A small-sized MWPC with 1 mm wire spacing as a beam/target chamber for nuclear experiments

We developed a small-sized multiwire proportional chamber with 1 mm wire spacing for a study of backward Λ production in high energy hadron-nucleus reactions. Two chambers were installed in a cylindrical drift chamber of the large aperture spectrometer FANCY in order to determine beam trajectories precisely. A position resolution of about 0.6 mm was obtained with a counting efficiency of 97%.     

Electroluminescent track chambers

Light yield and space resolution are measured for electroluminescent chambers without electron multiplication and in the proportional regime. The investigation has been performed in order to get the information necessary for the construction of a track projection chamber. Widths have been obtained (fwhm) for the image of one electron; the results are 1.9 mm for the chamber without electron multiplication and 1.4 mm for the proportional electroluminescent chamber.     

Rotation numbers for quasi-periodically forced monotone circle maps

Rotation numbers have played a central role in the study of (unforced) monotone circle maps. In such a case it is possible to obtain a priori bounds of the form „ - 1/n ≤(1/n)(y_n - y₀) ≤„ + 1/n, where (1/n)(y_n - y₀) is an estimate of the rotation number obtained from an orbit of length n with initial condition y₀, and „ is the true rotation number. This allows rotation numbers to be computed reliably and efficiently. Although Herman has proved that quasi-periodically forced circle maps also possess a well-defined rotation number, independent of initial condition, the analogous bound does not appear to hold. In particular, two of the authors have recently given numerical evidence that there exist quasi-periodically forced circle maps for which y_n - y₀ - „n is not bounded. This renders the estimation of rotation numbers for quasi-periodically forced circle maps much more problematical. In this paper, a new characterization of the rotation number is derived for quasiperiodically forced circle maps based upon integrating iterates of an arbitrary smooth curve. This satisfies analogous bounds to above and permits us to develop improved numerical techniques for computing the rotation number. Additionally, the boundedness of y_n - y₀ - „n is considered. It is shown that if this quantity is bounded (both above and below) for one orbit, then it is bounded for all orbits. Conversely, if for any orbit y_n - y₀ - „n is unbounded either above or below, then there is a residual set of orbits for which y_n - y₀ - „n is unbounded both above and below. In proving these results a min-max characterization of the rotation number is also presented. The performance of an algorithm based on this is evaluated, and on the whole it is found to be inferior to the integral based method.     

ΔE−E Telescope systems for detecting charged particles produced with a “white” neutron beam

Highly stable ΔE−E telescope systems consisting of plastic scintillation detectors are operated as flux monitors in a “white” neutron beam between 15 and 50 MeV. Multiple telescope systems consisting of large area silicon ΔE detectors and NaI E detectors are set up in a scattering chamber to investigate charged particle reactions induced by fast neutrons up to 50 MeV.     

Large-area uniform dust-free plasma CVD

In the weak magnetic field perpendicular to the discharge electric field, both the electrons and positive ions are transported in the direction of E×B drift by the space charge electric field produced by the preceded electrons. As a result, radicals are generated uniformly outside of discharge space between the electrodes in the direction of E×B drift. On the other hand, negatively charged heavy particles such as dust particles can be removed from discharge space in the direction opposite to E×B drift of plasmas. The authors have studied the transport mechanisms of magnetized dusty plasmas and its applications for the large-area uniform a-Si:H thin film deposition in plasma CVD methods. This paper reviews the transport phenomena and the transport mechanisms of dust particles and the results of film preparation under particle-free process conditions.     

An Investigation of the Measurements Systems Analysis “Analytic Method” for Attribute Gages

Three automotive corporations have developed and sanctioned the recently revised reference manual entitled Measurement Systems Analysis. This “standard” contains a procedure, called the “analytic method,” whose purpose is to estimate the gage bias and gage repeatability of an attribute gage. An improved estimation procedure for this standard is presented. The improved estimation procedure yields more accurate estimates than those obtained using the procedures currently presented in the standard. In addition, the improved procedure allows more flexibility in data collection than the current test protocol. A simulation study that evaluates the estimation procedure of the current standard and compares it with the improved estimation procedure is presented. Errors that are contained in the present standard are also noted.     

