Pulsed Linear Accelerator Research Articles

Short latency vestibular evoked potentials in the Japanese quail (Coturnix coturnix japonica).

Short-latency vestibular-evoked potentials to pulsed linear acceleration were characterized in the quail. Responses occurred within 8 ms following the onset of stimuli and were composed of a series of positive and negative peaks. The latencies and amplitudes of the first four peaks were quantitatively characterized. Mean latencies at 1.0 g ms-1 ranged from 1265 +/- 208 microseconds (P1, N = 18) to 4802 +/- 441 microseconds (N4, N = 13). Amplitudes ranged from 3.72 +/- 1.51 microV (P1/N1, N = 18) to 1.49 +/- 0.77 microV (P3/N3, N = 16). Latency-intensity (LI) slopes ranged from -38.7 +/- 7.3 microseconds dB-1 (P1, N = 18) to -71.6 +/- 21.9 microseconds dB-1 (N3, N = 15) and amplitude-intensity (AI) slopes ranged from 0.20 +/- 0.08 microV dB-1 (P1/N1, N = 18) to 0.07 +/- 0.04 microV dB-1 (P3/N3, N = 11). The mean response threshold across all animals was -21.83 +/- 3.34 dB re: 1.0 g ms-1 (N = 18). Responses remained after cochlear extirpation showing that they could not depend critically on cochlear activity. Responses were eliminated by destruction of the vestibular end organs, thus showing that responses depended critically and specifically on the vestibular system. The results demonstrate that the responses are vestibular and the findings provide a scientific basis for using vestibular responses to evaluate vestibular function through ontogeny and senescence in the quail.

Short Latency Vestibular Evoked Potentials in the Chicken Embryo1

Electrophysiological responses to pulsed linear acceleration stimuli were recorded in chicken embryos incubated for 19 or 20 days (E19/E20). Responses occurred within the first 16 ms following the stimulus onset. The evoked potentials disappeared following bilateral labyrinthectomy, but persisted following cochlear destruction alone, thus demonstrating that the responses were vestibular. Approximately 8 to 10 response peaks could be identified. The first 4 positive and corresponding negative components (early peaks with latencies < 6.0 ms) were scored and latencies and amplitudes quantified. Vestibular response latencies were significantly longer (P < 0.01) and amplitudes significantly smaller (P < 0.001) than those observed in 2-week-old birds. Mean response threshold for anesthetized embryos was -15.9dBre 1.0 g/ms, which was significantly higher (P < 0.03) than those observed in 2-week-old birds (-23.0dBre 1.0 g/ms). Latency/intensity functions (that is, slopes) were not significantly different between embryos and 2-week-old animals, but amplitude/intensity functions for embryos were significantly shallower than those for 2-week-old birds (P < 0.001). We presume that these differences reflect the refinement of sensory function that occurs following 19 to 20 days of incubation. The recording of vestibular evoked potentials provides an objective, direct and noninvasive measure of peripheral vestibular function in the embryo and, as such, the method shows promise as an investigative tool. The results of the present study form the definitive basis for using vestibular evoked potentials in the detailed study of avian vestibular ontogeny and factors that may influence it.

A radiation detection system for high-energy computerized tomography using CdZnTe detectors

This work presents a particular application in which cadmium-zinc telluride (CdZnTe) detectors are used in photoconductive mode in a high-energy computerized tomography system for industrial applications. A first-generation tomography facility has been set up at the University of Bologna, based on a 12-MeV pulsed linear accelerator X-ray source and a single 10/spl times/10/spl times/2 mm/sup 3/ CdZnTe detector. The obtained results show that CdZnTe detectors exhibit better timing performances than CdTe detectors, and are thus more suitable for tomographic applications. Special-purpose signal conditioning electronics have been developed in order to compensate slow and fast signal fluctuations induced by temperature variations and Linac instabilities, In such a way, the dynamic range of the detector has been improved up to more than 3 orders of magnitude. A set of images was acquired in order to evaluate the overall performances of the tomographic facility. >

Short latency vestibular evoked responses to linear acceleration stimuli in small mammals: masking effects and experimental applications.

Different potential were recorded from a site close to the 8th nerve in chinchillas in response to linear acceleration pulses. Acoustic masking allowed us to distinguish between an early response (within 1 ms after initiation of the acceleration) of probable vestibular origin and later responses of probable cochlear origin. The latter were abolished by intense acoustic masking and by surgical ablation of the cochlea. The early potential was slightly reduced by simultaneous acoustic masking with white noise above 65 dB SPL and was most sensitive to 1 kHz narrow band masking. Vestibular neurons seem to be stimulated by high frequency movements of their hair cell cilia, and vestibular compound action potentials can be recorded as soon as a sufficient number of neurons are brought to a synchronized response. These vestibular evoked potentials may provide a tool for experimental studies on vestibular function in laboratory animals.

