314 research outputs found

    An improved method for estimating the neutron background in measurements of neutron capture reactions

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    The relation between the neutron background in neutron capture measurements and the neutron sensitivity related to the experimental setup is examined. It is pointed out that a proper estimate of the neutron background may only be obtained by means of dedicated simulations taking into account the full framework of the neutron-induced reactions and their complete temporal evolution. No other presently available method seems to provide reliable results, in particular under the capture resonances. An improved neutron background estimation technique is proposed, the main improvement regarding the treatment of the neutron sensitivity, taking into account the temporal evolution of the neutron-induced reactions. The technique is complemented by an advanced data analysis procedure based on relativistic kinematics of neutron scattering. The analysis procedure allows for the calculation of the neutron background in capture measurements, without requiring the time-consuming simulations to be adapted to each particular sample. A suggestion is made on how to improve the neutron background estimates if neutron background simulations are not available.Comment: 11 pages, 9 figure

    Integral measurement of the 12C(n, p)12B reaction up to 10 GeV

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    The integral measurement of the 12C(n, p)12B reaction was performed at the neutron time-offlight facility n TOF at CERN. The total number of 12B nuclei produced per neutron pulse of the n TOF beam was determined using the activation technique in combination with a time-of-flight technique. The cross section is integrated over the n TOF neutron energy spectrum from reaction threshold at 13.6 MeV to 10 GeV. Having been measured up to 1 GeV on basis of the 235U(n, f) reaction, the neutron energy spectrum above 200 MeV has been re-evaluated due to the recent extension of the cross section reference for this particular reaction, which is otherwise considered a standard up to 200 MeV. The results from the dedicated GEANT4 simulations have been used to evaluate the neutron flux from 1 GeV up to 10 GeV. The experimental results related to the 12C(n, p)12B reaction are compared with the evaluated cross sections from major libraries and with the predictions of different GEANT4 models, which mostly underestimate the 12B production. On the contrary, a good reproduction of the integral cross section derived from measurements is obtained with TALYS-1.6 calculations, with optimized parameters.European Atomic Energy Communitys (Euratom) Seventh Framework Programme FP7/2007-2011-CHANDA (No. 605203)Narodowe Centrum Nauki (NCN)-UMO-2012/04/M/ST2/00700Croatian Science Foundation-No. 168

    Search for Light Gauge Bosons of the Dark Sector at the Mainz Microtron

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    A new exclusion limit for the electromagnetic production of a light U(1) gauge boson {\gamma}' decaying to e^+e^- was determined by the A1 Collaboration at the Mainz Microtron. Such light gauge bosons appear in several extensions of the standard model and are also discussed as candidates for the interaction of dark matter with standard model matter. In electron scattering from a heavy nucleus, the existing limits for a narrow state coupling to e^+e^- were reduced by nearly an order of magnitude in the range of the lepton pair mass of 210 MeV/c^2 < m_e^+e^- < 300 MeV/c^2. This experiment demonstrates the potential of high current and high resolution fixed target experiments for the search for physics beyond the standard model.Comment: 4 pages, 7 figure

    Osteogenesis imperfecta: pregled suvremenih spoznaja o radiologiji koštanoga sustava i nove genetske spoznaje

