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Alvarez Romero JT, De La Cruz Hernandez D, Cabrera Vertti MR. The dependence of NKRvs KR: the initial, thermal, volumetric recombination and screening effect on the efficiency of collected charges on the calibration of si hdr 1000 plus well chambers with 192ir hdr sources. Biomed Phys Eng Express 2022; 8. [PMID: 35039465 DOI: 10.1088/2057-1976/ac4c2a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2021] [Accepted: 01/17/2022] [Indexed: 11/11/2022]
Abstract
By using the statistical techniques of ANOVA: mean test and regression, it was found that the NKRcalibration factor of Standard Imaging (SI) model HDR 1000 plus chambers presents a quadratic dependence with the reference air kerma rateKR(from 6.9 mGy h-1to 43.9 mGy h-1). In order to understand and correct this dependency one model is presented for total recombination:ks=I300/I150=1+kini+ kd+kvolI300+kscreenI3002, wherekiniis the initial recombination,kdthe thermal diffusion recombination,kvolthe volumetric recombination andkscreenthe screening for the currents/charges collected at the potential differences of 300 and 150 V. In conclusion, the total recombinationksis composed by onekiniwith a constant contribution of 0.019%, onekdcontribution of 0.017%, onekvolI300contribution from 0.022% to 0.138%, and thekscreenI3002effects from 0.002% to 0.09% in the range ofKRrate above. However, when this model forksis applied to try to correct the quadratic dependence of theNKRvs KR, explicitly there is no improvement in the variation range of 0.5% of theNKRvs KR.Nonetheless, it allows to obtainNKRvalues consistent with a uc≤ 0.7 %, which is less than 1.25% reported in the literature by ADCL or SSDL.
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Affiliation(s)
- Jose Trinidad Alvarez Romero
- SSDL/IONIZING RADIATION METROLOGY DEPARTMENT, Instituto Nacional de Investigaciones Nucleares, CARRETERA FERDERAL MEXICO TOLUCA S/N, CARRETERA FERDERAL MEXICO TOLUCA S/N, Ocoyoacac, State of Mexico, 52750, MEXICO
| | - Daniel De La Cruz Hernandez
- SSDL/IONIZING RADIATION METROLOGY DEPARTMENT, Instituto Nacional de Investigaciones Nucleares, Carretera Federal México Toluca S/N, Ocoyoacac, State of Mexico, 52750, MEXICO
| | - Mario Raymundo Cabrera Vertti
- SSDL/IONIZING RADIATION METROLOGY DEPARTMENT, Instituto Nacional de Investigaciones Nucleares, CARRETERA FERDERAL MEXICO TOLUCA S/N, Ocoyoacac, State of Mexico, 52750, MEXICO
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Schönfeld AB, Schönfeld AA, Looe HK, Poppe B, de Wilde RL. Experimental determination of the recombination correction factor kS for SNC 125c, SNC 350p and SNC 600c ionization chambers in pulsed photon beams. Z Med Phys 2020; 30:300-304. [DOI: 10.1016/j.zemedi.2020.03.001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2019] [Revised: 03/06/2020] [Accepted: 03/06/2020] [Indexed: 10/24/2022]
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Hansen JB, Culberson WS, DeWerd LA. A convex windowless extrapolation chamber to measure surface dose rate from 106 Ru/ 106 Rh episcleral plaques. Med Phys 2019; 46:2430-2443. [PMID: 30873611 DOI: 10.1002/mp.13488] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2018] [Revised: 02/19/2019] [Accepted: 02/28/2019] [Indexed: 11/08/2022] Open
Abstract
PURPOSE A convex windowless extrapolation chamber was developed as a primary measurement device to determine surface dose rate from curved 106 Ru/106 Rh episcleral plaques. METHODS A convex extrapolation chamber without an entrance window was constructed for this work, and surface dose rate measurements were performed with two curved CCB-type 106 Ru/106 Rh plaques (S/N 2545 and 2596) manufactured by Eckert & Ziegler BEBIG. FARO ® Gage measurements were performed to verify the radius of curvature for the convex electrode and the concave plaque surface. Furthermore, the collecting electrode area was verified through capacitance measurements. Chamber correction factors for divergence and backscatter were generated using the EGSnrc cavity user code. For each source, surface dose rate was measured with the convex extrapolation chamber and compared with on-contact measurements made with curved un-laminated EBT3 film strips. A Monte Carlo correction was generated for radiochromic film measurements to account for volume averaging