Polytetrafluoroethylene free radical dosimeter for ionizing radiation dose measurement

Abstract

The invention discloses a polytetrafluoroethylene free radical dosimeter for ionizing radiation dose measurement. The polytetrafluoroethylene free radical dosimeter is a spherical particle or a solid tablet prepared from polytetrafluoroethylene micro powder through the processes of mould pressing, sintering and the like. The polytetrafluoroethylene micro powder is polytetrafluoroethylene suspension resin generated through free radical polymerization of tetrafluoroethylene monomers, the tensile strength is larger than or equal to 30 MPa, the particle size is 200-300 microns, the melting point is larger than or equal to 322 DEG C, and the volume density is 550-590 g / L. The effective range of the polytetrafluoroethylene free radical dosimeter is 1-180 kGy, the free radical response of the dosimeter and the irradiation dose keep a direct proportion linear relation, the coefficient of determination R2 is equal to 0.999, and the polytetrafluoroethylene free radical dosimeter is especially suitable for ionizing radiation dose measurement of 100-180 kGy dose; and the total uncertainty of ionizing radiation ESR dose measurement is less than 5.02%.

Description

Technical Field

[0001] The invention belongs to the technical field of solid free radical dosimeters, and in particular relates to a polytetrafluoroethylene free radical dosimeter for measuring ionizing radiation dose. Background Art

[0002] The application of ionizing radiation lies in the effect of its radiation energy transfer, and the effect of radiation energy transfer is measured quantitatively by the amount of dose absorbed by the irradiated object. After the expected irradiation dose is set and the controllable irradiation process is implemented, the measurement of absorbed dose should be completed by establishing and maintaining a technically and economically reasonable and regulatory compliant dose measurement system. At present, there are a variety of dose measurement systems in the industry according to different measurement accuracy and application scenarios. Dosimeters, as radiation dose equivalent carriers, are important components of dose measurement systems. They are irradiated together with the irradiated object according to the irradiation process and equivalently represent the absorbed dose. The response value is read by the dose measurement device and substituted into the relevant dose response function to obtain its radiation dose value.

[0003] Solid free radical dosimeters were discovered by international peers as early as the 1950s. Among them, alanine dosimeters became the first choice due to their excellent metrological performance. Their preparation and application matured in the 1980s. The alanine-ESR dose measurement method was determined by the IAEA and used as the standard dosimeter and transfer dosimeter designated by the IDAS International Dose Assurance Service Program. my country successively released the first edition in 1996 and the new edition in 2008, GB / T16639-2008 "Standard Method for Using Alanine-ESR Dose Measurement System". At present, alanine dosimeters have become the dosimeters with the best metrological performance such as measurement accuracy, bioequivalence and traceability in China and abroad. However, alanine dosimeters also have some shortcomings. Whether there are materials that are equivalent to alanine dosimeters or have better metrological performance that can be used is also a direction that researchers of solid free radical dosimeters continue to explore.

[0004] Polytetrafluoroethylene (PTFE for short) is a high molecular polymer with the molecular formula (C2F4)n. It has many excellent properties, such as heat and corrosion resistance, non-stick self-lubrication, excellent dielectric properties and very small friction coefficient. It is widely used in the manufacture of various high-performance components and plays an important role in the fields of medicine, chemical industry, electronics, machinery, metallurgy and mining.

[0005] Polytetrafluoroethylene has the property that ionizing radiation can induce free radicals, and there is a possibility of being used as a free radical dosimeter. The inventors have conducted a large number of irradiation and electron spin resonance (ESR) test experiments and found that polytetrafluoroethylene has the characteristics of generating stable free radical response to radiation and being in a linear relationship proportional to the radiation dose. Through a series of experiments, it is proved that PTFE is feasible as a raw material for solid free radical dosimeter in terms of technology and economy, especially in terms of high and low temperature resistance, high dose resistance and dose response stability.