Electrical resistance drift of molybdenum silicide thin film temperature sensors

For a thermometer to be of practical use, its accuracy of temperature indication must be within a tolerable range. In this paper, patterned molybdenum disilicide (MoSi₂) thin film temperature sensors were fabricated to study their thermoresistance, i.e. resistance vs. temperature (R-T) characteristics. The R-T characteristic of MoSi₂ thin films exhibits a positive deviation from linearity (termed “superlinearity”) instead of showing a simple linearity as for most metals. This superlinear behavior was attributed to thermal expansion and the consequent decrease in the Debye characteristic temperature of MoSi₂. For long-term duration at elevated temperatures, the variation in thickness and composition of the sensor film due to oxidation and other factors may produce drift in the electrical resistance. In this study, the electrical resistance drifts of the sensors as a function of time at temperatures of 1200, 1300 and 1350 °C are presented. For the sensor film tested at 1300 °C, the resistance drift due to the thickness change of the sensor layer was well corrected with the help of an analysis of the oxidation rate of the sensor material. On the other hand, the in-depth composition profile analyzed by Auger electron spectroscopy (AES) indicated no significant composition variation, implying that we could neglect the correction factor for the composition variation in the present study. After the thickness factor was corrected for, a minor drift was still observed; this was also found for the same sensor film tested in an Ar ambient. The exact source of the minor drift is not well understood; further investigations are required.     

Laser calibration of drift chambers

A nitrogen laser was used to simulate tracks of charged particle in a drift chamber. With this technique it is possible to test a drift chamber with high spatial resolution in its entire volume. By changing the amount of ionization the behaviour of the chamber has been tested near the threshold and the response of the whole read-out chain has been adjusted for the range of signal amplitudes of the Landau distribution. A very precise drift speed measurement has been performed in different conditions of drift voltage and gas concentrations.     

Prototype tests of two controlled geometry drift chambers

This report presents results on the performance of two new drift chamber geometries, which were optimized for space resolution and two-track separation. The best performance requires isochronous drift collection, low electron diffusion, and careful signal shaping. The role of the mobility of electrons and positive ions is emphasized.We tested two geometries, and at a gas pressure of 1 atm we found $\text{σ ? 60–70 μ}\text{m}$ for the single-track resolution and $\text{Δ ? 600 μ}\text{m}$ for the two-track separation.     

Performance of a prototype drift Chamber with 100 MHz FADC readout

Rectangular drift chamber cells have been constructed and tested using an electron test beam facility at DESY. A systematic study of the time, spatial, energy and double track resolutions with a 100 MHz FADC readout is presented. The spatial resolution is 100 to 120 μm and the double track resolution is 2.5 mm with an Ar:C₂H₆ (50:50) gas mixture at atmospheric pressure. The resolution obtained corresponds to 6% resolution for a 72-layer chamber.     

Large diameter radial semiconductor drift chambers for low noise radiation detection

A semiconductor drift chamber with cylindrical symmetry has been investigated theoretically for its suitability as a low noise radiation detector. The signal/noise of a silicon drift chamber at room temperature is likely to be determined by the detector dark current and the drift chamber should be superior in performance to a conventional pn junction detector of equivalent dimensions. A device of 48 mm diameter and 300 μm thickness is predicted to be capable of an energy resolution of less than 5 keV fwhm at 300 K. This is about seven times better than that predicted for its conventional counterpart.     

Characteristics of a mini Drift chamber

The characteristics of a drift chamber with 3 mm drift gap were investigated at a particle beam momentum of 10 GeV/c. The chamber has good linearity of the drift characteristics. It was tested and could reliably work in a particle flux of ∼ 3 × 10⁵ s⁻¹ cm⁻². A spatial resolution of ∼ 45 μm in the centre of the drift gap has been achieved.     

Uncertainty in relative energy resolution measurements

We suggest a new method for the determination of the detector relative energy resolution and its uncertainty based on spline approximation of experimental spectra and a statistical bootstrapping procedure. The proposed method is applied to the spectra obtained with NaI(Tl) scintillating detectors and ¹³⁷Cs sources.

The spectrum histogram with background subtracted channel-by-channel is modeled by cubic spline approximation. The relative energy resolution (which is also known as pulse height resolution and energy resolution), defined as the full-width at half-maximum (FWHM) divided by the value of peak centroid, is calculated using the intercepts of the spline curve with the line of the half peak height. The value of the peak height is determined as the point where the value of the derivative goes to zero. The residuals, which are normalized over the square root of counts in a given bin (y-coordinate), obey the standard Gaussian distribution. The values of these residuals are randomly re-assigned to a different set of y-coordinates where a new “pseudo-experimental” data set is obtained after “de-normalization” of the old values. For this new data set a new spline approximation is found and the whole procedure is repeated several hundred times, until the standard deviation of relative energy resolution becomes stabilized. The standard deviation of relative energy resolutions calculated for each “pseudo-experimental” data set (bootstrap uncertainty) is considered to be an estimate for relative energy resolution uncertainty.

It is also shown that the relative bootstrap uncertainty is proportional to, and generally only two to three times bigger than, , which is the relative statistical count uncertainty (N_tot is the total number of counts under the peak).

The newly suggested method is also applicable to other radiation and particle detectors, not only for relative energy resolution, but also for any of the other parameters in a measured spectrum, like peak position, shape parameters, etc.     