Vestibular short latency responses to pulsed linear acceleration in unanesthetized animals

Linear acceleration transients were used to elicit vestibular compound action potentials in non-invasively prepared, unanesthetized animals for the first time (chicks, Gallus domesticus, n=33). Responses were composed of a series of up to 8 dominant peaks occurring within 8 msec of the stimulus. Response amplitudes for 1.0 g stimulus ranged from 1 to 10 μV. A late, slow, triphasic, anesthesia-labile component was identified as a dominant response feature in unanesthetized animals. Amplitudes increased and latencies decreased as stimulus intensity was increased (MANOVA P < 0.05). Linear regression slope ranges were: amplitudes = 1.0–5.0 μV/g; latencies = − 300 to −1100 μ sec/g. Thresholds for single polarity stimuli (0.035 ± 0.022 g, n = 11) were significanly lower than those of alternating polarity (0.074 ± 0.028 g, n = 18, P < 0.001). Bilateral labyrinthectomy eliminated responses whereas bilateral extirpation of cochleae did not significantly change response thresholds. Intense acoustic masking (100/104 dB SL) produced no effect in 2 animals, but did produce small to moderate effects on response amplitudes in 7 others. Changes were attributed to effects on vestibular end organs. Results of unilateral labyrinth blockade (tetrodotoxin) suggest that P1 and N1 preferentially reflect ipsilateral eight nerve compound action potentials whereas components beyond approximately 2 msec reflect activity from vestibular neurons that depend on both labyrinths. The results demonstrate that short latency vestibular compound action potentials can be measured in unanesthetized, non-invasively prepared animals.

Monitoring of ten-nanoseconds radiation pulses using ionization electrons

A thin-walled parallel-plate ionization chamber with high bandwidth is described by means of which (using O 2 filling) the presentation of the beam time profile of linear accelerator pulses of a few 10 ns duration is achieved. Filled with air the chamber can be used for the presentation of μm pulses. The intensity limits and the time resolution of the method are discussed.

The electronics and data acquisition system for the wire imaging synchrotron radiation detector at the SLC

The Stanford Large Collider (SLC), located at the Stanford Linear Accelerator Center, collides electrons and positrons produced in the linear accelerator pulse by pulse. The energy of each beam is determined by measuring the angle of deflection of the beam in the SLC extraction lines. Each extraction line consists of two bending magnets that produce synchrotron radiation, and a spectrometer analyzing magnet that deflects the beam. The synchrotron light is detected by using the emission of electrons produced by Compton scattering off Cu-Be wires. The electronics used to detect the approximately 180 fC of charge on the wire is described. The performance of the system, including the equivalent noise charge, crosstalk stability, and reliability are discussed. >

Measuring the Mass and Width of the Z0: The Status of the Energy Spectrometers

The Stanford Linear Collider (SLC) 1 ocated at the Stanford Linear Accelerator Center (SLAC) ll'd co I es electrons and positrons produced in the linear accelerator pulse by pulse. The object is to produce collisions energetic enough to produce the heavy intermediate vector boson, the 2 '. An essential component of the SLC physics program is the precise knowledge of the center-of-mass energy of each inter- action. We measure the energy of each collision by using two energy spectrometers. The spectrometers are located in extraction lines of each beam. We will measure the-energy of each beam to 20 MeV or 5 parts in 104. We report here on the status of the energy spectrometer system.

Short latency vestibular responses to pulsed linear acceleration

Far-field vestibular responses to pulsed linear cranial acceleration have not been reported in detail for any species. In this study, precisely defined pulsed linear accelerations were used to elicit vestibular neural responses recorded from the surfaces of the skulls of 23 White Leghorn chicks. Traditional signal averaging techniques were used to resolve responses. At moderate intensities, responses consisted of a series of four to seven dominant peaks occurring within a period of 8 ms, having amplitudes between 0.3 and 20 μV peak-to-peak. The mean response threshold was 0.120 ± 0.045 g. Latencies and amplitudes varied systematically as a function of stimulus intensity. Hypothermia prolonged response latencies. Response peaks did not invert on stimulus inversion, were present in response to cranial but not trunk acceleration, were not attenuated by broad-band auditory masking or by ambient light conditions, and disappeared with complete bilateral destruction of the labyrinth. The results rule out major contributions from auditory, somatosensory, and visual modalities and support the hypothesis that the responses reflect bilateral neural activity in the vestibular system. The findings suggest that direct noninvasive assessment of peripheral vestibular function can be achieved using pulsed linear acceleration stimuli.

