Bremsstrahlung Gamma Rays Research Articles

Characteristics of radiation safety for synchrotron radiation and X-ray free electron laser facilities

Radiation safety problems are discussed for typical electron accelerators, synchrotron radiation (SR) facilities and X-ray free electron laser (XFEL) facilities. The radiation sources at the beamline of the facilities are SR, including XFEL, gas bremsstrahlung and high-energy gamma ray and photo-neutrons due to electron beam loss. The radiation safety problems for each source are compared by using 8 GeV class SR and XFEL facilities as an example.

Comment on “‘Seed’ electrons from muon decay for runaway mechanism in the terrestrial gamma ray flash production,” by Gerson S. Paiva, Antonio C. Pavão, and Cristiano C. Bastos

Comment on “‘Seed’ electrons from muon decay for runaway mechanism in the terrestrial gamma ray flash production,” by Gerson S. Paiva, Antonio C. Pavão, and Cristiano C. Bastos

Gamma-ray signatures of annihilation to charged leptons in dark matter substructure

Due to their higher concentrations and small internal velocities, Milky Way subhalos can be at least as important as the smooth halo in accounting for the GeV positron excess via dark matter annihilation. After showing how this can be achieved in various scenarios, including in Sommerfeld models, we demonstrate that, in this case, the diffuse inverse-Compton emission resulting from electrons and positrons produced in substructure leads to a nearly-isotropic signal close to the level of the isotropic GeV gamma-ray background seen by Fermi. Moreover, we show that HESS cosmic-ray electron measurements can be used to constrain multi-TeV internal bremsstrahlung gamma rays arising from annihilation to charged leptons.

Observation of an Energetic Radiation Burst from Mountain-Top Thunderclouds

During thunderstorms on 20 September 2008, a simultaneous detection of gamma rays and electrons was made at a mountain observatory in Japan located 2770 m above sea level. Both emissions, lasting 90 sec, were associated with thunderclouds rather than lightning. The photon spectrum, extending to 10 MeV, can be interpreted as consisting of bremsstrahlung gamma rays arriving from a source which is 60-130 m in distance at 90% confidence level. The observed electrons are likely to be dominated by a primary population escaping from an acceleration region in the clouds.

Potential Uses of ERL-Based $\gamma$-Ray Sources

We expand upon the idea of using gamma-rays for nuclear photoflssion of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">238</sup> U at the giant dipole resonance to generate rare neutron-reach nuclei. The SPIRAL II project proposes the employment of 10-20-MeV Bremsstrahlung gamma-rays generated by a 45-MeV electron beam /http://ganinfo.in2p3.fr/research/ developments/ spiral2/ index.html/. In this paper, we explore the possibility of using a Compton gamma-ray source for such a process. The Collider Accelerator Department at Brookhaven National Laboratory is developing high-current (up to 1 A), high-brightness (down to 1-mm ldr mrad normalized emittance), and high-energy energy-recovery linacs (up to 20-GeV electron beam energy for eRHIC). These electron beams are perfectly suited for generating photon beams with tremendous average power, approaching the megawatt level. The range of photon's energy extends from subelectronvolts from free-electron lasers to 10 GeV from the Compton process. In this paper, we focus on a gamma-ray source for producing rare isotopes.

Effects of Compton Scattering on the Gamma-Ray Spectra of Solar Flares

Abstract Using the fully relativistic GEANT4 simulation toolkit, Monte Carlo simulation was applied to the transport of energetic electrons generated in solar flares, and resultant bremsstrahlung gamma-ray spectra were calculated. The solar atmosphere was approximated by 10 vertically stacked zones. The simulation took into account two important physical processes: that the bremsstrahlung photons emitted by precipitating relativistic electrons are strongly forward beamed toward the photosphere, and that the majority of these gamma-rays must be Compton backscattered by the solar atmosphere in order to reach the observer. Then, the Compton degradation was found to make the observable gamma-ray spectra much softer than predicted by simple analytic calculations. The gamma-ray signals were found to be enhanced by several conditions, including a broad pitch-angle distribution of the electrons, a near-limb flare longitude, and a significant tilt in the magnetic field lines if the flare longitude is rather small. These results successfully explain several important flare properties observed in the range of hard X-ray to gamma-ray, in particular including those obtained with Yohkoh. A comparison of the Yohkoh spectrum, from a GOES X3.7 class limb flare on 1998 November 22, with a simulation assuming a broad electron pitch-angle distribution suggests that gamma-rays from this particular solar flare were a mixture of direct bremsstrahlung photons and their Comptonization.

