Spread In Arrival Times Research Articles

Investigating the effect of depth of interaction on coincidence time resolution

Abstract The timing properties of scintillator-based detectors are a matter of importance in a wide range of fields. As fast scintillators progress and the sensors that preserve the quantized nature of the luminescent signal evolve, the optical transfer time may not always be negligible in ultra-fast time measurement. The present paper discusses the implications of this in a specific configuration for ultra-fast time measurement. To this end, we consider factors influencing the time spread such as the distribution of depth of interaction, non-instantaneous scintillation emission mechanism, and optical transport kinetics. Although such a topic has previously been studied by researchers, the aim of this work is focused on analyzing the detailed factors that govern arrival time spread. From these factors, we are able to obtain the post-interaction time spread, and we then derived the optical transfer time spread (OTTS) by a weighted sum of post-interaction time spread based on the cumulative density function of the depth of interaction. Based on the rejection sampling method, we could obtain the set of arrival times by the OTTS, and then the coincidence time resolution of radioactive sources was calculated. Consequently, we found that the difference in the attenuation coefficient causes the difference in the arrival time distribution, but it does not lend a significant contribution to the coincidence time resolution. In addition, when radiation with different energies is incident, the emission mechanism has a dominant effect on the time resolution, and thus incident radiation having higher energy in the same detector system has a higher light yield, which can exhibit better timing resolution compared to radiation with relatively low energy.

Neutrino signals of lightcone fluctuations resulting from fluctuating spacetime

One of the most common expectations of a quantum theory of gravity is that spacetime is uncertain or fluctuating at microscopic scales, making it a stochastic medium for particle propagation. Particles traversing this spacetime may experience fluctuations in travel times or velocities, together referred to as lightcone fluctuations, with even very small effects potentially accumulating into observable signals over large distances. In this work we present a heuristic model of lightcone fluctuations and study the resulting modifications to neutrino propagation, including neutrino decoherence and arrival time spread. We show the expected scale of such effects due to ``natural'' Planck scale physics and consider how they may be observed in neutrino detectors, and compare the potential of neutrinos to $\ensuremath{\gamma}$-ray astronomy. Using simulations of neutrino mass states propagating in a fluctuating environment, we determine an analytic decoherence operator in the framework of open quantum systems to quantitatively evaluate neutrino decoherence resulting from lightcone fluctuations, allowing experimental constraints on neutrino decoherence to be connected to Planck scale fluctuations in spacetime and $\ensuremath{\gamma}$-ray results.

Optimality of transmitter location in a wireless network with RAKE receivers

In this study, the authors consider a transmitter location finding problem in a wireless network equipped with RAKE receivers. In these types of receivers, fading is mitigated in the wireless communication channel. This fading is due to multiple versions of the transmitted signal at a spread of arrival times. In the RAKE receiver, a certain number of them are needed – called strongest – to have received signal strength above a threshold. In the optimum location finding problem, the number of bad receiving points determined based on a proposed error function is minimised. Two different criteria, which are defined through the RAKE receiver architecture, form this error function. Thus, a multi-objective optimisation problem is herein solved in order to solve transmitter location finding problem. The proposed optimisation method contains a jointly designed ray tracing engine (RTE) and genetic algorithm (GA). The algorithm is applied on a sample environment, which is fully simulated with RTE. The GA, which is integrated to RTE, determines optimum location(s) of transmitters. The results show that the proposed method perfectly finds the best locations of the minimum number of transmitters.

Corner-cube retro-reflector instrument for advanced lunar laser ranging

Lunar laser ranging (LLR) has made major contributions to our understanding of the Moon's internal structure and the dynamics of the Earth-Moon system. Because of the recent improvements of the ground-based laser ranging facilities, the present LLR measurement accuracy is limited by the retro-reflectors currently on the lunar surface, which are arrays of small corner-cubes. Because of lunar librations, the surfaces of these arrays do not, in general, point directly at the Earth. This effect results in a spread of arrival times, because each cube that comprises the retroreflector is at a slightly different distance from the Earth, leading to the reduced ranging accuracy. Thus, a single, wide aperture corner-cube could have a clear advantage. In addition, after nearly four decades of successful operations the retro-reflectors arrays currently on the Moon started to show performance degradation; as a result, they yield still useful, but much weaker return signals. Thus, fresh and bright instruments on the lunar surface are needed to continue precision LLR measurements. We have developed a new retro-reflector design to enable advanced LLR operations. It is based on a single, hollow corner cube with a large aperture for which preliminary thermal, mechanical, and optical design and analysis have been performed. The new instrument will be able to reach an Earth-Moon range precision of 1-mm in a single pulse while being subjected to significant thermal variations present on the lunar surface, and will have low mass to allow robotic deployment. Here we report on our design results and instrument development effort.

