A method for testing radon in sediment using a pulsed ionization chamber radon detector 224 Ra's Method

Abstract

The present invention provides a method for testing radon in sediment by using a pulsed ionization chamber radon detector. 224 The present invention uses a new type of radon measuring instrument, the pulsed ionization chamber radon measuring instrument (PIC), to quantitatively distinguish and measure the half-life characteristics of different radon isotopes. 220 Rn activity, and then according to the principle of long-term decay equilibrium of radioactive isotopes, the 224 The present invention does not need to carry a helium cylinder, has low test cost, a simple and portable test device, high test efficiency, and is convenient for on-site testing.

Description

Technical Field

[0001] The present invention relates to the field of analytical testing technology, and in particular to a method for testing radon in sediment using a pulsed ionization chamber radon detector. 224 Ra's method. Background Art

[0002] Short half-life radium isotopes ( 224 Ra, T 1 / 2 =3.66d) is suitable for studying short-time oceanographic processes (a few days to a few weeks). Some researchers have used 224 Ra studied the 224 Ra / 228 Th imbalance phenomenon, and then with the help of 224 Ra / 228 The Th imbalance method quantifies the exchange flux of trace metals, nutrients, and dissolved organic carbon at the sediment-water interface. 224 The universal test method for Ra is the radium synchronous delay counter method. This method can accurately and quickly measure the 224 Ra activity, its measurement accuracy is ±5% to 7%, and its reproducibility is ±5%. However, the radium synchronous delay counter requires high-purity helium as carrier gas during use, the test cost is high, and the required helium cylinder is not easy to carry, which limits its application in field tests. Summary of the invention

[0003] The purpose of the present invention is to provide a method for testing radon in sediment using a pulsed ionization chamber radon detector. 224 The testing method of Ra adopts the testing method of the present invention, and does not need to carry a helium cylinder, has low testing cost, and the testing device is simple and easy to carry, has high testing efficiency, and is convenient for on-site testing.

[0004] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0005] The present invention provides a method for testing radon in sediment by using a pulsed ionization chamber radon detector. 224 The method of Ra comprises the following steps:

[0006] (1) 224 The sediment standard sample of Ra is placed in a sample tray, which is connected to the sample tray, an air pump and a pulsed ionization chamber radon detector to form a test system;

[0007] Turn on the air pump to circulate the gas in the test system for at least 5 minutes to release the sediment standard sample. 220 Rn gas and sediment standard samples 224 Ra reaches radioactive equilibrium, and the activity of Rn in the test system is tested for the first time, and the result is 222Rn and 220 The sum of the counting rates of Rn, C1, is in cpm;

[0008] Turn off the air pump, close the inlet and outlet valves of the pulse ionization chamber radon detector, and let it stand for at least 5 minutes to allow the pulse ionization chamber radon detector to 220 Rn completely decays and disappears, and the second continuous test of Rn activity in the pulsed ionization chamber radon detector is carried out, and the result is 222 The counting rate of Rn is C2, in cpm;

[0009] According to formula 1, the content of the standard sediment sample was calculated. 224 Ra count rate;

[0010] The sediment standard sample 224 Ra count rate C p = in the sediment standard sample 220 The count rate C of Rn d = C1-C2 formula 1;

[0011] (2) Repeat step (1) to obtain different 224 Ra activity gradient in sediment standard samples 224 Ra count rate;

[0012] Different 224 Ra activity gradient in sediment standard samples 224 The counting rate of Ra is the vertical axis, different 224 Ra activity gradient in sediment standard samples 224 The activity of Ra is plotted on the horizontal axis. 224 Activity-count rate standard curve of Ra;

[0013] (3) Testing the sediment sample to be tested according to the method of step (1) to obtain 224 The counting rate of Ra is 224 The activity-count rate standard curve of Ra was used to calculate the content of Ra in the sediment sample to be tested. 224 The activity of Ra.

[0014] Preferably, the sediment sample to be tested and the sediment standard sample are of the same type.

[0015] Preferably, the flow rate of the air pump is 0.5 to 3 L / min.

[0016] Preferably, the moisture content of the sediment sample to be tested and the sediment standard sample is independently 0-70%.

