Probe and method for measuring lifetime of fission neutron-rich nuclear state

Abstract

The present invention relates to the technical field of nuclear radiation energy spectrum measurement, and in particular to a probe and method for measuring the lifetime of fission neutron-rich nuclear states, wherein a photomultiplier tube is coupled to the exit end of a main detector, a secondary detector is arranged around the periphery of the main detector, and the secondary detector forms an exit window toward the end of the photomultiplier tube; a photon information readout device is coupled to the exit window of the secondary detector. The main detector is used to detect the full energy peak event of a target gamma ray, and the Compton scattered photons escaping from the main detector are detected by the peripheral secondary detector to output signals, and are anti-coincident with the output signal of the main detector, so that the Compton scattering events that pass through the main detector and enter the scintillation crystal are not recorded, thereby effectively reducing the Compton continuous background in the gamma energy spectrum, achieving the purpose of suppressing the Compton effect and improving the peak-to-Compton ratio, being beneficial to energy spectrum analysis, and realizing high-precision measurement of the nuclear state lifetime of fission neutron-rich nuclear fragments.

Description

Technical Field

[0001] The invention relates to the technical field of nuclear radiation energy spectrum measurement, and in particular to a probe and a method for measuring the lifetime of a fission neutron-rich nuclear state. Background Art

[0002] The energy level lifetime of an atomic nucleus is a very important physical quantity that characterizes the nuclear state and is also one of the important parameters in nuclear spectroscopy research. The transition probability and deformation parameters between energy levels can be obtained by measuring the lifetime. The transition probability of the atomic nucleus energy level can accurately reflect the intrinsic properties of the atomic nucleus and is one of the most important contents in nuclear structure research. The transition probability described in theory is directly related to the wave function of the initial and final states of the transition. Affected by the assumptions of the nuclear structure model, measuring the energy level lifetime is the best test of the theoretical model.

[0003] The spontaneous fission fragments of the experimental target nucleus are often distributed in the light and heavy fission fragment regions, and the lifetimes of most nuclear states in the fission fragments are unknown. Among them, about 7% of the fission fragments have isobaric states. At present, the β-γ-γ coincidence technique is mostly used to measure the excited state of the fission of neutron-rich nuclei with lifetimes in the ps-ns order. In order to measure the excited state lifetime of atomic nuclei with high precision, an anti-Compton spectrometer is often used to suppress the Compton effect, which is more conducive to energy spectrum analysis. The conventional anti-Compton instrument is composed of a high-purity germanium (HPGe) main detector and a bismuth germanate (BGO) secondary detector. When the gamma rays emitted by the sample under test are incident on the main detector, the photons that undergo the Compton effect will generate non-full-energy peak signals, and will be scattered into the signals generated by the anti-coincidence shielding detector. These signals are not recorded by the spectrometer through the anti-coincidence electronic circuit, which can reduce the Compton continuous background in the gamma energy spectrum, thereby suppressing the Compton effect and improving the peak-to-Compton ratio.

[0004] However, the gamma energy spectra measured by traditional anti-Compton instruments often have problems such as low peak-to-Compton ratio and low Compton suppression factor. They are also relatively expensive, have poor adaptability to the environment, and have limitations in long-term stability and performance. They cannot meet the demand for high-precision measurement of ps-ns nuclear state lifetimes of fission neutron-rich fragment nuclei. Summary of the invention

[0005] The present invention provides a probe and method for measuring the lifetime of fission neutron-rich nuclear states, so as to solve the defects of low peak-to-Compton ratio and low Compton suppression factor in the gamma energy spectrum measured by the traditional anti-Compton instrument, and realize the high-precision measurement of the ps-ns level nuclear state lifetime of fission neutron-rich fragment nuclei.

[0006] The present invention provides a probe for measuring the lifetime of a fission neutron-rich nuclear state, comprising a main detector, a photomultiplier tube, a secondary detector and a photon information readout device, wherein one end of the main detector is constructed with a photon incident port, and the other end is constructed as an output end; the photomultiplier tube is coupled to the output end of the main detector and is externally connected to a data acquisition system of a mass spectrometer; the secondary detector is arranged around the periphery of the main detector, and an output window is constructed at the end of the secondary detector facing the photomultiplier tube; the photon information readout device is coupled to the output window of the secondary detector and is externally connected to the data acquisition system of the mass spectrometer.

