Development of a diffusion chamber for passive discriminative

Development of a diffusion chamber for passive discriminative measurements of radon/thoron concentration in dwellings F. Torabi Nabil, S. M. Hosseini Pooya, M. Taheri, M. Shamsaie Zafarghandi Presented by: S. M. Hosseini Pooya (Ph. D) National Radiation Protection Department Iran Nuclear Regulatory Authority 1

Introduction q Radon (222 Rn) has the most contribution in annually natural exposure of the human via inhalation of the gas. q Thoron (220 Rn) may have the same effects (even be more hazardous) due to the long lived of its daughters. q As well most of the radon detectors are also sensitive to the thoron and may be affected on accurate measurements by the presence of thoron in media. q Thus some of the researches are focused on the designing of discriminative systems for separated measurements of these isotopes. q Most of the suggested systems have complicated designs (in active methods) and etching conditions (in passive methods). q A home-made passive diffusion chamber which is based on SSNTD, has been used for many years for passive radon measurements in dwellings in Iran. q In this research first the operation and calibration method of the chamber have been described for both radon and thoron measurements. q Then the design is developed for separated measurements of radon/thoron, and the measurement characteristics of the detector are discussed in detail. 2

Structure of home-made diffusion chamber: for Radon measurements 3

4 Voltage: 800 V Frequency: 2 k. Hz Time: 3 hr Temp. : 25 ° C Etchant PEW: %15 KOH + %40 C 2 H 5 OH + %45 H 2 O) 4

The volume of calibration chamber for Radon is 50 liters and for Thoron is 4 liters 5

The calibration curve of the chamber for Radon S= 13. 55 (Track. cm-2. Bq-1. l. day-1) The calibration curve of the chamber for Thoron S= 0. 83 (Track. cm-2. Bq-1. l. day-1) 6

Home-Made Radon Diffusion Chamber Reference values by NIRS Measured values by diffusion chamber Activity Exposure time (h) Rn conc. (Bq. m-3) Int. Rn conc. (k. Bq. h. m-3) Rn conc. (Bq. m-3) Int. Rn conc. Difference (k. Bq. h. m-3) Low 100 1022 ± 59 102 ± 6 1033. 6 ± 70 103. 36 ± 7. 2 Medium 50 8818 ± 221 441 ± 11 8409 ± 720 420. 43 ± 36 4. 60% High 100 8753 ± 270 875. 3 ± 27 8478 ± 760 847. 88 ± 75 3. 20% 1% 7

A. Double-filter diffusion chamber & 212 Po detector B. Double-film diffusion chamber 8

Developed diffusion chamber: Radon detector the outside detector: 212 Po detector Double-filter diffusion chamber + 212 Po detector Attenuator(Lexan 75µm) • It attenuates only the particles of 8. 78 Me. V of 212 Po to the energies between 0. 5 to 1 Me. V and absorbs all of the other particles of the daughters. Detector(Lexan 250µm) Detector holder 9

v The thickness of 75± 2 μm has been calculated by Trim Code v The thickness of 75± 2μm is achievable by soaking of the 250μm Lexan films in the Aqueous solution of Ethylenediamine for 4 hours at 25 C as : 75% C 2 H 4(NH 2)2+25% H 2 O 10

Sensitivity of the diffusion chamber for radon measurements The MDL values of the diffusion chamber for radon measurements S= 8. 95 (Track. cm-2. Bq-1. l. day-1) 11

Sensitivity of the outer Lexan film for 212 Po measurements The MDL values of the outer Lexan film for 212 Po measurements S=7. 96 (Track. cm-2. Bq-1. m 3. day-1) 12

v The outer Lexan film only can measure the concentration of 212 Po CTn(Thoron concentration)can be calculated by: The average value of FTn (Equilibrium Factor) is 0. 03 in dwellings, 0. 913 is the Equilibrium Coefficient, 100/64 is the reverse value of branching ratio in decay chain of 212 Po 13

Cap & fiber glass filter Detector holder Fiber filter Filterglass holder ü The upper film detects Radon+ Thoron Detector ü The lower film detects only the Radon Detector holder Double-film diffusion chamber 14

Sensitivity of the diffusion chamber for radon measurements The MDL values of the diffusion chamber for radon measurements S(upper film)=2. 06 S(lower film)=1. 60 15

Sensitivity of the diffusion chamber for Thoron measurements The MDL values of the diffusion chamber for Thoron measurements S=0. 056(Track. cm-2. Bq-1. l. day-1) 16

Conclusion q A home-made passive diffusion chamber which is based on Lexan SSNTD, has been developed for simultaneous measurements of radon/thoron in dwellings. q The sensitivity of the chamber shows that it is appropriate for seasonal measurements of radon in an extended range of concentrations. q The sensitivity of the double-film chamber shows that it is appropriate for seasonal measurements of thoron in areas with high thoron concentrations, while the double-filter method is appropriate for that of low concentration. q The advantages of the method are including its small size, light weight and simple etching process. 17

Thank you! 18