[0017] Preferably, the first continuous test time is 0.5 to 6 hours.

[0018] Preferably, the second continuous test time is 0.5 to 4 hours.

[0019] Preferably, the step (3) further comprises calculating the amount of 224 Relative standard deviation of Ra activity.

[0020] Preferably, the calculation of the sediment sample to be tested 224 The method for calculating the relative standard deviation of the activity of Ra comprises the following steps:

[0021] Calculate the first continuous test according to equation 2 and equation 3 222 Rn and 220 The standard deviation of the sum of the count rates of Rn,

[0022]

[0023] N1=C1×T1 Formula 3;

[0024] In the above formula 2 and formula 3, σ1 is the first continuous test 222 Rn and 220 The standard deviation of the sum of the count rates of Rn, cpm; N1 is the count value of the first continuous test, times; T1 is the first continuous test time, min;

[0025] Calculate the second continuous test according to Equation 4 and Equation 5 222 The standard deviation of the count rate of Rn,

[0026]

[0027] N2=C2×T2 Formula 5;

[0028] In the above formula 4 and formula 5, σ2 is the second continuous test 222 The standard deviation of the count rate of Rn, cpm; N2 is the count value of the second continuous test, times; T2 is the second continuous test time, min;

[0029] According to formula 6 224 The relative standard deviation δ of the activity of Ra;

[0030]

[0031] Preferably, the masses of the sediment sample to be tested and the sediment standard sample are independently 1 to 60 g.

[0032] The present invention uses a new type of radon measuring instrument, the pulsed ionization chamber radon measuring instrument (PIC), to quantitatively distinguish and measure the half-life characteristics of different radon isotopes. 220 Rn activity, and then according to the principle of long-term decay equilibrium of radioactive isotopes, the224 The present invention does not need to carry a helium cylinder, has low test cost, a simple and portable test device, high test efficiency, and is convenient for on-site testing.

[0033] The testing principle of the present invention is as follows:

[0034] 224 Ra undergoes α decay and produces gaseous daughters 220 Rn, due to 224 Ra(T 1 / 2 =3.66d) has a much longer half-life than its daughter 220 Rn(T 1 / 2 =55.6s) half-life, according to the principle of long-term equilibrium of radioisotopes, 220 After five times the half-life of Rn (i.e. five minutes), 224 Ra and 220 Therefore, with the help of PIC radon detector, it is possible to measure 224 Gaseous daughter of Ra 220 Indirect determination of Rn in sediment 224 Ra content.

[0035] It should be noted that the test result of PIC is the sum of radon isotopes in the gas. The parent nuclide of radon isotopes is radium isotope (Ra). There are four natural radioactive radium isotopes in nature, namely 228 Ra(T 1 / 2 =5.75y), 226 Ra(T 1 / 2 =1620y), 224 Ra(T 1 / 2 =3.66d) and 223 Ra(T 1 / 2 =11.4d), when they decay, they will produce three Rn isotopes, namely 222 Rn(T 1 / 2 =3.83d), 220 Rn(T 1 / 2 =55.6s) and 219 Rn(T 1 / 2 = 3.96s). Since the test object of the ionization chamber is the positive and negative charges generated by ionization of air by alpha particles, PIC cannot directly distinguish 222 Rn, 220 Rn and 219 Rn. To obtain the three nuclides in the gas separately 220 Rn activity, the present invention designs the following scheme:

[0036] First, due to 223 Ra content in sediments is extremely low and 219The half-life of Rn is very short and can therefore be ignored during sediment testing. 219 Rn 220 Impact of Rn test.

[0037] Secondly, due to 222 Rn(T 1 / 2 =3.83d) and 220 Rn(T 1 / 2 =55.6s) have very different half-lives and 220 The half-life of Rn is relatively shorter, so it can be measured first. 222 Rn and 220 The sum of the Rn counting rates (C1) is calculated, and then the PIC inlet and outlet valves are closed (equivalent to removing the sample Rn source). The entire PIC radon detection system is sealed for 5 minutes until the ionization chamber 220 After Rn completely decays, the value measured by PIC is the 222 Rn count rate (C2). During the entire test time 222 The decay of Rn itself can be ignored, and the difference between the two measurement results is 220 The count rate C of Rn d , sediment samples 224 Ra count rate C p With offspring 220 Rn count rate C d equal:

