RU2837644C1 - Scintillation detector - Google Patents

Abstract

FIELD: measuring.

SUBSTANCE: invention relates to detection of ionizing radiation. Detector, intended for detecting ionizing radiation, contains SrI₂(Eu) scintillators and an array of silicon photomultipliers SiPM, wherein includes a combination of four individual scintillation crystals SrI₂(Eu), with formation of structure of matrix of silicon photomultipliers SiPM, in which each scintillation crystal is connected to four SiPMs, connected through coincidence and signal coding circuits with SiPM of neighbouring crystals, which provide suppression of dark noise SiPM, lowering the detection threshold and the number of signal pickup channels equal to the number of crystals in the detector.

EFFECT: high efficiency of detecting radiation, suppressing thermal noise of photodetectors and reducing the energy threshold for detecting signals with a minimum number of electronic reading channels.

1 cl, 4 dwg

Description

Field of technology to which the invention relates

The invention relates to highly efficient scintillation detectors of ionizing radiation with an ultra-low threshold for registering energy releases and can be used in nuclear and atomic physics, in radiometric and spectrometric equipment. As a rule, such equipment uses classical inorganic scintillators NaI(Tl), CsI(Tl) or their analogues. Such scintillators of a relatively large volume with a high light output provide an energy threshold for registering radiation at a level of 20-40 keV, and individual detectors of small sizes can have a registration threshold of 10 keV. These detectors cannot provide a lower registration threshold, since classical scintillators have a light output of less than 60,000 photons/MeV, and standard photomultipliers have a quantum efficiency of less than 30%. As a rule, a uniquely high light collection can only be obtained from a small-sized scintillator with a volume of the order of several cubic centimeters, which limits the efficiency of detecting ionizing radiation, especially X-rays and gamma radiation.

State of the art

Technical solution RU 2 750 130 C1 is known - SEARCH SCINTILLATION DETECTOR OF GAMMA RADIATION FOR WORK IN A WIDE TEMPERATURE RANGE. The patent describes a scintillation detector based on a scintillator with a high light output NaI(Tl) or CsI(Tl) and a SiPM photodetector. The invention achieved an event detection threshold of 40 keV in the temperature range from -65°C to 70°C.

Also known is the technical solution RU 2 225 017 C2 - METHOD OF DIFFERENTIAL STABILIZATION OF THE SPECTROMETRIC CHANNEL OF THE SCINTILLATION UNIT OF DETECTING GAMMA RADIATION BY A REFERENCE PEAK. The patent describes a method of reducing the registration threshold of a scintillation detector based on a NaI(Tl) scintillator and a photomultiplier. The patent also describes a method of signal analysis, which made it possible to reduce the registration threshold to 15 keV.

The closest to the claimed solution is the SC-MacroPixel-MCA gamma-ray detector manufactured by CapeScint (USA) (https://capescint.com/wp-content/uploads/Scintillation-Probe-SC-MacroPixel-MCA-Datasheet.pdf). This detector consists of a single SrI ₂ (Eu) scintillator measuring 14x14x25.4 mm ³ and a matrix of four silicon photomultipliers. The declared energy threshold of registration is 10 keV. Such a relatively low threshold of registration is provided by the unique light output of the SrI2 (Eu) scintillator, about 100-120 thousand photons/MeV, and the small size of the crystal, providing the best light collection. The disadvantage of this device is the low efficiency of radiation registration, due to the small size of the scintillator, and the high thermal noise of the photodiode matrix, which does not allow the registration threshold to be reduced below 10 keV.

Disclosure of the essence of the invention

The task that the claimed invention is aimed at solving is the creation of a highly efficient detector of ionizing radiation with an energy detection threshold of about 1 keV.

The technical result consists in increasing the efficiency of radiation registration, suppressing thermal noise of photodetectors and reducing the energy threshold for signal registration with a minimum number of electronic reading channels.

