Method and System for Determining the Calibration Factor at Different Times in Radon Measurement in a Scintillation Chamber

Abstract

This invention relates to a method and system for determining the calibration factor of a scintillation chamber at different times for radon detection, and pertains to the field of nuclear radiation detection technology. Based on the relationship between the calibration factor of the scintillation chamber after equilibrium and the average detection efficiency of radon and its progeny, the calibration factor of the scintillation chamber after equilibrium is obtained by constructing a scintillation chamber model and simulating its detection efficiency for alpha particles of different energies of radon and its progeny. Then, based on the decay laws of radon and its progeny, a relationship model is established between the calibration factor of the scintillation chamber after equilibrium and the calibration factors at other different times, thereby determining the calibration factor values ​​at different times. This method has no particular limitations on the specific size of the scintillation chamber and is theoretically applicable to scintillation chambers of all sizes. Furthermore, it can directly determine the calibration factor of the scintillation chamber at different times for radon detection without actual experimental operation, thus enabling rapid calibration of the radon concentration in the scintillation chamber.

Description

Technical Field

[0001] This invention relates to the field of nuclear radiation detection technology, and in particular to a method and system for determining the calibration factor at different times when measuring radon in a scintillation chamber. Background Technology

[0002] The principle of radon measurement using the scintillation chamber method is that alpha particles released by radon and its progeny in the scintillation chamber strike the inner wall of the scintillation chamber coated with ZnS(Ag), producing a flash. These flashes are then converted into electrical pulses by a photomultiplier tube. After the pulse signal is amplified by electronic circuitry, the number of pulses is recorded. The radon concentration in the scintillation chamber is determined based on the calibration factor after 3 hours. In the literature "Sensintaffar EL, Windham S T. Calibration of scintillation cells for radon-222 measurements at the US Environmental Protection Agency[J]. Journal of research of the National Institute of Standards and Technology, 1990, 95(2):143," EL Sensintaffar et al. transferred radon samples from an air mixture to a sparse scintillation chamber and sealed it for more than 4 hours. They used the relationship between the net count rate of alpha particles and radon activity to calculate the calibration factor. Zhao Guizhi et al. established a method for calibrating radon concentration in a scintillation chamber based on the relationship between the average detection efficiency of alpha particles after equilibrium and the scintillation chamber calibration factor. The scintillation chamber method for radon measurement cannot distinguish between alpha particles of different energies and usually requires a long time to complete the measurement.

[0003] The literature “Wang Zhengxia, Li Zhiqiang, Li Yanqiu, Zhang Shuyan, Xu Yong, Li Lei. Research on rapid calibration method based on small scintillation chamber radon meter [J]. Journal of Sichuan University (Natural Science Edition), 2022, (02): 146-150” and Chinese patent literature CN114637040A both disclose a rapid calibration method based on a small scintillation chamber radon meter. The method uses the radon concentration of the radon source as the radon standard concentration. After sampling and filtering, the radon is injected into the scintillation chamber of the radon meter. First, the radon concentration in the scintillation chamber during calibration and the scale factor value of the measurement cycle corresponding to the initial calibration are calculated. Then, according to the relationship model between the initial calibration scale factor and the scale factor values ​​of other measurement cycles, the scale factor values ​​of other measurement cycles are determined. That is, the scale factor of other different short measurement cycles is calibrated by measuring a set of scale factors of long measurement cycles. The implementation of the above method requires the following conditions: 1. The distance between any two points in the scintillation chamber is less than the range of the alpha particles released by the decay of Rn-222 and its progeny. 2. The calibration factor needs to be determined experimentally using a standard radon source. However, the 500ml scintillation chambers currently used in the market do not meet condition 1, meaning that the calibration factor values ​​at different times cannot be determined using this method. Furthermore, using a standard radon source to experimentally calibrate the calibration factor also suffers from operational inconvenience. Summary of the Invention

[0004] One of the objectives of this invention is to provide a method for determining the calibration factor of radon measurement at different times in a scintillation chamber without physical experiments, thereby achieving rapid calibration of the radon concentration in the scintillation chamber.

