Showing papers in "IEEE Transactions on Nuclear Science in 1964"

The Transient Response of Transistors and Diodes to Ionizing Radiation

Abstract: Mathematical models describing the response of diodes and transistors to ionizing radiation are derived from the continuity and diffusion equations and, in the case of the transistor, the charge control model. Solutions are obtained for both steady-state and transient radiation environments. In addition to being of use in understanding device behavior, these solutions also indicate those device parameters which must be optimized to reduce transient response and therefore provide criteria for the design and/or selection of devices with minimum response. A model is also presented which describes the nonlinear effect of collector multiplication upon the collector photocurrent of a transistor. This model is used as a basis for explaining and predicting the nonlinear relation between the peak photo-response and the radiation dose which has been observed in some devices.

CaI2 and CaI2(Eu) Scintillation Crystals

Abstract: Scintillation crystals of CaI2 and CaI2(Eu) have been produced which iypically show pulse heights of 180% relative to NaI(Tl). The emission spectra for both pure and activated materials are well matched to a S-ll phototube response. Pure CaI2 has a decay time of 0.55, ?sec; CaI2(Eu) has a 0.79, ?sec decay time. Though this material is difficult to grow and to package, performance results thus far obtained are encouraging.

Semiconductor Lithium-Ion Drift Diodes as High-Resolution Gamma-Ray Pair Spectrometers

Abstract: Germanium and silicon p-i-n diodes with active volumes up to 2 cm3 have been fabricated using the lithium-ion drift technique. p-type germanium doped with either gallium or zinc (5-10 ohm-cm) and boron-doped silicon (1100 ohm-cm) were the base materials. Diodes were operated at 77°K in conjunction with a low noise amplifier system (270 RMS electron-holes). They have been used as gamma-ray pair spectrometers, germanium diodes giving a resolution of 7 keV (FWHM) at 2.75 MeV gamma-ray energy increasing to 10 keV at 7.64 MeV; resolution from a silicon device was slightly inferior. A germanium diode has been used as the central detector in a triple-crystal pair spectrometer incorporating two NaI scintillators. This arrangement improved the ratio of the height of the pair peak to the background below the peak from 7:1 to 150:1 for 2.75 MeV gamma-rays from a Na24 source.

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 a particles produced in nuclear reactions have previously been identified by use of ?E 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 re striction on the technique, since dE/dx changes as the particle passes through the ?E counter. For the E(dE/dx) product to have any real meaning, the ?E 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 ?E (thickness T) and E counter, but employs the empirical relationship, Range = a E1.73, where a depends on the type of particle. Using this relationship, one can show T/a = (E + ?E)1.73 - E1.73. 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 ?E 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.

Thick Junctions Made with Nuclear Compensated Silicon

Abstract: It is known that making detectors with great depletion depth is related to the availability of high resistivity Si, generally obtained by compensation. We have experimented a new compensating technique, based on the production of P-31, in situ, by nuclear transmutation of Si by thermal neutrons. After annealing, very high resistivity Si (200 000 ?. cm at 300° K) has been obtained by this method. NIP structures with great depletion depth obtained by nuclear compensation are described, as an example of the possibilities of this new technique.

A Low-Noise Charge-Sensitive Preamplifier with a Field-Effect Transistor in the Input Stage

Abstract: The excellent energy resolution of semiconductor radiation detectors has generated a need for charge-sensitive transistorized preamplifiers which have low values of noise line-widths. The application of field-effect transistors in charge-sensitive configurations was investigated, and a low-noise preamplifier was consequently developed. The preamplifier has a junction field-effect transistor in the input stage. The field-effect transistor is connected in cascode with the second stage bipolar transistor which has its collector load bootstrapped by a White follower. The bias stabilization is adequate for normal operation of the preamplifier over an FET temperature range from room temperature to liquid nitrogen temperature. Measured values of the preamplifier noise line-width as a function of pulse-shaping time constants, total input capacitance, and temperature are presented. Formulas are included for the theoretical determination of the noise line-width, Application of the formulas requires knowledge of the parameters of the preamplifier and pulse-shaping circuitry and the noise characteristics of the FET. The FET noise characteristics are shown as experimentally determined graphs of narrow-band equivalent noise resistance versus frequency, temperature, and bias point. Preamplifier noise line-widths less than 1.6 kev fwhm for silicon detectors (189 rms electronic charges) and slopes less than 0.06 kev/pf (7.1 rms electronic charges per pf) were obtained when the FET was cooled to the optimum temperature which was approximately 125°K.