[0006] Patent document [Yang Jifang, Li Deming, Hu Shuhua. Energy response of lithium fluoride-polytetrafluoroethylene beta dose meter [J]. Nuclear Electronics and Detection Technology, Issue 1, 1982] discloses a lithium fluoride-polytetrafluoroethylene beta dose meter element [LiF-(C2F4)n], containing 30% LiF (Mg, Ti) and 70% polytetrafluoroethylene, formed by hot pressing and sintering; the product specifications are 10mm in diameter and 0.73mm in thickness (mass thickness is 120mg / cm 2 ) disc, which can be made thinner and has a certain degree of flexibility, and is suitable for measuring the beta dose at the end of the human body (such as fingers). However, the lithium fluoride-polytetrafluoroethylene beta dose meter involved in the document uses the principle of thermoluminescence to store the received radiation energy and then convert it into an electrical signal by heating and releasing the light signal (photomultiplier tube) to display the dose, and belongs to a thermoluminescence detector (TLD); its working principle is completely different from the polytetrafluoroethylene free radical dose meter of the present invention. Summary of the invention

[0007] The purpose of the present invention is to provide a polytetrafluoroethylene free radical dosimeter for measuring ionizing radiation dose, so as to solve the problems existing in the prior art in that the dosimeter element has high temperature resistance, high-dose irradiation resistance, wide measuring range and good physical properties.

[0008] In order to achieve the above object, the technical solution of the present invention is:

[0009] The polytetrafluoroethylene free radical dosimeter for measuring ionizing radiation dose of the present invention is characterized in that the spherical particles or solid tablets are made of polytetrafluoroethylene micropowder through molding and sintering processes;

[0010] The polytetrafluoroethylene powder is a polytetrafluoroethylene suspension resin generated by free radical polymerization of tetrafluoroethylene monomer, with a tensile strength of ≥30MPa, a particle size of 200-300μm, a melting point of ≥322°C, and a bulk density of 550-590g / L; the CAS number is 9002-84-0, such as DF-102 produced by Shandong Dongyue Polymer Materials Co., Ltd., and the cleanliness is first-class.

[0011] The method for preparing the polytetrafluoroethylene free radical dosimeter for measuring ionizing radiation dose of the present invention comprises the following steps:

[0012] S1, molding the polytetrafluoroethylene powder at room temperature and 40-55 MPa, maintaining the pressure for 3-10 minutes to complete the molding, and obtaining a green billet; and allowing the green billet to stand at room temperature for at least 50 minutes;

[0013] S2, sending the green billet into a sintering furnace; performing direct sintering or step sintering for 40 to 100 hours at a maximum sintering temperature of 350 to 390° C. (preferably 360 to 380° C.), and cooling the green billet naturally with the sintering furnace after sintering to obtain a clinker;

[0014] S3, processing the clinker into particles or tablets of a specified size by an automated turning process, thereby obtaining the polytetrafluoroethylene free radical dosimeter.

[0015] In the above process, if the molding pressure is not enough or the sintering temperature is too low, the structure of the sintered PTFE solid will not be dense and cannot meet the subsequent turning process. The final dosimeter is also prone to cracking, crushing and other problems.

[0016] Preferably, the green billet is in the shape of a cylinder with a diameter of 50±1 mm and a height of 50±1 mm.

[0017] Preferably, the step-by-step sintering process is as follows: the first step preheating stage: heating rate 50-80°C / h to 200°C and then keeping warm for 15-36h, the second step molten viscous flow stage: heating rate 30-60°C / h to 345°C and keeping warm for 30-48h, the third step sintering stage: heating rate 30-60°C / h and keeping warm for 24-40h. The method of slow heating step-by-step sintering can restrict the thermal motion of PTFE molecular chains, fully fuse PTFE particles, and finally obtain a PTFE rod with a denser structure.

[0018] Preferably, the density of the clinker is 2.25 g / cm 3 ±1%.

[0019] Furthermore, the polytetrafluoroethylene free radical dose meter is a micro-pellet particle with a diameter of 4±0.02mm, a thickness of 2.4±0.02mm, and a weight of 63.5±0.5mg.