[0038] C p =C d =C1-C2. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 FIG. 1 is a diagram of the experimental device used in the present invention. DETAILED DESCRIPTION

[0040] The present invention provides a method for testing radon in sediment by using a pulsed ionization chamber radon detector. 224 The method of Ra comprises the following steps:

[0041] (1) 224 The sediment standard sample of Ra is placed in a sample tray, which is connected to the sample tray, an air pump and a pulsed ionization chamber radon detector to form a test system;

[0042] Turn on the air pump to circulate the gas in the test system for at least 5 minutes to release the sediment standard sample. 220 Rn gas and sediment standard samples 224 Ra reaches radioactive equilibrium, and the activity of Rn in the test system is tested for the first time, and the result is 222 Rn and 220The sum of the counting rates of Rn, C1, is in cpm;

[0043] Turn off the air pump, close the inlet and outlet valves of the pulse ionization chamber radon detector, and let it stand for at least 5 minutes to allow the pulse ionization chamber radon detector to 220 Rn completely decays and disappears, and the second continuous test of Rn activity in the pulsed ionization chamber radon detector is carried out, and the result is 222 The counting rate of Rn is C2, in cpm;

[0044] According to formula 1, the content of the standard sediment sample was calculated. 224 Ra count rate;

[0045] The sediment standard sample 224 Ra count rate C p = in the sediment standard sample 220 The count rate C of Rn d = C1-C2 formula 1;

[0046] (2) Repeat step (1) to obtain different 224 Ra activity gradient in sediment standard samples 224 Ra count rate;

[0047] Different 224 Ra activity gradient in sediment standard samples 224 The counting rate of Ra is the vertical axis, different 224 Ra activity gradient in sediment standard samples 224 The activity of Ra is plotted on the horizontal axis. 224 Activity-count rate standard curve of Ra;

[0048] (3) Testing the sediment sample to be tested according to the method of step (1) to obtain 224 The counting rate of Ra is 224 The activity-count rate standard curve of Ra was used to calculate the content of Ra in the sediment sample to be tested. 224 The activity of Ra.

[0049] like Figure 1 As shown, the present invention first 224 The sediment standard sample of Ra is placed in a sample tray, which is connected to the sample tray, an air pump and a pulsed ionization chamber radon detector to form a test system.

[0050] The present invention does not have any special limitation on the pulsed ionization chamber radon detector (PIC), and any PIC known in the art can be used. The present invention has no special requirements on the connection method of the sample tray, air pump and pulsed ionization chamber radon detector, and the connection method known in the art can be used, which is common knowledge in the art. The present invention has no special requirements on the type of the sediment standard sample, and specifically it can be clay, silt sand, etc. In the present invention, the moisture content of the sediment standard sample is preferably 0 to 70%. Those skilled in the art can select a suitable moisture content according to the particle size of the sediment standard sample. In the present invention, the mass of the sediment standard sample is preferably 1 to 60g, more preferably 10 to 50g, and further preferably 20 to 40g.

[0051] After the test system is formed, the present invention turns on the air pump to circulate the gas in the test system for at least 5 minutes to release the sediment standard sample. 220 Rn gas and sediment standard samples 224 Ra reaches radioactive equilibrium, and the activity of Rn in the test system is tested for the first time, and the result is 222 Rn and 220 The sum of the counting rates of Rn is C1, in cpm.

[0052] In the present invention, the flow rate of the air pump is preferably 0.5 to 3.0 L / min, more preferably 1.0 to 2.0 L / min.

