Bremsstrahlung Measurements Research Articles

Results of recent bremsstrahlung measurements on few-body systems at KVI

A series of bremsstrahlung measurements have been performed with the superconducting cyclotron, AGOR, at KVI. These measurements, on the proton-proton and proton-deuteron systems, aim to investigate the nucleon-nucleon interaction as the nucleons go off their mass shell. Cross sections and analyzing powers have been measured for all possible exit channels of both systems with an incident proton energy of 190 MeV, which is below the particle-production threshold. Preliminary results of the real-photon as well as virtual-photon production are presented and compared to theoretical predictions.

Measurements of the virtual bremsstrahlung yields in the p+p system

In this paper recent results obtained from the p+ p→ p+ p+ e ++ e − experiment are presented. This experiment has been performed with a 190 MeV polarized proton beam obtained from the new cyclotron AGOR at KVI in Groningen. Differential cross sections have been obtained in exclusive measurements in which all four exit particles have been measured in a coincidence setup between SALAD and TAPS. The data are compared with LET calculations. A reasonable agreement is found for virtual-photon invariant masses up to 80 MeV/c 2.

Proton-proton bremsstrahlung at 310 MeV

Proton-proton bremsstrahlung measurements have been made at 310 MeV by the WASA-PROMICE collaboration [1] at the CELSIUS storage ring. Detailed measurements of proton-proton coincidences in the forward direction yielded kinematically complete data mainly for events with high-energy gammas in the CM system. Measurements of coincidences between a forward-going proton and a wide-angle photon yielded complementary information over a large range of gamma energies. The total data sample obtained provides accurate information on the pp bremstrahlung cross section over a large fraction of the phase space.

Efficiency calibration of a Si(Li) detector in the low-energy region using electron bremsstrahlung

In the low-energy region the determination of the detector efficiency is complicated by the fact of nonavailability of certificated calibration sources. To solve this problem the use of electron bremsstrahlung for determining the relative photon detection efficiency of a Si(Li) detector in the low-energy range 0.5–19 keV is proposed. The calibration is based on energy dispersive measurements of electron bremsstrahlung emitted by an X-ray tube. Model spectra are computed from thick-target bremsstrahlung spectra in a semiclassical approximation and from a physical model for the detector response. Model spectra are fitted to the measured spectra using a parametric adaptor term. Thereby, the error of the determined detector efficiency is approximately 5%.

Measurement of gas bremsstrahlung from electron storage rings

Bremsstrahlung is produced in electron storage rings when the particle beam interacts with the storage ring components or with the residual gas molecules in the storage ring vacuum. The interaction of the particle beam with the gas molecules occurs continuously during storage ring operation. At straight sections of a storage ring, the gas bremsstrahlung contribution from each interaction adds up to produce a narrow monodirectional photon beam that travels down the beamlines. At the Advanced Photon Source (APS), where the stored electron beam energy is 7 GeV, gas bremsstrahlung generated in the straight sections of the insertion device beamlines, which is a total of 15.38 m in effective length, can be significant. This paper presents the results of the bremsstrahlung spectrum and energy measurements from the insertion device beamlines of the APS using a hermetic lead glass calorimeter. The calorimeter consists of 25 lead glass blocks, each 6.3 cm × 6.3 cm × 35 cm, stacked into a 5 × 5 array. Phototubes connected to the lead glass blocks collected the signals. The calorimeter is calibrated using the maximum energy of the observed bremsstrahlung spectrum. The total energy radiated and the bremsstrahlung spectrum were measured as a function of the storage ring beam current for both electrons and positrons of 7 GeV energy. Vacuum in the straight section was continuously monitored, and measurements to determine the nature of the residual gas inside the storage ring were performed. The measured bremsstrahlung spectra are fitted to a function that shows an approximate 1 E behavior. The gas bremsstrahlung rate from the APS undulator beamline straight path of 15.38 m is measured as 60.0 ± 2.0 GeV/s/nT/mA. Significant contribution of bremsstrahlung from sources other than the residual gas molecules is observed. The maximum bremsstrahlung energy measured in a beamline during the experiment is 369.0 ± 22.0 GeV/s/nT/mA.

Determination of phosphorus by instrumental neutron activation and bremsstrahlung measurement in bone samples

A non destructive method based on the31P(n,γ)32P reaction for the assay of phosphorus in bone samples is described. This method involves a thermal neutron irradiation of 2 minutes in a reactor followed by the measurement of the bremsstrahlung produced by the β− of32P in a Ge-detector surrounded by an anti-Compton shield. Accuracy and precision were tested by analysing the certified NIST 1486 Bone Meal reference material and tri-calcium phosphate (Ca3(PO4)2) samples. The value obtained for the reference material was in good agreement with the certified value and with relative standard deviation of 4.1% the precision was acceptable. The value obtained for Ca3(PO4)2 shows a deviation of −6% from the expected value, reflecting the effect of the sample density in bremsstrahlung measurement.