[0020] The polytetrafluoroethylene free radical dosimeter for ionizing radiation dose measurement of the present invention is used for ionizing radiation ESR dose measurement system, free radical ESR detection is X-band-frequency 9.257300-9.258100GHz, the range is 1-180kGy, and the total uncertainty is less than 5.02%.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The effective range of the polytetrafluoroethylene free radical dosimeter of the present invention is 1 to 180 kGy, which is much higher than the other dose meter ranges (1 to 90 kGy) currently used in the radiation processing industry. The free radical response maintains a proportional linear relationship with the radiation dose, and the coefficient of determination R 2 =0.999, which is particularly suitable for ionizing radiation dose measurement of 100-180 kGy; the irradiation response in the gamma ray dose field is not affected by the dose rate; the influence on the gamma ray and electron beam energy dependence is negligible; the total uncertainty of ionizing radiation ESR dose measurement is <5.02%, showing excellent metrological performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is the response curve of the free radical dosimeter P1 within the irradiation dose range of 1 to 180 kGy.

[0024] Figure 2 This is the dose rate distribution diagram of a gamma irradiation field (cobalt source activity 2.5MCi).

[0025] Figure 3 This is the dose response diagram of the free radical dosimeter P1 at different measurement times after irradiation.

[0026] Figure 4 This is the attenuation curve of the free radical dosimeter P1 at the initial stage of attenuation after irradiation.

[0027] Figure 5 This is the decay curve of the free radical dosimeter P1 in the middle stage of decay after irradiation.

[0028] Figure 6 This is the decay curve of the free radical dosimeter P1 in the late decay stage after irradiation.

[0029] Figure 7 This is the irradiation response curve of the free radical dosimeter P1 at different energies (2 to 40 kGy). DETAILED DESCRIPTION

[0030] Those skilled in the art should recognize that the present embodiment is only used to illustrate the present invention, and is not used to limit the present invention. Any changes or modifications to the embodiment within the scope of the present invention are within the scope of the claims of the present invention.

[0031] Example 1 (Step Sintering / Pellets)

[0032] A polytetrafluoroethylene free radical dosimeter for measuring ionizing radiation dose, wherein the polytetrafluoroethylene micropowder used is DF-102 polytetrafluoroethylene suspension resin produced by Shandong Dongyue Polymer Materials Co., Ltd.; and the preparation method thereof comprises the following steps:

[0033] S1, molding polytetrafluoroethylene powder at room temperature and 50Mpa, and completing the molding after holding the pressure for 6 minutes; taking out the green billet to obtain a cylinder with a diameter of 50mm and a height of 50mm; and leaving the green billet at room temperature for 60 minutes;

[0034] S2, the green material was sent into the sintering furnace, and the step sintering was carried out for 72 hours under the condition of the highest sintering temperature of 370℃ and nitrogen protection. The heating process of the step sintering was as follows: in the first step preheating stage, the heating rate was 60℃ / h to 200℃ and then kept warm for 16 hours; in the second step molten viscous flow stage, the heating rate was 60℃ / h to 345℃ and then kept warm for 32 hours; in the third step sintering stage, the heating rate was 60℃ / h to 370℃ and then kept warm for 24 hours; after the sintering was completed, the temperature was naturally cooled with the sintering furnace to obtain a density of 2.25g / cm 3 ±1%, uniform clinker;

[0035] S3, processing the clinker into micro-pellets of a specified size by an automated turning process, thereby obtaining a polytetrafluoroethylene free radical dosimeter.

[0036] The free radical dosimeter P1 of Example 1 is a micro-pellet particle with a diameter of 4±0.02 mm, a thickness of 2.4±0.02 mm, and a weight of 63.5±0.5 mg. 3000 tablets of Example 1 were processed, and the intra-batch weight uniformity was 1.0% (n=10).

