MeV Electron Beam Research Articles

Surface modification of multiwalled carbon nanotubes network through high energy electron beam and its implications on thermoelectric properties

In this work we demonstrate the surface modifications in free standing network of multi walled carbon nanotubes (MWCNTs) upon irradiation with 10 MeV electron beam. The irradiated samples initially showed an electrical conductivity enhancement along with keeping almost constant Seebeck coefficient up to dose of 50 kGy. At higher dose levels (>50 kGy) the electrical conductivity starts decreasing. In depth characterization of irrdaited MWCNT sheet samples using Raman spectroscopy, x-ray photoelectron spectroscopy, thermogravimetric studies and morphological analysis revealed that the impact of high energy electron beam on MWCNT creates C-O types of defects which induces a p-type doping in MWCNT. However at higher dose these defects starts annihilating. So the present work demonstrates the high energy electron beam is an alternative to modify the thermoelectric properties of MWCNTs owing to defect engineering.

Microstructure and magnetization study of Li and Li–Zn ferrites synthesized by an electron beam

Lithium ferrites are widely used in high frequency electronic devices. The present work reports structural and magnetization analysis of lithium (Li0.5Fe2.5O4) and lithium-zinc (Li0.4Fe2.4Zn0.2O4) ferrites synthesized by electron beam heating (RT) of powdered and compacted samples. The synthesis was carried out at 600 and 750 °C for up to 120 min using 2.4 MeV electron beam generated by an ILU-6 pulsed electron accelerator. The characteristics of the samples synthesized by RT were compared with the ones of samples obtained by traditional thermal heating under the same temperature and time conditions. From XRD and thermomagnetometric analyses, α-Li0.5Fe2.5O4 ordered spinel phase and Li0.5(1−x)Fe2.5−0.5xZnxO4 ferrite phase with different zinc substitution were formed from Fe2O3/Li2CO3 and Fe2O3/Li2CO3/ZnO reagents, respectively. RT synthesis significantly increases the rate of interaction between the initial powders and, as a consequence, the rate of ferrite phase formation. In this case, lithium-containing ferrites can be successfully achieved from compacted powders at 750 °C, which is lower than the temperature of synthesis in conventional thermal heating. The average crystallite sizes calculated from the XRD and BET analyses were 114 nm for Li, 120 nm for Li–Zn ferrites and 142 for Li, 150 nm for Li–Zn, respectively. The specific saturation magnetization and Curie temperature were estimated and are 60 emu/g for Li, 70 emu/g for Li–Zn ferrites and 632 °C for Li, 492 °C for Li–Zn ferrites, respectively. The data obtained in this work are of considerable interest for the creation of a technology for producing ferrites at low synthesis temperatures.

Experimental study of medical isotopes 62,64Cu and 68Ga production using intense picosecond laser pulse

Radioisotopes are indispensable agents in medical diagnosis and treatment, among which copper-62, 64 (62,64Cu) and gallium-68 (68Ga) are medical isotopes widely used in positron emission tomography (PET) imaging. Experiments that generate these radioisotopes via laser-induced photonuclear reactions were performed on the XingGuangIII laser facility of the Laser Fusion Research Center in Mianyang. High-charge ( ∼ 40 nC) MeV electron (e− ) beams were generated with 100 terawatts, picosecond laser pulses. The e− beams were then impinged on a metal stack composed of Ta foil and activation plates (natural Cu and Ga2O3), producing high-energy bremsstrahlung x-rays and medical isotopes 62,64Cu and 68Ga, respectively. The characteristic emissions of the produced 62,64Cu and 68Ga were detected off-line , and the production yields of 62,64Cu and 68Ga were obtained to be of the order of 106 per laser shot. For electrons with energy higher than 8 MeV, the dependence of isotope production efficiency (per e− ) on electron temperature () is investigated through Geant4 simulations. It is found that the production efficiency increases with the . At ∼ 10 MeV, the values are 10−4 for 62Cu and 2 × 10 − 5 for 68Ga, respectively. The prospect of producing the medical isotopes 62,64Cu and 68Ga are further evaluated using a table-top femtosecond laser system of high repetition. With a repetition rate of 100 Hz, their activity is expected to reach 0.2 GBq for 62Cu, 0.1 GBq for 64Cu and 0.05 GBq for 68Ga, respectively. Such activity would meet the required dose for clinical PET imaging, indicating the great potential to produce medical isotopes with an all-optical, high-repetition laser system.

