CN115657106A - Scintillator detector with ultralow background and peak stabilizing function - Google Patents
Scintillator detector with ultralow background and peak stabilizing function Download PDFInfo
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- CN115657106A CN115657106A CN202211357880.9A CN202211357880A CN115657106A CN 115657106 A CN115657106 A CN 115657106A CN 202211357880 A CN202211357880 A CN 202211357880A CN 115657106 A CN115657106 A CN 115657106A
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Abstract
The invention belongs to the field of nuclear radiation monitoring, and provides a scintillator detector with ultralow background and a peak stabilizing function. According to the scintillator detector, the metal sheet is covered with a layer of fluorescent material, so that the count caused by the embedded source is distinguished from the gamma ray count to be detected in real time, the background count of monitoring equipment is greatly reduced, and the defects that the embedded stable peak source is large in fluctuation due to emissivity and difficult to deduct in real time are overcome.
Description
Technical Field
The invention belongs to the field of nuclear radiation monitoring, and particularly relates to a scintillator detector with ultralow background and a peak stabilizing function.
Background
Scintillator detectors detect nuclear radiation by the property of converting nuclear radiation into fluorescence using certain substances, commonly referred to as fluorescent substances or scintillators. The photomultiplier converts these weak optical signals into photoelectrons, which are amplified by multistage multiplication and finally output electric pulses that can be directly measured, and the device is called a scintillator detector.
In the engineering application process of a gamma energy spectrometer based on a scintillator detector, due to the influence of environmental temperature and other factors, the electronics is often unstable, peak position drift can be generated, and finally the system is unstable. The influence of temperature is important in the factors, and the temperature influence is embodied as follows: the temperature-dependent type photoelectric detector comprises (1) the influence of temperature change on the luminous efficiency of a scintillator, (2) the multiplication coefficient of a photomultiplier is easily influenced by temperature, and (3) electronic components on a signal amplification board are easily influenced by temperature. In order to improve the working stability and the measurement accuracy of the energy spectrum monitoring equipment, it is very necessary to stabilize the spectrum of the scintillator energy spectrometer.
The principle of peak stabilization is as follows: the real-time peak position is adjusted to the reference peak position by comparing the real-time peak position of the stable peak source with the reference peak position and properly adjusting the signal amplification factor. The premise for realizing the function is as follows: the temperature drift proportion of the peak position of the stable peak source and the gamma ray response peak position is the same.
The reference peaks commonly used in peak stabilization can be divided into two main categories: (1) Embedding an electroluminescent light source at the front end of the crystal or the photomultiplier; and (2) embedding a radioactive source in the front end of the crystal. The peak-stabilizing of the radioactive source is generally more stable and reliable than that of the electroluminescent light source. Commonly used peak-stabilizing radioactive sources are: 241 am, its half-life is longer, its gamma equivalent energy in scintillator is higher (2.5 MeV-3.5 MeV), can avoid overlapping with the gamma peak to be measured whose energy is below 2.5 MeV.
In gamma radiation performance spectrum measurement, in order to enable equipment to measure radioactive substances with lower activity, background radiation in a measurement environment needs to be reduced to a very low level, the most common measure is to adopt substance shielding to reduce the probability of gamma rays and cosmic rays entering a detector in the environment, when external gamma radiation is shielded, background counting generated due to the self-radioactivity of the detector is located at the primary position, fig. 6 shows a background spectrum measured by a detection device in a shielding body, and as can be seen from fig. 6, the stable peak source counting is not neglected in the background counting, occupies a larger energy spectrum range and is difficult to deduct through an energy interval. In order to facilitate peak searching, the activity of the peak-stabilized source is not suitable to be too small, and the particle emissivity fluctuation of the peak-stabilized source is large, so that a stable counting rate can be obtained by long-time averaging, which is not favorable for quickly measuring low radioactivity. Therefore, it is necessary to find a method for real-time discrimination and background subtraction to eliminate the adverse effect of the stationary source on the low background measurement.
The general structure of the existing scintillation crystal containing an embedded source is shown in fig. 1, a scintillation crystal 11 is used as a nuclear radiation sensitive medium, the energy of gamma rays and alpha rays acting with the scintillation crystal is converted into fluorescence which can be measured by a photomultiplier, the fluorescence enters the photomultiplier after passing through a transparent light guide glass 12, a reflective material is added between the scintillation crystal 11 and an outer casing 10, and a sealed space formed by the outer casing 10 and the light guide glass 12 is used for preventing the crystal from being impacted and deliquesced.
The existing scintillator detector with the embedded peak stabilizing source is difficult to measure gamma rays with energy range upper limit higher than or close to the equivalent gamma energy of the peak stabilizing source, the corresponding energy peak of the embedded peak stabilizing source in the energy spectrum is easy to enter the energy window range of the gamma rays to be measured, and the embedded peak stabilizing source causes larger fluctuation of counting rate and is difficult to distinguish in real time, which is not beneficial to low background measurement, improving the response speed of equipment and influencing the performance index of the whole measuring system.