[0005] To achieve the above objectives, the present invention employs the following solution: a method for determining the calibration factor at different times in a scintillation chamber for radon measurement, comprising the following steps:

[0006] I. Determine the calibration factor of the scintillation chamber after equilibrium through simulation experiments;

[0007] A scintillation chamber model was constructed, and the detection efficiency of single-energy alpha particles generated by radon and its progeny within the model was simulated using a computer. The simulated detection efficiency was then substituted into the following formula to calculate the calibration factor K0 of the scintillation chamber after equilibrium:

[0008]

[0009] In the above formula, η R η A and η C The values ​​represent the detection efficiencies of the scintillation chamber for alpha particles generated by Rn-222, Po-218, and Bi-214, respectively, with V being the volume of the scintillation chamber in m³. 3 ;

[0010] II. Based on the calibration factor K0 value of the scintillation chamber after equilibration, determine the calibration factor values ​​K for other different times t using the following formula.x :

[0011]

[0012] in,

[0013]

[0014] In the above formula, λ R , λ A , λ B , λ C The decay constants (s) of Rn-222, Po-218, Pb-214, and Bi-214 are respectively. -1 ), λ R =2.1×10 -6 s -1 , λ A =3.8×10 -3 s -1 , λ B =4.3×10 -4 s -1 , λ C =5.9×10 -4 s -1 , t0=10800s.

[0015] In one embodiment of the present invention, a system for determining the calibration factor at different times in a scintillation chamber for radon measurement is also provided, comprising:

[0016] The model building unit is used to build a scintillation chamber model in a computer based on the input scintillation chamber parameters.

[0017] The simulation unit is used to simulate the detection efficiency of alpha particles in a scintillation chamber model in a computer.

[0018] The data processing unit is used to calculate the calibration factor K0 of the scintillation chamber after equilibrium based on the detection efficiency of alpha particles in the scintillation chamber model obtained from the simulation unit and the following formula:

[0019]

[0020] In the above formula, η R η A and η C The values ​​represent the detection efficiencies of the scintillation chamber for alpha particles generated by Rn-222, Po-218, and Bi-214, respectively, with V being the volume of the scintillation chamber in m³. 3 ;

[0021] Furthermore, based on the calculated scale factor K0 value of the scintillation chamber after equilibrium, the scale factor values ​​K for other different times t are determined using the following formula.x :

[0022]

[0023] in,

[0024]

[0025] In the above formula, λ R , λ A , λ B , λ C The decay constants (s) of Rn-222, Po-218, Pb-214, and Bi-214 are respectively. -1 ), λ R =2.1×10 -6 s -1 , λ A =3.8×10 -3 s -1 , λ B =4.3×10 -4 s -1 , λ C =5.9×10 -4 s -1 , t0=10800s.

[0026] This invention, based on the relationship between the calibration factor of the scintillation chamber after equilibrium and the average detection efficiency of radon and radon progeny, constructs a scintillation chamber model and simulates its detection efficiency for alpha particles of different energies of radon and radon progeny to obtain the calibration factor of the scintillation chamber after equilibrium. Then, according to the decay law of radon and its progeny, a relationship model is established between the calibration factor of the scintillation chamber after equilibrium and the calibration factors at other different times, thereby determining the calibration factor values ​​at different times. The deviation between the calibration factor values ​​of the scintillation chamber at different times determined by the above method and the experimentally measured values ​​is less than 5%, and the two results are basically consistent, proving that the method is feasible. It is particularly worth mentioning that this method has no particular restrictions on the specific size of the scintillation chamber, is applicable to scintillation chambers commonly used in the industry, and can directly determine the calibration factor of the scintillation chamber at different times for radon measurement without actual experimental operation, thus enabling rapid calibration of the radon concentration in the scintillation chamber. Attached Figure Description

[0027] Figure 1 A simplified decay chain diagram of radon and its decay products;

[0028] Figure 2 A visualization model of the scintillation chamber;

[0029] Figure 3 Schematic diagram of the scintillation chamber calibration factor experimental verification device;

[0030] Figure 4-6 The energy spectra of alpha particles at energies of 5.49 MeV, 6.00 MeV, and 7.69 MeV are shown.

