Green and red scintillator crystals with plastic fiber optics were used to investigate their application as optical fiber dosimeters. In Part 1, the radiation beam is perpendicular to the system with 20x20cm2 half field. We have a linear response for both systems with doubling the MU starting from 1MU up to 1024MU. Here we define the SOBR (Signal to Optical Background Ratio) to be the response of total signal (crystal and fiber) divided by the background (fiber) signal. The SOBR of red and green with no filter were 16.58 and 17.74 respectively. When we added the filter, the SOBR for red and green became 11.03 and 66.72 respectively. In Part 2, we changed the field to X=1cm, Y1=5cm and Y2=1cm. The SOBR for red and green with no filter are 44.43 and 45.47. After we added the filter, the SOBR for red and green became 15.62 and 1684. This change in field shape gave us a higher SOBR, especially when the filter was added. In Part 3, we tested the angular response of our detector. Both systems increased their response when gantry angle reach 45° and -45° (315°). When the filter was added, a change of a factor of 2 in response remained. When the crystal was then rotated and pointed in the direction of the gantry, good response was obtained from range 90° to -90° (270°). The response of green system was within 2.5%. For the red system, a large step about 10% was observed. Conversion of the fiber fluorescence and Cerenkov radiation in the scintillator crystal and transmission to the detector is a problem in all optical fiber systems, including the dual fiber system, that remains to be addressed.

Green and red scintillator crystals with plastic fiber optics were used to investigate their application as optical fiber dosimeters. In Part 1, the radiation beam is perpendicular to the system with 20x20cm2 half field. We have a linear response for both systems with doubling the MU starting from 1MU up to 1024MU. Here we define the SOBR (Signal to Optical Background Ratio) to be the response of total signal (crystal and fiber) divided by the background (fiber) signal. The SOBR of red and green with no filter were 16.58 and 17.74 respectively. When we added the filter, the SOBR for red and green became 11.03 and 66.72 respectively. In Part 2, we changed the field to X=1cm, Y1=5cm and Y2=1cm. The SOBR for red and green with no filter are 44.43 and 45.47. After we added the filter, the SOBR for red and green became 15.62 and 1684. This change in field shape gave us a higher SOBR, especially when the filter was added. In Part 3, we tested the angular response of our detector. Both systems increased their response when gantry angle reach 45° and -45° (315°). When the filter was added, a change of a factor of 2 in response remained. When the crystal was then rotated and pointed in the direction of the gantry, good response was obtained from range 90° to -90° (270°). The response of green system was within 2.5%. For the red system, a large step about 10% was observed. Conversion of the fiber fluorescence and Cerenkov radiation in the scintillator crystal and transmission to the detector is a problem in all optical fiber systems, including the dual fiber system, that remains to be addressed.

This study was undertaken to compare the response of three dosimeters to different environments. Comanche Peak Nuclear Power Plant wants to replace the current badge of record. The RaDos DIS-1 direct-ion storage dosimeter (DIS-1) and the Landauer InLight optically stimulated luminescence dosimeter (OSL) are the two candidates for replacement of the Panasonic UD-802 thermoluminescence dosimeter (TLD). The dosimeters were compared in five categories: dose linearity, dose-rate linearity, fade response, humidity response, and the angular dependence of the dosimeters. The major results include verified linear relationship evidence for dose and doserate and a better fade response for both the DIS-1 and OSL. The TLDs faded by 9.2% over a month and the DIS-1 and OSL faded by 4.2% and 1%, respectively. Following a dose of 557.5 mrem, the dosimeters were exposed to different relative humidites. The dose to the DIS-1 and OSL did not change drastically while the TLDs dose readout was reduced by 10%. Finally, the angular dependence of the dosimeters was compared and the worst responses were 66% at 90° in the horizontal orientation for the OSL and 1.7% at 90° in the horizontal orientation for the DIS-1. Based on the results of these tests the OSL seems like a more viable candidate for the new badge or record.

