Microtron Accelerator Research Articles

Probing Effect of 6MeV Electron Beam Irradiation on Haemoglobin Protein Using Spectroscopic Techniques.

In this work, we study the effect of 6MeV electron beam irradiation on the physicochemical properties of lyophilized Human Haemoglobin A (HbA). Electron beams generated from Race Track Microtron accelerator with energy 6MeV were used to irradiate HbA at fluences of 5 × 1014 e-/cm2 and 10 × 1014 e-/cm2. Pristine and electron beam irradiated HbA were characterized using UV-visible and Fourier transform infrared spectroscopy (FTIR) spectroscopy. The interfacial tension of the aqueous solutions of HbA are also analysed by pendant drop method. Absorbance intensity, % transmittance and interfacial tension decrease with fluence. The peak position of the Soret band (λsoret = 404nm) remains unaffected by the fluences. FTIR spectroscopy confirms the changes in the secondary structure of the haemoglobin. In the amide band I, the percentage of α-helix reduced from 8% to 1%, and an increase in β-sheet (19% to 29%) and β helix (6.3% to 15%) is observed. Interfacial tension decreases from 46.0mN/m and 44.0mN/m with increase in irradiation dose. These finding provides realistic guideline for biological cells exposure to electron beam radiation doses.

Methodology for measuring photonuclear reaction cross sections with an electron accelerator based on Bayesian analysis

Accurate measurements of photonuclear reaction cross sections are crucial for a number of applications, including radiation shielding design, absorbed dose calculations, reactor physics and engineering, nuclear safeguard and inspection, astrophysics, and nuclear medicine. Primarily motivated by the study of the production of selected radionuclides with high-energy photon beams (mainly 225Ac, 47Sc, and 67Cu), we have established a methodology for the measurement of photonuclear reaction cross sections with the microtron accelerator available at the Swiss Federal Institute of Metrology (METAS). The proposed methodology is based on the measurement of the produced activity with a High Purity Germanium (HPGe) spectrometer and on the knowledge of the photon fluence spectrum through Monte Carlo simulations. The data analysis is performed by applying a Bayesian fitting procedure to the experimental data and by assuming a functional trend of the cross section, in our case a Breit-Wigner function. We validated the entire methodology by measuring a well-established photonuclear cross section, namely the 197Au(γ, n)196Au reaction. The results are consistent with those reported in the literature.

Reconstruction of high energy thunderstorm radiation effects on soil matrix using Monte Carlo simulations

Due to their electromagnetic properties, thunderclouds can act as natural particle accelerators. Electrons accelerated in the thunderclouds can reach energies up to tens of MeV. Large populations of high energetic electrons formed by avalanche growth driven by electric fields in the Earth atmosphere called Relativistic Runaway Electron Avalanches (RREA) propagate through matter. They are decelerated and deflected in the course of collisions with particles in the atmosphere and emit gamma rays known as bremsstrahlung. The produced gamma rays can further trigger photonuclear reactions in the air and soil. This article reports on the work of project CRREAT (Research Centre of Cosmic Rays and Radiation Events in the Atmosphere), studying various lightning-related phenomena in various ways, both in situ and in the laboratory. This paper focuses on the simulation of the laboratory experiments at the Microtron accelerator in Prague and the neutron generator in Ostrava, where we irradiated various soil samples with 20 MeV electron beams. Experiments showed which radionuclides can be formed during the reactions of high-energy electrons with various soils and can be as targeted products in the thunderstorm radiation effect analysis. Radionuclides produced in exposed samples were measured using a highpurity germanium (HPGe) detector. A computer simulation was done with a simple source and sample geometry using the general-purpose 3D Monte Carlo code PHITS.

Gain and efficiency of table-top terahertz free-electron lasers driven by a microtron accelerator

There are difficulties in developing high-power and small-size terahertz (THz) sources that can be used for field applications. In an attempt to design small-size THz free-electron laser (FEL) devices capable of producing higher output powers in the THz spectral region of 1–2 THz, we have developed a microtron accelerator that can accelerate electron beams to 3–6 meV, with a macropulse current of more than 40 mA. The new THz FELs use hybrid electromagnetic (EM) undulators that are two to four times shorter in length than the previous undulator and waveguide resonators with mode cross-sectional areas that are more than two times smaller than the parallel-plate waveguide in the existing FEL. We confirm that the gains and losses of the compact FELs are sufficient for lasing, and we estimate that average output power of approximately 1 W is possible with an efficiency approximately 10 times greater than the existing FEL. The minimum size of the THz FEL system, including a high-voltage pulse modulator, is estimated to be approximately 1.5 m × 2.0 m.

