Radiation Processing Dosimetry Research Articles

Mechanistic study of the acidic aqueous solution of chrome alum chemical dosimeter: Steady state, pulse radiolysis and conductivity studies

It is crucial to have an efficient and reliable approach to ensure an optimum traceability in high dose range and high dose rate dosimetry for radiation processing (food irradiation, surgery devices sterilization …). Chemical solution dosimeters are well suited for this purpose. By using γ-irradiation and pulse radiolysis, we evaluated the performances of the chrome alum KCr(SO4)2·12H2O based on the radiation induced oxidation of Cr3+ to Cr6+ in N2O-saturated aqueous solutions buffered at pH 4 by the hydroxyl radical (•OH). With combination of spectrophotometric and conductometric measurements, a mechanism has been put forward to elucidate the oxidation of Cr3+ leading to Cr6+. The suggested mechanism involves an initial adduct formation, [Cr3+ – •OH], that enables inner-sphere electron transfer. As far as dosimetry is concerned, this study showed that the absorbance at 350 nm of the radiation induced Cr6+ increases linearly with the dose with a yield of G (Cr6+) = 0.128 μmol J−1. No dose rate effect was observed up to 80 kGy min−1. This aqueous solution could be used for chemical dosimetry, mainly in the high dose range (up to 5 kGy) and high dose rate (up to 80 kGy min−1). The main advantage of using this aqueous solution is its equivalence to human tissue in terms of radiation absorption properties.

Radiation dosimetry for quality control of silicon wafer using electron beam

Dosimetry studies using electron beams were performed with energies of up to 3 MeV, 2mA with various trolley speeds on the silicon wafer. The silicon wafer came with diameters of 152.4 and 203.2 mm with a thickness of 0.5 mm. The irradiations were performed by utilising the EPS 3000 Cockcroft-Walton type 3.0 MeV, 90 kwatts electron beam (EB) accelerator. Plastic film dosimeter, cellulose triacetate (CTA) was used as a dosimeter with a UV-vis spectrophotometer as the readout system. The dose setting in this investigation was ~100 kGy for 152.4 mm diameter and ~160 kGy for 203.2 mm diameter, which was based on the requirements of the customer. The acceptable dose value was set (± 10%) for better performance of the silicon wafer. It was important to comply with the international standards protocol for dosimeters in radiation processing dosimetry. The results showed that the dose and temperature decreased with increasing the speed. The optimum dose for both diameter of wafers when irradiate at electron beam current of 2 mA and the voltage of 3 MeV is at speed of 0.89 m/min. Based on these studies, it was found that it is important to control the speed of the trolley as it affects the irradiation conditions (e.g., temperature and dose measurements).

Dose rate mapping of an industrial 60Co irradiator using an online photodiode-based dosimetry system

In this work, a housemade dosimetry system based on a thin photodiode is applied for online mapping of dose rates, between 2.6 and 37.7 Gy/h, delivered by a Panoramic 60Co industrial facility. The operational principle of the dosimeter relies on the real-time acquisition of the induced currents from the irradiated diode operating in the short-circuit mode without externally applied voltage. The radial mapping of the radiation field is performed by rotating the diode around the central axis of the panoramic irradiator, covering 360° at intervals of 18°. The results are benchmarked with alanine dosimeters, Monte Carlo simulations, and reference dose rates retrieved from the facility calibration. The overall consistency of the whole data complies with the maximum response variation (8%, k = 2) recommended by the International Standard Protocols for routine dosimeters in radiation processing dosimetry. It reveals that the photodiode-dosimetry system is a reliable alternative to map dose rate fields and the effectiveness of Monte Carlo simulations as a predictive tool for dose rate measurements in an irradiator.

