- Email: [email protected]
EPR dosimetric potential of ammonium oxalate monohydrate in radiation technology
Radiation Physics and Chemistry 162 (2019) 121–125
Contents lists available at ScienceDirect
Radiation Physics and Chemistry journal homepage: www.elsevier.com/locate/radphyschem
EPR dosimetric potential of ammonium oxalate monohydrate in radiation technology
T
M.A.H. Rushdia,∗, W.B. Beshirb a b
Sudan Atomic Energy Commission, Khartoum, Sudan National Center for Radiation Research and Technology, Atomic Energy Authority (AEA), P.O. Box 8029, Nasr City, Cairo, Egypt
A R T I C LE I N FO
A B S T R A C T
Keywords: Radiation dosimetry EPR spectrometer Ammonium oxalate Radiation technology
This study aims to examine the dosimetric properties of the ammonium oxalate monohydrate (COONH4)2H2O irradiated by 60Co gamma-rays. The EPR spectra of ammonium oxalate have the spectroscopic splitting g-factors of 2.0095 and 2.0047. Results indicate that the dose-response curves have a good linearity in the range between 10 and 1000Gy. Slight sub-linearity has been found in high dose region up to 25 kGy. The effects of temperature and humidity on the EPR signal amplitude of the irradiated samples were studied. Stability of the irradiation rods upon storage (signal fading) was also investigated. Energy dependence has been found within 38% at the range below 100 keV. The dosimeter displayed an increasing response by approximately 4% over the energy range 6–10 MeV. The overall uncertainty of this dosimetry system is 4.64% (σ2) in low dose range and 3.67% for the high dose range.
1. Introduction
paramagnetic species formed in ammonium oxalate P.I. Premovic‘ (PremovicK.J.A and Herak, 1972), the expected radicals formed upon irradiation at room temperature were –O2CC. OH− and –O2CC.O2, the first radical is more stable than the other (C2O4−). The aim of this investigation is to find a suitable dosimetric material to meet the criteria of being tissue equivalent, having narrow EPR spectrum containing strong and stable radical. The material should provide good reproducibility and small energy dependence and should not be affected by temperature and humidity.
Electron paramagnetic resonance (EPR) spectroscopy has been applied as a useful quantitative technique to investigate the effects of radiation over several applications Burns and Flockhart (1990). The free radicals are formed by ionizing radiation. In crystalline materials they may be trapped in the crystalline phase and, in consequence, become very long-lived Lund, Shiotani (Lund et al., 2011), EPR analysis of such material could be used for dosimetry. Amino acid alanine is now widely recognized as a reference dosimetry system in industrial applications. Several studies of radiation-induced paramagnetic radicals in organic acid salts have been investigated. The need for a dosimeter with tissue equivalent is a condition to avoid any correction in low energy beam, especially for radiation therapy. Among these organic acids, oxalic acid and its salts have been found as a useful tool for dosimetry P.I. Premovic‘ (PremovicK.J.A and Herak, 1972). Some oxalates have reported recently such as Li- and Mg-oxalates which have been studied as a sensitive ESR dosimeter Hassan, Ulusoy (Hassan et al., 2000) and calcium oxalate investigated its EPR signal to be used in dosimetry Thompson and Schwarcz (2008). In this work, the selected oxalate is ammonium oxalate. It has a molar weight of 142.11 g/mol and a density of 1.5 g/cm3 in crystal form. It is not toxic, but some conditions should be avoided such as dust generation and excess heat. Early work has been done to understand the
∗
2. Experimental 2.1. Dosimeter preparation A reagent grade powder of ammonium oxalate monohydrate (COONH4)2H2O (99%, molecular weight, 142.11, from LOBA chemie PVT. TLD Mumbai, India) with ethylene-vinyl acetate (EVA) (TEC-Bond 232/12, Power Adhesives Limited, England) and paraffin wax (Congealing point 65–71 °C, BDH) were used for the preparation. To prepare the dosimeter: EVA/Paraffin mixture of equal weight is melted at 70 °C and well-homogenized by mechanical stirring. Then, ammonium oxalate powder is added gradually into the melted binder for complete mixing. The rod batches of 50% (COONH4)2H2O by weight are prepared. Before cooling, the melted mixtures are pulled into
Corresponding author. , E-mail address: [email protected] (M.A.H. Rushdi).
https://doi.org/10.1016/j.radphyschem.2019.05.003 Received 19 March 2018; Received in revised form 15 March 2019; Accepted 1 May 2019 Available online 03 May 2019 0969-806X/ © 2019 Elsevier Ltd. All rights reserved.
