MeV Pulsed Electron Beam Research Articles

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.

Dosimetric and preparation procedures for irradiating biological models with pulsed electron beam at ultra-high dose-rate

PurposePreclinical studies using a new treatment modality called FLASH Radiotherapy (FLASH-RT) need a two-phase procedure to ensure minimal uncertainties in the delivered dose. The first phase requires a new investigation of the reference dosimetry lying outside the conventional metrology framework from national metrology institutes but necessary to obtain traceability, repeatability, and stability of irradiations. The second consists of performing special quality assurance procedure prior to irradiation. Materials and MethodsThe Oriatron eRT6 (PMB-Alcen, France) is an experimental high dose-per-pulse linear accelerator, delivering a 6 MeV pulsed electron beam with mean dose-rates, ranging from a few Gy/min up to thousands of Gy/s. Absolute dosimetry is investigated with alanine, thermo-luminescent dosimeters (TLD) and radiochromic films as well as an ionization chamber for relative stability. The beam characteristic and dosimetry are prepared for three different setups. ResultsA cross-check between alanine, films and TLD revealed a dose agreement within 3% for dose-rates between 0.078 Gy/s and 1050 Gy/s, showing that these dosimeters are suitable for absolute dosimetry for FLASH-RT. In absence of appropriate setup dependent corrections, active dosimetry can reveal dose deviations up to 15% of the prescribed dose. These differences reduce to less than 3% when our dosimetric procedure is applied. ConclusionWe developed procedures to accurately irradiate biological models. Our method is based on validated absolute dosimeters and extends their use to routine FLASH irradiations. We reached an agreement of 3% between the delivered and prescribed dose and developed the requirements needed for workflows of preclinical and clinical studies.

Radiobiological characterization of the very high dose rate and dose per pulse electron beams produced by an IORT (intra operative radiation therapy) dedicated linac

Background: Intra operative radiation therapy (IORT) is a cancer treatment modality combining surgery and radiation therapy that permits the delivery of a large single dose of radiation at the time of the tumour resection. During the last years, IORT has become a widespread technique in clinical routine. This was possible thanks to the recent development of small dedicated, and hence very flexible, electron accelerators suitable for a surgical operation environment. However, the electron beams produced by these dedicated linacs are different with respect to those produced by linacs used in conventional radiation therapy in terms of dose rate (dose delivered/time of irradiation), dose per pulse (dose delivered per emitted beam pulse) and energy spectrum. In particular the very high dose rate and dose per pulse (i.e., respectively about 20 and 100 times greater than those of conventional radiation therapy) pose some radiobiological questions that have not yet been fully investigated. The aim of this work was to evaluate the relative biological effectiveness (RBE) of the IORT beams through the experimental construction of dose-response curves for cell survival. Methods: Since breast cancer represents the elective malignancy for treatment by IORT, clonogenic survival was assayed in the MCF-7 cell line from breast tissue malignant adenocarcinoma as a function of dose for different dose rates (5, 25 and 75 Gy/min) and doses per pulse (4.2 and 7.4 cGy/pulse). Irradiations were performed at the IORT accelerator Novac7 (Hitesys SpA, Italy) delivering electrons at the nominal energy of 7 MeV. For comparison, irradiations were also carried out with a conventional radiotherapy accelerator (ClinacR DHX, Varian), providing a 6 MeV pulsed electron beam and 6 MV X-rays (dose rate and dose-per-pulse 2 Gy/min and 0.1 cGy/pulse respectively) as reference irradiations. Results: The IORT beam effectiveness was found almost the same with varying dose rate (5, 25 and 75 Gy/min) and dose per pulse (4.2 and 7.4 cGy/pulse). No significant difference was also found between IORT and conventional electron beams, while 6 MV X-rays (beam used in the conventional treatment of breast cancer) proved to be more effective. Conclusions: Data show that cell killing effectiveness of the electron beams from the IORT accelerator does not differ significantly from that of an electron beam used in conventional radiotherapy. This suggests that changes in the dose rate and dose per pulse, up to the values of 75 Gy/min and 7.4 cGy/pulse, do not affect the radiobiological characteristics of the beam. In the light of our results, new experimental data are needed to better compare the RBE of a IORT breast cancer treatment (5–9 MeV electron beams, 21 Gy at the 90% isodose level in single fraction) and the RBE of a conventional breast cancer treatment (6 MV X-rays, 2 Gy per fraction, 30 fractions).