A Survey of the Applications and Limitations of Various Types of Detectors in Radiation Energy Measurement

Abstract: This paper provides a collection of data relevant to the use of various types of semiconductor detector in nuclear spectroscopy and gives examples of the use of detectors in specific experimental applications. Basic data on absorption of various kinds of radiation in germanium and silicon are given, and these are related to the characteristics of different types of semiconductor detectors. A brief outline of the optimization procedure for the detector-amplifier system to obtain good energy resolution follows. Included in a brief review of applications of detectors are examples in the fields of a-particle spectrometry, high-energy particle reactions, and low-temperature nuclear alignment studies.

Multiplication in the Fission Fragment Pulse Height Response of Silicon Surface Barriers

Abstract: A number of investigators have observed multiplication phenomenon in the response of silicon surface barriers to fission fragments. In many cases, this multiplication is anomalous in the sense that it occurs at electric field intensities well below that required for avalanche multiplication. One group has suggested that this phenomenon is related to a "threshold depth". 1 However, other results from investigations of the response of surface barriers to fission fragments2 and heavy ions3 for a wide range of silicon resistivities and bias voltages have exhibited no systematic evidence to support the concept of a "threshold depth". In the work reported here, we demonstrate that multiplications at anomalously low field strengths can be significantly reduced by surface treatment after fabrication and can be reduced or eliminated by the proper surface treatment and control of the thickness of the front electrode. A possible multiplication mechanism based on the concept of tunneling injection through the oxide layer, which was first suggested by Gibson and Miller4, is discussed in terms of these experimental results. Fabrication techniques which minimize the tendency to multiply, together with other detailed design criteria for optimizing the performance of fission fragment and heavy ion spectrometers, are also presented.

Plasma Diagnostics with Short Electromagnetic Pulses

Abstract: The propagation of short electromagnetic pulses in an ionized medium and the reflection of transient pulses from bounded ionized regions is discussed. Analytical expressions for transient oscillations in reflected and propagated electromagnetic fields excited by a unidirectional pulse are derived for certain simple cases. The transient oscillations show a periodicity which is directly related to the plasma frequency and are useful for nearly instantaneous plasma diagnostics. An experiment is described in which the reflection and transmission of unidirectional pulses of approximately 1 nanosecond duration is observed in the afterglow of a coaxial discharge tube. In addition to the dispersion of the quasi TEM mode in the coaxial test tube a transient oscillation with much lower periodicity is also observed and interpreted as arising from a surface-wave propagating near the interface between glass walls and the annular ionized region. This surface-wave propagates only at frequencies below the plasma frequency of the ionized region and its application for diagnostics of dense plasma is indicated.

Study of Surface Effects in Thick Lithium Drifted Silicon Radiation Detectors

Abstract: Leakage current in lithium drifted detectors is a very sensitive function of surface condition. In this paper some attempts at gaining a better understanding of the relevant surface phenomena are reported. N-type conduction layers were found which extended from the lithium-rich side across the depleted material to an inversion layer on the p-type material, at the other end of the detector. Regions of high electric field exist in the vicinity of the i-p boundary. By measuring surface potentials and solving Laplace's equation in the depletion region, one can compute electric field configurations as well as net charge concentration at the surface. Collection probability for pairs generated in the surface layer was measured and found to be independent of bias above VB /m=simeq/ 1 volt. A model for the generation of surface currents is proposed. Measurements indicate that most of the surface current is created in the region of high field. Finally, the number of occupied surface states is computed and found to be, at low bias, of the order of 1/104 times the number of atoms at the Si surface.

