Silicon carbide has a potential for solar UV radiation monitoring: extremely resistant to UV radiation damage, nearly-blind to visible and infrared radiation and less sensitive to temperature ...variations than standard radiometric systems. A radiometer composed by three SiC photodiodes has been designed, manufactured and tested under solar radiation. Two photodiodes are equipped with filters in the UVB (280–315
nm) and UVA (315–400
nm) ranges while a third is filtered to match the erythemal action spectrum. UVA, UVB components of the solar radiation as well as UV index (UVI) at the earth's surface have been determined in two site positions in Tuscany, Italy. Data as a function of day-light allowed us to evaluate total optical thickness for UVA and UVB:
τ
UVA=0.46 and
τ
UVB=1.8. UVI values measured during the year well compares with computed ones used for weather forecast procedures.
Diamond dosimetry: Outcomes of the CANDIDO and CONRAD INFN projects Bucciolini, M.; Borchi, E.; Bruzzi, M. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
10/2005, Letnik:
552, Številka:
1
Journal Article
Recenzirano
This paper reviews the main results of the study, carried out in the framework of the Italian National Institute of Nuclear Physics (INFN, Istituto Nazionale di Fisica Nucleare) projects, namely ...CANDIDO and CONRAD, on natural and synthetic diamond-based dosimeters for clinical radiotherapy. Characteristics of diamond such as radiation hardness, high sensitivity, tissue equivalence, etc., make this material interesting for dosimetry applications. For some years, natural diamonds have been commercially available for on-line radiotherapy dosimetry. Nevertheless, recent developments in the “Chemical Vapour Deposition” (CVD) technique have addressed the attention on synthetic samples that potentially could be grown at low cost and with features suitable for dosimetric use. Several samples, differently grown and with different electrical contacts, have been compared by measuring their current response during irradiation with high-energy photon, electron and proton beams. Properties of dosimetric interest such as linearity, pre-irradiation dose, dose rate dependence, stability and rise time have been investigated. The results obtained so far within the INFN collaboration demonstrate the suitability of natural diamond detectors for many radiotherapy applications and the great potential of CVD diamond-based devices even though, at present, the commercial natural diamond dosimeters have a better behaviour with respect to the synthetic samples. Further efforts have to be made mainly to improve the dynamic of response and performance stability.
A quantitative model of radiation-induced carrier transient conductivity has been used to explain the influence of very high neutron irradiation (up to 2×10
15
cm
−2 1
MeV equivalent) on the trapping ...and recombination mechanisms of Chemical Vapor Deposited polycrystalline diamond devices, prepared for particle tracking. The model fits very well room temperature measurements of radiation-induced conductivity at different levels of thermal de-trapping, i.e. with different amounts of charged deep traps. The analysis in this paper depicts three types of traps, close to the band-edge, characterized by different values of capture cross-sections, and a broad recombination center. The traps form a continuous distribution, with a constant density of states per unit energy in the investigated energy range (0.2
eV). The density of states is determined from the current behavior vs. thermal de-trapping time. The structure of the deep recombination centers is unaffected by neutron irradiation. On the other hand, the concentration values of the traps with lower cross-sections increase after irradiation. A saturation effect is observed which has been previously reported M. Bruzzi et al., Diamond Relat. Mater. 10 (2001) 601 by use of Thermally Stimulated Current spectroscopy (TSC).
In the present work, the bulk degradation of SiC in hadron (pion and proton) fields, in the energy range between 100
MeV and 10
GeV, is characterised theoretically by means of the concentration of ...primary defects per unit fluence. The results are compared to the similar ones corresponding to diamond, silicon and GaAs.
We report on the design, manufacturing and first characterisation of pad diodes, test structures and microstrip detectors processed with high resistivity magnetic Czochralski (MCz) p- and n-type Si. ...The pre-irradiation study on newly processed microstrip detectors and test structures show a good overall quality of the processed wafers. After irradiation with 24
GeV/
c protons up to 4×10
14
cm
-2 the characterisation of n-on-p and p-on-n MCz Si sensors with the
C–
V method show a decrease of the full depletion voltage and no space charge sign inversion. Microscopic characterisation has been performed to study the role of thermal donors in Czochralski Si. No evidence of thermal donor activation was observed in n-type MCz Si detectors if contact sintering was performed at a temperature lower than 380
°C and the final passivation oxide was omitted.
