Bremsstrahlung Measurements Research Articles

Bremsstrahlung measurements in the near infrared on ASDEX

In the ASDEX Thomson scattering system the scattered light of a Nd:YAG laser beam (λ=1064 nm) is measured to obtain electron density and temperature profiles every 16 ms. The same system is continuously used to measure bremsstrahlung in the near infrared, allowing determination of radial Zeff profiles. Some characteristic examples of radiation and Zeff profiles are given. The time resolution of the detection system (≤50 kHz) is sufficiently high to observe fast MHD phenomena such as sawtooth instabilities around the q=1 surface and density fluctuations in the plasma edge. Furthermore, the diagnostic can also be used for real time control of the electron density. This applies in particular in cases where large sawteeth and pellet injection generate counting errors in the interferometer signal. The relation between the line density n and the central chord bremsstrahlung signal Ub was investigated for different heating scenarios in a wide density range.

Excitation and ionization of freon molecules. I. Absolute oscillator strengths for the photoabsorption (12–740 eV) and the ionic photofragmentation (15–80 ev) of CF 4

Absolute photoabsorption oscillator strengths (cross sections) for the valence shell of CF 4 have been measured using dipole (e, e) spectroscopy in the equivalent photon energy range 12–200 eV. The present results are in good agreement with optical measurements obtained using synchrotron radiation in the range 12–70 eV and also with earlier reported oscillator strengths derived from electron impact measurements in the range 12–37 eV. Predicted values obtained by extrapolation of the valence shell continuum to high energies are in excellent agreement with published measurements obtained using X-ray characteristic lines and bremsstrahlung radiation. Carbon 1s and fluorine 1s photoabsorption spectra obtained by Bethe-Born conversion of earlier reported inner shell electron energy loss spectra of CF 4 have been placed on an absolute intensity scale by normalizing on atomic cross sections in the respective 1s photoionization continuum regions. The results are compared with bremsstrahlung measurements. The photoionization efficiency and also the ion photofragmentation branching ratios have been determined from time of flight mass spectra measured using dipole (e, e+ion) coincidence spectroscopy at equivalent photon energies ranging from the first ionization threshold up to 80 eV. Absolute partial oscillator strengths for molecular and dissociative photoionization have been derived. The nature of the dipole induced breakdown pathways of CF 4 is investigated by combining the present oscillator strength measurements for molecular and dissociative photoionization with previously published photoelectron data. On the basis of the present work, a revised set of absolute electronic state partial oscillator strengths for CF 4 are presented.

In-situ measurement of tritium partial pressure by bremsstrahlung counting method

To measure tritium pressure in fuel processing systems in DT burning fusion devices, the applicability of a bremsstrahlung counting method was examined by using an apparatus for supply and recovery of highly concentrated tritium gas. For the measurement of bremsstrahlung, a newly designed proportional counter showed a considerably high sensitivity to the measurement of bremsstrahlung. In addition, the bremsstrahlung counting rate showed excellent linearity to tritium partial pressure when the total pressure was below 100 Torr. Above this upper pressure limit, the counting rate deviated downward from the linear relation. The deviation, however, could be represented quite well by a simple exponential function of pressure. It was shown that the tritium partial pressure in the hydrogen isotope gases could be determined in the range from 5 × 10−2 to 760 Torr. Consequently, the present methods is quite useful for in-situ and non-destructive measurements of tritium partial pressure in the fuel processing systems of thermo-nuclear fusion devices.

Dayside energetic electron precipitation over the South Pole (λ = 75°)

Balloon bremsstrahlung measurements of electron precipitation between 25 and 500 keV were made near South Pole station, 75° invariant latitude, between December 15, 1985 and January 15, 1986. On January 2 and 3, 1986, a period of low to moderate geomagnetic activity, precipitation with characteristic (average) energy E0 in the range 20‐200 keV was observed on the dayside, i.e., between ∼ 0500 and ∼ 1500 local magnetic time. In one event, with E0 initially 150 keV, 35‐keV electrons arrived 9 min later than 350‐keV ones; here the trapped energetic electron population may have been enhanced during an injection in the midnight sector and drifted eastward to undergo precipitation in the morning sector. In another event, E0 was 200 keV, but the least energetic electrons arrived within < 0.5 min of the most energetic, indicating a scattering process close to the station. These are the first published reports known to us of precipitating electrons at L > 10 with fluxes measured in the entire energy range from 20 keV to over 250 keV. Near noon on both days, effects were seen in the data that suggest passage of the cusp or polar cap boundary into the field of view of the balloon sensors.