Detection system based on monochromator for visible bremsstrahlung measurements of HT-6M tokamak

A detection system based on a monochromator for visible bremsstrahlung measurements is constructed. A new line-free spectral portion and stray light level, which affect the Z eff measurements considerably, are carefully investigated under different discharge conditions. The results show that the contribution of line emissions to the continuum for this system does not exceed 10%. It can be further reduced to 3% if an interference filter with a full width at half-maximum of 500 Å is applied.

New Experimental Data and What It Tells Us About the Sources and Acceleration of Cosmic Rays

This paper summarizes new data in several fields of astronomy that relate to the origin and acceleration of cosmic rays in our galaxy and similar nearby galaxies. Data from radio astronomy shows that supernova remnants, both in our galaxy and neighboring galaxies, appear to be the sources of most of the accelerated electrons observed in these galaxies. γ-ray measurements also reveal several strong sources associated with supernova remnants in our galaxy. These sources have γ-ray spectra that are suggestive of the acceleration of cosmic-ray nuclei. Cosmic-ray observations from the Voyager and Ulysses spacecraft suggest a source composition that is very similar to the solar composition but with distinctive differences in the 4He, 12C,14 N and 22Ne abundances that are the imprint of giant W-R star nucleosynthesis. Injection effects which depend on the first ionization potential (FIP) of the elements involved are also observed, in a manner similar to the fractionization observed between the solar photosphere and corona and also analogous to the preferential acceleration observed for high FIP elements at the heliospheric solar wind termination shock. Most of the 59Ni produced in the nucleosynthesis of Fe peak nuclei just prior to a SN explosion appears to have decayed to 59Co before the cosmic rays have been accelerated, suggesting that the59 Ni is accelerated at least 105 yr after it is produced. The decay of certain K capture isotopes produced during cosmic-ray propagation has also been observed for the first time. These measurements suggest that re-acceleration after an initial principal acceleration cannot be large. The high energy spectral indices of cosmic-ray nuclei show a significant charge dependent trend with the index of hydrogen being -2.76 and that of Fe -2.61. The escape length dependence of cosmic rays from our galaxy can now be measured up to ~300 GeV nucl-1 using the Fe sec/Fe ratio. This escape length is ∼P-0.05 above 10 GeV nucl-1 leading to a typical source spectral index of (2.70±0.10) -0.50 = -2.20 for nuclei. This is similar to the source index of -2.3 inferred for electrons within the errors of ±0.1 in the index for both components. Spacecraft measurements in the outer heliosphere suggest that the local cosmic-ray energy density is ~2eV cm-3 – larger than previously assumed. Gamma-ray measurements of electron bremsstrahlung below 50 MeV from the Comptel experiment on CGRO show that fully 20–30% of this energy is in electrons, several times that previously assumed. New estimates of the amount of matter traversed by cosmic rays using measurements of the B/C ratio are also higher than earlier estimates – this value is now ~10 g cm-2 at 1 GeV nucl-1. Thus altogether cosmic rays are energetically a more important component of our galaxy than previously assumed. This has implications both for the types of sources that are capable of accelerating cosmic rays and also for the role that cosmic rays may play in ionizing the diffuse interstellar medium.

Characteristic x rays and electron energy distribution function in anisotropical hot plasmas

Characteristic x-ray lines of heavy ions are used as threshold indicators for the number of plasma electrons with an energy higher than the orbital electron binding energy of the initial vacancy for the corresponding x-ray transition. For heavy ion plasmas the intensity ratio between x-ray lines of different series shows how the mean energy of the electron changes with the operating conditions of an electron cyclotron resonance ion source. With the combination of line intensity and bremsstrahlung measurements, information on the anisotropy of the electron energy distribution function is obtained. Characteristic and continuous radiation is recorded at the same time and with the same apparatus. Therefore, errors are extremely small.

Experimental study of the hot and warm electron populations in an electron cyclotron resonance argon–oxygen–hydrogen plasma

Measurements of bremsstrahlung down to 7 keV emitted from a 7.25 GHz electron cyclotron resonance discharge and the deconvolution of the spectra using a newly developed integration method yield the exact electron distribution function. Two separate electron populations with temperatures about 3 and 25 keV and with densities about (0.2...4)108 cm−3 were recorded. First, results are obtained for the behavior of these populations belonging to the mixture (argon–oxygen–hydrogen). Gas mixing increases the densities of these populations, but hardly changes the temperatures.