We performed a study of charge collection distance (CCD) on medium to high-quality prototypes of diamond sensors prepared by Chemical Vapor Deposition (CVD). We studied the Charge Collection ...Efficiency in these materials supposing that it is limited by the presence of a recombination level and a distribution of trap levels centered at
1.7
eV
from the band-edge. We also supposed that the exposition to ionizing radiation can make the trap levels ineffective (
pumping effect). We have shown that these assumptions are valid by correlating the CCD to the pumping efficiency. Moreover, we have shown that the pumping efficiency is bias-dependent. We have explained our experimental results assuming that trapped carriers generate an electric field inside the diamond bulk.
Experimental results and simulations of Charge Collection Efficiency (CCE) of Current Injected Detectors (CIDs) are focused. CID is a concept where the current is limited by the space charge. The ...injected carriers will be trapped by the deep levels. This induces a stable electric field through the entire bulk regardless of the irradiation fluence the detector has been exposed. Our results show that the CCE of CIDs is about two times higher than of regular detectors when irradiated up to 1×10
16
cm
−2. The higher CCE is achieved already at −50
°C temperatures.
High-bandgap semiconductor dosimeters for radiotherapy applications Pini, S.; Bruzzi, M.; Bucciolini, M. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
11/2003, Letnik:
514, Številka:
1-3
Journal Article
Recenzirano
We present a comparison between the performance of on-line radiotherapy dosimeters made with different high-bandgap semiconductor materials. We analysed the performances of a Schottky diode made with ...an epitaxial n-type 4H–SiC and a Chemical Vapour Deposited (CVD) diamond film with ohmic contacts. The current response of the dosimeters has been tested under exposure to a Co60 γ-source and to 6MV photons beam from a linear accelerator. The dose range covered is 0.1–10Gy with dose rates 0.1–10Gy/min. The two devices show a charge response linear with the dose when a constant dose rate is used. The SiC diode current response increase linearly with the dose rate; for diamond a quasi-linear behaviour is observed. The epitaxial SiC device shows no priming effects and a fast velocity of response, due to the low density of lattice defects in this material. The diamond performances are affected by trapping–detrapping mechanisms at defects with energy levels at ∼1eV. To de-activate these levels the diamond sample has been pre-irradiated with fast neutrons up to a fluence of 5×1014cm−2. The sensitivity of the two devices compare favourably to those of standard silicon dosimeters.
CERN RD39 Collaboration develops radiation-hard cryogenic silicon detectors. Recently, we have demonstrated improved radiation hardness in novel Current Injected Detectors (CID). For detector ...characterization, we have applied cryogenic Transient Current Technique (C-TCT). In beam tests, heavily irradiated CID detector showed capability for particle detection. Our results show that the CID detectors are operational at the temperature -50degC after the fluence of 1 times 10 16 1 MeV neutron equivalent/cm 2 .
There are two key approaches in our CERN RD 39 Collaboration efforts to obtain ultra-radiation-hard Si detectors: (1) use of the charge/current injection to manipulate the detector internal electric ...field in such a way that it can be depleted at a modest bias voltage at cryogenic temperature range (⩽150
K), and (2) freezing out of the trapping centers that affects the CCE at cryogenic temperatures lower than that of the liquid nitrogen (LN
2) temperature.
In our first approach, we have developed the advanced radiation hard detectors using charge or current injection, the current injected diodes (CID). In a CID, the electric field is controlled by injected current, which is limited by the space charge, yielding a nearly uniform electric field in the detector, independent of the radiation fluence. In our second approach, we have developed models of radiation-induced trapping levels and the physics of their freezing out at cryogenic temperatures.
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