Radiobiological characterization of the very high dose rate and dose per pulse electron beams produced by an IORT (intra operative radiation therapy) dedicated linac

Background: Intra operative radiation therapy (IORT) is a cancer treatment modality combining surgery and radiation therapy that permits the delivery of a large single dose of radiation at the time of the tumour resection. During the last years, IORT has become a widespread technique in clinical routine. This was possible thanks to the recent development of small dedicated, and hence very flexible, electron accelerators suitable for a surgical operation environment. However, the electron beams produced by these dedicated linacs are different with respect to those produced by linacs used in conventional radiation therapy in terms of dose rate (dose delivered/time of irradiation), dose per pulse (dose delivered per emitted beam pulse) and energy spectrum. In particular the very high dose rate and dose per pulse (i.e., respectively about 20 and 100 times greater than those of conventional radiation therapy) pose some radiobiological questions that have not yet been fully investigated. The aim of this work was to evaluate the relative biological effectiveness (RBE) of the IORT beams through the experimental construction of dose-response curves for cell survival. Methods: Since breast cancer represents the elective malignancy for treatment by IORT, clonogenic survival was assayed in the MCF-7 cell line from breast tissue malignant adenocarcinoma as a function of dose for different dose rates (5, 25 and 75 Gy/min) and doses per pulse (4.2 and 7.4 cGy/pulse). Irradiations were performed at the IORT accelerator Novac7 (Hitesys SpA, Italy) delivering electrons at the nominal energy of 7 MeV. For comparison, irradiations were also carried out with a conventional radiotherapy accelerator (ClinacR DHX, Varian), providing a 6 MeV pulsed electron beam and 6 MV X-rays (dose rate and dose-per-pulse 2 Gy/min and 0.1 cGy/pulse respectively) as reference irradiations. Results: The IORT beam effectiveness was found almost the same with varying dose rate (5, 25 and 75 Gy/min) and dose per pulse (4.2 and 7.4 cGy/pulse). No significant difference was also found between IORT and conventional electron beams, while 6 MV X-rays (beam used in the conventional treatment of breast cancer) proved to be more effective. Conclusions: Data show that cell killing effectiveness of the electron beams from the IORT accelerator does not differ significantly from that of an electron beam used in conventional radiotherapy. This suggests that changes in the dose rate and dose per pulse, up to the values of 75 Gy/min and 7.4 cGy/pulse, do not affect the radiobiological characteristics of the beam. In the light of our results, new experimental data are needed to better compare the RBE of a IORT breast cancer treatment (5–9 MeV electron beams, 21 Gy at the 90% isodose level in single fraction) and the RBE of a conventional breast cancer treatment (6 MV X-rays, 2 Gy per fraction, 30 fractions).

Structural, electromagnetic, and dielectric properties of lithium-zinc ferrite ceramics sintered by pulsed electron beam heating

Structural, electromagnetic, and dielectric properties of Li0.4Fe2.4Zn0.2O4 lithium-zinc ferrite sintered by 2.4 MeV pulsed electron beam heating at 1050 °С for 2 h were investigated. The formation of ferrite with a single-phase cubic spinel structure was confirmed by X-ray diffraction analysis. The average grain size of ferrite ceramic was determined by SEM analysis and its value was 1.7 µm. The radiation-thermal sintered samples are characterized by a saturation magnetization of 67.8 emu/g, the Curie temperature of 508 °C, AC electrical resistivity of 2.4×104 Ω cm (at 25 °C). The frequency dependences of permittivity and the loss tangent were obtained in (20 – 2×106) Hz frequency range. The behavior of ε′ is characterized by high dispersion caused by relaxation polarization in the investigated frequency range. The results were compared to the LiZn ferrite characteristics sintered by traditional thermal heating.

Standardization of CalyculinA induced PCC assay and its advantages over Okadaic acid PCC assay in Biodosimetry applications.