An accelerator based multi-coincidence electron-photon spectrometer for the measurement of bremsstrahlung and inner-shell ionization cross-sections

A new system for the measurement of coincidences between electrons and photons has been devised. This system, which is coupled with a 300 keV electron accelerator, will allow the user to measure electron-electron and electron-photon coincidences between any number of detectors simultaneously. Advantages of such a setup include the ability to carry out multiple scattering experiments simultaneously with just one beam. Also, provided enough detectors are available, coincidence measurements can be made at various angles simultaneously in one run. Details on the implementation of this system are presented.

Comment on “Photon spectrum of the neutron-proton Bremsstrahlung at 170 MeV”: Contributions of np → dγ to inclusive photon energy spectra from np and pd collisions near 200 MeV

Several years ago, a measured photon energy spectrum from np collisions was presented as a measurement of free np Bremsstrahlung, and subsequently theoretical groups compared the data to their model calculations of the process np → npγ [F. Malek, A. Nifenecker, J.A. Pinston, F. Schussler, S. Drissi, J. Julien, Phys. Lett. B 266 (1991) 391]. We point out that in np collisions, np capture ( np → dγ) is important and cannot be ignored. It contributes approximately 30% of the cross section for photons above 40 MeV. Capture also makes a significant contribution to the photon spectra produced in p- d collisions, and possibly has a role in p-nucleus collisions. In the former case, better agreement between theory and experiment is obtained when (quasifree) capture is included.

A verification of the Monte Carlo code MCNP for thick target bremsstrahlung calculations.

The bremsstrahlung spectra from thick targets of Be, Al, and Pb are calculated using the Monte Carlo code MCNP (Monte Carlo N-particle). The current version of MCNP (v.4A) incorporates a coupled electron-photon transport scheme that allows the user to estimate the photon fluence produced from primary electron interactions. The simulation parameters are based on bremsstrahlung measurements of 15 MeV electrons incident on thick targets of Be, Al, and Pb at various angles between 0 degree and 90 degrees. The integrated yield and mean energy of each bremsstrahlung spectrum is calculated for the three targets at these angles. For angles less than 60 degrees the integrated yield calculated by MCNP4A is within 6% of measured values for the three targets. Furthermore, predicted mean energy is within 7% of the values derived from measurement for all angles tested. Also compared are the performances of two MCNP4A fluence tallies; a next-event estimator (detector tally) and a track length estimator (cell tally). Timing studies indicate the detector tally will perform the integrated yield calculations to a precision of 1% approximately 10 to 50 times faster than the conventional cell tally for an emission angle of 0 degree.

Photoemission and Inverse Photoemission Studies of SiO2

Occupied and unoccupied electron states of amorphous silicon dioxide film supported on Si crystal are studied by using X-ray photoemission and, for the first time, X-ray inverse photoemission (X-ray bremsstrahlung isochromat method). A special care was undertaken to minimize decomposition of silicon oxide during X-ray bremsstrahlung measurements. The experimental spectra are compared with theoretical band structure calculations for amorphous SiO2 from the literature and good overall agreement is found. PACS numbers: 71.25.Tn, 79.20.Kz, 79.60.Ht

Use of bremsstrahlung radiation to monitor y-90 tumor and whole body activities during experimental radioimmunotherapy in mice

Large differences in uptake between tumors, even for the same size, frequently observed in clinical and experimental radioimmunotherapy (RAIT), make monitoring of uptake in individual tumors imperative in comparing protocols. 90Y, widely-used for RAIT, emits no gamma radiation and absorption of the beta particle in tissue makes its detection unsuitable for in vivo monitoring. We tested whether bremsstrahlung radiation, produced when betas are decelerated by nuclei, could be used to monitor tumor uptake. Subcutaneous human LS174T colon carcinoma tumors were grown in the upper thigh of nude mice and labeled antibody injected intracardially. With the tumor placed in the 2 cm-diameter aperture in a lead collimator, photons with energies from 100 to 200 keV transmitted through plastic, which absorbed the beta particles, were counted to maximize shielding from the rest of the body. The contribution of the normal tissues was subtracted by counting the non-tumor-bearing leg in the same position. Excretion was calculated from whole body activity determined by removing the collimator, placing the mouse in a syringe surrounded by tissue-equivalent material 10 cm from the detector, and counting photons between 200 and 740 keV to minimize the effect of tissue attenuation. For tumors larger than 0.14 gm, a good correlation was obtained between the in vivo bremsstrahlung measurements and the measurements on excised tumors in a calibrated well counter. Similar excretion rates observed in all the animals suggested that the whole body counting was accurate. Bremstrahlung detection appears feasible and reliable for monitoring both tumor and whole body activities.