[0037] The PTFE dosimeter of the present invention is a dosimeter used for detecting free radical concentration and converting dose values ​​by an ESR electron spin resonance spectrometer, and its three-dimensional dimensions must be kept within a certain range to meet the requirements of the ESR spectrometer for measuring the inner cavity scanning space. On the premise of meeting the spectrometer measurement conditions, a free radical dosimeter of a corresponding shape can be prepared, while considering the maintenance and weakening degree of the mechanical strength of the dosimeter after high-dose irradiation.

[0038] Comparative Example 1 (thin sheet)

[0039] The clinker of Example 1 is processed into a thin sheet dosimeter P2 with a length of 15 mm, a width of 4 mm, and a thickness of 1 mm by an automated turning process. This geometric size is more suitable for radiation types with low penetrating power, such as electron beam irradiation, because of its thin thickness, while taking into account the requirements of ESR spectrometer detection conditions.

[0040] Two groups of thin sheet dosimeters P2 (4 sheets in each group) were irradiated with 75kGy and 150kGy doses respectively. The results showed that after 75kGy irradiation, the dosimeter sheet P2 was slightly bent and deformed, resulting in uncertain dimensions; after 150kGy irradiation, the dosimeter sheet became brittle and easy to break, which had an unfavorable impact on the detection uncertainty of the ESR spectrometer, thus violating the principle requirements of stability and consistency as a dosimeter.

[0041] Comparative Example 2

[0042] S1, molding polytetrafluoroethylene powder at room temperature and 50Mpa, and completing the molding after holding the pressure for 10 minutes; taking out the green billet to obtain a cylinder with a diameter of 50mm and a height of 50mm; and leaving the green billet at room temperature for 60 minutes;

[0043] S2, the raw material billet is sent into the sintering furnace, and directly sintered at a maximum sintering temperature of 350°C under nitrogen protection. The sintering temperature rising process is: at a heating rate of 60°C / h, directly heating to a maximum sintering temperature of 350°C, and sintering is carried out under this condition for 90 hours to obtain a clinker billet.

[0044] Relevant tests on the raw material in the sintering furnace showed that when the sintering temperature was 350°C, different crystal forms appeared on the surface and in the center of the raw material sample. The center area showed the same crystal form as the PTFE raw material, indicating that the raw material was not fully sintered and was "half-cooked", and the homogeneity of the raw material was insufficient.

[0045] Comparative Example 3

[0046] The green material of comparative example 2 was fed into a sintering furnace and directly sintered at a maximum sintering temperature of 390°C under nitrogen protection. The sintering temperature was raised to a maximum sintering temperature of 390°C at a heating rate of 150°C / h. The green material was sintered for 90 hours under this condition to obtain a density of about 2.23 g / cm 3 The clinker blank is processed into micro-pellets of specified size by an automated turning process to obtain a polytetrafluoroethylene free radical dosimeter.

[0047] Related tests show that due to the high sintering temperature and heating rate, the sintering degree of each area of ​​the blank is inconsistent and the expansion is uneven, the tensile properties are significantly reduced, and the "overburning" phenomenon occurs. The dosimeter's requirements for material homogeneity cannot be met.

[0048] Test experiment example

[0049] The polytetrafluoroethylene free radical dosimeter of Example 1 was tested.

[0050] 1. Measurement conditions and methods

[0051] The irradiated polytetrafluoroethylene free radical dosimeter was tested by BRUKER-ESR5000 electron paramagnetic resonance spectrometer after being stationary for 0.5h. The test room temperature was 23℃ and the humidity was 50%RH. The measurement frequency of Bruker ESR5000 spectrometer was 9.255±0.01GHZ in the X-band and the temperature in the resonance cavity was 32±1℃. The measurement parameters were as follows: central magnetic field 330.1Mt, scanning width 3.00mm, modulation amplitude 1.000mT, microwave power 10mW, scanning time 5s, and measurement time 18s. A quartz tube with a diameter of 4.2mm was used to place the dosimeter in the resonance cavity of the spectrometer for measurement. The reference material was ruby.