In the present study an attempt was made to estimate coefficients of dose response curves for PCC aberrations induced by CalyculinA and Okadaic acid, using 60Co gamma radiation and 8 MeV pulsed electron beam for biodosimetry application. The modified method outlined by Puig et al. 2013 was used to conduct Calyculin A and Okadaic acid induced PCC assay in human blood lymphocytes.Chemical treatment was given for the last 1 h of a 48 h culture. The study was carried out in the dose range 2.5 to 20 Gy using 60Co gamma rays and 8 MeV pulsed electron beam. Results show a linear dose dependent increase with a slope of 0.047 ± 0.001 from Calycalin A PCC and 0.048 ± 0.002 form Okadaic acid PCC. The slope of the fragments curve was 0.327 ± 0.006 from Calyculin A and 0.328 ± 0.006 from Okadaic acid PCC. Further, dose calibration studies were carried out for 8 MeV electron using Calyculin A PCC assay and the obtained slope from ring yield was 0.054 ± 0.002 and 0.427 ± 0.009 from fragment yield.

DOSE-RESPONSE STUDY USING MICRONUCLEUS CYTOME ASSAY: A TOOL FOR BIODOSIMETRY APPLICATION.

The present study is aimed at obtaining in vitro dose-response data for the induction of micronucleus (MN) and nucleoplasmic bridges (NPBs) in human lymphocytes using 60Co-gamma rays and 8 MeV pulsed electron beam. An attempt was made to validate the possibility of applying NPBs as new biodosimetry endpoint in the dose range of 0-6 Gy. A total of 1000 binucleated cells (BNCs) per dose point were evaluated for the frequency of MN and NPBs. From the study, it is clear that the dose-response increase of MN and NPBs is linear quadratic in nature. The study provides linear and quadratic parameter for biodosimetry application. The relative biological effectiveness value of the 8 MeV electron beam was estimated using slope values and is found to be 1.18 ± 0.01 for MN/BNCs, 1.27 ± 0.02 for the fraction of BNCs with MN, 1.16 ± 0.13 for MN/(BNCs with MN) and 1.09±0.01 for NPBs.

Studies on electron beam induced DNA damage and repair kinetics in lymphocytes by alkaline comet assay

Background: Exposure to ionizing radiaon is known to induce oxidave stress followed by damage to crical biomolecules like lipids, proteins and DNA through radiolysis of cellular water. Since radiaon has been widely used as an important tool in therapy of cancer, the detailed invesgaon regarding the DNA damage and repair kinecs would help to predict the radiaon sensivity of cells. The present study is focused on quanficaon of DNA damage and repair kinecs of human peripheral blood lymphocytes a%er 8 MeV pulsed electron beam irradiaon in vitro . Materials and Methods: DNA damage and repair kinecs in human blood cells were studied using alkaline comet assay. The dose-response curves for the dose range of 0-5 Gy were established using 8 MeV electron beam. Repair kinecs was studied by incubang the cells from 0 to 90 min at 37°C a%er irradiaon. For quanficaon of DNA damage, percentage Tail DNA, Tail length, Tail moment and Olive Tail moment were used as a comet parameter. Results and Conclusion: The study reveals that, inducon of DNA damage by 8 MeV pulsed electron beam is near linear with a negligible negave quadrac component at high doses. This small quadrac component is a5ributed to high dose rate during the pulsed irradiaon. The DNA repair hal%ime and mean repairme for human blood lymphocytes were found to be varying between 9.29 - 23.78 min and 13.41 - 34.31 min respecvely. The repair rate is found to be maximum in inial 15 minutes and almost constant a%er 60 min.

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.

Assessment of electron and gamma-induced dna damage in human peripheral blood by alkaline comet assay

In the present study, the effect of electron and gamma irradiation on the induction of DNA damage in human peripheral blood cells was investigated using comet assay. Blood samples were irradiated with an 8 MeV pulsed electron beam at a dose rate of 100 Gy min -1 . Gamma irradiation was carried out at a dose rate of 2 Gy min -1 using 60 Co gamma source. The total dose delivered to the samples was varied from 0 to 4 Gy. Samples were maintained at 0° C before irradiation, and the comet assay was carried out immediately after irradiation. Electrophoresis was performed at a field strength of 0.74 V cm -1 for 25 min at 4°C. A dose-dependent increase in DNA damage was observed. From the observed DNA damage, the relative biological effectiveness (RBE) for electron radiation with reference to gamma radiation on induction of DNA damage has been calculated.