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    Osteogenesis imperfecta is a genetically and clinically heterogeneous disorder of bone and connective tissue characterized by osteoporosis, fragile bones, hyperextensible joints, dentinogenesis imperfecta, bluish coloration of the sclerae, and adult-onset hearing loss. Medical history, careful physical examination, radiographic features of fractures, and biochemical analysis of skin collagen are the four cornerstones of accurate diagnosis. As osteogenesis imperfecta affects the whole skeleton, radiologic diagnostic features could be seen on any bone at any age of the patient. A radiology specialist should be aware of subtle changes seen on radiographs of axial skeleton (i.e. skull, spine and pelvic bones) and appendicular skeleton (i.e. long and short bones of extremities) as well as of specific osteogenesis features (i.e. ÔÇťpopcornÔÇŁ calcifications) and difficult differential diagnosis (i.e. hypertrophic callus formation versus osteosarcoma; child abuse fractures versus true osteogenesis imperfecta). About 300 different mutations have been identified within COL1A1 and COL1A2 genes that encode the chains of type I collagen. More than 90% of these are heterozygous single base pair mutations unique to the affected individuals within families. Depending on the location of the mutation within the collagen gene, these produce a variety of clinical pictures which range from mild (OI type 1), lethal (OI type 2) to severely deforming (OI type 3) and mildly deforming (OI type 4). Each of the four types has a common radiologic appearance that helps in establishing the diagnosis. However, recent findings have confirmed that new genes other than type I collagen could be responsible for three new types of OI (OI type 5; OI type 6 and rhizomelic OI). Here we describe the complexity of the phenotype-genotype correlation in OI, and the recently proposed new classification.Osteogenesis imperfecta (OI) je genetski i klini─Źki heterogena bolest kosti i vezivnoga tkiva s odrednicama: osteoporoza; lomljivost kostiju; labavost zglobova, dentinogenesis imperfecta; plavi─Źaste bjeloo─Źnice i nagluhost u odrasloj dobi. Klju─Ź to─Źne dijagnoze su ─Źetiri bitna postupka: precizna anamneza; pa┼żljiv fizikalni pregled; uo─Źavanje radiolo┼íkih zna─Źajka prijeloma i promjena kostiju i biokemijska analiza kolagena ko┼że. Uobi─Źajena je podjela na ─Źetiri tipa OI: od blagog (tip 1), letalnog (tip 2) do te┼íko deformiraju─çeg (tip 3) i umjereno deformiraju─çeg oblika (tip 4). Svaki od ─Źetiri tipa ima zasebne radiolo┼íke zna─Źajke koje poma┼żu kod postavljanja to─Źne dijagnoze i klasificiranja. Dijagnosti─Źko-radiolo┼íki znaci postoje na cijelom mi┼íi─çno ko┼ítanom sustavu od novoro─Ĺena─Źke do kasne ┼żivotne dobi. Za radiologa je va┼żno prepoznati brojne si─çu┼íne i specifi─Źne promjene na rendgenogramima aksijalnog (lubanja, kralje┼ínica, zdjelica) i apendikularnog (kosti udova) skeleta. Znaci korisni u diferenciranju osteosarkoma prema stvaranju hipertrofi─Źnog ko┼ítanog kalusa kod OI i drugi posebni znaci bolesti, primjerice metafizne ÔÇťpopcornÔÇŁ kalcifikacije, prepoznaju se dobrom radiolo┼íkom obradom. Dosad je otkriveno oko 300 razli─Źitih mutacija na COL1A1 i COL1A2 genima odgovornima za oblikovanje lanaca kolagena tip I. Klini─Źka slika OI razlikuje se prema mjestu mutacije na genu za kolagen. Nedavni nalazi su potvrdili da i drugi geni, uz kolagen tip 1, mogu biti odgovorni za nastanak tri nova tipa OI: tip 5; tip 6 i rizomeli─Źni tip OI. Nadalje, u tekstu je opisana slo┼żenost fenotipske i genotipske korelacije, kao i nedavno predlo┼żena nova klasifikacija OI

    Precision X-ray spectroscopy of kaonic atoms as a probe of low-energy kaon-nucleus interaction

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    In the exotic atoms where one atomic 1s1s electron is replaced by a KÔłĺK^{-}, the strong interaction between the KÔłĺK^{-} and the nucleus introduces an energy shift and broadening of the low-lying kaonic atomic levels which are determined by only the electromagnetic interaction. By performing X-ray spectroscopy for Z=1,2 kaonic atoms, the SIDDHARTA experiment determined with high precision the shift and width for the 1s1s state of KÔłĺpK^{-}p and the 2p2p state of kaonic helium-3 and kaonic helium-4. These results provided unique information of the kaon-nucleus interaction in the low energy limit.Comment: 4 pages, 1 figure, proceedings for oral presentation at the ICNFP2015 conference, Kolymbari, Cret

    Strong interaction studies with kaonic atoms

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    The strong interaction of antikaons (K-) with nucleons and nuclei in the low energy regime represents an active research field connected intrinsically with few-body physics. There are important open questions like the question of antikaon nuclear bound states - the prototype system being K-pp. A unique and rather direct experimental access to the antikaon-nucleon scattering lengths is provided by precision X-ray spectroscopy of transitions in low-lying states of light kaonic atoms like kaonic hydrogen isotopes. In the SIDDHARTA experiment at the electron-positron collider DA?NE of LNF-INFN we measured the most precise values of the strong interaction observables, i.e. the strong interaction on the 1s ground state of the electromagnetically bound K-p atom leading to a hadronic shift and a hadronic broadening of the 1s state. The SIDDHARTA result triggered new theoretical work which achieved major progress in the understanding of the low-energy strong interaction with strangeness. Antikaon-nucleon scattering lengths have been calculated constrained by the SIDDHARTA data on kaonic hydrogen. For the extraction of the isospin-dependent scattering lengths a measurement of the hadronic shift and width of kaonic deuterium is necessary. Therefore, new X-ray studies with the focus on kaonic deuterium are in preparation (SIDDHARTA2). Many improvements in the experimental setup will allow to measure kaonic deuterium which is challenging due to the anticipated low X-ray yield. Especially important are the data on the X-ray yields of kaonic deuterium extracted from a exploratory experiment within SIDDHARTA.Comment: Proc. Few Body 21, 4 pages, 2 figure

    Measurements of the \gamma * p --> \Delta(1232) reaction at low Q2

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    We report new p(eÔâŚ,eÔÇ▓p)¤ÇÔłś(\vec{e},e^\prime p)\pi^\circ measurements in the ╬ö+(1232)\Delta^{+}(1232) resonance at the low momentum transfer region utilizing the magnetic spectrometers of the A1 Collaboration at MAMI. The mesonic cloud dynamics are predicted to be dominant and appreciably changing in this region while the momentum transfer is sufficiently low to be able to test chiral effective calculations. The results disagree with predictions of constituent quark models and are in reasonable agreement with dynamical calculations with pion cloud effects, chiral effective field theory and lattice calculations. The reported measurements suggest that improvement is required to the theoretical calculations and provide valuable input that will allow their refinements
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