Bremsstrahlung Energy Spectra Research Articles

Angular Distribution of Bremsstrahlung Spectral Temperature Measured in a Full Dimension of ECR Ion Source Using NaI(TI) Detector

Measurement of angular distribution (AD) of the bremsstrahlung spectral temperature from a full dimension of the Electron Cyclotron Resonance Ion Source (ECRIS) along the beam axis is challenging. To overcome some challenges, this paper presents the AD of the bremsstrahlung spectral temperature measured in a full dimension of the ECRIS along the beam axis using data obtained from the Busan Center of Korea Basic Science Institute (KBSI). The bremsstrahlung spectral temperature from 28-GHz ECR Ion source at the KBSI was measured in six, three, and nine azimuthal angles at the injection, centre, and extraction sides of the ECRIS using three round type thallium-activated sodium iodide (NaI(TI)) scintillation detectors. Monte Carlo simulation based on the Geant4 software package was performed to take the geometrical acceptance and energy-dependent detection efficiency into account due to large non-uniformity in the material budget. True bremsstrahlung energy spectra from the 28-GHz ECR ion source were obtained using the inverse-matrix deconvolution method. The unfolding method was based on a full geometry of the Geant4 model of the ECRIS plasma. The results show that in all three measurement locations, the highest value of the spectral temperature was at an angle of 30∘ coincident with one of the maximum angles of the ECRIS plasma shape.

Comparison of End-Point Energies of Bremsstrahlung Photons from 28- GHz ECR Ion Source in Three Measurement Locations

Bremsstrahlung photons measurement show elevated energy emission beyond critical energy in 28-GHz ECR and its nature is not revealed. Thus, the aim of this study is to unveil the nature of high end-point energies at the three measurement locations. Bremsstrahlung photons from a 28-GHz ECR ion source were measured at Busan center of Korean Basic Science Institute (KBSI). The gamma-ray detection system consists of three round type NaI(Tl) scintillation detectors placed 62 cm radially from the beam axis at the three measurement locations namely injection, centre and extraction sides of an ECR ion source, and a NaI(Tl) scintillation detector placed at the view port for monitoring photon intensity along the beam axis. Such design of the experiment was based on the inner structure of the ECR ion source and the shape of the ECR plasma. Also, bremsstrahlung photons were measured by exchanging the detector positions for studying systematic uncertainties. Monte Carlo simulation based on the Geant4 package was performed to take geometrical acceptance and the energydependent detection efficiency into account due to large non-uniformity in the material budget. True bremsstrahlung energy spectra from the 28-GHz ECR ion source were extracted using an inverse matrix unfolding method. The measured high end-point energies at the three measurement locations were 1.68 MeV, 1.72 MeV and 2.04 MeV for the injection, centre and extraction sides, respectively. The high end-point energy values of the measured bremsstrahlung photons beyond the theoretical energy value of 1.33 MeV were found to be correlated with the structure of the ECR ion source and the shape of the ECR plasma. Furthermore, the high end-point energy values resulting from the bremsstrahlung photons measurements in the 28-GHz ECR plasma are due to the higher number of unconfined electrons arriving at the chamber wall easily, and producing higher bremsstrahlung photons. The unconfined electrons are the results of imperfect magnetic confinement that cause electrons to escape from the plasma volume.

Characterization of bremsstrahlung and γ-rays of fuel debris

The characterization of bremsstrahlung and γ-rays from fuel debris differs from that of spent fuels evaluated to date, due to factors such as material composition and release of volatile fission products. In this work, in order to clarify the conditions under which the effect of bremsstrahlung compared to the total photons (bremsstrahlung and γ-rays) in fuel debris is maximized, the average energies and dose rates from the energy spectra of bremsstrahlung and γ-rays on the fuel debris surface were obtained using a Monte Carlo simulation. In the simulation, the average energies and dose rates were evaluated with consideration of the composition, size, fission product release, and retrieval time of the fuel debris. The simulation showed that the composition with the largest amount of change to the average total photons energy caused by bremsstrahlung was the molten fuel debris, and the composition with the maximum fraction of bremsstrahlung in the dose rate was the UO2. The maximum value of the fraction of bremsstrahlung in the dose rate was evaluated to be about 17%. This work is expected to contribute to the prediction of the radiation characteristics of the fuel debris that will be retrieved from the Fukushima Daiichi Nuclear Power Station in the near future.

