| 41. |
- Bardies, Manuel, et al.
(författare)
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Quantitative imaging for clinical dosimetry
- 2006
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Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - : Elsevier BV. - 0167-5087 .- 0168-9002. ; 569:2, s. 467-471
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Tidskriftsartikel (refereegranskat)abstract
- Patient-specific dosimetry in nuclear medicine is now a legal requirement in many countries throughout the EU for targeted radionuclide therapy (TRT) applications. In order to achieve that goal, an increased level of accuracy in dosimetry procedures is needed. Current research in nuclear medicine dosimetry should not only aim at developing new methods to assess the delivered radiation absorbed dose at the patient level, but also to ensure that the proposed methods can be put into practice in a sufficient number of institutions. A unified dosimetry methodology is required for making clinical outcome comparisons possible.
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| 42. |
- Batkov, Konstantin, et al.
(författare)
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Unperturbed moderator brightness in pulsed neutron sources
- 2013
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Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - : Elsevier BV. - 0167-5087 .- 0168-9002. ; 729, s. 500-505
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Tidskriftsartikel (refereegranskat)abstract
- The unperturbed neutron brightness of a moderator can be defined from the number of neutrons leaving the surface of a moderator completely surrounded by a reflector. Without openings for beam extraction, it is the maximum brightness that can be theoretically achieved in a moderator. The unperturbed brightness of a cylindrical cold moderator filled with pure para-H-2 was calculated using MCNPX; the moderator dimensions were optimised, for a fixed target and reflector geometry corresponding to the present concept for the BS spallation source. This quantity does not depend on openings for beam extraction and therefore can be used for a first-round optimisation of a moderator, before effects due to beam openings are considered. We find that such an optimisation yields to a factor of 2 increase with respect to a conventional volume moderator, large enough to accommodate a viewed surface of 12 x 12 cm(2): the unperturbed neutron brightness is maximum for a disc-shaped moderator of 15 cm diameter, 1.4 cm height. The reasons for this increase can be related to the properties of the scattering cross-section of paraH(2), to the added reflector around the exit surface in the case of a compact moderator, and to a directionality effect. This large optimisation gain in the unperturbed brightness hints towards similar potentials for the perturbed neutron brightness, in particular in conjunction with advancing the optical quality of neutron delivery from the moderator to the sample, where by Lionville theorem the brightness is conserved over the beam trajectory, except for absorption and similar type losses. (C) 2013 Elsevier B.V. All rights reserved
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| 43. |
- Bentley, Phillip, et al.
(författare)
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Correction of optical aberrations in elliptic neutron guides
- 2012
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Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - : Elsevier BV. - 0167-5087 .- 0168-9002. ; 693, s. 268-275
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Tidskriftsartikel (refereegranskat)abstract
- Modern, nonlinear ballistic neutron guides are an attractive concept in neutron beam delivery and instrumentation because they offer increased performance over straight or linearly tapered guides. However, like other ballistic geometries they have the potential to create significantly non-trivial instrumental resolution functions. We address the source of the most prominent optical aberration, namely coma, and we show that for extended sources the off-axis rays have a different focal length from on-axis rays, leading to multiple reflections in the guide system. We illustrate how the interplay between coma, sources of finite size, and mirrors with non-perfect reflectivity can therefore conspire to produce uneven distributions in the neutron beam divergence, a source of complicated resolution functions. To solve these problems, we propose a hybrid elliptic-parabolic guide geometry. Using this new kind of neutron guide shape, it is possible to condition the neutron beam and remove almost all of the aberrations, whilst providing the same performance in beam current as a standard elliptic neutron guide. We highlight the positive implications for neutron scattering instruments that this new shape can bring. (c) 2012 Elsevier B.V. All rights reserved.
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| 44. |
- Bevilacqua, Riccardo, et al.
(författare)
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A procedure for the characterization of electron transmission through Frisch grids
- 2015
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier. - 0168-9002 .- 1872-9576 .- 0167-5087. ; 770, s. 64-67
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Tidskriftsartikel (refereegranskat)abstract
- In Frisch grid ionization chambers special attention must be paid to the operating voltages in order to avoid unwanted collection of electrons on the Frisch grid. Collection of electrons on the grid will lead to a decreased signal to noise ratio and consequently a deteriorated energy resolution. Furthermore, systematic errors in the determination of the angular distribution will be introduced. Theoretical formulas for minimized collection of electrons on the grid were derived by Bunemann et al. [3] in the special case of a Frisch grid consisting of a plane of parallel wires. No such formulas exist for other grid geometries and a careful calibration procedure is needed. We describe here a procedure for characterizing the Frisch grid in terms of its transparency to electrons for a grid consisting of a mesh of crossed wires.
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| 45. |
- Biedron, Sandra G., et al.