The yield for two-photon emission from radiation of thick targets by a 109Cd- 113mCd radioactive source

Lehtihet and Quarles have reported the measurement of the two-photon yield from the radiation of thick targets of Ag, Au, and Pb by a 109Cd radioactive source which has recently been found to have a significant component of 113mCd. This means that there was a component of energetic electrons that was not considered in the original comparison of the data to a model calculation. Also, recent measurements of thick-target double bremsstrahlung produced by an electron beam have led to the development of a new, more rigorous model for the two-photon yield which can now be compared with the 109Cd- 113mCd data. The 113mCd component also produces a significant contribution to the coincidence yield from the coincidence of a single bremsstrahlung photon and a scattered electron. It is shown that the new model, with the single bremsstrahlung electron-photon coincidence contribution, provides a good description of the data.

Free-free light absorption in strongly coupled plasmas

The light absorption coefficient is evaluated in strongly coupled plasmas. Analysis is based on the calculation of the dynamic collision frequency of electron-ion scattering. Under plasma conditions when electron scattering has quantum character, the Born approximation for screened electron-ion interaction is used. In the case of classical scattering non Born corrections become essential at high frequencies. Interpolation formulas for the collision frequency and Gaunt factor are presented at intermediate frequencies. Theoretical calculations are compared with measurements of bremsstrahlung for dense Ar and Al plasmas and computer simulation data.

Neutron-proton bremsstrahlung experiments

It is well known that charged particles emit bremsstrahlung radiation when they are accelerated. Classical electron bremsstrahlung occurs when a proton is emitted by an electron accelerated in the field of a nucleus. The bremsstrahlung process also occurs in the scattering of nucleons, for which it is the lowest energy inelastic process that can occur. Like electron bremsstrahlung, nucleon-nucleon bremsstrahlung also requires the exchange of a virtual particle to conserve energy and momentum. In electron bremsstrahlung a virtual photon is exchanged but with two nucleons a meson can be exchanged. Unlike electron bremsstrahlung, in nucleon-nucleon bremsstrahlung the photon can originate from the exchanged meson. This exchange contribution has been shown in calculations to be a significant fraction of bremsstrahlung events. Thus bremsstrahlung serves as a probe of exchange currents in the nucleon-nucleon interaction. Because of a lack of a free neutron target or an intense neutron beam, few measurements of neutron-proton bremsstrahlung exist, each having poor statistical accuracy and poor energy resolution. The white neutron source at the Weapons Neutron Research (WNR) target area at the Los Alamos Meson Physics Facility (LAMPF) produces neutrons with energies from below 50 to above 400 MeV. Using time-of-flight techniques and a liquid hydrogen target, we are measuring the outgoing photons of energies up to 250 MeV at gamma ray angles of around 90° relative to the incident beam. Protons scattered at very forward angles are also detected in coincidence with the gamma rays.

Propagation of bremsstrahlung X rays through the atmosphere

To understand auroral phenomena and associated magnetospheric processes, balloon-borne measurements of bremsstrahlung X rays produced by electrons precipitating in our atmosphere have been made by various scientists. Measurements made by balloon-borne payloads have an advantage over direct measurements of electrons by satellites or rockets as these measurements provide an intense coverage at one location. These observations are usually made between 30–35 km altitude, and to relate them to the parent electron flux at the top of the atmosphere, it is necessary to understand the effect of propagation of X rays through the terrestrial atmosphere from ~100 km to the detection altitude (~30 km).

Measurement of light impurity densities and Zeff in JET using x-ray tomography

In the vast majority of plasmas produced in the JET tokamak the x-ray emission at energies above about 1 keV is dominated by bremsstrahlung radiation from the background deuterium ions, and both bremsstrahlung and recombination radiation from one or two light impurity species such as beryllium and carbon. Under these circumstances local values of impurity densities and concentrations, or alternatively of the effective charge Zeff of the ion mixture, are derived from tomographic measurements of the local x-ray emissivity at energies above 1–3 keV, in conjunction with measurements of electron density and temperature profiles. These calculations are performed using the intrinsic emissivities due to the impurity ions. The emissivities into the relevant energy bands, determined by the detector and filter characteristics, were calculated assuming coronal ionization equilibrium, and tabulated as a function of electron temperature. This method offers a good spatial and temporal resolution, and is successfully applied to most plasma conditions where the relative proportions of impurities are known. We also present a detailed sensitivity study to assess the effects of errors in the input data, and a comparison with established methods based on visible bremsstrahlung measurements, and charge exchange spectroscopy.