Bremsstrahlung hard x-ray source driven by an electron beam from a self-modulated laser wakefield accelerator

An x-ray source generated by an electron beam produced using a Self-Modulated Laser Wakefield Accelerator (SM-LWFA) is explored for use in high energy density science facilities. By colliding the electron beam, with a maximum energy of 380 MeV, total charge of >10 nC and a divergence of 64 × 100 mrad, from a SM-LWFA driven by a 1 ps 120 J laser, into a high-Z foil, an x/gamma-ray source was generated. A broadband bremsstrahlung energy spectrum with temperatures ranging from 0.8 to 2 MeV was measured with an almost 2 orders of magnitude flux increase when compared with other schemes using LWFA. GEANT4 simulations were done to calculate the source size and divergence.

Improved quantitative 90 Y bremsstrahlung SPECT/CT reconstruction with Monte Carlo scatter modeling.

In 90 Y microsphere radioembolization (RE), accurate post-therapy imaging-based dosimetry is important for establishing absorbed dose versus outcome relationships for developing future treatment planning strategies. Additionally, accurately assessing microsphere distributions is important because of concerns for unexpected activity deposition outside the liver. Quantitative 90 Y imaging by either SPECT or PET is challenging. In 90 Y SPECT model based methods are necessary for scatter correction because energy window-based methods are not feasible with the continuous bremsstrahlung energy spectrum. The objective of this work was to implement and evaluate a scatter estimation method for accurate 90 Y bremsstrahlung SPECT/CT imaging. Since a fully Monte Carlo (MC) approach to 90 Y SPECT reconstruction is computationally very demanding, in the present study the scatter estimate generated by a MC simulator was combined with an analytical projector in the 3D OS-EM reconstruction model. A single window (105 to 195-keV) was used for both the acquisition and the projector modeling. A liver/lung torso phantom with intrahepatic lesions and low-uptake extrahepatic objects was imaged to evaluate SPECT/CT reconstruction without and with scatter correction. Clinical application was demonstrated by applying the reconstruction approach to five patients treated with RE to determine lesion and normal liver activity concentrations using a (liver) relative calibration. There was convergence of the scatter estimate after just two updates, greatly reducing computational requirements. In the phantom study, compared with reconstruction without scatter correction, with MC scatter modeling there was substantial improvement in activity recovery in intrahepatic lesions (from >55% to >86%), normal liver (from 113% to 104%), and lungs (from 227% to 104%) with only a small degradation in noise (13% vs. 17%). Similarly, with scatter modeling contrast improved substantially both visually and in terms of a detectability index, which was especially relevant for the low uptake extrahepatic objects. The trends observed for the phantom were also seen in the patient studies where lesion activity concentrations and lesion-to-liver concentration ratios were lower for SPECT without scatter correction compared with reconstruction with just two MC scatter updates: in eleven lesions the mean uptake was 4.9 vs. 7.1MBq/mL (P=0.0547), the mean normal liver uptake was 1.6 vs. 1.5MBq/mL (P=0.056) and the mean lesion-to-liver uptake ratio was 2.7 vs. 4.3 (P=0.0402) for reconstruction without and with scatter correction respectively. Quantitative accuracy of 90 Y bremsstrahlung imaging can be substantially improved with MC scatter modeling without significant degradation in image noise or intensive computational requirements.

