Long-term (10 years) prognostic value of a normal thallium-201 myocardial exercise scintigraphy in patients with coronary artery disease documented by angiography

In order to assess the prognostic significance of normal exercise thallium-210 myocardial scintigraphy in patients with documented coronary artery disease, we studied the incidence of cardiac death and non-fatal myocardial infarction in 69 symptomatic patients without prior Q wave myocardial infarction, who demonstrated one or more significant coronary lesions (stenosis ≤70%) on an angiogram performed within 3 months of scintigraphy (Group 1). These patients were compared to a second group of 136 patients with an abnormal exercise scintigram, defined by the presence of reversible defect(s) and angiographically proven coronary artery disease (Group 2), and to a third group of 102 patients with normal exercise scintigraphy without significant coronary lesions (stenosis ≥30%) or with normal coronary angiography (Group 3). In contrast to coronary lesions observed in Group 2, patients in Group I presented more frequently with single- vessel disease (83% vs 35%, P>0·0001) and with more distal lesions (55% vs 23%, P>0·0001). Over a mean follow-up period of 8·6 years, one fatal and eight non-fatal cases of myocardial infarction were observed in Group 1. The majority of patients in Group 1 were treated medically: only 24 (35%) underwent myocardial revascularization, usually by coronary angioplasty. There was no significant difference in the incidence of combined major cardiac events (cardiac death, non-fatal myocardial infarction) in patients with normal exercise scintigraphy, with or without documented coronary artery disease (Groups 1 and 3), while the incidence was higher in Group 2. However, while the mortality remained very low in Group 1, the incidence of non-fatal myocardial infraction was not different from that of Group 2, where most patients underwent revascularization procedures. In conclusion, patients with coronary artery disease and a normal exercise thallium-201 myocardial scintigram usually have mild coronary lesions (single-vessel disease, distal location) and good long-term prognosis, with a low incidence of cardiac deat

Use of Silicon Carbide as Beam Intercepting Device Material: Tests, Issues and Numerical Simulations

Silicon Carbide (SiC) stands as one of the most promising ceramic material with respect to its thermal shock resistance and mechanical strengths. It has hence been considered as candidate material for the development of higher performance beam intercepting devices at CERN. Its brazing with a metal counterpart has been tested and characterized by means of microstructural and ultrasound techniques. Despite the positive results, its use has to be evaluated with care, due to the strong evidence in literature of large and permanent volumetric expansion, called swelling, under the effect of neutron and ion irradiation. This may cause premature and sudden failure, and can be mitigated to some extent by operating at high temperature. For this reason limited information is available for irradiation below 100°C, which is the typical temperature of interest for beam intercepting devices like dumps or collimators. This paper describes the brazing campaign carried out at CERN, the results, and the theoretical and numerical approach used to characterize the extent of the swelling phenomenon with radiation, as well as the p+ irradiation test program to be conducted in the next future

A Clamped Be Window for the Dump of the HiRadMat Experiment at CERN

At CERN, the High Radiation to Materials facility (HiRadMat) is designed to test accelerator components under the impact of high-intensity pulsed beams and will start operation in 2012. In this frame an LHC TED-type dump was installed at the end of the line, working in nitrogen over-pressure, and a 254μm-thick beryllium window was placed as barrier between the inside of the dump and the external atmosphere. Because of the special loading conditions, a clamped window design was especially developed, optimized and implemented, the more standard welded window not being suitable for such loads. Considering then the clamping force and the applied differential pressures, the stresses on the window components were carefully evaluated thanks to empirical as well as numerical models, to guarantee the structural integrity of the beryllium foil. This paper reports on choices and optimizations that led to the final design, presenting also comparative results from different solutions and the detailed results for the adopted one

Internal H0/H- Dump for the Proton Synchrotron Booster Injection at CERN

In the frame of the LHC Injectors Upgrade Project at CERN (LIU), the new 160MeV H- Linac4 will inject into the four existing PS Booster rings after the conversion of H- into H+ in a stripping foil. Given a limited stripping efficiency and possible foil failures, a certain percentage of the beam is foreseen to remain partially (H0) or completely (H-) unstripped. An internal dump installed into the chicane magnet to stop these unstripped beams is therefore required. This paper presents the conceptual design of the internal dump, reviewing loading assumptions, design constraints, limitations and integration studies. Power evacuation through the thermal contact between the core and the external active cooling is addressed and, finally, results from the numerical thermo-mechanical analyses are reported