Radiation Physics and Chemistry 162 (2019) 121–125
M.A.H. Rushdi and W.B. Beshir
polypropylene (PP) tubes (inner diameter 3.5 mm) then left to harden at room temperature for an additional 24 h. The rods (diameter 3.5 mm, 20 mm length) are stored in the darkness at room temperature for further investigations Waldeland, Hole (Waldeland et al., 2010). The average total weight of the prepared rods of 50%, of ammonium oxalate, is 0.186 ± 0.005 g. 2.2. EPR spectrometer and measurements Ammonium oxalate rod dosimeters are analyzed at room temperature on a Bruker, EMX EPR spectrometer (X-band) and a rectangular cavity of ER4102. The EPR investigations were analyzed at the following parameters; receiver gain, 7.96 × 103; modulation amplitude, 0.4 mT; microwave power, 2.533 mW; central field, 3450.61G; microwave frequency, 9.71 GHz; modulation frequency, 100 kHz; time constant, 81.92 ms; sweep time, 20.48 ms; sweep width, 200G; number of scans used for low doses, 5. The dosimeter length of 2 mm was chosen by considering the effective volume of the cavity of the ESR reading system Kojima, Haruyama (Kojima et al., 1993). A DPPH, reference sample, was selected to check the stability of spectrometer and to correlate the signal height (SH) of the dosimeter to the SH of DPPH. The dose-response of the dosimeter was plotted in terms of correlated SH (SHdosimeter/SHDPPH × weight of the rod, g) against absorbed dose.
Fig. 2. EPR spectrum of irradiated ammonium oxalate to 10 kGy, (Microwave power: 2.533 mW, modulation amplitude: 4 G).
(g2 = 2.0047 ± 0.0017) Fig. 2, this could be related to the radicals recombination. An unclear feature of EPR signal was obtained in the rod and powder samples before irradiation even with high microwave power values. The microwave power dependence of the EPR signal was investigated. The signal intensity increases as a function of the square root of microwave power up to 1.59 mW (corresponding to power 2.533 mW). It is worth mentioning that using low microwave power values may increase the S/N ratio on another side the use of high microwave power might broad the EPR lines. The best selection of the power value better to be located above the linear region Olsson, Lund (Olsson et al., 2000). See Fig. 3.
2.3. Irradiation process The rod dosimeters were irradiated from 10Gy to 25 kGy by 60Co source (GammaCell 220E) with the dose rate of 1.56 kGy/h. The source was calibrated by alanine reference standard dosimeter according to ASTM E1026-13 (Standard, 1026). A poly (methyl methacrylate) (PMMA) 5 mm holder/phantom was used for irradiation of the rods to make sure electronic equilibrium during irradiation.
3.2. Dose response function
3. Results and discussion
The observed relationship between absorbed dose and the peak-topeak height of the ESR first derivative line suggests a linear function in the dose range from 10 to 1000Gy with correlation coefficient, (r2 = 0.999) see Fig. 4. Nonlinear relationship with 3rd polynomial function and correlation coefficient, (r2 = 0.999) showed in Fig. 5 for dose range from 5 to 25 kGy.
3.1. EPR spectra and power dependence The EPR spectra of ammonium oxalate rods were achieved after irradiation with absorbed doses of 10Gy up to 25 kGy. Fig. 1 shows the EPR spectra of the ammonium oxalate irradiated to 100Gy which has gfactor of (g1 = 2.00957 ± 0.0038) with line-width of 0.62 mT, this EPR signal will be considered as the main dosimetric signal and identified as oxalate radicals –O2CC. OH− produced when the electron is injected from a carbon atom of the oxalate ion –O2CC. OH− upon irradiation P.I. Premovic‘ (PremovicK.J.A and Herak, 1972). Small signal started to create at high doses above 1 kGy with splitting factor
3.3. Effect of humidity levels on the dosimeter response The influence of relative humidity (RH), to the dosimeter response during irradiation, was investigated= by irradiating the rods to a dose of 1 kGy at different relative humidities. Equilibrium RH conditions during irradiation were maintained by storing the rods for 72 h before
Fig. 1. EPR spectrum of ammonium oxalate, unirradiated and irradiated (absorbed dose 100 Gy, (Microwave power: 2.533 mW, modulation amplitude: 4 G).
Fig. 3. The dependence of EPR signal intensity (g-factor = 2.00957) on microwave power. 122
Radiation Physics and Chemistry 162 (2019) 121–125
M.A.H. Rushdi and W.B. Beshir
dosimeter may depend on its water content, the greater the moisture content of the rod dosimeter, the stronger is the height signal found. Response at humidity below 30% showed reduced sensitivity. Another increase was also observed at a relative humidity greater than 75% (∼16%). The increase can be explained by the fact that the rod dosimeter was subjected to EPR laboratory environment and due to that the rod dosimeter became a bit dry. The rate of drying also increases with modulation amplitude in the range of 0.28–1.4 mT Sleptchonok, Nagy (Sleptchonok et al., 2000). Higher modulation amplitude supplies the rods with higher temperatures during the measurement. It is interesting to note that the rod dosimeter is slightly affected between 30 and 75% relative humidity, the response affected by 0.07% among this range, therefore it is suggested to avoid using the dosimeter below or above this range. (See Fig. 6). 3.4. Effect of irradiation temperature on the dosimeter response Fig. 4. Dose response curves of ammonium oxalate rod dosimeter (50%) irradiated by 60Co γ-rays at a series of absorbed doses. Dose range; 10–1000 Gy; represented by 1st order function (r2 = 0.999).