Characterization of a thin photodiode as a routine dosimeter for low-dose radiation processing applications

The characterization of a dosimetry system based on a commercial PIN photodiode as a routine dosimeter in a 60Co industrial facility is reported. The main parameters of the dose rate response (repeatability, reproducibility, and angular dependence) and the dose response (dependence on both dose rate and accumulated dose) are investigated. The results obtained, within a dose rate range of 3.7–52.8 Gy/h and doses up to 200 Gy, fully adhere to the standard protocols established for radiation processing dosimetry. The diode performance as a routine dosimeter is validated by the good overall agreement with radiochromic films and alanine dosimetry.

Performance Characterization of Dosimeters Based on Radiation-Hard Silicon Diodes in Gamma Radiation Processing

The dosimetric response of silicon diodes produced with distinct engineering technologies, Magnetic Czochralski (MCz), and standard Float Zone (Fz), has been investigated, aiming at their use for online dosimeters in gamma radiation processing applications. The p+-n-n+ junction diodes, 300 µm thick with an active area of 25 mm2, are operated as online radiation dosimeters in the short-circuit current mode. In this case, the key dosimetric quantity is the dose rate, which is correlated with the output current from the diode subjected to radiation. Thus, the dose is obtained offline by the integration of the corresponding current signal. The irradiations are performed with an industrial Gammacell 60Co facility at 2.3–2.44 kGy/h covering doses up to 275 kGy. Under continuous irradiation, both diodes delivered current signals whose intensities decreased with accumulated doses. Mitigation of this decay has been accomplished by pre-irradiating the devices to 700 kGy. Polynomial functions best represent the dose responses for either pristine or preirradiated diodes. The relevant dosimetric parameters as response stability, charge sensitivity, and repeatability of current signals (<5%) reveal the better performance of the MCz diode. It is important to note that the whole dataset fully complies with the international standard protocols for routine dosimeters in radiation processing dosimetry. Regarding radiation damage, which in unbiased diodes manifests primarily in the decay of current sensitivity, the results also showed greater tolerance of the MCz diode. Based on these studies, large availability, and better cost-effectiveness, it is possible to endorse the potential use of MCz devices as online routine dosimeters in radiation processing applications. However, the data reproducibility with the accumulated dose, the dose lifespan, and the effect of the irradiation conditions (e.g., temperature, relative humidity, and dose fractionating) remain to be investigated. Works in this direction are currently in progress.

Ob-Servo Sanguis irradiator dose mapping at the Philippine Nuclear Research Institute using MCNP5 annular ring voxels

Dosimetry in radiation processing is a prerequisite for regulating the delivered absorbed dose to a material. Dosimetric measurements, however, are incapable of measuring the doses over the entire irradiation area due to impracticality. Although researchers have been using Monte Carlo simulation to calculate the entire spatial distribution of doses for different irradiation systems, it has never been done with a self-shielded Ob-Servo Sanguis irradiator. In this paper, a comprehensive absorbed dose rate mapping of Ob-Servo Sanguis irradiator at the Philippine Nuclear Research Institute is presented using MCNP5 annular ring voxels that were validated with ethanol-chlorobenzene (ECB) dosimeter measurements. Acting as the rotation plane, a 27 cm × 25 cm cardboard with 15 ECB dosimeters attached at multiple locations was rotated at constant angular velocity while exposed to five stationary vertically arranged 60Co sources. The simulated results are in good agreement with the measured dose rates. The locations with optimum dose rates were in the center, 10 cm away from the axis of rotation. At the time of measurement, the maximum and minimum dose rates were 3.18 kGy/h and 1.33 kGy/h, respectively. Considering the radiation source decay, the simulation can determine the absorbed dose rate anytime and anywhere within the irradiation chamber.

