[en] Full text: In this work, we present the preliminary results about the evaluation of dose-rate influence on the response of rad-hard epitaxial (EPI) diodes for on-line gamma-ray dosimetry using Co-60 irradiators. The diodes used were processed at University of Hamburg on n-type 75 micrometer thick epitaxial silicon layer (nominal resistivity of 69 Ohm.cm) grown on a highly doped n-type 300 micrometer thick Czochralski (Cz) silicon substrate. Two samples of EPI diodes were investigated: EPI-08 and EPI-10 - both non-irradiated previously. These devices, with 5mm x 5mm active area, were housed in a PMMA probe and connected, in a photovoltaic mode, to a Keithley 617 electrometer. The EPI-10 device irradiation was performed in the Radiation Technology Center at IPEN-CNEN/SP using a Co-60 irradiator (Gammacell 220 - Nordion) which delivers a dose rate of 2.16 kGy/h, while the EPI-08 device irradiation was performed in Nuclear Energy Department at UFPE/PE using the same model Co-60 irradiator, but with a dose-rate of 7.47 kGy/h. During the irradiation, the devices photocurrents were monitored as a function of the exposure time. The diodes were irradiated at room temperature. The dose-response curves of the EPI diodes were achieved through the integration of the current signals as a function of the exposure time. The normalized current signals as a function of the dose evidenced a decrease of about 60 percent from the initial current for the first 100 kGy dose received. After 500 kGy of exposure, the current signals stabilize (ou maintain stable). The dose-response curves behave as a second order polynomial fit, with correlation coefficients of about 0.99991 and 0.99995, respectively to EPI-10 and EPI-08 diodes. The preliminary results obtained evinced that the EPI diodes response are not dose-rate dependent within the range of 2.16 kGy/h up to 7.47 kGy/h. On the other hand, the devices studied are tolerant to radiation damages for total absorbed doses of approximately 550 kGy and can be used as reliable alternative on-line dosimeters in high doses radiation processing. (author)

[en] Full text: Several advantages of silicon diodes which include small size, low cost, high sensitivity and wide availability, make them suitable for dosimetry and for radiation field mapping. However, the small radiation tolerance of ordinary silicon devices has imposed constraints on their application in intense radiation fields such as found in industrial radiation processes. This scenario has been changed with the development of radiation hard silicon devices to be used as track detectors in high-energy physics experiments. Particularly, in this work it is presented the dosimetric results obtained with a batch of nine junction silicon diodes developed, in the framework of CERN RD50 Collaboration, as good candidates for improved radiation hardness. These diodes were produced with 300 micrometer n-type silicon substrate grown by standard float zone technique and processed by the Microelectronics Center of Helsinki University of Technology. The samples irradiation was performed using a Co-60 irradiator (Gammacell 220) which delivers a dose-rate of 2 kGy/h. During the irradiation, the unbiased diodes were connected through low-noise coaxial cables to the input of a KEITHLEY 617 electrometer, in order to monitor the devices photocurrent as a function of the exposure time. To study the response uniformity of the batch of nine diodes as well the sensitivity dependence on the absorbed dose, they were irradiated with different doses from 5 kGy up to 50 kGy. The sensitivity response of each device was investigated through the on-line measurements of the current signals as a function of the exposure time. For doses up to 5 kGy, all diodes exhibited a current decay of almost six percent in comparison with the value registered at the start-time of the irradiation. However, this decrease in the current sensitivity is much smaller than those observed with ordinary diodes for the same absorbed dose. The dose-response curves of the devices were also investigated through the plot of the charge generated in the depletion region of the diodes (obtained via integration of the current signals versus time) as a function of the absorbed dose. Similar dose-response curves (with second order polynomial fit) were obtained for all diodes. These results were used to verify both the uniformity and short-term repeatability of the devices. It still remains to be investigated the feasibility of using these float zone diodes for routine on-line radiation processing monitoring. (author)