Neutron activation experiments for bremsstrahlung characterization studies

Activation experiments were conducted to assess the bremsstrahlung continuum produced from the activation of the 7Li isotope and the subsequent short-lived 13 MeV beta decay of 8Li (T1/2 = 843 ms). The combination of the high energy beta-decay and the high atomic numbered metals used in piping for 7Li liquid metal coolants is a scenario in which bremsstrahlung production is a principal shielding concern. A series of fast pneumatic activation experiments have been performed to obtain the spectral distributions of bremsstrahlung gamma-rays transmitted through stainless steel shield samples. Detectors were used in both pulse-height and multichannel scaling analysis modes for energy spectra determination and half-life verification, respectively. Experimental results were utilized to validate the electron transport and bremsstrahlung production models used in the Monte Carlo MCNP code.

Accelerator dosimetry at free electron lasers in Hamburg

On 27 April 2006 a vacuum ultra violet free electron laser (FEL) named free electron laser in Hamburg (FLASH) producing intense beams of 13.1 nm laser light became operational. A 260 m long, 1 GeV superconducting electron linear accelerator (linac) drives the FLASH. The electron linac is made of an array of superconducting niobium cavities developed at DESY on TESLA technology. During the FEL operation a parasitic radiation field of photoneutrons and bremsstrahlung gamma rays persists in the linac containment tunnel. Sophisticated measurement and control devices, based on radiation-sensitive commercial off the shelf (COTS) microelectronic components, have been installed near the FLASH linac. Therefore, it becomes necessary to characterise these stray radiations, in order to predict the radiation effects on electronics. This paper summarises the features of novel radiation dosimeters and accelerator dosimetry techniques developed by our group. The utilisation of valuable radiation dosimetry data gathered from the experiments at FLASH to predict the radiation field characteristics of the future European X-ray free electron laser (XFEL) driven by a 20 GeV superconducting electron linac is highlighted.

Neutron events in the underground monitor of the Tien Shan high-altitude station

The neutron multiplicity M spectrum was measured at the neutron monitor installed in the underground room of the Tien Shan high-altitude station (3340 m above sea level) of the Lebedev Physical Institute under a ground layer 20 m of water equivalent thick. To a first approximation, the differential multiplicity spectrum is power-law: dN/dM = 0.3 · M−3.7m−2s−1. The spectrum intensity is lower than the intensity of events in the ground-based NM64 supermonitor by a factor of 350–450. The spectrum slope exponent γ + 1 = 3.7 ± 0.1 is identical to the exponent of the energy spectrum of bremsstrahlung gamma-rays of energetic muons (above 1 TeV) generated in a lead absorber of the monitor. In this case, the experimental intensity is hundred times higher than the expected intensity of events from muon bremsstrahlung. The spatial distribution of neutrons in the monitor suggests that they are produced by single particles. The temporal distribution of neutrons in the monitor is exponential with lifetime constant τ = 360 − 390 µs. Difficulties are indicated in the interpretation of the multiplicity spectrum by electromagnetic and nuclear interactions of muons in the monitor without involving new penetrating particles.

Supersymmetric model of gamma ray bursts

We propose a model for gamma ray bursts in which a star subject to a high level of fermion degeneracy undergoes a phase transition to a supersymmetric state. The burst is initiated by the transition of fermion pairs to sfermion pairs which, uninhibited by the Pauli exclusion principle, can drop to the ground state of minimum momentum through photon emission. The jet structure is attributed to the Bose statistics of sfermions whereby subsequent sfermion pairs are preferentially emitted into the same state (sfermion amplification by stimulated emission). Bremsstrahlung gamma rays tend to preserve the directional information of the sfermion momenta and are themselves enhanced by stimulated emission.