within the active layer and effects of phantom scatter. Additionally, extrapolation chamber results for each plaque were compared with scintillation detector measurements performed by the manufacturer. For the second source (S/N 2596), a comparison was also made with the Monte Carlo-corrected surface dose rate measured at the National Physical Laboratory (NPL) using cylindrical alanine pellets. Finally, source measurements were performed using conventional ionization chambers (Exradin A26, A1SL, and A20) within a custom fixture to investigate the transfer of extrapolation chamber surface dose rate to clinics. RESULTS For the first 106 Ru/106 Rh plaque (S/N 2545), average surface dose rate from the convex windowless extrapolation chamber was found to be 1.5% higher than the corresponding value from curved un-laminated EBT3 film measurements and 5.6% lower than the manufacturer value. For the second source (S/N 2596), the extrapolation chamber surface dose rate was 2.5% higher than the un-laminated EBT3 film result, 4.5% lower than the manufacturer value, and 3.9% higher compared to corrected alanine measurements made at NPL. Total uncertainty in the extrapolation chamber measurement was estimated to be approximately ± 7.0% (k = 2). For the plaque measurements made using conventional ionization chambers with a custom fixture, surface dose rate from the transfer technique was found to agree within 3.8% with the expected convex extrapolation chamber result for S/N 2596. CONCLUSIONS A convex windowless extrapolation chamber was developed as a primary measurement device for 106 Ru/106 Rh plaques. Through comparison with the extrapolation chamber, the accuracy of surface dose rate measurements from current dosimetry techniques was assessed and agreement was seen within 5.6%. Finally, it was found that conventional ionization chambers could be calibrated with a reference 106 Ru/106 Rh plaque in order to transfer the extrapolation chamber result for surface dose rate to clinics.
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Affiliation(s)
- Jon B Hansen
- Department of Medical Physics, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI, 53705, USA
| | - Wesley S Culberson
- Department of Medical Physics, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI, 53705, USA
| | - Larry A DeWerd
- Department of Medical Physics, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI, 53705, USA
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Hansen JB, Culberson WS, DeWerd LA. Surface dose rate from a flat 106Ru/106Rh episcleral plaque measured with a planar windowless extrapolation chamber and un-laminated EBT3 film. RADIAT MEAS 2019. [DOI: 10.1016/j.radmeas.2018.12.002] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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5
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Güngör G, Aydın G, Mustafayev TZ, Özyar E. Output factors of ionization chambers and solid state detectors for mobile intraoperative radiotherapy (IORT) accelerator electron beams. J Appl Clin Med Phys 2019; 20:13-23. [PMID: 30632271 PMCID: PMC6370992 DOI: 10.1002/acm2.12522] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2018] [Revised: 12/06/2018] [Accepted: 12/09/2018] [Indexed: 11/11/2022] Open
Abstract
Purpose The electron energy characteristics of mobile intraoperative radiotherapy (IORT) accelerator LIAC® differ from commonly used linear accelerators, thus some of the frequently used detectors can give less accurate results. The aim of this study is to evaluate the output factors (OFs) of several ionization chambers (IC) and solid state detectors (SS) for electron beam energies generated by LIAC® and compare with the output factor of Monte Carlo model (MC) in order to determine the adequate detectors for LIAC®. Methods The OFs were measured for 6, 8, 10, and 12 MeV electron energies with PTW 23343 Markus, PTW 34045 Advanced Markus, PTW 34001 Roos, IBA PPC05, IBA PPC40, IBA NACP‐02, PTW 31010 Semiflex, PTW 31021 Semiflex 3D, PTW 31014 Pinpoint, PTW 60017 Diode E, PTW 60018 Diode SRS, SNC Diode EDGE, and PTW 60019 micro Diamond detectors. Ion recombination factors (ksat) of IC were measured for all applicator sizes and OFs were corrected according to ksat. The measured OFs were compared with Monte Carlo output factors (OFMC). Results The measured