Use of the variance-covariance technique for determination of the radiation quality in a pulsed linear accelerator

Recent recommendations of a joint task group of the ICRU and ICRP have established the microdosimetric quantity “lineal energy” as the parameter of choice for determination of the radiation quality for purposes of radiation protection. Unlike linear energy transfer (LET or stopping power), lineal energy can be measured directly for tissue-equivalent volumes with dimensions of relevance to radiobiology (of the order of 1 μm). Conventional proportional-counter spectroscopy, the method most frequently utilized for determination of linear energy spectra, is impractical for short-duty cycle pulsed machines. A technique for determination of the dose mean lineal energy, utilizing the relative variance and covariance of two proportional counters operated in synchrony with the beam pulse, is described. Design and construction of a new ultraminiature proportional counter for use in high-dose-rate fields is described. This extremely small cross section (0.25 mm 2) counter should make multi-event measurements practical in the beam of a pulsed linear electron accelerator at full dose rate and single-event measurements at slightly reduced intensities; this in turn should make possible the microdosimetric determination of photoneutron contamination in megavoltage photon beams.

Pulsed linear acceleration as a vestibular stimulus in electrophysiological investigations

A simple method of generating precisely defined pulsed linear acceleration stimuli was developed and used to study vestibular responses to cranial acceleration. Electromechanical shakers were coupled to a stimulus platform. The platform, in turn, was used to couple stimuli to the skull. Movements were controlled by a voltage waveform ( V(t)) applied to shakers. Software algorithms were used to synthesize voltage functions ( V(t)). The resulting acceleration was monitored [ a(t)] and used to generate velocity [ v(t)] and position [ x(t)] functions (first and second integrals of a(t), respectively). The characteristics of stimuli used in physiological experiments are described. The system provides precise control of the timing and amplitude of acceleration, velocity and position pulses to the cranium and has proved to be valuable in developing noninvasive electrophysiological measures of peripheral and central vestibular function.

Pulse radiolysis system based on ELU-6E LINAC

Basic parameters and operating characteristics of the linear microwave accelerator ELU-6 and pulse radiolysis system are given. LINAC can operate in single pulse mode or with repetition of 10 to 200 pps. In nanosecond mode electron pulses of 7, 10 and 17 ns, beam currents≧10 A and an energy of 8 MeV are generated. In microsecond mode, duration of pulses can be varied from 0.3 to 4.5 μs, beam current up to 1.2 A and energy not less than 5 MeV are available. Versatile pulse radiolysis system enables routine optical measurements in the range from 350 to 2500 nm on the time scale from 10 ns to a few seconds. Transient signals are recorded by a 400 MHz storage Tektronix oscilloscope or by an IWATSU TS8123 digital oscilloscope linked to an Apple II microcomputer incorporated into the Institute computer system. A set up for pulse conductivity measurements with μs resolution time is also available.

Microdosimetry of Pulsed Radiation Fields Employing the Variance Method

The relationship between dose mean lineal energy and relative variance has been exploited previously to derive yD from the calculated variance in current measurements in steady and uniform radiation fields. Recently Kellerer and Rossi made the observation that utilization of two detectors can make the variance technique practicable in time-varying fields. We report here the first measurements of yD for 10 MeV X rays and 9 and 18 MeV electrons from a pulsed linear accelerator using the variance method. Two independent analog-to-digital converters were used to obtain data from two spherical proportional counters in synchrony with the beam pulse. The method is described in detail and results are reported for site diameters of 1/2, 1, and 2 microns. Data for an accurate determination of yD can be obtained with this technique in less than 1 min, making possible an essentially "on line" determination of yD or zD in a clinical situation.

RIIM Accelerator Beam Experiments

A pulsed linear accelerator assembly, RIIM (RADLAC II Module), composed of an injector plus a number of post accelerating gaps was built and successfully operated. The injector and the post accelerating gaps were powered by water strip pulse forming and transmission lines. A high-current, high-voltage, foilless diode injector was used and an annular 40-kA relativistic electron beam was produced and further accelerated through the post accelerating gaps. The final beam energy was close to the sum of injector and gap voltages and equal to 9 MeV.

Voltage Breakdown in S-Band Linear Accelerator Cavities

Voltage breakdown is one of the major limiting factors in the design of a high accelerating gradient linear accelerator structure. A multiple-use cavity test system was developed to establish the criteria for voltage breakdown in S-band pulsed electron linear accelerator cavities, in terms of cavity geometry, accelerating gradient, RF pulse shape and repetition rate, surface finish, temperature and external magnetic field. The experimental set-up and test procedure, as well as the experimental results, are presented.

Neutron beams for the study of condensed matter: A view of the first half-century

Abstract Neutron diffraction was first demonstrated in 1936 but awaited the development of the nuclear reactor before becoming a practical technique for the study of condensed matter. Neutrons have unique advantages for the location of hydrogen atoms, the recognition of magnetic architecture and the study of crystal vibrations and atomic and molecular motions. The techniques available exploit the optical properties of neutrons over a wavelength range from O5 to 500 Å. Progress has gone hand in hand with a steady increase of reactor flux over 50 years but future improvements may depend on pulsed linear accelerators as the source of neutrons.