This thesis investigates the response to ionising radiation, of p-type Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) (REM Oxford (UK)) and a reader system developed by the Centre for Medical Radiation Physics, The University of Wollongong, to determine their feasibility for measurements of dose during radiotherapy treatment (in vivo dosimetry (IVD)). Two types of MOSFET probes were used -"single sensitivity", for measuring low doses, and "dual sensitivity", to measure both high and lose doses. Sensitivity, linearity of response with dose, and response changes with accumulated dose and direction of incident radiation (angular dependence) were investigated. The average sensitivity reduction over the lifetime of the probes was 22.37% with a standard deviation of 0.63%. This reduction in sensitivity can be corrected for by the use of "drift equations". MOSFETs have a limited "lifetime" due to saturation effects with increasing accumulated dose. Saturation occurred at an average of 40 Gray (Gy) accumulated dose, for the high sensitivity probes investigated. The high sensitivity probes were linear within 1.6% for doses between 5 and 140 cGy, and 3.8% for the high sensitivity probes for doses between 50 and 500 cGy. Drift (changes in readings with time since irradiation due to electronic processes) over the long-term (from hours to weeks following irradiation) has been previously well characterised in the literature. This work focuses on shortterm drift, within the first few seconds or minutes following irradiation, being the most clinically relevant for in vivo measurements. Drift is investigated for various reading methods, such as reading frequency, and delays between irradiation and readings. It is shown that sensitivity, and consequently dose determination, is significantly influenced by the reading methodology. During the first five minutes following an irradiation, drift increased inversely with delivered dose, and was greater for probes having accumulated dose of > 20 Gy (2.0 -16.2% compared with 1.2 -7.4% for < 20 Gy probes). During the first five minutes following an irradiation, drift increased inversely with delivered dose, and was greater for probes having accumulated dose of > 20 Gy (2.0 -16.2% compared with 1.2 -7.4% for < 20 Gy probes). When two post-irradiation readings were taken following an irradiation, the difference between them generally increased as the time interval between the two readings increased, by up to 8.8%. Delays in taking pre-and post-irradiation readings resulted in drift of up to 5.7% or 9.3% respectively, compared with readings without a delay. These results emphasise the necessity for consistent methodologies between calibration and measurement in the clinical situation. Greater sensitivity was measured with the epoxy bubble, rather than the substrate side, facing the beam. The greatest variation, for orientations other than the bubble side facing directly towards the beam, was 10%, or 5% uncertainty in dose. The variations with angle were found to be reproducible, so that appropriate correction factors could be applied to correct measurements at angles other than with the sensitive area of the probes facing directly towards the radiation beam. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1368262 / Thesis (M.Sc.) -- University of Adelaide, School of Chemistry and Physics, 2009

The growing interest towards polysiloxane-based radiation detection systems is related with the several advantages that polysiloxanes offer in comparison with other state-of-the-art plastic materials used in scintillation, like polyvinyltoluene and polystyrene. In this respect, polysiloxane elastomers offer higher thermal stability, flexibility and radiation hardness than the traditional plastic counterpart. For this reason, the study of polysiloxane-based systems for the detection of several types of radiation such as neutrons, high-energy photons and charged particles has recently received increasing attention by the scientific community. In this thesis, we report the current advances on both organic and hybrid polysiloxane-based radiation detection systems for scintillation and passive dosimetry applications. In this framework, we will start from the recent advances on organic polysiloxane-based scintillators for the detection of fast neutrons, with particular emphasis on their pulse-shape discrimination capabilities, allowing for the distinction of neutrons from the γ-ray background. The other and main part of the thesis will be then dedicated to hybrid nanostructured polysiloxane-based radiation detection systems. In this context, latest progress on polysiloxane scintillators embedding 6LiF nanocrystals for thermal neutron detection will be presented, with particular focus on the role of the nanocrystal size and dispersion in the detection performances. Subsequently, polysiloxane/quantum dots nanocomposites will be investigated for their possible use in both scintillation and passive dosimetry. In this latter application, the optical properties of the samples are analyzed after irradiation, with the aim to correlate the radiation-induced effects with the radiation dose. Lastly, the role of the polymer matrix in the post-irradiation optical response of the nanocrystals will be investigated.

In the event of large scale public radiation exposures, a means of rapid personal radiation dosimetry would provide a valuable tool for environmental and human health protection as well as for possible criminal investigations (in the event of terrorist dirty bombs). This thesis describes a method of sensitizing synthetic quartz oscillators, found in many timekeeping devices such as watches and cellular phones, to function as radiation dosimeters. Experiments on the sensitization of synthetic quartz crystals from watch oscillators were performed by subjecting the quartz to thermal treatments in the range of 200°C to 800°C. The lengths of treatments ranged from numerous one hour cycles to week-long single anneal treatments and combinations of the two. All treatments were designed to mimic factors that are known to cause sensitization in geologic quartz grains (Botter-Jensen, Larsen et al., 1995). The greatest sensitization was observed in crystals treated to 800°C for one week and then subjected to two series of heating, irradiation, and optical exposures. These crystals were able to recover doses as low as 0.5 Gray at an error within 10% of the delivered dose. This work is the first stage of development for creating dual purpose quartz oscillator-dosimeters which could be used in watches, cellular phones, clocks, and nearly all equipment requiring a timekeeping component. In the future, experiments should be conducted to show definitively that crystals still function as 32.768 kHz oscillators after annealing and that oscillators trap charge while in operation. / Thesis / Master of Science (MSc)

No description available.