The energy spectrum of primary cosmic rays estimated by using the arrival time spread of air shower particles

The primary energy of cosmic rays in the energy region above 10 16 eV has been studied with the use of a compact extensive air shower (EAS) array which consists of 8 scintillation counters in 200m 2 area. We report on the simulation results for estimating the primary energy and its spectrum by using Linsley's method, and on the improvement of the determination accuracy of the primary energy by applying the zenith angle restricted observation of EAS muons with the new array as well as a brief description of the apparatus.

Primary energy spectrum of cosmic rays obtained by arrival time spread of particles in EAS

The Large Area Air Shower (LAAS) group has been performing a network observation of extensive air showers (EAS) by using compact arrays. According to J. Linsley, the primary energy of EAS can be estimated from the spread of the arrival times of EAS particles, even with a small array. A shift register system for clocking the arrival times was installed in an array (OUS1) which is located in Okayama University of Science. Analyzing the OUS1 data, we obtained the primary energies of large air showers.

Real time ultrafast spectroscopy of shock front pore collapse

Shock-wave induced nanopore collapse (average diameter 100 nm) at 4.2 GPa in a 3-μm-thick poly-methyl methacrylate (PMMA) layer is measured in real time using coherent anti-Stokes Raman spectroscopy (CARS). Pore collapse is monitored via CARS transitions of a dye probe embedded in the porous medium. A pore collapse time constant of 3 ns in PMMA is in poor agreement with hydrodynamic pore collapse models but in excellent agreement with a viscoplastic model that uses the “shock viscosity” determined from the PMMA viscoelastic response to shock. The shock viscosity is more than 12 orders of magnitude smaller than the ordinary viscosity. A downstream gauge of polycrystalline anthracene monitors changes in the steeply rising shock front (<25 ps rise time) after passing through the porous medium or a scattering medium with 100-nm-diam scatterers. The anthracene is a two-dimensional (2D) shock gauge that provides a time sequence of CARS spectra S(t,λ). The 2D gauge is shown to be capable of discriminating between a shock front that gradually rises with time constant tr or a bunch of steeply rising shocklets with an arrival time spread equal to tr. The transmitted shock front is shown to consist of a bunch of steep shocklets with an arrival time spread of 550 ps.

Modelling of photoinduced discharge of photoreceptors under pulsed photoexcitation: small and large signal xerographic time-of-flight analysis

A general theoretical model for the photoinduced discharge of a charged photoreceptor is developed by considering non-dispersive charge transport in a high-resistivity semiconductor (insulator in the dark), point form representations of Ohm's law, Gauss's law and Maxwell's equations for the total current, and the trapping and release rate equations. The rate equations incorporate arbitrary strengths of trapping, release, and trap saturation for a single level of traps. In contrast to most previous works, the trap filling effect is fully incorporated into the model which allows its effects to be studied. These equations were combined to create a single general second-order nonlinear partial differential equation which governs the behaviour of the electric field during photoinduced discharge. The general differential equation for the field was then solved numerically using boundary conditions that are representative of pulsed illumination. Solutions were obtained under low injection (0.1% of surface charge) and high injection (10%, 50%, and 99% of surface charge) conditions. Trapping parameters in the model could be adjusted to represent a wide range of trapping conditions including trap saturation. In each case, the time evolution of the discharge was monitored by calculating the trapped and untrapped charge densities at regular intervals throughout the discharge. By differentiating the calculated surface voltage V, the rate discharge dV/dt was also monitored, because it is an experimentally accessible quantity that is widely used in xerographic time-of flight measurements. Results obtained under low injection conditions demonstrated that the dispersion in the charge packet increased with larger values of the mobility reduction factor and smaller values of the trapping and release rates, and r, respectively. Increased charge packet dispersion was seen to cause increased dispersion in dV/dt near the transit time. The temporal spread of arrival times analytically predicted by the Schmidlin equation was found to be in good agreement with the present model in the small signal mode. High injection results illustrated that the dispersion of the charge packet and |dV/dt| increased dramatically with increased injection strength. Under extremely high injection, the dispersion is primarily determined by the amount of injection. The effect of trap saturation under high injection conditions was also investigated. Increased trap saturation caused the packet to become more spread out during the early stages of the discharge. This caused significant decay in |dV/dt| before the shallow-trap controlled transit time, but did not significantly affect the overall dispersion in |dV/dt|.