Elastic differential cross section of ep scattering fitted via the differential cross section of eq scatterings with cloud-covering effects

The angular-averaged differential cross section (dcs) of the elastic electron-proton (ep) scattering, covering ${Q}^{2}<1.0\text{ }\text{ }{\mathrm{GeV}}^{2}$, was fitted via a combined modified $eq$-scatterings where $q$ is a point particle. The modifications represent the cloud-covering effects to $q$. An energy-decaying ratio (edr) was derived by inspecting the generated $dc{s}_{ep}$ from the form factor data gathered at Mainz Microtron (A1-Collaboration) and Continuous Electron Beam Accelerator Facility (Jefferson Laboratory) when compared to the $dc{s}_{eq}$ with modified relativistic recoil factor. The diminishing cloud layer, edr, has a decay rate of $\ensuremath{-}2.8$ for the datasets under investigation. The formulated spin bare mass (SBM) and spin effective mass (SEM) fitting models use the bare and effective $u$ and $d$-quark masses, respectively, while spin with other criteria bare mass (SCBM) and spin with other criteria effective mass (SCEM) integrate other considerations. Three comparison methods were used and all of them favor the models with other additional considerations. SCEM was the most favored model in general.

Synergetic effects of 1 MeV electron irradiation on the surface erosion in polyimide by atomic oxygen

Erosion studies of polyimide, exposed to high energy electrons and atomic oxygen, is necessary in view of its application in space vehicles. Here we present the erosion studies and degradation characteristics of polyimide after its sequential exposure to 1 MeV pulsed electron beam from Microtron accelerator and ~12 eV oxygen ions from a plasma reactor in the laboratory. The fluence of electrons was varied from 5 × 1014 to 2.0 × 1015 electrons/cm2 and that of oxygen ions from ~5 × 1016 to 2 × 1017 ions cm−2. The post irradiated and virgin polyimide samples were characterized by gravimetric analysis and contact-angle measurements. The morphological and spectroscopic information were obtained with Scanning Electron Microscopy, Fourier Transform Infra-Red spectroscopy, and photo-absorption spectroscopy. The erosion yield, surface wettability and the surface roughness were seen to be much higher when exposed to both the radiations as compared to either of them, reflecting the synergetic effects.

Measurement of doubly differential electron bremsstrahlung cross sections at the end point (tip) for C, Al, Te, Ta and Au

We have used the low-energy beam line of the São Paulo Microtron accelerator to study the maximum energy transfer point (tip) of electron–atom bremsstrahlung spectra for C, Al, Te, Ta and Au. Absolute cross sections differential in energy and angle of the emitted photon were measured for various electron kinetic energies between 20 and 100 keV, and photon emission angles of 35◦, 90◦ and 131◦. The bremsstrahlung spectra were collected with three HPGe detectors and their response functions were evaluated analytically. Rutherford backscattering spectrometry allowed us to obtain the thicknesses of the targets with good accuracy. We propose a simple model for the tip region of the bremsstrahlung spectrum emitted at a given angle, whose adjustable parameters are the mean energy of the incident beam and its spread as well as an amplitude. The model was fitted simultaneously to the pulse-height distributions recorded at the three angles, determining the doubly differential cross sections from the corresponding amplitudes. The measured values have uncertainties between 3% and 13%. The agreement of the experimental results with the theoretical partial-wave calculations of Pratt and co-workers depends on the analyzed element and angle but is generally satisfactory. In the case of Al and Au, the uncertainty attributed to the theory is probably overestimated.

Nondestructive Inspection System for Special Nuclear Material Using Inertial Electrostatic Confinement Fusion Neutrons and Laser Compton Scattering Gamma-Rays

A Neutron/Gamma-ray combined inspection system for hidden special nuclear materials (SNMs) in cargo containers has been developed under a program of Japan Science and Technology Agency in Japan. This inspection system consists of an active neutron-detection system for fast screening and a laser Compton backscattering gamma-ray source in coupling with nuclear resonance fluorescence (NRF) method for precise inspection. The inertial electrostatic confinement fusion device has been adopted as a neutron source and two neutron-detection methods, delayed neutron noise analysis method and high-energy neutron-detection method, have been developed to realize the fast screening system. The prototype system has been constructed and tested in the Reactor Research Institute, Kyoto University. For the generation of the laser Compton backscattering gamma-ray beam, a race track microtron accelerator has been used to reduce the size of the system. For the NRF measurement, an array of LaBr3(Ce) scintillation detectors has been adopted to realize a low-cost detection system. The prototype of the gamma-ray system has been demonstrated in the Kansai Photon Science Institute, National Institutes for Quantum and Radiological Science and Technology. By using numerical simulations based on the data taken from these prototype systems and the inspection-flow, the system designed by this program can detect 1 kg of highly enriched 235U (HEU) hidden in an empty 20-ft container within several minutes.