"The MCNP6 radiation transport code was used to quantify changes in the absorbed dose tissue conversion factors for LiF, Al2O3, and silicon-based electronic dosimeters. While normally calibrated in-air and applied to all general geometric measurements, tissue conversion factors for each dosimeter were obtained at various depths in a simulated water phantom and compared against the standard in-air calibration method. In these experiments, a mono-energetic photon source was modeled at energies between 30 keV and 300 keV for a point-source placed at the center of a water phantom, a point-source placed at the surface of the phantom, and for a 10-cm radial field geometry. Again, mono-energetic photon source was modeled up to 1300 keV for a disk-source placed at the surface of the phantom and dosimetric calculations were obtained for water, LiF, Al2O3, and silicon at depths of 1 mm to 35 cm from the source. The dosimeter’s absorbed dose conversion factor was calculated as a ratio of the absorbed dose to water to that of the dosimeter measured at a specified phantom depth. The dosimeter’s calibration value also was obtained for both mono and polyenergetic source and the calibration value from poly-energetic source was compared with the intensity weighted average calibration value from mono-energetic photon. The calculated changes in the tissue conversion factors are significant because the American Association of Physicists in Medicine (AAPM) recommend that measurements of a brachytherapy or diagnostic source be made with an overall uncertainity of 5% or better. Yet, based on results, the absorbed dose tissue conversion factor for a LiF dosimeter was found to deviate from its calibration value by up to 9%, an Al2O3 dosimeter by 43%, and a silicon dosimeter by 61%. These uncertainties are in addition to the normal measurement uncertainties. By applying these tissue correction factors, these data may be used to meet the AAPM measurement requirements for mono-energetic and poly-energetic sources at measurement depths up to 35 cm under the irradiation geometries investigated herein. "

[Abstract]This dissertation presents the development, testing and application of a chemical film UV dosimeter based on the polymer Poly (2, 6-dimethyl-1, 4-phenylene oxide) (PPO) prepared especially for long – term high – exposure underwater use. Initial testing of the dosimeter was performed in a water tank within a controlled laboratory environment with an artificial UV source in which various optical and physical properties of the film were rigorously tested such as UV dose and depth response, cosine response, interdosimeter variation, dose rate independence, dark reaction, watermarking effect, exposure additivity and visible and UVA wavelength response. In each of these tests the PPO dosimeter displayed results proving that it could be reliably used in aquatic environments at a level of accuracy only slightly lower than what could be expected for in – air dosimetric measurements. The use of a polyethylene derived neutral density filter (NDF) was then employed with the PPO dosimeter in order to extend exposure time. Results from this investigation showed that the polyethylene NDF could extend the effective life time of the PPO dosimeter by as much as five days in early autumn. Following this the PPO dosimeter was calibrated in the field to the solar erythemal action spectrum in – air and to the solar UVB spectrum in clear water, creek water, sea water and dam water over the duration of a year. In both the in – air and underwater calibrations it was found that the response of the PPO dosimeter lasted over a much greater amount of time when compared to the more commonly used polysulphone dosimeter and also varied with the modulation of the incident solar spectrum brought on by changing SZA and fluctuations in atmospheric column ozone. Additionally, it was discovered that in – air and underwater calibration regimes could not be interchanged and that the PPO dosimeter response underwater is dependent upon water type, but only when transmission spectra differed between two water types by a difference on average of more than 5% across the UVB waveband. As a final test, the PPO dosimeter was deployed over a year to take UVB exposure measurements with the use of a custom built submersible float in three different real – world field environments that included a creek, a sea water tank and a stagnant dam. Exposures could be measured reliably up to a depth of 5 cm in the creek water and the dam water and up to and possibly beyond a depth of 35 cm in the sea water. From the sea water PPO dosimeter measurements a series of attenuation coefficients were estimated for each season. These coefficients showed reasonable agreement when compared to attenuation coefficient calculations made using a calibrated spectrometer in the same sea water, further proving the usefulness of the PPO dosimeter.

Universiẗat, Diss., 2002--Heidelberg.