Реконструкция действующего спектра тормозного излучения медицинских линейных ускорителей электронов по глубинным распределениям дозы в водном фантоме

Purpose: Development of the bremsstrahlung spectrum reconstruction method of medical electron linear accelerators (ELA) with different field sizes on the base of the deep dose distributions in a water phantom and determination of photon spectra for Varian Trilogy accelerator 6 MV. 
 Material and methods: The proposed methodology is based on the use of dose kernels algorithm of point monoenergetic monodirectional source (pencil beam (PB)) for the deep dose distribution calculation, created different cross-section beams of in a water phantom, and experimental measurements of these distributions. For solving the inverse problem is applied Toolbox routines 'ptimtool knowing mathematical package MATLAB to solve.
 Results: Bremsstrahlung energy spectrum generated medical accelerator Varian Triology with different sizes of square fields from 3×3 up to 40×40 cm and average energy photons, depending on the size of the fields were received. Dose kernels for a set of defined energies PB were calculated. Depth dose distribution in a water phantom, calculated using the obtained spectra and dose kernels agree well with measurement dose distributions. 
 Conclusion: The proposed technique reconstruction of bremsstrahlung spectrum of electron linear accelerator is adequate. Average energy spectra of bremsstrahlung photons for Varian Trilogy Accelerator in regime 6 MV varies from 1.71 to 1.43 MeV depending on the field size.

Development and evaluation of an improved quantitative 90Y bremsstrahlung SPECT method

Yttrium-90 ((90)Y) is one of the most commonly used radionuclides in targeted radionuclide therapy (TRT). Since it decays with essentially no gamma photon emissions, surrogate radionuclides (e.g., (111)In) or imaging agents (e.g., (99m)Tc MAA) are typically used for treatment planning. It would, however, be useful to image (90)Y directly in order to confirm that the distributions measured with these other radionuclides or agents are the same as for the (90)Y labeled agents. As a result, there has been a great deal of interest in quantitative imaging of (90)Y bremsstrahlung photons using single photon emission computed tomography (SPECT) imaging. The continuous and broad energy distribution of bremsstrahlung photons, however, imposes substantial challenges on accurate quantification of the activity distribution. The aim of this work was to develop and evaluate an improved quantitative (90)Y bremsstrahlung SPECT reconstruction method appropriate for these imaging applications. Accurate modeling of image degrading factors such as object attenuation and scatter and the collimator-detector response is essential to obtain quantitatively accurate images. All of the image degrading factors are energy dependent. Thus, the authors separated the modeling of the bremsstrahlung photons into multiple categories and energy ranges. To improve the accuracy, the authors used a bremsstrahlung energy spectrum previously estimated from experimental measurements and incorporated a model of the distance between (90)Y decay location and bremsstrahlung emission location into the SIMIND code used to generate the response functions and kernels used in the model. This improved Monte Carlo bremsstrahlung simulation was validated by comparison to experimentally measured projection data of a (90)Y line source. The authors validated the accuracy of the forward projection model for photons in the various categories and energy ranges using the validated Monte Carlo (MC) simulation method. The forward projection model was incorporated into an iterative ordered subsets-expectation maximization (OS-EM) reconstruction code to allow for quantitative SPECT reconstruction. The resulting code was validated using both a physical phantom experiment with spherical objects in a warm background and a realistic anatomical phantom simulation. In the physical phantom study, the authors evaluated the method in terms of quantitative accuracy of activity estimates in the spheres; in the simulation study, the authors evaluated the accuracy and precision of activity estimates from various organs and compared them to results from a previously proposed method. The authors demonstrated excellent agreement between the experimental measurement and Monte Carlo simulation. In the XCAT phantom simulation, the proposed method achieved much better accuracy in the modeling (error in photon counts was -1.1 %) compared to a previously proposed method (errors were more than 20 %); the quantitative accuracy of activity estimates was excellent for all organs (errors were from -1.6 % to 11.9 %) and comparable to previously published results for (131)I using the same collimator. The proposed (90)Y bremsstrahlung SPECT reconstruction method provided very accurate estimates of organ activities, with accuracies approaching those previously observed for (131)I. The method may be useful in verifying organ doses for targeted radionuclide therapy using (90)Y.

Tritium depth profile in matter using an imaging plate

A method to detect tritium non-destructively in regions deeper than the escape depth of beta rays is being developed using bremsstrahlung induced by beta rays with an imaging plate (IP). An IP made of europium-doped BaFBr(I), a photostimulated luminescence (PSL) material, is a two-dimensional radiation sensor. The bremsstrahlung energy spectrum is a continuum with photon energies, varying based on the atomic number and thickness of the target (or absorbing) material. When tritium migrates into matter, the bremsstrahlung energy spectrum distribution would change. The PSL intensity of the IP is affected by this energy spectrum variation. In order to quantify the amount of tritium in deeper regions with the IP technique, a tritium depth profile is required.In this study, a new method of obtaining a tritium depth profileusing the combined technique of the IP and thin absorbers is presented.