Poly(vinyl alcohol)/heteropolyacid nanocomposites as new materials for radiochromic dosimetry in radiation processing

AbstractRadiochromic films composed of polymer matrices and organic dyes are widely used for routine dosimetry purposes in operation of various radiation facilities—gamma and X‐ray‐irradiation, electron accelerators, and so on. However, the sensitivity of these films rapidly decreases at doses exceeding 30–50 kGy due to a saturation of their optical response, making them unsuitable for accurate dosimetry in radiation processing of polymers and composites where doses up to 200 kGy are typically employed. To overcome this limitation, the use of inorganic substances as the coloring agents of polymer‐based radiochromic films was proposed in this paper, specifically, heteropolyacidacid H3PW12O40 (tungstophosphoric acid) in the matrix of poly(vinyl alcohol) (PVA). Nanocomposite PVA/H3PW12O40 films were prepared by solution casting and their optical responses toward 60Co gamma radiation and beams of 6 MeV electrons for a dose range of 10–200 kGy were investigated. It was established that upon exposure to gamma rays and electron beams, the films turn blue and a broad absorption band at 750 nm appears in their spectra. Importantly, the radiation‐induced optical absorption increases in a linear fashion up to the dose of 150 kGy and only slightly deviates from linearity at 200 kGy. Moreover, it was found that the PVA/H3PW12O40 films have a long shelf life, are dose‐rate independent within a wide range, and color‐stable after irradiation. All these features make the nanocomposite PVA/H3PW12O40 films promising for use as routine dosimeters and dose labels in a much wider range of high doses as compared to radiochromic films based on organic dyes.

A comparison between rad-hard float zone silicon diodes as gamma dosimeter in radiation processing

In this work, we report on the results obtained with rad-hard Standard Float Zone (STFZ) and Diffused Oxygenated Float Zone (DOFZ) silicon diodes in radiation processing dosimetry. The dosimetric probes were designed to operate in the direct current mode, as on-line radiation dosimeter. The irradiation of the samples was performed using a 60Co source with a dose rate of almost 2.4 kGy/h. The current response of each diode was measured as a function of the exposure time in steps from 5 kGy up to 50 kGy to achieve a total absorbed dose of 275 kGy. In this dose range it is observed a significant decrease in the photocurrent generated in both devices due to gamma radiation defects produced in their active volumes. To mitigate this effect, the samples were pre-irradiated with Co-60 gamma rays at 700 kGy. Despite of being less sensitive, these devices presented stable and reproducible current signals with a relative sensitivity decrease of about 19% within the whole range of dose studied. The dose-response curves of the pre-irradiated diodes showed quadratic behavior with correlation coefficient higher than 0.9999 for total absorbed dose up to 275 kGy. The comparison of the FZ and DOFZ responses evidenced that the latter was slightly superior to the first. However, it is important to note that all pre-irradiated diodes can be used as gamma dosimeters in radiation processing applications.

Two-parametric model of electron beam in computational dosimetry for radiation processing

Computer simulation of irradiation process of various materials with electron beam (EB) can be applied to correct and control the performances of radiation processing installations. Electron beam energy measurements methods are described in the international standards. The obtained results of measurements can be extended by implementation computational dosimetry. Authors have developed the computational method for determination of EB energy on the base of two-parametric fitting of semi-empirical model for the depth dose distribution initiated by mono-energetic electron beam. The analysis of number experiments show that described method can effectively consider random displacements arising from the use of aluminum wedge with a continuous strip of dosimetric film and minimize the magnitude uncertainty value of the electron energy evaluation, calculated from the experimental data.Two-parametric fitting method is proposed for determination of the electron beam model parameters. These model parameters are as follow: E0 – energy mono-energetic and mono-directional electron source, X0 – the thickness of the aluminum layer, located in front of irradiated object. That allows obtain baseline data related to the characteristic of the electron beam, which can be later on applied for computer modeling of the irradiation process.Model parameters which are defined in the international standards (like Ep– the most probably energy and Rp – practical range) can be linked with characteristics of two-parametric model (E0, X0), which allows to simulate the electron irradiation process. The obtained data from semi-empirical model were checked together with the set of experimental results. The proposed two-parametric model for electron beam energy evaluation and estimation of accuracy for computational dosimetry methods on the base of developed model are discussed.