(författare)
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Evolution of transverse modes in a high-gain free-electron laser
- 2004
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Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - : Elsevier BV. - 0167-5087 .- 0168-9002. ; 528:1-2, s. 443-447
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Tidskriftsartikel (refereegranskat)abstract
- At the point of saturation in a high-gain free-electron laser (FEL) the light is fully transversely coherent. The number and evolution of the transverse modes is important for the effective tune-up and subsequent operation of FELs based on the photon beam characterization and in designing multi-module devices that rely on relatively stable saturation distances in each module. In the latter, this is particularly critical since each section will seed another module. Overall, in a single- or multi-module device, experimental users will desire stability in power and in photon beam quality. Using a numerical simulation code, the evolution of the transverse modes in the high-gain free-electron laser (FEL) is examined and is discussed. In addition, the transverse modes in the first few higher nonlinear harmonics are investigated.
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| 46. |
- Biedron, Sandra G., et al.
(författare)
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Measurements of nonlinear harmonic generation at the Advanced Photon Source's SASE FEL
- 2002
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Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - 0167-5087. ; 483:1-2, s. 94-100
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Tidskriftsartikel (refereegranskat)abstract
- SASE saturation was recently achieved at the Advanced Photon Source's SASE FFL in the low-energy undulator test line at 530 nm and 385 urn. The electron beam microbunching becomes more and more prominent until saturation is achieved. This bunching causes nonlinear harmonic emission that extends the usefulness of a SASE system in achieving shorter FEL wavelengths for the same electron beam energy. We have investigated the intensity of the fundamental and second harmonic undulator radiation as a function of distance along the undulator line and present the experimental results and compare them to numerical simulations. In addition, we have measured the single-shot second harmonic spectra as well as the simultaneous fundamental and second harmonic spectra and present the experimental results. (C) 2002 Elsevier Science B.V. All riudits reserved.
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| 47. |
- Biedron, Sandra G., et al.
(författare)
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The sensitivity of nonlinear harmonic generation to electron beam quality in free electron lasers
- 2002
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Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - 0167-5087. ; 483:1-2, s. 101-106
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Tidskriftsartikel (refereegranskat)abstract
- The generation of harmonics through a nonlinear mechanism driven by bunching at the fundamental has sparked interest as a path toward enhancing and extending the usefulness of an X-ray free-electron laser (FEL) facility. The sensitivity of the nonlinear harmonic generation to undulator imperfections, electron beam energy spread, peak current, and emittance is important in an evaluation of the process. Typically, linear instabilities in FELs are characterized by increased sensitivity to both electron beam and undulator quality with increasing harmonic number. However, since the nonlinear harmonic generation mechanism is driven by the growth of the fundamental, the sensitivity of the nonlinear harmonic mechanism is not expected to be significantly greater than that of the fundamental. In this paper, we study the effects of electron beam quality, more specifically, emittance, energy spread, and peak current, on the nonlinear harmonics in a 1.5-Angstrom FEL, and show that the decline in the harmonic emission roughly follows that of the fundamental. (C) 2002 Elsevier Science B.V. All rights reserved.
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| 48. |
- Björneholm, Olle, et al.
(författare)
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Free clusters studied by core-level spectroscopies
- 2009
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576 .- 0167-5087. ; 601:1-2, s. 161-181
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Forskningsöversikt (refereegranskat)abstract
- In this review we describe the development and current status of free clusters studied using core-level spectroscopies. This topic ranges from simple model systems, such as rare gas clusters, to molecular clusters, and clusters of solids, held together by ionic, covalent and metallic bonding.
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| 49. |
- Bohgard, Mats, et al.
(författare)
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MeV Protons for the Characterization of Aerosols in Work Environments
- 1981
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Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - 0167-5087. ; 181:1-3, s. 459-463
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Tidskriftsartikel (refereegranskat)abstract
- In this paper the advantages of accelerator-based chemical analysis of work environment aerosols are discussed. Use of the PIXE method is central, but in order to take full advantage of the possibilities of an accelerator laboratory, it should be combined with nuclear methods such as particle-induced nuclear reactions and/or particle scattering for simultaneous measurements of light elements. It is also important to develop optimum sampling techniques for the analytical methods required. Some information about the current set-up in Lund is given. In a companion paper, the potential of PIXE for work environment tasks is illustrated by a summary of the design of two major studies. Some results are also included.
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| 50. |
- Boisvert, V, et al.
(författare)
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Characterization of oxygen dimer-enriched silicon detectors
- 2005
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Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - : Elsevier BV. - 0167-5087 .- 0168-9002. ; 552:1-2, s. 49-55
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Tidskriftsartikel (refereegranskat)abstract
- Various types of silicon material and silicon p(+)n diodes have been treated to increase the concentration of the oxygen dimer (02) defect. This was done by exposing the bulk material and the diodes to 6 MeV electrons at a temperature of about 350 degrees C. FTIR spectroscopy has been performed on the processed material confirming the formation of oxygen dimer defects in Czochralski silicon pieces. We also show results from TSC characterization on processed diodes. Finally, we investigated the influence of the dimer enrichment process on the depletion voltage of silicon diodes and performed 24 GeV/c proton irradiations to study the evolution of the macroscopic diode characteristics as a function of fluence.
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