Structural characterization, defect evolution and luminescence properties of natural CaF2 under 10 MeV electron irradiation

Present study investigates the response of various coloured variants of natural fluorite (CaF2) to 10 MeV electron beam irradiation at accumulated dose of 5–10 MGy. The fluorite specimens did not show any post irradiation radioactivity. However, after irradiation the specimens developed purple colouration of different shades depending on the dose. In-depth characterization of the as-received and irradiated specimens using XPS and Raman spectroscopy confirm the relocation of fluorine (F) anions at interstitial sites and formation of metallic calcium (Ca). The calculated displacement cross sections for F and Ca indicate that it is easier to form fluorine anion interstitials within lattice structure. However, the estimated lower fraction of interstitial fluorine (∼14%) as compared to metallic Ca (>50%) is attributed to their surface diffusion and desorption. Electron irradiation was found to cause photoluminescence quenching in all the CaF2 specimens that is likely caused by a radiation-induced formation of competing recombination channels.

Microstructural evolution of polymer derived SiC ceramics and SiC/SiC composite under 1.8MeV electron irradiation

Continuous silicon carbide fiber reinforced silicon carbide matrix composites (SiC/SiC) are promising candidate materials for nuclear applications. Herein, SiC ceramics and SiC/SiC composite were prepared by a polymer deriving method, and irradiated using a 1.8 MeV electron beam. The microstructural evolution and radioluminescence performance were investigated, and the results showed that the SiC ceramics and the SiC/SiC composite all exhibited evident amorphization after the electron irradiation. In addition, the radioluminescence intensity of the SiC ceramics and the SiC/SiC composite was too low owing to the self-absorption of the free carbon in the polymer derived SiC ceramics.

TUDY OF THE INITIAL MAGNETIC PERMEABILITY OF LiTiZnMnFERRITES OBTAINED BY LIQUID-PHASE SINTERING UNDER RADIATION-THERMAL AND THERMAL CONDITIONS

The measuring the temperature dependence of the initial permeability was used to study the features of phase and structural transformations in lithium-titanium ferrites as a function of time, heating and cooling rates, and the temperature of liquid-phase sintering under thermal and radiation-thermal heating. Ferrite was synthesized from powder mixture by solid-phase synthesis. A low-melting additive bismuth dioxide was used to obtain the ferrite ceramics by liquid-phase sintering. RT sintering was carried out by heating the samples with a pulsed (1.5–2.0) MeV electron beam. It was established that the additive leads to a less defective state of sintered ferrites, while the action of radiation enhances this effect in the early stages of sintering. The regularities of the influence of the heating and cooling rates of compacted samples on the change in the initial magnetic permeability of sintered ferrites are established.

Measuring the cross section of the N15(α,γ)19F reaction using a single-fluid bubble chamber

$^{15}$N($\alpha$,$\gamma$)$^{19}$F is believed to be the primary means of stellar nucleosynthesis of fluorine. Here we present the use of a single-fluid bubble chamber to measure the cross section of the time-inverse photo-dissociation reaction. The method benefits from a luminosity increase of several orders of magnitude due to the use of a thicker liquid target -- when compared to thin films or gas targets -- and from the reciprocity theorem. We discuss the results of an experiment at the Thomas Jefferson National Accelerator Facility, where the cross section of the photodisintegration process $^{19}$F($\gamma$, $\alpha$)$^{15}$N was measured by bombarding a superheated fluid of C$_3$F$_8$ with bremsstrahlung $\gamma$-rays produced by impinging a 4 - 5.5 MeV electron beam on a Cu radiator. From the photodissociation yield the cross section was extracted by performing a convolution with a Monte Carlo-generated $\gamma$-ray beam spectrum. The measurement produced a cross section that was then time inverted using the reciprocity theorem. The cross section for the $^{15}$N($\alpha$,$\gamma$)$^{19}$F reaction was determined down to a value in the range of hundreds of picobarns. With further improvements of the experimental setup the technique could potentially push cross section measurements down to the single picobarn range.