Analysis of the Power System from an Electron Beam Accelerator and the Correlation with the Theoretical Dosimetry for Radiation Processing

Analysis of the Power System from an Electron Beam Accelerator and the Correlation with the Theoretical Dosimetry for Radiation Processing

Using polycarbonate dyed with dansyl chloride for dosimetry in radiation processing

Abstract Preparation and characteristics evaluation of the polycarbonate films 20 μm in thickness containing Dansyl chloride as a routine dosimeter in radiation processing facilities were studied. The sensitivity of these films and the linearity of dose-response curves were investigated under 60Co γ-rays in a dose range of 0–100 kGy, and the obtained results were compared with the commercial CTA and FWT film dosimeters. The results show that the maximum absorbance appeared at 370 nm in all the investigated dose range. The dyed films were found to be stable enough in mediums with high degrees of humidity and temperature, to be reliably used in radio-applications. The effects of pre-irradiation (shelf-life) and post-irradiation storage in dark and in indirect sunlight were also discussed. The films which were made displayed stable characteristics when stored in dark, within 1% at 25 ℃, 3 months after irradiation.

Thermoluminescence characteristics of zinc lithium borate glass activated with Cu+ (ZnO–Li2O–B2O3:Cu+) for radiation dosimetry

Copper doped zinc lithium borate glass was prepared by solid state melt quenching method and characterized using X-ray diffractometry. The effect of varying concentration of dopant CuO on thermoluminescence (TL) properties of zinc lithium borate is reported in this paper. The best annealing temperature and time were found to be 300 °C and 30 min respectively. While the optimal heating rate was 3 °C. Glow curves with single peaks for all concentrations were obtained. The TL intensity increases with the increase of dopant concentration and radiation dose from 0.5 to 4 Gy. Time-base thermal fading was stable. Attractive reusability and kinetic parameters of the phosphor were also achieved. These outstanding features show that our dosimeter has the potential ability to use for radiation processing dosimetry.

Polycarbonate-based benzo-δ-sultam films for high-dose dosimetry in radiation processing

Abstract In this work characteristics of the polycarbonate films with 20 μm in thickness containing different weight percentage of Benzo-δ-sultam were studied for use as a high dose dosimetry system in radiation processing facilities. The sensitivity of the dosimeters and the linearity of dose-response curves were investigated under 60Co γ-rays in a dose range of 0–100 kGy, and obtained results were compared with the commercial CTA and FWT film dosimeters. The results show that the absorbance at 348 nm depends linearly on the dose in the investigated dose range. The effects of pre-irradiation (shelf-life) and post-irradiation storage in dark and in indirect sunlight are also discussed. The results show that the dosimeters characteristics are stable within 1% at 25 ℃, 3 months after the irradiation.

Development of ion exchange membrane for possible use in radiation processing dosimetry

Gamma radiation-induced polymerization of acrylic acid (AAc) onto polyvinylbutyral (PVB) film has been carried out under nitrogen atmosphere. The grafted film of PVB-g-PAAc was allowed to react with solutions of two ionic dyes (ion exchange), namely brilliant green (BG) or methylene green (MEG). The results show that these new dosimeter films of PVBBG and PVBMEG may be useful for high-dose radiation dosimetry applications. We concluded that, the useful absorbed dose range of the dyed films extends up to about 400 and 300 kGy respectively.

4. General Aspects of Dosimetry for Radiation Processing

4. General Aspects of Dosimetry for Radiation Processing

4. General Aspects of Dosimetry for Radiation Processing

4. General Aspects of Dosimetry for Radiation Processing

Hyper pure quartz as a promising material for retrospective and radiation processing dosimetry using ESR technique

