Method for measuring specific activity of carbon dioxide C-14 in air based on plastic scintillation microspheres

Abstract

The invention relates to a method for measuring the specific activity of carbon dioxide C-14 in air based on plastic scintillation microspheres, which comprises the following steps: step 1, sample treatment: absorbing carbon dioxide in air by adopting alkali liquor, taking the alkali liquor which fully or partially absorbs the carbon dioxide, putting the alkali liquor into a liquid scintillation bottle, adding the plastic scintillation microspheres into the liquid scintillation bottle, oscillating and uniformly mixing, and taking out the sample; a C-14 sample is obtained; adding the same amount of plastic scintillation microspheres into ultrapure water, oscillating and uniformly mixing to obtain a background sample; step 2, determination: storing the C-14 sample and the background sample in a dark place for T time, placing the C-14 sample and the background sample in a liquid flash instrument, measuring for t time, and recording the count of the C-14 sample and the background sample within the t time; and calculating the specific activity of C-14 in the air. According to the method, the sample pretreatment time is short, the workload is low, the monitoring frequency is greatly improved, and the C-14 in the environment can be monitored more comprehensively.

Description

Technical Field

[0001] The invention belongs to the technical field of carbon dioxide C-14 specific activity detection, and in particular relates to a method for measuring the carbon dioxide C-14 specific activity in the air based on plastic scintillation microspheres. Background Art

[0002] Monitoring carbon-14 (C-14) in the nuclear environment and accurately measuring its levels are essential for assessing the safety of nuclear facilities and ensuring that no radioactive materials leak; this not only helps monitor the potential impact of nuclear activities on the surrounding environment, but is also essential for protecting public health and the ecological environment.

[0003] However, the existing method for detecting carbon-14 (C-14) in the environment is derived from the industry standard "Sampling and Determination Method of 14C in Air" (EJ / T 1008-1996). After carbon dioxide is absorbed by sodium hydroxide solution, the mixture of alkali solution and scintillation fluid will produce a strong chemiluminescence interference signal. Therefore, calcium chloride needs to be added to the alkali solution that has absorbed carbon dioxide, and the precipitate is collected, dried and suspended, and then mixed with the scintillation fluid. This process is not only complicated to operate, but also time-consuming, which affects the efficiency and real-time performance of monitoring. Summary of the invention

[0004] The purpose of the present invention is to overcome the defects in the prior art and provide a method for measuring the specific activity of carbon dioxide C-14 in the air based on plastic scintillation microspheres. The method has short sample pretreatment time and low workload, greatly improves the monitoring frequency, and can achieve more comprehensive monitoring of C-14 in the environment.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] A method for measuring the specific activity of carbon dioxide C-14 in air based on plastic scintillation microspheres comprises the following steps:

[0007] Step 1, sample treatment: use alkali solution to absorb carbon dioxide in the air, transfer the alkali solution that has absorbed all or part of the carbon dioxide into a liquid scintillation bottle, add plastic scintillation microspheres thereto, shake and mix evenly, and obtain a C-14 sample; add an equal amount of plastic scintillation microspheres to ultrapure water, shake and mix evenly, and obtain a background sample;

[0008] Step 2, determination: After the C-14 sample and the background sample are stored in the dark for T time, they are placed in a liquid scintillation counter to measure the time t, and the counts of the C-14 sample and the background sample within the time t are recorded; the specific activity of C-14 in the air is calculated using the following calculation formula (1):

[0009]

[0010] in,

[0011] a C-14 is the specific activity of C-14 in air; N is the count of the C-14 sample; N B is the count of the background sample; t is the measurement time; ε is the counting efficiency; M is the molar amount of the alkali solution.

[0012] The count refers to the total number of readings of the instrument during the measurement time.

[0013] As a further technical solution, the counting efficiency ε is calibrated using standard substances. The specific calibration method is as follows: take the same volume of plastic scintillation microspheres, add the same volume of matrix as the alkaline solution, and the matrix is ​​a Na2CO3 solution. 14 C standard solution (solution 14 The activity A of C is known), and a C-14 standard sample is prepared. The background sample is replaced with ultrapure water. The standard sample and background sample are measured with a liquid scintillation counter, and the counting efficiency is calculated as follows.

[0014]

[0015] Where ε is the counting efficiency, N S is the count of the C-14 standard sample; N B is the count of the background sample; t is the measurement time, unit is s; A is the activity of the added C-14 standard source.

[0016] As a further technical solution, the amount of alkaline solution that absorbs carbon dioxide is equal to the amount of ultrapure water; the amount of plastic scintillating microspheres added to the alkaline solution that absorbs carbon dioxide is equal to the amount of plastic scintillating microspheres added to the ultrapure water.