The technical result is achieved in that the detector intended for recording ionizing radiation, containing a SrI2(Eu) scintillator and a matrix of silicon photomultipliers SiPM, is distinguished by the fact that it includes four individual SrI2(Eu) scintillation crystals, with the formation of a structure of a matrix of silicon photomultipliers SiPM, in which each scintillation crystal is connected to four SiPM, connected through coincidence circuits and signal encoding with SiPM of adjacent crystals, which provide suppression of dark noise of SiPM, lowering of the registration threshold and maintaining the number of signal pickup channels equal to the number of crystals in the detector. The use of four crystals provides a large volume of the scintillator, necessary for effective recording of ionizing radiation. At the same time, individual signal pickup from each crystal provides optimal light collection and a minimum energy registration threshold, which is additionally reduced due to the coincidence circuits used in the SiPM matrix. The combined use of coincidence and coding circuits provides a number of signal acquisition channels equal to the number of individual crystals in the detector, which allows the use of standard analog-to-digital converter microcircuits with four analog inputs.

Brief description of the drawings

Fig. 1 shows the structure of the detector module consisting of four SrI2(Eu) crystals and a matrix of silicon photomultipliers having direct optical contact with the scintillators. On the left is the structure of the matrix of photodetectors from individual SiPMs with individual numbers from 1 to 16, indicated in the figure. On the right is a side view of the detector. 17 - individual scintillation crystals, 18 - SiPM matrix.

Fig. 2 shows the organization of coincidence circuits and coding of signals from the detector module for suppressing the dark current of SiPM. Due to the coding of the channels for reading signals from different scintillation crystals, the number of reading electronic channels remains minimal and equal to the number of crystals used in the detector module. 1-16 – serial numbers of individual silicon photomultipliers of the SiPM matrix; 19 – comparators; 20 – coincidence circuits; 21 – circuit or, generating a common trigger for recording an event.

Fig. 3 shows the spectrum of low-amplitude signals from the detector, demonstrating the detector's operation in the single-photon counting mode and used for calibrating the detector. Here, the peaks in the order of increasing amplitude correspond to the registration of one, two, and three photons.

Fig. 4 shows the low-energy part of the energy release spectrum from the gamma source ²⁴¹ Am in a scintillation detector. The numbers indicate the energies in keV of the corresponding gamma lines. The left peak, corresponding to an energy of 2 keV, demonstrates the possibility of using the detector to register events with an energy release of 1 keV.

Implementation of the invention

The approaches proposed above were tested on an experimental detector consisting of four SrI2(Eu) scintillation crystals, each measuring 15x15x25 mm ³ . These crystal sizes were chosen as optimal for light collection and signal reading using four photodiodes, each measuring 6x6 mm ² . The length of the crystal ensures low light absorption inside the scintillator itself. The structure of the detector module, consisting of four SrI2(Eu) crystals, and a photodiode matrix having direct optical contact with the scintillators is shown in Fig. 1.

In order to reduce the energy threshold of registration, a scheme of coincidences and encoding of signals from the SiPM matrix is implemented, shown in Fig. 2, which allows to significantly reduce the thermal noise of silicon photomultipliers while maintaining the minimum number of channels of the readout electronics. As can be seen in Fig. 2, every two SiPMs of one crystal are combined with two SiPMs of the neighboring crystal. Thus, a cross-combination of individual photomultipliers from different crystals occurs. Registration of an event in one crystal leads to the operation of two SiPM groups, the signals from which are fed to comparators 19, and then to the coincidence scheme 20. The generation of a common trigger for recording an event in the amplitude-to-digital converters occurs in the common OR scheme 21. The resulting specific light collection of the presented detector exceeds the value of 30 photoelectrons/keV, which allows to set the threshold in each of the comparators at the level of 15 photoelectrons. Simultaneous operation of two comparators and, accordingly, one of the coincidence schemes provides a registration threshold of about 1 keV. This threshold is confirmed by the low-energy part of the spectrum from the radioactive source ²⁴¹ Am, shown in Fig. 3. The leftmost peak with an energy of 2 keV corresponds to electron transitions in the shells of the strontium atom, which is part of the scintillator.

Claims (1)

A detector intended for recording ionizing radiation, containing SrI ₂ (Eu) scintillators and a matrix of SiPM silicon photomultipliers, characterized in that it includes a combination of four individual SrI ₂ (Eu) scintillation crystals, with the formation of a structure of a matrix of SiPM silicon photomultipliers, in which each scintillation crystal is connected to four SiPMs connected through coincidence circuits and signal encoding with SiPMs of adjacent crystals, which ensure suppression of SiPM dark noise, a decrease in the registration threshold and a number of signal pickup channels equal to the number of crystals in the detector.