Search for quantum states of the neutron in a gravitational field: gravitational levels

The neutron could occupy quantum stationary states if it is trapped between the Earth's gravitational field on one side and the Fermi quasi-potential of a mirror on the other side. The quantum states cause a strong variation in neutron density, both for separate energy levels and for a mixture of low-energy states. The use of a position sensitive UCN (ultracold neutron) detector allows simultaneous measurement of the position probability density distribution in the total range of interest and increases significantly the statistics, making possible such an experiment. In this article we describe a specially developed neutron spectrometer and a method of measurement of such quantum states.     

Large area microchannel plate detector with amorphous silicon pixel array readout for fast neutron radiography

Fast neutron radiography is a non-destructive testing technique with a variety of industrial applications and the capability for element sensitive imaging for contraband and explosives detection.

Commonly used position sensitive detectors for fast neutron radiography are based on charge coupled devices (CCDs) and scintillators. The limited format of CCDs implies that complex optical systems involving lenses and mirrors are required to indirectly image areas that are larger than 8.6 cm×11.05 cm. The use of optics reduces the light collection efficiency of the imaging system, while the efficiency of hydrogen rich scintillators exploiting the proton recoil reaction is limited by the hydrogen concentration and the magnitude of the neutron scattering cross-section.

The light conversion step inevitably involves a tradeoff in scintillator thickness between light yield and spatial resolution.

The development of large area amorphous silicon (a-Si) panel flat panel photodiode arrays and direct neutron-to-charge converters based on microchannel plates, provide an attractive new form of high resolution, large area, fast neutron imaging detector for the non-destructive imaging of large structures. This paper describes some recent results of both Monte Carlo simulations and measurements for such a detector.     

Design and test of a large-area scintillation detector for fast neutrons

A plastic scintillator array of 3.4 m² total area for the detection of neutrons in medium-energy nucleon–nucleon reactions was constructed and built. Calibration procedures for the detector were developed which allow the monitoring of gain shifts by means of muons from the cosmic radiation. Experiments were performed in order to calibrate the efficiency simulations and study the performance of the detector using the d+t→+n reaction at 14.7 MeV neutron energy and proton-induced deuteron breakup at 300 MeV.     

On the importance of measuring all three components of the remanent field in radiation-induced demagnetization experiments

In the following we present a new analysis of the data obtained after an irradiation of magnets with a 2 GeV electron beam under various conditions (with or without a target placed in front of the magnets). This analysis, based on the measured magnetic field, indicates the importance of a precise determination of the three components of the magnetization for a better understanding of the demagnetization process.     

State discrimination of two pure states with a fixed rate of inconclusive answer

We investigate the optimum strategy for state discrimination of two pure states when the probability of inconclusive answers is fixed. By varying a given rate of inconclusive probabilities, the strategy optimally interpolates between Unambiguous and Minimum-Error discrimination, the two standard approaches to quantum state discrimination. We derive the explicit expressions of all the probabilities using an ancillary system and introducing unitary transformations which act on the input states and produce the output measured on the ancilla. By exploring physically accessible transformation acting on the input states, we present an optical scheme to implement the state discrimination.     

单传感器声纳浮标场的盲分离算法

声纳浮标作为海上反潜力量的重要组成部分之一,具有隐蔽性能好,探测范围广等优点。单传感器声纳浮标作为声纳浮标的一种,因其结构简单而具有广泛的应用。文章以被动接收为背景,尝试用盲分离技术综合多个单传感器声纳浮标的输出对目标辐射信号进行恢复,仿真实验验证了盲分离技术的可行性。     

Magnetic field effect on highly excited states near ionization potential of nitric oxide

Fluorescence excitation spectra due to the A ²∑–X ²Π transition of gaseous nitric oxide (NO) were measured in magnetic fields, H; ranging from 0 ≤ H ≤ 10 T. Lines in the observed spectra were assigned by using quantum mechanical calculations. Based on the assignment, two-color resonance-enhanced multiphoton ionization spectra via a single Zeeman sublevel in the A state were measured to observe the effect of magnetic fields on electronic states near the ionization potential (IP). Complicated structures due to strong n- and l-mixing in highly excited Rydberg states were observed below the IP. It was found that new resonance appears above the IP for H ≤ 4T. By using a semi-classical calculation, this resonance was assigned to the quasi-Landau resonance, which was observed for the first time in molecules.

© 2003 Elsevier Ltd. All rights reserved.     

Neutron laminography—a novel approach to three-dimensional imaging of flat objects with neutrons

Computed tomography (CT) is a three-dimensional (3D) imaging method which, for compact or prolate (i.e. rather isotropically extended around the rotation axis) specimens, can yield artefact-free reconstructed cross-sections. Laterally extended specimens like plate-like objects, however, are much less amenable to CT since reliable projection data cannot be acquired from angles where the plate is oriented parallel to the irradiation direction.To overcome this drawback, computed laminography (CL) was introduced recently to imaging set-ups at synchrotron storage rings. Here, we report on the first implementation of computed laminography with neutron radiation, showing measurements that were performed at the ANTARES neutron imaging facility at the FRM II research reactor of Technische Universität München. In general, neutrons are highly interesting probes for imaging since they provide a sensitivity to chemical elements very different from X-rays, yielding complementary information about the specimens investigated. Like for X-ray laminography, we avoid the projection directions where the beam is parallel to the long extensions of the specimen. We accomplish this by tilting of the rotation axis with respect to the transmitted-beam to an angle smaller than 90° (which would be the limiting case of CT) and roughly aligning the specimen's surface normal parallel to this rotation axis. The principles of neutron laminography are introduced and first test experiments are described.     

