Device and system for measuring alpha and beta radiation activity of radioactive aerosols of artificial origin

Abstract

Device (100) for measuring alpha radiation activity and beta radiation activity of radioactive aerosols of artificial origin enriched on a dust filter (40), comprising: - a first particle detector (10) in the form of an ionization chamber, in particular a pulsed one, which is designed to generate a first count rate depending on the alpha radiation activity, - a second particle detector (20) designed to generate a second count rate depending on the beta radiation activity, and - an evaluation unit (50) designed to determine the alpha radiation activity and the beta radiation activity as a function of the first count rate and the second count rate.

Description

[0001] DE 10 2013 209 630 A1 discloses a method and a device for measuring airborne alpha and beta radiation of artificial origin.

[0002] DE 36 02 519 A1 discloses a radiation measuring device.

[0003] US Patent 3,555,278 A discloses a radiation detector for the separate measurement of alpha and beta radiation.

[0004] The US 2003 / 0 040 877 A1 reveals a gas-filled alpha detector.

[0005] DE 102010 000 836 A1 discloses a method and a device for measuring airborne alpha and beta radiation of artificial origin using a semiconductor detector.

[0006] The invention is based on the objective of providing a device and a system for measuring the alpha radiation activity and beta radiation activity of radioactive aerosols of artificial origin, which also delivers reliable measurement results in the event of rapid changes in the concentration of natural nuclides.

[0007] The device according to the invention is used to measure the alpha radiation activity and the beta radiation activity of radioactive aerosols of artificial origin that are concentrated on a dust filter.

[0008] The device includes a first particle detector in the form of an ionization chamber, preferably one operated in pulsed mode, which is designed to generate a first count rate as a function of the alpha radiation activity. The first particle detector can, for example, be a gas flow ionization chamber operated in pulsed mode.

[0009] The device also features a second particle detector designed to generate a second count rate depending on the beta radiation activity.

[0010] The device also includes an evaluation unit, for example in the form of a microprocessor system, which is designed to determine the alpha radiation activity and the beta radiation activity as a function of the first count rate and the second count rate.

[0011] The first particle detector is designed to record an energy deposition spectrum of alpha radiation activity. Since the maximum energy of natural alpha particles is 8.8 MeV, the first particle detector can be approximately 10 cm deep. This allows the alpha particles to release all their energy through ionization, resulting in a precise energy deposition spectrum. This is further enhanced by the integration of a Frisch grid a few centimeters in front of the anode of the first particle detector, minimizing the dependence of an alpha signal on the origin of the alpha radiation. The Frisch grid is positively biased with a significantly lower high voltage than the high voltage of the anode.The alpha pulses obtained from the anode, for example with the help of a preamplifier, are fed to several single-channel discriminators with specific energy thresholds in order to determine the number of pulses in different energy spectrum ranges.

[0012] The evaluation unit is designed to suppress alpha and beta radiation activity of natural radioactive nuclides based on the recorded energy deposition spectrum of the alpha radiation activity. Reference is also made to the applicant's disclosure in EP 3 982 163 A1, which describes how alpha and beta radiation activity of natural radioactive nuclides can be suppressed based on a recorded energy deposition spectrum of alpha radiation activity. This disclosure is hereby expressly incorporated into the present description to avoid repetition. In contrast to EP 3 982 163 A1, according to the invention, the beta particles are measured with a separate detector, for example, in the form of a proportional counter, but are nevertheless compensated for using the energy deposition spectrum of the first particle detector.In the EP 3 982 163 A1, alpha particles and beta particles are measured using the same Si semiconductor detector.

[0013] The evaluation unit is designed to suppress the alpha radiation activity of natural radioactive nuclides based on proportions of a first (alpha) count rate with associated energies in an energy range around the nuclides Po-218 and Bi-212 and / or to suppress the beta radiation activity of natural radioactive nuclides based on proportions of a second (alpha) count rate with associated energies in an energy range above 5.8 MeV.

[0014] In one embodiment, the evaluation unit is configured to determine the alpha radiation activity of artificial radioactive nuclides based on components of a third count rate with associated energies in an energy range between a first and a second energy threshold. The first energy threshold lies, for example, just above the electronic and detector noise. The second energy threshold corresponds, for example, to the maximum alpha energy of typical artificial nuclides, at approximately 5.8 MeV.

[0015] In one embodiment, the second particle detector is a proportional counter, a Geiger-Müller counter, or a scintillation counter.

[0016] In one embodiment, the device has a third particle detector for suppressing background radiation, in particular gamma radiation and cosmic radiation.

[0017] In one embodiment, the third particle detector is a proportional counter, a Geiger-Müller counter, or a scintillation counter.

[0018] The system includes a device, as described above, for measuring the alpha and beta radiation activity of radioactive aerosols of artificial origin, which are concentrated on a dust filter. The system also includes the dust filter itself.

[0019] In one embodiment, the first particle detector is the particle detector located closest to the dusting filter, followed by the second particle detector and optionally the third particle detector.

[0020] In one embodiment, the dust filter has a pore size of at most 5 µm.

