Donald A. Landis

A new particle identifier technique for Z = 1 and Z = 2 particles in the energy range > 10 MeV

Abstract Protons, deuterons, tritons, helium-3 and α particles produced in nuclear reactions have previously been identified by use of ΔE and E counters to determine dE/dx and E. Multiplying these together produces an output that is dependent on the type of particle. This technique is based on the theoretical relationship between dE/dx, E and the mass and charge of the particle. Unfortunately there is an obvious restriction on the technique, since dE/dx changes as the particle passes through the ΔE counter. For the E(dE/dx) product to have any real meaning, the ΔE counter must be thin and absorb only a small part of the total energy. This limits the use of this technique in a given experiment to small energy ranges and to selected types of particle. The new identifier also uses a ΔE (thickness T) and E counter, but employs the empirical relationship: Range = aE1.73, where a depends on the type of particle. Using the relationship, one can show T/a = (E+ΔE) 1.73 −E 1.73 . The identifier employs logarithmic elements to calculate this quantity and to produce an output that has a fixed value for each type of particle. The thickness of the ΔE counter is not limited to a very small value, and the identifier can cope with mixtures of all five types of particle, each covering a fairly wide energy range. Experimental results using this identifier and lithium drifted silicon detectors are presented and illustrate the clear separation between He3 and He4 particles (difficult to achieve with the multiplier type of identifier).

Accurate determination of the ionization energy in semiconductor detectors

Abstract The average energy g3 expended for electron-hole pair generation in silicon and germanium lithium-drifted detectors by gamma rays, electrons, and alpha particles has been measured as a function of temperature. These data indicate that the difference between eα and ee− in silicon is considerably less than previously reported, and in germanium eα ∼ ee−.

Signal Processing for Semiconductor Detectors

This is a tutorial paper designed to provide a balanced perspective on the processing of signals produced by semiconductor detectors. The general problems of pulse shaping to optimize resolution with constraints imposed by noise, counting rate and rise time fluctuations are discussed.

A time-zero detector utilizing isochronous transport of secondary electrons

Abstract A time-zero detector has been developed for use in reaction product mass identification which has as its novel feature a 180° isochronous transport of secondary electrons in a magnetic field. The secondary electrons produced when particles pass through a thin carbon foil are accelerated to approximately 2 keV by a parallel-wire harp of 99% transmission. The accelerated electrons are then transported 180° in a uniform magnetic field of 80 G containing a collimator placed at the 90° position. A background suppression grid is placed just in front of the electron detector which is comprised of two microchannel plates in series acting as an electron multiplier. The device allows placement of the thin foil perpendicular to the fragment flight path and permits shielding of the electron detector from the beam and reaction products while using only modest accelerating voltages. The time-of-flight resolutions measured between this timing detector and a 120 μm silicon detector when using 104 MeV 16O ions and 8.78 MeV alpha particles were 90 and 150 ps, respectively (full widths at half maxima).

Pulsed Feedback Tecniques for Semicondctor Detector Radiation Spectrometers

Methods of applying pulsed-charge feedback to the charge-sensitive preamplifiers used with semiconductor detectors are discussed. All have in commn the accumulation of radiation-induced charge pulses on a feedback capacitor to produce a voltage ramp at the output of the feedback stage, which is reset at an appropriate point by pulsing a charge feedback path. Advantages of pulsed feedback over the conventional dc feedback techniques are discussed, together with the precautions required to reduce the effect of the large reset pulse on the later electronics. The application of pulsed-light feedback to low energy X-ray spectrometers is discussed and results are presented. We also discuss sane aspects of this system that tend to limit its high-rate performance. A brief account of the use of a transistor current-switch feedback system to reduce overload problems in high-energy ?-ray spectrometers is also given.

Identification of nuclear fragments by a combined time-of-flight, ΔE-E technique☆

Abstract Nuclear fragments of Z = 5 to 10 that resulted from the interaction of 5.5-GeV protons with uranium have been identified by a combined time-of-flight, ΔE - E technique. A thin ΔE detector was used so that the ΔE - E information provided only element resolution, not isotopic resolution. However, the measurement of the time-of-flight between the ΔE and E detectors together with the energy deposited in the E detector allowed the fragment mass to be determined. This technique enabled us to observe not only the major isotopes of these elements but also such neutron-rich nuclei as 18 C and 20 N. An improved algorithm for power-law particle identification is also described.

High Rate X-Ray Fluorescence Analysis by Pulsed Excitation

We describe the application of pulsed X-ray excitation to X-ray fluorescence spectrometry as a method for increasing the output counting rate of the system by a substantial factor. Using a pulsed X-ray tube that is immediately turned off when a signal is detected, and held off during the pulse processing time, it is possible to eliminate the need for a pulse pile-up rejection. We have achieved output counting rates significantly greater than with conventional operation for equivalent shaping networks. No significant degradation in spectrometer resolution was observed at the increased counting rates.

Design Philosophy for High-Resolution Rate and Throughput Spectroscopy Systems

The paper describes the philosophy behind the design of a pulse processing system used in a semiconductor detector x-ray spectrometer to be used for plasma diagnostics at the Princeton TFTR facility. This application presents the unusual problems of very high counting rates and a high-energy neutron background while still requiring excellent resolution. To meet these requirements three specific new advances are included in the design: (i) A symmetrical triangular pulse shape is employed in the main pulse-processing channel. A new simple method of generating a close approximation to the symmetrical triangle has been developed. (ii) To cope with the very wide dynamic range of signals while maintaining a constant fast resolving time, approximately symmetrical triangular pulse shaping is also used in the fast pulse pile-up inspection channel. (iii) The demand for high throughput has resulted in a re-examination of the operation of pile-up rejectors and pulse stretchers. As a result a technique has been developed that, for a given total pulse shaping time, permits approximately a 40% increase in throughput in the system. Performance results obtained using the new techniques are presented.

A SPECTROMETER FOCAL PLANE DETECTOR FOR HEAVY IONS

Abstract A resistive-wire position-sensitive proportional transmission counter has been built for the detection of heavy ions in the focal plane of a magnetic spectrometer. The 45 × 6 cm2 counter measures position and energy loss with a resolution of 0.7 mm and 8–10% respectively. Time-of-flight is measured with a plastic scintillator behind the proportional counter. The position, time and energy loss signals are used to identify heavy ions with unit mass and atomic number resolution up to about A = 20, Z = 10.

Transistor Reset Preamplifier for High Rate High Resolution Spectroscopy

Pulsed transistor reset of high resolution charge sensitive preamplifiers used in cooled semiconductor spectrometers can sometimes have an advantage over pulsed light reset systems. Several versions of transistor reset spectrometers using both silicon and germanium detectors have been built. This paper discusses the advantages of the transistor reset system and illustrates several configurations of the packages used for the FET and reset transistor. It also describes the preamplifer circuit and shows the performance of the spectrometer at high rates.