (an ideal Gaussian is characterized by T _w / T _peak ≈ 2.0). In the absence of a slow emission component, the generated pulse would be much more symmetrical, and the microscopic dead time would be much less: T _peak = 1.20τ _ds ; T _w ≈T _D = 3.0τ _ds ; T _w / T _peak ≈2.5. It is for these parameters that the transfer characteristic of the spectrometer, shown in FIG. 3. The task of obtaining shorter formed detector pulses, while condition (6) is fulfilled and, accordingly, the increase in speed of the spectrometer is partially solved in a standard way - by shortening the one shown in FIG. 6. a two-component exponential pulse with the help shown in FIG. 1 differentiation schemes with "compensation of the pole zero" (PZ-differentiator). Moreover, due to the fact that the pulse consists of two components, it is impossible to obtain a single-component unipolar pulse with an arbitrarily small decay time constant at the output of the differentiator. A scintillation burst LF (t) in the presence of two emission components in the first approximation is described by expression (7):

where E _γ is the energy left by the γ-quantum in the substance of the scintillator;

LY - light output of scintillator, photons per keV of absorbed energy;

A _f and A _s are the relative intensities of the fast and slow components;

τ _df and τ _ds are the time constants of the emission of the fast and slow components.

The current pulse I (t) at the photocathode of the photoelectron multiplier (or other photosensor) is described by the same function with the corresponding coefficients:

where QE is the quantum efficiency of the photosensor.

If the current (or voltage) impulse represented one exponent, for example, the slow I _s (t), and was described by the second part of expression (8), then by choosing the differentiator parameters accordingly, an exponential impulse would be obtained at its output with any number decreased times the time constant τ _out = R ₁ ⋅ R ₂ C / (R ₁ + R ₂ ). Indeed, applying the Laplace transform, we have the image of the pulse at the input of the PZ-differentiator:

where p is the complex variable of the Laplace transform.

The transfer function of the P-Z-differentiator in the operator form is given by the expression (10):

where m is a coefficient showing how many times τ _in decreases.

Coefficient m, for that shown in FIG. 1 implementation of the differentiator is equal to:

If we choose R ₁ C = τ _in = τ _ds , then by multiplying (9) and (10) and shortening the brackets in the denominator (9) and in the numerator (10), we again obtain the operator function that describes the exponential signal, but already with a time constant τ _out , which is m times smaller than the initial τ _ds . This is the compensation of the pole (denominator) of the signal image by the zero (numerator) of the transfer function of the differentiator.

In the case when the pulse is a superposition of 2 or more exponentials, an attempt to perform “short” differentiation when τ _out ≤ τ _df only leads to the formation of emission signals of opposite polarity due to the fact that the differentiator parameters are not consistent with the constant time exponent fast. The resulting surge increases the duration of the generated detector pulses T _w , and the speed of the spectrometer decreases. In FIG. Figure 8 shows the action of a differentiator with pole compensation by zero on both components and on the pulse as a whole, which is their superposition. A strictly unipolar impulse is obtained for m = 1.195. In this case, a negative outlier with an amplitude of ≈1% of V _max generated by the fast component is compensated by the shortened slow component. A stronger shortening (m> 1.195) leads to an increase in the ejection of the fast component, the formation of a negative ejection in the total pulse and, consequently, an increase in its duration. After integration with 3 active integrators with τ _int = τ _df = 225 ns, a quasi-Gaussian pulse is formed with the parameters: T _peak = 1.2τ _ds ; Tw = T _D = 3.0τ _ds ; T _w / T _Peak ≈2.5. The same parameters are achieved when the initial pulse has only one fast component. If the initial current pulse consists of a larger number of components, for example 3, as in the case of the CsI: T1 scintillator [Grodzicka M. et al. Characterization of CsI: T1 at a wide temperature range (-40 ° C to + 22 ° C). Nucl. Instr. & Meth. in Phys. Res. A 707 (2013) 73-79], where τ ₁ = 730 ns (47.5%), τ ₂ = 3.1 μs (30%), τ ₃ = 16 μs (22.5%), then a single shortening of the initial pulse with pole compensation of zero, it turns out to be ineffective. To collect 95% of the photons, it is necessary to provide T _peak = 1.5τ ₃ , and the admissible value of the degree of shortening without the formation of an outlier is m = 1.25. 3-fold active integration with τ _int = 1.5τ ₂ gives quasi-Gaussian pulses with the desired value of T _peak (1.5τ ₃ ) and unimportant symmetry - the ratio T _w / T _peak ≈3.1. This is significantly worse than in the case of integration of 2-component signals from NaI: T1 (here T _w / T _peak ≈ 2.70).