[0021] In one embodiment, the dust filter is a membrane filter.

[0022] In one embodiment, an entrance window of the first particle detector has an area of ​​at least 20 cm². 2 on.

[0023] The invention enables the determination of the alpha and beta activity of artificial radionuclides in ambient air by enriching aerosols on a membrane filter using a combination of different detector technologies, for example: a gas flow ionization chamber with a fresh grating in pulse mode for alpha particle spectroscopy, a gas flow proportional counter for beta particles, and a gas flow proportional counter for cosmic radiation in anticoincidence circuits with the beta proportional counter and for measuring external gamma radiation for computational correction of the beta channel. Furthermore, radon compensation is performed using alpha spectroscopy based on the alpha spectrum of the daughter nuclides of the natural noble gases radon and thoron.

[0024] The invention is described in detail below with reference to the drawings. These schematically show: Fig. 1 a block diagram of a system for measuring alpha radiation activity and beta radiation activity of radioactive aerosols of artificial origin enriched on a dust filter, and Fig. 2 an exemplary energy deposition spectrum obtained using a first particle detector of the in Fig. The system shown in 1 is included.

[0025] Fig. Figure 1 shows a block diagram of a system for measuring alpha radiation activity and beta radiation activity of radioactive aerosols of artificial origin enriched on a dust filter 40.

[0026] In addition to the dust filter 40, the system includes a device 100 for measuring the alpha radiation activity and the beta radiation activity of radioactive aerosols of artificial and natural origin that are concentrated on a dust filter 40.

[0027] The device 100 has a first particle detector 10 in the form of a pulsed ionization chamber, which is designed to generate a first count rate depending on the alpha radiation activity.

[0028] The device 100 further features a second particle detector 20 in the form of a proportional counter tube, which is designed to generate a second count rate depending on the beta radiation activity.

[0029] The device 100 further features a third particle detector 30 for suppressing background radiation, in particular gamma radiation and cosmic radiation.

[0030] The device 100 further includes an evaluation unit 50, which is designed to determine the alpha radiation activity and the beta radiation activity as a function of the first count rate and the second count rate.

[0031] The first particle detector 10 is designed to enable the recording of an energy deposition spectrum of the alpha radiation activity. For this purpose, the first particle detector 10 has a cathode 12, a Frisch grid 11, and an anode 13. A voltage HV is applied to the Frisch grid 11. G A voltage of HV is applied to and at the anode 13. A to.

[0032] An amplifier 53 of the evaluation unit 50 is coupled to the anode 13. A number of single-channel discriminators 56, for example three single-channel discriminators 56, are connected downstream of the amplifier 53. For illustrative purposes, only a single single-channel discriminator 56 is shown. The single-channel discriminators 56 serve to determine count rates in different spectral ranges of the energy deposition spectrum of the alpha radiation activity. The output of the single-channel discriminators 56 serves as an input for a microprocessor 57, which evaluates the output signals or pulses of the single-channel discriminators 56.

[0033] The second particle detector 20 has a cathode 22 and an anode 21. An amplifier 52 of the evaluation unit 50 is coupled to the anode 21. A discriminator 55 is connected downstream of the amplifier 52. The output of the discriminator 55 serves as the input for the microprocessor 57, which evaluates the output signal or pulses of the discriminator 55. A voltage HV is applied to the anode 21. b to.

[0034] The third particle detector 30 has a cathode 32 and an anode 31. A voltage HV is applied to the anode 31. sAn amplifier 51 of the evaluation unit 50 is coupled to the anode 31. A discriminator 54 is connected downstream of the amplifier 51. The output of the discriminator 54 serves as the input for the microprocessor 57, which evaluates the output signal of the discriminator 54. Furthermore, there is a cross-connection between the discriminator 54 and the discriminator 55 to implement a so-called veto logic. In this respect, reference is made to the relevant technical literature.

[0035] The evaluation unit 50 is designed to suppress alpha radiation activity and beta radiation activity of natural radioactive nuclides based on the recorded energy deposition spectrum of the alpha radiation activity.

[0036] The evaluation unit 50 is designed to suppress the alpha radiation activity of natural radioactive nuclides in the energy range of artificial alpha nuclides based on proportions of a first alpha count rate with associated energies in an energy range around the nuclides Po-218 and Bi-212, and to suppress the beta radiation activity of natural radioactive nuclides based on proportions of a second alpha count rate with associated energies in an energy range above 5.8 MeV.

[0037] The evaluation unit 50 is further equipped to determine the alpha radiation activity of the artificial radioactive nuclides based on proportions of a third count rate with associated energies in an energy range between a first energy threshold and a second energy threshold.

[0038] The first particle detector 10 is the particle detector closest to the dust filter 40, followed by the second particle detector 20 and then the third particle detector 30.

[0039] The dust filter 40 has a pore size of no more than 5 µm. The dust filter 40 is a membrane filter.

[0040] An entrance window of the first particle detector 10 has an area of ​​at least 20 cm². 2 on.