Dose Rate Effect of Pulsed Electron Beam on Micronucleus Frequency in Human Peripheral Blood Lymphocytes

The micronucleus assay in human peripheral blood lymphocytes is a sensitive indicator of radiation damage and could serve as a biological dosimeter in evaluating suspected overexposure to ionising radiation. Micronucleus (MN) frequency as a measure of chromosomal damage has also extensively been employed to quantify the effects of radiation dose rate on biological systems. Here we studied the effects of 8 MeV pulsed electron beam emitted by Microtron electron accelerator on MN induction at dose rates between 35 Gy min-1 and 352.5 Gy min-1. These dose rates were achieved by varying the pulse repetition rate (PRR). Fricke dosimeter was employed to measure the absorbed dose at different PRR and to ensure uniform dose distribution of the electron beam. To study the dose rate effect, blood samples were irradiated to an absorbed dose of (4.7+/-0.2) Gy at different rates and cytogenetic damage was quantified using the micronucleus assay. The obtained MN frequency showed no dose rate dependence within the studied dose rate range. Our earlier dose effect study using 8 MeV electrons revealed that the response of MN was linear-quadratic. Therefore, in the event of an accident, dose estimation can be made using linear-quadratic dose response parameters, without adding dose rate as a correction factor.

6MeV pulsed electron beam induced surface and structural changes in polyimide

Thin films of polyimide (PMDA-ODA, Kapton) having 50 μm thickness were irradiated with 6 MeV pulsed electron beam. The bulk and surface properties of pristine and irradiated samples were characterized by several techniques such as stress–strain measurements, Fourier Transform Infrared (FTIR), UV–vis spectroscopy, contact angle, atomic force microscopy (AFM) and profilometry. The tensile strength, percentage elongation and strain energy show an enhancement from pristine value of 73–89 MPa, 10–22% and 4.75–14.2 MJ/m3 respectively at the maximum fluence of 4 × 1015 electrons/cm2. This signifies that polyimide being an excessively aromatic polymer is crosslinked due to high-energy electron irradiation. In surface properties, the contact angle shows a significant decrease from 59° to 32° indicating enhancement in hydrophilicity. This mainly attributes to surface roughening, which is due to the electron beam induced sputtering. The surface roughening is confirmed in AFM and profilometry measurements. The AFM images clearly show that surface roughness increases after electron irradiation. Moreover, the roughness average (Ra) as measured from surface profilograms is found to increase from 0.06 to 0.1. The FTIR and UV–vis spectra do not show noticeable changes as regards to scissioning of bonds and the oxidation. This work leads to a definite conclusion that 6 MeV pulsed electron beam can be used to bring about desired changes in surface as well as bulk properties of polyimide, which is considered to be a high performance space quality polymer.

The effect of electron and gamma irradiation on the induction of micronuclei in cytokinesis-blocked human blood lymphocytes

The effect of electrons and gamma irradiation on the induction of micronuclei in cytokinesis-blocked human peripheral blood lymphocytes was investigated to understand the relative biological effectiveness (RBE) of electrons compared with gamma rays. Blood samples were irradiated with an 8 MeV pulsed electron beam, at a mean instantaneous dose rate of 2.6 x 10(5) Gy s(-1). Gamma irradiation was carried out at a dose rate of 1.98 Gy min(-1) using (60)Co gamma source. A dose-dependent increase in micronuclei yield was observed. The dose-response relationships for induction of micronuclei fitted well to a linear-quadratic relationship and the coefficients alpha and beta of the dose-response curve were estimated by fitting the data using error-weighted minimum chi (2) method. The RBE of 8 MeV electrons were found to be near unity as compared with gamma rays.

Damage induced by 90 MeV silicon ions in crystalline silicon

Samples of n-type crystalline silicon were exposed to different fluences, ranging from 1.25 to 5×1014 ions/cm2, of 90 MeV silicon ions. The induced disorder in the surface region was studied by grazing-angle x-ray-diffraction and optical reflection spectroscopy, and that in the bulk was studied by measuring the lifetime of the excess minority carriers generated by a 1 MeV pulsed electron beam. Both in the surface region, as well as in the bulk, the degree of induced lattice defects was found to increase with an increase in the ion fluence. The value of the damage coefficient, estimated from the lifetime of the minority carriers, gradually increased from 1.2×10−10 to 8.9×10−10 cm2 s−1 over the range of ion fluences. These results indicate that 90 MeV silicon ions create an appreciable number of defects in crystalline silicon, the concentration of which increases from the surface to their projected range of ∼31 μm, and at higher fluences secondary defects are also produced in the bulk. Even at the highest fluence used the energy deposited through electronic loss had no observable effect on annealing the induced defects.

