Orientational Coherent Effects of High-Energy Particles in a LiNbO3 Crystal.

A bent lithium niobate strip was exposed to a 400-GeV/c proton beam at the external lines of CERN Super Proton Synchrotron to probe its capabilities versus coherent interactions of the particles with the crystal such as channeling and volume reflection. Lithium niobate (LiNbO3) exhibits an interplanar electric field comparable to that of Silicon (Si) and remarkable piezoelectric properties, which could be exploited for the realization of piezo-actuated devices for the control of high-energy particle beams. In contrast to Si and germanium (Ge), LiNbO3 shows an intriguing effect; in spite of a low channeling efficiency (3%), the volume reflection maintains a high deflection efficiency (83%). Such discrepancy was ascribed to the high concentration (10(4) per cm2) of dislocations in our sample, which was obtained from a commercial wafer. Indeed, it has been theoretically shown that a channeling efficiency comparable with that of Si or Ge would be attained with a crystal at low defect concentration (less than ten per cm2). To better understand the role of dislocations on volume reflection, we have worked out computer simulation via dynecharm++ Monte Carlo code to study the effect of dislocations on volume reflection. The results of the simulations agree with experimental records, demonstrating that volume reflection is more robust than channeling in the presence of dislocations.

Investigation of the Electromagnetic Radiation Emitted by Sub-GeV Electrons in a Bent Crystal.

The radiation emitted by 855 MeV electrons via planar channeling and volume reflection in a 30.5-µm-thick bent Si crystal has been investigated at the MAMI (Mainzer Mikrotron) accelerator. The spectral intensity was much more intense than for an equivalent amorphous material, and peaked in the MeV range in the case of channeling radiation. Differently from a straight crystal, also for an incidence angle larger than the Lindhard angle, the spectral intensity remains nearly as high as for channeling. This is due to volume reflection, for which the intensity remains high at a large incidence angle over the whole angular acceptance, which is equal to the bending angle of the crystal. Monte Carlo simulations demonstrated that incoherent scattering significantly influences both the radiation spectrum and intensity, either for channeling or volume reflection. In the latter case, it has been shown that incoherent scattering increases the radiation intensity due to the contribution of volume-captured particles. As a consequence, the experimental spectrum becomes a mixture of channeling and pure volume reflection radiations. These results allow a better understanding of the radiation emitted by electrons subjected to coherent interactions in bent crystals within a still-unexplored energy range, which is relevant for possible applications for innovative and compact x-ray or γ-ray sources.

Steering of a sub-GeV electron beam through planar channeling enhanced by rechanneling.

We report the observation of efficient steering of a 855 MeV electron beam at MAMI (MAinzer MIkrotron) facilities by means of planar channeling and volume reflection in a bent silicon crystal. A 30.5 µm thick plate of (211) oriented Si was bent to cause quasimosaic deformation of the (111) crystallographic planes, which were used for coherent interaction with the electron beam. The experimental results are analogous to those recorded some years ago at energy higher than 100 GeV, which is the only comparable study to date. Monte Carlo simulations demonstrated that rechanneling plays a considerable role in a particle's dynamics and hinders the spoiling of channeled particles. These results allow a better understanding of the dynamics of electrons subject to coherent interactions in a bent silicon crystal in the sub-GeV energy range, which is relevant for realization of innovative x-ray sources based on channeling in periodically bent crystals.

Coherent effects of high-energy particles in a graded Si(1-x)Ge(x) crystal.

A graded Si(1-x)Ge(x) crystal has been manufactured for operation with high-energy protons to excite coherent interactions of the particles with the crystal such as channeling and volume reflection. The crystal had the shape of a parallelepiped though its (111) atomic planes were curved at a radius of 25.6 m because of the graded Ge content. The crystal was exposed to a 400 GeV/c proton beam at the external lines of CERN Super Proton Synchrotron to probe its capability to steer high-energy particles. Measured deflection efficiency was 62.0% under planar channeling and 96.0% under volume reflection. Such values are critically compared to their counterparts for a standard bent Si crystal under peer conditions. A Monte Carlo simulation of the dynamics of channeled and volume reflected particles in a graded crystal including the effect of Ge impurities and of lattice dislocations has been carried out. We found that the effect of crystal imperfections spoiled the efficiency of channeling while it negligibly affected the performance of volume reflection. We finally propose the usage of the graded crystal as a primary scatterer to aid halo collimation for the new generation of hadronic machines. As a unique feature, a properly cut graded crystal circumvents the problem of the miscut angle, which is currently a severe limitation for implementation of crystal-assisted collimation.

Broad and intense radiation accompanying multiple volume reflection of ultrarelativistic electrons in a bent crystal.

The radiation emitted by 120 GeV/c electrons traversing a single bent crystal under multiple volume reflection orientation is investigated. Multiple volume reflection in one crystal occurs as a charged particle impacts on a bent crystal at several axial channeling angles with respect to a crystal axis. The resulting energy-loss spectrum of electrons was very intense over the full energy range up to the nominal energy of the beam. As compared to the radiation emission by an individual volume reflection, the energy-loss spectrum is more intense and peaks at an energy 3 times greater. Experimental results are compared to a theoretical approach based on the direct integration of the quasiclassical Baier and Katkov formula. In this way, it is possible to determine the mean number of photons emitted by each electron and, thus, to extract the single-photon spectrum, which is broad and intense. The soft part of the radiation spectrum is due to the contribution of coherent interaction between electrons and several reflecting planes intersecting the same crystal axis, whereas the hard part is mainly connected to coherent bremsstrahlung induced by correlated scattering of electrons by atomic strings (string of strings scattering and radiation). The radiation generation by multiple volume reflection takes place over a broad angular range of the incident beam with respect to coherent bremsstrahlung and channeling radiation in straight crystals. Therefore, this type of radiation can be exploited for applications, such as beam dump and collimation devices for future linear colliders.

