JPH06265639A - Method for fractional measurement of many nuclear species with liquid scintillator - Google Patents

Abstract

PURPOSE:To correct quenching without using an external standard radiation source and to perform the fraction of many nuclear species by comparing the spectrum obtained by multiplying the reference spectrum of each nuclear species by a specified strength coefficient. CONSTITUTION:In a preparation step, the reference spectrum of each nuclear species in each quenching level is obtained and stored as the waveform. Then, a background spectrum is formed and preserved. Thereafter, the energy spectrum of a sample, wherein many nuclear species are mixed state, is measured and stored into a recording medium. Then, the optimizing process of the synthesized spectrum with respect to the sample spectrum is executed. The synthesized spectrum is obtained by synthesizing the reference spectrum and the background spectrum. Each nuclear species is multiplied by the specified strength coefficinet as weighting. The sample spectrum and the synthesized spectrum are compared and the closest approximation is performed. Then, the amount of each nuclear species is computed, and the radioactivity of each nuclear species is computed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid scintillator-based multinuclide fractionation measuring method for fractionally measuring radioactivity and the like of a plurality of radionuclide in a sample liquid using the liquid scintillator.

[0002]

2. Description of the Related Art Monitoring of radiation is important for radiation control in radiation handling facilities. Further, in the field of analysis / inspection using a radioisotope, it is necessary to accurately and separately measure which nuclide is contained in a sample solution and to what extent. Therefore, as a method of measuring radiation, radiation measurement using a liquid scintillator has been conventionally performed. In this radiation measurement, a sample to be measured is mixed in a liquid scintillation solution, the radiation generated in the sample is captured as light emission of a scintillator, and this is detected by, for example, a photomultiplier tube. And
Radioactivity of the sample is converted from the detection result, that is, the pulse count number.

However, in the radiation measurement using such a liquid scintillator, although the measurement can be performed with high sensitivity, there is a problem that the detection accuracy is deteriorated due to so-called quenching. As is well known, this quenching is a phenomenon that when a sample is mixed into a liquid scintillation solution, the solution is colored, and as a result, the generated light is attenuated (quenched) and the detection pulse becomes small.

Here, FIG. 6 shows the waveform change of the spectrum due to quenching. As can be seen, the greater the quenching, the more the waveform is biased towards the low energy region.

Therefore, conventionally, as a method for performing radiation measurement while correcting the quenching level,
Internal standard source method and channel ratio method are used. However, such a method has a drawback that only the radiation measurement of a mononuclide can be practically performed, and therefore, a multinuclide fractionation measuring method using, for example, γ rays is used as an external standard radiation source. That is, the spectrum change due to quenching of the sample is corrected with reference to the spectrum change due to the γ-ray having a known radiation dose.

[0006]

However, as described above, the above-mentioned conventional multinuclide fractionation method requires the γ-ray irradiation mechanism and its shielding mechanism inside the measuring apparatus, which makes the apparatus extremely large. There was a problem that it would be a hanging. There is also a problem that the management and handling of the γ-ray source is complicated.

The present invention has been made in view of the above-mentioned conventional problems, and corrects the quenching that inevitably occurs in a liquid scintillator without using an external standard radiation source such as a γ-ray source, and is a multinuclide. Another object of the present invention is to provide a multinuclide fractionation measuring method using a liquid scintillator capable of simultaneously fractionating.

[0008]

In order to achieve the above object, the invention according to claim 1 is to separate the standard samples of known specific activity prepared for each nuclide to be separated into liquid scintillation solutions. Put in, and gradually change the quenching level of the solution from 0 to a predetermined level,
Obtaining the energy spectrum of each nuclide at each quenching level, a reference spectrum preparation step of storing them as a reference spectrum, a sample measurement step of measuring the energy spectrum of the sample, and the reference of each nuclide at the same quenching level Each of the quenching levels includes a synthetic spectrum creating step of synthesizing a spectrum by multiplying a nucleus type by a predetermined intensity coefficient, and a comparing step of comparing the synthetic spectrum with the sample spectrum to obtain a residual that is a mismatch amount. Each time, the synthetic spectrum creation step and the comparison step are repeatedly executed while varying the intensity coefficient for each nuclide separately, and the combination of the intensity coefficients that minimizes the residual and the quenching level at that time are determined. From the combination of the determination step and the determined strength coefficient Characterized in that it comprises a nuclide amount calculation step of converting the amount of a.