Disclosure of Invention
The invention aims to overcome the defects in the prior art, and provides the scintillator detector with ultralow background and the peak stabilizing function, so that the count caused by the embedded source is distinguished from the count of gamma rays to be detected in real time, the background count of monitoring equipment is greatly reduced, and the defects that the embedded peak stabilizing source has large fluctuation of emissivity and is difficult to deduct in real time are overcome.
In order to realize the purpose, the invention adopts the following technical scheme: the scintillator detector comprises a metal sheet with a uniformly plated radioactive source on the surface, an outer casing, a scintillation crystal, light guide glass, a photomultiplier, a front panel and an energy spectrum processing system with pulse shape recognition capability, wherein the metal sheet with the uniformly plated radioactive source on the surface is covered with a layer of fluorescent material.
In the technical scheme, the energy spectrum temperature drift characteristics of the fluorescent material and the scintillation crystal are consistent, the emission spectrum of the fluorescent material cannot be coincided with the absorption spectrum of the scintillation crystal, and the emission spectrum of the fluorescent material is matched with the used photomultiplier.
In the above technical solution, when the scintillation crystal adopts NaI (Tl), the fluorescent material may be: laBr 3 :Ce、CsI(Tl)、ZnS、CsF、CdWO 4 LYSO, GSO, etc.
In the above technical solution, the fluorescent material may be made into a coating or made into a crystal.
According to the scintillator detector, the metal sheet is covered with the fluorescent material, the alpha ray energy emitted by the radioactive source plated on the metal sheet is absorbed by the fluorescent material, the shapes of electric pulse signals output after conversion and amplification of the photomultiplier are different due to the fact that the fluorescent characteristics of the fluorescent material are different from those of the scintillation crystal, and the two signals can be discriminated in real time by adopting a pulse shape recognition technology, so that the purpose of real-time deduction of counting caused by a stable peak source is achieved, the background of equipment is reduced, the lower limit of detection of the equipment is reduced, and the response speed of the equipment is improved.
Drawings
FIG. 1 is a schematic diagram of a conventional scintillation crystal including an embedded source.
Wherein: 9. metal sheet, 10 external casing, 11 scintillation crystal and 12 light-conducting glass.
FIG. 2 is a diagram of a typical scintillator detector pre-amplification circuit.
FIG. 3 is a schematic view of a scintillator detector of the present invention.
Wherein: 1. the device comprises a metal sheet, 2 fluorescent materials, 3 an outer casing, 4 a scintillation crystal, 5 light guide glass, 6 a photomultiplier, 7 a front panel and 8 an energy spectrum processing system.
Fig. 4 is a graph of gamma signal pulses measured using the scintillator detector shown in fig. 3.
FIG. 5 is a graph of a peak stabilized source pulse measured using the scintillator detector shown in FIG. 3.
Fig. 6 is a mixed energy spectrum of an undifferentiated gamma ray and a stationary source.
FIG. 7 is a background spectrum of gamma rays after real-time subtraction of a stationary source.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present invention more comprehensible, embodiments accompanying figures are described in detail below. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein, but rather should be construed as broadly as the present invention is capable of modification in various respects, all without departing from the spirit and scope of the present invention.
It will be understood that when an element is referred to as being "secured to" another element, it can be directly on the other element or intervening elements may also be present. When an element is said to be "connected" to another element, it may be directly connected to the other element or may be present as an intervening element.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
Referring to the relevant literature, the following formula is readily available:
in formula (1):
n b : background count rate (cps);
T c : a response time;
R 1 : a primary calibration factor;
c: a constant;
in the formula (2):
n b : background count rate (cps);
t: a time constant;
R 1 : a primary calibration coefficient;
as can be seen from equation (1), in order to increase the response speed of the device, the background count of the device needs to be reduced.
From equation (2), it can be seen that to lower the lower detection limit of the device, the background count of the device also needs to be lowered.
It follows that device performance can be significantly improved by reducing the device background count.
With reference to the relevant literature, the following formula can be derived:
in the above formula, U (t) is the output pulse voltage of the preamplifier, E d The energy of deposition of an incident particle in the scintillator, k is a constant, τ 0 Is the luminescence decay time constant, τ, of the scintillator p Is the forward time constant.
From the formula (3), under the condition that the preamplifier parameter is not changed, the preamplifier output pulse shape is determined by the luminescence decay time constant of the scintillator, so that the alpha rays emitted by the stationary source and the gamma rays emitted by the nuclide to be detected can be respectively measured by adopting fluorescent materials with different luminescence decay time constants, and then the two rays are distinguished in real time by adopting a pulse shape recognition system, so that an ultralow background environment is created for gamma ray measurement.
As shown in fig. 3, an embodiment of the present invention provides a scintillator detector with an ultra-low background and a peak stabilizing function, including a metal sheet 1 with a surface uniformly plated with a radioactive source, a fluorescent material 2, an outer casing 3, a scintillation crystal 4, a light guide glass 5, a photomultiplier 6, a front panel 7, and an energy spectrum processing system 8 with a pulse shape recognition capability, where the outer casing 3 is coated outside the scintillation crystal 4, the light guide glass 5 is disposed on the top of the scintillation crystal 4, the outer casing 3 and the light guide glass 5 form a sealed space, the photomultiplier 6 and the front panel 7 are disposed on the light guide glass 5, the front panel 7 is connected to the energy spectrum processing system 8, the bottom of the scintillation crystal 4 is provided with the metal sheet 1 with the surface uniformly plated with the radioactive source, the metal sheet 1 is covered with a layer of the fluorescent material 2, and a reflective material is added between the scintillation crystal 4 and the outer casing 3.
