TrueBeam STx is a new linac that can produce high dose rate photon beams up to 2400 UM/min by removing the flattening filter. Higher dose rates would potentially reduce treatment time, for instance ...in the case of extracranial stereotactic radiotherapy. A quality assurance programme dedicated to the specificities of FFF beams must be elaborated before any clinical exploitation. Some parameters previously used for flattened beams need to be rethought. The behaviour of detectors in high dose rates must be examined. The following parameters were measured in our centre for 6 MV and 10 MV FFF beams. Quality index (TPR20,10) and recombination factors (ks) were measured with the reference chamber FC65-G. Relative measurements were performed for field sizes from 3 × 3 cm2 to 40 × 40 cm2 : scatter factors (Sc,p), percentage depth dose curves and profiles. Several methods to describe the profiles were compared. Quality index values are similar to the results found in literature. ks reach a maximum value of 1.018 for the X10FFF beam. Surface dose is higher andmaximumdose is closer to the surface for FFF than for flattened beams. DS, dmax and Sc,p values show weak variationwith field size. Profiles show a typical peak in the central region. The acquisition method was modified to account for the important signal fluctuations in this central part. The renormalization at the inflection point introduces an uncertainty around 10% on the penumbra measurement. The renormalization at the profile shoulder gives more accurate results. FFF characteristics are reproducible between linacs of different centres. Experience acquired with flattened beams will mostly be preserved. However, some parameters employed to describe the profiles become obsolete for FFF beams. Physicist will have to come to a consensus in order to characterise FFF beams in a complete yet simple manner.
Low-lying dipole and quadrupole states Lanza, E. G.; Pellegri, L.; Andrés, M. V. ...
The European physical journal. A, Hadrons and nuclei,
12/2019, Letnik:
55, Številka:
12
Journal Article
Recenzirano
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We briefly review the main properties of the low-lying dipole states known as Pygmy Dipole Resonance trying to select the main one which could define this new excitation mode. A good candidate ...seems to be the isoscalar-isovector mixing. This mixing, more effective at the nuclear surface, has been proved by both theoretical and experimental investigations. On the other hand, the study of the low-lying quadrupole states does not seem to provide clear evidence for a new excitation mode. The theoretical approaches used to investigate the quadrupole response reach different conclusions and the experimental data can only clearly establish the multipolarities of the states and their one-phonon character. Moreover, cross section calculations are not sensitive enough to disentangle between quadrupole states which are considered, in one of the theoretical approach, as due to different excitation mode.
The CLYC-6 and CLYC-7 response to γ-rays, fast and thermal neutrons Giaz, A.; Pellegri, L.; Camera, F. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
02/2016, Letnik:
810
Journal Article
Recenzirano
Odprti dostop
The crystal Cs2LiYCl6:Ce (CLYC) is a very interesting scintillator material because of its good energy resolution and its capability to identify γ-rays and fast/thermal neutrons. The crystal ...Cs2LiYCl6:Ce contains 6Li and 35Cl isotopes, therefore, it is possible to detect thermal neutrons through the reaction 6Li(n, α)t while 35Cl ions allow to measure fast neutrons through the reactions 35Cl(n, p)35S and 35Cl(n, α)32P. In this work two CLYC 1″×1″ crystals were used: the first crystal, enriched with 6Li at 95% (CLYC-6) is ideal for thermal neutron measurements while the second one, enriched with 7Li at >99% (CLYC-7) is suitable for fast neutron measurements. The response of CLYC scintillators was measured with different PMT models: timing or spectroscopic, with borosilicate glass or quartz window. The energy resolution, the neutron-γ discrimination and the internal activity are discussed. The capability of CLYC scintillators to discriminate γ rays from neutrons was tested with both thermal and fast neutrons. The thermal neutrons were measured with both detectors, using an AmBe source. The measurements of fast neutrons were performed at the Frascati Neutron Generator facility (Italy) where a deuterium beam was accelerated on a deuterium or on a tritium target, providing neutrons of 2.5MeV or 14.1MeV, respectively. The different sensitivity to thermal and fast neutrons of a CLYC-6 and of a CLYC-7 was additionally studied.
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