[0017] As a further technical solution, the alkali solution is a sodium hydroxide solution or a lithium hydroxide solution; the molar concentration of the alkali solution is 0.01 mol / L to 10 mol / L, preferably 1 mol / L.

[0018] As a further technical solution, the T time is 0.01-100h, preferably 12h.

[0019] As a further technical solution, alkaline solution is used to absorb carbon dioxide in the air. The specific operation is: adding alkaline solution into a glass bottle, and then passing air into the alkaline solution to absorb carbon dioxide in the air.

[0020] As a further technical solution, the air introduction time is 0.01-30 days.

[0021] As a further technical solution, both C-14 samples and background samples are prepared in liquid scintillation bottles.

[0022] As a further technical solution, the liquid scintillation bottle is a glass liquid scintillation bottle or a plastic liquid scintillation bottle.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The present invention adopts plastic scintillation microspheres to replace the scintillation liquid in the traditional technology for sample pretreatment, which can be directly mixed with the alkaline solution absorbed with carbon dioxide without generating signal interference. Compared with the use of scintillation liquid in the traditional technology, the sample pretreatment steps are greatly simplified, the analysis time is shortened, the workload is reduced, and within the same time, the monitoring frequency of carbon dioxide C-14 is increased, thereby realizing more comprehensive monitoring of C-14 in the environment. DETAILED DESCRIPTION

[0025] The following will be combined with a clear and complete description of the technical solution of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than 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.

[0026] In the present invention, plastic scintillation microspheres are prior art, and the specific preparation method can refer to the preparation method of polystyrene scintillation microparticles disclosed in patent CN202210257955.X, the preparation method of polystyrene scintillation microspheres disclosed in patent CN202110301099.9, and the preparation method of plastic scintillation microspheres disclosed in patent CN202210257909.X.

[0027] Example 1

[0028] Calibration of counting efficiency ε:

[0029] In a 20mL glass liquid scintillation bottle, add 20mL of plastic scintillation microspheres, and then add 10mL of C-14 standard solution (solvent is Na2CO3 solution), activity is 100Bq, shake thoroughly for 10 minutes to allow the plastic scintillation microspheres and solution to disperse evenly, and obtain the C-14 standard sample;

[0030] The background sample was replaced by ultrapure water.

[0031] Place the C-14 standard sample and background sample in a liquid scintillation counter and measure for 10 minutes to obtain the counts and calculate the counting efficiency of the sample. S =23590;N B =271;t=600s;A=100Bq;

[0032]

[0033] Where ε is the counting efficiency, N Sis the count of the C-14 standard sample; N B is the count of the background sample; t is the measurement time, unit is s; A is the activity of the added C-14 standard source.

[0034] Example 2

[0035] A method for measuring the specific activity of carbon dioxide C-14 in air based on plastic scintillation microspheres comprises the following steps:

[0036] Prepare a 1 mol / L sodium hydroxide solution with sodium hydroxide and ultrapure water, take 10 mL into a glass bottle, and then use a vacuum pump to pass air into the sodium hydroxide solution at a gas flow rate of 1 L / min for 5 days;

[0037] Place 20 mL of plastic scintillation microspheres in a 20 mL glass liquid scintillation bottle, transfer 10 mL of sodium hydroxide solution that has absorbed carbon dioxide into the glass liquid scintillation bottle, and shake thoroughly for 10 minutes to evenly disperse the plastic scintillation microspheres and the solution to obtain a C-14 sample;

[0038] Place 20 mL of plastic scintillation microspheres in a 20 mL glass liquid scintillation bottle, transfer 10 mL of ultrapure water to the glass liquid scintillation bottle, and shake thoroughly for 10 minutes to allow the plastic scintillation microspheres and solution to disperse evenly to obtain a background sample;

[0039] The C-14 sample and the background sample were placed in a dark room away from light for 12 hours, and then placed in a liquid scintillation counter for measurement for 12 hours. The counts of the C-14 sample and the background sample within 12 hours were recorded. In this embodiment, N = 19886; N B＝ 19440; t = 12 hours, ε = 39%; M = 0.01 mol;

[0040]

[0041] In the formula, a C-14 is the specific activity of C-14 in air; N is the count of the C-14 sample; N B is the count of the background sample; t is the measurement time; ε is the counting efficiency; M is the molar amount of the alkali solution.

[0042] It was determined that the specific activity of C-14 in the air of this embodiment was 0.22 Bq / gC.