According to the second aspect of the present invention, the reference spectrum preparation step further measures and stores the background spectrum at each quenching level, and the determination step further adds the background spectrum. It is characterized in that the composite spectrum is created and the spectrum comparison is executed.

Further, in the invention according to claim 3, the judging step judges a quenching level at which the residual is minimized and a quenching level at which the residual is next smaller, and the two quenching levels are used. An intermediate spectrum represented by a quenching parameter representing the degree of quenching using the reference spectrum of the two basic forms as a basic form, and the residual difference due to the comparison between the sample spectrum and the synthetic spectrum in which the intermediate spectrum is synthesized is further The method further comprises a re-optimization step of determining an optimal combination of the intensity coefficient and the quenching parameter to be reduced.

[0011]

According to the structure described in claim 1, the reference spectrum of each nuclide at each quenching level is first obtained in the reference spectrum preparation step. Then, these reference spectra are stored as a waveform.

Next, after the energy spectrum of the sample is measured in the sample measuring step, the determining step is executed.

In this determination step, the combination of the intensity coefficients that minimizes the residual is obtained by repeatedly executing the synthetic spectrum creating step and the spectrum comparing step. That is, since the synthetic spectrum is created with the energy spectrum actually measured in the reference spectrum preparation step as an element, it is possible to reproduce a waveform approximate to the sample spectrum by appropriately combining the intensity coefficients for each nuclide. It will be possible.

Therefore, since the combination of the intensity coefficients judged in this judging step represents the quantity of each nuclide, the quantity ratio of each nuclide and the radioactivity of each nuclide are converted in the nuclide quantity calculating step. It becomes possible.

As described above, according to the present invention, an external standard radiation source such as a γ-ray source is not necessary at all, and extremely high-precision quenching correction is realized.

According to the second aspect of the present invention, the background spectrum is measured in the reference spectrum preparation step, and the background spectrum is added in the judgment step to create a synthetic spectrum. Accurate multinuclide separation can be realized in the form including the ground.

Further, according to the invention of claim 3, when the true quenching level is between any two of the stepwise set quenching levels, the reference is obtained by creating the intermediate spectrum. The spectrum waveform can be finely corrected, and the optimal combination of intensity coefficients can be obtained with higher accuracy. That is, there is an advantage that the quenching correction accuracy can be improved without increasing the number of stages of the quenching level set in the reference spectrum preparation step.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a preferred embodiment of a multinuclide fractionation measuring method using a liquid scintillator according to the present invention, and FIG. 1 is a process chart showing each step thereof.

First, the principle of the present invention will be described with reference to FIG.

FIG. 2 shows a sample spectrum S as a result of measuring a multinuclide mixed sample using a liquid scintillator. This sample spectrum S is the energy spectrum F _{1 of} the two nuclides in the example shown in FIG.
It is the sum of F ₂ and the background spectrum B, and accordingly, the general formula (1) is shown in FIG. 2 as a reference. As shown in FIG. 2, when a multinuclide mixed sample is measured, the sample spectrum S is expressed as a composite of a plurality of spectra, but generally, the above-mentioned quenching problem occurs, so that each of the waveform elements is a waveform element. Separation of nuclide spectra and determination of quantity are difficult.

Therefore, in the present invention, as will be described later in detail, a reference spectrum is prepared as a basic waveform for each nuclide at each quenching level, these reference spectra are synthesized by an appropriate combination, and the synthesized spectrum is obtained. The amount of each nuclide is determined based on the comparison between the sample spectrum S and the sample spectrum S. Specifically, a residual, which will be described later, obtained by subtracting the synthetic spectrum from the sample spectrum is obtained, and the amount of each nuclide is determined by minimizing the residual.

Here, the residual is defined as follows.

[0024] However, Y _i = synthetic spectrum and y _i = sample spectrum will be described below with reference to specific examples of a method for fractionating multinuclear species by a liquid scintillator to which the above-described principle of the present invention is applied.

In FIG. 1, in step 101, a reference spectrum is created and stored. Specifically, the specific activity (Adp
Standard samples of known m) are individually placed in liquid scintillation solution. Then, a quencher is sequentially added to the solution to intentionally cause quenching, the quenching level is changed stepwise (0 to N), and the energy spectrum of each nuclide at each quenching level is obtained.

In the present embodiment, the light emission of the liquid scintillator is detected by the photomultiplier tube, and the output signal thereof is analyzed by the multichannel analyzer,
Energy spectrum is sought. Here, the determined reference spectrum of each nuclide at each quenching level is recorded on the recording medium.