High Temperature Nuclear Particle Detector

Abstract: In many applications it is necessary to use sensors which are capable of operating in regions of either high ambient temperature or radiation flux or both. Such conditions may occur in reactor cores, casings of nuclear engines, etc. For applications of this type a nuclear particle detector has been developed fron silicon carbide (SiC) which can detect charged particles, and, with the addition of a fissionable coating,, thermal neutrons at temperatures in excess of 700°C. In a limited test of radiation resistance, selected diodes have been irradiated up to 1014 protons/cm2, with alternating irradiation and annealing. At this dosage, (roughly equivalent to 1016nvt) some permanent degradation of the properties occurred. It has been shown that the crystal perfection and the purity of the original crystal are of extreme importance in preparing the detector. The junction structure must also be tailored so that efficient counting is obtained.

Multiplier Phototubes for Single Electron Counting

Abstract: Typical operating characteristics of ITT Industrial Laboratories' special purpose multiplier phototubes are described, with particular emphasis on the ability of these tubes to count single photoelectrons with minimum interference from dark noise. This ability, of particular significance in the detection of low energy quanta, including single photons, follows from the Poisson-like output pulse height distribution observed in the tubes in which a well-defined most probable pulse amplitude appears, compared to a more complex but lower amplitude dark noise pulse height spectrum. Other features of these tubes, such as adjustable cathode size and shape, electrical deflection for automatic gain calibration, alignment and image tracking, and reduction of dark noise with cooling, are also described.

Silicon P-N Junction Radiation Detectors for the Telstar® Satellite

Abstract: This paper describes the development and testing of the silicon p-n junction nuclear particle detectors which have been ued in the radiation experiments of the TELSTAR® communication satellite, and the Relay and Explorer XV satellites. The sensitive element of the detector is a diffused mesa diode of 10,000 to 20,000 ohm-cm p-type silicon. It is encapsulated in a transistor-type can with a thin (0.3 mil) Kovar window. In spite of the encapsulation, surface reliability was a major development problem. An extensive reliability testing program revealed several types of surface instability. Nevertheless, a high degree of reliability was achieved in most of the detectors, including those which were used on satellites.

Evaluation of the C-70045A High-Speed Photomultiplier

Abstract: Measurements were made of the time spread, pulse response, and other characteristics of the C-70045A 14stage photomultiplier which was developed for high-speed timing applications with scintillation and Cerenkov radiation detection. Rise times and time jitters are given. Some measurements of the scintillation decay time of two plastic scintillators are reported. (D.L.C.)

Rectifying Process in Surface Barrier Detectors

Abstract: As a part of research on surface barrier detectors the formation of rectifying contacts has been studied for gold on n-type silicon. It has been observed that rectifying properties appear only if the ambient gas gives negative surface charges upon adsorption. Experiments have been performed with several gases (air, oxygen...). During the formation process, the variation of reverse current is strongly modified if a d. c. field is applied. This effect shows the importance of oxygen ions in the process leading to inversion layer.

Use of Ferroelectrics for Gamma-Ray Dosimetry

Abstract: A gamma-ray dosimeter employing a poled ferroelectric as the transducer element has been studied. Irradiation with gamma rays causes a release of charge by the ferroelectric element. The magnitude of the charge released has been determined experimentally to vary linearly with gamma-ray dose. The current in a shunting resistor with no external voltage applied varies linearly with gamma-ray dose rate. A constant of proportionality of 10-12 coul per rad (H2O) per cm2 of electroded ferroelectric surface has been measured for polycrystalline Pb(Zr.65 Ti.35)O3 + 1 w% Nb2O5 irradiated in the Sandia Pulsed Reactor. The contribution to the charge release from the neutron irradiation has been determined experimentally to be negligible. Irradiation in the 0.6 Mvp flash X-ray also produces a linear relationship between current and gamma-ray dose rate. A similar release of charge has been observed in poled ceramic barium titanate.

