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D. Bar

Publications and source records attributed to D. Bar.

32 records · Page 2Linked to original sources
arXiv2006

Advances in imaging THGEM-based detectors

The thick GEM (THGEM) [1] is an "expanded" GEM, economically produced in the PCB industry by simple drilling and etching in G-10 or other insulating materials (fig. 1). Similar to GEM, its operation is based on electron gas avalanche multiplication in sub-mm holes, resulting in very high gain and fast signals. Due to its large hole size, the THGEM is particularly efficient in transporting the electrons into and from the holes, leading to efficient single-electron detection and effective cascaded operation. The THGEM provides true pixilated radiation localization, ns signals, high gain and high rate capability. For a comprehensive summary of the THGEM properties, the reader is referred to [2, 3]. In this article we present a summary of our recent study on THGEM-based imaging, carried out with a 10x10 cm^2 double-THGEM detector.

physics.med-ph↗
arXiv2006

Thick GEM-like (THGEM) detectors and their possible applications

Thick GEM-like (THGEM) electrodes are robust, high gain gaseous electron multipliers, economically-manufactured by standard drilling and etching of thin printed circuit board or other materials. Their operation and structure are similar to that of standard GEMs but with 5 to 20-fold expanded dimensions. Due to the larger hole dimensions they provide up to 10^5 and 10^7 charge multiplication, in a single- and in two-electrode cascade, respectively. The signal rise time is of a few ns and the counting-rate capability approaches 10 MHz/mm^2 at 10^4 gains. Sub-mm localization precision was demonstrated with a simple, delay-line based 2D readout scheme. These multipliers may be produced in a variety of shapes and sizes and can operate in many gases. They may replace the standard GEMs in many applications requiring very large area, robust, flat, thin detectors, with good timing and counting-rate properties and modest localization. The properties of these multipliers are presented in short and possible applications are discussed.

physics.ins-det↗
arXiv2006

The effects of related experiments

The effects of the experiment itself upon the obtained results and, especially, the influence of a large number of experiments are extensively discussed in the literature. We show that the important factor that stands at the basis of these effects is that the involved experiments are related and not independent and detached from each other. This relationship takes, as shown here, different forms for different situations and is found in entirely different physical regimes such as the quantum and classical ones.

physics.data-an↗
arXiv2006

The band-gap structure and the singular character of the bounded large array of potential barriers

The bounded one dimensional multibarrier potential shows signs of chaos, phase transition and a transmission probability of unity for certain values of its total length $L$ and the ratio $c$ of total interval to total width. Like the infinite Kronig-Penney system, which is arranged along the whole spatial region, the bounded multibarrier potential has a band-gap structure in its energy spectrum. But unlike the Kronig-Penney system, in which the gaps disappear for large energies, these gaps do not disappear for certain values of $L$ and $c$. The energy is discontinuous even in parts of the spectrum with no gaps at all. These results imply that the energy spectrum of the bounded multibarrier system is singular.

quant-ph↗
arXiv2005

The effect of increasing the rate of repetitions of classical reactions

Using quantum theory operator methods we discuss the general reversible reactions $A_1+A_2+... A_r \leftrightarrow B_1+B_2+... +B_s$, where $r$ and $s$ are arbitrary natural positive numbers. We show that if either direction of the reaction is repeated a large number of times $N$ in a finite total time $T$ then in the limit of very large $N$, keeping $T$ constant, one remains with the initial reacting particles only. We also show that if the reaction evolves through different possible paths of evolution, each of them beginning at the same side of the reaction, proceeds through different intermediate consecutive reactions and ends at the other side, then one may ``realize'' any such path by performing in a dense manner the set of reactions along it. The same results are also numerically demonstrated for the specific reversible reaction $A+B \leftrightarrow A+C$. We note that similar results have been shown to hold also in the quantum regime.

physics.data-an↗
arXiv2004

Internet websites statistics expressed in the framework of the Ursell-Mayer cluster formalism