[0053] 224 Ra undergoes α decay and produces gaseous daughters 220 Rn, due to 224 Ra(T 1 / 2 =3.66d) has a much longer half-life than its daughter 220 Rn(T 1 / 2 =55.6s) half-life, according to the principle of long-term equilibrium of radioisotopes, 220 After five times the half-life of Rn (i.e. five minutes), 224 Ra and 220 There are four natural radioactive radium isotopes in nature, namely 228 Ra(T 1 / 2 =5.75y), 226 Ra(T 1 / 2 =1620y), 224 Ra(T 1 / 2 =3.66d) and 223 Ra(T 1 / 2 =11.4d), when they decay, they will produce three Rn isotopes, namely 222 Rn(T 1 / 2 =3.83d), 220 Rn(T1 / 2 =55.6s) and 219 Rn(T 1 / 2 = 3.96s). Since the test object of the ionization chamber is the positive and negative charges generated by ionization of air by alpha particles, PIC cannot directly distinguish 222 Rn, 220 Rn and 219 Therefore, in the first continuous test stage, the test results of PIC are radon isotopes in the gas ( 222 Rn, 220 Rn and 219 Rn). 223 Ra content in sediments is extremely low and 219 The half-life of Rn is very short and can therefore be ignored during sediment testing. 219 Rn 220 Therefore, the first continuous test stage obtained is 222 Rn and 220 The sum of the activities (count rates) of Rn.

[0054] In the present invention, the unit of counting rate is cpm, i.e. counts per minute, which is the number of decays of the radioactive element per minute observed by the instrument, and corresponds to the activity of the radioactive element at the corresponding stage determined by PIC.

[0055] The present invention has no special requirement on the upper limit of the time of the gas circulation.

[0056] In the present invention, the time of the first continuous test is preferably 0.5 to 6 hours, more preferably 2 to 4 hours. The longer the time of the first continuous test, the higher the count value, and the smaller the test error of this stage. The first continuous test time can be determined according to the need of the test error. The calculation method of the error will be described in detail later.

[0057] get 222 Rn and 220 After the sum of the counting rates of Rn and Rn is C1, the present invention closes the inlet and outlet valves of the pulsed ionization chamber radon detector and leaves it to stand for at least 5 minutes to allow the pulsed ionization chamber radon detector to 220 Rn completely decays and disappears, and the second continuous test of Rn activity in the pulsed ionization chamber radon detector is carried out, and the result is 222 The counting rate C2 of Rn is expressed in cpm.

[0058] In the present invention, the standing time is preferably 5 to 10 minutes.

[0059] In the present invention, the time of the second continuous test is preferably 0.5 to 4 hours, more preferably 1 to 3 hours. The longer the time of the second continuous test, the higher the count value, and the smaller the test error of this stage. The second continuous test time can be determined according to the needs of the test error. The calculation method of the error will be described in detail later.

[0060] get 222 Rn and 220 The sum of the count rates of Rn and C1 222 After the counting rate C2 of Rn is calculated, the present invention calculates the number of standard sediment samples according to Formula 1. 224 Ra count rate;

[0061] The sediment standard sample 224 Ra count rate C p = in the sediment standard sample 220 The count rate C of Rn d =C1-C2 formula 1.

[0062] The present invention repeats the above steps to obtain different 224 Ra activity gradient in sediment standard samples 224 The counting rate of Ra; then 224 Ra activity gradient in sediment standard samples 224 The counting rate of Ra is the vertical axis, different 224 Ra activity gradient in sediment standard samples 224 The activity of Ra is plotted on the horizontal axis. 224 Activity-count rate standard curve of Ra.

[0063] The present invention has no special requirements for the drawing process of the standard curve. After drawing the standard curve, the present invention obtains 224 Linear equation and correlation coefficient R of Ra activity-count rate 2 , correlation coefficient R 2 The closer it is to 1, the higher the accuracy of the test method of the present invention. In the present invention, the linear equation is preferably as shown in Formula 7: C1-C2=kA 标 +bFormula 7, where (C1-C2) is 224 Count rate of Ra, A 标 For standard samples 224 Ra activity, k is the instrument efficiency, and b is the content of the sediment sample before spiking. 224 Ra background value.

[0064] get 224 After the activity-count rate standard curve of Ra is obtained, the present invention tests the sediment sample to be tested according to the above steps and methods to obtain the 224 The counting rate of Ra is224 The activity-count rate standard curve of Ra was used to calculate the content of Ra in the sediment sample to be tested. 224 The activity of Ra.

[0065] In the present invention, the type of the sediment sample to be tested is preferably the same as the type of the sediment standard sample. For example, if the sediment standard sample is silty sediment, the sample to be tested also needs to be silty sediment.