A non conventional method of UHE cosmic ray detection

A mini array of eight plastic scinitillators (Bicron B-416) each viewed by photomultiplier tubes (EMI 9807B) covering a total carpet area of 2 m 2 is installed in the roof of the Physics Building, Gauhati University, for the study of Giant Extensive Air Showers produced by UHE cosmic rays in the atmosphere. All the eight detectors are connected to a data acquisition system capable of recording arrival time spread of secondary particles up to 2.5 μs. Fast electronic circuits are employed to measure the density of shower particles as well as their arrival time spread with a resolution of 10 ns. The array is in operation since September 1996. We present here the method in detail and a theoretical estimation of the measured parameters.

Analysis of integrate-and-fire neurons: synchronization of synaptic input and spike output.

A new technique for analyzing the probability distribution of output spikes for the integrate-and-fire model is presented. This technique enables us to investigate models with arbitrary synaptic response functions that incorporate both leakage across the membrane and a rise time of the postsynaptic potential. The results, which are compared with numerical simulations, are exact in the limit of a large number of small-amplitude inputs. This method is applied to the synchronization problem, in which we examine the relationship between the spread in arrival times of the inputs (the temporal jitter of the synaptic input) and the resultant spread in the times at which the output spikes are generated (output jitter). The results of previous studies, which indicated that the ration of the output jitter to the input jitter is consistently less than one and that it decreases for increasing numbers of inputs, are confirmed for three classes of the integrate-and-fire model. In addition to the previously identified factors of axonal propagation times and synaptic jitter, we identify the variation in the spike-generating thresholds of the neurons and the variation in the number of active inputs as being important factors that determine the timing jitter in layered networks. Previously observed phase differences between optimally and suboptimally stimulated neurons may be understood in terms of the relative time taken to reach threshold.

A new experimental setup to study UHE cosmic ray based on measurement of arrival time spread of secondary particles from EAS

A new experimental setup has been developed in the Mini Array Research Laboratory, Gauhati University to study UHE Cosmic rays by measuring the arrival time spread of the secondary particles from Extensive Air Showers (EAS) produced by primary particles of energy ≥10 15 eV. The setup consists of fast timing detectors, necessary electronics and microprocessor based data acquisition system. In this paper we discuss details about the hardware and software aspect of the experimental setup.

Study of a mini-array for the Linsley effect in cosmic-ray air showers

The arrival-time distribution of shower particles far from the core has been measured as a function of shower axis distance at the Akeno Observatory by a cluster of 64 scintillators (total area 16 m2) located near the centre of the 1 km2 array. More than 3500 1 km2 array events and about 300 20 km2 array events have been analysed. The authors compare parameters tau (exponential fit to arrival times), sigma (conventional dispersion) and tr (rise time) for the specification of the spread in arrival times. From a measurement of time spread, the shower axis distance can be determined with an uncertainty of 25 to 30% with this detector system. The resulting uncertainty in shower size, including a 60% uncertainty in particle density measurement, is 120 to 140%. The resultant smearing of changes in slope of the frequency spectrum of incident showers is calculated. The smearing masks all but the gross changes in slope. The method may be useful for anisotropy studies, when a system for finding direction is included.

On the collapse and violent relaxation of protoglobular clusters

During the formation of stellar systems such as globular clusters, low-mass subcondensations which eventually form stars must retain a geometric size throughout the collapse process that is small compared to the characteristic distance separating them. If the local velocity dispersion of the subcondensations is small, the overall dimension of the system can decrease substantially before reaching a dynamical equilibrium state. The maximum collapse factor is deduced by examining the growth of the velocity dispersion and the spread in arrival times at the origin caused by local and global fluctuations. It is shown, analytically as well as in a series of N-body simulations, that the maximum reduction in the characteristic dimension of a system of N fragments with an initial homogeneous distribution subject to N exp 1/2 fluctuations is proportional to N exp 1/3. Direct physical collisions between low-mass subcondensations are therefore unlikely to occur in protoglobular clusters. The results are discussed in the context of fragmentation and violent relaxation.

Longitudinal Diffusion Coefficients Misnamed

In ion drift velocity measurements, the spread in arrival time of the drifting ions has led to evaluation of a so-called longitudinal diffusion coefficient, ${D}_{L}$. It is shown that the spread in arrival times is attributable to the simple statistical fluctuation associated with addition of many nearly random free paths. On this basis, the value of ${D}_{L}$ derived from the data on the assumption that a true diffusion, dependent on an ion density gradient, is involved is shown to rise as the square of the drift velocity. Such a rise is observed experimentally, setting in when the drift velocity exceeds a minimum value. The real diffusion coefficient is then less than that reported as ${D}_{L}$.