Evaluation by thickness of a linear accelerator target at 6-20 MeV electron beam in MCNP6

This study quantitatively evaluated the source term of a linear accelerator according to target thickness for a 6-20 MeV electron beam using MCNP6. The elements of the target were tungsten and copper, and a composite target and single target were simulated by setting different thickness parameters depending on energy. The accumulation of energy generated through interaction with the collided target was evaluated at 0.1-mm intervals, and F6 tally was used. The results indicated that less than 3% reference error was maintained according to the MCNP recommendations. At 6, 8, 10, 15, 18, and 20 MeV, the energy accumulation peaks identified for each target were 0.3 mm in tungsten, 1.3 mm in copper, 1.5 mm in copper, 0.5 mm in tungsten, 0.5 mm in tungsten, and 0.5 mm in tungsten. For 8 and 10 MeV in a single target consisting only of copper, the movement of electrons was confirmed at the end of the target, and the proportion of escaped electrons was 0.00011% and 0.00181%, respectively.

Development of a compact linear accelerator to generate ultrahigh dose rate high-energy X-rays for FLASH radiotherapy applications.

In recent years, the FLASH effect, in which ultrahigh dose rate (UHDR) radiotherapy (RT) can significantly reduce toxicity to normal tissue while maintaining antitumor efficacy, has been verified in many studies and even applied in human clinical cases. This work evaluates whether a room-temperature radio-frequency (RF) linear accelerator (linac) system can produce UHDR high-energy X-rays exceeding a dose rate of 40Gy/s at a clinical source-surface distance (SSD), exploring the possibility of a compact and economical clinical FLASH RT machine suitable for most hospital treatmentrooms. A 1.65m long S-band backward-traveling-wave (BTW) electron linac was developed to generate high-current electron beams, supplied by a commercial klystron-based power source. A tungsten-copper electron-to-photon conversion target for UHDR X-rays was designed and optimized with Monte Carlo (MC) simulations using Geant4 and thermal finite element analysis (FEA) simulations using ANSYS. EBT3 and EBT-XD radiochromic films, which were calibrated with a clinical machine Varian VitalBeam, were used for absolute dose measurements. A PTW ionization chamber detector was used to measure the relative total dose and a plane-parallel ionization chamber detector was used to measure the relative normalized dose of each pulse. The BTW linac generated 300-mA-pulse-current 11 MeV electron beams with 29kW mean beam power, and the conversion target could sustain this high beam power within a maximum irradiation duration of 0.75 s. The mean energy of the produced X-rays was 1.66 MeV in the MC simulation. The measured flat-filter-free (FFF) maximum mean dose rate of the room-temperature linac exceeded 80Gy/s at an SSD of 50cm and 45Gy/s at an SSD of 67.9cm, both at a 2.1cm depth of the water phantom. The FFF radiation fields at 50cm and 67.9cm SSD at a 2.1cm depth of the water phantom showed Gaussian-like distributions with 14.3 and 20cm full-width at half-maximum (FWHM) values, respectively. This work demonstrated the feasibility of UHDR X-rays produced by a room-temperature RF linac, and explored the further optimization of system stability. It shows that a simple and compact UHDR X-ray solution can be facilitated for both FLASH-RT scientific research and clinical applications.

6 MeV electron beam induced TL dosimetric properties of CaF2:Dy nanophosphor

The present paper reports the thermoluminescence properties of 6 MeV electron irradiated Dy doped CaF2 nanophosphors (NPs), at different doses from 25 Gy to 1.2 kGy. Here, the chemical co-precipitation method was used to prepare the CaF2:Dy nanophosphor with an optimized concentration of Dy dopants. The structural and morphological configuration of the nanophosphor were investigated by using X-Ray Diffraction (XRD) and Field Emission Scanning Electron Microscope, which confirms the FCC phase exhibiting crystallite size ∼54 nm and particle size of 88 nm, respectively. In the case of thermoluminescence properties, it is observed that 1 mol % doped NPs possess a simple and single glow curve at 230 °C at the electron fluence of 75 × 1011 e/cm2 (750 Gy). The linearity of absorbed dose-response is found to be linear with increase in electron fluence (dose) from 25 × 1010 e/cm2 (2.5 Gy) to 75 × 1011 e/cm2 (750 Gy). The fading and reproducibility characteristics have been explored and the kinetic parameters were calculated by using GCD and peak shape method etc.

