On the theory of generation of a polarized muon-photon shower in crystals under different initial conditions

The process of formation of a polarized muon-photon shower in crystals has been investigated under the following initial conditions: (i) a shower is generated by a high-energy longitudinally polarized initial muon and (ii) a shower is generated by a circulaly polarized high-energy γ photon. Analytical expressions have been obtained for the distribution functions of polarized shower muons and γ photons in the medium and comparative analysis of the number of shower particles under different initial conditions has been performed.     

Particle detectors for the future antiproton Paul trap of the ASACUSA experiment at CERN

Two detectors which will be used to commission a superconducting radiofrequency Paul trap for antiprotons, now being constructed at CERN and MPQ, are described. One is a microwire secondary electron emission monitor which will nondestructively measure the spatial profile of a low energy (E= 10?100 keV) antiproton beam. The other is a system of electromagnetic shower counters which will detect the secondary particles emerging from the antiproton annihilations occurring in the trap.     

Simulation of electromagnetic shower formation in a Germanium crystal

Abstract

When high-energy electrons penetrate crystalline matter, the successive processes of photon emission and pair production form an electromagnetic shower. If the incident electrons are directed along the crystal axis, the cross section for photon emission is drastically enhanced because electrons in ‘channeling’ states feel a strong electric field continuously. Experiments designed to detect this effect were performed at CERN. The results showed an anomalous peak in the energy loss spectrum of the emerging electrons. In this paper, we report results of a Monte-Carlo simulation of shower formation in a Germanium crystal. Our results agree with the experimental data more quantitatively than previous simulations. We simulated a shower formation by incident photons as well.     

Angular resolution of an array of tracking-chamber detectors for use in high-energy gamma-ray astronomy

Summary We describe a method of analysis for the reconstruction of the arrival direction of a high-energy photon impacting on the top of the atmosphere by using the directions of the particles on the shower front as measured by a ground-based array of tracking chambers uniformly distributed on a square surface; as an example, an array with enclosed surface of (120×120) m² has been considered. Estimates on the accuracy of reconstruction are given, after application of the method to computer-simulated shower directions as a function of the number of ?smapling? detectors and of their accuracy in the measurement of the ?local? shower direction. Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990.     

Implications of collider experiments for detecting cold dark matter

By investigating the space of parameters of the minimal supersymmetric extension of the Standard Model, it is shown that an observation of at least one supersymmetric particle in high-energy experiments would increase considerably the importance of highly sensitive low-energy experiments aimed at detecting cold-dark-matter particles assumed to be neutralinos, the lightest supersymmetric particles, which are stable. On the other hand, nonobservation of direct signals from dark matter in such experiments can have a pronounced effect on the strategy of high-energy searches for the light charged Higgs boson.     

Controlled Quantum Teleportation of Superposed Coherent State Using GHZ Entangled Coherent State

Controlled quantum teleportation of superposed coherent states using GHZ entangled 3-mode coherent states is studied. Proposed scheme can be implemented experimentally using linear optical components such as a symmetric lossless beam splitter, two phase-shifters and two photon counters. Fidelity is found close to unity for appreciable mean number of photons in coherent states and is 0.99 for mean photon number equal to two.

     

基于嵌入式EPICS的合肥光源储存环束流损失监测系统

针对合肥光源储存环恒流运行(Top-off)改造等性能提升的需要,研制了新型的基于嵌入式EPICS架构的储存环束流损失监测(BLM)系统,用于监测储存环中束流损失发生的位置和大小。新BLM处理器获取储存环各处双PIN型光电二极管传感器所采集的簇射电子的信号,分析处理后通过各个处理器内部的嵌入式系统所运行的EPICS程序将数据实时发布到加速器控制网络,使中控室能够实时获取束损的数据。新BLM系统能够实时对双PIN型传感器进行自检操作,排查故障隐患,提高了系统运行的效率和可靠性,经过试运行表明,新BLM系统可完全满足合肥光源恒流的运行需要。     

On the interpretation of the results of the experimental test of the Askar’yan effect

The effect of the environment on the results of measuring the radio radiation spectrum is considered in the experimental simulation of the cascade shower by a high-energy γ-ray beam in a dense medium. The calculation shows that the character of the measured energy spectrum depends on the location of the receiving antenna with respect to the shower axis.     