[0007] According to a probe for measuring the lifetime of a fission neutron-rich nuclear state provided by the present invention, the main detector is a cerium-doped lanthanum bromide crystal, and the secondary detector is a thallium-doped cesium iodide crystal.

[0008] According to a probe for measuring the lifetime of a fission neutron-rich nuclear state provided by the present invention, the main detector is cylindrical, the secondary detector is annular, and the main detector is entirely penetrated and fixed inside the annular hole of the secondary detector.

[0009] According to a probe for measuring the lifetime of a fission neutron-rich nuclear state provided by the present invention, the secondary detector includes a plurality of arc-shaped anti-Con units, and the plurality of anti-Con units are assembled around the periphery of the main detector to form the secondary detector, and the anti-Con units are constructed toward the end of the photomultiplier tube to form an exit window.

[0010] According to a probe for measuring the lifetime of a fission neutron-rich nuclear state provided by the present invention, the photon information readout device includes a plurality of silicon photomultiplier tubes of the same size, and the plurality of silicon photomultiplier tubes of the same size are spliced ​​at the exit window of the secondary detector to form a silicon photomultiplier tube readout circuit.

[0011] According to a probe for measuring the lifetime of fission neutron-rich nuclear states provided by the present invention, except for the surface coupled to the photomultiplier tube, the remaining surfaces of the main detector are covered with a reflective layer; except for the outer surface coupled to the photon information readout device, the remaining outer surfaces of the secondary detector are also covered with the reflective layer.

[0012] According to a probe for measuring the lifetime of a fission neutron-rich nuclear state provided by the present invention, the reflective layer is covered with a shielding shell.

[0013] According to a probe for measuring the lifetime of a fission neutron-rich nuclear state provided by the present invention, the reflective layer is an ESR reflective film, and the shielding shell is an aluminum shell.

[0014] According to a probe for measuring the lifetime of a fission neutron-rich nuclear state provided by the present invention, a flange is provided on the outer peripheral fixing sleeve of the photomultiplier tube, and the flange is used to be fixedly connected to an external detector bracket; a plurality of through holes are provided on the flange, and the through holes are used to pass external cables.

[0015] The present invention also provides a method for measuring the lifetime of a fission neutron-rich nuclear state, which is applicable to any of the above-mentioned probes for measuring the lifetime of a fission neutron-rich nuclear state, comprising: a neutron-rich nucleus fissions into an excited state, and after deexcitation, a gamma ray is released into a main detector, and the gamma ray undergoes a Compton effect in the main detector; based on the main detector detecting the gamma ray full energy peak event, a full energy peak signal is generated, and the generated full energy peak signal is introduced into a data acquisition system of a mass spectrometer through a photomultiplier tube; based on a secondary detector capturing Compton scattered photons or single escaped photons from the main detector The 0.511MeV gamma rays that escape and double escape generate Compton scattering signals, which are introduced into the data acquisition system of the mass spectrometer through the photon information readout device; the total energy peak signal is anti-coincided with the Compton scattering signal obtained by the data acquisition system of the mass spectrometer to exclude simultaneous events and remove the interference of Compton scattered photons to generate a gamma energy spectrum, and the gamma rays of known different energies generated after the deexcitation of the fission fragments are selected from the anti-coincided gamma energy spectrum to be consistent with the time spectrum of the main detector, and the difference between the two times is the nuclear state lifetime of the fission neutron-rich.

[0016] The probe and method for measuring the lifetime of fission neutron-rich nuclear states provided by the present invention is a compact anti-coincidence gamma ray detection probe composed of a main detector and a secondary detector. The main detector and the secondary detector have different decay times. The main detector is used to detect the target gamma ray full energy peak event, and the secondary detector is used to detect the escaped Compton scattering event, so as to achieve the purpose of anti-coincidence measurement. When the gamma ray enters the main detector, if the photons after Compton scattering escape the main detector, most of them will be absorbed by the secondary detector and recorded. The pulses recorded by the main detector and the secondary detector are input into the linear pulse amplifier respectively, and then the two pulses are simultaneously input into the analysis channel and anti-coincidence channel of the anti-coincidence circuit. The pulses output by the anti-coincidence circuit exclude time-correlated events, that is, the Compton scattered photons escaping from the main detector are detected by the output signal of the peripheral secondary detector, and anti-coincident with the output signal of the main detector, so that the Compton scattering events that pass through the main detector and enter the scintillation crystal are not recorded, thereby effectively reducing the Compton continuous background in the gamma energy spectrum, achieving the purpose of suppressing the Compton effect and improving the peak-to-Compton ratio, which is beneficial to energy spectrum analysis and realizes high-precision measurement of the nuclear state lifetime of fission neutron-rich nuclear fragments. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 The present invention is a schematic diagram of the appearance of a probe for measuring the lifetime of a fission neutron-rich nuclear state.

