Comments on “A correction algorithm for detector nonuniformity in computed tomography”

In this paper we comment on the publication “A correction algorithm for detector nonuniformity in computed tomography” by Sun et al. (Nucl. Instr. and Meth. A 505 (2003) 552).     

Optimal measurement of signal over noise ratio with constrained filter transfer functions

The problem of optimal measurement of a signal in presence of noise is treated in detail by Baldinger and Franzen (Adv. Electron. Electron Phys. 8 (1956) 225), Radeka and Karlovac (Nucl. Instr. and Meth. 52 (1967) 86) and Gatti and Manfredi (La Rivista Nuovo Cimento 9(1) (1986) 1), and the filter transfer function optimizing the signal over noise ratio is well known. These calculations deals with unconstrained optimization, that is the filter transfer function may assume any value. In this paper functional analysis techniques are applied to optimize the filter transfer function in presence of linear constraints.     

Uranium fluoride and metallic uranium as target materials for heavy-element experiments at SHIP

In this contribution we describe the production and application of uranium targets for synthesis of heavy elements. The targets are prepared from uranium fluoride (UF₄) and from metallic uranium with thin carbon foils as backing. Targets of UF₄ were produced by thermal evaporation in a similar way as the frequently applied targets out of Bi, Bi₂O₃, Pb, PbS, SmF₃, and NdF_3, prepared mostly from isotopically enriched material [Birgit Kindler, et al., Nucl. Instr. and Meth. A 561 (2006) 107; Bettina Lommel, et al., Nucl. Instr. and Meth. A 561 (2006) 100]. In order to use more intensive beams and to avoid scattering of the reaction products in the target, metallic uranium is favorable. However, evaporation of metallic uranium is not feasible at a sustainable yield. Therefore, we established magnetron sputtering of metallic uranium. We describe production and properties of these targets. First irradiation tests show promising results.     

Analytical estimation of dynamic apertures limited by the wigglers in storage rings

By applying the general dynamic aperture formulae for the multipoles in a storage ring developed by Gao (Nucl. Instr. and Meth. A 451 (2000) 545), in this paper, we give the analytical formulae for the dynamic apertures limited by the wigglers in storage rings and their validities have been confirmed by comparing with numerical simulation results.     

Optical analysis of spherical mirrors of telescopes: The lens-less Schmidt case

The light distribution on the focal surface of spheric mirrors designed for telescopes in the lens-less Schmidt configuration is calculated analytically using geometrical optics.This analysis was motivated by considerations of the design of the AUGER fluorescence detector [J. Abraham, et al., Nucl. Instr. and Meth. A 533 (2004) 50]. Its geometrical parameters are used in the examples.     

Boron foils for RDDS experiment

Application of the deposition method based on the vibrational motion of micro particles in an electrostatic field [I. Sugai, Nucl. Instr. and Meth. A 397 (1997) 81] is described for the production of isotopic ¹¹B foils. The method proved suitable for target production of this typically brittle material when a very flat target surface was required. The goal to produce ¹¹B targets of 160–350 μg/cm² was achieved by depositing the boron on a thin foil substrate, such as Nb and Sn. The coated foil was stretched flat before it was mounted on a frame.     

Covariances between gamma-ray energies

Covariances between experimental data are as significant as variances both in the evaluation of uncertainties and to perform statistical tests. If standard data are used in calibrations, covariances must be taken into account. Covariances are also necessary in order to update values every time when new data are obtained. In this paper we determined covariances between the most important gamma-ray energies for use in Ge-semiconductor detectors calibration recently published by Helmer and van der Leun (Nucl. Instr. Meth. A 450 (2000) 35).     

The kinematic separator VASSILISSA performance and experimental results

Within the last five years the kinematic separator VASSILISSA [A.V. Yeremin et al., Nucl. Instr. and Meth. A 274 (1989) 528; and A.V. Yeremin et al., Preprint JINR E15-90-347, Dubna 1990] has been used for investigations of neutron deficient evaporation residues (ER) produced in heavy ion fusion reactions. In the course of this work optimization of the ion-optical and other systems of the separator including improvements of the focal plane detector system have been made. As a result, the separation efficiency values ranging from 3 to 30% were achieved for ERs produced in the reactions with heavy ions ranging from ¹⁶O to ⁴⁰Ar. The suppression factors >10¹⁹ for the full energy beam particles and >10⁴ for multinucleon transfer reaction products were achieved. The results of the performed experiments illuminating the separator performance are briefly presented.     