Reparameterization invariance of NRQED self-energy corrections and improved theory for excited D states in hydrogenlike systems

Canonically, the quantum electrodynamic radiative corrections in bound systems have been evaluated in photon energy regularization, i.e., using a noncovariant overlapping parameter that separates the high-energy relativistic scales of the virtual quanta from the nonrelativistic domain. Here, we calculate the higher-order corrections to the one-photon self-energy calculation with three different overlapping parameters (photon energy, photon mass and dimensional regularization) and demonstrate the reparameterization invariance of nonrelativistic quantum electrodynamics (NRQED) using this particular example. We also present new techniques for the calculation of the low-energy part of this correction, which lead to results for the Lamb shift of highly excited states that are important for high-precision spectroscopy.     

Quantum key distribution using quantum-correlated photon sources

Quantum key exchanges using weak coherent (Poissonian) single-photon sources are open to attack by a variety of eavesdropping techniques. Quantum-correlated photon sources provide a means of flagging potentially insecure multiple-photon emissions and thus extending the secure quantum key channel capacity and the secure key distribution range. We present indicative photon-counting statistics for a fully correlated Poissonian multibeam photon source in which the transmitted beam is conditioned by photon number measurements on the remaining beams with non-ideal multiphoton counters. We show that significant rejection of insecure photon pulses from a twin-beam source cannot be obtained with a detector having a realistic quantum efficiency. However quantum-correlated (quadruplet or octuplet) multiplet photon sources conditioned by high efficiency multiphoton counters could provide large improvements in the secure channel capacity and the secure distribution range of high loss systems such as those using the low earth orbit satellite links proposed for global quantum key distribution. Received 14 July and Received in final form 20 November 2001     

Measurements on electron beams in pulsed hollow-cathode discharges

Two different regimes of electron beams have been reported in the pulsed hollow cathode discharge-a low-current, high-energy beam, and a relatively high-current beam of low energy. The high-energy beam is related to the hollow cathode geometry and is found to be present even in the absence of subsequent gas breakdown, while the low-energy beam is always associated with voltage breakdown. Detailed measurements of the spatial and temporal distribution of the electron beam transported beyond a semitransparent anode associated with gas breakdown are reported. In particular, a high-energy component is observed after electrical breakdown. Low-energy electron beams are observed to be transported beyond the anode throughout the main discharge period     

Evaluation of the dosimetric characteristics of a radiophotoluminescent glass dosimeter for high-energy photon and electron beams in the field of radiotherapy

We aimed to evaluate the suitability of a glass dosimeter (GD) for high-energy photon and electron beams in experimental and clinical use, especially for radiation therapy. We examined the expanded dosimetric characteristics of GDs including dose linearity up to 500 Gy, uniformity among GD lots and for individual GDs, the angular dependence, and energy dependence of 4 therapeutic x-ray qualities. In addition, we measured the dosimetric features (dose linearity, uniformity, angular dependence, and energy dependence) of the GD for electron beams of 10 different electron energy qualities. All measurements with the exception of dose linearity for photon beam were performed in a water phantom. For high-energy photon beams, dose linearity has a linear relationship for a dose ranging from 1 to 500 Gy with the coefficient of determination; R² of 0.998. The uniformity of each GD of dose measurements was within ±0.5% for four GD lots and within ±1.2% for 80 GDs. In terms of the effects of photon beam angle, lower absorbed doses of within 1.0% were observed between 60° and 105° than at 90°. The GD energy dependence of 4 photon beam energy qualities was within ±2.0%. On the other hand, the result of the dose linearity for high-energy electron beams showed well fitted regression line with the coefficient of determination; R² of 0.999 between 6 and 20 MeV. The uniformity of GDs exposed to the nominal electron energies 6, 9, 12, 16, and 20 MeV was ±1.2%. In terms of the angular dependence to electron beams, absorbed doses were within 2.0% between 60° and 105° than at 90°. In evaluation of the energy dependence of the GD at nominal electron energies between 5 and 20 MeV, we obtained responses between 1.1% and 3.5% lower than that for a cobalt-60 beam. Our results show that GDs can be used as a detector for determining doses when a high-energy photon beam is used, and that it also has considerable potential for dose measurement of high-energy electron beam.     

Characterization of a scintillating fiber-optic dosimeter for photon beam therapy

Abstact  A scintillating fiber-optic dosimeter has many advantages such as real-time readout, high-resolution measurement, water-equivalence and no corrections for temperature, pressure and humidity. Organic scintillator which has water or tissue equivalent characteristics is very important to measure absorbed dose, dose rate and dose distributions exactly without any corrections and due to its small size, the sensitive volume enables accurate dose measurements in regions of high dose gradients with high spatial resolution. In this study, a scintillating fiber-optic dosimeter with an organic scintillator is fabricated to measure high-energy photon beam from a clinical linear accelerator. And we have measured linear responses of a fiber-optic dosimeter according to dose rates and monitor units of a clinical linear accelerator. Also, a percent depth dose curve for 6MV photon beam with different field sizes are obtained.     