[0019] Figure 2 The present invention is a schematic diagram of the cross-sectional structure of a probe for measuring the lifetime of a fission neutron-rich nuclear state.

[0020] Figure 3 It is a structural schematic diagram of the main detector and the photomultiplier tube provided by the present invention.

[0021] Figure 4 It is a top view schematic diagram of the secondary detector provided by the present invention.

[0022] Figure 5 It is a side view schematic diagram of the anti-kang unit provided by the present invention.

[0023] Figure 6 It is a front view schematic diagram of the anti-kang unit provided by the present invention.

[0024] Figure 7 It is the standard source before and after the inversion of the fission neutron-rich nuclear state lifetime measurement process provided by the present invention. 60 Co energy spectrum.

[0025] Figure 8 It is the standard source before and after the inversion of the fission neutron-rich nuclear state lifetime measurement process provided by the present invention. 137 Cs energy spectrum.

[0026] Figure numerals: 1. main detector; 2. photomultiplier tube; 3. secondary detector; 4. photon information readout device; 5. reflection layer; 6. shielding shell; 7. flange; 8. through hole. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] In the description of the embodiments of the present invention, it should be noted that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present invention.

[0029] In the description of the embodiments of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the embodiments of the present invention can be understood according to specific circumstances.

[0030] In the embodiments of the present invention, unless otherwise clearly specified and limited, the first feature being "above" or "below" the second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, the first feature being "above", "above" and "above" the second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. The first feature being "below", "below" and "below" the second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0031] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the embodiment of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0032] Combine the following Figures 1 to 8 The probe and method for measuring the lifetime of fission neutron-rich nuclear states of the present invention are described.

[0033] One embodiment of the present invention provides a probe for measuring the lifetime of a fission neutron-rich nuclear state, in combination with Figure 1 and Figure 3As shown, the probe includes a main detector 1, a photomultiplier tube 2, a secondary detector 3 and a photon information readout device 4, wherein one end of the main detector 1 is constructed with a photon incident port, and the other end is constructed as an output end; the photomultiplier tube 2 is coupled to the output end of the main detector 1, and is externally connected to the data acquisition system of a mass spectrometer; the secondary detector 3 is arranged around the outer periphery of the main detector 1, and the end of the secondary detector 3 facing the photomultiplier tube 2 is constructed with an output window; the photon information readout device 4 is coupled to the output window of the secondary detector 3, and is externally connected to the data acquisition system of a mass spectrometer.

[0034] It is understandable that the probe for measuring the fission neutron-rich nuclear state lifetime of this embodiment is a compact anti-coincidence gamma-ray detection probe composed of a main detector 1 and a secondary detector 3, which can improve the accuracy of measuring the ps-ns level nuclear state lifetime of fission neutron-rich fragment nuclei. It is necessary to understand that the decay time of the main detector 1 and the secondary detector 3 are different. The main detector 1 is used to detect the target gamma-ray full energy peak event, and the secondary detector 3 is used to detect the escaped Compton scattering event to achieve the purpose of anti-coincidence measurement; see Figure 2 As shown, the secondary detector 3 is a hollow cylindrical structure, and the internal cavity is used to accommodate the main detector 1. The main detector 1 is a cylindrical structure, and is coupled with the photomultiplier tube 2 for reading, and the upward end of the secondary detector 3 is read by a high-gain, low-voltage, and magnetic field-insensitive photon information readout device 4. When gamma rays enter the main detector 1, if the photons after Compton scattering escape from the main detector 1, most of them will be absorbed by the secondary detector 3 and recorded. The pulses recorded by the main detector 1 and the secondary detector 3 are respectively input into the linear pulse amplifier, and then the two pulses are simultaneously input into the analysis channel and the anti-coincidence channel of the anti-coincidence circuit. The pulses output by the anti-coincidence circuit exclude time-related events, that is, the Compton scattered photons escaping from the main detector 1 are detected by the output signal of the peripheral secondary detector 3, and are anti-coincident with the output signal of the main detector 1, so that the Compton scattering events that pass through the main detector 1 and enter the scintillation crystal are not recorded, thereby effectively reducing the Compton continuous background in the gamma energy spectrum, achieving the purpose of suppressing the Compton effect and improving the peak-to-Compton ratio, which is beneficial to energy spectrum analysis and realizes high-precision measurement of the nuclear state lifetime of fission neutron-rich nuclear fragments.

