Digital pulse shape discrimination

Pulse-shape discrimination (PSD) has been utilised for about 40 years as a method to obtain estimates for dose in mixed neutron and photon fields. Digitizers that operate close to GHz are currently available at a reasonable cost, and they can be used to directly sample signals from photomultiplier tubes. This permits one to perform digital PSD rather than the traditional, and well-established, analogoue techniques. One issue that complicates PSD for neutrons in mixed fields is that the light output characteristics of typical scintillators available for PSD, such as BC501A, vary as a function of energy deposited in the detector. This behaviour is more easily accommodated with digital processing of signals than with analogoue signal processing. Results illustrate the effectiveness of digital PSD.     

Identification of continuous‐time delayed systems using an input pulse of arbitrary shape

Abstract

This article resolves difficulties of continuous identification often encountered in field testing, such as unsteady initial states, unknown disturbances, and noise‐corrupted measurements. The unique feature of the proposed method is that it divides the identification problem into two simpler estimation problems based on pulse testing of arbitrary shape. Sequential algorithms are developed to deal with the first estimation problem subjected to the zero portion of the input and then to solve the remaining problem subjected to the arbitrary portion of the input. The method provides a convenient way to fit model predictions to output measurements in the face of unknown initial states and static disturbances. Simulation results demonstrate that the use of the integral filter renders the method rather robust with respect to noise and model structure mismatch.     

Group velocity of probe light pulse in an open lambda system

The group velocity of the probe light pulse (GVPLP) propagating through an open Λ-type atomic system with a spontaneously generated coherence is investigated when the weak probe and strong driving light fields have different frequencies. It is found that adjusting the detuning or Rabi frequency of the probe light field can realize switching of the GVPLP from subluminal to superluminal. Changing the relative phase between the probe and driving light fields or atomic exit and injection rates can lead to GVPLP varying in a wider range, but cannot induce transformation of the property of the GVPLP. The absolute value of the GVPLP always increases with Rabi frequency of the driving light field increasing. For subluminal and superluminal propagation, the system always exhibits the probe absorption, and GVPLP is mainly determined by the slope of the steep dispersion.     

Theory of the undulator superradiance of an electron beam pulse in the group synchronism regime

The properties of the superradiance of a short electron beam pulse moving in an undulator field and exciting a waveguide mode field under group synchronism conditions are analyzed. This regime is shown to be characterized by the maximum growth rate of superradiance instability. The development of such instability results in bunching of the particles and the coherent emission of a short electromagnetic pulse by the beam pulse. Pis’ma Zh. Tekh. Fiz. 25, 8–16 (April 26, 1999)     

A pulse shape analysis algorithm for HPGe detectors

A pulse shape analysis (PSA) algorithm for segmented HPGe detectors is discussed and some test cases are analysed. The procedure allows the identification of the number of interactions inside a segment and their radial positions. An important characteristic of the algorithm is that it does not need the induced signals of the neighbouring segments as it is based on the comparison between the current pulse from the net charge collecting segment and a basis of reference signals. The calculation time that is required to analyse one event scales linearly with the number of interactions to disentangle. The efficiency of the algorithm for the correct identification of the number of interaction points and their radial position calculated for 600 keV γ-rays ranges from 65% to 95% depending on the complexity of the analysed event.     

电子轰击离子源脉冲离化电子流的测量

本文讨论了脉冲测量技术在飞行时间质谱计电子轰击离子源中测量脉冲离化电子流的应用 ,分析了平均电流测量方法测量脉冲离化电子流的局限性 ,给出了实际的脉冲测量电路     

Attenuation of electron gun generated surges in an electron beam evaporation system using ferrite beads

Vacuum breakdown is a very common problem during the operation of any electron gun, more so for e-guns used for vacuum evaporation. This not only spoils the coating or welding job but also causes damage to the electronics of the power system. This paper discusses an approach to attenuate the breakdown current near the gun itself, so that the surge does not propagate to cause any detrimental effect on the power source and thereby on the job. In this paper, ferrite beads on both the feed lines have been used to suppress the high frequency content and reduce the amplitude of the breakdown signal. An induction coil sensor has been designed to monitor the breakdown signal. The high frequency surge in the MHz range could be attenuated to a lower range of KHz by use of ferrite bead. A detailed quantitative analysis of the breakdown signal has been presented in this paper.     

The interaction between pulse shape and strain hardening in dynamic plastic response

The effect of pulse shape on the dynamic plastic response of a single-degree-of-freedom system with rigid-strain-hardening behavior is investigated. The duration of response and final displacement are found to depend exactly on three parameters defined in terms of simple integrals of the pulse shape and material constants. These three parameters, however, lack an obvious physical interpretation. Consequently, a second set of three parameters is proposed which approximately accounts for the effect of pulse shape on the determination of the response duration and final displacement. Two of these parameters are the amplitude and duration of an equivalent rectangular pulse which has the same area and centroid as the applied pulse. The third parameter represents the amount of strain hardening and is determined from the strain-hardening coefficient and a measure of the effective pulse length.     