In the above embodiment, the energy spectrum temperature drift characteristics of the fluorescent material 2 and the scintillation crystal 4 should be consistent, the emission spectrum of the fluorescent material 2 cannot coincide with the absorption spectrum of the scintillation crystal 4, and the emission spectrum of the fluorescent material 2 should match the photomultiplier tube used. If only the fluorescence quenching time is considered, when the scintillation crystal 4 uses NaI (Tl), the fluorescent material 2 may be: laBr 3 :Ce、CsI(Tl)、ZnS、CsF、CdWO 4 LYSO, GSO, etc.
In the above embodiment, the fluorescent material 2 can be made into a coating or a crystal; the thickness is less than or equal to 10um. When the coating is formed, the fluorescent material 2 is ensured to be as thin and uniform as possible so as to realize stable fluorescence conversion rate and obtain a stable peak source energy peak with high resolution; the fluorescent material 2 is prevented from being too thick and too large, so that the detector is prevented from being too sensitive to gamma ray response, and the peak stabilizing effect is further prevented from being influenced.
Fig. 4 and 5 are signal pulses measured using the scintillator detector shown in fig. 3. It can be seen from a comparison of fig. 4 and 5 that the gamma signal pulse shape differs significantly from the stationary source pulse shape, with pulse widths at 1/3 the pulse height differing by approximately a factor of 1, and therefore being easier to distinguish.
The scheme of the invention distinguishes the count caused by the embedded source from the count of the gamma rays to be detected in real time, greatly reduces the background count of the monitoring equipment, and eliminates the embedded sourceThe peak stability source has the defects of large fluctuation of emissivity and difficult real-time deduction. FIG. 6 is a mixed spectrum of an undifferentiated gamma ray and a stationary source, where A is the stationary source peak and B is 40 K emits gamma-ray energy peak, and figure 7 is the gamma-ray background energy spectrum after real-time deduction of the stable peak source. From the comparison between fig. 7 and fig. 6, it can be found that the subtraction effect is good, the background of the device is greatly reduced, and the device is favorable for measuring low radioactivity.
Those matters not described in detail in this specification are well within the knowledge of those skilled in the art.
It will be understood by those skilled in the art that the foregoing is only an exemplary embodiment of the present invention, and is not intended to limit the invention to the particular forms disclosed, since various modifications, substitutions and improvements within the spirit and scope of the invention are possible and within the scope of the appended claims.
Claims (6)
1. The utility model provides an ultra-low background just possesses scintillator detector of stationary peak function, includes that the surface evenly plates the sheetmetal of radiation source, outer covering, scintillation crystal, leaded light glass, photomultiplier, preceding board of putting, the energy spectrum processing system who possesses pulse shape recognition ability, characterized by: and a layer of fluorescent material is covered on the metal sheet with the surface uniformly plated with the radioactive source.
2. The ultra-low background and peak-stabilizing scintillator detector of claim 1, wherein: the energy spectrum temperature drift characteristics of the fluorescent material and the scintillation crystal are consistent, the emission spectrum of the fluorescent material cannot coincide with the absorption spectrum of the scintillation crystal, and the emission spectrum of the fluorescent material is matched with the used photomultiplier.
3. The ultra-low background and peak-stabilizing scintillator detector of claim 1, wherein: when NaI (Tl) is used for the scintillation crystal, the fluorescent material is LaBr 3 :Ce、CsI(Tl)、ZnS、CsF、CdWO 4 LYSO, or GSO.
4. The ultra-low background and peak-stabilizing scintillator detector of claim 1, wherein: the fluorescent material is a coating or is a crystal.
5. The ultra-low background and peak-stabilizing scintillator detector of claim 4, wherein: the thickness of the fluorescent material is less than or equal to 10um.
6. The ultra-low background and peak-stabilizing scintillator detector of claim 1, wherein: the external cladding of scintillation crystal, scintillation crystal top are equipped with leaded light glass, and outer cladding and leaded light glass constitute confined space, be equipped with photomultiplier on the leaded light glass and put the board before with, put the board before with the energy spectrum processing system connection, the scintillation crystal bottom is equipped with the sheetmetal that the surface evenly plated the radiation source, is equipped with the fluorescent material coating on the sheetmetal, adds between scintillation crystal and the outer cladding and establishes reflecting material.
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| CN202211357880.9A CN115657106A (en) | 2022-11-01 | 2022-11-01 | Scintillator detector with ultralow background and peak stabilizing function |
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| CN202211357880.9A CN115657106A (en) | 2022-11-01 | 2022-11-01 | Scintillator detector with ultralow background and peak stabilizing function |
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