SU‐E‐I‐56: Computational Internal Dosimetry Methods as Applied to the UF Series of Hybrid Phantoms

Purpose: To compute specific absorbed fractions for monoenergetic photons and electrons for all UF hybrid ICRP‐reference phantoms. Ultimately, radionuclide S values will be calculated for all radionuclides of interest in nuclear medicine. Methods: Voxelized versions of the UF newborn hybrid computational phantoms were used in conjunction with the radiation transport code MCNPX v2.6 to determine the absorbed fraction of energy per unit mass (SAF) for a variety of source‐target organ combinations for 21 photon and electron energies. A method known as a fluence‐to‐dose response function was used, for the first time in a model of the newborn child, to determine the absorbed dose to active marrow and total shallow marrow, the radiosensitive tissues of the skeleton. A novel method for minimizing the poor statistics associated with electron transport was also introduced. First, a simulation was completed which only tracked primary electrons, giving the dose contribution solely attributed to collisional energy losses. Next, a simulation was completed which recorded the initial energy of any photons produced by the primary electrons. Monoenergetic photon SAFs, determined previously, were then weighted according to each monoenergetic electron bremsstrahlung energy spectrum so as to procure low uncertainty photon dose from the primary electrons. Results: The novel method for electron dosimetry was benchmarked and found to be an accurate and effective way of reducing the uncertainty associated with electron cross‐dose. S values were generated for Tc‐99m and compared to estimates provided by OLINDA/EXM 1.0. Noticeable differences were seen for both self‐dose and cross‐dose scenarios. Conclusion: The work performed represents a state‐of‐the‐art internal dosimetry model, and once dosimetry has been performed on the entire UF series of phantoms, the results will be incorporated into an online accessible software package which can be of use in imaging and dose optimization for pediatric nuclear medicine patients.

Photofission of 235U and 237Np with Bremsstrahlung Photons below 20 MeV: Measurements of Delayed Neutron Yields and Time Spectra

Recently, new applications based on detection of delayed neutrons (DNs) or delayed photons produced during photofission have shown the need for new basic nuclear data. Indeed, available data for DNs are scarce, incomplete, and sometimes contradictory. An experimental campaign has been dedicated to DN measurements for some important actinides with a bremsstrahlung end-point energy spectrum up to 20 MeV. The experiments were carried out at the electron accelerator facility ELSA installed at the Commissariat à l’Energie Atomique (CEA) center of Bruyères-le-Châtel, France. Delayed neutrons were measured by 12 3He counters embedded in an annular polyethylene cylinder. Delayed neutron absolute yields were determined. Different irradiation-decay time combinations allowed the extraction of the averaged six-group parameters of DNs. Similarly to the nuclear reactor physics, these groups are formed by lumping DN precursors according to their half-lives. The DN time dependence is then expressed by the sum of group contributions.In this paper, DN absolute yields and six-group parameters for 235U at 15 and 18 MeV and 237Np at 15 MeV are presented. The 235U and 237Np absolute DN yields are found slightly lower than those published in the literature. For 235U, the six-group parameters show no dependence on incident electron energy from 10 to 18 MeV. In addition, the group parameters are very close to those of 237Np. This work helped to resolve the discrepancies of the photofission DN parameters for 235U while the six-group parameters for 237Np are reported for the first time.

Deexcitation of plasma by relativistic electrons

The characteristics of the electromagnetic radiation generated as a result of the interaction of relativistic electrons with a plasma are investigated. The main attention is paid to the analysis of the effect of broadening mechanisms on the bremsstrahlung energy spectrum of the relativistic electrons propagating in a carbon plasma upon deexcitation of its components.