Wave-packet study of hyperthermal alkali ion neutralization at metal surfaces

Resonant neutralization of 50 eV Na⁺ ions impinging on Cu(100) surfaces is studied, focusing on events where the incident particle undergoes multiple collisions within the first surface layers of the samples. Specific trajectories are generated, via molecular dynamics simulations, in which the projectile comes out interacting, on long time scales, either with a single surface atom or with the valence band of the solid. The resulting three-body problem is modelled by a semi-empirical, one-electron potential that incorporates: (i) the effect of a plane metal surface, with projected band gap, and (ii) the contributions of the projectile, whose charge state will be eventually investigated, as well as of the substrate atom. On this basis, a wave-packet propagation algorithm is constructed to establish the reverse evolution of the affinity orbital of the projectile. The calculated neutralization probability is compared with the results of a model Hamiltonian of the Anderson-Newns type (Nucl Instr Meth 2009;B267:578) and is found in good agreement with the angle resolved neutral fraction measured by Keller et al. (Phys Rev Lett 1995;75:1654).     

Time dependent analysis of short-range monopole wake fields driven by accelerated electron beams

Combinations of integral transforms and Green's function are employed in order to obtain the distribution of the short-range monopole wake fields driven by accelerated electron beams in a cylindrical cavity. This constituted an alternative but simpler and more versatile method to the normal mode expansion which we used earlier to solve for such a distribution (Salah and Dolique, Nucl. Instr. and Meth. A 431 (1999) 27). Whereas direct comparisons of the resulting analytical expressions are found difficult to directly compare, numerical illustration of results obtained from both approaches show excellent agreements and hence confirm the fact that both approaches are equivalent.     

A technique of measuring and correcting emittance dilutions due to accelerator structure misalignments

This paper describes a method of reducing the transverse emittance dilution in linear colliders due to transverse wakefields arising from misaligned accelerator structures. The technique is a generalization of the Wake-Free [T.O. Raubenheimer, Nucl. Instr. and Meth. A 306 (1991) 61] correction algorithm. The structure errors are measured locally by varying the bunch charge and/or bunch length and measuring the change in the beam trajectory. The structure errors can then be corrected by varying the trajectory or moving the structures. The results of simulations are presented demonstrating the viability of the technique.     

BENT — A software for raytracing of X-rays on bent oblique cut crystals

A software BENT is designed for raytracing of synchrotron radiation (SR) on bent oblique cut crystals. In this software, the SR source data can be generated by other existing software such as SHADOW [B. Lai and F. Cerrina, Nucl. Instr. and Meth. A246 (1986) 337.], and the image data after raytracing by BENT is arranged in the same way as is done by SHADOW. So analysis and continued tracing by SHADOW can be performed. The software BENT is used in designing the oblique cut bent crystal monochromator of the 4W1C beamline at the Synchrotron Radiation Laboratory, BEPC. Some of the results are presented.     

Cellular automaton and Kalman filter based track search in the HERA-B pattern tracker

The paper describes track reconstruction package OTR/ITR-CATS developed for the Pattern Tracker of the HERA-B experiment. This package employs a combined approach for track reconstruction based on the use of a cellular automaton for track searching and the Kalman filter techniques for track fitting. A similar reconstruction strategy is already successfully applied to the Vertex Detector System (VDS) (Nucl. Instr. and Meth. A 489 (2002) 389). However, hit efficiencies and resolutions of the Pattern Tracker lower than those of the VDS require much more delicate implementation of the method.

The package developed has been tested on simulated data. The results of the tests regarding reconstruction efficiency, accuracy of estimates and computing time are presented.     

A detailed study of the interaction mechanisms for Si(Li) detector response functions by the direct Monte Carlo approach

A direct Monte Carlo (DMC) calculation of the complete response functions of Si(Li) detectors for low energy X-rays (keV) is proposed. Interaction mechanisms for X-rays in the sensitive volume of the detector and in the surrounding material are investigated in detail. Response functions at several energy values are calculated and compared with the corresponding experimental ones. The present approach uses a detailed simulation of individual interactions rather than the simple range formulation used by Gardner et al. [Nucl. Instr. and Meth. A242 (1986) 399] and gives better results in some cases. The physical model and calculation method presented here can be applied widely to low energy X-ray fluorescence analysis and other complicated photon spectrum analyses. In principle it is also suited for Ge detectors.     

Energy measurement of 50 MeV proton beam with a NaI(Tl) scintillator

Energy measurement of 50 MeV proton beam produced on the AVF MC-50 Cyclotron was conducted using a detector telescope with a NaI(Tl) scintillator as an E counter. Protons of various energies, elastically and inelastically scattered from the ¹²C target nucleus were measured at four different angles of 35°, 40°, 50° and 55°. We applied the chi-square method to determine the beam energy, which showed a well defined minimum chi-square corresponding to a beam energy of 49.6 ± 2.3 MeV at the 68% confidence level. Also the light output response of NaI(Tl) to proton energies between 31 and 44 MeV is linear within 0.5 MeV and is in good accord with the recent result of Romero et al. [Nucl. Instr. and Meth. A 301 (1991) 241].     