The temperature during irradiation affects the radical production that is reflected in the measured response of the dosimeter Desrosiers, Cooper (Desrosiers et al., 2004). The analysis of the rod dosimeter relative response to irradiation temperature has been examined from 20 to 50 °C, which revealed significant influence gradually increasing in response (∼3%) from 30 °C until 40 °C. (∼9%) increasing in dosimeter response has been shown up to 50 °C. However, in the range between 20 and 30 °C, a slight increase in response been observed. (See Fig. 7). 3.5. Post-irradiation stability Investigation of long-term stability of (COONH4)2 rod dosimeter is plotted in Fig. 8, which presented good characteristics over 53 days of storage. The signal amplitude of the rod dosimeter gradually decreases by approximately 11% during 9 days, which means that the process of recombination of the two radicals reaches saturation after this period. After that, the accumulated radicals stabilized until the end of the study with variation in response not exceed 4%. The DPPH reference sample has been used for every measured point. If the irradiated dosimeter is analyzed through 10 days after irradiation, the time of analysis during routine measurements and calibration should be standardized; otherwise, a correction factor should be applied.
Fig. 5. Dose response curves of ammonium oxalate rod dosimeter (50%) irradiated by 60Co γ-rays at a series of absorbed doses. Dose range; 5–25 kGy; represented by 3rd order function (r2 = 0.999).
3.6. Energy dependence This study is essential as it reflects the dosimeter's energy efficiency Attix (2008). Fig. 9 illustrates the mass energy absorption coefficient, μen/ρ for ammonium oxalate rod dosimeter (Zeff = 4.0014) and alanine
Fig. 6. Discrepancy of EPR response of (COONH4)2 rod dosimeter normalized to RH 33% as a function of RH during irradiation (Absorbed dose = 1 kGy).
irradiation in tightly closed jars over appropriate saturated salt solutions except for 0% RH was maintained over dried silica gel. The saturated salt solutions used are MgCl2.6H2O 33%, Na2Cr2O7.2H2O 54%, SrCl2 71% and KNO3 92% Greenspan (1977). Ammonium oxalate dosimeter signal noticeably increase from 0% to 30%, the response of the
Fig. 7. Discrepancy of EPR response of ammonium oxalate rod dosimeter normalized to response of 20 °C as a function of irradiation temperature (Absorbed dose = 1 kGy). 123
Radiation Physics and Chemistry 162 (2019) 121–125
M.A.H. Rushdi and W.B. Beshir
(Zeff = 3.9365) relative to water (material in the sensitive volume Zeff = 3.3349) versus photon energies range of 0.001–10 MeV. These calculations were based on the data presented online at NIST physical reference data Hubbell and Seltzer (1995) and in ICRU Report 44 D. R. White (White et al., 1989). The relative number of radicals for the ammonium oxalate shows independent of radiation energy in the range from 0.1 to 6 MeV (dominated by Compton scattering). As well as very small dependence, 4% at 10 MeV has been observed (dominated by pair production). Valid correction factors for the apparent minor energy dependence of the two systems should be determined below 100 keV. This effect is mainly due to the photoelectric interaction which is dominated below 60 keV at these low Zeff Gunderson and Tepper (2007). 3.7. Uncertainty estimation The various sources of uncertainty in the estimation of the absorbed dose in the low and high dose range Taylor (2009) were evaluated in order to estimate the sensitivity coefficients of each of the identified uncertainty parameters Adams (2002). Dose uncertainties of type A (evaluated by statistical methods from a series of repeated observations; uA) and type B (evaluated by non-statistical methods; uB i.e. was taken from manufacturer-supplied calibration) are combined to estimate the total uncertainty in the evaluated dose from dosimeter, (see Table 1). The batch non-uniformity of 10-rod dosimeters has been investigated by determination of the fluctuations in the response of each dosimeter, the coefficient of variation was found to be 0.95%. The uncertainty of the goodness-of-fit was calculated from the residual analysis. This value was estimated as 1.69% and 0.95% for low and high doses respectively. The environmental effects were applied since the study reached high values of temperature (above 50 °C) and humidity (above 80%) IAEA (IAEA, 2008). The combined standard uncertainty evaluated by both types of uncertainties was approximately 2.32% in the dose range between 10 and 1000Gy and 1.83% in the dose range from 5 to 25 kGy. By multiplying the combined uncertainty for each range by a coverage tfactor of 2.05 to yield the expanded uncertainty of ± 4.64% and ± 3.67% for low and high doses respectively at an approximate level of confidence 95%.
Fig. 8. Post-irradiation signal of ammonium oxalate rod dosimeter relative to that value measured immediately after irradiation (zero time) against storage time, (53 days). The dosimeter is irradiated to 100 Gy.
Fig. 9. The mass energy absorption coefficient, μen/ρ, of ammonium oxalate rod dosimeter (50%) and alanine normalized to water versus photon energy in the range of 0.001–10 MeV.