Background reduction by pulse shape discrimination in a multiwire plutonium lung monitor

Investigations have been made on the reduction of background count rate, by pulse shape discrimination, in a xenon multiwire proportional chamber designed as a monitor for plutonium lung contamination. A simple discrimination system was employed in which waveform crossover time was employed as a measure of anode charge rise time. An estimate was made for the minimum detectable activity, for a 40 min count, of 45 nCi (1.7 kBq). This figure compares favourably with that of the phoswich monitor currently employed.     

Nitriding of stainless steel in plasma of a pulse electron beam

The formation of a hardened layer with low-temperature (400°C)nitriding of grade 12Kh18N10T stainless steel in plasma of a pulse electron beam which is generated under continuous and pulse conditions at equal average current (2.6 A) and electron energy (200 eV) is studied. In spite of intense ion sputtering of the surface during the pulse, both nitriding conditions yielded equal quantities of thickness and hardness of the layer, which indicated that neutral atomic nitrogen plays a main role during nitriding.     

Experimental evaluation of an MnBi optical memory system

An experimental optical memory system is described for evaluating the optical memory characteristics of MnBi films. The preparation procedure for obtaining large uniform films is discussed. These films require about 10 mW of laser power to write 1-μm bits and a coincident field of 600 Oe to erase them. A packing density of 1.5 × 10⁸bit/in²with a typical signal-to-noise ratio of 10 is readily achieved. Large area films have been sample tested and found to be of usable quality over 99.9 percent of the area. Test bits have been repeatedly cycled to the Curie point more than 10⁶times retaining an adequate signal-to-noise ratio.     

Subharmonic emissions from microbubbles: effect of the driving pulse shape

The aims of this work are to investigate the response of the ultrasonic contrast agents (UCA) insonified by different arbitrary-shaped pulses at different acoustic pressures and concentration of the contrast agent focusing on subharmonic emission. A transmission setup was developed in order to insonify the contrast agent contained in a measurement chamber. The transmitted ultrasonic signals were generated by an arbitrary wave generator connected to a linear power amplifier able to drive a single-element transducer. The transmitted ultrasonic pulses that passed through the contrast agent-filled chamber were received by a second transducer or a hydrophone aligned with the first one. The radio frequency (RF) signals were acquired by fast echographic multiparameters multi-image novel apparatus (FEMMINA), which is an echographic platform able to acquire ultrasonic signals in a real-time modality. Three sets of ultrasonic signals were devised in order to evaluate subharmonic response of the contrast agent respect with sinusoidal burst signals used as reference pulses. A decreasing up to 30 dB in subharmonic response was detected for a Gaussian-shaped pulse; differences in subharmonic emission up to 21 dB were detected for a composite pulse (two-tone burst) for different acoustic pressures and concentrations. Results from this experimentation demonstrated that the transmitted pulse shape strongly affects subharmonic emission in spite of a second harmonic one. In particular, the smoothness of the initial portion of the shaped pulses can inhibit subharmonic generation from the contrast agents respect with a reference sinusoidal burst signal. It also was shown that subharmonic generation is influenced by the amplitude and the concentration of the contrast agent for each set of the shaped pulses. Subharmonic emissions that derive from a nonlinear mechanism involving nonlinear coupling among different oscillation modes are strongly affected by the shape of the ultrasonic driving pulse.     

Calculated fraction of an incident current pulse that will be accelerated by an electron linear accelerator and comparisons with experimental data

In a series of previous papers, calculated results obtained using a one-dimensional ballistic model were presented to aid in the design of a prebuncher for the Oak Ridge Electron Linear Accelerator. As part of this work, a model was developed to provide limits on the fraction of an incident current pulse that would be accelerated by the existing by the accelerator. In this paper experimental data on this fraction are presented and the validity of the model developed previously is tested by comparing calculated and experimental data. Part of the experimental data is used to fix the physical parameters in the model and then good agreement between the calculated results and the rest of the experimental data is obtained.     

Real time electron tunneling and pulse spectroscopy in carbon nanotube quantum dots

We investigate a quantum dot (QD) in a carbon nanotube (CNT) in the regime where the QD is nearly isolated from the leads. An aluminum single electron transistor (SET) serves as a charge detector for the QD. We precisely measure and tune the tunnel rates into the QD in the range between 1 kHz and 1 Hz, using both pulse spectroscopy and real-time charge detection, and measure the excitation spectrum of the isolated QD.     

Features of pulse substrate bias voltage generation with electron tubes

Features of pulse substrate bias voltage generation with electron tubes in different operation modes are considered. The overstressed mode with low anode voltage and return of electrons to the grid has practical significance at bias voltages in the kilovolt range under the conditions of large substrate current fluctuations. This mode ensures small bias voltage fluctuations and effective use of the primary DC voltage. When the substrate current spontaneously rises above the critical value, the tubes automatically decrease the bias voltage and suppress current spikes and arcing. Such approach may be used in PVD processes, for ion surface treatment and ion plasma immersion implantation.     

Use of charge integrating ADCs with pulse shape discriminators for neutron-gamma discrimination

A simple method is presented for the use of CAMAC charge integrating ADCs with CANBERRA 2160 pulse shape discriminators to separate neutrons from gamma rays in a neutron detection system.