[0043] Example 3

[0044] A method for measuring the specific activity of carbon dioxide C-14 in air based on plastic scintillation microspheres comprises the following steps:

[0045] Prepare a 2 mol / L lithium hydroxide solution with sodium hydroxide and ultrapure water, take 10 mL into a glass bottle, and use a vacuum pump to pass air into the lithium hydroxide solution at a gas flow rate of 2 L / min for 4 days;

[0046] Place 20 mL of plastic scintillation microspheres in a 20 mL glass liquid scintillation bottle, then transfer 10 mL of lithium hydroxide solution that has absorbed carbon dioxide into the glass liquid scintillation bottle, and shake thoroughly for 20 minutes to allow the plastic scintillation microspheres and solution to disperse evenly to obtain a C-14 sample;

[0047] Place 20 mL of plastic scintillation microspheres in a 20 mL glass liquid scintillation vial, transfer 10 mL of ultrapure water into the glass liquid scintillation vial, and shake thoroughly for 10 minutes to mix the plastic scintillation microspheres and the solution evenly to obtain a background sample;

[0048] The C-14 sample and the background sample were placed in a dark room away from light for 12 hours, and then placed in a liquid scintillation counter for measurement for 12 hours. The counts of the C-14 sample and the background sample within 12 hours were recorded. In this embodiment, N = 20386; N B =19445; t = 12 hours; ε = 39%; M = 0.02 mol;

[0049]

[0050] In the formula, a C-14 is the specific activity of C-14 in air; N is the count of the C-14 sample; N B is the count of the background sample; t is the measurement time; ε is the counting efficiency; M is the molar amount of the alkali solution.

[0051] It was determined that the specific activity of C-14 in the air of this embodiment was 0.23 Bq / gC.

[0052] The above-described embodiments are only preferred embodiments of the present invention, and are not exhaustive of the feasible implementations of the present invention. For those skilled in the art, any obvious changes made thereto without departing from the principles and spirit of the present invention should be considered to be included in the scope of protection of the claims of the present invention.

Claims

1. A method for measuring the specific activity of carbon dioxide C-14 in air based on plastic scintillation microspheres, characterized in that: The steps include: Step 1, sample treatment: use alkali solution to absorb carbon dioxide in the air, transfer the alkali solution that has absorbed all or part of the carbon dioxide into a liquid scintillation bottle, add plastic scintillation microspheres thereto, shake and mix evenly, and obtain a C-14 sample; add an equal amount of plastic scintillation microspheres to ultrapure water, shake and mix evenly, and obtain a background sample; Step 2, determination: After the C-14 sample and the background sample are stored in the dark for T time, they are placed in a liquid scintillation counter to measure the time t, and the counts of the C-14 sample and the background sample within the time t are recorded; the specific activity of C-14 in the air is calculated using the following calculation formula (1): in, aC-14 is the specific activity of C-14 in air; N is the count of the C-14 sample; N B is the count of the background sample; t is the measurement time; ε is the counting efficiency; M is the molar amount of the alkali solution.

2. A method for measuring the specific activity of carbon dioxide C-14 in air based on plastic scintillation microspheres according to claim 1, characterized in that: The amount of alkali solution that absorbs carbon dioxide is equal to the amount of ultrapure water; the amount of plastic scintillating microspheres added to the alkali solution that absorbs carbon dioxide is equal to the amount of plastic scintillating microspheres added to the ultrapure water.

3. The method for measuring the specific activity of carbon dioxide C-14 in air based on plastic scintillation microspheres according to claim 1, characterized in that: The alkali solution is a sodium hydroxide solution or a lithium hydroxide solution; the molar concentration of the alkali solution is 0.01 mol / L to 10 mol / L, preferably 1 mol / L.

4. The method for measuring the specific activity of carbon dioxide C-14 in air based on plastic scintillation microspheres according to claim 1, characterized in that: The T time is 0.01-100h, preferably 12h.

5. The method for measuring the specific activity of carbon dioxide C-14 in air based on plastic scintillation microspheres according to claim 1, characterized in that: Alkali solution is used to absorb carbon dioxide in the air. The specific operation is: add alkali solution into a glass bottle, and then pass air into the alkali solution to absorb carbon dioxide in the air.

6. The method for measuring the specific activity of carbon dioxide C-14 in air based on plastic scintillation microspheres according to claim 5, characterized in that: The air ventilation time is 0.01-30 days.

7. The method for measuring the specific activity of carbon dioxide C-14 in air based on plastic scintillation microspheres according to claim 1, characterized in that: Both C-14 samples and background samples were prepared in liquid scintillation vials.

8. The method for measuring the specific activity of carbon dioxide C-14 in air based on plastic scintillation microspheres according to claim 7, characterized in that: The liquid scintillation bottle is a glass liquid scintillation bottle or a plastic liquid scintillation bottle.

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