OFs of IBA PPC05, PTW Advanced Markus, PTW Pinpoint, PTW microDiamond, and PTW Diode E detectors are in good agreement with OFMC. The maximum deviations of IBA PPC05 OFs to OFMC are −1.6%, +1.5%, +1.5%, and +2.0%; for PTW Advanced Markus +1.0%, +1.5%, +2.0%, and +2.0%; for PTW Pinpoint +2.0%, +1.6%, +4.0%, and +2.0%; for PTW microDiamond −1.6%, +2%, +1.1%, and +1.0%; and for PTW Diode E −+1.7%, +1.7%, +1.3%, and +2.5% for 6, 8, 10, and 12 MeV, respectively. PTW Roos, PTW Markus, IBA PPC40, PTW Semiflex, PTW Semiflex 3D, SNC Diode Edge measured OFs with a maximum deviation of +5.6%, +4.5%, +5.6%, +8.1%, +4.8%, and +9.6% with respect to OFMC, while PTW Diode SRS and IBA NACP‐02 were the least accurate (with highest deviations −37.1% and −18.0%, respectively). Conclusion The OFs results of solid state detectors PTW microDiamond and PTW Diode E as well as the ICs with small electrode spacing distance such as IBA PPC05, PTW Advanced Markus and PTW Pinpoint are in excellent agreement with OFMC. The measurements of the other detectors evaluated in this study are less accurate, thus they should be used with caution. Particularly, PTW Diode SRS and IBA NACP‐02 are not suitable and their use should be avoided in relative dosimetry measurements under high dose per pulsed (DPP) electron beams.
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Affiliation(s)
- Görkem Güngör
- Department of Medical Physics, Medipol University Institute of Health Sciences, Istanbul, Turkey.,Department of Radiation Oncology, Acıbadem Mehmet Ali Aydınlar University School of Medicine, Istanbul, Turkey
| | - Gökhan Aydın
- Department of Radiation Oncology, Acıbadem Mehmet Ali Aydınlar University School of Medicine, Istanbul, Turkey
| | - Teuta Zoto Mustafayev
- Department of Radiation Oncology, Acıbadem Mehmet Ali Aydınlar University School of Medicine, Istanbul, Turkey
| | - Enis Özyar
- Department of Radiation Oncology, Acıbadem Mehmet Ali Aydınlar University School of Medicine, Istanbul, Turkey
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Kouwenberg J, de Pooter J, Wolterbeek H, Denkova A, Bos A. Alpha radiation dosimetry using Fluorescent Nuclear Track Detectors. RADIAT MEAS 2018. [DOI: 10.1016/j.radmeas.2018.04.009] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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7
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Hansen JB, Culberson WS, DeWerd LA. Windowless extrapolation chamber measurement of surface dose rate from a 90 Sr/ 90 Y ophthalmic applicator. RADIAT MEAS 2018. [DOI: 10.1016/j.radmeas.2017.11.003] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Stevenson AW, Crosbie JC, Hall CJ, Häusermann D, Livingstone J, Lye JE. Quantitative characterization of the X-ray beam at the Australian Synchrotron Imaging and Medical Beamline (IMBL). JOURNAL OF SYNCHROTRON RADIATION 2017; 24:110-141. [PMID: 28009552 DOI: 10.1107/s1600577516015563] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/18/2016] [Accepted: 10/04/2016] [Indexed: 06/06/2023]
Abstract
A critical early phase for any synchrotron beamline involves detailed testing, characterization and commissioning; this is especially true of a beamline as ambitious and complex as the Imaging & Medical Beamline (IMBL) at the Australian Synchrotron. IMBL staff and expert users have been performing precise experiments aimed at quantitative characterization of the primary polychromatic and monochromatic X-ray beams, with particular emphasis placed on the wiggler insertion devices (IDs), the primary-slit system and any in vacuo and ex vacuo filters. The findings from these studies will be described herein. These results will benefit IMBL and other users in the future, especially those for whom detailed knowledge of the X-ray beam spectrum (or `quality') and flux density is important. This information is critical for radiotherapy and radiobiology users, who ultimately need to know (to better than 5%) what X-ray dose or dose rate is being delivered to their samples. Various correction factors associated with ionization-chamber (IC) dosimetry have been accounted for, e.g. ion recombination, electron-loss effects. A new and innovative approach has been developed in this regard, which can provide confirmation of key parameter values such as the magnetic field in the wiggler and the effective