Widely tunable electron bunch trains for the generation of high-power narrowband 1–10 THz radiation

Terahertz radiation enables the coherent excitation of many fundamental modes, such as molecular rotation, lattice vibration and spin precession. To excite the transient state of matter far out of equilibrium, high-power and tunable narrowband terahertz radiation sources have been in great demand for years. However, the terahertz source available at present cannot meet these tunability and power demands, leaving a large scientific gap that has yet to be fully explored. Here we convert the energy modulation induced by the nonlinear longitudinal space charge force to a density modulation and experimentally demonstrate the generation of electron bunch trains with modulation frequencies that are adjustable between 1 and 10 THz. The electron bunch trains can be directly used to produce tunable high-power narrowband terahertz radiation that fully covers the long-standing ‘terahertz gap’, which will open up many more possibilities in terahertz science. A tunable terahertz radiation pulse is demonstrated based on a linear accelerator. The emission frequency of this terahertz radiation is tunable from 1 to 10 THz by changing the bunching frequency of a 34 MeV electron beam. The pulse energy is at the submillijoule level.

Characterization of relativistic electron–positron beams produced with laser-accelerated GeV electrons

The characterization of an electron–positron beam generated from the interaction of a multi-GeV electron beam with a lead plate is performed using GEANT4 simulations. The dependence of the positron beam size on driver electron beam energy and lead converter thickness is investigated in detail. A pancake-like positron beam structure is generated with a monoenergetic multi-GeV driver electron beam, with the results indicating that a 5 GeV driver electron beam with 1 nC charge can generate a positron beam with a density of 1015–1016 cm−3 at one radiation length of lead. In addition, we find that electron–positron beams generated using above-GeV electron beams have neutralities greater than 0.3 at one radiation length of lead, whereas neutralities of 0.2 are observed when using a 200 MeV electron beam. The possibility of observing plasma instabilities in experiments is also examined by comparing the plasma skin depth with the electron–positron beam size. A quasi-neutral electron–positron plasma can be produced in the interaction between a 1 nC, 5 GeV electron beam and lead with a thickness of five radiation lengths. Our findings will aid in analyzing and interpreting laser-produced electron–positron plasma for laboratory astrophysics research.

BEAM MATCHING EVALUATION OF TWO SIMILAR LINEAR ACCELERATORS.

To evaluate the beam-matching of two Siemens Primus medical linear accelerators (Linacs), the output factor (Sc,p), wedge factor, quality index (TPR20/10), percentage depth dose (PDD) and beam profiles were compared for 6 and 15MV photon beams. The output factor, the PDD and the beam profile for electron beam compared for 5, 7, 8, 10 and 12MeV electron beams. The gamma (γ) analysis of 2mm/2% and 3mm/3% was performed. According to the measurements, it can be said that 6MV photon beams in all field sizes (except 4×4cm2) are beam matched. For 15MV, although the PDDs were matched in all field sizes (except 4×4cm2) for both 2mm/2% and 3mm/3% γ criteria, beam profiles in field sizes larger than 10×10cm2 for 3mm/3% and in field sizes larger than 8×8cm2 for 2mm/2% were not matched. The electron beams in all applicator sizes (except 5×5cm2 applicator) pass the acceptance γ criteria of 3mm/3% (γ<1). Electron beams do not fulfill beam matched in case of the acceptance γ criteria of 2mm/2%.

Development of a 6 MeV electron beam energy Linac for fruit sterilization

Treatment of fresh fruits, meat, and food with ionizing radiation has been frequently chosen to destroy harmful pathogenic microorganisms and oriental fruit flies. Electron beam linear accelerator (Linac) is commonly used as the source of irradiation to produce photons and electrons in megavolt energy. A 6 MeV Linac designed for medical therapy has been developed for fresh fruit sterilization at Synchrotron Light Research Institute (SLRI). Some physical design and beam dynamic results of the electron gun and 6 MeV Linac will be presented in this paper. Testing of each subsystem and installation of the 6 MeV Linac with major auxiliary systems will be described in this paper. It is the first system designed, fabricates, and tested in-house for the fruit sterilization application at SLRI. Measurement results of the Linac properties are presented as a resonant frequency and coupling coefficient at low power called a cold test. The Linac system with all sub-systems and the auxiliary systems will be installed and tested before x-rays production. During commissioning some electron beam parameters out of the electron gun and the Linac exit will be measured.