Investigation of timing properties of a thin multiwire proportional chamber with Csl photocathode

A measurement of the time distribution of signals due to single electrons created at the CsI photocathode in a thin multiwire proportional chamber is described. The full width at half maximum (FWHM) has been measured to be 8.3 ns. Calculations, which include different drift lengths, diffusion and electronic noise, agree well with the measured distribution. A timing resolution of about 1 ns FWHM is expected for Cherenkov radiation in 1 cm of NaF crystal, giving rise to approximately 30 photoelectrons from the CsI photocathode.     

A new method for reducing DNL in nuclear ADCs using an interpolation technique

The paper describes a new method for reducing the DNL associated with nuclear ADCs. The method named the “interpolation technique” is utilized to derive the quantisation steps corresponding to the last n bits of the digital code by dividing quantisation steps due to higher significant bits of the DAC, using a chain of resistors. Using comparators, these quantisation steps are compared with the analog voltage to be digitized, which is applied as a voltage shift at both ends of this chain. The output states of the comparators define the n bit code. The errors due to offset voltages and bias currents of the comparators are statistically neutralized by changing the polarity of quantisation steps as well as the polarity of analog voltage corresponding to last n bits) for alternate A/D conversion. The effect of averaging on the channel profile can be minimized. A 12 bit ADC was constructured using this technique which gives DNL of less than ±1% over most of the channels for conversion time of nearly 4.5 μs. Gatti's sliding scale technique can be implemented for further reduction of DNL. The interpolation technique has a promising potential of improving the resolution of existing 12 bit ADCs to 16 bit, without degrading the percentage DNL significantly.     

Design and tests of the z-coordinate drift chamber system for the opal central detector at LEP

A system of drift chambers has been designed to make high resolution measurements of the z-coordinates of charged tracks at the outer radius of the OPAL central detector at LEP. The unit module of this detector is a 25 cm drift length bidirectional cell with six sense wires in a thin 50 cm wide by 29 mm high drift slot. Tests indicate that the chamber has a wide and stable electric field operating range and its performance is unaffected by small misalignments between the drift electric field and an external magnetic field. The drift cell was found to have uniform acceptance up to its geometrical boundaries, and the z-resolution for beam tracks normal to the chamber was measured to be in the range of 40–175 μm.     

Virtual anode as a source of low-frequency oscillations of a high-current electron beam

We have studied the transport of a relativistic electron beam with supercritical current in a cylindrical drift chamber in the presence of an ion flux. A theoretical analysis of the electron-ion flux dynamics was based on the coarse particle PIC method (code SOM). Simultaneous injection of a supercritical electron beam and a weak-current low-energy ion beam may result in the formation of a virtual anode in addition to the electron virtual cathode in a drift chamber. The virtual anode exhibits periodic pulsations. Numerical results obtained for hydrogen and nitrogen ions show that the ratio of the frequencies of these pulsations is inversely proportional to the square root of the ion mass ratio. These oscillations of the virtual anode lead to temporal modulation, at the same frequency, of both electron and ion currents at the drift chamber output.     

A simultaneous hit finding and timing method for pulse shape analysis of drift chamber signals

An algorithm for the analysis of the digitized signal waveform of drift chamber pulses is described which yields a good multihit resolution and an accurate drift time determination with little processing time. The method has been tested and evaluated with measured pulse shapes from the full size prototype of the OPAL central detector which were digitized by 100 MHz FADCs.     

A position sensitive ionisation chamber for measurement of fission fragments and medium mass heavy ions

A position sensitive ionisation chamber telescope is described with ΔE_gas---E_gas sections which can measure simultaneously the specific energy loss ΔE, energy E and the position of heavy ion reaction products in the median plane. The position information is derived by having a split ΔE structure and by adopting the pulse division method for the signals collected by the two ΔE sections. For on-line angle calibration, the E-part of the anode structure is also split into five segments. The detector was tested with fission fragments from a ²⁵²Cf spontaneous fission source and with heavy ions from the pelletron tandem accelerator. Simultaneous measurement of ΔE and E gives good separation for heavy and light fission fragment groups. The position resolution is found to be 1.1 mm for fission fragments. The detector has been used in heavy ion reaction studies for measuring fission fragments, providing good separation from projectile-like particles.     

The dependence of penetration velocity on impact velocity

Recent experimental measurements show that eroding long-rod penetration velocity is a linear function of impact velocity over a very wide range of impact velocities and for an interesting range of rod–target material combinations. These experiments all show that U=a+bV, where U and V are the penetration and impact velocity, respectively, and “a” and “b” are constants for given projectile and target materials. Numerical simulations also show that U=a+bV. The accumulation of these results suggests that a linear relationship between penetration and impact velocity may be fundamental over a very large range of impact velocities. A linear relationship between penetration and impact velocity has a number of implications. Some implications of this result for the Tate–Alekseevskii model are briefly examined in this paper.