[0066] The present invention preferably calculates the linear equation corresponding to the standard curve to obtain the content of the sediment sample to be tested. 224 The activity of Ra is calculated 224 The activity of Ra is a theoretically calculated activity. 224 Ra activity C 理论 =(C1-C2) / kFormula 8.

[0067] In order to ensure the accuracy of the test, the present invention preferably also includes calculating the 224 Relative standard deviation of Ra activity.

[0068] In the present invention, the calculation of the sediment sample to be tested 224 The method for calculating the relative standard deviation of the activity of Ra comprises the following steps:

[0069] Calculate the first continuous test according to equation 2 and equation 3 222 Rn and 220 The standard deviation of the sum of the count rates of Rn,

[0070]

[0071] N1=C1×T1 Formula 3;

[0072] In the above formula 2 and formula 3, σ1 is the first continuous test 222 Rn and 220 The standard deviation of the sum of the count rates of Rn, cpm; N1 is the count value of the first continuous test, times; T1 is the first continuous test time, min;

[0073] Calculate the second continuous test according to Equation 4 and Equation 5 222 The standard deviation of the count rate of Rn,

[0074]

[0075] N2=C2×T2 Formula 5;

[0076] In the above formula 4 and formula 5, σ2 is the second continuous test 222The standard deviation of the count rate of Rn, cpm; N2 is the count value of the second continuous test, times; T2 is the second continuous test time, min;

[0077] According to formula 6 224 The relative standard deviation δ of the activity of Ra;

[0078]

[0079] In the present invention, the sediment sample to be tested 224 The actual activity of Ra is C 实际 =C 理论 ×(1±δ).

[0080] The following is a description of the method for testing the radon content in sediments using the pulsed ionization chamber radon detector provided by the present invention in combination with the embodiments. 224 The method of Ra is described in detail, but they should not be understood as limiting the scope of protection of the present invention.

[0081] Example 1

[0082] Take 6 different 224 The silt sediment standard sample with Ra activity gradient was prepared using Figure 1 The experimental device shown in the figure adjusts the water content of the sediment standard sample to 30%, turns on the air pump, adjusts the air pump flow rate to 1L / min, and circulates the gas in the system for 5 minutes to release the water in the sediment standard sample. 220 Rn gas and sediment standard samples 224 Ra reaches radioactive equilibrium, and then Rn in the test system is tested continuously for 2 hours to obtain 222 Rn and 220 The sum of the count rates of Rn is C1. Turn off the air pump, close the PIC inlet and outlet valves, and let it stand for at least 5 minutes to allow the PIC 220 Rn completely decays and disappears. The Rn activity in PIC is tested continuously for 2 hours and the result is 222 The counting rate of Rn is C2, and the difference between the two measurement results (C1-C2) is the number of 220 The counting rate of Rn, that is, 224 The counting rate of Ra is different 224 Ra activity gradient in sediment standard samples 224 The counting rate of Ra is the vertical axis, different 224 Ra activity gradient in sediment standard samples 224 The activity of Ra is taken as the horizontal axis, and the sediment is plotted 224 The activity-count rate standard curve of Ra is fitted with a linear equation and R 2 Value, linear equation is: C1-C2=0.2A 标+1.6 formula 9.

[0083] Take 20g of silty sediment and place it in the sample tray. Test it according to the same test process and test conditions as the sediment standard sample. Adjust the weight ratio of water to dry sediment in the sediment to 0.3 (consistent with the standard sample). Turn on the air pump and adjust the air pump flow rate to 1L / min. Circulate the gas in the system for 5 minutes. Then, perform the first continuous test of Rn in the test system for two hours. The total Rn count rate C1 is 5.0cpm. Close the PIC inlet and outlet valves and let it stand for 5 minutes to allow the PIC to 220 Rn completely decays and disappears, affecting the 222 The Rn activity was tested for a second time for 2 hours. 222 The count rate C2 of Rn is 0.8 cpm. The difference between the two measurements is the 220 The count rate of Rn, 5.0cpm-0.8cpm=4.2cpm, in the sediment 224 Ra and system 220 Rn is in radioactive duration equilibrium, so the instrument 224 The counting rate of Ra is 4.2 cpm. For silty sediment samples, the efficiency of the standard sample is 0.2 cpm / dpm. 2 >0.99. According to formula 9, the 224 The theoretical activity of Ra is 4.2 cpm / 0.2 (cpm / dpm) / 20 g=1.05 dpm / g.