Measurement of pion-proton bremsstrahlung for pions at 299 MeV.

We have measured the fivefold differential cross section ${d}^{5}$\ensuremath{\sigma}/d${\ensuremath{\Omega}}_{\ensuremath{\pi}}$d${\ensuremath{\Omega}}_{\ensuremath{\gamma}}$${\mathrm{dE}}_{\ensuremath{\gamma}}$ for the process ${\ensuremath{\pi}}^{+}$p\ensuremath{\rightarrow}${\ensuremath{\pi}}^{+}$p\ensuremath{\gamma} with incident pions of energy 299 MeV. The angular regions for the outgoing pions (55\ifmmode^\circ\else\textdegree\fi{}\ensuremath{\le}${\ensuremath{\theta}}_{\mathrm{lab}{}^{\ensuremath{\pi}}\mathrm{\ensuremath{\le}}95}$\ifmmode^\circ\else\textdegree\fi{}), and photons (${\ensuremath{\theta}}_{\mathrm{lab}{}^{\ensuremath{\gamma}}=241\mathrm{\ifmmode^\circ\else\textdegree\fi{}}\ifmmode\pm\else\textpm\fi{}10}$\ifmmode^\circ\else\textdegree\fi{}) in coplanar geometry are selected to maximize the sensitivity to the radiation from the magnetic dipole moment of the ${\ensuremath{\Delta}}^{++}$(1232) resonance. At low photon energies, the data agree with the soft-photon approximation to pion-proton bremsstrahlung. At forward pion angles the data agree with older data and with the latest theoretical calculations for 2.3${\ensuremath{\mu}}_{p}$\ensuremath{\le}${\ensuremath{\mu}}_{\ensuremath{\Delta}}$\ensuremath{\le}3.3${\ensuremath{\mu}}_{p}$. However at more backward pion angles where no data existed, the predictions fail.

On the performance of a straight acceleration tube with axial gradient modulation

An earlier inclined field configuration has been replaced by a straight field configuration in the acceleration tube of the 5 MV electrostatic accelerator at the Institute of Nuclear Research, with the aim of improving lateral position stability of the beam at the tube exit. Making use of the so-called decoupling sections proposed by Herb [1], axial gradient modulation has been introduced by conic electrodes arranged periodically in shorted sections along the tube axis, in order to prevent secondary electrons from travelling long distances towards the terminal. Good beam stability has been achieved at high, medium and very low beam currents as a result of this modification. The voltage holding properties did not show any observable change. The results obtained from a series of bremsstrahlung measurements performed with thermoluminescent dose meters in the stack of the machine and around the vessel clearly indicate the main electron suppression properties of this tube geometry.

Electron Energy Increase of a REB-Ring by Major Radius Compression

Measurement of X-ray bremsstrahlung emitted from REB rings formed in SPAC-Vl toroidal device elucidated that major radius compression of the ring raises energies of the ring electrons. At the compression ratio of 2.0, the ring current rose from 24 kA to 50 kA. The highest energy of electrons that was estimated by hard X-ray spectrum measurement increased from ∼1 MeV to ∼2 MeV. The energy distribution of REB was broadly spread. During the compression, the current of ring I R and the major radius R are governed by the relation I R · R =const. Some discussions on this relation are given in which energy spread of the beam electrons and the change in the magnetic flux enclosed by the ring are taken into consideration.

Measurement of the efficiency of solid state detectors using atomic-field bremsstrahlung

We report on the current status of our efforts to use the atomic-field bremsstrahlung spectrum from the bombardment of thin-film targets by an electron beam to measure the photon energy dependence of the efficiency of HPGe and Si(Li) detectors. Results are presented for an HPGe detector from 15 to 100 keV and for an Si(Li) detector from 2 to 40 keV. Points on the efficiency curve are also obtained using calibrated radioactive sources for comparison and for absolute normalization. Problems associated with the background in bremsstrahlung measurements are also discussed.