[0052] According to the physical properties of the dosimeter material, compared with the alanine dosimeter, polytetrafluoroethylene has physical properties such as greater hardness, higher density, lower water absorption, and higher melting temperature than alanine. Its radiation resistance (radiation dose when degradation occurs) is also better than that of the alanine dosimeter. Therefore, in theory, the impact of temperature and humidity on the performance of its dosimeter will not be greater than that of the alanine dosimeter.

[0053] 2. Zero-dose test analysis of dosimeter microchip

[0054] Take 10 P1 dosimeters and conduct zero-dosage ESR test to detect their free radical background level. The test data is shown in Table 1. From Table 1, it can be seen that the background free radical concentration response Hpp average of this batch of dosimeters is 24.9401, and the minimum signal-to-noise ratio is 43.8853dB>25dB spectrometer minimum setting value; the background dose response average is 0.0244kGy, and the signal-to-noise ratio average is 58.0955dB, indicating that the free radical background concentration response of the dosimeter microchip is stable and can meet the use of the irradiation processing dose measurement system.

[0055] Table 1 Zero dose ESR response test data table

[0056]

[0057] 3. Irradiation calibration ESR measurement

[0058] 14 groups (3 in each group) of free radical dosimeters P1 were dynamically irradiated in a 60Coγ irradiator with an activity of 2.5MCi at the same time. The dose points were 1kGy, 2.5kGy, 5.0kGy, 10kGy, 20kGy, 30kGy, 40kGy, 50kGy, 65kGy, 75kGy, 85kGy, 130kGy, 180kGy, and 250kGy, with a total of 14 dose points and an irradiation temperature of 30-55.0℃. The alanine dosimeter compared by the Institute of Metrology was used for value assignment and calibration. The irradiation calibration ESR measurement data of the free radical dosimeter P1 are shown in Table 2.

[0059] Table 2 Radiation calibration ESR measurement data of free radical dosimeter P1

[0060]

[0061]

[0062] It can be seen from Table 2 that as the irradiation dose increases, the free radical response signal per mg (Hpp value) also increases accordingly. In the irradiation dose range of 1 to 182 kGy, the dose response curve of the free radical dosimeter P1 shows a good positive proportional linear relationship, and the coefficient of determination R of the fitting curve is 2 =0.999; the response curve of the free radical dosimeter P1 within the irradiation dose range of 1 to 180 kGy is shown in Figure 1 . When the irradiation dose is in the range of 182-251 kGy, the corresponding Hpp value jumps from 248 to 1443, showing a nonlinear sudden increase. The preliminary analysis shows that the radiation chemical effect causes the change of the molecular structure inside the material, resulting in a drastic change in the number of free radicals. According to the performance requirements of the dosimeter in actual applications, the section of 1-180 kGy with good and stable linear response of the dosimeter is intercepted as the use range of the free radical dosimeter P1.

[0063] 4. Test the influence of rotation uncertainty

[0064] A group of free radical dosimeters P1 (4 in each group) were irradiated with 200 kGy. Then, according to the method specified in GB / T16639-2008, the quartz tube loaded with free radical dosimeter P1 was rotated at 0°, 90°, 180° and 270° respectively to measure its response on ESR. The data and calculation results are shown in Table 3. According to the formula The combined uncertainty is calculated to be 0.06%, which is in line with and better than the acceptance standard of foreign alanine dosimeters of less than 0.4%.

[0065] Table 3 Rotational uncertainty test data of free radical dosimeter P1

[0066]

[0067]

[0068] 5. Test the impact of rollover uncertainty

[0069] A group of free radical dosimeters P1 (2 in each group) were selected and irradiated with 200 kGy. Then, according to the method specified in GB / T16639-2008, the dosimeters were turned upside down and ESR tested respectively. The combined uncertainty is calculated to be 0.12%. The data and calculation results are shown in Table 4, which proves that the influence of flipping on the dose measurement results is very small and can be ignored.