[0084] Error calculation: Total radon error in the first continuous test: 5 cpm x 120 min = 600 times, standard deviation of the counting rate

[0085] Second continuous test 222 Rn error: 0.8×120min=96 times, standard deviation of counting rate

[0086] therefore 224 Relative standard deviation of Ra

[0087] Therefore, the sediment sample 224 The actual activity of Ra is C 实际 =1.05dpm / g×(1±0.05)=1.05±0.05dpm / g.

[0088] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for testing radon in sediment using a pulsed ionization chamber radon detector 224 The method of Ra comprises the following steps: (1) 224 The sediment standard sample of Ra is placed in a sample tray, which is connected to the sample tray, an air pump and a pulsed ionization chamber radon detector to form a test system; Turn on the air pump to circulate the gas in the test system for at least 5 minutes to release the sediment standard sample. 220 Rn gas and sediment standard samples 224 Ra reaches radioactive equilibrium, and the activity of Rn in the test system is tested for the first time, and the result is 222 Rn and 220 The sum of the counting rates of Rn, C1, is in cpm; Turn off the air pump, close the inlet and outlet valves of the pulse ionization chamber radon detector, and let it stand for at least 5 minutes to allow the pulse ionization chamber radon detector to 220 Rn completely decays and disappears, and the second continuous test of Rn activity in the pulsed ionization chamber radon detector is carried out, and the result is 222 The counting rate of Rn is C2, in cpm; According to formula 1, the content of the standard sediment sample was calculated. 224 Ra count rate; The sediment standard sample 224 Ra count rate C p = in the sediment standard sample 220 The count rate C of Rn d = C1-C2 formula 1; (2) Repeat step (1) to obtain different 224 Ra activity gradient in sediment standard samples 224 Ra count rate; Different 224 Ra activity gradient in sediment standard samples 224 The counting rate of Ra is the vertical axis, different 224 Ra activity gradient in sediment standard samples 224 The activity of Ra is plotted on the horizontal axis. 224 Activity-count rate standard curve of Ra; (3) Testing the sediment sample to be tested according to the method of step (1) to obtain 224 The counting rate of Ra is 224 The activity-count rate standard curve of Ra was used to calculate the content of Ra in the sediment sample to be tested. 224 The activity of Ra.

2. The method according to claim 1, characterized in that The sediment sample to be tested and the sediment standard sample are of the same type.

3. The method according to claim 1, characterized in that The flow rate of the air pump is 0.5-3 L / min.

4. The method according to claim 1, characterized in that: The moisture content of the sediment sample to be tested and the sediment standard sample are independently 0-70%.

5. The method according to claim 1, characterized in that The time of the first continuous test is 0.5 to 6 hours.

6. The method according to claim 1, characterized in that The second continuous test time is 0.5 to 4 hours.

7. The method according to claim 1, characterized in that The step (3) also includes calculating the amount of sediment sample to be tested. 224 Relative standard deviation of Ra activity.

8. The method according to claim 7, characterized in that The calculation of the sediment sample to be tested 224 The method for calculating the relative standard deviation of the activity of Ra comprises the following steps: Calculate the first continuous test according to equation 2 and equation 3 222 Rn and 220 The standard deviation of the sum of the count rates of Rn, N1=C1×T1 Formula 3; In the above formula 2 and formula 3, σ1 is the first continuous test 222 Rn and 220 The standard deviation of the sum of the count rates of Rn, cpm; N1 is the count value of the first continuous test, times; T1 is the first continuous test time, min; Calculate the second continuous test according to Equation 4 and Equation 5 222 The standard deviation of the count rate of Rn, N2=C2×T2 Formula 5; In the above formula 4 and formula 5, σ2 is the second continuous test 222 The standard deviation of the count rate of Rn, cpm; N2 is the count value of the second continuous test, times; T2 is the second continuous test time, min; According to formula 6 224 The relative standard deviation δ of the activity of Ra; 9. The method according to claim 1, characterized in that: The masses of the sediment sample to be tested and the sediment standard sample are independently 1 to 60 g.

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