• Journal of Radiation Protection and Research
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• v.34 no.2
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• pp.43-48
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• 2009

When the PDD (percentage depth dose) in the megavoltage beams is measured in the water phantom, the polarity and ion recombination effects of ionization chambers with depth in water are not usually taken into consideration. We try to investigate if those variations with depth should be taken into consideration or could be ignored for the thimble type semiflex ionization chamber (PTW $31010^{TM}$, SN 1551). According to the recommendation of IAEA TRS-398, the 4 representative depths of $d_s$, $d_{max}$, $d_{90}$ and $d_{50}$ were used for the electron beams. For the photon beams, the 4 depths were arbitrarily chosen for the photon beams, which were $d_s$, $d_{max}$, $d_{10}$ and $d_{20}$. For the high energy photon beam both polarity and ion recombination factors of the chamber with depth in water gives the good agreements within the maximum $\pm$0.2%, while the $C_{polS}$ with depth came within the maximum $\pm$ 0.4% and the $C_{IRS}$ within the maximum $\pm$0.6% in every electron beam used. This study shows that PDI (percentage depth ionization) could be a good approximation to PDD for the chamber used.

• Journal of Sensor Science and Technology
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• v.8 no.3
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• pp.219-225
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• 1999

The purpose of this study is to measure such parameters as TMR, OAR, TSF for small beams ranging in size from 12.5mm to 40mm by diode, ionization chamber, film, TLD and to determine proper detectors for the measurement of 6MV small x-ray beams. Diode and film show good results within 2% error for the TMR measurement of the beam as small as beam with diameter 12.5mm. Diode and film have excellent spatial resolution in the OAR measurement and the comparison between two detectors shows the error within 3%. But TMR and OAR can not be measured accurately by the ionization chambers. The TSF by diode and TLD records 0.890.96 for the beams with diameter 12.5mm 40mm. The TSF determined by 0.125cc ionization chamber and markus ionization chamber for the larger beams than the beams with diameter 25mm agrees within 2% comparing with that of diode and TLD.

• Journal of radiological science and technology
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• v.32 no.2
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• pp.205-212
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• 2009

The response correction factor ( h) is a factor to convert the response of the chamber in solid phantom to the response in water. In RW3 solid phantom, the dependency of beam quality and depth for high energy X-rays are known characteristics, however the dependency of field size, SSD, and chamber type are unknown. In this work we have studied the unknown characteristics on the dependency of response correction factor. The farmer type chamber (FC65G) and small chamber (CC13) were used and two beam qualities of 6 and 15 MV were evaluated. The measured response correction factors at the depth of 5 cm and 10 cm were h = 1.015 and 1.021 for 6 MV X-rays, and h = 1.024 and 1.029 for 15 MV X-rays. In conclusion the response correction factor did not depend on the field size and SSD while depending on the beam quality and depth. In the chambers, there are small differences between the two chambers used in this study but we think additional study for more chambers should be required. The results in this study can be used for analyzing the measured values from ionization chamber dosimetry in RW3.

• Radiation Oncology Journal
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• v.15 no.1
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• pp.65-69
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• 1997

Purpose : To obtain the actual dose distribution from measured data by doconvolution method using the measured ion chamber response function. Materials and Methods : The chamber response functions for 2 ionization chambers (diameter 5mm, 6.4mm) were measured. and dose Profiles were measured for $10{\times}20cm^2$ field size using two different detectors. The deconvolution of chamber response function from the measured data were performed for these Profiles. The same procedures were repeated for 4MV, 6MV and 1 SMV photon energies. Results : Different dose Profiles were obtained for the same field with the chambers which have the different response functions. Nearly the same results could be obtained with deconvolution for the profiles from various detectors. Conclusion : The effect of the chamber response function can be extracted by deconvolution method. Deconvolved dose profile using various ionization chambers gave better dose distributions. Technical improvements are needed for practical application.

• Nuclear Engineering and Technology
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• v.52 no.7
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• pp.1511-1516
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• 2020

The Korea Research Institute of Standards and Science (KRISS) established a new standard of the absorbed dose to water in LINAC X-ray beams. To confirm the equivalence of the new standard with other national metrology institutes (NMIs), a bilateral comparison study of the absorbed dose to water in high energy X-ray beams was performed between the KRISS and the National Metrology Institute of Japan (NMIJ). The comparison was made in-directly. Three transfer chambers were calibrated in the high energy X-ray beams by both laboratories and the calibration coefficients were compared. The average ratios of the calibration coefficients of the three transfer chambers obtained by the KRISS to those obtained by the NMIJ were 1.004, 1.006, 1.006, 1.007 for 6, 10, 15 and 18 MV X-ray beams, respectively. The calibration coefficients obtained at the KRISS were higher than those at the NMIJ but they were in good agreement within the expanded uncertainty of 1.0% (k = 2). The results of this study will be used as the evidence for the KRISS standard being comparable with those of other NMIs, temporarily, in the interim period up to finalizing a key comparison study, BIPM.RI(I)-K6 managed by the Consultative Committee for Ionizing Radiation.