No abstract available

[en] Full text. The use of semiconductor detectors has increased in radiotherapy practice since 1980s due to mainly their fast processing time, small sensitive volume and high relative sensitivity to ionizing radiation. Other major advantages of Si devices are excellent repeatability, good mechanical stability, high spatial resolution and the energy independence of mass collision stopping powers ratios (between silicon and water for electron beams with energy from 4 up to 20 MeV). However, ordinary silicon devices are very prone to radiation damage effects. In the last years, the development of radiation tolerant silicon detectors for High Energy Physics experiments has overcome this drawback. In this work we present the preliminary results obtained with a rad-hard epitaxial silicon diode as on-line clinical electron beam dosimeter. The diodes with 25 mm² active area, were housed in a PMMA probe and connected, in a photovoltaic mode, to a Keithley 6517B electrometer. During all measurements, the diodes were held between PMMA plates, placed at Zref and centered in a radiation field of 10 cm x 10 cm, with the SSD kept at 100 cm. The devices dosimetric response was evaluated for 6, 9, 12, 15, 18 e 21 MeV electron beams from a Siemens KD 2 Radiotherapy Linear Accelerator, located at Sirio-Libanes Hospital. The radiation induced current in the diodes was registered as a function of the exposure time during 60 s for a fixed 300 MU. To study the short term repeatability, current signals were registered for the same radiation dose, for all energies. The dose-response of the diodes was achieved through the integration of the current signals as a function of the exposure time. The results obtained in the energy range of 6 up to 21 MeV evidenced that, for the same average dose rate of 5.0 cGy/s, the current signals are very stable and repeatable in both cases. For all energies, data shows good instantaneous repeatability with a percentage variation coefficient better than 2.38 and 2.01 to MCZ and FZ respectively. The dose-response curves are linear with correlation coefficients R² of about 0.99992 to MCZ diode and 0.99994 to FZ diode. Charge sensitivities are better than 0.71 μC/Gy and 0.58 μC/Gy to MCZ and FZ respectively, showing that MCZ diode is more sensitive than FZ diode. However, it still remains to be investigated the origin of the strong energy dependence observed on the electron beam energy for both diodes. Such studies are under way. (author)

No abstract available

[en] The dosimetric response of an epitaxial (EPI) silicon diode for clinical electron beams was investigated using Siemens KD2 and Primus Linear Accelerators. All measurements were performed with the diode unbiased and operating in the short-circuit current mode using a PMMA phantom. Within the energy range of 6 MeV–21 MeV, the output current signals exhibited good instantaneous repeatability (CV≤2.4%), measured through switching on/off the electron beams. Furthermore, the diode showed a quite linear response, given by the charge versus absorbed dose, with charge sensitivities higher than 0.86 μC/Gy. The percentage depth dose profile (PDD) and transversal dose profile (TDP) were also measured in PMMA. The PDD and TDP results were in excellent agreement with those calculated with Monte Carlo code using the OncentraMasterPlan^® Treatment Planning System (TPS). However, despite of showing energy dependence effects, neither dark currents increase nor memory effects were observed in the device response.

[en] The dosimetric response characterization and beam data acquisition performance of a miniature Float Zone (FZ) silicon diode for photon beams was investigated using Novalis TX linear accelerator (Varian Medical Systems^®). In all measurements the unbiased diode operated in a short-circuit mode, connected to the input of a Keithley 6517B electrometer using a water phantom. For photon beams of the 6 and 15 MV the results presented good repeatability (coefficient of variation ≤1.6%), measured through switching on/off the photon beams. Moreover, the diode showed a quite linear response, given by the charge versus absorbed dose, with charge sensitivities higher than 6.9 nC/Gy. The output factor, percentage depth dose profile (PDD) and transversal dose profile (TDP) were also measured in a water phantom. For small field sizes, the output factor values using the FZ diode were compared with measurements obtained with a SFD (Stereotactic Field Diode) commercial diode and the differences were 5.4%, 2.5% and 1.3% for the field sizes of 1 × 1, 2 × 2 and 3 × 3 cm². For larger field sizes (≥4 × 4 cm²), the maximum difference found was 0.7% in comparison with values obtained with a CC13 ionization chamber. Thus, the result demonstrates that the unshielded FZ diode has the potential to be used for measuring of, as it performed acceptably well for both small and large field sizes. The TDP experimental results obtained with the FZ diode for field sizes of: 1 × 1 cm², 2 × 2 cm² and 4 × 4 cm² are in agreement with experimental results acquired with several commercial detectors. Through the TDP study, the comparison of the field penumbra size confirmed the excellent spatial resolution of the miniature diode. However, the PDD study, requires further investigation. - Highlights: • Dosimetric response characterization of FZ Si diodes for photon beams was studied. • Beam data acquisition performance of FZ diodes for photon beams was investigated. • The FZ diode presented good short term repeatability operating in short-circuit mode. • The results of the penumbra profiles confirmed the good spatial resolution of the FZ. • Output factor study of the FZ matched with different detectors