[0035] In some embodiments of the probe for measuring the lifetime of fission neutron-rich nuclear states of the present invention, the main detector 1 is a cerium-doped lanthanum bromide crystal, and the decay time of the cerium-doped lanthanum bromide crystal is 16ns; the secondary detector 3 is a thallium-doped cesium iodide crystal, and the decay time of the thallium-doped cesium iodide crystal is 1000ns. In some specific examples, the main detector 1 is cylindrical, the secondary detector 3 is annular, and the main detector 1 is integrally fixed inside the annular hole of the secondary detector 3.

[0036] Combination Figure 1 and Figure 2As shown, the outer thallium-doped cesium iodide crystal (secondary detector 3) is cylindrical, and the cerium-doped lanthanum bromide crystal (main detector 1) is set in it. The gamma ray of the anti-Kang spectrometer with this layout is incident from the bottom of the main detector 1 toward the photomultiplier tube 2. Since the light yield of the LaBr3 (Ce) crystal is 63000 photos / MeV, and the light yield of the CsI (Tl) crystal is 54000 photos / MeV, the light yield of the two crystals is close, and the detection efficiency is close, which is conducive to forming an anti-Kang detector; the density of CsI (Tl) is 4.51g / cm 3 The relatively large density is conducive to shielding and reducing the pollution of the external background. The CsI(Tl) crystal (anticoincidence crystal) surrounding the LaBr3(Ce) crystal captures the Compton scattered photons or single escaped and double escaped 0.511MeV gamma rays escaping from the LaBr3(Ce) crystal to anticoincidence the low-energy Compton photon continuous spectrum generated in the LaBr3(Ce) crystal, suppressing the Compton platform to improve the peak-to-Compton ratio and energy resolution, thereby achieving high-precision measurement of the nuclear state lifetime of fission neutron-rich fragment nuclei.

[0037] In some other embodiments of the probe for measuring the lifetime of fission neutron-rich nuclear states of the present invention, the secondary detector 3 includes a plurality of Figure 5 and Figure 6 The arc-shaped reflective unit shown is composed of a plurality of reflective units assembled around the periphery of the main detector 1 to form a secondary detector 3 , and the end of the reflective unit facing the photomultiplier tube 2 forms an exit window.

[0038] It is understandable that the secondary detector 3 includes a number of arc-shaped anti-Kan units, which are assembled to form a hollow cylinder and surrounded by the main detector 1. The top of the anti-Kan unit facing the photomultiplier tube 2 is constructed to form an exit window for coupling and connecting the photon information reading device 4. It should be understood that the number of anti-Kan units is limited by the material cost and the crystal size of the secondary detector 3, and four pieces are preferred. In some specific examples, the main detector 1 is a cerium-doped lanthanum bromide crystal, which is cylindrical in shape, with a diameter of 55mm, a height of 75.4mm, and a decay time of 16ns. The secondary detector 3 is a thallium-doped cesium iodide crystal, which is composed of four arc-shaped anti-Kan units to form a hollow cylindrical structure, with an inner diameter of 63.5mm, a depth of 90mm, and a decay time of 1000ns. The cylindrical main crystal LaBr3 (Ce) is embedded in the secondary detector 3 of the hollow cylindrical structure composed of four arc-shaped CsI (Tl). Two crystals with different decay times are used as the main detector 1 to detect the full energy peak of the target gamma ray, and the other is used to detect the secondary detector 3 of Compton scattering. The gamma ray is incident from the bottom of the main detector 1 toward the photomultiplier tube 2, and the secondary detector 3 reflects the Compton scattered photons escaping from the main detector 1 or the single-escaping or double-escaping 0.511MeV gamma rays.