Monitoring Linear Accelerator Output Constancy and Overall Performance Using the PTW Quickcheckwebline

Daily morning quality assurance (QA) for all available beams using conventional phantom measures only output and beam quality. PTW QUICKCHECKwebline (PTW QCw) is a compact movable light-weight dosimetry equipment used for daily QA, capable of measuring flatness, symmetry, beam quality and output constancy of a given beam in a single exposure. The purpose of this study was to analyze and monitor the output constancy of a medical linear accelerator using PTW QCw and assess the overall performance of the PTW QCw. The output parameters of 4, 6 and 15 MV photon beams and 4, 6, 8, 10, 12 and 15 MeV electron beams of the Elekta Synergy linear accelerator in Kathmandu Cancer Center were analyzed. It was found in the study that all the parameters were well within the recommended tolerance limit of ±3%. Some known modifications in the settings of the linear accelerator gantry, couch, and collimator were introduced separately during the exposures, and the percentage variations from the baseline values were noted to check the sensitivity of the PTW QCw using 6 MV photon beam. The PTW QCw was able to detect the deviations introduced to the external irradiation conditions for both photon and electron beams under daily testing conditions. The results from this study suggest that daily dosimetric consistency measurements using the PTW QCw helps to monitor the overall performance of the linear accelerator.

TopasOpt: An open-source library for optimization with Topas Monte Carlo.

To describe and test TopasOpt: a free, open-source and extensible library for performing mathematical optimization of Monte Carlo simulations in Topas. TopasOpt enables any Topas model to be transformed into an optimization problem, and any parameter within the model to be treated as an optimization variable. Three case studies are presented. The starting model consists of a 10 MeV electron beam striking a tungsten target. The resulting bremsstrahlung X-ray spectrum is collimated by a primary and secondary collimator before being scored in a water tank. In the first case study (electron phase space optimization), five parameters describing the electron beam were treated as optimization variables and assigned a random starting value. An objective function was defined based on differences of depth-dose and profiles in water between the original (ground truth) model and a given model generated by TopasOpt. The problem was solved using Bayesian Optimization and the Nelder-Mead method. One hundred iterations were run in each case. In the second case study, (collimator geometry optimization), this process was repeated, but three geometric parameters defining the secondary collimator were treated as optimization variables and assigned random starting values, and forty iterations were run. In the third case study, the optimization was repeated with different number of primary particles to study the effect of noise on convergence. For case 1 (phase space optimization), both optimization algorithms successfully minimized the objective function, with absolute mean differences in profile dose of 0.4% (Bayesian) and 0.3% (Nelder-Mead) and 0.2% in depth-dose for both algorithms. The beam energy was recovered to within 1%, however some parameters had relative errors of up to 171% - a result consistent with the known X-ray dose is insensitivity to many electron beam parameters. For case 2 (geometry optimization), absolute mean differences in profile dose were 0.6% (Bayesian) and 0.9% (Nelder-Mead), and 0.5% and 0.9% in depth-dose. The maximum percentage error in any parameter was 9% with Bayesian Optimization and 28% with Nelder-Mead. Finally, the Bayesian Optimization algorithm was demonstrated to be robust to moderate levels of noise; when the standard deviation of the objective function was 16% of the mean, the maximum error in any parameter value was 16%, and the absolute mean difference in dose was 0.9% (profile) and 0.8% (depth-dose). An open-source library for optimization with Topas Monte Carlo has been developed, tested, and released. This tool will improve accuracy and efficiency in any situation in which the optimal value of a parameter in a Monte Carlo simulation is unknown. Applications for this tool include (1) The design of new components (2) Reverse engineering of models based on limited experimental or published data, and (3) Tuning of Monte Carlo "hyper parameters" such as variance reduction, physics settings, or scoring parameters.