4. Conclusions This paper investigates the potential applicability of ammonium oxalate monohydrate as an EPR dosimeter sensitive to gamma radiation. It has a relatively wide range of dose response. It also has good
Table 1 Uncertainty parameters monitoring by ammonium oxalate rod dosimeter (50%) in the low and high dose range. Uncertainty parameters
Dose rate calibration by reference dosimeter Irradiation facility b Sensitivity variation of EPR spectrometer c Reproducibility of EPR spectrometer d Batch uniformity of the dosimeter Uncertainty of calibration curve fitting Irradiation temperature during calibration Effect of irradiation temperature Effect of irradiation humidity Post-irradiation EPR response stability Combined standard uncertainty (uc), (1σ) Overall uncertainty (2σ)
Type of uncertainty
a
B B A A A A B A A A
a
Standard uncertainty % Low doses
High doses
1.15 0.25 0.24 0.37 0.95 1.69 0.12 0.03 0.13 0.04 2.32 4.64
1.15 0.25 0.24 0.37 0.95 0.92 0.12 0.03 0.13 0.04 1.83 3.67
Quoted from calibration certificate. It includes geometry effect, source decay correction, timer setting and nonuniform gamma field (type B). c Estimated from measurements of EPR signal intensity of the dosimeter while the dosimeter was fixed in the rectangular cavity. d Estimated from measurements of EPR signal intensity of an irradiated rod, while the dosimeter was taken out and returned to the rectangular cavity between each measurement. b
124
Radiation Physics and Chemistry 162 (2019) 121–125
M.A.H. Rushdi and W.B. Beshir
References
linear dose response in the range of 10–1000Gy. The sharp signal of –O2CC.OH− has a g-factor of 2.0095 with line-width 0.62 mT which is preferred in dosimetric studies. A small signal has been generated at high doses with g-factor 2.00469. High and low humidity can affect the dosimetry response, therefore, it's better to use the dosimeter between 30 and 75 relative humidity. The stability of the radical at room temperature indicates that ammonium oxalate loses ∼11% of its initial value after a period of 53 days with considered that the signal continues decaying for approximately 9 days until the free radical formed is stabilized which probably due to the radical's recombination process. In addition, study of energy dependence has been carried out and shows discrepancy on the dosimeter response. Determination of the correction factor should be a part of measurements when use the dosimeter under low energy level. The obtained EPR dosimetric properties of ammonium oxalate monohydrate show that, it could be used in some applications such as food preservation and disinfestation and sterile insect technique.
Adams, T.M., 2002. G104-A2LA Guide for Estimation of Measurement Uncertainty in Testing. American Association of Laboratory Accreditation Manual, pp. 10–18. Attix, F.H., 2008. Introduction to Radiological Physics and Radiation Dosimetry. John Wiley & Sons. Burns, D., Flockhart, B., 1990. Application of quantitative EPR 333, 37–48. Desrosiers, M.F., et al., 2004. A study of the alanine dosimeter irradiation temperature coefficient in the− 77° C to+ 50° C range. Radiat. Phys. Chem. 71 (1), 365–370. Greenspan, L., 1977. Equilibrium relative humidity of some saturated salt solutions 25oC. J. Res. National Bureau Standards,A 81. Gunderson, L.L., Tepper, J.E., 2007. Clinical Radiation Oncology. Elsevier Health Sciences. Hassan, G.M., Ulusoy, U., Ikeya, M., 2000. Radical formation in lithium and magnesium oxalate. Jpn. J. Appl. Phys. 39 (11R), 6236. Hubbell, J.H., Seltzer, S.M., 1995. Tables of X-Ray Mass Attenuation Coefficients and Mass Energy-Absorption Coefficients 1 keV to 20 MeV for Elements Z= 1 to 92 and 48 Additional Substances of Dosimetric Interest. National Inst. of Standards and Technology-PL, Gaithersburg, MD (United States) (Ionizing Radiation Div). IAEA, 2008. Measurement Uncertainty - A Practical Guide For Secondary Standards Dosimetry Laboratories. IAEA, Austria. Kojima, T., et al., 1993. Alanine ESR Dosimetry system for routine use in radiation processing. Radiat. Phys. Chem. 42 (4), 757–760. Lund, A., Shiotani, M., Shimada, S., 2011. Applications of quantitative ESR. In: Principles and Applications of ESR Spectroscopy. Springer, pp. 409–438. Olsson, S.K., Lund, E., Lund, A., 2000. Development of ammonium tartrate as an ESR dosimeter material for clinical purposes. Appl. Radiat. Isot. 52 (5), 1235–1241. Premovic, P.I., K.J.A, Herak, J.N., 1972. Electron spin resonance study of irradiated single crystals of ammonium oxalate monohydrate. J. Phys. Chem. 76, 3274. Sleptchonok, O.F., et al., 2000. Advancements in accuracy of the alanine dosimetry system. Part 1. The effects of environmental humidity 57 (2), 115–133. Standard, A., E1026 “standard practice for using Fricke reference standard dosimetry system”. Annual Book of Standards. 12. Taylor, B.N., 2009. Guidelines for Evaluating and Expressing the Uncertainty of NIST Measurement Results. DIANE Publishing. Thompson, J., Schwarcz, H., 2008. Electron paramagnetic resonance dosimetry and dating potential of whewellite (calcium oxalate monohydrate). Radiat. Meas. 43 (7), 1219–1225. Waldeland, E., et al., 2010. Radical formation in lithium formate EPR dosimeters after irradiation with protons and nitrogen ions. Radiat. Res. 174 (2), 251–257. White, D.R., Griffith, R.V., Spokas, J.J., 1989. Tissue Substitutes in Radiation Dosimetry and Measurement os23 International Commission on Radiation Units and Measurements, Bethesda, Md., U.S.A.
Funding The authors received no external funding for this study. Acknowledgments We thank Eva Lund (Department of Medicine and Care, Radiation Physics, Faculty of Health Sciences Linköping University, Sweden) for assistance with scientific guidance and comments that greatly improved the manuscript. Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.radphyschem.2019.05.003.