We show that it is possible to generalize the Ursell-Mayer cluster formalism so that it may cover also the statistics of Internet websites. Our starting point is the introduction of an extra variable that is assumed to take account, as will be explained, of the nature of the Internet statistics. We then show, following the arguments in Mayer, that one may obtain a phase transition-like phenomena

physics.data-an↗
arXiv2004

Diffusion-limited reaction for the one-dimensional trap system

We have previously discussed the one-dimensional multitrap system of finite range and found the somewhat unexpected result that the larger is the number of imperfect traps the higher is the transmission through them. We discuss in this work the effect of a small number of such traps arrayed along either a constant or a variable finite spatial section. It is shown that under specific conditions, to be described in the following, the remarked high transmission may be obtained for this case also. Thus, compared to the theoretical large number of traps case these results may be experimentally applied to real phenomena

physics.class-ph↗
arXiv2004

Time-resolved fast neutron imaging: simulation of detector performance

We have analyzed and compared the performance of two novel fast-neutron imaging methods with time-of-flight spectroscopy capability. Using MCNP and GEANT code simulations of neutron and charged-particle transport in the detectors, key parameters such as detection efficiency, the amount of energy deposited in the converter and the spatial resolution of both detector variants have been evaluated.

physics.ins-det↗
arXiv2004

Phase transition in the bounded one-dimensional multitrap system

We have previously discussed the diffusion limited problem of the bounded one-dimensional multitrap system where no external fiel is included and pay special attention to the transmission of the diffusing particles through the system of imperfect traps. We discuss here the case in which an external field is included to each trap and find not only the transmission but also the energy associated with the diffusing particles in the presence and absence of such fields. From the energy we find the specific heat $C_h$ and show that for certain values of the parameters associated with the multitrap system it behaves in a manner which is suggestive of phase transition. Moreover, this phase transition is demonstrated not only through the conventional single peak at which the specific heat function is undifferentiable but also through the less frequent phenomenon of double peaks.

physics.class-ph↗
arXiv2003

Dynamical effects of a one-dimensional multibarrier potential of finite range

We discuss the properties of a large number N of one-dimensional (bounded) locally periodic potential barriers in a finite interval. We show that the transmission coefficient, the scattering cross section $σ$, and the resonances of $σ$ depend sensitively upon the ratio of the total spacing to the total barrier width. We also show that a time dependent wave packet passing through the system of potential barriers rapidly spreads and deforms, a criterion suggested by Zaslavsky for chaotic behaviour. Computing the spectrum by imposing (large) periodic boundary conditions we find a Wigner type distribution. We investigate also the S-matrix poles; many resonances occur for certain values of the relative spacing between the barriers in the potential.

quant-ph↗
arXiv2002

Phase transitions in a one-dimensional multibarrier potential of finite range

We have previously studied properties of a one-dimensional potential with $N$ equally spaced identical barriers in a (fixed) finite interval for both finite and infinite $N$. It was observed that scattering and spectral properties depend sensitively on the ratio $c$ of spacing to width of the barriers (even in the limit $N \to \infty$). We compute here the specific heat of an ensemble of such systems and show that there is critical dependence on this parameter, as well as on the temperature, strongly suggestive of phase transitions.

quant-ph↗
arXiv2002

Quantum field theory and dense measurement

We show, using quantum field theory, that performing a large number of identical repetitions of the same measurement does not only preserve the initial state of the wave function (the Zeno effect), but also produces additional physical effects. We first demonstrate that a Zeno type effect can emerges also in the framework of quantum field theory, that is, as a quantum field phenomenon. We also derive a Zeno type effect from quantum field theory for the general case in which the initial and final states are different. The basic physical entities dealt with in this work are not the conventional once-perfomed physical processes, but their $n$ times repetition where $n$ tends to infinity. We show that the presence of these repetitions entails the presence of additional excited state energies, and the absence of them entails the absence of these excited energies. We also show that in the presence of these repetitions the Schroedinger equation may be derived from the functional generalization of quantum mechanics.

quant-ph↗