A Rigorous Least-Squares Analysis of Complex Gamma-Ray Spectra with Partial Compensation for Instrumental Instability

Abstract: The least-squares method for analyzing multichannel gamma-ray spectra is one of great power and versatility, but its full potential is difficult to realize due to instrumental instabilities. For sources having low or moderate activities and for which the counting times range from a few minutes to several hours, the most important instabilities are long term drifts in zero-energy channel-intercept and gain. A computer routine based on the use of a special reference source is described, which can detect changes in zero-intercept of as little as 0.05 channels (for a 512 channel analyzer), and in gain of as little as 0.1%. By prior transformation of the data to compensate for these effects, and by the use of appropriate weighting factors in the least-squares analysis, the goodness of fit is dramatically improved. Often, the goodness of fit indicator "chi-squared over degrees of freedom" is reduced from a value in excess of three, to a value which does not differ significantly from unity. The weighting procedure described takes into account the statistical errors in both the complex spectrum which is to be analyzed, and in the reference spectra which are its components. These computer methods have been applied to the analysis of gamma-spectra from biological materials containing low activities of the natural series of radionuclides, and of atomic fallout products.

Gasdynamic Diagnosis of High-Speed Flows Expanded from Plasma States

Abstract: : A number of methods of determining quantities are described which define the flow in low density, hypersonic wind tunnels which use plasma generators to heat the working fluid. Although the fluid was heated to a plasma state initially, with a typical bulk temperature of 12,000 R, the measurements reported were for the purpose of calibrating the flow in the aerodynamic nozzle of a wind tunnel where it is desirable that the fluid be recombined before or during the expansion to high speeds. All of the methods considered may be classed as gas dynamic or aerodynamic as opposed to, say, spectroscopic methods. Measurements of total enthalpy, total and static pressure, and local mass flux are discussed, with descriptions of the equipment and typical results included. The emphasis is placed on procedures not requiring assumptions for the data reduction which cannot be checked. An appendix containing an account of the effect on nozzle flow which was caused by one method of swirling gas injection into the plasma generator electrode section is also included.

The field-effect transistor-its characteristics and applications

Abstract: The characteristics of the junction gate field-effect transistor and the basic relations among its parameters are described. Some figures of merit are derived in terms of its physical parameters and the limitations considered. Applications in nuclear instrumentation are discussed. Some advantages of field-effect transistors are in high input impedance, low noise at very low and medium frequencies, and a wide operating temperature range (-200°C to +100°C). In addition, the field-effect transistor represents a new circuit element - voltage (charge) controlled conductance with fast response. Field-effect transistors are particularly suitable for low noise amplifiers at low and medium frequencies, for high input impedance amplifiers (as for integrators), for charge-sensitive amplifiers, and for analogue multipliers. They can also be applied as controllable feedback elements.

Radiation Damage in Lithium Drifted p-i-n Junctions

Abstract: A major effect of radiation damage of semiconductor junction detectors is the decrease of charge carrier lifetime. The thick depletion regions and low fields usually employed in p-i-n junctions makes them particularly sensitive to radiation damage. A study of the changes of electron trapping lengths in silicon p-i-n junctions as a function of radiation damage by Co60 gamma rays is presented. Significant changes of collection efficiency and collection time were observed at doses (~105R) which are considered negligible for damage in p-n junctions. The variations of reverse current and noise were small for these low doses. A method of fabrication and encapsulation of p-i-n junction radiation detectors is described which utilizes ion drifting from a localized source of lithium and a gold-silicon alloy seal.

Junction Counters Produced by Ion Implantation Doping

Abstract: Boron ions of 500 Kev and 100 Kev energy (0.7 microns and 0.14 microns range respectively) from a Van de Graaff accelerator have been used to fabricate 1/2 - inch diameter junction counters by bombarding the surface of etched 5000 ?-cm and 10, 000 ?-cm n-type silicon slices. After being passed through an analyzing magnet to obtain a spectroscopically pure beam, the ions were scanned by electrostatic deflection plates to obtain uniform irradiation of the samples. Boron concentration could be varied as a function of depth in the crystal by programmed rotation of the slices about an axis perpendicular to the beam. After post-irradiation annealing at 300°C to remove radiation damage, evaporated aluminum contacts were applied to the front and electroless nickel to the back. Initial investigation resulted in diodes with leakage as low as 10 ?a at -100 volts and reverse breakdown voltage greater than -400 volts. The thinnest dead layer was 0.2 microns. Pulse height spectra taken with Po210 alpha particles (5.3 Mev), in general contained large numbers of counts at low pulse heights, presumably due to carrier trapping in radiation-induced crystal defects. The best counter had a resolution of 50 Kev with insignificant low energy noise.