Investigations on nonlinear optical properties of electron beam treated Gd:ZnO thin films for photonic device applications

In this article, we report the third-order nonlinear optical properties of electron beam irradiated gadolinium-doped zinc oxide (GZO) thin films prepared using the spray pyrolysis deposition technique. GZO thin films were treated with an electron beam from a variable energy microtron accelerator at dose rates ranging from 1–5 kGy. Nonlinear optical measurements were conducted by employing the single beam Z-scan technique. A continuous wave He–Ne laser operating at 633 nm was used as the source of excitation. Closed aperture Z-scan results reveal that the films exhibit self-defocusing nonlinearity. Open aperture Z-scan results exhibit a switching over phenomena of reverse saturable absorption to saturable absorption for thin film irradiated at 3 kGy, indicating the influence of electron beams on optical nonlinearity. The significant change in third-order nonlinear optical susceptibility χ(3) ranging from 2.14 × 10−3 to 3.12 × 10−3 esu is attributed to the effect of electron beam irradiation. The study shows that the nonlinear coefficients of GZO films can be tuned by electron beams for use in nonlinear optical device applications.

Timing in a FLASH

A prototype detector, called FLASH (Fast Light Acquiring Start Hodoscope), was built to provide precise Time-of-Flight (TOF) measurements and reference timestamps for detector setups at external beam lines. Radiator bars, made of synthetic fused silica, were coupled to a fast MCP-PMT with 64 channels and read out with custom electronics using Time-over-Threshold (TOT) for signal characterization. The TRB3 system, a high-precision TDC implemented in an FPGA, was used as data acquisition system. The performance of a system consisting of two FLASH units was investigated at a dedicated test experiment at the Mainz Microtron (MAMI) accelerator using its 855MeV electron beam. The TOT measurement enabled time walk corrections and an overall TOF resolution of ∼70ps could be achieved which translates into a resolution of ∼50ps per FLASH unit. The intrinsic resolution of the frontend electronics including the TDC was measured to be less than 25ps.

Measurement of the parity violating asymmetry in the quasielastic electron-deuteron scattering and improved determination of the magnetic strange form factor and the isovector anapole radiative correction

A new measurement of the parity-violating asymmetry in the electron-deuteron quasielastic scattering for backward angles at $⟨{Q}^{2}⟩=0.224\text{ }\text{ }{(\mathrm{GeV}/c)}^{2}$, obtained in the A4 experiment at the Mainz Microtron accelerator (MAMI) facility, is presented. The measured asymmetry is ${A}_{PV}^{d}=(\ensuremath{-}20.11\ifmmode\pm\else\textpm\fi{}0.8{7}_{\mathrm{stat}}\ifmmode\pm\else\textpm\fi{}\phantom{\rule{0ex}{0ex}}1.0{3}_{\mathrm{sys}})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$. A combination of these data with the proton measurements of the parity-violating asymmetry in the A4 experiment yields a value for the effective isovector axial-vector form factor of ${G}_{A}^{e,(T=1)}=\ensuremath{-}0.19\ifmmode\pm\else\textpm\fi{}0.43$ and ${R}_{A}^{(T=1),\mathrm{anap}}=\ensuremath{-}0.41\ifmmode\pm\else\textpm\fi{}0.35$ for the anapole radiative correction. When combined with a reanalysis of measurements obtained in the G0 experiment at the Thomas Jefferson National Accelerator Facility, the uncertainties are further reduced to ${G}_{M}^{s}=0.17\ifmmode\pm\else\textpm\fi{}0.11$ for the magnetic strange form factors, and ${R}_{A}^{(T=1),\mathrm{anap}}=\ensuremath{-}0.54\ifmmode\pm\else\textpm\fi{}0.26$.