A gamma-ray spectrometer system for fusion applications

A NaI scintillator spectrometer system for the measurement of gamma-ray spectra in tokamak discharges has been developed and installed on the Frascati Tokamak Upgrade. Two NaI scintillators are viewing the plasma at two different angles with respect to the equatorial plane. The main features of the spectrometer system (energy range: 0.3–23 MeV) and of the unfolding technique used to restore physical spectra from the pulse-height distributions are described: a method of solution with regularisation for matrix equations of large size, allowing to process count distributions with significant statistical noise, has been developed. A dedicated software, portable to any platform, has been written both for the acquisition and the analysis of the spectra. The typical gamma-ray spectra recorded in hydrogen and deuterium discharges, also with additional heating, are presented and discussed; two components have been observed: (a) thick-target bremsstrahlung gamma-rays produced by runaway electrons hitting the inconel poloidal limiter and/or the vessel; and (b) neutron capture gamma-rays generated in the detector shielding and tokamak structures. The maximum energy resulting from the bremsstrahlung spectra is in agreement with the runaway energy predicted by a test particle model of runaway electron dynamics.

Effect of the plasma density scale length on the direction of fast electrons in relativistic laser-solid interactions

The angular distribution of bremsstrahlung gamma rays produced by fast electrons accelerated in relativistic laser-solid interaction has been studied by photoneutron activation in copper. We show that the gamma-ray beam moves from the target normal to the direction of the k(laser) vector as the scale length is increased. Similar behavior is found also in 2D particle-in-cell simulations.

Use of delayed gamma spectra for detection of actinides (U,Pu) by photofission

The development of non-destructive methods to inspect nuclear waste containers is important for radioactive waste management and non proliferation purposes. Among methods using nuclear radiation as a probe, instrumental photon activation analysis (IPAA) seems to be a promising way forward. We have previously developed an IPAA method to determine the mass of actinides in radioactive waste sealed in concrete by counting the delayed neutron emission after photofission. This method does not determine the nature of the actinides detected. Such additional useful information may, however, be derived from analysis of the delayed gamma emission spectrum. The main topic of this paper is to show how analysis of the delayed gamma spectra may overcome some of the limitations of delayed neutron analysis. Target samples of 93% and 25% enriched 235 U and Pu were irradiated with bremsstrahlung gamma-rays produced by 15-MeV electrons from a linear accelerator. The gamma-rays spectra for each of the two uranium isotopes studied reveals a distinctive intensity distribution which is the consequence of modification of light-wing fission products distribution.

Distribution of energetic particles and secondary radiation according to orbital station “MIR” data obtained in 1991

A set of instruments for measuring energetic particle fluxes, containing two neutron detectors under different plexiglas shielding thicknesses, a scintillation detector, measuring energy release >0. I MeV and 0.5 MeV and a Geiger counter were launched onboard OS ‘MIR’. The latitude dependencies of the cosmic ray measurements were obtained and studied. The distributions of primary particle fluxes (protons and electrons) as well as secondary particle fluxes (bremsstrahlung gamma-rays and neutrons) produced in interactions of radiation belt particles with the station materials were obtained. The electron belt, generated during the storm of March 24 1991, is studied.

Evaluation of the Undesired Neutron Dose Equivalent to Critical Organs in Patients Treated by Linear Accelerator Gamma Ray Therapy

A careful theoretical and experimental evaluation has been made in order to estimate the neutron dose equivalent for critical organs of patients treated by gamma ray therapy. The machine employed in these studies is the linear electron accelerator MD Class Mevatron, Siemens, installed at the S. Giovanni Battista A.S. Hospital in Torino (Italy) and used for tumour therapy. A calculational method was developed, using two suitable 3D Monte Carlo computer codes: the EGS4 code (Electron Gamma Shower), which evaluates bremsstrahlung gamma rays and photo-neutron production in the accelerator head and the MCNP code (Monte Carlo Neutron and Photon Transport), which simulates the neutron transport and evaluates the organ dose equivalents. In addition, two sets of measurements were made during treatment sessions with 2 Gy therapeutic gamma dose: (a) by means of thermoluminescence dosemeters TLD-600 and TLD-700 placed at various depths inside an anthropomorphic phantom in positions corresponding to the organs; (b) in vivo by albedo neutron personal dosemeters UD-802, National Panasonic, positioned on the patients according to the organs. The agreement between experimental and theoretical data is good. The neutron organ dose equivalents are by no means negligible; for instance HT varies from 2.65 mSv on the thyroid to 42.02 mSv on testes, if normalised to one Gy of maximum absorbed dose in the pelvis, of the primary gamma beam if 15 MeV maximum energy (10 cm × 10 cm field size and source-skin distance of 1 m).