Samples of highly purified naturally occurring silicon dioxide (SiO 2) commercially named clear fused quartz (CFQ), both in bulk and in powder form were exposed to 4 and 8 MeV electrons from a linear accelerator (radiotherapy unit) at doses between 0.5 and 60 Gy (minimum and maximum attainable dose, respectively). After irradiation, the samples were subjected to electron spin resonance (ESR) analysis readout to test their use as a mean of measuring absorbed doses in the samples. A good linearity between the absorbed dose (from 2 Gy up to the maximum dose applied of 60 Gy) and the ESR intensity of the samples was observed while a poor linearity at low doses (between the absorbed dose from 0.5 to 10 Gy and the ESR intensity) is seen. The background intensity in the case of the powder was higher than for the cylindrical samples and the ESR intensity was also lower in the former case, which gave rise to a dose curve response with a lower slope for the powders. No energy dependence was apparent for electrons of 4 and 8 MeV energy. The thermal fading of CFQ at room temperature showed a relatively sharp decay of ∼30% over a period of 10 days after which the decay rate was negligible for a measured period of 80 days. The results in this study plus the previous work done (gamma irradiation of the samples) by the authors suggest that the materials could, by using the ESR technique, be a suitable candidate for alternative dose measurements in radiation processing and retrospective dosimetry.

Dosimetry characterization of tetrazolium violet-polyvinylalcohol films

The dosimetry characteristics of the polyvinylalcohol-based tetrazolium violet film has been studied in order to check its suitability for routine dosimetry in radiation processing. Our investigations reveal that this dosimeter film can be used for process control in radiation sterilization, but its application range depends on the concentration of the dye and the solvents used. The effects of irradiation temperature and humidity, dye concentration, pH of the solvent as well as the stability of the response of the films before and after irradiation were investigated and determined.

Aspartame tablets—gamma dose response and usability for routine radiation processing dosimetry using spectrophotometry

Aspartame tablets were studied for gamma dose response, using spectrophotometric read-out method. The optimum concentration for ferrous ions was 2 × 10 - 4 mol dm - 3 and xylenol orange with 2.5 × 10 - 1 mol dm - 3 of sulphuric acid for the optimum acidity in FX solution. Wavelength of maximum absorbance is 548 nm. Post-irradiation stability is appreciable i.e. for not less than one month. Dose response is non-linear with third order polynomial fit, in the dose range of 1000–10000 Gy. This system of aspartame was further used for carrying out relative percentage dose profile measurement in Gamma Cell-220. Results obtained were inter-compared with that of a glutamine dosimeter, which showed that maximum difference between the values of aspartame and glutamine systems is within ± 10 % .

Thermally stimulated luminescence studies for dysprosium doped strontium tetraborate

In this paper TL studies of Dy 3 + doped SrB 4 O 7 compound are reported by β -ray irradiation for the first time. The polycrystalline powder samples of dysprosium doped SrB 4 O 7 :Dy phosphor were prepared by a solid-state reaction in air at high temperature and the TL glow curves and TL emission spectrum after β -ray irradiation was studied from 50 to 250 kGy dose range. The TL studies of Sr 0.93 Dy 0.07 B 4 O 7 sample show main TL glow peak at 497 K, and the 497 K glow peak show great stability for a long time. The trap parameters namely activation energy ( E ) , order of kinetics ( b ) , and frequency factor ( s ) of main peak of the Sr 0.93 Dy 0.07 B 4 O 7 sample at 497 K were determined using glow curve shape (Chen's) methods. The TL emission bands at about 480, 575, 660 and 750 nm of the SrB 4 O 7 :Dy phosphor is attributed to the characteristic emission from f–f transitions of Dy 3 + ion. The distributions of trap produced by the irradiation of β -ray can be altered greatly by the change of the concentrations of Dy 3 + ion doped in SrB 4 O 7 host and, all peak temperatures shift to higher temperature, this will be favorable for TL output. The TL-dose response of the SrB 4 O 7 :Dy polycrystalline powder sample to β -ray radiation in the range from 50 to 250 kGy for radiation processing dose levels is almost linearity. The experiment results showed that SrB 4 O 7 :Dy potential use as the materials of β -ray thermoluminescence dosimeter (TLD) for radiation processing dosimetry.