Simulation on a photocathode-based microtron using a 3D PIC code

The Korea Atomic Energy Research Institute (KAERI) has used a microtron accelerator based on a thermionic cathode for operating a compact terahertz (THz) FEL, where the electrons are emitted and accelerated automatically during the radio-frequency (RF) macro-pulse over threshold power for their emission. Usually a thermionic cathode is embedded inside the microtron cavity for electron-beam emission, and at the same time acceleration is due to the input RF source. In this case, the accelerator scheme is simple, but just a fraction of the emitted electrons are accelerated, and the electron bunch length is uncontrollable due to the RF phase condition for acceleration. In this paper, a photocathode-based microtron which is able to produce high peak (∼100 A) and ultrashort (∼1 ps) electron bunch is studied to adapt it for an electron injector of a THz generator. Especially, we analyzed the electron beam dynamics along the accelerating trajectory with a 3D PIC-code to find the optimized RF phase and laser input time.

Development of an S-band cavity-type beam position monitor for a high power THz free-electron laser.

A cavity-type beam position monitor (BPM) has been developed for a compact terahertz (THz) free-electron laser (FEL) system and ultra-short pulsed electron Linac system at the Korea Atomic Energy Research Institute (KAERI). Compared with other types of BPMs, the cavity-type BPM has higher sensitivity and faster response time even at low charge levels. When electron beam passes through the cavity-type BPM, it excites the dipole mode of the cavity of which amplitude depends linearly on the beam offset from the center of the cavity. Signals from the BPM were measured as a function of the beam offset by using an oscilloscope. The microtron accelerator for the KAERI THz FEL produces the electron beam with an energy of 6.5 MeV and pulse length of 5 μs with a micropulse of 10-20 ps at the frequency of 2.801 GHz. The macropulse beam current is 40 mA. Because the microtron provides multi-bunch system, output signal would be the superposition of each single bunch. So high output signal can be obtained from superposition of each single bunch. The designed position resolution of the cavity-type BPM in multi-bunch is submicron. Our cavity-type BPM is made of aluminum and vacuum can be maintained by indium sealing without brazing process, resulting in easy modification and cost saving. The resonance frequency of the cavity-type BPM is 2.803 GHz and the cavity-type BPM dimensions are 200 × 220 mm (length × height) with a pipe diameter of 38 mm. The measured position sensitivity was 6.19 (mV/mm)/mA and the measured isolation between the X and Y axis was -39 dB. By measuring the thermal noise of system, position resolution of the cavity-type BPM was estimated to be less than 1 μm. In this article, we present the test results of the S-band cavity-type BPM and prove the feasibility of the beam position measurement with high resolution using this device.

Chemical dosimeters for electron beam dosimetry of microtron accelerator

The variable energy microtron at Mangalore University has been used to study the effect of radiation on different materials and biological systems. While studying the effects of radiation, it is essential to have complete knowledge of absorbed dose. In the present study the dose due to 8 MeV electron beam from microtron accelerator has been calculated using chemical dosimeters. The uniformity of dose distribution at various points of the irradiation area also has been calibrated. From the dosimetry studies it is observed that there is a linear relation between dose and electron numbers over a wide range of absorbed doses. It is evaluated that the electron counts of about 1.15 × 1014 corresponds to an absorbed dose of 100 Gy and a field size of about 4 × 4 cm is available at 30 cm distance from the beam exit window over which the dose distribution is uniform.

Measurement and estimation of isomeric cross section of 137Ba(n, n′)137mBa reaction using accelerator based neutron source

The isomeric cross section of 137Ba(n, n′)137mBa reaction over the neutron energy from 1keV to 4MeV has been calculated using TALYS-1.2 nuclear code. The variations of cross section with level densities and effective imaginary potentials have been studied to obtain the best fit with the excitation function. The reaction cross section for Barium was also measured in continuous neutron energy using the Microtron accelerator based neutron source. In this case, the bremsstrahlung radiation emitted by impinging 6MeV electrons on the e–γ primary target (tungsten) was allowed to fall on the γ–n secondary target (beryllium) to produce continuous neutrons and further barium was irradiated at 00 with respect to the incoming neutrons. It is observed that the experimental cross section for Barium is in good agreement with TALYS code and also evaluated data of EXFOR. Deviation factor has been determined for measuring and theoretical cross sections by TALYS-1.2 found to be around 14.71.

