Pulse shape simulation for segmented true-coaxial HPGe detectors

A new package to simulate the formation of electrical pulses in segmented true-coaxial high purity germanium detectors is presented. The computation of the electric field and weighting potentials inside the detector as well as of the trajectories of the charge carriers is described. In addition, the treatment of bandwidth limitations and noise are discussed. Comparison of simulated to measured pulses, obtained from an 18-fold segmented detector operated inside a cryogenic test facility, are presented.     

Matrix formalism and singular-value decomposition for the location of gamma interactions in segmented HPGe detectors

Modern coaxial and planar HPGe detectors allow a precise determination of the energies and trajectories of the impinging gamma-rays. This entails the location of the gamma interactions inside the crystal from the shape of the delivered signals. This paper reviews the state of the art of the analysis of the HPGe response function and proposes methods that lead to optimum signal decomposition. The generic matrix method allows fast location of the interactions even when the induced signals strongly overlap.     

Universal relations for the strongly-interacting Fermi gas

Shina Tan has derived some universal relations that hold for any state of a system consisting of fermions with two spin states that have a large scattering length. These relations involve an intensive quantity called the contact that measures the number of pairs of atoms that are very close together. We show how these relations can be derived in the framework of quantum field theory using standard renormalization methods and the operator product expansion. They allow the contact density to be identified as the expectation value of a local operator constructed out of quantum fields.     

Reference electrodes for low-temperature gas sensors

The behavior of sodium oxide bronzes in contact with sodium-conducting solid electrolytes in atmospheres of oxygen, carbon dioxide, hydrogen sulfide, and humid air was investigated. The exchange currents at the Na_xCoO_y/NASICON interface was determined. It is shown that among the sodium-cobalt oxide bronzes the β-phase of the composition Na_0.6CoO₂ is the most reversible one (exchange current 236 μA/cm²). Paper presented at the 1st Euroconference on Solid State Ionics, Zakynthos, Greece, 11–18 Sept. 1994     

Clustering of continuous distributions of charge

An investigation is carried out of the association and clustering of equimolar mixtures of oppositely charged Gaussian charge distributions (CDs) of the form ～ exp ( ? r²?/2α²), where r is the separation between the centres of charge and α governs the extent of charge spreading (α→0 is the point charge limit). The results of molecular dynamics (MD) and Ornstein–Zernike integral equation with the mean spherical approximation (MSA) and hypernetted-chain (HNC) closures are compared for these systems. The MD and HNC radial distribution functions, g(r), agree very well for not too small α. The MD and MSA, g(r), also agree well for α ≈ 1 and greater. The potential energy per particle for the three methods also agrees well over a wider range of α values, better than might be expected from inspection of the radial distribution functions, because the dominant contributions to U come predominantly from intermediate and long distance ranges where there is good agreement between the g(r) from the MSD and HNC closures. The nature of the association and clustering of the charges as a function of α is explored through the mean nearest neighbour distance for unlike and like species and the mean and root-mean-square force. The velocity and force autocorrelation functions are also calculated; they show increasingly oscillatory behaviour in the small α limit, originating in vibrations of a pair of CDs of opposite sign.     

Preoscillation charge distributions in a cylindrical magnetron

Based on notions concerning the nature of diffuse motion of electrons in a magnetron which were expounded in previous papers by the authors with application to a plane magnetron, a diffusion equation is derived for a cylindrical magnetron. By solving this equation it is clarified that at least for H > 1.5 H_cr the major part of the electron cloud is in a mode close to the static synchronous mode.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 15, No. 2, pp. 282–290, February, 1972.     

Pulse shapes from electron and photon induced events in segmented high-purity germanium detectors

Experiments built to search for neutrinoless double beta-decay are limited in their sensitivity not only by the exposure but also by the amount of background encountered. Radioactive isotopes in the surrounding of the detectors which emit gamma-radiation are expected to be a significant source of background in the GERmanium Detector Array, GERDA. Methods to select electron induced events and discriminate against photon induced events inside a germanium detector are presented in this paper. The methods are based on the analysis of the time structure of the detector response. Data were taken with a segmented GERDA prototype detector. It is shown that the analysis of the time response of the detector can be used to distinguish multiply scattered photons from electrons. PACS 23.40.-s; 14.60.Pq;29.40.-n     

Universal scaling of conserved charge in stochastic diffusion dynamics

We explore the Kibble-Zurek scaling of conserved charge using stochastic diffusion dynamics.The characteristic scales τKZ and lKZ are determined and used to properly rescale the traditional correlation function and cumulant.We construct universal functions for the two-point correlation C(y1-y2;τ)and the second-order cumulant K(△y,τ)of the conserved charge in the critical regime,both of which are,near the critical point,insensitive to both the initial temperature and a parameter in the mapping between the 3 D Ising model and the hot QCD system.     