Heavy Particle Radiation Damage Effects in Lithium Drifted Silicon Detectors

Abstract: Deterioration of charged-particle resolution-width, for p-i-n detectors prepared by lithiumion-drift techniques, was observed during bombardment with protons, and alpha particles. During exposure the resolution-width increased without loss of rectification when damage was confined to the intrinsic region. Significant deterioration in response was observed for 108 particles/cm2. Rapid loss of rectification was observed during exposure to neutrons at energies mostly in the range of from 1 to 10 MeV and for a flux of 109 neutrons/cm2/sec. The damage effects were studied with several detectors having an electron resolution-width of 15 to 20 keV at room temperature, and a window thickness of approximately 1 mg/cm2. Limitations on recovery, by further drift treatment, were observed for an integrated charged-particle flux in excess of 1012 particles/cm2. The response of these detectors to electrons before and after damage, and to heavy charged particles during production of damage and after recovery, is described.

An Automatic Lithium Drifting Apparatus for Silicon and Germanium Detectors

Abstract: Drifting a thick lithium-drifted counter (silicon and germanium) is a time-consuming operation that frequently results in a poor device, owing to inadequate knowledge of progress of the drifting operation. The drifting apparatus described here automatically controls the temperature of the detector that is being drifted to maintain the leakage current at a preselected value. While drifting proceeds, a continuous measurement is made of the distance of the lithium-drifted region from the opposite face of the wafer. When the drifted region reaches 30 mil or less from the back of the wafer a meter indicates the thickness of the undrifted region and, when this thickness falls below a preselected value, the temperature of the detector is automatically reduced to room temperature. The need for constant supervision of the drifting operation is thereby eliminated, and reliance on theoretical drift-rate calculations to predict the drift-through time is avoided. The technique has been applied to the manufacture of lithium -drifted silicon detectors with excellent results. The application of the technique to lithiumdrifted germanium ? detectors is also discussed briefly.

Fast Analogue Multipliers with Field-Effect Transistors

Abstract: The solution time of analogue multipliers using field-effect transistors is investigated. This time is ultimately limited by the charging time of the field-effect transistor junction. In typical devices suitable for analogue multiplication the charging time is found to be about 10-20 nsec for a multiplication error of less than one percent. A four quadrant pulse amplitude multiplier circuit is described, whose solution time is equal to the field-effect transistor charging time.

On Cooled Anodes in Contact with a Laminar Arc-Heated Flow

Abstract: This paper is concerned with the physics and operating characteristics of cooled anodes In contact with an arc-heated laminar plasma flow in a constant area duct. Various modes of anode behavior are identified and described. Some Influences of gas type, flow rate, arc current, anode material and geometry are demonstrated. A theory is developed to explain the low-current mode of the anode characteristic. It is shown that the local current density on the anode surface is related approximately to the surface's local bias relative to its electrically floating voltage. Anode current distribution data is presented; the distribution is shown to be unstable above a transition bias volt,. age, with the current concentrating intensely on the edge of the anode toward the cathode. Neighboring points on the duct wall are shown to be electrically independent. This fact greatly simplifies an interpretation of anode phenomena. The information presented makes a fairly complete picture of the physical behavior of finite-length, cooled anodes in contact with fully-developed laminar plasma-arc flows.

Recent Photomultiplier Developments at RCA

Abstract: Data on transit time and rise time for numerous types of photomultipliers are presented. Two new photomultipliers designed to provide superior time resolution are discussed. The properties of existing types designed for energy spectroscopy are reviewed. New types designed to reduce dark noise due to radioactive contaminants, dark current, and leakage are described and performance data presented. Some of the advantages of the K2CsSb photocathode are shown. The development of photomultipliers for severe environments is reviewed. Two new families of tubes for this service are described.