[0031] Figure 7-8 The theoretical scaling factor K of the scintillation chamber at different times x With experimental scale factor K ex The relationship diagram. Detailed Implementation

[0032] To help those skilled in the art better understand the improvements of this invention compared to the prior art, the invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0033] I. Simulation of α-particle detection efficiency in scintillation chamber

[0034] Monte Carlo simulations of alpha particle transport within a scintillation chamber are one of the most effective methods for estimating the alpha particle detection efficiency of a scintillation chamber. In this embodiment, a model of an ST-203 scintillation chamber is constructed using Geant4 on a Linux system to simulate the detection efficiency of the scintillation chamber for a single alpha emitter produced by radon and its progeny. The ST-203 scintillation chamber is a commonly used and representative scintillation chamber. Its internal cavity is approximately spherical, with a diameter of 9.85 cm and a volume of 500 mL. The scintillation chamber is divided into four equal-volume compartments by plexiglass partitions. Both the inner walls and the partitions are coated with ZnS(Ag), and each compartment has the same alpha particle detection efficiency. Therefore, the scintillation chamber model can be simplified to a quarter-sphere, with an outer shell made of ZnS(Ag) and an inner layer filled with air. Since the bottom of the scintillation chamber is the observation window and is not coated with ZnS(Ag), Boolean operations can be used to cut the bottom of the scintillation chamber during model construction. The visualization model is shown below. Figure 2 As shown.

[0035] In Geant4, the simulation process involves customizing particle properties and adding relevant physical processes. The G4GeneralParticleSource method is used to customize the alpha particle source, which is isotropically emitted and randomly distributed within the scintillation chamber. Since alpha particles primarily undergo inelastic collisions with airborne particles, resulting in ionization, the physical processes can be simulated using Geant4's built-in QBBC electromagnetic interaction model. Under natural environmental conditions, 10 alpha particles are emitted based on the constructed scintillation chamber model. 4 Alpha particles with different energies (5.49 MeV, 6.00 MeV, 7.69 MeV) were used to simulate their detection efficiency in a scintillation chamber.

[0036] II. Determining the calibration factor of the scintillation chamber after equilibrium based on simulation results

[0037] It is known that radon (Rn-222) decays upon entering a scintillation chamber until it produces the stable nuclide Pb-206. During this decay, the number of nuclei changes according to a sequential decay law. However, the half-lives of each daughter nuclide are different, with Pb-210 having the longest half-life. Therefore, the daughter nuclides following Pb-210 are not practically meaningful for studying the calibration factor of the scintillation chamber. Thus, the decay chain of radon and its daughter nuclides can be simplified as follows: Figure 1 As shown.

[0038] from Figure 1 It can be seen that only Rn-222, Po-218 and Po-214 nuclides can produce alpha particles in the entire decay chain. However, the half-life of Po-214 is very short, only 164 μs. Therefore, the alpha particles produced by Po-214 are regarded as being directly produced by Bi-214.

[0039] If the radon concentration in the scintillation chamber remains constant during sampling, and the radon distribution within the scintillation chamber is uniform at t=0, then, assuming the measurement time is t, the radon concentration is determined based on the relationship between the scintillation chamber's calibration factor and the net total alpha particle count rate collected by the calibrator at that time. The formula for measuring radon concentration in the scintillation chamber is:

[0040] C = KN(Δt) (1);

[0041] In the formula, C is the radon concentration in the scintillation chamber (Bq·m³). -3 K is the scale factor of the scintillation chamber at different times (Bq·m). -3 ·cpm -1 N(Δt) represents the total net alpha particle count (cpm) generated by the decay of Rn-222, Po-218, and Bi-214 at different times.