thickness of key filters. IMBL commenced operation in December 2008 with an Advanced Photon Source (APS) wiggler as the (interim) ID. A superconducting multi-pole wiggler was installed and operational in January 2013. Results are obtained for both of these IDs and useful comparisons are made. A comprehensive model of the IMBL has been developed, embodied in a new computer program named spec.exe, which has been validated against a variety of experimental measurements. Having demonstrated the reliability and robustness of the model, it is then possible to use it in a practical and predictive manner. It is hoped that spec.exe will prove to be a useful resource for synchrotron science in general, and for hard X-ray beamlines, whether they are based on bending magnets or insertion devices, in particular. In due course, it is planned to make spec.exe freely available to other synchrotron scientists.
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Affiliation(s)
- Andrew W Stevenson
- Australian Synchrotron, 800 Blackburn Road, Clayton, Victoria 3168, Australia
| | - Jeffrey C Crosbie
- School of Science, RMIT University, GPO Box 2476, Melbourne, Victoria 3001, Australia
| | - Christopher J Hall
- Australian Synchrotron, 800 Blackburn Road, Clayton, Victoria 3168, Australia
| | - Daniel Häusermann
- Australian Synchrotron, 800 Blackburn Road, Clayton, Victoria 3168, Australia
| | - Jayde Livingstone
- Australian Synchrotron, 800 Blackburn Road, Clayton, Victoria 3168, Australia
| | - Jessica E Lye
- School of Science, RMIT University, GPO Box 2476, Melbourne, Victoria 3001, Australia
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Aza E, Caresana M, Cassell C, Charitonidis N, Harrouch E, Manessi G, Pangallo M, Perrin D, Samara E, Silari M. Instrument intercomparison in the pulsed neutron fields at the CERN HiRadMat facility. RADIAT MEAS 2014. [DOI: 10.1016/j.radmeas.2013.12.009] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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10
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Zhao Q, Wu H, Cheng CW, Das IJ. Dose monitoring and output correction for the effects of scanning field changes with uniform scanning proton beam. Med Phys 2011; 38:4655-61. [PMID: 21928638 DOI: 10.1118/1.3609417] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE The output of a proton beam is affected by proton energy, Spread-Out Bragg Peak (SOBP) width, aperture size, dose rate, and the point of measurement. In a uniform scanning proton beam (USPB), the scanning field size is adjusted (including the vertical length and the horizontal width) according to the treatment field size with appropriate margins to reduce secondary neutron production. Different scanning field settings result in beam output variations that are investigated in this study. METHODS The measurements are performed with a parallel plate Markus chamber at the center of SOBP under the reference condition with 16 cm range, 10 cm SOBP, and 5 cm air gap. The effect of dose rate on field output is studied by varying proton beam current from 0.5 to 7 nA. The effects of scanning field settings are studied by varying independently the field width and length from 12 x 12 to 30 x 30 cm2. RESULTS The results demonstrate that scanning field variations can produce output variation up to 3.80%. In addition, larger output variation is observed with scanning field changes along the stem direction of the patient dose monitor (PDM). By investigating the underlying physics of incomplete charge collection and the stem effects of the PDM, an analytical model is proposed to calculate USPB output with consideration of the scanning field area and the PDM stem length that is irradiated. The average absolute difference between the measured output and calculated output using our new correction model are within 0.13 and 0.08% for the 20 and 30 cm snouts, respectively. CONCLUSIONS This study proposes a correction model for accurate USPB output calculation, which takes account of scanning field settings and the PDM stem effects. This model may be used to extend the existing output calculation model from one snout size to other snout sizes with customized scanning field settings. The study is especially useful for calculating field output for treatment without individualized patient specific measurements.