[0039] In some embodiments of the probe for measuring the lifetime of fission neutron-rich nuclear states of the present invention, the photon information readout device 4 includes a plurality of silicon photomultiplier tubes of the same size, and the plurality of silicon photomultiplier tubes of the same size are spliced ​​at the exit window (end of the anti-con unit) of the sub-detector 3 to form a silicon photomultiplier tube readout circuit. Specifically, at the top of the sub-detector 3 facing the photomultiplier tube 2, that is, at the top of the four arc-shaped anti-con units, four photon information readout devices 4 are coupled correspondingly, and each photon information readout device 4 is composed of 7 pieces of the same size (6.4×6.4mm 2 ) are spliced ​​together, and the top of the anti-conversion unit is the ring-shaped photon information readout device 4. In some specific examples, the model of the photomultiplier tube 2 is R13089, and the transit time is 20ns. To maintain the consistency of the signal amplitude, the working voltage range of the photomultiplier tube 2 is: -900~-1200V; the photon information readout device 4 can use a multi-pixel photon counter, model s14160, with a wavelength response range of: 270~900nm, and its working voltage range is: 46~48V.

[0040] In other embodiments of the probe for measuring the lifetime of fission neutron-rich nuclear states of the present invention, in combination with Figure 1 and Figure 4 As shown, except for the surface coupled to the photomultiplier tube 2, the other surfaces of the main detector 1 are covered with a reflective layer 5; except for the outer surface coupled to the photon information readout device 4, the other outer surfaces of the secondary detector 3 are also covered with a reflective layer 5.

[0041] It can be understood that the main detector 1 is embedded in the secondary detector 3. The main detector 1 and the secondary detector 3 are wrapped with a reflective layer 5 except for the part coupled with the optical read-out component for reading. The reflective layer 5 can be an ESR (Enhanced Specular Reflector) reflective film. The ESR reflective film is a mirror reflective film with ultra-high reflectivity, which can efficiently reflect light from the light source. It is used to improve the light collection efficiency while also protecting the detector.

[0042] Furthermore, in some other embodiments of the probe for measuring the lifetime of fission neutron-rich nuclear states of the present invention, a shielding shell 6 is further provided outside the reflective layer 5. The reflective layer 5, the main detector 1, the photomultiplier tube 2, the secondary detector 3, and the photon information readout device 4 are all placed in the shielding shell 6. It can be understood that the main detector 1 uses LaBr3 (Ce) crystal, which is easily deliquescent in the air. Therefore, after the main detector 1 is coupled with the photomultiplier tube 2, a layer of aluminum shell with a thickness of 1.5 mm is wrapped around the periphery for sealing and light protection to form the shielding shell 6 of the main detector 1. Similarly, the outer surface of the secondary detector 3 is also covered with a shielding shell 6, and the shielding shell 6 outside the secondary detector 3 can effectively shield cosmic rays and background rays in the environment.

[0043] In some embodiments of the probe for measuring the lifetime of fission neutron-rich nuclear states of the present invention, see again Figure 1 As shown, a flange 7 is fixedly sleeved on the periphery of the photomultiplier tube 2, and the flange 7 is used to be fixedly connected to an external detector bracket; a plurality of through holes 8 are provided on the flange 7, and the through holes 8 are used to pass external cables for input and output of signals and high voltage.

[0044] The method for measuring the lifetime of a fission neutron-rich nuclear state provided by the present invention is described below. The method for measuring the lifetime of a fission neutron-rich nuclear state described below and the probe for measuring the lifetime of a fission neutron-rich nuclear state described above can be referred to each other.

[0045] A specific embodiment of the present invention provides a method for measuring the lifetime of a fission neutron-rich nuclear state, comprising the following steps: a neutron-rich nucleus fissions into an excited state, and after deexcitation, a gamma ray is released into a main detector 1, and the gamma ray undergoes a Compton effect in the main detector 1. Based on the detection of the gamma ray full energy peak event by the main detector 1, a full energy peak signal is generated, and the generated full energy peak signal is introduced into the data acquisition system of the mass spectrometer through the photomultiplier tube 2. Based on the capture of the Compton scattered photons or the single-escaped or double-escaped 0.511MeV gamma rays escaping from the main detector 1 by the secondary detector 3, a Compton scattering signal is generated, and the generated Compton scattering signal is introduced into the data acquisition system of the mass spectrometer through the photon information readout device 4. The Compton scattering signal obtained by the data acquisition system of the mass spectrometer is anti-correlated with the total energy peak signal to exclude simultaneous events, remove the interference of Compton scattered photons, generate a gamma energy spectrum, and select gamma rays of known different energies produced after deexcitation of fission fragments from the anti-correlated gamma energy spectrum to match them with the time spectrum of the main detector 1. The difference between the two times is the lifetime of the fission neutron-rich nuclear state.