125
Contents lists available at ScienceDirect
Radiation Physics and Chemistry journal homepage: www.elsevier.com/locate/radphyschem
EPR dosimetric potential of ammonium oxalate monohydrate in radiation technology
T
M.A.H. Rushdia,∗, W.B. Beshirb a b
Sudan Atomic Energy Commission, Khartoum, Sudan National Center for Radiation Research and Technology, Atomic Energy Authority (AEA), P.O. Box 8029, Nasr City, Cairo, Egypt
A R T I C LE I N FO
A B S T R A C T
Keywords: Radiation dosimetry EPR spectrometer Ammonium oxalate Radiation technology
This study aims to examine the dosimetric properties of the ammonium oxalate monohydrate (COONH4)2H2O irradiated by 60Co gamma-rays. The EPR spectra of ammonium oxalate have the spectroscopic splitting g-factors of 2.0095 and 2.0047. Results indicate that the dose-response curves have a good linearity in the range between 10 and 1000Gy. Slight sub-linearity has been found in high dose region up to 25 kGy. The effects of temperature and humidity on the EPR signal amplitude of the irradiated samples were studied. Stability of the irradiation rods upon storage (signal fading) was also investigated. Energy dependence has been found within 38% at the range below 100 keV. The dosimeter displayed an increasing response by approximately 4% over the energy range 6–10 MeV. The overall uncertainty of this dosimetry system is 4.64% (σ2) in low dose range and 3.67% for the high dose range.
1. Introduction
paramagnetic species formed in ammonium oxalate P.I. Premovic‘ (PremovicK.J.A and Herak, 1972), the expected radicals formed upon irradiation at room temperature were –O2CC. OH− and –O2CC.O2, the first radical is more stable than the other (C2O4−). The aim of this investigation is to find a suitable dosimetric material to meet the criteria of being tissue equivalent, having narrow EPR spectrum containing strong and stable radical. The material should provide good reproducibility and small energy dependence and should not be affected by temperature and humidity.
Electron paramagnetic resonance (EPR) spectroscopy has been applied as a useful quantitative technique to investigate the effects of radiation over several applications Burns and Flockhart (1990). The free radicals are formed by ionizing radiation. In crystalline materials they may be trapped in the crystalline phase and, in consequence, become very long-lived Lund, Shiotani (Lund et al., 2011), EPR analysis of such material could be used for dosimetry. Amino acid alanine is now widely recognized as a reference dosimetry system in industrial applications. Several studies of radiation-induced paramagnetic radicals in organic acid salts have been investigated. The need for a dosimeter with tissue equivalent is a condition to avoid any correction in low energy beam, especially for radiation therapy. Among these organic acids, oxalic acid and its salts have been found as a useful tool for dosimetry P.I. Premovic‘ (PremovicK.J.A and Herak, 1972). Some oxalates have reported recently such as Li- and Mg-oxalates which have been studied as a sensitive ESR dosimeter Hassan, Ulusoy (Hassan et al., 2000) and calcium oxalate investigated its EPR signal to be used in dosimetry Thompson and Schwarcz (2008). In this work, the selected oxalate is ammonium oxalate. It has a molar weight of 142.11 g/mol and a density of 1.5 g/cm3 in crystal form. It is not toxic, but some conditions should be avoided such as dust generation and excess heat. Early work has been done to understand the
∗
2. Experimental 2.1. Dosimeter preparation A reagent grade powder of ammonium oxalate monohydrate (COONH4)2H2O (99%, molecular weight, 142.11, from LOBA chemie PVT. TLD Mumbai, India) with ethylene-vinyl acetate (EVA) (TEC-Bond 232/12, Power Adhesives Limited, England) and paraffin wax (Congealing point 65–71 °C, BDH) were used for the preparation. To prepare the dosimeter: EVA/Paraffin mixture of equal weight is melted at 70 °C and well-homogenized by mechanical stirring. Then, ammonium oxalate powder is added gradually into the melted binder for complete mixing. The rod batches of 50% (COONH4)2H2O by weight are prepared. Before cooling, the melted mixtures are pulled into
Corresponding author. , E-mail address: [email protected] (M.A.H. Rushdi).
https://doi.org/10.1016/j.radphyschem.2019.05.003 Received 19 March 2018; Received in revised form 15 March 2019; Accepted 1 May 2019 Available online 03 May 2019 0969-806X/ © 2019 Elsevier Ltd. All rights reserved.
Radiation Physics and Chemistry 162 (2019) 121–125
M.A.H. Rushdi and W.B. Beshir
polypropylene (PP) tubes (inner diameter 3.5 mm) then left to harden at room temperature for an additional 24 h. The rods (diameter 3.5 mm, 20 mm length) are stored in the darkness at room temperature for further investigations Waldeland, Hole (Waldeland et al., 2010). The average total weight of the prepared rods of 50%, of ammonium oxalate, is 0.186 ± 0.005 g. 2.2. EPR spectrometer and measurements Ammonium oxalate rod dosimeters are analyzed at room temperature on a Bruker, EMX EPR spectrometer (X-band) and a rectangular cavity of ER4102. The EPR investigations were analyzed at the following parameters; receiver gain, 7.96 × 103; modulation amplitude, 0.4 mT; microwave power, 2.533 mW; central field, 3450.61G; microwave frequency, 9.71 GHz; modulation frequency, 100 kHz; time constant, 81.92 ms; sweep time, 20.48 ms; sweep width, 200G; number of scans used for low doses, 5. The dosimeter length of 2 mm was chosen by considering the effective volume of the cavity of the ESR reading system Kojima, Haruyama (Kojima et al., 1993). A DPPH, reference sample, was selected to check the stability of spectrometer and to correlate the signal height (SH) of the dosimeter to the SH of DPPH. The dose-response of the dosimeter was plotted in terms of correlated SH (SHdosimeter/SHDPPH × weight of the rod, g) against absorbed dose.