A monitor for gamma radiation at zero degrees from the SLC collision point

Bremsstrahlung gamma rays are emitted in a narrow forward cone while the electron and positron beams are being measured with carbon fibers at the SLC (the linear collider at the Stanford Linear Accelerator Center). Beam-beam deflections which occur at the collision point also emit softer gamma rays, called beamstrahlung. A device to detect these gammas is described. It has a converter to produce electron-positron pairs and a gas Cherenkov volume to detect them in the presence of a large, low energy, radiation background. The system is used for beam diagnostics at the SLC.

Analysis of fissionable material using delayed gamma rays from photofission

The energetic gamma-ray spectra from the fission products of photofission have been investigated to determine whether photofission can identify heavily shielded fissionable material. Target samples of natural thorium, 93% enriched 235U, natural uranium, and 93% enriched 239Pu were irradiated with bremsstrahlung gamma rays produced by 10-MeV electrons from a small linear accelerator. The gamma-ray spectra for each of the four isotopes studied reveal a distinctive intensity distribution. For example, the intensity ratio of the pair of gamma rays at 1436 keV ( 138Cs) and 1428 keV ( 94Sr) is 1.9 for 235U, 2.4 for 238U, 1.7 for 232Th and 1.4 for 239Pu.

Analyse multielementaire des cheveux par photoactivation nucleaire

Photonuclear activation with 18 and 35 MeV bremsstrahlung beams and gamma ray spectrometry has been used to determine the concentrations of 14 elements in human hair. A careful study of interferences made possible a nondestructive analysis with practical limits of detection between 0.1 and 100 μg·g.

One-Dimensional Gamma-Ray and Photoneutron Shielding Calculations for the Elmo Bumpy Torus Proof of Principle Device

One-dimensional radiation transport calculations have been performed to obtain estimates of the nuclear heat loads and biological dose rates due to bremsstrahlung gamma rays and photoneutrons in the ELMO Bumpy Torus proof of principle device. The bremsstrahlung gamma rays arise because of electron impingement on the magnetic coil assemblies, and these gamma rays in turn produce photoneutrons through interactions in the high-Z shielding materials. For a 1-MW electron power loss, /sup 238/U and tungsten coil shield thicknesses of 22.5 and 27.3 mm, respectively, were found sufficient to limit the nuclear heat load on a single superconducting coil to 10 W. The estimated lead and concrete primary shield thicknesses required to reduce the biological dose rate due to bremsstrahlung gamma rays to 2.5 mrem/h were calculated to be 0.318 and 1.92 m, respectively. Because of photoneutron production, however, lead by itself was not found to be an acceptable biological shield.

Predictions of Induced Background Radiations at Gamma/X-Ray Experiment Envelopes in NASA Spacecraft

This work seeks to predict secondary radiation levels induced in spacecraft structures by space protons. The radiations analyzed are secondary neutrons from spallation and evaporation reactions and gamma and beta rays from the decay of induced radioactivity, as sources of interfering background to spaceborne measurements of galactic and planetary gamma rays below 10 MeV. The spacecraft considered are the Multi-Mission Spacecraft (MMS) and the Space Shuttle, modeled as spherical shells. The proton environment is that of the South Atlantic Anomaly, as well as cosmic ray protons. The induced radioactivity is analyzed in terms of its interference with various gamma-ray lines of astrophysical interest, as well as its contribution to several spectral regions of the gamma-ray continuum. The buildup of the line and continuum radioactivity background is predicted for a period of nearly 9 months in orbit (~4100 orbits). In addition, background contributions from cosmic ray electron bremsstrahlung and earth gamma-ray albedo are estimated.