[0046] It can be understood that the method for measuring the lifetime of fission neutron-rich nuclear states in this embodiment is based on the fast time characteristics of LaBr3(Ce) and the fast time delayed coincidence method of CsI(Tl) crystal to measure the nuclear state lifetime. Through the fission fragment-β-γ-γ quadruple coincidence technology, the solar cell detector is the injection detector of the fission fragment, and high purity germanium (HPGe) is used as the β-γ coincidence timing probe in the delayed coincidence system to measure the energy level lifetime. In addition, the LaBr3(Ce) crystal of a main detector 1 is used to select gamma rays, and the γ-γ-γ(t) coincidence event between HPGe and LaBr3(Ce) is recorded, and the energy resolution is used to measure the lifetime of the energy level. The γ3 detected by HPGe with high detection rate is opened, and the γ1 and γ2 detected by LaBr3(Ce) that are consistent with it are selected. The energy level between γ1 and γ2 is the lifetime energy level to be measured. Then the LaBr3(Ce) detector is used to open the door, and the time signals of γ1 and γ2 are used as "start" and "stop" respectively to extract the time spectrum. The CsI(Tl) crystal of the secondary detector 3 on the outer layer of the LaBr3(Ce) crystal surrounding the main detector 1 is used to obtain the system through the digital plug-in XIA, and the counts of energy deposition occurring in the secondary detector 3 are deducted from the energy spectrum, thereby obtaining a better peak-to-noise ratio and peak-to-compton ratio, which is beneficial to energy spectrum analysis.

[0047] It should be understood that before the probe is used to measure the lifetime of fission neutron-rich nuclear states, the LaBr3(Ce) crystal of the main detector 1 should be tested with or without the CsI(Tl) crystal, and the effect of the Compton test of the CsI(Tl) crystal should be understood by the changes in the Compton platform in its energy spectrum.

[0048] First, the main detector 1 made of LaBr3 (Ce) crystal was tested without the anti-coronavirus test of the secondary detector 3. The anti-coronavirus effect of the secondary detector 3 made of CsI (Tl) crystal was understood by the change of the Compton platform in the LaBr3 (Ce) energy spectrum. The radiation sources used in the test were 60 Co. 137 Cs.

[0049] The second step is to select and test the anti-coincidence unit of the sub-detector 3. Before using the CsI (Tl) crystal for anti-coincidence, it is necessary to package and test a total of four CsI (Tl) crystals for each anti-coincidence unit. Each CsI (Tl) crystal is coupled to a photon information readout device 4. Before assembly, it is necessary to select CsI (Tl) crystals with basically consistent signal amplitudes. To ensure that the signal amplitude of each CsI (Tl) is kept within the range of 200~300mV, a negative voltage of 46~48V is applied to each silicon photomultiplier (SiPM) constituting the photon information readout device 4. Four CsI (Tl) crystals with similar signal amplitudes are selected from them to form an anti-coincidence detection unit, that is, to form a complete sub-detector 3.

[0050] Perform the test again to see if the main detector 1 is healthy with the secondary detector 3. Figure 7 and Figure 8 As shown, the ROOT analysis software can be used to integrate the Compton platform comparison results of two standard sources before and after reverse ionization into one spectrum.

[0051] In the process of measuring the fission neutron-rich nuclear state lifetime using the probe, the test conditions of the main detector 1 are kept unchanged. The counts of energy deposition in the secondary detector 3 are deducted from the energy spectrum through the fast time delay coincidence method and the data acquisition system of the mass spectrometer (digital XIA acquisition system). The energy spectrum of LaBr3(Ce) with and without the anti-Compton mode is preliminarily compared and analyzed, and a better peak-to-Compton ratio and Compton suppression factor are obtained. 137 Cs and 60 The peak-to-Compton ratios of the two Co radioactive sources are 16.52 and 43.55 (1.332 MeV), and the Compton suppression factors are 2.19 and 1.62, respectively. Figure 7 , 8 The counts of energy deposition in the crystal of the secondary detector 3 are deducted from the energy spectrum to obtain a better peak-to-noise ratio and peak-to-Compton ratio, which is beneficial to energy spectrum analysis, effectively reduces the continuous background interference caused by Compton scattered photons, and effectively improves the measurement accuracy of the lifetime of neutron-rich nuclear states.