Fig. 2. EPR spectrum of irradiated ammonium oxalate to 10 kGy, (Microwave power: 2.533 mW, modulation amplitude: 4 G).
(g2 = 2.0047 ± 0.0017) Fig. 2, this could be related to the radicals recombination. An unclear feature of EPR signal was obtained in the rod and powder samples before irradiation even with high microwave power values. The microwave power dependence of the EPR signal was investigated. The signal intensity increases as a function of the square root of microwave power up to 1.59 mW (corresponding to power 2.533 mW). It is worth mentioning that using low microwave power values may increase the S/N ratio on another side the use of high microwave power might broad the EPR lines. The best selection of the power value better to be located above the linear region Olsson, Lund (Olsson et al., 2000). See Fig. 3.
2.3. Irradiation process The rod dosimeters were irradiated from 10Gy to 25 kGy by 60Co source (GammaCell 220E) with the dose rate of 1.56 kGy/h. The source was calibrated by alanine reference standard dosimeter according to ASTM E1026-13 (Standard, 1026). A poly (methyl methacrylate) (PMMA) 5 mm holder/phantom was used for irradiation of the rods to make sure electronic equilibrium during irradiation.
3.2. Dose response function
3. Results and discussion
The observed relationship between absorbed dose and the peak-topeak height of the ESR first derivative line suggests a linear function in the dose range from 10 to 1000Gy with correlation coefficient, (r2 = 0.999) see Fig. 4. Nonlinear relationship with 3rd polynomial function and correlation coefficient, (r2 = 0.999) showed in Fig. 5 for dose range from 5 to 25 kGy.
3.1. EPR spectra and power dependence The EPR spectra of ammonium oxalate rods were achieved after irradiation with absorbed doses of 10Gy up to 25 kGy. Fig. 1 shows the EPR spectra of the ammonium oxalate irradiated to 100Gy which has gfactor of (g1 = 2.00957 ± 0.0038) with line-width of 0.62 mT, this EPR signal will be considered as the main dosimetric signal and identified as oxalate radicals –O2CC. OH− produced when the electron is injected from a carbon atom of the oxalate ion –O2CC. OH− upon irradiation P.I. Premovic‘ (PremovicK.J.A and Herak, 1972). Small signal started to create at high doses above 1 kGy with splitting factor
3.3. Effect of humidity levels on the dosimeter response The influence of relative humidity (RH), to the dosimeter response during irradiation, was investigated= by irradiating the rods to a dose of 1 kGy at different relative humidities. Equilibrium RH conditions during irradiation were maintained by storing the rods for 72 h before
Fig. 1. EPR spectrum of ammonium oxalate, unirradiated and irradiated (absorbed dose 100 Gy, (Microwave power: 2.533 mW, modulation amplitude: 4 G).
Fig. 3. The dependence of EPR signal intensity (g-factor = 2.00957) on microwave power. 122
Radiation Physics and Chemistry 162 (2019) 121–125
M.A.H. Rushdi and W.B. Beshir
dosimeter may depend on its water content, the greater the moisture content of the rod dosimeter, the stronger is the height signal found. Response at humidity below 30% showed reduced sensitivity. Another increase was also observed at a relative humidity greater than 75% (∼16%). The increase can be explained by the fact that the rod dosimeter was subjected to EPR laboratory environment and due to that the rod dosimeter became a bit dry. The rate of drying also increases with modulation amplitude in the range of 0.28–1.4 mT Sleptchonok, Nagy (Sleptchonok et al., 2000). Higher modulation amplitude supplies the rods with higher temperatures during the measurement. It is interesting to note that the rod dosimeter is slightly affected between 30 and 75% relative humidity, the response affected by 0.07% among this range, therefore it is suggested to avoid using the dosimeter below or above this range. (See Fig. 6). 3.4. Effect of irradiation temperature on the dosimeter response Fig. 4. Dose response curves of ammonium oxalate rod dosimeter (50%) irradiated by 60Co γ-rays at a series of absorbed doses. Dose range; 10–1000 Gy; represented by 1st order function (r2 = 0.999).