Characterisation of the bremsstrahlung generated by a 450 MeV superconducting electron linac using the inverse calculation method based on a genetic algorithm

The bremsstrahlung energy spectrum generated by the 450 MeV electron linac driving the vacuum ultra violet free electron laser FLASH (free electron laser in Hamburg) operated by DESY was measured with TLD-700 detectors and unfolded using a technique based on a genetic algorithm. The half (1/2), one-fourth (1/4) and tenth (1/10) value layer thickness of lead were estimated to be 1.0, 4.0 and 20 mm, respectively. The peak and average photon energy were calculated from the unfolded bremsstrahlung spectrum and found to be 0.5 and 0.8 MeV, respectively.

Sample geometry and efficiency determination of bremsstrahlung radiation of 90Sr on gamma detection systems

The bremsstrahlung radiation energy spectra were produced by hard beta-emitters the 90Sr-90Y contaminated tea sample sources placed in a copper cylinder (cylinder counting geometry) and encapsulated in two Cu discs (sandwich counting geometry). These energy spectra were directly measured by using two separate gamma-ray spectrometers with a coaxial 110% efficient HpGe detector and a 110 cm3 HpGe well-type detector. The minimum detectable activity and the absolute efficiency of beta-activity for the sandwich and cylinder geometries were found to be 23 Bq . kg-1 and (1.67±0.04)% and 55 Bq . kg-1 and (2.61±0.05)%, respectively. These results indicate that the bremsstrahlung radiation counting method can be applied to some environmental studies when high efficient HpGe detectors, especially well-type HpGe are used.

A MONTE CARLO SIMULATION OF PHOTON BEAM GENERATED BY A LINEAR ACCELERATOR

ntroduction: Monte Carlo simulation is the most accurate method of simulating radiation transport and predicting doses at different points of interest in radiotherapy. A great advantage of the Monte Carlo method compared to the deterministic methods is the ability to deal accurately with any complex geometry. Its disadvantage is the extremely long computing time required to obtain a dose distribution with good statistical accuracy. Materials and Methods: The MCNP-4C Monte Carlo code was used to simulate a 9 MV photon beam from a Neptun 10PC linear accelerator. The accelerator was modeled as a complete unit consisting of a target, exit window, initial collimator, primary collimator, flattening filter, monitor chamber and secondary collimator. The geometrical details and the composition of each component was either obtained from the manufacturer or was directly measured. The simulation of the source was performed in a two step process. Initially, the electron source was defined. Secondly, the bremsstrahlung energy spectra and the fluence distribution at the scoring planes were used to define the photon source. The simulated electron beam energy followed a Gaussian distribution, with FWHM equal to 12% in nominal energy. The used intensity distribution of the electron beam also followed a Gaussian distribution with a FWHM equal to 0.34 cm. To compute the photon beam data a 50 × 50 × 40 cm 3 water phantom located at SSD = 100 cm was simulated. The depth dose and the dose profile curves were calculated for four different field sizes (5×5, 10×10, 20×20 and 30×30 cm 2 ) and compared against the measured values. The low-energy cut-off for the photons and electrons was 10 and 500 KeV, respectively. The measurements were carried out by using a Scanditronix dose scanning system and a 0.12 cm 3 RK ionization chamber. Results: To verify the simulated model, the calculated Monte Carlo dose data were compared against the corresponding measured values. The energy spectra and the angular distribution of the x-ray beam generated by the Neptun 10PC linac was examined. The result showed an efficiency of about 73% for the production of bermsstrahlung photon by the target. The agreement between the calculated and the measured depth dose and the dose profile was generally better than 2% for all the fields. Discussion and Conclusion: The simulation of the Neptun 10PC linac performed in this work is capable of computing the depth dose data and the beam profiles in water phantom for all the predefined fields including 5×5, 10×10, 20×20 and 30×30 cm 2 . Therefore, it can be concluded that MCNP-4C is a suitable tool for the dose calculation in radiotherapy. The simulated linac machine and the resulting data can be used to predict the dose distribution in all complex fields.