Modification of a medical linac to a polymer irradiation facility

A linear accelerator for X-ray therapy has been modified to generate a 5 MeV pulsed electron beam. The main objective is to irradiate polymeric materials in open air in order to alter their chemical and mechanical properties. To meet the radiation protection standards a shielding has been built round the target. Safety is guaranteed by a fail-safe secured programmable logic controller (PLC) monitored by a personal computer. The accelerator can be monitored and controlled by a graphics oriented and menu driven program running on the personal computer. In addition, a control panel has been designed and built to show warning signals and to set various linac parameters. A description of the accelerator modification and of the new control system is presented.

Radiation damage and minority carrier lifetime in crystalline silicon

The lifetime of the minority carriers in p and n type crystalline silicon was measured with 1 MeV pulsed electron beam. Silicon samples were exposed to different fluences of 1 and 6 MeV electron, 14 MeV neutrons, thermal neutrons and 60Co gamma rays and the value of the radiation damage coefficient for each sample was estimated by monitoring variations in the minority carrier lifetime with radiation fluence. It is found that 14 MeV neutrons can be effectively used in reducing the lifetime of minority carriers in silicon and therefore have potential in controlling parameters of semiconductor devices.

Time resolved study of the luminescence produced by the pulse radiolysis of D2O vapor

D2O vapor was irradiated using a 0.53 MeV pulsed electron beam and the 200–900 nm wavelength range was examined for luminescence emission from excited fragments. Spectral lines of the OD (C 2∑+→A 2∑+) and the OD (A 2∑+→X 2Π) transitions were observed, as were the Balmer transitions of deuterium between n=6→n=2 and n=3→n=2, and the oxygen transitions O+(3p 4D0→3s 4P),O(3p 5P→3s 5S0), and O(3p 3P→3s 3S0). Values were obtained for the natural lifetimes, quenching rate constants, and quenching cross sections at 298 K for the majority of the above excited species. The natural lifetimes and quenching data obtained for the transitions of excited OD and oxygen species were, as expected, similar to the values obtained for the corresponding species in H2O vapor. However, Balmer D transitions exhibited shorter natural lifetimes and smaller quenching cross sections than the corresponding Balmer H transitions. The differences in quenching rate were much larger than the effect of isotopic substitution on collision frequency. Both lifetime and quenching differences were attributed to greater population of the p sublevels in excited D as compared with H.

ChemInform Abstract: TIME RESOLVED 360 TO 600 NM LUMINESCENCE PRODUCED BY THE PULSE RADIOLYSIS OF WATER VAPOR

Water vapor was excited by a 0.53 MeV pulsed electron beam and examined for luminescence emission in the 360–600 nm region. Spectral lines arising from the Balmer transitions H(n=4→n=2), H(n=5→n=2), and H(n=6→n=2) of the hydrogen atom and the transitions 3p4D05/2→3s4P3/2, 3p4D07/2→ 3s4P5/2, and 3p4D01/2→3s4P1/2 of the O+ ion were observed. The Balmer lines were found to be quenched by water vapor with rate constants at 293 K of (9.77±0.26)×10−9, (10.67±0.45)×10−9, and (12.3±2.3)×10−9 cm3 molecule−1 s−1, respectively. The excited O+ ions were also quenched strongly by water vapor but line intensities were insufficient for rate measurements to be carried out.

A search for H 3* emission from electron-pulse-irradiated hydrogen gas

No H 3 * emission was detected when hydrogen gas was irradiated by a 0.53 MeV pulsed electron beam at pressures which lead to the production of H 3 * in a hollow cathode discharge. The intensity of any such emission must be considerably less than 0.1% of the intensity of the Balmer α emission observed from the system.

Time resolved 360 to 600 nm luminescence produced by the pulse radiolysis of water vapor

Water vapor was excited by a 0.53 MeV pulsed electron beam and examined for luminescence emission in the 360–600 nm region. Spectral lines arising from the Balmer transitions H(n=4→n=2), H(n=5→n=2), and H(n=6→n=2) of the hydrogen atom and the transitions 3p4D05/2→3s4P3/2, 3p4D07/2→ 3s4P5/2, and 3p4D01/2→3s4P1/2 of the O+ ion were observed. The Balmer lines were found to be quenched by water vapor with rate constants at 293 K of (9.77±0.26)×10−9, (10.67±0.45)×10−9, and (12.3±2.3)×10−9 cm3 molecule−1 s−1, respectively. The excited O+ ions were also quenched strongly by water vapor but line intensities were insufficient for rate measurements to be carried out.