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Affiliation(s)
- Qingya Zhao
- IU Health Proton Therapy Center, IUHPTC, Bloomington, Indiana 47408, USA.
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Arbabi K, Larijani MM, Ramazanov M. Evaluation of a new ionisation chamber fabricated with carbon nanotubes. RADIATION PROTECTION DOSIMETRY 2010; 141:222-227. [PMID: 20603276 DOI: 10.1093/rpd/ncq177] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
Ionisation chambers are the most practical and important radiation measurement devices due to their high sensitivity and relatively constant response with wide range of applied potential. In this work, a new plane-parallel ionisation chamber is proposed using carbon nanotubes as sensing electrodes. Some characteristics of the new chamber such as cable effect, leakage current and reproducibility are investigated. The polarisation effects, besides voltage effect and linearity are also verified. All tests are performed using a 60Co gamma radiation source. The obtained results are compared with that of a standard ionisation chamber (PTW Roos W34001 plane-parallel ion chamber) and international code of practice on dosimetry (i.e. IAEA TRS No. 381).
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Affiliation(s)
- K Arbabi
- Agricultural Medical and Industrial Research School (AMIRS), Nuclear Science and Technology Research Institute (NSTRI), PO Box 31485-498, Karaj, Iran
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Bruggmoser G, Saum R, Schmachtenberg A, Schmid F, Schüle E. Determination of the recombination correction factorkSfor some specific plane-parallel and cylindrical ionization chambers in pulsed photon and electron beams. Phys Med Biol 2006; 52:N35-50. [PMID: 17202615 DOI: 10.1088/0031-9155/52/2/n01] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
It has been shown from an evaluation of the inverse reading of the dosemeter (1/M) against the inverse of the polarizing voltage (1/V), obtained with a number of commercially available ionization chambers, using dose per pulse values between 0.16 and 5 mGy, that a linear relationship between the recombination correction factor kS and dose per pulse (DPP) can be found. At dose per pulse values above 1 mGy the method of a general equation with coefficients dependent on the chamber type gives more accurate results than the Boag method. This method was already proposed by Burns and McEwen (1998, Phys. Med. Biol. 43 2033) and avoids comprehensive and time-consuming measurements of Jaffé plots which are a prerequisite for the application of the multi-voltage analysis (MVA) or the two-voltage analysis (TVA). We evaluated and verified the response of ionization chambers on the recombination effect in pulsed accelerator beams for both photons and electrons. Our main conclusions are: (1) The correction factor k(S) depends only on the DPP and the chamber type. There is no influence of radiation type and energy. (2) For all the chambers investigated there is a linear relationship between kS and DPP up to 5 mGy/pulse, and for two chambers we could show linearity up to 40 mGy/pulse. (3) A general formalism, such as that of Boag, characterizes chambers exclusively by the distance of the electrodes and gives a trend for the correction factor, and therefore (4) a general formalism has to reflect the influence of the chamber construction on the recombination by the introduction of chamber-type dependent coefficients.
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Affiliation(s)
- G Bruggmoser
- Univ.-Klinikum Freiburg, Klinik f Strahlenheilkunde, FB Med. Physik, Freiburg, Germany.
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13
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Nariyama N. Ion recombination in parallel-plate free-air ionization chambers for synchrotron radiation. Phys Med Biol 2006; 51:5199-209. [PMID: 17019033 DOI: 10.1088/0031-9155/51/20/008] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The saturation characteristics of two sizes of parallel-plate free-air ionization chambers were investigated for synchrotron radiation at bending-magnet, wiggler and undulator beamlines of SPring-8. The gaps of the electrodes were 4.2 and 85 mm. The monoenergetic photon energies ranged from 10 to 115.56 keV and the air kerma rates from 0.2 mGy s-1 to 150 kGy s-1. Ion recombination at the high dose rate was found to be smaller than that predicted by Boag's expression, which was based on volume recombination, and the difference increased with an applied electric field. In the high dose rate region, the reciprocal of the current was linear to the reciprocal of the electric field near saturation, which represented the occurrence of initial recombination and diffusion loss. At the low electric field and the low dose rate, the reciprocal of the current was linear to the reciprocal of the square of the electric field. The reduction of total ion recombination was attributed to the shift of the contribution from volume recombination to initial recombination and diffusion loss.