The experimental setup of the Interaction in Crystals for Emission of RADiation collaboration at Mainzer Mikrotron: Design, commissioning, and tests.

Silicon/germanium flat/bent crystals are thin devices able to efficiently deflect charged particle GeV-energy beams up to a few hundreds of µrad; moreover, high intensity photons can be efficiently produced in the so-called Multi-Volume Reflection (MVR) and Multiple Volume Reflections in One Crystal (MVROC) conditions. In the last years, the research interest in this field has moved to the dynamic studies of light negative leptons in the low energy range: the possibility to deflect negative particles and to produce high intensity γ sources via the coherent interactions with crystals in the sub-GeV energy range has been proved by the ICE-RAD (Interaction in Crystals for Emission of RADiation) Collaboration at the MAinzer MIkrotron (MAMI, Germany). This paper describes the setup used by the ICE-RAD experiment for the crystals characterization (both in terms of deflection and radiation emission properties): a high precision goniometer is used to align the crystals with the incoming beam, while a silicon based profilometer and an inorganic scintillator reconstruct, respectively, the particle position and the photon spectra after the samples. The crystals manufacturing process and their characterization, the silicon profilometer commissioning at the CERN PS T9 beamline, and the commissioning of the whole setup installed at MAMI are presented.

[Therapy of vasculitis in children]. / Terapia delle vasculiti in età pediatrica.

Therapy of vasculitis syndromes varies considerably according to different forms and gravity. Mild cases often heal spontaneously. In other cases, when the causal factors are known, the removal of the offending antigen or the treatment of an underlying primary disease are sufficient to obtain remission. In the vasculitis syndromes, in which the causal factors are unknown, therapy is based on various associations of nonsteroidal antiinflammatory drugs, antiplatelet drugs, anticoagulants, corticosteroids and cytotoxic drugs, depending on the type, extention and gravity of disease. In most severe systemic necrotizing vasculitis, therapy with corticosteroids and cytotoxic drugs must be protracted for months, with inevitable side-effects, particularly severe in children. Pulse therapy with intravenous bolus of high doses of methylprednisolone seems to offer a new valid therapeutic approach, but is still under investigation. Plasmapheresis may be successful in acute and grave forms. High dose intravenous gammaglobulin therapy is indicated in the prevention of coronary involvement of Kawasaki disease. In this review these problems and therapeutic regimes suggested by different Authors are discussed, with particular attention to their application in childhood.

[Vasculitis associated with connectivitis]. / Vasculiti associate a connettiviti.

A great number of vasculitis in childhood is associated with Rheumatic disease. Vascular lesions involve small vessels of various organs. These are described in systemic lupus erythematosus, juvenile rheumatoid arthritis, dermatomyositis, scleroderma, mixed connective tissue disease, Behçet syndrome, Sjögren syndrome.

[Chylothorax in a newborn infant]. / Chilotorace in neonato.

A case of chylothorax in newborn is described. A the fifteenth day a sudden respiratory distress for chylothorax has appeared. A continuous drainage, after thoracenteses, has been placed; the clinic course has been favourable and, at five day, we have started with MCT feeding.

[Treatment using immucytal in children with recurrent respiratory infections: an Italian multicenter experience]. / Terapia con immucytal di bambini affetti da infezioni respiratorie recidivanti: esperienza Italiana policentrica.

120 children, 71 male and 49 female, aged between 2 years and 15 years (mean 6.15 +/- 3.52 years) with recurrent respiratory infections, were treated with Immucytal, an immunomodulator of bacterial origin, based on membrane proteoglycan fractions plus bacterial ribosomes. The children, selected on the basis of the previous year's clinical score, were treated according to a random design with either Immucytal or placebo, using the same dosage of one puff per nostril plus one puff in the oropharyngeal cavity three times a day, as follows: 1st month: two weeks' treatment, one week wash out, one week's treatment. 2nd, 3rd, 4th months: two weeks' treatment, two week's wash out. Monthly throughout the treatment period the frequency and severity of airway infections episodes were assessed using the same score as for admission. Blood chemistry test, immunological assays (circulating Ig, lymphocyte subpopulations, Merieux Multitest in vivo blastization test) and respiratory tests (spirometry using a pneumotachigraph) were done before and after the treatment. 118/120 children completed treatment; the two dropouts were in the placebo group, one for compliance and the other because of headaches. Respiratory symptoms improved significantly in the actively treated children already from the first month, but not in the placebo group. This improvement consisted of reduction of the respiratory infectious episodes in both the upper and lower airways. No changes were noted in respiratory function parameters. From the immunological viewpoint, there were significant rises in serum IgA and IgM and enhanced skin response tot he Multitest; there was no change in the percentages of different circulating lymphocyte subpopulations.(ABSTRACT TRUNCATED AT 250 WORDS)

Volume reflection dependence of 400 GeV/c protons on the bent crystal curvature.

The trend of volume reflection parameters (deflection angle and efficiency) in a bent (110) silicon crystal has been investigated as a function of the crystal curvature with 400 GeV/c protons on the H8 beam line at the CERN Super Proton Synchrotron. This Letter describes the analysis performed at six different curvatures showing that the optimal radius for volume reflection is approximately 10 times greater than the critical radius for channeling. A strong scattering of the beam by the planar potential is also observed for a bend radius close to the critical one.