A new measurement of the cosmic-ray antiproton-to-proton flux ratio between 1 and 100 GeV is presented. The results were obtained with the PAMELA experiment, which was launched into low-Earth orbit ...on-board the Resurs-DK1 satellite on June 15th 2006. During 500 days of data collection a total of about 1000 antiprotons have been identified, including 100 above an energy of 20 GeV. The high-energy results are a tenfold improvement in statistics with respect to all previously published data. The data follow the trend expected from secondary production calculations and significantly constrain contributions from exotic sources, e.g., dark matter particle annihilations.
Abstract
Upstream of the efficiency of proton or carbon ion beams in cancer therapy, and to optimize hadrontherapy results, we analysed the chemistry of Fricke solutions in track-end of 64-MeV ...protons and 1.14-GeV carbon ions. An original optical setup is designed to determine the primary track-segment yields along the last millimetres of the ion track with a sub-millimetre resolution. The Fe
3+
-yield falls in the Bragg peak to (4.9 ± 0.4) × 10
–7
mol/J and 1.9 × 10
–7
mol/J, under protons and carbon ions respectively. Beyond the Bragg peak, a yield recovery is observed over 1 mm for proton beams. It is attributed to the intermediate-LET of protons in this region where their energy decreases and energy distribution becomes broader, in relation with the longitudinal straggling of the beam. Consequently to this LET decrease in the distal part of the Bragg peak, Fe
3+
-yield increases. For the first time, this signature is highlighted at the chemical level under proton irradiation. Nevertheless, this phenomenon is not identified for carbon ion beams since their straggling is lower. It would need a greater spatial resolution to be observed.
Antiparticles account for a small fraction of cosmic rays and are known to be produced in interactions between cosmic-ray nuclei and atoms in the interstellar medium, which is referred to as a ...'secondary source'. Positrons might also originate in objects such as pulsars and microquasars or through dark matter annihilation, which would be 'primary sources'. Previous statistically limited measurements of the ratio of positron and electron fluxes have been interpreted as evidence for a primary source for the positrons, as has an increase in the total electron+positron flux at energies between 300 and 600 GeV (ref. 8). Here we report a measurement of the positron fraction in the energy range 1.5-100 GeV. We find that the positron fraction increases sharply over much of that range, in a way that appears to be completely inconsistent with secondary sources. We therefore conclude that a primary source, be it an astrophysical object or dark matter annihilation, is necessary.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Ocular melanoma has been treated using proton therapy at the Centre Antoine Lacassagne (CAL) since 1991, following the commissioning of the 65 MeV cyclotron MEDICYC and its associated beam-lines a ...few years earlier. The dedicated eye-line is optimized for shallow tumors and sharp penumbrae and provides state-of-the-art quality of care. The cyclotron, beam-lines and treatment systems, which are maintained exclusively by the staff at CAL, have proven to be exceptionally robust with up-times consistently above 95%. The systems are however aging and need to be replaced to ensure a continuation of ocular treatments with MEDICYC. This paper describes the development and performance of a new treatment control and dose measurement system for MEDICYC. Software and hardware architectural design choices are discussed in context of the requirements for dose delivery precision, robustness and patient safety. The performance of the treatment delivery, dose monitoring and beam quality assurance systems are presented.
The PAMELA satellite experiment has measured the cosmic-ray positron fraction between 1.5
GeV and 100
GeV. The need to reliably discriminate between the positron signal and proton background has ...required the development of an ad hoc analysis procedure. In this paper, a method for positron identification is described and its stability and capability to yield a correct background estimate is shown. The analysis includes new experimental data, the application of three different fitting techniques for the background sample and an estimate of systematic uncertainties due to possible inaccuracies in the background selection. The new experimental results confirm both solar modulation effects on cosmic-rays with low rigidities and an anomalous positron abundance above 10
GeV.