[0070] Table 4 Test data of the rollover uncertainty of the free radical dosimeter P1

[0071]

[0072] 6. Effect of dose rate

[0073] In the gamma dose field, static irradiation and dynamic irradiation were used to irradiate the same dose (D≈14kGy) to four free radical dosimeters P1. The dose rate range of static irradiation points was 3-4kGy / h, and the dose rate range of dynamic irradiation points was 2.7-122.2kGy / h. The free radical response data of the irradiated samples detected by ESR, the dose rate distribution of a gamma irradiation field (cobalt source activity 2.5MCi) is shown in Figure 2 The irradiation response data of different dose rates are shown in Table 5.

[0074] Table 5 Comparison of irradiation response at different dose rates

[0075]

[0076] From Table 5 and Figure 3 It can be seen that under the same irradiation dose, the dose response deviation of the free radical dosimeter P1 is 0.61%, that is, the effect of the dose rate on the polytetrafluoroethylene free radical dosimeter can be ignored.

[0077] 7. Impact of measurement time

[0078] After irradiation with 13 kGy, the free radical dosimeter P1 was placed in a 25°C environment for 0.5 h, 2.0 h, 4.0 h, 6.0 h, 8.0 h, 24 h, 48.0 h, 96 h, 7 d, 14 d, and 21 d, and then the free radical response was detected by ESR. The results are shown in Table 6 and Figure 4 .

[0079] Table 6 Dose response data of free radical dosimeter P1 at different measurement times

[0080]

[0081]

[0082] It can be seen from Table 6 that after the PTFE free radical dosimeter is irradiated, as the detection time increases, its free radical response Hpp value gradually decays, and the decay rate also gradually decreases from fast to slow. After 96 hours, the decay rate tends to a constant (such as Figure 3 ).

[0083] In order to measure the attenuation process of the polytetrafluoroethylene free radical dosimeter, the attenuation process of the free radical dosimeter P1 is divided into three intervals according to the experimental data and the different attenuation rates, namely, the attenuation is fast in the early attenuation period (0.5-8h), the attenuation is slow in the middle attenuation period (8-96h), and the attenuation is stable in the late attenuation period (96-21d). The attenuation curves of the three intervals are as follows: Figure 4 , Figure 5 , Figure 6 :

[0084] from Figures 5 to 7 It can be seen that during the attenuation process of the free radical dose meter P1, the attenuation rate gradually decreases, from 0.62% / h in the early attenuation to 0.05% / h in the middle attenuation, and then to 0.008% / h in the late attenuation, showing a step-by-step linear attenuation. The coefficient of determination R of the fitting curve is 2 They are 0.96, 0.99 and 0.92 respectively, and the attenuation linear law can be simulated well.

[0085] 8. Impact of Energy Dependence

[0086] The free radical dosimeter P1 (pellet) was irradiated with 2-40 kGy in 10 MeV electron beam and 2.5 MCi 60Co gamma ray device, respectively. The response data curves of gamma irradiation and electron beam irradiation are shown in Figure 7 .

[0087] Figure 7 The trends of the two response curves to 10MeV electron beam irradiation and 2.5MCi 60Coγ-ray irradiation are highly consistent, and the fitting curve coefficients are 0.9998 and 0.9983, respectively. It can be seen that the radiation responses of the polytetrafluoroethylene free radical dosimeter to the two energies of electron beam or gamma ray are basically the same, indicating that there is no energy dependence under this condition.

[0088] 9. Uncertain evaluation

[0089] The uncertainty of the P1 micropellet dosimeter was analyzed in accordance with GB / T 16509-2008 “Guidelines for the Assessment of Uncertainty in Dose Measurement in Radiation Processing”. The comprehensive uncertainty was 5.02%. The results are shown in Table 7, which meets the requirement of ISO / ASTM 52628:2020 that the uncertainty of the dosimeter measurement system is less than 6% (K=2).