Experimental cavitation investigation of the electromagnetic PbBi pump with rotating permanent magnets

Electromagnetic induction pumps with rotating permanent magnets (EMP) are used mostly in experimental setups, where operation safety and reliability are crucial. Such pumps can face flow parameter decrease when operating at a low inlet pressure compared with those gained at higher inlet pressure values. The pump's developed flow rate increase does not correspond to the magnetic rotor rotation rate increase at the lower inlet pressure caused by the cavitation process at the pumpâs inlet tract. The study focuses on critical cavitation numbers at several inlet tract sections under severe cavitation conditions which prevent the flow rate increase. The current study is an experimental approach to characterize the pump operation parameters using cavitation numbers and comparing them with the literature data. Figs 7, Refs 13

CFD analysis and optimization of a liquid lead-bismuth loop target for ISOL facilities

In the context of the forthcoming next generation of Radioactive Ion Beams (RIBs) facilities based on an Isotope Separation On Line (ISOL) method, the development of production targets capable of dissipating the high power deposited by the primary beam is a major challenge. The concept of a high-power target based on a liquid Pb–Bi loop incorporating a heat-exchanger and a diffusion chamber was proposed within EURISOL DS and is being developed within the LIEBE1 project. Due to the non-static character of the target, specific hydrodynamics issues are of concern. In this paper, these issues are studied mostly based on three-dimensional (3D) Computational Fluid Dynamics analysis of the flow of the Lead Bismuth Eutectic (LBE) target, resulting in optimized designs. The concept and hydrodynamic challenges of generating RIBs from a liquid-metal-loop target irradiated with a high-power primary beam are presented. The optimization of the target design has been conducted keeping in mind the need for a fast and efficient release of short-lived isotopes. This study shows that approximately 100 ms after the proton pulse the irradiated liquid-metal is entirely and uniformly evacuated from the irradiation volume and spread in a shower of small droplets (100-μm radii), in order to reduce the diffusion length of isotopes. Solutions to deal with the typical cavitation risk due to the presence of low-pressure zones in the liquid have also been found and simulated

Development of a proton-to-neutron converter for radioisotope production at ISAC-TRIUMF

At ISAC-TRIUMF, a 500 MeV proton beam is impinged upon "thick" targets to induce nuclear reactions to produce reaction products that are delivered as a Radioactive Ion Beam (RIB) to experiments. Uranium carbide is among the most commonly used target materials which produces a vast radionuclide inventory coming from both spallation and fission-events. This can also represent a major limitation for the successful delivery of certain RIBs to experiments since, for a given mass, many isobaric isotopes are to be filtered by the dipole mass separator. These contaminants can exceed the yield of the isotope of interest by orders of magnitude, often causing a significant reduction in the sensitivity of experiments or even making them impossible. The design of a 50 kW proton-to-neutron (p2n) converter-target is ongoing to enhance the production of neutron-rich nuclei while significantly reducing the rate of neutron-deficient contaminants. The converter is made out of a bulk tungsten block which converts proton beams into neutrons through spallation. The neutrons, in turn, induce pure fission in an upstream UCx target. The present target design and the service infra-structure needed for its operation will be discussed in this paper.</p

Production and release of ISOL beams from molten fluoride salt targets

In the framework of the Beta Beams project, a molten fluoride target has been proposed for the production of the required 10(13) Ne-18/s. The production and extraction of such rates are predicted to be possible on a circulating molten salt with 160 MeV proton beams at close to 1 MW power. As a most important step to validate the concept, a prototype has been designed and investigated at CERN-ISOLDE using a static target unit. The target material consisted of a binary fluoride system, NaF:LiF (39:61 mol.%), with melting point at 649 degrees C. The production of Ne beams has been monitored as a function of the target temperature and proton beam intensity. The prototype development and the results of the first online tests with 1.4 GeV proton beam are presented in this paper. (C) 2014 Elsevier B.V. All rights reserved