A new proton beam-line dedicated to R&D programs has been developed at CentreAntoine Lacassagne (CAL), in Nice (France), in collaboration with the Centrenational d'études spatiales (CNES). This is ...the second beam-line of the MEDICYC 65 MeV cyclotron that is currently in operation, the first being the clinical ‘eye-line’ used for ocular proton therapy. The R&D beam-line is proposed with two configurations, the first producing a Gaussian narrow beam of a few mm width, the second a 100 mm diameter flat beam with a homogeneity better than ±3%. The energy range is (20 - ∼60) MeV, where the exact upper limit depends on the beam configuration being used. The energy spread of the non-degraded beam is (0.3 ± 0.1) MeV. A beam current between 10 pA and 10 μA can be produced with a stability better than 0.2% above 100 pA, and 2% below. The beam can be monitored online at a precision better than 5% in the flux range 1E5 (1E6) – 1E9 (1E10) p/cm2/s for a flat (Gaussian) configuration, although work is in progress to extend this range. Targeted applications for the R&D beam-line are instrumentation research, radiation tolerance tests of components and radiobiology.
•A high-availability 60 MeV proton beam-line dedicated for R&D is operational.•The beam-line can provide a 100 mm homogenous beam over a large flux interval.•Alternatively, a Gaussian beam of a few mm standard deviation can be produced.•The beam-line has been designed for radiation tolerance tests, instrumentation R&D and research in radiobiology.
Radiotherapy with protons (PT) is a standard treatment of ocular tumors. It achieves excellent tumor control, limited toxicities, and the preservation of important functional outcomes, such as ...vision. Although PT may appear as one homogenous technique, it can be performed using dedicated ocular passive scattering PT or, increasingly, Pencil Beam Scanning (PBS), both with various degrees of patient-oriented customization.
MEDICYC PT facility of Nice are detailed with respect to their technical, dosimetric, microdosimetric and radiobiological, patient and tumor-customization process of PT planning and delivery that are key. 6684 patients have been treated for ocular tumors (1991–2020). Machine characteristics (accelerator, beam line, beam monitoring) allow efficient proton extraction, high dose rate, sharp lateral and distal penumbrae, and limited stray radiation in comparison to beam energy reduction and subsequent straggling with high-energy PBS PT. Patient preparation before PT includes customized setup and image-guidance, CT-based planning, and ocular PT software modelling of the patient eye with integration of beam modifiers. Clinical reports have shown excellent tumor control rates (∼95%), vision preservation and limited toxicity rates (papillopathy, retinopathy, neovascular glaucoma, dry eye, madarosis, cataract).
Although demanding, dedicated ocular PT has proven its efficiency in achieving excellent tumor control, OAR sparing and patient radioprotection. It is therefore worth adaptations of the equipments and practice.
Some of these adaptations can be transferred to other PT centers and should be acknowledeged when using non-PT options.
La protonthérapie est un traitement de précision pour les tumeurs oculaires. Elle permet d’obtenir un excellent taux de contrôle tumoral, et parfois de préserver la vision. La protonthérapie peut être réalisée en diffusion passive ou en Pencil Beam Scanning (PBS), avec différents niveaux de personnalisation possibles et differentes performances en fonction des caracteristiques liées au patient, à la tumeur et à la fonction visuelle avant traitement.
Les caractéristiques du faisceau et équipements du cyclotron médical MEDICYC de Nice sont décrits en termes de production d’ions, d’accessoires modificateurs du faisceau, de processus dosimétriques, de caractéristiques microdosimétriques et radiobiologiques.
Les caractéristiques du cyclotron MEDICYC permettent une extraction efficace, un débit de dose élevé, une énergie adaptée aux profondeurs des tumeurs oculaires (≤ 65MeV), des pénombres latérales et distales réduites en diffusion passive et des radiations parasites minimales. La préparation du patient comprend une planification par tomodensitométrie pour modéliser un œil géométrique avec le logiciel et intégrer des modificateurs de faisceau, des accessoires personalisés conformant la dose (collimateur, filtre équivalent tissu, blépharostats etc) et un guidage par l’image en ligne. Les études cliniques (6684 patients, 1991–2020) ont montré d’excellents taux de contrôle des tumeurs (∼95 %), une préservation de la vision chez de nombreux patients à des degrés variables en fonction de la présentation initiale de la maladie et des taux de toxicité limités (papillopathie, rétinopathie, glaucome néovasculaire, œil sec, madarose, cataracte).