Next, at step 102, as described above,
Background spectra have been created and stored. That is, similar to step 101 described above,
Now, the background spectrum at each quenching level is obtained without the standard sample, and the spectrum is stored in the storage medium. In the multinuclide fractionation method according to the present invention, as described below, the background spectrum can be treated in the same manner as a normal nuclide spectrum, and the fractionation accuracy can be improved. It should be noted that the results of step 101 and step 102 existing as the preparation process can be written in advance in, for example, a ROM in an actual device.

Next, at step 103, as in the conventional case,
The energy spectrum of the sample in which the polynuclear species are mixed is measured. However, in this embodiment, an external standard radiation source such as a γ-ray source is not required. Note that this sample spectrum is also temporarily stored in the recording medium.

Next, in step 104, step 10
Optimization processing of the synthetic spectrum with respect to the sample spectrum obtained in 3 is executed. Here, the synthetic spectrum is a synthesis of the reference spectrum and the background spectrum of all nuclides at any quenching level, and in the synthesis, a predetermined intensity coefficient (quantification coefficient) is weighted for each nuclide. It is hung as. The optimization here is to find the optimum combination of the intensity coefficients that most approximates the composite spectrum to the sample spectrum, in other words, minimizes the residual. Specifically, the least squares method is applied to each quenching level using each intensity coefficient as a parameter, and a combination of intensity coefficients having the smallest residual is obtained.

Therefore, by executing this step 104, as a result, the optimum combination of the intensity coefficients that minimizes the residual is obtained for each quenching level.

3 and 4 show examples of execution results of step 104. In this example, ³ H and ¹⁴ C are shown as nuclides to be separated. As shown in FIG. 3, the residual is minimized when the quenching level Q is 3 to 4, and it is determined from this that the quenching level Q of the sample is 3 to 4. Further, the amount of each nuclide at that time is obtained by the intensity coefficient of the nuclide type shown in FIG. That is, the intensity coefficient represents the ratio to the reference spectrum and the dose ratio of each nuclide, in other words, the radioactivity of each nuclide.

Then, in step 105, the quantity of each nuclide is calculated from the intensity coefficient of each nuclide obtained as described above, and the radioactivity of each nuclide is calculated. Specifically, with reference to the radioactivity of the standard sample used in step 101, the actual radioactivity is converted from the obtained intensity coefficient.

As described above, after the steps 104 and 105 which are understood as the analysis process, the calculated radioactivity and the like are displayed on the display in step 106.

As described above, according to the multinuclide separation measuring method using the liquid scintillator of this embodiment, it is possible to simultaneously separate the multinuclide while correcting the quenching level without using an external standard radiation source or the like. Is. Since the reference spectrum, which is the actual measurement spectrum, is used as a reference for the classification, a classification result that is not affected by the characteristics of the detection system can be obtained.

Next, FIG. 5 shows, as a modified example of this embodiment, the steps for performing the re-optimization process. This re-optimization process is inserted into AA 'shown in FIG.

As shown in FIG. 3, the above step 10 is performed.
In steps up to 4, if the true quenching level is between the discretely set quenching levels, it cannot be determined. On the other hand, it is possible to increase the number of steps of the quenching level, but it is inevitable that the amount of data to be recorded increases and the calculation processing time also increases.

Therefore, step 107 and step 10
In No. 8, the fact that the waveform change of the reference spectrum between quenching levels is almost continuous is utilized, whereby an intermediate spectrum is created and compared with the sample spectrum to further reduce the residual error. .

In FIG. 5, in step 107, the quenching level with the smallest residual and the quenching level with the next smallest are determined. For example, in the example shown in FIG. 3, 3 and 4 are determined as the quenching level.

Next, step 108 will be described.
For each nuclide from the two reference spectra at the two quenching levels determined in step 107, the nuclide m
The intermediate spectrum of is expressed by the following third equation.

Gm (n) = A {(1-Q) * Dm, I (n) + Q * Dm, I + 1 (n)} (Formula 3) Dm, I (n): quenching level I, nuclide m reference spectrum n: channel Q: quenching parameter (0 to 1) A: intensity (quantity) parameter That is, in the third equation, the intermediate spectrum Gm (n) is a reference spectrum of quenching level I and a reference spectrum of I. It has shown that it is an intermediate spectrum waveform of.