Evaluation using m.c.n.p. code of the bremsstrahlung energy spectrum produced by interactions between structural materials and accelerated electrons

In order to design the biological shield of industrial accelerator plants, it is needed to have a good knowledge of the bremsstrahlung energy spectrum and the intensity of the bremsstrahlung produced by electron interactions with both products (usually water equivalent) and structural materials such as concrete, iron, aluminium. Using the MCNP code, a normalized bremsstrahlung energy spectrum was obtained for materials with average atomic number lower than or equal to 13 and irradiated with 5 and 10 Mev electrons, respectively; multiplying the spectrum by suitable coefficients, it was possible to obtain the real spectrum for materials such as water, concrete, aluminium and iron. The MCNP results have been obtained with relative error less than 2%.

The dependence of AKR production on the intensity and energy spectra of auroral bremsstrahlung

Our limited knowledge of the energy dependence of electron precipitation associated with auroral kilometric radiation (AKR) production is improved with the use of bremsstrahlung x‐ray measurements. Simultaneous observations of bremsstrahlung x‐rays above 2 keV from the Polar Ionospheric X‐ray Imaging Experiment (PIXIE) on the POLAR satellite are compared with the frequency distributions of AKR waves measured with the Plasma Wave Instrument (PWI) on the GEOTAIL satellite. Various AKR characteristics such as the low‐ and high‐ frequency cutoffs and the frequencies at peak intensity are compared with various x‐ray parameters such as the magnetic local times of emission, the total intensities, and the spectral shapes. In particular, it is found that higher fluxes of x‐rays occur when the various cutoffs are at lower frequency. Also, higher AKR cutoff frequencies are associated with higher e‐folding x‐ray energy spectra.

ベータ線による制動放射線エネルギースペクトルの計算

Bremsstrahlung energy spectra induced by beta ray from radionuclides 3H, 63Ni, 14C, 147Pm, 90Sr, 32P and 90Yare calculated by using numerical data of radiation yield published by Berger et. al. and compared with those obtained from classical approximate expressions of Wu and Segré. The results for 3H, 63Ni, 14C and 147Pm are in good agreement with those from Segré's, while spectra from such as 32P and 90Y are similar to those obtained by using Wu's expression. The result for 90Sr is in fair agreement with those from Wu's and Segré's.

Search for Hot Gas in the Local Group with ASCA

Abstract An X-ray study was made to examine whether some part of the soft X-ray background is coming from hot gas in the Local Group. For this purpose, four consecutive pointings were made with ASCA toward a sky region between M31 and M33, which is close to the direction of the center of the Local Group. By comparing the X-ray surface brightness in this sky direction with that in another blank sky region near the north equatorial pole, an upper limit on any soft excess X-ray background was determined to be $2.8 \times 10^{-9} \,\mathrm{erg} \,\mathrm{cm}^{-2} \,\mathrm{s}^{-1} \,\mathrm{sr}^{-1}$ with a 90% confidence level statistical error. Assuming an optically-thin thermal bremsstrahlung energy spectrum (Raymond–Smith model) for a temperature of 1 keV and a $\beta$-model electron density distribution for a core radius of 100 kpc for the X-ray halo, the upper limit of the central plasma density was obtained to be $1.3 \times 10^{-4} \,\mathrm{cm}^{-3}$. The plasma column density is too low to contribute significantly to the observed quadrupole anisotropy in the cosmic microwave background.

Application of a low-background gamma-ray spectrometer to the determination of [formula omitted

A method for quantitative determination of 90Sr with a germanium γ-ray spectrometer is presented. The bremsstrahlung energy spectrum produced by high-energy beta particles from the 90Sr source encapsulated in a given absorbing material is measured. The idea was tested on various types of low-background germanium γ-ray spectrometers. The optimisation of absorber thickness for aluminium, iron, copper, cadmium, tantalum and lead is presented. The lowest achieved detection limit for a 10% efficiency HPGe detector was 0.38 Bq/sample which allows this method to be applied to some environmental studies.

Generation of bremsstrahlung by an electron beam

The problem of generation of x- and y-radiations in interaction of an electron beam with a layer of a substance having a large Z is considered theoretically. Energy and angular spectra of bremsstrahlung are obtained for various energies of the electron beam.