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A probe for measuring the lifetime of a fission neutron-rich nuclear state, characterized in that: include: A main detector (1), the main detector (1) being cylindrical, one end of the main detector (1) being configured with a photon incident port, and the other end being configured as an output port; A photomultiplier tube (2), the photomultiplier tube (2) being coupled to the output end of the main detector (1) and externally connected to a data acquisition system of a mass spectrometer; A secondary detector (3), the secondary detector (3) being arranged around the periphery of the main detector (1), the secondary detector (3) comprising a plurality of arc-shaped anti-Kang units, the plurality of anti-Kang units being assembled around the periphery of the main detector (1) to form the secondary detector (3), the anti-Kang units being constructed toward the end of the photomultiplier tube (2) to form an exit window; A photon information readout device (4), the photon information readout device (4) is coupled to the exit window of the secondary detector (3) and is externally connected to a data acquisition system of a mass spectrometer; each of the anti-conductive units is coupled to one of the photon information readout devices (4), the photon information readout device (4) comprises a plurality of silicon photomultiplier tubes of the same size, and the plurality of silicon photomultiplier tubes of the same size are spliced ​​at the exit window of the anti-conductive unit to form a silicon photomultiplier tube readout circuit.

2. The probe for measuring the lifetime of fission neutron-rich nuclear states according to claim 1, characterized in that: The main detector (1) is a cerium-doped lanthanum bromide crystal, and the secondary detector (3) is a thallium-doped cesium iodide crystal.

3. The probe for measuring the lifetime of fission neutron-rich nuclear states according to claim 1 or 2, characterized in that: The main detector (1), except for the surface coupled to the photomultiplier tube (2), has its remaining surfaces covered with a reflective layer (5); the secondary detector (3), except for the outer surface coupled to the photon information readout device (4), has its remaining outer surfaces also covered with the reflective layer (5).

4. The probe for measuring the lifetime of fission neutron-rich nuclear states according to claim 3, characterized in that: The reflective layer (5) is covered with a shielding shell (6).

5. The probe for measuring the lifetime of fission neutron-rich nuclear states according to claim 4, characterized in that: The reflective layer (5) is an ESR reflective film, and the shielding shell (6) is an aluminum shell.

6. The probe for measuring the lifetime of fission neutron-rich nuclear states according to claim 1 or 2, characterized in that: The outer periphery of the photomultiplier tube (2) is fixedly sleeved with a flange (7), and the flange (7) is used to be fixedly connected to an external detector bracket; the flange (7) is provided with a plurality of through holes (8), and the through holes (8) are used to pass external cables.

7. A method for measuring the lifetime of a fission neutron-rich nuclear state, characterized in that: A probe for measuring the lifetime of a fission neutron-rich nuclear state according to any one of claims 1 to 6, comprising: The neutron-rich nucleus fissions into an excited state, and after deexcitation, releases gamma rays that enter the main detector (1), and the gamma rays produce a Compton effect in the main detector (1); Based on the main detector (1), the gamma-ray full-energy peak event is detected to generate a full-energy peak signal, and the generated full-energy peak signal is introduced into the data acquisition system of the mass spectrometer through the photomultiplier tube (2); The secondary detector (3) captures Compton scattered photons or single-escaped or double-escaped 0.511 MeV gamma rays escaping from the primary detector (1) to generate Compton scattered signals, and the generated Compton scattered signals are introduced into the data acquisition system of the mass spectrometer through the photon information readout device (4); The Compton scattering signal obtained by the data acquisition system of the mass spectrometer is anti-correlated with the total energy peak signal to exclude simultaneous events and remove the interference of Compton scattered photons, thereby generating a gamma energy spectrum. Gamma rays of known different energies generated after deexcitation of fission fragments are selected from the anti-correlated gamma energy spectrum and matched with the time spectrum of the main detector (1). The difference between the two times is the lifetime of the fission neutron-rich nuclear state.

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