Bound electron states in a system of coupled quantum waveguides in a transverse electric field

It is shown that a bound electron state exists in a system of quantum waveguides laterally coupled via a small window and placed in a transverse electric field. A field-induced shift of the eigenvalue is estimated using a variational method.     

On the possible use of a commercial Penning gauge as a magnetic field sensor

Penning sensors were originally conceived to extend the measurement range of cold-cathode gauges in the direction of low pressures by introducing an additional constant magnetic field. This paper examines the possibility of using a commercially available sensor to measure magnetic field by keeping pressure constant. For the preliminary tests reported, a commercial Penning gauge was exposed to magnetic fields in the range of a few tens of mT to 1.1 T. Three different regimes were identified. In the first, up to 150 mT, the measured current increases linearly with the applied magnetic field. Following a very irregular transition region of the order of 50 mT, for fields between 200 mT and 1.1 T, the measured current decays relatively smoothly. The results suggest that the principle may be applicable for the measurement of steady-state fields in harsh environments, with high temperature and neutron fluence.     

Improvement of the seismic noise attenuation performance of the Monolithic Geometric Anti-Spring filters for gravitational wave interferometric detectors

The Monolithic Geometric Anti-Spring (GAS) filter is one of the most efficient vertical seismic isolation devices for Gravitational Wave (GW) interferometers. However, the attenuation of this filter was previously limited to around 60 dB due to the high frequency saturation associated with the filter's distributed mass—a problem typical of passive mechanical filters. We show that it is possible to circumvent this limit using a compensation wand based on the Center Of Percussion (COP) effect. When this device is mounted in parallel with the blade springs of a GAS filter, attenuation improves to 80 dB in the region above 10 Hz. Using this device it is therefore possible to design simpler attenuation chains consisting of fewer stages.     

自由空间量子密钥分发中的信号同步解决方案

针对目前自由空间量子密钥分发（QKD）中的信号同步这一难点问题,提出一种采用外置光信号来解决信号同步问题的方案——光同步方案。在发送端利用声光调制器将外置激光器的连续激光分割成周期光脉冲序列,并作为同步光信号发送给接收端。接收端采用光电倍增管接收同步光脉冲信号,生成一个与发送端严格同步的信号,以此作为接收端的时基标准来进行单光子计数。采用高频的内部时钟信号来“监视”接收到的同步信号,从而提高计数准确性。该方案具有长距离性、无线性、低复杂度等特点,已成功应用于一个基于B92协议的自由空间QKD系统中。     

Flat-response neutron detector using spatial distribution of thermal neutrons in a moderator

We propose a novel neutron detector that realized flat-response using information of a spatial distribution of thermal neutrons in a moderator. The proposed detector consists of a ³He position sensitive proportional counter (PSPC) and a cylindrical moderator surrounding the ³He PSPC. The cylindrical detector is irradiated by neutrons along the cylinder axis. The spatial response of the ³He PSPC is used to correct the detector response into flat-response. We adopt a weighting method to achieve flat-response, in which detected neutrons weighted depending on their detected positions are accumulated as the detector response. Through Monte Carlo simulation studies, we confirm that the flat-response neutron detector can be realized by correcting the response of the proposed detector using the weights determined by a multiple least square method (MLSM). Additionally, fundamental property of the ³He PSPC is experimentally investigated to check applicability to the proposed flat-response neutron detector. We conclude that we should take account of the end effect when determining the weights and correcting the detector response.     

Variation of the electrochemical potential difference in a gravitational field

We have determined the variation of the electrochemical potential difference in a gravitational field, and the results agree to within 4% with the predictions of the Equivalence Principle (EP). Thus, EP has again been verified, but unlike previous experiments, this experiment involved charged particles. The results were obtained using a DC SQUID in which the two junctions were separated vertically by about 7 cms. The junctions, which were phase-locked to an external microwave source, acted as two very precise batteries. Because of the gravitational red-shift of the radiation, a voltage difference of 1:10¹⁷existed between these batteries, giving a net EMF in the SQUID loop in the absence of other effects of about 2×10^-21volts. The loop EMF determined by the rate of change of flux in the loop was however less than 1×10^-22volts, thus demonstrating the additional variation in the potential difference due to the gravitational field.     

The solution of the inverse problem of gravitational potential using a set of measurements of different field elements

A numerical solution of the inverse problem of the gravitational field at a single point is obtained using six field elements for a point, a spherical cap, a differential spherical sector and a vertical segment. In the system of six equations obtained, the unknowns are the mass of the body, the depth of its center, and the second, third, and fourth degree moments. The accuracy of the solution of this system is ten times higher than when using three field elements. __________ Translated from Izmeritel’naya Tekhnika, No. 5, pp. 3–8, May, 2007.     

Heat exchange with laminar upflow of supercritical helium in a gravitational field

This paper considers the problem of calculating heat exchange in cases where there is an appreciable effect of thermogravitation and laminar upflow of supercritical helium in heated vertical, circular tubes. A procedure for calculating heat exchange in such situations is presented. This was developed using the rule for selecting coefficients in finite-difference relationships.     

碳纳米管冷阴极超高真空鞍场规的电场模拟与实验研究

在静电鞍场规的基础上研制了一种碳纳米管(CNT)冷阴极鞍场规(SFG).这种冷阴极鞍场规具有电极尺寸小,吸放气率低,热效应低,功耗低的特点.本文首先计算了碳纳米管冷阴极鞍场规的电场分布,计算结果表明,二极型碳纳米管电子枪的引出栅极的正电位在低于100 V的情况下对环形阳极鞍场规的轴向电位分布影响很少;并且在现有条件下对规管参数进行了测试,实验测定的规管对空气的灵敏度是1.05 Pa-1,规管功耗由热阴极规的0.9瓦减小到7毫瓦.