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Affiliation(s)
- Nobuteru Nariyama
- Japan Synchrotron Radiation Research Institute, Beamline Division, Kouto 1-1-1, Sayo, Hyogo 679-5198, Japan.
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Takata N, Tran NT, Kim E, Marsoem P, Kurosawa T, Koyama Y. Loss of ions in cavity ionization chambers. Appl Radiat Isot 2005; 63:805-8. [PMID: 16026988 DOI: 10.1016/j.apradiso.2005.05.039] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Ion losses due to initial recombination, volume recombination, and back diffusion were each determined by measurements and calculations for different size cylindrical ionization chambers and spherical ionization chambers. By measuring signal currents from these ionization chambers irradiated with (60)Co gamma rays, two groups of ion losses were obtained. (Group 1) Ion loss due to initial recombination and diffusion, which changes proportionally to the inverse of the voltage applied to the ionization chambers; (and group 2) ion loss due to volume recombination, which changes proportionally to the inverse of the square of the applied voltage. The diffusion loss was obtained separately by computing electric field distributions in the ionization chambers. It was found that diffusion loss is larger than initial recombination loss for the cylindrical ionization chambers and vise versa for the spherical ionization chambers.
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Affiliation(s)
- N Takata
- Ionizing Radiation Section, NMIJ/AIST, Tsukuba 305-8568, Japan.
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Park S, Kim H, Kim Y, Kang S, Kim J, Kim J. Saturation characteristics of the ionization chamber at a low dose rate. Radiat Phys Chem Oxf Engl 1993 2005. [DOI: 10.1016/j.radphyschem.2005.01.005] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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16
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Takata N, Matiullah. Dependence of the value of m on the lifetime of ions in parallel-plate ionization chambers. Phys Med Biol 2000. [DOI: 10.1088/0031-9155/36/4/004] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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17
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Johansson BE, Bahar-Gogani J, Wickman G. General collection efficiency in liquid iso-octane and tetramethylsilane used as sensitive media in a thimble ionization chamber. Phys Med Biol 1999; 44:2161-70. [PMID: 10495111 DOI: 10.1088/0031-9155/44/9/304] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The general collection efficiency in the dielectric liquids iso-octane (CaH18; 2-2-4 trimethylpentane) and tetramethylsilane (Si(CH3)4), used as sensitive media in a thimble liquid ionization chamber (LIC) with a liquid layer thickness of 1 mm, has been studied. Measurements were made for continuous radiation at varying dose rates using 140 keV photons from the decay of 99mTc for chamber polarizing voltages of 50, 100 and 500 V. The maximum dose rate in each measurement session was about 150 mGy min(-1). The experimental results were compared with theoretical general collection efficiencies calculated by the equation for the general collection efficiency in gases. The results show that the general collection efficiency in a thimble LIC for continuous radiation can be calculated with the equation for the general collection efficiency in gas ionization chambers, using the same chamber geometry correction factors and analogous characteristic ion recombination parameters for the dielectric liquids.
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Affiliation(s)
- B E Johansson
- Radiation Physics Department, Umeå University, Sweden.
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Abstract
The parameter m2 governing the volume recombination in ionization chambers has been measured under conditions which allow strict application of the basic theory. The method consists of measuring the ratio of ionization currents I(V1) and I(V2) obtained at two given voltages V1 and V2 as a function of I(V1). The value of m2 is derived from a linear extrapolation to zero current. Several pairs of voltages (V1, V2) were used. The value of m2 obtained in this work is 3.97 x 10(14) s m(-1) C(-1) V(2) with a relative uncertainty of 1.7%. The dependence of m2 on atmospheric conditions has also been investigated.