The temperature during irradiation affects the radical production that is reflected in the measured response of the dosimeter Desrosiers, Cooper (Desrosiers et al., 2004). The analysis of the rod dosimeter relative response to irradiation temperature has been examined from 20 to 50 °C, which revealed significant influence gradually increasing in response (∼3%) from 30 °C until 40 °C. (∼9%) increasing in dosimeter response has been shown up to 50 °C. However, in the range between 20 and 30 °C, a slight increase in response been observed. (See Fig. 7). 3.5. Post-irradiation stability Investigation of long-term stability of (COONH4)2 rod dosimeter is plotted in Fig. 8, which presented good characteristics over 53 days of storage. The signal amplitude of the rod dosimeter gradually decreases by approximately 11% during 9 days, which means that the process of recombination of the two radicals reaches saturation after this period. After that, the accumulated radicals stabilized until the end of the study with variation in response not exceed 4%. The DPPH reference sample has been used for every measured point. If the irradiated dosimeter is analyzed through 10 days after irradiation, the time of analysis during routine measurements and calibration should be standardized; otherwise, a correction factor should be applied.
Fig. 5. Dose response curves of ammonium oxalate rod dosimeter (50%) irradiated by 60Co γ-rays at a series of absorbed doses. Dose range; 5–25 kGy; represented by 3rd order function (r2 = 0.999).
3.6. Energy dependence This study is essential as it reflects the dosimeter's energy efficiency Attix (2008). Fig. 9 illustrates the mass energy absorption coefficient, μen/ρ for ammonium oxalate rod dosimeter (Zeff = 4.0014) and alanine
Fig. 6. Discrepancy of EPR response of (COONH4)2 rod dosimeter normalized to RH 33% as a function of RH during irradiation (Absorbed dose = 1 kGy).
irradiation in tightly closed jars over appropriate saturated salt solutions except for 0% RH was maintained over dried silica gel. The saturated salt solutions used are MgCl2.6H2O 33%, Na2Cr2O7.2H2O 54%, SrCl2 71% and KNO3 92% Greenspan (1977). Ammonium oxalate dosimeter signal noticeably increase from 0% to 30%, the response of the
Fig. 7. Discrepancy of EPR response of ammonium oxalate rod dosimeter normalized to response of 20 °C as a function of irradiation temperature (Absorbed dose = 1 kGy). 123
Radiation Physics and Chemistry 162 (2019) 121–125
M.A.H. Rushdi and W.B. Beshir
(Zeff = 3.9365) relative to water (material in the sensitive volume Zeff = 3.3349) versus photon energies range of 0.001–10 MeV. These calculations were based on the data presented online at NIST physical reference data Hubbell and Seltzer (1995) and in ICRU Report 44 D. R. White (White et al., 1989). The relative number of radicals for the ammonium oxalate shows independent of radiation energy in the range from 0.1 to 6 MeV (dominated by Compton scattering). As well as very small dependence, 4% at 10 MeV has been observed (dominated by pair production). Valid correction factors for the apparent minor energy dependence of the two systems should be determined below 100 keV. This effect is mainly due to the photoelectric interaction which is dominated below 60 keV at these low Zeff Gunderson and Tepper (2007). 3.7. Uncertainty estimation The various sources of uncertainty in the estimation of the absorbed dose in the low and high dose range Taylor (2009) were evaluated in order to estimate the sensitivity coefficients of each of the identified uncertainty parameters Adams (2002). Dose uncertainties of type A (evaluated by statistical methods from a series of repeated observations; uA) and type B (evaluated by non-statistical methods; uB i.e. was taken from manufacturer-supplied calibration) are combined to estimate the total uncertainty in the evaluated dose from dosimeter, (see Table 1). The batch non-uniformity of 10-rod dosimeters has been investigated by determination of the fluctuations in the response of each dosimeter, the coefficient of variation was found to be 0.95%. The uncertainty of the goodness-of-fit was calculated from the residual analysis. This value was estimated as 1.69% and 0.95% for low and high doses respectively. The environmental effects were applied since the study reached high values of temperature (above 50 °C) and humidity (above 80%) IAEA (IAEA, 2008). The combined standard uncertainty evaluated by both types of uncertainties was approximately 2.32% in the dose range between 10 and 1000Gy and 1.83% in the dose range from 5 to 25 kGy. By multiplying the combined uncertainty for each range by a coverage tfactor of 2.05 to yield the expanded uncertainty of ± 4.64% and ± 3.67% for low and high doses respectively at an approximate level of confidence 95%.
Fig. 8. Post-irradiation signal of ammonium oxalate rod dosimeter relative to that value measured immediately after irradiation (zero time) against storage time, (53 days). The dosimeter is irradiated to 100 Gy.
Fig. 9. The mass energy absorption coefficient, μen/ρ, of ammonium oxalate rod dosimeter (50%) and alanine normalized to water versus photon energy in the range of 0.001–10 MeV.
