The near-infrared radioluminescence and dosimetric properties of Yb-doped silica optical fibers, coupled with an optical detector prototype based on an avalanche photo-diode, were studied by irradiating the fibers with clinical beams generated by a Varian Trilogy accelerator. The performances of the system in standard and small field sizes have been also investigated comparing the output factor, percent depth dose and off axis ratio measurements of the prototypal dosimetric system with other commercial sensors.
The results demonstrated that the drawback due to the stem effect in Yb-doped silica optical fibers can be managed in a simple but effective way by optical filtering. These features, together with the accuracy and precision achieved by Ybdoped fibers in relative dose assessments make the device promising for in-vivo dosimetry studies in radiation therapy.
Rare earths-doped silica optical fibers have shown promising results for ionizing radiation monitoring, thanks to their radio-luminescence (RL) properties. However, the use of these systems for accurate and precise dosimetric measurements in radiation fields above the Cerenkov energy threshold, like those employed in radiation therapy, is still challenging, since a spurious luminescence, namely the “stem effect,” is also generated in the passive fiber portion exposed to radiation. The spurious signal mainly occurs in the UV-VIS region, therefore a dopant emitting in the near infrared may be suitable for an optical discrimination of the stem effect.
In this work, the RL and dosimetric properties of Yb-doped silica optical fibers, produced by sol-gel technique, are studied, together with the methods and instruments to achieve an efficient optical detection of the Yb3+ emission, characterized by a sharp line at about 975 nm.
The results demonstrate that the RL of Yb3+ is free from any spectral superposition with the spurious luminescence. This aspect, in addition with the suitable linearity, reproducibility, and sensitivity properties of the Yb-doped fibers, paves the way to their use in applications where an efficient stem effect removal is required.
The recent progresses in the development and characterization of doped silica fiber optics for dosimetry applications in the modern radiation therapy, and for high energy physics experiments, are presented and discussed. In particular, the main purpose was the production of scintillating fiber optics with an emission spectrum which can be easily and efficiently distinguished from that of other spurious luminescent signals originated in the fiber optic material as consequence of the exposition to ionizing radiations (e.g. Cerenkov light and intrinsic fluorescence phenomena). In addition to the previously investigated dopant (Ce), other rare earth elements (Eu and Yb) were considered for the scintillating fiber optic development. The study of the luminescent and dosimetric properties of these new systems was carried out by using X and gamma rays of different energies and field sizes.
In the last decade, the interest in scintillating fiber optics for ionizing radiation monitoring is constantly increasing.
Among the fields of possible applications of these sensors, radiation therapy represents a driving force for the research
and development of new devices. In fact, the small dimensions of fiber optics based detectors, together with their realtime
response, make these systems extremely promising both in quality assurance measurements of intensity modulated
radiotherapy beams, and in in-vivo dosimetry. On the other hand, two specific aspects might represent limiting factors:
(i) the “stem effect”, that is the spurious luminescence originating as a consequence of the irradiation of the light guide,
and (ii) the “memory effect”, that is the radioluminescence sensitivity increase during prolonged exposition to ionizing
radiation, typical of many scintillating materials.
These two issues, representing the main challenges to face for the effective use of scintillating fiber as dosimeters in
radiotherapy, were studied considering amorphous silica matrices prepared by sol-gel method and doped with europium.
The origin of the stem effect was investigated by means of spectral measurements of the doped fibers irradiated with Xrays
and electrons of different energies, field sizes and orientations. New approaches for removing the stem effect on the
basis of the radioluminescent spectral analysis are presented and discussed. Furthermore, the causes and phenomenology
of the memory effect are described, considering also the effect of dose accumulation with different dose rates and
energies of ionizing radiation.
About 20 μm thick Ce-doped Lu3Al5O12 thin films grown by Liquid Phase Epitaxy and thin plates of similar thickness
prepared by mechanical cutting and polishing from Czochralski grown crystals are used in 2D-imaging experiment down
to μm 2D-resolution. Their scintillation response is also measured under α-particle excitation and performance of film
and bulk material is mutually compared. Furthermore, scintillation and thermoluminescence characteristics of UV
emitting Sc-doped LuAG grown by Czochralski method are presented since this system is a candidate material for UV
emission-based 2D sensors with improved diffraction limit with respect to the presently used Ce-doped aluminum
Scintillating materials, able to convert energy of ionizing radiation into light in the visible-UV interval, are presently
used in a wide class of applications such as medical imaging, industrial inspection, security controls and high energy
In the last few years we studied and developed a new radiation sensor based on silica-glass fiber-optic technology. In its
simplest configuration such device is composed by a short portion (about 10 mm) of scintillating fiber coupled to a
photomultiplier through a suitably long passive silica fiber.
In this work, we present new results concerning the characterization of silica based Ce and Eu doped fibers glasses
obtained by a modified sol-gel method and drawn by a conventional drawing tower for optical fibers. The radio-luminescence
of Eu doped fibers is rather weak; moreover it displays a marked sensitivity increase during subsequent
irradiations, preventing the use of such fibers in dosimetry. On the other hand Ce-doped fibers show very high radiation
hardness, signal stability and reproducibility, and high sensitivity to radiations with energies from 10 keV to several
tens of MeV. Numerous tests with photons (X and gamma rays), electrons, and protons have already been successfully
At the early stage of its market introduction it is the smallest radiation sensor, also compared to MOSFET and diode
technology and it appears to be the ideal choice for in vivo measurements in medical field or remote sensing.
Gamma radiation induced absorption processes of various scintillating materials were studied at room temperature.
Single crystal of PbWO4, Ce-doped YAlO3 and Ce(Pr)-doped Y(Lu)3Al5O12 were irradiated by 60Co and doses ranging
between 1-500 Gy. Broad induced absorption spectra obtained were decomposed into separate Gaussian components and
tentatively ascribed to specific color centres. Supporting thermoluminescence and electron paramagnetic resonance
experiments were performed to reveal the nature of charge carrier traps. The influence of codoping by aliovalent ions is
also shown and discussed.
In this paper different sol gel syntheses strategies are adopted in order to produce Ce-doped silica-glasses scintillators with improved properties.
Variations on the synthesis procedure are adopted to reduce the hydroxyl content of the sol gel glass; to this purpose, a fluorine derivative of silicon alkoxide was added in the sol gel reaction.
Since a drawback of Ce-doped sol gel glasses is the partial oxidation of Ce3+ to Ce4+ in the matrix probably occurring during the sintering procedure, both Ce-doped xerogel and fluorinated xerogel were treated under reducing atmosphere (H2:Ar) instead of the usual oxidizing atmosphere.
Glasses obtained in such ways are compared with commercial synthetic glasses and with previously produced sol gel samples by spectroscopic IR absorption measurements, and by radio-luminescence experiments.
New Ce3+ - doped high-grade silica glasses are synthesized by a modified sol-gel method, to be used as scintillators for
the detection of X-rays and low energy particles. These glasses have efficiency a factor of 2 higher than state-of-the-art Bi4Ge3O12 crystals, high radiation hardness and high compatibility with the silica-based photonic technology. Powder-in-tube and rod-in-tube techniques are used to fabricate low-loss optical fibres with 135, 220 and 660 microns diameter. Device prototypes are obtained by fusion-splicing these fibres to commercial high numerical aperture optical fibres.