[0042] When using the scintillation chamber method to measure radon, the radon concentration is generally measured starting 3 hours after sampling. At this time, radon and its progeny in the scintillation chamber reach dynamic equilibrium, and the weights of the three types of alpha particles produced are equal. Therefore, the detection efficiency of the scintillation chamber for alpha particles can be expressed as the average detection efficiency of the three. After equilibrium is reached, the calibration factor K0 of the scintillation chamber and the average detection efficiency are related. Satisfy the following relations:

[0043]

[0044] In the formula, V represents the volume of the scintillation chamber, in meters (m³). 3 The average detection efficiency of the scintillation chamber for alpha particles for:

[0045]

[0046] In the formula η R η A and η CThese represent the detection efficiencies of the scintillation chamber for α particles generated by Rn-222, Po-218, and Bi-214, respectively. Substituting equation (3) into equation (2) yields the calibration factor of the scintillation chamber after equilibrium:

[0047]

[0048] Under natural environmental conditions, based on the constructed scintillation chamber model, 10 [units of something] were emitted respectively. 4 Alpha particles with different energies (5.49 MeV, 6.00 MeV, and 7.69 MeV) were simulated for their detection efficiency in a scintillation chamber. The energy spectra of the three alpha particles are shown below. Figure 4 As shown.

[0049] Figure 4-6 The figures represent the energy spectra of alpha particles with energies of 5.49 MeV, 6.00 MeV, and 7.69 MeV, respectively. Entries indicate the number of alpha particles collected by the scintillation chamber at energies of 5.49 MeV, 6.00 MeV, and 7.69 MeV: 8093, 8707, and 9626, respectively. Based on the ratio of the number of collected alpha particles to the number of emitted alpha particles, the detection efficiency η of the scintillation chamber for 5.49 MeV alpha particles can be obtained. R The detection efficiency is 80.93%; the detection efficiency η for 6.00 MeV α particles is... A The detection efficiency is 87.07%; the detection efficiency η for 7.69 MeV α particles is... C The result is 96.26%. Substituting the above result into equation (4), the calibration factor K0 of the scintillation chamber after equilibrium is obtained as 12.6 Bq·m. -3 ·cpm -1 .

[0050] III. Establishing a model relating the calibration factor of the scintillation chamber after equilibrium to the calibration factors at other different times.

[0051] It is known that radon and its decay products continuously decay within the scintillation chamber from the end of sampling until equilibrium is reached. Assuming that the number of α particles produced by the decay of Rn-222 remains constant throughout the entire process, the relationship between the number of α particles collected in the scintillation chamber and Rn-222, Po-218, and Bi-214 is as follows:

[0052] N(Δt)=N R η R +N A v A +N c η C (5);

[0053] In the formula, N(Δt) is the total net count rate of α particles collected in the scintillation chamber at time t; N R N A N CLet N represent the alpha decay numbers produced by Rn-222, Po-218, and Bi-214 at time t, respectively. After 3 hours of rest, radon and its progeny in the scintillation chamber reach dynamic equilibrium, and the weights of the three alpha particle productions are equal. At this point, N... R =N A =0.9731×N R (N R =N A ≈N C 0.9731 represents the ratio of the number of decaying Bi-214 atoms to radon atoms in transient equilibrium. The relationship between the number of alpha particles collected in the scintillation chamber and Rn-222, Po-218, and Bi-214 is as follows:

[0054] N(Δt0)=N R (η R +η A ++0.9731×η C (6);

[0055] In the formula, t0 represents the 3rd hour (180th minute), i.e., t0 = 10800 s; Δt0 represents the unit time from 10740 s to 10800 s; N(Δt0) is the net total alpha particle count rate collected in the scintillation chamber at time t0. Given that the radon concentration at time t0 is equal to that at different times t, then K0 and K... x Satisfy the following relations:

[0056] C=K0N(Δt0=K x N(Δt) (7);

[0057] In the formula K x The scale factor of the scintillation chamber at different times is obtained according to equations (5), (6), and (7):

[0058]

[0059] Based on the decay relationships of radon and its decay products, the radioactivity A of Rn-222, Po-218, and Bi-214 can be obtained. R (t), A A (t), A C The change of (t) with time satisfies the following equation:

[0060]

[0061]

[0062]

[0063] in:

[0064]

[0065]

[0066]

[0067]

[0068] In the formula λ R , λ A , λ B , λ C The decay constants (s) of Rn-222, Po-218, Pb-214, and Bi-214 are respectively. -1 ), where λ R =2.1×10 -6 s -1 , λ A =3.8×10 -3 s -1 , λ B =4.3×10 -4 s -1 , λ c =5.9×10 -4 s -1 Let A0 be the radioactivity of radon in the scintillation chamber at t = 0. Then, at time t, the number of α particles produced per unit time by the decay of Rn-222, Po-218, and Bi-214 in the scintillation chamber are respectively N. R N A N C :

[0069]

[0070]

[0071]

[0072] Since the number of α particles generated by the decay of Rn-222 remains constant throughout the process, the number of α particles generated by the decay of Rn-222 per unit time in the scintillation chamber at times t and t0 is equal. Therefore, equation (12) can be expressed as:

[0073]

[0074] Substituting equations (13), (14), and (15) into equation (8), the scale factor of the scintillation chamber at different times is calculated as follows:

[0075]

[0076] In the formula:

[0077]

[0078]

[0079] A and B represent the ratios of the number of decaying atoms of Po-218 and Bi-214 to radon at different times in transient equilibrium.

[0080] Substituting equation (16) into equation (7) yields the formula for calculating radon concentration:

[0081]

[0082] Equation (17) is the formula for calculating the radon concentration in the scintillation chamber at different measurement times. Based on the detection efficiency of the scintillation chamber for a single α emitter generated by radon and its progeny, the calibration factor of the scintillation chamber after equilibrium, and the net count rate of total α particles generated by the decay of radon and its progeny at different times as measured experimentally, the radon concentration in the scintillation chamber can be calculated, thereby achieving rapid calibration of the radon concentration in the scintillation chamber.

[0083] IV. Experimental Verification and Error Analysis

[0084] The radon concentration calibration method using a scintillation chamber was experimentally verified. The scintillation chamber calibration factor experimental setup mainly consists of an ST-203 scintillation chamber manufactured by Beijing Nuclear Instrument Factory, an FD125 radon-thorium analyzer, and a BHC336 calibrator. Figure 3 As shown. The experimental environment temperature ranged from 10℃ to 35℃, humidity was around 50%, and air pressure was standard atmospheric pressure. To reduce counting errors and ensure that the photoelectric signals generated by alpha particles produced by radon and its decay products hitting the inner wall of the scintillation chamber and the organic partition could be recorded, the working high voltage of the BHC336 calibrator was set to -528V, and the lower threshold was set to 0.7V. In this experiment, the scintillation chamber was first cleaned with a vacuum pump, and then the background count in the scintillation chamber was measured using an FD125 radon-thorium analyzer. Then, the scintillation chamber was evacuated (a vacuum degree less than 0.1MPa was defined as a vacuum) and clamped with a spring clamp. A 1mL syringe was used to draw 1mL of radon source from the container and inject it into the vacuum scintillation chamber through the decay filter. Then, the spring clamp on one side of the rubber tube was loosened to allow the air pressure inside and outside the scintillation chamber to equalize before clamping and letting it stand. The entire sampling process was completed within 5 minutes.

[0085] After sampling, the scintillation chamber was placed on an FD125 radon-thorium analyzer. The calibrator's acquisition time and number of samplings were set to measure the total alpha particle count rate N generated by the decay of radon and its progeny in the scintillation chamber at different times. The radon concentration C in the scintillation chamber was calculated by substituting the calibration factor K0 of the scintillation chamber obtained from the simulation after equilibrium and the total alpha particle count rate measured at time t0 in the experiment into equation (1). Then, the experimental calibration factor K of the scintillation chamber at different times was calculated based on the radon concentration C and equation (1). ex .