Successful test of a prototype hadron blind detector

We have constructed and tested a threshold Cherenkov detector inspired by the conceptual design of Giomataris and Charpak (Nucl. Instr. and Meth. A 310 (1991) 589). The basic design consists of a gas radiator followed by a photosensitive wire chamber using a solid Csl photocathode. The photon detector lies directly in the particle path and is required to have single photo-electron sensitivity and yet be insensitive to the passage of a charged particle. We have altered the design by adding a thin LiF window. This window allows one to separate the radiator and avalanche volumes, giving greater flexibility in the gas choices. Our detector was operated with C₂F₆ as the radiator gas at lengths of 120, 80, and 40 cm. The avalanche gas was 95%He + 5% CH₄. At 95% electron efficiency, the pion efficiency was 1/333, 1/150, and 1/100 for each of the lengths listed above.     

Characterization and improvement of thin natural diamond detectors for spectrometry of heavy ions below 1 MeV/amu

In our previous paper [V.Kh. Liechtenstein, N.V. Eremin, R. Golser, W. Kutschera, A.A. Paskhalov, A. Priller, P. Steier, Ch. Vockenhuber, S. Winkler, Nucl. Instr. and Meth. A 521 (2004) 203], first results on the evaluation of thin natural diamond-based detectors (NDDs) as an energy spectrometer for heavy ions in the energy range below 1 MeV/amu were presented. Although results were promising, the energy resolution of the detector was limited by an unexpected high-energy loss in the “dead layer” of the entrance window. In this paper, we report a significant improvement in the spectrometric properties of two highly selected and carefully treated NDDs with electrical contacts made of carbon and gold films as thin as about 10 and 20 μg/cm², respectively, instead of much thicker aluminum contacts used before. In particular, for the NDD with thin carbon contact an energy resolution of 7.6% for ¹⁹⁷Au-ions at 20.6 MeV was obtained. The energy cut-off of the detectors was reduced to 0.9 and 1.5 MeV for carbon and gold contact, respectively. The measured data on energy cut-off for different projectiles are compared with calculations, which yields an estimate of the thickness of the dead layers. Long-term irradiation runs proved stable spectroscopic performance of the detectors, in spite of the inherent “pumping” effects and imperfections of pulse height distributions. Our data suggest that NDD-based spectrometers might outperform other detector types in applications where very fast detectors with high radiation tolerance are required.     

A steering procedure for the fast vertex fitting method

The fast vertex fitting method [P. Billoir and S. Qian, Nucl. Instr. and Meth. A 311 (1992) 139] has been enhanced by a steering procedure which performs the track selection to insure the vertex fitting quality. Meanwhile, a sign error in a formula in the above publication has been corrected.     

The cathode strip chamber data acquisition electronics for CMS

Data Acquisition (DAQ) electronics for Cathode Strip Chambers (CSC) [CMS Collaboration, The Muon Project Technical Design Report, CERN/LHCC 97-32, CMS TDR3, 1997] in the Compact Muon Solenoid (CMS) [CMS Collaboration, The Compact Muon Solenoid Technical Proposal, CERN/LHCC 94-38, 1994] experiment at the Large Hadron Collider (LHC) [The LHC study group, The Large Hadron Collider: Conceptual Design, CERN/AC 1995-05, 1995] is described. The CSC DAQ system [B. Bylsma, et al., in: Proceedings of the Topical Workshop on Electronics for Particle Physics, Prague, Czech Republic, CERN-2007-007, 2007, pp. 195–198] includes on-detector and off-detector electronics, encompassing five different types of custom circuit boards designed to handle the high event rate at the LHC. The on-detector electronics includes Cathode Front End Boards (CFEB) [R. Breedon, et al., Nucl. Instr. and Meth. A 471 (2001) 340], which amplify, shape, store, and digitize chamber cathode signals; Anode Front End Boards (AFEB) [T. Ferguson, et al., Nucl. Instr. and Meth. A 539 (2005) 386], which amplify, shape and discriminate chamber anode signals; and Data Acquisition Motherboards (DAQMB), which controls the on-chamber electronics and the readout of the chamber. The off-detector electronics, located in the underground service cavern, includes Detector Dependent Unit (DDU) boards, which perform real time data error checking, electronics reset requests and data concentration; and Data Concentrator Card (DCC) boards, which further compact the data and send it to the CMS DAQ System [CMS Collaboration, The TriDAS Project Technical Design Report, Volume 2: Data Acquisition and High-level Trigger, CERN/LHCC 2002-26, 2002], and serve as an interface to the CMS Trigger Timing Control (TTC) [TTC system http://ttc.web.cern.ch/TTC/intro.html] system.Application Specific Integrated Circuits (ASIC) are utilized for analogous signal processing on front end boards. Field Programmable Gate Arrays (FPGA) are utilized on all boards in the system to provide programmability. The DAQ system has been installed and commissioned, and is ready for LHC data taking.