Another disadvantage of the classic scintillation spectrometer prototype [Belousov M.R. et al. Portable scintillation gamma-ray spectrometer STARK-01. Analytics and control V. 15 (2011) No. 4. from. 429-438] with crystals having several luminescence components, it is associated with a significant change in the time constants of the scintillation components under the influence of temperature (see Fig. 5, for example). In FIG. 9 based on data from [Moszynski M. et al. Temperature dependences of LaBr3 (Ce), LaCl3 (Ce) and NaI (T1) scintillators. Nucl. Instr. & Meth. in Phys. Res. A 568 (2006) 739-751] presents the change in the generated detector pulse when the temperature decreases from room temperature to -22 ° C (a typical situation for portable γ-spectrometers in the field, where the permissible lower temperature limit can be -25 ° C).

It can be seen that the duration of the generated detector pulse T _w and, accordingly, the microscopic dead time T _D increase by 2 times, i.e. with decreasing temperature, the speed of the spectrometer decreases by the same number of times. This is critically many.

The disadvantages of the scintillation spectrometer prototype [Belousov M.R. et al. Portable scintillation gamma-ray spectrometer STARK-01. Analytics and control V. 15 (2011) No. 4. from. 429-438] are as follows:

1. With two or more scintillator emission components, there are limitations to the permissible degree of shortening of the detector pulses - only the slowest component can be shortened and after shortening it remains slower than the previous, faster component.

2. Due to the strong temperature dependence of the emission time constants of the scintillation burst components, the optimal shortening of the primary detector pulses is possible only in a narrow temperature range.

The objective of the invention is to provide a gamma spectrometer with scintillators having several emission components, in which the energy of scintillation flashes is fully transformed into the amplitudes of electrical pulses, whose duration is minimal to achieve maximum speed and is stable over a wide range of operating temperature.

This problem is solved by the fact that the spectrometer, the processor of the detector pulses of which may contain a shortening circuit with pole compensation by zero, introduces additional similar shortening circuits with time constants from the inputs that are pairwise equal to the time constants of the exponential components of the primary electric pulse that are shortened at the output of the optically coupled with a photosensor scintillator, while the time constants from the outputs of the mentioned circuits are chosen large, the decay time constant of the nearest faster component to prevent the formation of an outlier of opposite polarity, and the time constants on the input side of the shortening circuits tuned to the exponential components of the primary signal automatically change when the operating temperature changes in accordance with the laws of the temperature change of the scintillator emission components.

The implementation of the spectrometer is shown in FIG. 10, where one of the possible designs is given. The inventive spectrometer contains in series: a detecting module 1, consisting of an optically connected inorganic scintillator with two or more emission constants and a vacuum (PMT) or semiconductor (SiPM) photomultiplier tube, as well as a high voltage photomultiplier power supply (high voltage source) and a scintillator temperature sensor ; linear amplifier 2; differentiation module 3, containing at least one differentiator with "compensation of the pole zero", whose time constant on the input side is consistent with the time constant of emission of the slowest component of the scintillation flash and varies as a function of the temperature of the scintillator synchronously with the temperature of the aforementioned radiation constant, and the constant time on the output side exceeds the time constant of the flashing of the nearest faster component; detector pulse processor 4, including a differentiator with “pole-zero compensation”, matched by input to one of the fast scintillator emission components, a baseline stabilizer, two or three sections of active integrators, an analog-to-digital converter, a spectrometer pulse timing device, an inspector superimposed pulses and corrector "dead" time of the spectrometer; controller with interface 5 for controlling the processor of detector pulses and two-way communication with a computer.