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Affiliation(s)
- M Boutillon
- Bureau International des Poids et Mesures, Sèvres, France
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19
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Zankowski C, Podgorsak EB. Determination of saturation charge and collection efficiency for ionization chambers in continuous beams. Med Phys 1998; 25:908-15. [PMID: 9650181 DOI: 10.1118/1.598269] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
The procedure recommended by radiation dosimetry protocols for determining the collection efficiency f of an ionization chamber assumes the predominance of general recombination and ignores other charge loss mechanisms such as initial recombination and ionic diffusion. For continuous radiation beams, general recombination theory predicts that f can be determined from a linear relationship between 1/Q and 1/V2 in the near saturation region (f > 0.7), where Q is the measured charge and V the applied chamber potential. Measurements with Farmer-type cylindrical ionization chambers exposed to cobalt-60 gamma rays reveal that the assumed linear relationship between 1/Q and 1/V2 breaks down in the extreme near-saturation region (f > 0.99) where Q increases with V at a rate exceeding the predictions of general recombination theory. A comprehensive model is developed to describe the saturation characteristics of ionization chambers. The model accounts for dosimetric charge loss (initial recombination, ionic diffusion, and general recombination) and nondosimetric charge multiplication in an ionization chamber, and suggests that charge multiplication plays a significant role under typical chamber operating conditions (300 V) used in radiation dosimetry. Through exclusion of charge multiplication from the measured chamber signal Q, the model predicts the breakdown of the 1/Q vs 1/V2 relationship and shows that the final approach to saturation is governed by initial recombination and ionic diffusion which are characterized by a linear relationship between 1/Q and 1/V. Collection efficiencies calculated with this model differ by up to 0.4% from those determined through a rigorous application of general recombination theory alone.
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Affiliation(s)
- C Zankowski
- McGill University, Department of Medical Physics, Montreal General Hospital, Québec, Canada
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Johansson B, Wickman G. General collection efficiency for liquid isooctane and tetramethylsilane used as sensitive media in a parallel-plate ionization chamber. Phys Med Biol 1997; 42:133-45. [PMID: 9015814 DOI: 10.1088/0031-9155/42/1/009] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The general collection efficiency has been measured in liquid isooctane (C8H18) and tetramethylsilane (Si(CH3)4) used as the sensitive media in a parallel-plate ionization chamber, with an electrode distance of 1 mm, intended for photon and electron dosimetry applications. The liquid ionization chamber was irradiated at different dose rates by 140 keV photons from the decay of radioactive 99mTc. The measurements were made at potential differences of 50, 100, 200 and 500 V. Measurements were performed for each liquid and electric field strength, with the decay rate of 99mTc used as the dose-rate reference. The maximum dose rate was about 150 mGy min-1 in each experiment. When the measured general collection efficiency values are compared with the theoretical predictions for collection efficiency in gases, it is found that the latter also describe the general collection efficiency in the two liquids within 1% of the saturation current for collection efficiencies down to 60% when using experimentally determined recombination rate constants and on mobilities characteristic of each of the liquids.
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Affiliation(s)
- B Johansson
- Radiation Physics Department, Umeå University, Sweden
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Geiger KW, Feist H, Böhm J. Ion losses in a plane-parallel ionisation chamber irradiated with a pulsed electron beam. Phys Med Biol 1980; 25:677-82. [PMID: 7454757 DOI: 10.1088/0031-9155/25/4/006] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Saturation curves for a plane-parallel ionisation chamber have been studied in a pulsed electron beam of 5.2 MeV initial energy as a function of chamber voltage, chamber depth and charge density liberated per pulse. It is shown that, if ion losses by diffusion and by initial recombination are appropriately considered, the remaining ion losses by volume recombination can be described by Boag's theory. The constant mu in this theory has been determined to be (2.7 +/- 0.1) x 10(10) V m C-1. This value is consistent with data on charge collection characteristics obtained using the same ionisation chamber exposed to continuous radiation from beta-sources.
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