Le niveau d’expertise et de personnalisation technico-physique est élevé en protonthérapie oculaire en diffusion passive et contribue certainement au bénéfice clinique observé bien qu’il n’existe pas de comparaison directe entre diffusion passive et active, ni d’étude possible pour une quantification formalisée de ce bénéfice clinique. Il est important de noter que certaines de ces adaptations pourraient être transférées en protonthérapie PBS.
The High Energy Stereoscopic System (H.E.S.S.) is an array of five imaging atmospheric Cherenkov telescopes located in the Khomas Highland in Namibia. Very high energy gamma rays are detected using ...the Imaging Atmospheric Cherenkov Technique. Using the fifth, larger telescope of the array with a huge mirror area of 600 m2, it was possible to lower the energy threshold down to ≈ 30 GeV. With this unique ability to observe large amounts of gamma rays in the high energy gamma-ray regime (< 100 GeV) by using the large effective area of the fifth telescope at these energies, the H.E.S.S. experiment is ideally suited to observe short time scale transient events like gamma-ray bursts (GRBs). Originally detected by the Vela satellites in 1967, GRBs are among the most energetic processes in the known Universe. Extrapolating the spectrum of long duration GRBs (i.e. a GRB duration of the order of a few seconds or above) measured by current satellite experiments like Fermi, which measured gamma rays up to 95 GeV for GRB 130427A, a detection of these phenomena with the H.E.S.S. array is possible. This paper will give an update on the H.E.S.S. Target of Opportunity (ToO) alert system. It is used for an immediate and fully automatic response to a prompt GRB alert received via the Gamma-Ray Coordinates Network (GCN). The key feature of this system is a fast repointing of the whole array to a new observation position. We will discuss the implementation of the ToO alert system as well as its overall performance. Moreover, we will show that software improvements alone reduced the average response time to a ToO alert to below 60s on average, a decrease by more than 50%.
We present a review of the experimental results obtained by PAMELA in measuring the (p, (p) over bar ) and e(+/-) abundance in cosmic rays. In this context, we discuss the interpretation of the ...observed anomalous positron excess in terms of the annihilation of dark matter particles as well as in terms of standard astrophysical sources. Moreover we show the constraints on dark matter models from (p) over bar data.
Launch of the space experiment PAMELA Casolino, M.; Picozza, P.; Altamura, F. ...
Advances in space research,
08/2008, Letnik:
42, Številka:
3
Journal Article
Recenzirano
Odprti dostop
PAMELA is a satellite borne experiment designed to study with great accuracy cosmic rays of galactic, solar, and trapped nature in a wide energy range (protons 80
MeV–700
GeV, electrons 50
MeV–400
...GeV). Main objective is the study of the antimatter component: antiprotons (80
MeV–190
GeV), positrons (50
MeV–270
GeV) and search for antimatter with a precision of the order of 10
−8. The experiment, housed on board the Russian Resurs-DK1 satellite, was launched on June 15th, 2006 in a 350
×
600
km orbit with an inclination of 70°. The detector is composed of a series of scintillator counters arranged at the extremities of a permanent magnet spectrometer to provide charge, time-of-flight, and rigidity information. Lepton/hadron identification is performed by a silicon–tungsten calorimeter and a neutron detector placed at the bottom of the device. An anticounter system is used offline to reject false triggers coming from the satellite. In self-trigger mode the calorimeter, the neutron detector, and a shower tail catcher are capable of an independent measure of the lepton component up to 2
TeV. In this work we describe the experiment, its scientific objectives, and the performance in the first months after launch.
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