• Nuclear Engineering and Technology
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• v.56 no.4
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• pp.1431-1440
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• 2024

The study aimed to develop a laser-based distance meter (LDM) to improve water surface identification for clinical MeV electron beam dosimetry, as inaccurate water surface determination can lead to imprecise positioning of ionization chambers (ICs). The LDM consisted of a laser ranging sensor, a signal processing microcontroller, and a tablet PC for data acquisition. I₅₀ (the water depth at which ionization current drops to 50 % of its maximum) measurements of electron beams were performed using six different types of ICs and compared to other water surface identification methods. The LDM demonstrated reproducible I₅₀ measurements with a level of 0.01 cm for all six ICs. The uncertainty of water depth was evaluated at 0.008 cm with the LDM. The LDM also exposed discrepancies between I₅₀ measurements using different ICs, which was partially reduced by applying an optimum shift of IC's point of measurement (POM) or effective point of measurement (EPOM). However, residual discrepancies due to the energy dependency of the cylindrical chamber's EPOM caused remained. The LDM offers straightforward and efficient means for precision water surface identification, minimizing reliance on individual operator skills.

• Progress in Medical Physics
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• v.13 no.2
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• pp.55-61
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• 2002

In this work, EPM (effective point of measurement) of parallel plate ionization chamber with three different spacing were investigated. If the plate separation is less than 2 mm one generally assumes that the effective point of measurement is just behind the front window of the parallel plate ionization chamber. For chamber with relatively large separation, such as the ones used for very accurate exposure measurements, this assumption breaks down and the EPM depends on plate separation and thickness of the front window. For parallel plate chambers, conventional theoretical analyses suggest that the EPM is the inner front wall and that it shifts towards the geometric centre of the chamber as the plate separation increases. The PP-IC (parallel plate ionization chamber) is fabricated using acrylic plate for the chamber medium and printed circuit board for electrical configuration. The various sizes of the sensitive volumes designed so far are 0.9, 1.9, and 3.1 cc. The gap between two electrodes ranges from 3, 6, and 10mm. Also the charge-to-voltage converter is designed to collect the electrons produced in the ionization chamber cavity. As the result of our experiment, the EPM shift was within 0.6 mm in photon beams and 0.4 mm to 2.5 mm in electron beams for the plate separation of 6 mm and 10 mm. EPM shifts towards the geometric center of the chamber as the plate separation increases.

• Nuclear Engineering and Technology
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• v.49 no.7
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• pp.1489-1494
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• 2017

The use of a room-temperature gamma spectrometer is an issue in environmental radiation monitoring. To monitor radionuclides released around a nuclear power plant, suitable instruments giving fast and reliable information are required. High-pressure xenon (HPXe) chambers have range of resolution and efficiency equivalent to those of other medium resolution detectors such as those using NaI(Tl), CdZnTe, and $LaBr_3:Ce$. An HPXe chamber could be a cost-effective alternative, assuming temperature stability and reliability. The CEA LIST actively studied and developed HPXe-based technology applied for environmental monitoring. Xenon purification and conditioning was performed. The design of a 4-L HPXe detector was performed to minimize the detector capacitance and the required power supply. Simulations were done with the MCNPX2.7 particle transport code to estimate the intrinsic efficiency of the HPXe detector. A behavioral study dealing with ballistic deficits and electronic noise will be utilized to provide perspective for further analysis.

• Journal of Radiation Protection and Research
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• v.12 no.1
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• pp.54-60
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• 1987

The quasi-exposure rate and the quasi-effective energy of the natural radiation in the field at 47 monitoring points around nuclear power plants have been studied with the pair filter thermoluminescence dosimeter system. The results of the six years observation showed that the relationship between the quasi-exposure rate $X_q$, and quasi-effective energy $E_q$ can be represented as a hyperbolic function: $X_q=A+C/(E_q-B)$, where the constants A and B correspond to the quasi-exposure rate of cosmic-rays and the minimum quasi-effective energy of natural radiation, respectively. Furthermore, the constant A is in close agreement with the values obtained by using ionization chambers and scintillation detectors. The constant B is approximately 0.68 MeV, closely corresponding to the mean energy of the photons emitted from natural uranium.

• Progress in Medical Physics
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• v.26 no.3
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• pp.178-184
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• 2015

The Markus ionization chamber(R) is a small plane parallel ionization chamber widely used in clinical electron beam dosimetry. Plane parallel chambers were recommended for low energy electron dosimetry with the beam quality at $R_{50}<4.0g/cm^2$ (${\bar{E}}{\approx}10MeV$) according to TRS-398 protocol. However, the quality correction factors ($k_{Q,Q_0}$) of the Markus chamber was not presented in TRS-398 protocol for electron beam quality at $R_{50}<2.0g/cm^2$ (${\bar{E}}{\approx}4MeV$). In this study, the $k_{Q,Q_0}$ factors of the Markus chambers (PTW-34045) for beam qualities at $R_{50}=1.0$, 1.4, 2.0, 2.5, 3.0, and $5.0g/cm^2$ were determined by Monte Carlo calculations (DOSRZnrc/EGSnrc) and the dosimetric formalism of quality correction factor. The derived $k_{Q,Q_0}$ values were evaluated using the produced data based on TRS-398 and TG-51 protocols and known values for the Markus chamber.