Measurement of cross section of (n, γ) reaction for, iodine, sodium and vanadium in the energy range 1 keV to 4 MeV using accelerator based neutron source

The cross sections of 127I(n, γ)128I, 23Na(n, γ)24Na and 51V(n, γ)52V reactions for Iodine, sodium and vanadium were measured at continuous energy spectrum using a Microtron accelerator based neutron source. In this case, the bremsstrahlung radiation emitted by impinging 6MeV electrons on the e–γ primary target (tungsten) was allowed to fall on the γ–n secondary target (beryllium) to produce continuous neutrons. The optimization of bremsstrahlung and neutron producing targets along with their spectra were estimated using FLUKA code. The cross sections of 127I(n, γ)128I, 23Na(n, γ)24Na and 51V(n, γ)52V reactions over the neutron energy from 1keV to 4MeV have been also calculated using the TALYS-1.2 and EMPIRE nuclear model codes. The variations of the cross sections with the level densities and effective imaginary potentials were studied to obtain the best fit of the excitation function. It is observed that the experimental cross sections for iodine, sodium and vanadium are in good agreement with the TALYS-1.2 and EMPIRE codes.

MEASUREMENT OF PHOTOFISSION CROSS-SECTION OF238UUSING MICROTRON FACILITY

Photofission cross-section of238U was measured using bremsstrahlung radiation energy 7.4–9.0 MeV with energy step of 0.4 MeV by employing Lexan polycarbonate film as solid state nuclear track detector (SSNTD). The photon intensity from the Microtron accelerator at a distance of 15 cm from the bremsstrahlung converter (tantalum target) facility was estimated to be 1010photons/sec using the code EGS-4. In this paper, details of the fission fragment angular distribution measurements of238U target using Lexan polycarbonate have been discussed. The photofission cross-section was calculated using the angular distribution of fission fragments and the results were compared with those obtained using the code EMPIRE-II and various barrier parameters of the RIPL-1, RIPL-2 libraries and with the new analytical fission barrier formula based on the Hugenholtz–Van Hove theorem. The present experimental measurements were in good agreement with the results obtained from the Empire-II code predictions for potential parameter taken from RIPL-1 and a newly developed analytical fission barrier formula.

Cell inactivation studies on yeast cells under euoxic and hypoxic condition using electron beam from microtron accelerator

In the case of sparsely ionizing radiation such as electron, the dose rate and the pattern of energy deposition of the radiation are the important physical factors which can affect the amount of damage in living cells. In the present study, the differences in the cell survival efficiency and dose rate effect in diploid yeast strains Saccharomyces cerevisiae X2180 and Saccharomyces cerevisiae D7 under euoxic and hypoxic condition have been quantified. Irradiation was carried out using 8 MeV pulsed electron beam from Microtron accelerator. The dose per pulse and pulse width of the beam used was 0.6 Gy and 2.3 μs, respectively, which correspond to an instantaneous dose rate of 2.6 × 105 Gy s−1. For survival studies doses were delivered at a rate of 50 pulses per second (an average dose rate of 1,800 Gy s−1). Fricke and alanine dosimeters were used to measure the dose delivered to the sample. A significant difference in the dose response has been observed under euoxic and hypoxic condition. Dose rate effect has been studied by changing the pulse repetition rate of the Microtron and the dose rate used was from 180 to 1800 Gy min−1. A significant dose rate effect was observed under euoxic condition for Saccharomyces cerevisiae X2180 but the same was absent under hypoxic condition. The dose rate effect was absent for Saccharomyces cerevisiae D7 under both irradiation condition. The survival curves are found to be sigmoidal in shape under both condition but with a wider shoulder under hypoxic condition. The D0 value and the Oxygen Enhancement Ratio (OER) at that point have been derived.

MAMI C – Results and Perspectives

The Mainz Microtron accelerator MAMI C provides a high intensity, polarized electron beam with an energy up to 1.6 GeV. Together with polarized targets, recoil polarimeters and dedicated detector systems this beam is used to measure spin observables with a precision necessary to have a significant impact on our understanding of strong interactions in the low energy regime where perturbative QCD is not applicable. In this article, an overview over selected recent results is given.

A Mott polarimeter operating at MeV electron beam energies

We have developed a Mott electron polarimeter for the Mainzer microtron (MAMI) accelerator in Mainz, Germany. At beam energies ranging between 1.0 and 3.5 MeV two double focusing magnet spectrometers collect elastically backscattered electrons from gold targets. In spite of the small spectrometer acceptance, a sufficient statistical efficiency is achieved to provide very fast measurements if beam currents typical for experiments at MAMI are being used. High reproducibility is achieved, demonstrating that the results of asymmetry measurements are independent of the primary beam current in a range from 0.004 to 45 μA at a level of <1% relative variation. Compared to low energy polarimeters of similar construction an improvement of a factor 2-3 in absolute accuracy seems possible.