In the third equation, when Q = 0,
Gm (n) becomes the I-th reference spectrum. On the other hand, Q
When = 1, Gm (n) becomes the I + 1th reference spectrum. Then, from Q = 0 to Q = 1, I
It is understood that the waveform of the intermediate spectrum shifts from the (1) th reference spectrum to the (I + 1) th reference spectrum.

Therefore, the third formula is introduced for each nuclide, and in the comparison between the synthetic spectrum obtained by synthesizing them and the sample spectrum, the third formula is adopted so that the residual error is minimized.
If the least squares method is applied with the strength coefficient and the quenching parameter of the equation as parameters, both the combination of the strength coefficient and the quenching parameter can be optimized. That is, the synthetic spectrum can be approximated to the sample spectrum.

Therefore, when the routine shown in FIG. 5 is executed, in step 105 shown in FIG. 1, the radioactivity and the like for each nuclide is calculated in the same manner as described above, and the corrected quenching is performed. The level will be determined. According to the above modification, it is possible to obtain the same effect as if the number of stages is equivalently increased without increasing the number of stages of the quenching level. Therefore, there is an advantage that the amount and radioactivity of each nuclide can be obtained with higher accuracy.

[0044]

As described above, according to the invention as set forth in claim 1, without using an external standard radiation source such as a γ-ray source, quenching correction can be performed with high accuracy and the dose and radiation of each nuclide. It is possible to request Noh etc. at the same time.

According to the second aspect of the present invention, since the background spectrum can be added to the synthetic spectrum, it is possible to appropriately separate multinuclear species without being influenced by external factors.

Further, according to the invention described in claim 3, it is possible to obtain the same effect as when the number of stages is equivalently increased without increasing the number of stages of the quenching level.
This has the effect of accurately determining the quenching level and more accurately determining the radioactivity of each nuclide.

[Brief description of drawings]

FIG. 1 is a flowchart showing each step of a multinuclide fractionation measuring method using a liquid scintillator according to the present invention.

FIG. 2 is an explanatory diagram showing a relationship between an energy spectrum of each nuclide and a sample spectrum obtained as a sum thereof.

FIG. 3 is an explanatory diagram showing a relationship between a quenching level and a residual.

FIG. 4 is an explanatory diagram showing an example of specific numerical values of the intensity coefficient for each nuclide at each quenching level.

FIG. 5 is a partial flowchart showing processing steps when re-optimization is performed by creating an intermediate spectrum.

FIG. 6 is an explanatory diagram showing a quenching phenomenon in the liquid scintillator.

[Explanation of symbols]

 S101, S102 preparation step S103 sample measurement step S104, S105 analysis step

Claims (3)

[Claims] 1. A standard sample of known specific activity prepared for each nuclide to be separated is separately put into a liquid scintillation solution, and the quenching level of the solution is set to 0.
To a predetermined level in steps, obtain the energy spectrum of each nuclide at each quenching level, store the reference spectrum as a reference spectrum, and the sample measurement step to measure the energy spectrum of the sample. , A synthetic spectrum creating step of synthesizing the reference spectrum of each nuclide at the same quenching level by multiplying a nuclear type by a predetermined intensity coefficient, and a comparing step of comparing the synthetic spectrum with the sample spectrum to obtain a residual difference which is a mismatch amount , And, for each of the quenching levels, the synthetic spectrum creating step and the comparing step are executed while varying the intensity coefficient for each nuclide separately, and the residual coefficient is minimized. A determination step of determining the combination and the quenching level at that time; Multinuclear fractionation measurement method by the liquid scintillator, characterized in that a combination of intensity coefficient including a nuclide amount calculation step of converting the amount of each species were. 2. The multinuclide fractionation measuring method using the liquid scintillator according to claim 1, wherein in the reference spectrum preparing step, a background spectrum at each quenching level is further measured and stored, and in the judging step, A method for fractionating and measuring multiple nuclides by a liquid scintillator, which comprises adding the background spectrum to create the composite spectrum and executing the spectrum comparison. 3. The multinuclide fractionation measuring method using a liquid scintillator according to claim 1, wherein the determining step determines a quenching level at which the residual is minimized and a quenching level at which the residual is next smallest, The reference spectrum at the two quenching levels is used as both basic forms to create an intermediate spectrum represented by a quetting parameter representing the degree of quenching, and the intermediate spectrum is synthesized for each nuclide and the sample spectrum and The method for discriminating and measuring multinuclide by a liquid scintillator, which comprises a re-optimization step of determining an optimal combination of the intensity coefficient and the queuing parameter, which results in a smaller residual error by the comparison.