[0090] Table 7 Uncertainty analysis table of free radical dosimeter P1

[0091]

[0092] Experiments have proved that the polytetrafluoroethylene free radical dosimeter of the present invention is suitable for the ESR dose measurement system of gamma ray and electron beam EB irradiation processing; the range of the micropellet free radical dosimeter P1 is 1-180kGy, and the comprehensive uncertainty of the ESR measurement system of the polytetrafluoroethylene free radical dosimeter is 5.02%, which meets the relevant provisions of ESR spectrometer measurement in GB / T16639-2008 and the requirement that the dose measurement system uncertainty is less than 6% (K=2) in ISO / ASTM52628:2020.

[0093] The batch production process of the polytetrafluoroethylene free radical dosimeter of the present invention requires precision, but is easy to control and transform into results. The procurement cost can be reduced by 30% compared with various dosimeters widely used in the market. It is a material innovation and high-range breakthrough in the field of dosimeters, and has significant economic and social benefits.

Claims

1. A polytetrafluoroethylene free radical dosimeter for measuring ionizing radiation dose, characterized in that: Spherical particles or solid tablets made of polytetrafluoroethylene powder through molding and sintering processes; The polytetrafluoroethylene powder is a polytetrafluoroethylene suspension resin generated by free radical polymerization of tetrafluoroethylene monomer, with a tensile strength of ≥30MPa, a particle size of 200-300μm, a melting point of ≥322°C, and a bulk density of 550-590g / L.

2. The method for preparing a polytetrafluoroethylene free radical dosimeter for measuring ionizing radiation dose according to claim 1, characterized in that: The following steps are involved: S1, molding the polytetrafluoroethylene powder at room temperature and 40-55 MPa, maintaining the pressure for 3-10 minutes to complete the molding, and obtaining a green billet; and allowing the green billet to stand at room temperature for at least 50 minutes; S2, sending the raw material into a sintering furnace; performing direct sintering or step sintering for 40 to 100 hours at a maximum sintering temperature of 350 to 390° C., and cooling the raw material naturally with the sintering furnace after sintering to obtain a clinker; S3, processing the clinker into particles or tablets of a specified size by an automated turning process, thereby obtaining the polytetrafluoroethylene free radical dosimeter.

3. The method for preparing a polytetrafluoroethylene free radical dosimeter for measuring ionizing radiation dose according to claim 2, characterized in that: The green billet is in the shape of a cylinder with a diameter of 50±1 mm and a height of 50±1 mm.

4. The method for preparing a polytetrafluoroethylene free radical dosimeter for measuring ionizing radiation dose according to claim 2, characterized in that: The maximum sintering temperature is 360-380°C.

5. The method for preparing a polytetrafluoroethylene free radical dosimeter for measuring ionizing radiation dose according to claim 2, characterized in that: The step-by-step sintering process is as follows: the first step preheating stage: heating rate of 50-80°C / h to 200°C and then keeping warm for 15-36h; the second step molten viscous flow stage: heating rate of 30-60°C / h to 345°C and keeping warm for 30-48h; the third step sintering stage: heating rate of 30-60°C / h to sintering for 24-40h.

6. The method for preparing a polytetrafluoroethylene free radical dosimeter for measuring ionizing radiation dose according to claim 2, characterized in that: The density of the clinker is 2.25 g / cm 3 ±1%.

7. The method for preparing a polytetrafluoroethylene free radical dosimeter for measuring ionizing radiation dose according to claim 2, characterized in that: The polytetrafluoroethylene free radical dosimeter is a micro-pellet particle with a diameter of 4±0.02 mm, a thickness of 2.4±0.02 mm, and a weight of 63.5±0.5 mg.

8. The polytetrafluoroethylene free radical dosimeter for ionizing radiation dose measurement according to claim 1, characterized in that: The free radical ESR detection is in the X-band - frequency 9.257300 ~ 9.258100 GHz, the range is 1 ~ 180 kGy, and the total uncertainty is less than 5.02%.

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