Impact of In-House Bolus Thickness on The Percentage of Surface Dose for 10 and 12 MeV Electron Beams

The surface dose on electron irradiation which is received by the skin does not reach 100%, so a bolus is needed as a compensator material in order to reach or approach 100%. This study aims to create, test, and describe the effect of different thicknesses of boluses that are made of 3D printed TPU, silicone sealant and resin on equivalence with tissue and the percentage of surface dose produced. A bolus with a size of 15x15 cm2 and with variations in thickness of 0.3 cm, 0.5 cm, and 1 cm was imaged by a CT-Scan to analyze the CT-Number value and relative electron density using imageJ software. After that, the bolus was irradiated by a Linac with an energy of 10 MeV and 12 MeV to measure the surface dose using an advances marcus detector. The result of this study showed that 3D printed TPU, silicone sealant and resin are similar to some soft tissues. Silicone sealant has the highest flexibility of the two boluses. In addition, silicone sealant also produces the highest increase in the percentage of surface dose in phantom.

Effect of boiling on the radiolysis of acetylacetone

The radiolysis of acetylacetone was studied at 295 and 413 K (boiling point) using 3 MeV electron beam. The degradation yield of acetylacetone increases from 0.57 (295 K) to 0.90 (413 K) μmol J−1. Boiling promotes the decay of hydrogen bonds and easier structural relaxation of heavy intermediates, which favors the redistribution of H atoms and a decrease in the probability of C–OH bond cleavages. Acetic acid and acetone are the main fragmentation products. However, the light fragmentation products represent only about 1/3 of the total mass of the final products. The main heavier products are 4-oxopent-2-en-2-yl acetate (0.073 μmol J−1) at 295 K and 4-hydroxy-2-pentanone (0.235 μmol J−1) at 413 K. Boiling conditions favor the variety of isomeric forms of radical combination products. In particular, the dimerization products of acetonyl are hexa-2,4-diene-2,5-diol and hexane-2,5-dione.

UV-induced charge-state conversion from the negatively to neutrally charged nitrogen-vacancy centers in diamond

Under ultraviolet (UV) excitation with photon energy larger than 4.5 eV, a charge-state conversion from negatively to neutrally charged nitrogen-vacancy (NV− to NV0) centers in diamond samples is realized. The UV-induced charge-state conversion is found to strongly depend on the N concentration in the sample and the irradiation fluence of the electron beam. For the samples with high N concentrations, low-fluence (2.5 × 1017 cm−2) 10-MeV electron beam irradiation usually leads to UV-induced charge-state conversion efficiency higher than that of the samples irradiated with high fluences (≥2.5 × 1018 cm−2). For the samples with a few ppm N, however, the charge-state conversion efficiency is relatively low in the cases of irradiation fluences in this work. Meanwhile, UV-induced NV0 luminescence exhibits temperature dependence different from that of visible-light excited NV0 or NV− centers; that is, the photoluminescence intensity does not reach saturation at temperatures lower than 135 K but decreases with the decrease in temperature. Based on the photoluminescence excitation spectra of NV0 centers in the UV region, the UV-induced charge-state conversion is suggested to involve free-hole generation, diffusion, and the capture by ground-state NV− centers.

UVSOR Synchrotron Facility Update

UVSOR is a Japanese low-energy synchrotron light source that has been operational since 1983. It has 750 MeV electron beam energy and a circumference of 53 m. The machine has undergone two major upgrades and is now called UVSOR-III, with a moderately small emittance of 17 nm·rad and is operated in the top-up mode at 300 mA. It has six undulators. Three in-vacuum undulators provide high-brightness VUV-SX light to the beamlines BL3U, BL4U, and BL6U. BL3U and BL4U are actively used for chemistry and life sciences using in situ and operando measurements, such as soft X-ray absorption and photoelectron spectroscopy. Since 2020, a unique photoelectron analyzer called the Momentum Microscope has been in operation in BL6U. Two variable polarization undulators provide high-brightness VUV light to the beamlines, BL5U and BL7U, which are used for solid-state physics through angle- and spin-resolved photoelectron spectroscopy. BL1U is equipped with two APPLE-II undulators in tandem and is used for various research purposes, including laser Compton scattering gamma rays. In addition to these beamlines, eight beamlines are operational which use bending magnet radiation, ranging from THz to tender X-rays. In 38 years of operation, we have dealt with and properly resolved machine problems, such as water leakage from magnet coils and cooling water flow paths in ultrahigh vacuum. Considering the machine’s declining competitiveness as a light source due to its aging and emerging demands in the low-energy area, we have started a design study on the future plan, as well as discussing it closely with the user community.