4. Conclusions This paper investigates the potential applicability of ammonium oxalate monohydrate as an EPR dosimeter sensitive to gamma radiation. It has a relatively wide range of dose response. It also has good
Table 1 Uncertainty parameters monitoring by ammonium oxalate rod dosimeter (50%) in the low and high dose range. Uncertainty parameters
Dose rate calibration by reference dosimeter Irradiation facility b Sensitivity variation of EPR spectrometer c Reproducibility of EPR spectrometer d Batch uniformity of the dosimeter Uncertainty of calibration curve fitting Irradiation temperature during calibration Effect of irradiation temperature Effect of irradiation humidity Post-irradiation EPR response stability Combined standard uncertainty (uc), (1σ) Overall uncertainty (2σ)
Type of uncertainty
a
B B A A A A B A A A
a
Standard uncertainty % Low doses
High doses
1.15 0.25 0.24 0.37 0.95 1.69 0.12 0.03 0.13 0.04 2.32 4.64
1.15 0.25 0.24 0.37 0.95 0.92 0.12 0.03 0.13 0.04 1.83 3.67
Quoted from calibration certificate. It includes geometry effect, source decay correction, timer setting and nonuniform gamma field (type B). c Estimated from measurements of EPR signal intensity of the dosimeter while the dosimeter was fixed in the rectangular cavity. d Estimated from measurements of EPR signal intensity of an irradiated rod, while the dosimeter was taken out and returned to the rectangular cavity between each measurement. b
124
Radiation Physics and Chemistry 162 (2019) 121–125
M.A.H. Rushdi and W.B. Beshir
References
linear dose response in the range of 10–1000Gy. The sharp signal of –O2CC.OH− has a g-factor of 2.0095 with line-width 0.62 mT which is preferred in dosimetric studies. A small signal has been generated at high doses with g-factor 2.00469. High and low humidity can affect the dosimetry response, therefore, it's better to use the dosimeter between 30 and 75 relative humidity. The stability of the radical at room temperature indicates that ammonium oxalate loses ∼11% of its initial value after a period of 53 days with considered that the signal continues decaying for approximately 9 days until the free radical formed is stabilized which probably due to the radical's recombination process. In addition, study of energy dependence has been carried out and shows discrepancy on the dosimeter response. Determination of the correction factor should be a part of measurements when use the dosimeter under low energy level. The obtained EPR dosimetric properties of ammonium oxalate monohydrate show that, it could be used in some applications such as food preservation and disinfestation and sterile insect technique.
Adams, T.M., 2002. G104-A2LA Guide for Estimation of Measurement Uncertainty in Testing. American Association of Laboratory Accreditation Manual, pp. 10–18. Attix, F.H., 2008. Introduction to Radiological Physics and Radiation Dosimetry. John Wiley & Sons. Burns, D., Flockhart, B., 1990. Application of quantitative EPR 333, 37–48. Desrosiers, M.F., et al., 2004. A study of the alanine dosimeter irradiation temperature coefficient in the− 77° C to+ 50° C range. Radiat. Phys. Chem. 71 (1), 365–370. Greenspan, L., 1977. Equilibrium relative humidity of some saturated salt solutions 25oC. J. Res. National Bureau Standards,A 81. Gunderson, L.L., Tepper, J.E., 2007. Clinical Radiation Oncology. Elsevier Health Sciences. Hassan, G.M., Ulusoy, U., Ikeya, M., 2000. Radical formation in lithium and magnesium oxalate. Jpn. J. Appl. Phys. 39 (11R), 6236. Hubbell, J.H., Seltzer, S.M., 1995. Tables of X-Ray Mass Attenuation Coefficients and Mass Energy-Absorption Coefficients 1 keV to 20 MeV for Elements Z= 1 to 92 and 48 Additional Substances of Dosimetric Interest. National Inst. of Standards and Technology-PL, Gaithersburg, MD (United States) (Ionizing Radiation Div). IAEA, 2008. Measurement Uncertainty - A Practical Guide For Secondary Standards Dosimetry Laboratories. IAEA, Austria. Kojima, T., et al., 1993. Alanine ESR Dosimetry system for routine use in radiation processing. Radiat. Phys. Chem. 42 (4), 757–760. Lund, A., Shiotani, M., Shimada, S., 2011. Applications of quantitative ESR. In: Principles and Applications of ESR Spectroscopy. Springer, pp. 409–438. Olsson, S.K., Lund, E., Lund, A., 2000. Development of ammonium tartrate as an ESR dosimeter material for clinical purposes. Appl. Radiat. Isot. 52 (5), 1235–1241. Premovic, P.I., K.J.A, Herak, J.N., 1972. Electron spin resonance study of irradiated single crystals of ammonium oxalate monohydrate. J. Phys. Chem. 76, 3274. Sleptchonok, O.F., et al., 2000. Advancements in accuracy of the alanine dosimetry system. Part 1. The effects of environmental humidity 57 (2), 115–133. Standard, A., E1026 “standard practice for using Fricke reference standard dosimetry system”. Annual Book of Standards. 12. Taylor, B.N., 2009. Guidelines for Evaluating and Expressing the Uncertainty of NIST Measurement Results. DIANE Publishing. Thompson, J., Schwarcz, H., 2008. Electron paramagnetic resonance dosimetry and dating potential of whewellite (calcium oxalate monohydrate). Radiat. Meas. 43 (7), 1219–1225. Waldeland, E., et al., 2010. Radical formation in lithium formate EPR dosimeters after irradiation with protons and nitrogen ions. Radiat. Res. 174 (2), 251–257. White, D.R., Griffith, R.V., Spokas, J.J., 1989. Tissue Substitutes in Radiation Dosimetry and Measurement os23 International Commission on Radiation Units and Measurements, Bethesda, Md., U.S.A.
Funding The authors received no external funding for this study. Acknowledgments We thank Eva Lund (Department of Medicine and Care, Radiation Physics, Faculty of Health Sciences Linköping University, Sweden) for assistance with scientific guidance and comments that greatly improved the manuscript. Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.radphyschem.2019.05.003.
125