The main differences of the inventive scintillation γ-spectrometer shown in FIG. 10 from the spectrometer prototype in FIG. 1, are as follows:

1. Differentiation module 3 has been introduced, containing one or more differentiators with "zero pole compensation". The total number of differentiators, including the detector pulses 4 available in the processor, is equal to the number of exponential components of the primary electric signal to be shortened. The input time constants of each of the differentiators are matched in pairs with the time constants of the components of the primary electric pulse to be shortened, and the output time constants must exceed the time constant of the nearest faster pulse component.

2. The time constants on the input side of the differentiators, designed to shorten the slow components of the pulse, change synchronously and in the same direction with a change in temperature as the corresponding scintillator time constants. For this, the temperature sensor of the scintillation crystal available in the detection module is used and the temperature dependences of the values of the slow illumination constants stored in the controller 5 are used.

The shortening of multicomponent detector pulses using the NaI: T1 scintillator as an example is illustrated in FIG. eleven.

The "PZ" differentiator 3 in FIG. 10 is tuned to the slow emission component of the NaI: T1 scintillator, i.e. τ _in1 = τ _ds = 1.1 μs. At room temperature, its “output” time constant is τ _out1 = τ _ds / 1,195, as described above. The initial part of the pulse at its output and its component components is shown in FIG. 11a (repeats FIG. 8). The second "PZ" -differentiator, located in this case in the processor of the detector pulses 4, is consistent with the fast emission component, i.e. τ _in2 = τ _df = 0.225 μs. The condition for obtaining a unipolar pulse with a minimum duration at the output of this differentiator is τ _out2 = τ _df / 1.25. The shape of the pulse at the output of the second “PZ” -differentiator and the two components comprising it are shown in FIG. 11b. A comparison of the graphs shows that the unipolar impulse is again obtained by mutual compensation of the twice shortened unipolar slow component and the negative part of the twice shortened fast component, whose transition through zero after the second shortening with the coefficient n = 1.25 occurs earlier. The result is a shorter unipolar pulse with an effective time constant τ _eff <τ _df . With a very high degree of accuracy, it can be argued that τ _eff = τ _df / n = 225 / 1.25 = 180 ns.

The possibility of obtaining shorter and strictly unipolar pulses in this way is proved mathematically rigorously.

The finally formed detector pulse (two “PZ” derivations and 3 stages of active integration) has the parameters: microscopic dead time T _D = T _w = 2.9τ _ds ; maximum time Tpeak = 1.15; T _w / T _peak ≈2.5.

With decreasing ambient temperature, due to the introduced adjustments of the "input" time constants τ _in1 and the first τ _in2 "PZ" differentiators according to the readings of the temperature sensor of the scintillation crystal, the shape of the generated detector pulses at the input of the analog-to-digital converter is constant. In FIG. Figure 12 shows the effect of the NaI scintillator temperature: T1 (Т = -20 ° C) on the shape of a quasi-Gaussian pulse under the following conditions: τ _ds = 1.6 μs, A _s = 0.6, τ _df = 450 ns, A _f = 0, 4 under conditions when the time constants of both differentiators are automatically adjusted (solid lines) and in the case of auto-tuning only τ _in1 (dashed line).

Comparing the data of FIG. 9 and FIG. 12, it can be seen that the temperature self-tuning of the time constant of only the “slow” differentiator 3 in FIG. 10 does not provide complete invariance of the pulse shape to temperature changes in the scintillator constants. The introduction of a second “P-Z” differentiator with a temperature-locked loop of the input time constant into the spectrometer structure is justified even when, under normal conditions, the shape and duration of the pulses after a single shortening can be considered satisfactory.

One of the possible technical implementations of the “P-Z” differentiator with the temperature-controlled time constant on the input side is shown in FIG. 13.