The 232Th and 238U(γ, f) reactions near threshold

Abstract The (γ, f) and (γ, n) cross-sections and the mean number v of neutrons per fission have been measured for 232Th and 238U between 5 and 10 MeV. A new method of making bremsstrahlung measurements resulted in data having a good combination of energy resolution and statistical accuracy. For 232Th observed subthreshold (γ, f) cross-section resonances and v values suggest the existence of two separate shallow wells superimposed on the double humped fission barrier. For 238U similar resonances between about 5.5 and 6.0 MeV cannot easily be interpreted in terms of the double humped fission barrier.

Visible spectroscopy surveys of the OHTE plasma (abstract)

A Jarrell-Ash 0.27-m triple grating spectrometer with a high-speed intensified diode array detector has been used to perform time-resolved surveys of the visible emission (2200-7000 Å) from the OHTE plasma. Using a 512 diode array, spectra are obtained every 516 μs during the shot. The spectral width of the scan is 150, 300, or 1200 Å depending on the grating selected. Surveys at up to 500 kA for OHTE plasmas indicate a complete absence of metal emission lines with the graphite bead vacuum liner. In the 5200-Å region, a clear iindow has been identified for optical bremsstrahlung measurements. Other details of the spectra will be discussed.

Morphological study of energetic electron precipitation events using the satellite Bremsstrahlung X Ray Technique

The precipitation of energetic electrons into the atmosphere is investigated with simultaneous measurements of bremsstrahlung X rays emitted from different local time sectors performed from the low‐altitude polar‐orbiting satellite P78‐1 with an array of X ray spectrometers (21–139 keV), each looking in a different direction. From the measurements spanning a broad interval in L, simultaneous profiles in local time are obtained of the intensities and energy spectra of the bremsstrahlung X rays which relate to the corresponding parameters for the precipitating electrons. From ∼0930 to ∼1400 MLT the average X ray intensity was found to decrease with increasing magnetic local time, whereas from ∼2200 to ∼0200 MLT, no clear trend with local time was evident. Within both of these local time intervals the average flux increased with increasing level of geomagnetic activity, and the data acquired near midnight were best organized by the AE index. The correlation between the fluxes of X rays emitted simultaneously at different magnetic local times decreased with increasing separation in local time, but a significant correlation still existed over separations as great as 3 hours. The energy spectrum was harder before midnight than after and harder before midnight than near noon. When a hard energy spectrum was observed in one local time sector, the spectra at other local times within 3 hours were significantly harder than average. From the entire set of data no evidence has been found for a distinct group of relativistic electron precipitation events.

Bremsstrahlung measurements with collimated thermoluminescent dosimeters around a tandem accelerator

Simple collimated sets of thermoluminescent dosimeters were used for measuring dose rate distribution curves in the bremsstrahlung field of an electrostatic accelerator. The increased axial resolution of the detector set resulted in curves clearly indicating local radiation maxima related to the electron optical properties of the acceleration tubes. Radiation data were compared to those calculated from secondary electron trajectories and to statistical data on resistor breakdowns in the voltage divider chain.

Determination of technetium-99 content in solutions by using Bremsstrahlung measurements

Determination of technetium-99 content in solutions by using Bremsstrahlung measurements

Experiments at TRIUMF on radiative processes

The current program of nucleon and pion radiative capture and proton–proton bremsstrahlung measurements at TRIUMF is described. Neutron radiative capture with polarized beam and target is suggested as a possible future experiment.

Pionic bremsstrahlung in heavy-ion collisions

Abstract We apply the bremsstrahlung model for pi on production to symmetric nuclear collisions at energies far below the single NN-threshold. All main features of recent neutral pion measurements can be explained by a single value of the deceleration parameter of the theory which is consistent with hydrodynamical calculations. Since the γ-ray bremsstrahlung also reflects the kinematics of its source, a simultaneous measurement of pion and γ-ray bremsstrahlung should be used to further test the collision dynamics. Results of our calculations for both kinds of radiation are presented. An extension of this approach to asymmetric systems is proposed.