[0086] The total number of alpha particles produced per unit time by the decay of radon and its progeny within the scintillation chamber at different times was measured using an FD125 radon-thorium analyzer. The average value was calculated after three repeated measurements. The calibration factor K0 of the scintillation chamber at time t0 is known to be 12.6 Bq·m. -3 ·cpm -1 The net count of α particles N(Δt0) in the scintillation chamber at time t0 was measured experimentally. Substituting this value into equation (1) yielded the radon concentration C in the scintillation chamber. The results are shown in Table 1.

[0087] Table 1 Radon concentration in the scintillation chamber

[0088]

[0089] Table 1 shows that there are differences between the data from the three experiments. This is due to factors such as background fluctuations in the scintillation chamber, inaccuracy of manual sampling, randomness of alpha particle generation, and statistical fluctuations. However, overall, the experimentally measured data conforms to the decay law of radioactive nuclides. Therefore, to reduce the alpha particle counting error caused by the above factors, the average value of the three experimental measurements is taken. Since the radon progeny remaining from the previous experiment will affect this experiment, it is necessary to deduct the background count in the scintillation chamber. The background count in the scintillation chamber was measured to be 8 cpm. The radon concentration C entering the scintillation chamber was calculated using equation (1) as C = 81526 Bq·m. -3 The experimental calibration factor K of the scintillation chamber at different times can be obtained by combining the total number of α particles produced per unit time by radon and its progeny decays in the scintillation chamber at different times with equation (1). ex This is compared with the theoretical scaling factor K of the scintillation chamber at different times. x The difference K between the two is compared. error =(K ex -K x ) / K ex ×100%, according to Equation (16) and Equation (1), the theoretical and experimental calibration factors of the scintillation chamber at 30 min, 60 min, 90 min and 120 min were calculated and the deviation between the two was calculated. The results are shown in Table 2.

[0090] Table 2. Scale factors of the scintillation chamber at 30 min, 60 min, 90 min, and 120 min.

[0091]

[0092] Table 2 shows that at the measurement times of 30 min, 60 min, 90 min, and 120 min, the theoretically calculated calibration factor and the calibration factor obtained from the experimental numerical analysis are basically consistent, with a deviation of less than 5%, proving that the theoretical calibration factor calculation formula for the scintillation chamber at these four times is feasible. Similarly, the theoretical calibration factor K of the scintillation chamber at different times is calculated. x and experimental scale factor K ex The relationship between time t and the change of time t, such as Figure 7 As shown; K of the scintillation chamber at different times x and K ex Error analysis was performed on both, and the results are as follows: Figure 8 As shown.

[0093] Depend on Figure 7 The experimental calibration factor K of the scintillation chamber at different times can be determined. ex With theoretical scale factor K x The curves are basically the same, from Figure 8 It can be known that the theoretical scale factor K of the scintillation chamber at different times is... x The experimental scale factor K obtained from experimental numerical analysis ex The deviation is less than 5%, proving that it is feasible to calculate the scale factor of the scintillation chamber at different times according to formula (16).

[0094] It should be noted that in this invention, the process of determining the theoretical calibration factor of radon measurement at different times in the scintillation chamber can be entirely performed using a computer. For example, a calibration factor determination system for radon measurement at different times in a scintillation chamber can be designed. This system may include a model building unit, a simulation unit, and a data processing unit. The model building unit is used to build a scintillation chamber model in the computer based on the scintillation chamber parameters input by the user. The simulation unit is used to simulate the detection efficiency of alpha particles in the scintillation chamber model in the computer. The data processing unit is used to calculate the calibration factor K0 of the scintillation chamber after equilibrium based on the detection efficiency of alpha particles in the scintillation chamber model obtained by the simulation unit and the aforementioned equation (4). It also uses the calculated calibration factor K0 of the scintillation chamber after equilibrium and the equation (16) to determine the calibration factor values ​​K at other different times t. x .