The effect of the thunderstorm activity on the tien shan neutron monitor data

Variations in the neutron monitor counting rate at the at the mountain level (3340 m above sea level) during the passage of electrically charged clouds above the installation have been investigated. It is established that the decrease in the counting rate with respect to fair-weather level is due to positive values of the atmospheric electric field (～40–50 kV m^?1). This effect is observed in the low-energy part of the neutron component intensity and is absent in the high-energy part (neutron emission multiplicity exceeds 6).     

Monte Carlo simulation of electron beam air plasma characteristics

A high-energy electron beam generator is used to generate a plasma in atmosphere. Based on a Monte Carlo toolkit named GEANT4, a model including complete physics processes is established to simulate the passage of the electron beam in air. Based on the model, the characteristics of the electron beam air plasma are calculated. The energy distribution of beam electrons (BEs) indicates that high-energy electrons almost reside in the centre region of the beam, but low-energy electrons always live in the fringe area. The energy deposition is calculated in two cases, i.e., with and without secondary electrons (SEs). Analysis indicates that the energy deposition of SEs accounts for a large part of the total energy deposition. The results of the energy spectrum show that the electrons in the inlet layer of the low-pressure chamber (LPC) are monoenergetic, but the energy spectrum of the electrons in the outlet layer is not pure. The SEs are largely generated at the outlet of the LPC. Moreover, both the energy distribution of BEs and the magnitude of the density of SEs are closely related to the pressure of LPC. Thus, a conclusion is drawn that a low magnitude of LPC pressure is helpful for reducing the energy loss in the LPC and also useful for greatly increasing the secondary electron density in dense air.     

单光子探测器量子效率的绝对自身标定方法

提出一种单光子探测器量子效率的绝对自身标定方案，利用光参量下转换过程中产生的光子对在时间上的相关性，先将参量光束分为两路，然后引入相对延时，使同时产生的孪生光子先后进入单光子探测器，然后将探测器之后的电路分为三路，其中一路直接进入计数器得到探测器所探测到的光子的总计数率，另两路用电路方法引入和光路相当的相对延时，经符合电路后进入计数器，得到前后到达探测器的光子对之间的符合计数率.这样，从符合计数率与总光子计数率之比即可在不需要任何其他探测器或者参照标准的情况下获得探测器的量子效率.文中给出两种方案，分别适     

Hadrons with energies higher than 50 MeV in EASes with <Emphasis Type="Italic">N</Emphasis><Subscript><Emphasis Type="Italic">e</Emphasis></Subscript> = 10<Superscript>5</Superscript>–10<Superscript>7</Superscript>

Characteristics of the hadronic component of EASes with hadron energies E _h > 50 MeV were measured on the CARPET-2 complex shower array at the Baksan Neutrino Observatory of the Institute for Nuclear Research, Russian Academy of Sciences. Hadrons were registered using a 6-NM-64 neutron monitor; the data collection system of this array enables us to register the time intervals between pulses of neutron monitor counters with an error of up to 1 μs. For EASes with N _e = 10⁵–10⁷ whose axes are located in CARPET, we obtain the dependence of the mean neutron multiplicity in the neutron monitor on the total number of charged particles in the EAS.     

Experimental investigation of deuteron photodisintegration in the δ-resonance region

Differential cross sections for the deuteron photodisintegration process were measured for photon energies between 200 and 440 MeV using the tagged photon beam facility of the Bonn 500 MeV synchrotron. At eight angles between 18° and 145° charged particles were detected simultaneously in time-of-flight spectrometers consisting of scintillation counters. Above the resonance region the measured cross sections agree fairly well with earlier results, whereas there are larger discrepancies at low photon energies.     

Ion beam application in genetic modification

People pay little attention to the interaction between low-energy ions and matter compared to that of high-energy ions. It is even more unusual to find studies of the interaction of low-energy ions and complicated organisms. The discovery of bioeffects induced by ion implantation has, however, opened a new branch in the field of ion beam applications in the life sciences. This paper reports recent advances in research on the role of low-energy ions in genetic modification     

Bileptons: present limits and future prospects

We define bileptons to be bosons coupling to a pair of leptons and construct the most general dimension four lagrangian involving scalar and vector bileptons. We concentrate on fields with lepton number 2, and derive model independent bounds on their masses and couplings from low-energy data. In addition, we study their signals in high-energy experiments and forecast the discovery potential of future colliders. Received: 24 April 1997 / Published online: 20 February 1998