Conditioning and power-handling of the cooled graphite limiter on PDX

A single graphite rail limiter was used for high power neutral beam injection experiments on PDX from February to July, 1982. The uncoated water-cooled limiter, with a total area of 800 cm 2, performed well in discharges of up to 7 MW of injected power. It was initially conditioned with high power ohmic discharges which removed absorbed and adsorbed impurities. After conditioning, carbon was the primary impurity which evolved from the limiter during high power neutral beam heated discharges. Visible Bremsstrahlung measurements of Z eff were employed to determine the effectiveness of the limiter in maintaining clean plasmas during neutral beam heating and as a measure of the conditioning of the limiter with time. Operation for a period of several months was required to condition the limiter surface to the point where neutral beam injection of 7 MW for 250 ms resulted in only a small rise in Z eff. Thermocouple measurements and a nonlinear cooling model were used to estimate both the absorbed power and the corresponding surface temperatures of the limiter. For the series of discharges studied, the power absorbed by the limiter was found to increase with input power at lower plasma currents, but was almost constant at large plasma current and beam power.

ELF emissions and relativistic electron precipitation

Simultaneous measurement of ELF emissions and bremsstrahlung X rays were made by using a balloon borne experiment flow from Fairbanks, Alaska, on September 30, 1976. Several intense auroral X ray bursts of 2–3 minute duration were detected that have been interpreted to be the result of relativistic electron precipitation (REP). Simultaneously, the intensity of ELF emissions increased and was also observed to have periodicities similar to those in the X ray flux. These combined measurements are evidence of magnetospheric wave‐particle processes contributing to electron precipitation. The presence of pulsations in the precipitating flux is the only report of this nature during relativistic precipitation. The data have been compared with precipitation and modulation theories, and we note that the data agree with a model in which ULF modulation of the emission growth rate occurs. It is postulated that this REP event resulted from ELF wave and electron interaction, possibly triggered by the ULF occurrence rather than directly by ULF electron interactions.

Optical behaviour of acceleration tubes studied in bremsstrahlung measurements

The ion-optical behaviour of acceleration tubes of different field structures has been studied by comparing the results of trajectory calculations with experimental data obtained in bremsstrahlung measurements.Intensities and end point energies of X-radiation were measured with a NaI(Tl) counter, while intensities and average energies were measured with thermoluminescent dosimeters (TLD). Dose rate distributions obtained with TLDs in the immediate vicinity of the tube were compared with those generated from data measured at the outer wall of the accelerator vessel. A similar procedure was followed in the case of homogeneous field tubes as well as for those of inclined fields with alternating or spiralling transversal components. The tubes were used for long operating times in a 5 MV Van de Graaff accelerator.

Electron confinement studies on the EBT-S Bumpy Torus Experiment using soft x-ray techniques

Soft x-ray bremsstrahlung measurements have been performed on the ELMO Bumpy Torus (EBT-S) plasma to determine the electron temperature Te and electron density density ne using a calibrated Si(Li) detector over a wide range of operating conditions. The purpose of this paper is to outline the necessary assumptions and essential x-ray techniques that are inherent in soft x-ray measurements in order to investigate the electron heating and confinement properties of EBT-S. In addition, by utilizing the electron density as determined by the soft x-ray measurements, the previous EBT-S confinement analyses have been extended. The steady-state plasma of EBT-S is heated by microwaves using a continuous wave (cw) gyrotron that can operate up to power levels of 200 kW. From the soft x-ray measurements, both the electron temperature and density are found to increase at higher microwave power levels. For operation at microwave power levels of 200 kW, Te approaches 1 keV while ne approaches 1.2×1012 cm−3. In general, confinement properties are found to improve with increased microwave power. The data are compared with neoclassical transport scaling and the electron transport is found to be collisionless (ν/Ω<1) as well as neoclassical.

A method for the determination of depth of a point source of beta emitter from bremsstrahlung measurements

A method is described to determine the depth of a point source of beta emitter which is inside a medium. The method involves the measurement of external bremsstrahlung produced in this medium. The external bremsstrahlung has a maximum in its energy distribution curve which provides a means to estimate the position of the beta emitter. Experiments have been done using two pure beta emitters 147Pm and 32P and the relation between peak position and depth variation in tissue-equivalent materials has been studied. The results show that the shift in the maximum of the experimentally determined bremsstrahlung spectra can be useful in estimating the depth at which the beta source is situated in a medium.