Pseudopotential charge distributions for characteristic k-states on the Fermi surface of aluminium

Stimulated by the existence of very anisotropic scattering effects in aluminium we have calculated wave functions and charge distributions for some selected k-state on the Fermi surface. For this purpose the pseudopotential method together with Ashcroft's potential has been used. The results show marked and characteristic differences in the various charge distributions and allow a qualitative interpretation of the scattering anisotropies observed in Hall effect experiments.     

A prototype scalable readout system for micro-pattern gas detectors

A scalable readout system(SRS) is designed to provide a general solution for different micro-pattern gas detectors in various applications.The system mainly consists of three kinds of modules:the ASIC card,the adapter card and the front-end card(FEC).The ASIC cards,mounted with particular ASIC chips,are designed for receiving detector signals.The adapter card is in charge of digitizing the output signals from several ASIC cards.The PEC,edged-mounted with the adapter,has field-programmable gate array(FPGA)-based reconfigurable logic and I/O interfaces,allowing users to choose different ASIC cards and adapters for different experiments,which expands the system to various applications.The FEC transfers data through Gigabit Ethernet protocol realized by a TCP processor(SiTCP) IP core in FPGA.By assembling a flexible number of FECs in parallel through Gigabit Ethernet,the readout system can be tailored to specific sizes to adapt to the experiment scales and readout requirements.In this paper,two kinds of multi-channel ASIC chip,VA140 and AGET,are applied to verify the scalability of this SRS architecture.Based on this VA140 or AGET SRS,one FEC covers 8 ASIC(VA140) cards handling 512 detector channels,or 4 ASIC(AGET) cards handling 256 detector channels,respectively.More FECs can be assembled in crates to handle thousands of detector channels.     

Universal conductance distributions in the crossover between diffusive and localization regimes

The full distribution of the conductance P(G) in quasi-one-dimensional wires with rough surfaces is analyzed from the diffusive to the localization regime. In the crossover region, where the statistics is dominated by only one or two eigenchannels, the numerically obtained P(G) is found to be independent of the details of the system with the average conductance as the only scaling parameter. For < or =2e(2)/h, the shape of P(G) remarkably agrees with those predicted by random matrix theory for two fluctuating transmission eigenchannels.     

Isospin restrictions on charge distributions in charmed-particle decays

The isospin properties of the semileptonic and non-leptonic charm-changing weak interactions lead to restrictions on the branching ratios of the different charge states that can occur in multi-particle decays of charmed particles. Upper and lower bounds imposed by isospin invariance on these ratios, and on the average number of charged decay products, are calculated for various charmed-particle decay modes. Simultaneous bounds on the branching ratios of two different charge distributions in the same decay mode, or in isospin-related decay modes, are presented. Branching ratios are also calculated under the statistical postulate that all the allowed invariant isospin channels contribute equally and incoherently in each decay mode.     

A study of charge distributions in inelastic proton-proton collisions

Charge distributions for the secondaries from inelastic proton-proton collisions are studied by means of new data from an experiment at 12 and 24 GeV/c (2 m HBC at CERN). By comparison with π^±p data at 16 GeV/c, the inclusive charge distributions for the fragments of an incident proton and pion, respectively, are analysed. In addition, the cross sections for charge exchange between cms hemispheres are presented for the various charged-particle multiplicities. For events with no more than one neutral particle, charge and baryon exchange between cms hemispheres are compared to those between clusters. For the inelastic two-prong reactions, the two-dimensional distributions in longitudinal phase space are presented.     

Quantum and classical binomial distributions for the charge transmitted through coherent conductor

We discuss controversial results for the statistics of charge transport through coherent conductors. Two distribution functions for the charge transmitted was obtained previously, one actually coincides with classical binomial distribution, the other is different, and we call it here quantum binomial distribution. We show that high-order charge correlators, determined by the either distribution functions, all can be measured in different setups. The high-order current correlators, starting with the third order, reveal (missed in previous studies) special oscillating frequency dependence on the scale of the inverted time flight from the obstacle to the measuring point. Depending on setup, the oscillating terms give substantially different contributions.