[0095] This embodiment, based on the relationship between the calibration factor of the ST-203 scintillation chamber after equilibrium and the average detection efficiency of radon and its progeny, uses Geant4 to simulate the detection efficiency of radon and its progeny alpha particles of different energies, obtaining the calibration factor of the scintillation chamber after equilibrium. Then, according to the decay law of radon and its progeny, a relationship model between the calibration factor of the scintillation chamber after equilibrium and the calibration factors at other different times is established. Experiments on the calibration factor of radon measurement at different times are conducted using the ST-203 scintillation chamber, and the experimental calibration factor of the scintillation chamber at different times is calculated based on the total net count rate of alpha particles generated by the decay of radon and its progeny in the scintillation chamber. The results show that the deviation between the theoretical and experimental values ​​of the calibration factor of the scintillation chamber at different times is less than 5%, and the two results are basically consistent, proving that the method is feasible. It should be noted that this method has no particular limitations on the specific size of the scintillation chamber and is theoretically applicable to most common scintillation chambers. The calibration factor of the scintillation chamber at different times can be directly determined without experimental operation, thus enabling rapid calibration of the radon concentration in the scintillation chamber.

[0096] The above embodiments are preferred implementations of the present invention. In addition, the present invention can be implemented in other ways. Any obvious substitutions without departing from the concept of the present invention are within the protection scope of the present invention. To facilitate understanding by those skilled in the art regarding the improvements of the present invention compared to the prior art, some drawings and descriptions of the present invention have been simplified, and for clarity, some other elements have been omitted from this application. Those skilled in the art should realize that these omitted elements also constitute the content of the present invention.

Claims

1. A method for determining the calibration factor at different times during radon measurement in a scintillation chamber, characterized in that, Includes the following steps: I. Determine the calibration factor of the scintillation chamber after equilibrium through simulation experiments; A scintillation chamber model was constructed, and the detection efficiency of single-energy alpha particles generated by radon and its progeny within the model was simulated using a computer. The simulated detection efficiency was then substituted into the following formula to calculate the calibration factor K0 of the scintillation chamber after equilibrium: ； In the above formula, , and The values ​​represent the detection efficiencies of the scintillation chamber for alpha particles generated by Rn-222, Po-218, and Bi-214, respectively, where V is the volume of the scintillation chamber, in units of... ; II. Based on the calibration factor K0 value of the scintillation chamber after equilibration, determine the calibration factor values ​​K for other different times t using the following formula. x : ； in, , ; In the above formula, ； ； ； ； , , , The decay constants (s) of Rn-222, Po-218, Pb-214, and Bi-214, respectively. -1 ), , , , , t0=10800s.

2. A system for determining the calibration factor at different times in a scintillation chamber for radon measurement, characterized in that it comprises: The model building unit is used to build a scintillation chamber model in a computer based on the input scintillation chamber parameters. The simulation unit is used to simulate the detection efficiency of alpha particles in a scintillation chamber model in a computer. The data processing unit is used to calculate the calibration factor K0 of the scintillation chamber after equilibrium based on the detection efficiency of alpha particles in the scintillation chamber model obtained from the simulation unit and the following formula: ； In the above formula, , and The values ​​represent the detection efficiencies of the scintillation chamber for alpha particles generated by Rn-222, Po-218, and Bi-214, respectively, where V is the volume of the scintillation chamber, in units of... ; Furthermore, based on the calculated scale factor K0 value of the scintillation chamber after equilibrium, the scale factor values ​​K for other different times t are determined using the following formula. x : ； in, , ; In the above formula, ； ； ； ； , , , The decay constants (s) of Rn-222, Po-218, Pb-214, and Bi-214, respectively. -1 ), , , , , t0=10800s.

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