[0041] Fig.Figure 2 shows an exemplary energy deposition spectrum, generated by the first particle detector 10, of alpha radiation activity from radioactive aerosols in the form of natural radon and thoron daughter nuclides enriched on the dust filter 40. The energy deposition spectrum describes the count rate in pulses per second (CPS) per channel as a function of the channel of a pulse height multichannel analyzer. The channels are proportional to the deposited alpha energy E.

[0042] The energy deposition spectrum shown depicts three energy thresholds S1, S2, and S3. The first energy threshold S1 is at approximately 400 keV, the second energy threshold S2 is at approximately 5500 keV, and the third energy threshold S3 is at approximately 6400 keV.

[0043] A region A1 between energy thresholds S1 and S2 designates the energy range of artificial and natural alpha particles or alpha nuclides. A region A3 above energy threshold S2 designates the energy range exclusively of natural alpha particles or alpha nuclides. A region A2 between energy thresholds S2 and S3 designates the energy range of the alpha nuclides Po-218 and Bi-212 and is above the range of artificial alpha nuclides.

[0044] A count rate R(alpha) corresponding to an alpha radiation activity and a count rate R(beta) corresponding to a beta radiation activity, for which a radiation activity of natural radioactive nuclides is suppressed, is calculated as follows: R(alpha)=ZA1−k1*ZA2*(1+k2*ZA2) R(beta)=ZB−k3*ZA3*(1+k4*ZA3) ZA1 is a count rate determined by the first particle detector 10 in the energy range A1, ZA2 is a count rate determined by the first particle detector 10 in the energy range A2, ZA3 is a count rate determined by the first particle detector 10 in the energy range A3, and ZB is a count rate determined by the second particle detector 20. k1 to k4 are constants.

[0045] Typical values ​​of the constants are: k1 = 1.00, k2 = -0.003, k3 = 0.31 and k4 = 0.0.

[0046] Beta particles are not measured using the first detector 10 because insufficient ionization occurs. Therefore, a second particle detector 20 is provided for the beta particles.

[0047] The count rate ZA2 (Po218 / Bi212 peak) is used for alpha compensation, as only then is the compensation independent of large changes in radon activity.

[0048] To compensate for the beta particles in the second particle detector 20, as with EP 3 982 163 A1, the count rate ZA3 above the energy threshold S2 is used, since this only originates from natural radon and thoron.

Claims

[1] Device (100) for measuring alpha radiation activity and beta radiation activity of radioactive aerosols of artificial origin concentrated on a dust filter (40), comprising: - a first particle detector (10) in the form of an ionization chamber, in particular a pulsed one, which is designed to generate a first count rate depending on the alpha radiation activity, - a second particle detector (20) designed to generate a second count rate depending on the beta radiation activity, and - an evaluation unit (50) designed to determine the alpha radiation activity and the beta radiation activity as a function of the first count rate and the second count rate, - wherein the first particle detector (10) is designed to enable the recording of an energy deposition spectrum of the alpha radiation activity, - wherein the evaluation unit (50) is configured to suppress alpha radiation activity and beta radiation activity of natural radioactive nuclides based on the recorded energy deposition spectrum of the alpha radiation activity, and - wherein the evaluation unit (50) is configured to suppress the alpha radiation activity of the natural radioactive nuclides based on proportions of a first alpha count rate with associated energies in an energy range around the nuclides Po-218 and Bi-212 and / or to suppress the beta radiation activity of the natural radioactive nuclides based on proportions of a second alpha count rate with associated energies in an energy range above 5.8 MeV. [2] Device (100) according to claim 1, characterized by , that - the first particle detector (10) has a Frisch grating (11). [3] Device (100) according to any one of the preceding claims, characterized by , that - the evaluation unit (50) is designed to determine the alpha radiation activity of the artificial radioactive nuclides based on proportions of a third count rate with associated energies in an energy range between a first energy threshold and a second energy threshold. [4] Device (100) according to any one of the preceding claims, characterized by , that - the second particle detector (20) is a proportional counter, a Geiger-Müller counter or a scintillation counter. [5] Device (100) according to any one of the preceding claims, characterized by , that - the device (100) has a third particle detector (30) for suppressing background radiation, in particular gamma radiation and cosmic radiation. [6] Device (100) according to claim 5, characterized by , that - the third particle detector (30) is a proportional counter, a Geiger-Müller counter or a scintillation counter. [7] System, exhibiting: - a device (100) for measuring alpha radiation activity and beta radiation activity of radioactive aerosols of artificial origin enriched on a dust filter (40), according to one of the preceding claims, and - the dust filter (40). [8] System according to claim 7, characterized by , that - the first particle detector (10) is the particle detector closest to the dust filter (40), followed by the second particle detector (20). [9] System according to claim 7 or 8, characterized by , that - the dust filter (40) has a pore size of no more than 5 µm. [10] System according to any one of claims 7 to 9, characterized by , that - the dust filter (40) is a membrane filter. [11] System according to any one of claims 7 to 10, characterized by , that - an entrance window of the first particle detector (10) an area of ​​at least 20 cm 2 exhibits.

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