High sensitivity transuranic waste assay by simultaneous photon and thermal-neutron interrogation using an electron linear accelerator

Simultaneous photon and neutron interrogation from electron linear accelerator pulses is used as the basis for a unique assay technique for transuranics. Both prompt and delayed neutrons from the induced fissions are counted on a single detction system, and the contributions from each interrogating flux are resolved. Detection limits (3σ) for 239Pu were estimated to be 3 mg for prompt fission neutrons and 6 mg for delayed neutrons. The technique also provides a clear distinction between fissile and fertile nuclides.

Statistical properties of complex states ofZn3067

High resolution neutron total and capture cross section measurements have been made on the separated isotope /sup 66/Zn in the energy range from a few keV to about 1 MeV using the neutron time-of-flight technique and the pulsed Oak Ridge Electron Linear Accelerator. The nominal resolution of the measurements was 0.07 ns/m. The total cross section data have been analyzed up to 380 keV using a multilevel R-matrix formalism and the capture data up to 130 keV using a least squares fit program. From these analyses we have obtained the values of the resonance parameters E/sub 0/, gGAMMA/sub n/, and GAMMA/sub ..gamma../, and values of average quantities: D/sub l/ = 0 = (4.62 +- 0.55) keV, D/sub l/ = 1 = (1.17 +- 0.14) keV, S/sub 0/ = (2.06 +- 0.36), S/sub 1/ = (0.66 +- 0.06), and S/sub 2/ = (0.50 +- 0.12) in units of 10/sup -4/ eV/sup -1/2/. The values of average radiation widths are (0.39 +- 0.06) eV for s-wave resonances and (0.190 +- 0.013) eV for p-wave resonances. The distributions of neutron reduced widths and of level spacings of s- and p-wave resonances show excellent agreement with the Porter-Thomas and Wigner distributions, respectively. The valuemore » of the ..delta../sub 3/ statistic for the long range correlation of s-wave energy levels is found to be in reasonable agreement with the theoretical prediction of Dyson and Mehta. A value of 0.59 +- 0.10 has been determined for the linear coefficient for the correlation between the neutron reduced widths and the radiation widths of 26 s-wave resonances. This value is highly significant and has a confidence level of 99.7%.« less

"Advanced Test Accelerator (ATA) Pulse Power Technology Development

The Advanced Test Accelerator (ATA) is a pulsed linear induction accelerator with the following design parameters: 50 MeV, 10 kA, 70 ns, and 1 kHz in a ten-pulse burst. Acceleration is accomplished by means of 190 ferrite-loaded cells, each capable of maintaining a 250 kV voltage pulse for 70 ns across a 1-inch gap. The unique characteristic of this machine is its 1 kHz burst mode capability at very high currents. This paper describes the pulse power development program which used the Experimental Test Accelerator (ETA) technology as a starting base. Considerable changes have been made both electrically and mechanically in the pulse power components with special consideration being given to the design to achieve higher reliability. A prototype module which incorporates all the pulse power components has been built and tested for millions of shots. Prototype components and test results are described.

Production and postacceleration of intense ion beams in magnetically insulated gaps

Experiments are described pertaining to the development of very high-current pulsed linear ion accelerators utilizing electron neutralization. A novel magnetically insulated gap using radial magnetic fields has been tested. It provides stable electron cloud confinement over microsecond time scales with no detectable leakage current. The gap can act as an ion injector when used in conjunction with a plasma source. Control of the electron cloud dynamics allows the injector to operate in an enhanced current density mode (10–50 times the Child-Langmuir limit) with high efficiency and with plasma source control of the current flow. Currents up to 20 kA at 100 kV applied voltage resulted when using a light-ion flashboard plasma source. Carbon beams were produced by extraction from a flowing plasma from a gun array. A 3-kA beam with equal fractions of C+ and C++ was extracted over a microsecond time scale with little proton contamination. The use of active plasma injection into the high-intensity magnetically insulated diode had the advantages of ion species control, reduction of gap damage, operation at constant impedance, elimination of plasma closure effects, and a demonstrated ability to control the extracted beam optics. Observations were also made of beam propagation and compared to fast neutralization models. Agreement was good, and an upper limit of 0.2% was calculated for the imbalance of ion and electron space charge. When using the carbon injector, two-thirds of the beam reached a second magnetically insulated gap where it was postaccelerated. The second gap had an applied voltage in the range 150 –200 kV with beam currents typically 2 kA. Observations were made of electrostatic focusing in the postacceleration gap. These were in good agreement with theory based on the concept of virtual electrodes determined by the neutralizing electron dynamics.