Shown in the circuit "a", the resistor R _adj plays the role of a variable divider of the pulse voltage supplied to R _i . When the engine R _{adj is} in its highest position, τ _in = C _d R _i . When the engine R _{adj is} in the lowest position, τ _in = ∝, i.e. The "P-Z" -differentiator turns into a regular CR-differentiator and at its output a unipolar pulse is obtained only in one case - when the voltage step that is infinite in time acts at the input. In practice, they always strive to fulfill the condition R _adj >> R _i . This ensures the constancy of the "output" time constant determined by the product of C _d by the resistance at the junction point R _i , R _o and C _d . The buffer cascade isolates the differentiator from the influence of subsequent electronic circuits.

Scheme "b" is completely similar to that considered. The role of the resistor R _adj here is performed by a linear amplifier with program-controlled gain (available in the form of microcircuits). With the indicated limits of gain variation, the effective value of τ _in can vary with a certain step within τ _{in_eff} = C _d R _i / (0.2 ÷ 5).

The technical result of the application of the inventive scintillation gamma-ray spectrometer is that the speed increases and the temperature range of the use of spectrometers with scintillation crystals, having two or more emission components with a significant temperature dependence of the emission constant, is expanded.

The list of figures of graphic images.

FIG. 1. Generalized structure of a classical scintillation γ-spectrometer

FIG. 2. Determination of microscopic dead time T _D. The arrows indicate the moments of occurrence of gamma rays initiating the generated detector pulses

FIG. 3. Transfer characteristic of a spectrometer with a NaI scintillator: T1

FIG. 4. Temperature dependences of the intensities of the NaI: T1 flashing components. Fast - fast (main) component; superfast - superfast component; slow - slow

FIG. 5. Temperature dependences of the luminescence time constants NaI: T1

FIG. 6. NaI: T1 flare shape and normalized time dependence of the number of emitted photons. The time in units of slow flash constant τ _ds = 1.1 μs

FIG. 7. Formed detector pulse at the output of the 3rd active integrator

FIG. 8. The action of the differentiator, consistent with the parameters of the slow component on the components of the pulse and on the pulse as a whole. The bases of the pulses are shown. The fast component is described by 2 exhibitors

FIG. 9. The temperature change of the generated pulse with a 1.195-fold shortened slow component for a spectrometer with a NaI: T1: τ _ds crystal increases with decreasing temperature to -22 ° C from 1.1 to 1.6 μs, the relative intensity A _s increases from 20 to 40% with a decrease in the relative intensity of the fast component from 80 to 60%

FIG. 10. The structure of the inventive scintillation γ-spectrometer

FIG. 11. The initial parts of the pulses after the first (a) and second (b) shortenings. The shortened fast component is described by 2 exhibitors

FIG. 12. Amplitude-normalized quasi-Gaussian pulses of a spectrometer with a NaI: T1 crystal and self-tuning of input time constants of “P-Z” differentiators at two temperatures. The solid line is the auto-tuning of the two differentiators, the dotted line is the auto-tuning of the differentiator of the slow component

FIG. 13. "PZ" -differentiators: a standard circuit with manual adjustment of the "input" time constant (a) and a differentiator with programmed control of the "input" time constant (b). A _adj - linear amplifier with programmable gain

Claims (1)

Scintillation spectrometer of ionizing radiation, containing a scintillation crystal with several emission components, for example, CsI: T1 or NaI: T1; a temperature sensor of the scintillation crystal and an internal-amplified photosensor in optical contact with the scintillation crystal, the output of which is connected to a low-impedance input of the electronic channel, including a linear amplifier, a processor of detector pulses and a controller with an interface of external devices, characterized in that between the output of the linear amplifier and analog the input of the processor of the detector pulses includes one or more differentiating circuits "with pole-zero compensation", time constants which, on the input side, are equal to the scintillator flashing time constants in pairs, and the time constants on the output side of the mentioned circuits are chosen larger than the decay time constant of the nearest faster component, while the differentiating circuits tuned by the inputs to the scintillator flashing constants with a significant dependence on the scintillator temperature, equipped with automatic adjustment devices according to the commands of the constant time controller from the input side to the temperature changes of the aforementioned nnyh decay time.

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